THE ECOLOGY OF INSECT PEST POPULATIONS
IN MAIZE STORAGE CRIBS IN NIGERIA
by
Richard Hugh Markham, B.A. (Nat. Sci.)
A thesis submitted for the degree of
Doctor of Philosophy of the University of London
and the Diploma of Imperial College.
Tropical Stored Products Centre, (Overseas Development Administration), London Road, Slough, Berkshire. March 1981 THE ECOLOGY OF INSECT PEST POPULATIONS
IN MAIZE STORAGE CRIBS IN NIGERIA
Richard Hugh Markham
Abstract
This study considered the insect populations infesting white dent maize stored in well-ventilated cribs at two localities in South West Nigeria. The pest complex was dominated by Sitophilus zeamais (Col.: Curculionidae) but included a great diversity of other pest species and natural enemies. The incidence of individual species was studied from pre-harvest infestation through six to ten months of storage and was shown to follow a consistent succession. The spatial distribution of insects within a crib was not uniform and individual species showed consistent patterns of distribution at a particular time. The seasonal incidence and distribution patterns of major species are discussed in terms of observed changes in grain moisture content, temperature and grain damage. The roles of intra- and interspecific relationships in limiting populations are considered. Sitophilus populations rapidly reach a 'plateau' and it is concluded that further significant increase is prevented by this insect's responses to its own high population density. The relationship between the field infestation and subsequent pest population increase in store is considered with particular reference to the effects of time of harvest, removal or retention of the husks and of damage* caused in the field by Lepidoptera larvae. Colonisation was found to be mainly by active migration of insects to the newly- loaded crib. Storage of maize in the husk provided no protection against insect damage although it did affect the distribution of insects between cobs. Techniques for sampling of insects from cribs are considered and the results of the study are discussed in terms of their implications for pest control strategies. iii.
TABLE OF CONTENTS
ABSTRACT ii TABLE OF CONTENTS iii LIST OF TABLES v LIST OF FIGURES viii
CHAPTER 1
Introduction 1
CHAPTER 2 THE PHYSICAL ENVIRONMENT 2.1 The Crib as a Drying Structure 6 2.2 Macroclimate at Ibadan 11 2.3 Microclimate and Physical Conditions within the Crib 16 2.3.1 Grain Moisture Content 17 2.3.2 Temperatures within the grain bulk 30 2.4 Maize as a substrate for Insect Development 36
CHAPTER 3 SAMPLING TECHNIQUES 3.1 Introduction 39 3.2 Insect Sampling:Constraints and Considerations 41 3.2.1 General Objectives 41 3.2.2 Choice of Sampling Universe 42 3.2.3 Insect Mobility . 42 3.2.4 Sampling Units and Variability 44 3.2.5 Sample Size in Relation to the Size of Cribs 52 3.2.6 Sample Size and Handling Time 53 3.3 Assessment of Insect Sampling Techniques 55 3.3.1 Iowa Corn Probe 56 3.3.2 Destructive Sampling of Whole Cribs 62 3.3.3 Replacement Sampling 63 3.3.4 Sampling to Estimate Recruitment 65 3.4 Extraction of Insects from Grain Samples 66 3.5 Damage Assessment 70
CHAPTER 4 INSECT DISTRIBUTION WITHIN THE CRIB 4.1 Introduction 73 4.2 Sampling and Analysis for Insect Distribution 75 4.3 Preliminary Distribution Trial 82 4.4 Long-Term Changes in Insect Distribution 85 4.5 Short-Term Changes in Insect Distribution 96 4.6 Distribution of Losses within the Cribs 115 4.7 Species Interaction and Habitat Selection 121 iv.
CHAPTER 5 THE INITIATION OF INFESTATION 5.1 Introduction 131 5.2 Pre-Harvest Infestation 135 5.3 The Effects of Harvesting Practice on Infestation 145 5.4 Persistent Effects of Pre-Harvest Damage 162 5.5 Sources of Storage Infestation 171
CHAPTER 6 THE INSECT COMMUNITY:COMPOSITION AND SUCCESSIONAL CHANGES 6.1 Introduction 175 6.2 Treatments and Sampling Techniques 177 6.3 The Abundance of Major Insect Groups and Changes in the Physical Environment 182 6.4 Incidence and Role of Individual Insect Species 189 6.4.1 Primary Pest Species 189 6.4.2 Secondary Pest Species - Coleoptera 196 6.4.3 Predatory Coleoptera 204 6.4.4 Heteroptera 204 6.4.5 Hymenoptera 207 6.4.6 Diptera 213 6.4.7 Psocoptera 213 6.4.8 Other Insect Groups 214 6.5 Other Arthropods 214 6.6 Vertebrates 216 6.7 Grain Weight Losses 217 6.8 Conclusions 220
CHAPTER 7 DISCUSSION: CHARACTERISTICS OF THE MAIZE CRIB SYSTEM AND • IMPLICATIONS FOR CONTROL STRATEGIES 223
APPENDIX .1 An annotated list of species of insects and 235 mites recorded from maize cribs at Ibadan and Ilora
APPENDIX II Collated data: Distribution Studies 250
APPENDIX III Collated data: Succession Studies 259
APPENDIX IV Methods for estimation of moisture content of ' 288 grain and cores
APPENDIX V Methods for analysis of grain weight loss 295
APPENDIX VI Collated analysis of variance tables 298
ACKNOWLEDGEMENTS 305
BIBLIOGRAPHY 306 LIST OF TABLES
CHAPTER 2 2.1 Probability levels from 3-factor analysis of variance of moisture contents from different positions in a crib, at four different stages during the storage season 2.2 Summary results of analysis: effects of time of day and position in crib on grain moisture content (Short-Term Distribution Trial) (a) probability levels from analysis of variance (b) treatment means 2.3 Summary results of analysis: effects of position in crib on grain moisture content (Termination of Short-Term Distribution Trial) (a) probability levels from analysis of variance (b) treatment means 2.4 Summary results of analysis: effects of time of day and position in crib on grain temperature (a) outline design (b) probability levels from analysis of variance (c) treatment means CHAPTER 3 3.1 Difference in adult insect abundance in probe samples from different positions in 3 cribs (Carpophilus) of 4 cribs (Sitophilus) (a) probability levels from a single factor analysis of variance (b) treatment means '3.2 Insect abundance in probe samples from different parts of a single crib (a) probability levels from a 3-factor anovar (b) treatment means 3.3 Effect of time after collection on numbers of insects emerging from grain samples
CHAPTER 4 4.1 Effect of sampling position within crib on insect numbers for (a) Sitophilus zeamais (b) Carpophilus dimidiatus 4.2 Results of Factorial Analysis of Variance for dispersion of Sitophilus zeamais in Long-Term Distribution Trial for: (a) adults (b) emergences 4.3 Results of Factorial Analysis of Variance for dispersion in Long-Term Distribution Trial of: (a) Carpophilus dimidiatus (b) Cathartus quadricollis vi.
4.4 Results of Factorial Analysis of Variance for dispersion of insects in Sample 4 (Long-Term Distribution Trial) 95 4.5 Analysis of crib totals from Short-Term Distribution Trial 100 4.6 Dispersion of adult insects within cribs: effect of time of day and sampling position on insect abundance (Short-Term Distribution Trial) 106 (a) probability levels from 3-factor analysis of variance (b) treatment means from factorial analysis of variance 4.7 Summary of adult insect distribution pattern (Short-Term Distribution Trial) 107 4.8 Distribution pattern of emergences (Short-Term Distribution Trial) based on 2-factor analysis of variance 112 (a) probability levels (b) treatment means 4.9 Summary results of analysis of variance: effect of position within crib on grain weight loss 119 (a) summary anovar table (b) treatment means 4.10 Correlation matrices showing associations between insect species and with two environmental parameters 124
CHAPTER 5 5.1 Summary results of field samples: infestation by major pest groups, grain damage and husk cover 138 5.2 Percentage of cobs infested by each species (or group) 139 5.3 Summary of sampling regime for Harvesting-Practice Trial 146 5.4 Selection of damaged and sound cobs for storage - Harvesting- Practice Trial 149 5.5 Effects of harvesting on adult insect populations comparison of adult insect numbers before harvest (field samples) and 24 hours after harvest (snapped and husked) ' 152 5.6 Effects of early harvesting on insect.populations 153 (a) .comparison of mean moisture contents (b) comparison of emergent insects (c) comparison of adult insects from early and late harvested maize 5.7 Effect of time of harvest and retention of husks on grain moisture content 155 5.8 Probability levels from analysis of variance: effects of time of harvest, removal of husks and position in crib on insect numbers 157 (a) adult insects - first storage sample (b) emergences - first storage sample (c) emergences - second storage sample
5.9 Effects of time of harvest and removal or retention of husks on adult insect infestation (first storage sample) 158 (a) Cathartus quadricollis (b) Oryzaephilus mercator (c) Gnatocerus maxillosus - (d) Palorus subdepressus 5.10 Effects ori emergences of time of harvest and removal/retention of husks at the time of: 159 (a) the first storage sample (b) the second storage sample 5.11 Effects of time of harvest on losses 160 5.12 Effects of field damage by Lepidoptera on initial infestation of maize by storage pests (Pre-Harvest Damage Trial) 167 (a) probability levels from 3-factor analysis of variance (b) mean number of insects emerging from samples 5.13 Effects of field damage on subsequent infestation in store 168 5.14 Effects of field damage on subsequent infestation in store 169 5.15 Progressive changes in mean moisture content and mean dry weight over storage period 170 5.16 Final weight loss (4 months in store) for maize damaged in the field by Lepidoptera (Pre-Harvest Damage Trial) 170
CHAPTER 6 6.1 Summary of crib 'treatments1 used for Succession Studies 181 6.2 Mean loss in dry weight at the end of the storage period 218 6.3 Weight loss in dry season cribs at termination: effect of position/sampling: 219 (a) mean .weight loss for different positions (b) probability levels from a 2-factor analysis of variance viii.
LIST OF FIGURES
CHAPTER 2 2.1 Examples of three traditional and one 'improved1 designs of maize cribs from S.W. Nigeria. 9 2.2 Examples of moisture content/relative humidity isotherms for rice, maize and sorghum 10 2.3 Climate at the study site, Ibadan: (a) weekly total rainfall (b) mean daily solar radiation 12 2.4 Climate at the study site: typical daily cycles of temperature and relative humidity: (a) during the wet season (b) during 'harmattan' conditions 2.5 Climate at the study site: minimum, maximum and mean daily temperature and relative humidity 14 2.6 Comparison of moisture content observed in maize from cribs at Ibadan with 'predicted' equilibrium moisture content 15 2.7 Variability in moisture content of grain and cores: (a) intercob variation in grain moisture content 18 (b) relationship between grain and core moisture content 19 2.8 Grain moisture content in samples from the centre of cribs at Ibadan and Ilora 21 2.9 Grain moisture content in different parts of a single crib 23 2.10 Design of factorial analysis of variance for moisture content data (long-term trial) . 24 2.11 Design of factorial analyses of variance for moisture content data (short-term trials) -27 2.12 Changes in temperature at different points (7) in. a single crib during a 24-hour period: (a) harmattan. conditions 31 (b) wet season conditions 32 2.13 Changes in temperature at different points (32) in a crib during a 24-hour period 33
CHAPTER 3 3.1 Distribution of Sitophilus zeamais (adults) on maize cobs stored Tin the husk' 45 3.2 Distribution of Sitophilus zeamais (adults) on maize cobs stored without husks. 46 3.3 Dependence of variance on mean for samples of Sitophilus adults 47 3.4 Distribution of emergences of major primary pests from cobs stored without husks. 48 3.5 Distribution of Cathartus quadricollis adults on maize cobs stored: 51 (a)1 in the husk1. (b) without husks 3.6 Scatter diagram showing lack of dependence of insect numbers on grain sample size for Iowa corn probe 57 3.7 Design for analysis of the effect of position in the crib on the number of insects collected in probe samples 58 3.8 Arrangements used for the rapid extraction of insects from samples of shelled grain and cobs 68 3.9 Weight loss of grain for cobs from sampled and (adjacent) unsampled parts of a crib under more and less intensive sampling regimes 71 CHAPTER 4 4.1 Modification of cribs for Distribution studies 76 (a) general view of crib (b) stacking of cobs in sampling tunnels 4.2 Designs for analysis of effects of position in crib on insect numbers (Distribution Trials) 81 (a) Preliminary and Long-Term Distribution Trials (b) Long-Term Distribution Trial (emergences) (c) Short-Term Distribution Trial 4.3 Distribution pattern of Sitophilus zeamais at different stages of the storage season (Long-Term Distribution Trial) 86 (a) Adults - no. insects/500g shelled grain @ 17% m.c. (b) Emergences- no'.s insects emerging during one week from 100 g. samples of shelled grain (fresh weight) 4.4 Distribution patterns of secondary pest species and natural enemies at different stages of the storage season (Long-Term Distribution Trial) 90 4.5 Experimental design and analysis for the Short-Term Distribution Trial: 97 (a) allocation of sampling times and sampling occasions in the 3 replicate cribs (b) analysis for effect of time of day and position within crib on insect numbers 4.6 Distribution of adult insects within cribs (Short-Term Distribution Trial) 101 4.7 Distribution of Sitophilus (Short-Term Distribution Trial): effect of East-West position and 'vertical' position 105 4.8 Distribution of emergences (Short-Term Distribution Trial). Numbers of insects emerging in one week from lOOg. samples of shelled grain 109 4.9 Progress of weight loss in different parts of a single crib (Long-Term Distribution Trial) 117 4.10 Distribution of weight loss within cribs (Short-Term ' Distribution Trial) 118 4.11 Summary of trends in environmental factprs 123 (a) weight loss of grain (dry weight basis) (b) grain moisture content (fresh weight basis) (c) grain temperatures at different times of day X .
CHAPTER 5 5.1 Summary of sampling programme from cribs (Harvesting- Practice Trial) 147
5.2 Arrangement of samples in crib (Pre-Harvest Damage Trial) 164
CHAPTER 6 6.1 Modification of cribs for succession trials 173 (a) structural modifications (b) arrangement of cobs for sampling 6.2 Incidence of major insect groups through the storage season 183 6.3 Seasonal incidence of major Coleoptera families 185 6.4 Changes in grain moisture content through the storage season 187 6.5 Increase in grain damage over the storage period 188 6.6 Seasonal incidence of Sitophilus zeamais (adults) 190 6.7 Seasonal incidence of Sitophilus zeamais and Sitotroga cerealella (emergences) 191 6.8 Seasonal incidence of Carpophilus spp. (Nitidulidae) 197 6.9 Seasonal incidence of main species of Silvanidae 198 6.10 Seasonal incidence of main species of Tenebrionidae 201 6.11 Seasonal incidence of main species of Heteroptera 206 6.12 Seasonal incidence of main species of Pteromalidae 208 6.13 Seasonal incidence of various parasitoids 209
APPENDIX IV.1 Drying curves for samples of whole grains APPENDIX IV.1 Drying curves for samples of ground grain APPENDIX IV.3 Drying curves for cores CHAPTER 1
THE ECOLOGY OF INSECT PEST POPULATIONS
IN MAIZE STORAGE CRIBS IN NIGERIA
INTRODUCTION:
Staple food grains in many areas of Tropical Africa, Latin
America, and South-East Asia are still largely stored using trad-
itional techniques. These include the use of small granaries holding, at most, only a few tons of grain. In dry areas such granaries are often closed structures with solid mud walls, but in more humid regions, where maize is the main cereal crop, the grain is characteristically stored 'on the cob1 in a ventilated granary, known as a 'crib1. The walls of the crib are of basketwork, matting or slats, or in some cases consist only of the cobs themselves, regularly stacked. These arrangements allow air to flow through the grain, drying it and, to some extent, inhibiting mould development. However, it also gives ready access to insect pests. While it is difficult to estimate .the losses caused by insects in such stores they are certainly potentially severe
(Parkin, 1956 and 1959; Hall, 1970; Pingale, 1970; Adams and Harman,
1977).
Grain losses can be markedly reduced by the use of sealed silos in which insecticide-treated, artificially dried grain is stored, (e.g.
Pingale, 1968); however, these techniques are, for a variety of reasons, impracticable in many situations (see Discussion, Chapter 7). Acc- ordingly, some effort has been devoted to the attempt to develop im- proved storage techniques which retain the basic concept of the crib: a ventilated structure, of low cost, which serves both for the drying and storage of grain on the farm. Both structural modifications and the use of insecticides of various kinds have been considered (Kockum, 2.
1953 and 1958; Cornes and Riley, 1962; Pointel, 1969; Schulten, 1972; de Lima, 1978; Boshoff, 1978; F.A.O., 1980); unfortunately, most of these studies have not given serious attention to the insect pest « populations which were supposed to be the cause of the storage problem.
After more than twenty years of field trials, no consistently reliable method exists for the control of insect pests in maize cribs (Hind- marsh, Tyler and Webley, 1979) and the ecology of the insects them- selves has been scarcely considered.
In contrast to this dearth of field data, many of the insect species which occur in cribs are very well known from laboratory studies and, to a much lesser extent, from studies of the bulk storage of grain in silos and warehouses. Various insects that are normally associated with stored products have proved ideal subjects for the work of physiologists and geneticists (see for instance, the monograph on Tribolium by Sokoloff, 1972, 1974 and 1977) and theoretical ecol- ogists (from the early works of Utida, 1941 and 1942, Crombie, 1944 and 1945, Park, 1948 and Birch, 1948, reviewed by Solomon, 1953 to more recent studies such as those of Bellows, 1979), while their physiology, behaviour and dynamics have been widely studied by applied biologists with specific regard to the storage environment (see, for instance, the numerous papers by Howe and Surtees which will be quoted later). Studies of storage pest ecology under realistic conditions have been relatively few and have considered mainly temperate conditions
(e.g. Coombs and Woodroffe, 1963, 1968 and 1973; Sinha, 1973) but some aspects have been investigated in tropical stores (Smith, 1963; Prevett, 1964;
Graham, 1970).
Against this background the aim of the current study is to provide some basic understanding of the ecology of a maize storage crib - 3.
to identify and describe the main attributes both of the physical environment and of the insect community that develops within it.
Such a study can only be a beginning. One type of crib in a single
locality was chosen for consideration and priority was given to observing as many features of that system as possible rather than trying to analyse particular aspects in detail experimentally. The
intention was not to evaluate the particular storage technique used, nor to try to provide solutions to the 'problems of crib storage*.
It is hoped, however, that the insights provided by this study can contribute to the improvement of research and assessment methods in
the applied field of crop preservation and so to the more rational evaluation of small-scale storage technology.
The selection of the physical and biological parameters to be considered largely reflects the practical context of the work. The progress of storage infestation was monitored by periodic sampling of infested grain to give estimates of the adult insect population
levels and net recruitment, grain moisture content and grain weight
loss. Different initial conditions were used to investigate the
initial source of infestation, the effects of grain damage in the field prior to harvest and the impact of different harvesting practices.
Particular attention was given to the evaluation of sampling methods and features of the insect populations such as distribution and move- ment which bear directly on them. Insect distribution was also con-
sidered in relation to temperature and moisture content gradients within the crib.
A maize crib must be considered as an integral part of a particular
farming system. Ibadan in S.W. Nigeria was chosen as the base for
this study, largely because in this area two crops of maize can be grown each year, with correspondingly flexible possibilities for storage trials. Maize is the main cereal crop and widely grown in the Ibadan area but, under current economic conditions, is not gen- erally stored in farmers' cribs for subsistence use. In the absence of a strong local tradition it was decided to base trials on specially constructed cribs using an 'improved' design developed by the F.A.O.
African Rural Storage Centre at Ibadan (F.A.O., 1980). The principles on which this system is based are considered in more detail later
(see Chapter 2), but essentially it depends on the use of an unusually narrow crib (80cm wide) whose slatted walls allow maximal airflow through the grain; the crop can be harvested soon after physiological maturity, at a much higher moisture content than is possible with most traditional designs. Such cribs are currently being introduced by some national extension services in West Africa.
Similarly, the maize varieties for these trials (TZPB and TZB) were chosen as. being typical of 'improved', high-yielding varieties which are now widely grown. It has often been reported that such varieties are more susceptible to storage insect attack than the trad- itional varieties which they displace (Dobie, 1974) and this appears to be true for these two varieties (Olusanya, pers. comm).
The picture of the maize crib that emerges from this study is a complex one. The community supported by the crib is a large and varied one in which insect species, including primary grain feeders, detritus feeders, predators and parasitoids, are prominent but in which mites and moulds also play an important role. At any particular time there are slight differences in the physical conditions in different parts of the crib and marked differences in the distribution of various insect species. With time, climatic conditions (and so conditions within the crib) vary according to daily and seasonal cycles, and on these changes are imposed the progressive change in the substrate as it dries and becomes increasingly damaged. The occurrence of the insect species, too, follows a consistent succession through the storage season, but within this succession individual species may be strongly constrained by biotic factors, such as competition and predation.
This thesis seeks to develop the theme of the maize crib as an ecosystem. The evidence is considered for the importance of various kinds of interaction within the insect community and between that community and its environment. The performance of the more important species is discussed in the light of their known physiological tol- erances, behaviour and dynamics. Finally, the conclusions of the biological studies are briefly considered in terms of their implications for insect control strategies and for the effort to develop improved crib storage techniques. 6.
CHAPTER 2
THE PHYSICAL ENVIRONMENT
2.1 The Crib as a Drying Structure
When maize reaches physiological maturity the grain has a moisture content of 30 - 35% (F.A.O. 1975). If such grain were to be harvested immediately and placed in a closed store it would rapidly be destroyed by a combination of mould and bacterial activity (and, to a lesser extent, its own respiration). The limiting conditions for damaging mould growth are determined primarily by the moisture content of the grain and the rate of airflow over it. The precise relationship between these factors is complex but, for practical purposes, in humid tropical areas such as Ibadan, shelled grain must be dried to a moisture content below 15% if it is to be safely stored in jute sacks, or to below 13% for storage in silos (Boshoff, pers. comm.). The more gen- eral statement is sometimes made that, for safe bulk storage, grain must have a moisture content below that which is in equilibrium with an air relative humidity of 70%; this is equivalent to a moisture content of 13.5% for maize at 27°C (Hall, 1970). In a climate where air i humidity is predominantly low, as in the northern savannah areas of
West Africa, maize left standing in the field will dry naturally to such a moisture content within a matter of days. However, in the more humid Guinea savannah and forest zones, this process may take several weeks and during this period losses to birds, rodents, insects and moulds may be severe (F.A.O. 1975).
Small quantities of grain harvested at high moisture content are traditionally hung up to dry in dwelling houses, outdoor 'kitchens', or trees, or they may be spread out on the ground during periods of sunshine. Larger quantities of grain may be dried artificially, using solar energy or in batch-driers using wood or hydrocarbon fuels; however, such methods are often prohibitively expensive in fuel costs or in the materials and/or labour required. In such situations a maize crib, acting as a combined drying and storage structure, may constitute a satis- factory alternative. The crib may be cheaply constructed, using locally available materials, during periods of low labour demand.
If suitably designed the crib can afford some protection against birds and rodents while the grain dries in the natural airflow through the structure. Drying of the maize can be hastened, and possibly some protection against insect attack achieved, by lighting a slow-burning fire under the crib - as is done in rural areas to the South of Ibadan
(Jambawai pers. comm.).
The use of cribs to dry and store maize has been investigated in several studies in Southern Nigeria. Cornes and Riley (1961) found that maize harvested at 20 - 25% m.c. dried in traditional cribs to
9 - 11% m.c. over six months of storage. 'Improved1 cribs with increased ventilation were found in one study to achieve higher rates of drying than a traditional crib over the first 20 days in store
(2% per 10 days and 1.5% per 10 days, respectively), drying thereafter being uniform (Cornes and Riley, 1962). In a later trial, however, under more humid conditions, no difference was found between the drying rates in cribs of three different designs, leading Cornes (1963) to conclude that there was no scope for improvement of drying rates in small cribs. Noting that the minimum daily relative humidity was higher than 60% for most of the year, he also concluded that the use of maize cribs was not satisfactory in this area.
Workers at the African Rural Storage Centre, Ibadan, studying the critical factors determining the rate of drying and the degree of mould development in cribs, concluded that the most important factor
was the width of the crib (F.A.O., 1980). It was shown that, even in
the most humid areas, if a crib with a maximum width of 60 cm. is used,
maize could safely be harvested and placed in it at a moisture content
of 30%; in less humid areas the 'safe' width could be progressively
increased (to approximately 80 cm under Ibadan conditions and to as much
as 150 cm. in drier northern areas). If the husks are retained on the
cob, as is the traditional practice in many areas, maize can be harvested
and stored in such a crib at a moisture content of 20% or below (Thorshaug,
1975). Traditional cribs may be 3m. or more in diameter but drying
rates in such structures do not seem to have been critically studied.
Typical designs of cribs, traditional and improved, are illustrated
in Figure 2.1.
The drying of grain depends on the equilibrium relationship between
grain moisture content and the relative humidity of the air; the
relationship (Figure 2.2) is characteristic for a particular grain
species, though it may vary slightly between varieties. Artificial drying
depends on the principle that heating air reduces its relative humidity
and so increases its tendency to absorb water from the grain. The
theory of moisture and relative humidity relationships in stored grains
and their measurement have been discussed by Mackay (1967), Pixton
(1967), Gough (1974) and Haward Hunt and Pixton (1974). As Boshoff
(1978) has pointed out, even during the wet season at a rather humid
location such as Ibadan, the mean daily relative humidity is 70 - 80%;
the corresponding equilibrium grain moisture content is 13.5 - 16.5%
and so maize harvested at a higher moisture content and stored in a
crib will dry towards this figure without the need for artificial drying. 9.
a) b)
d)
FIGURE 2.1 Examples of traditional low-ventilation maize cribs from S.W. Nigeria and an 'improved' design : a) large-diameter crib from Shawunju, near Abeokuta. b) 'inverted-cone' crib from Ofiki, Oyo State, c) 'smoking crib' in which the drying rate is increase by lighting a slow-burning fire beneath the platform; a traditional design from Shawunju. d) 'improved', highly ventilated crib from F.A.O. African Rural Storage Season, Ibadan. 10.
30
maize (desorpt1on) * * malzo (adsorption) * * 25 rfc© (dosorptfon) ^ • I
sorghum (desorptlon) 20 \
o
£ 15
C (0 c 10 U)
5 -
0 0 10 20 30 40 50 60 70 80 90 100 R.H. / *
FIGURE 2.2 Examples of moisture content/relative humidity isotherms
for three cereal crops : drying curves only for rice and
sorghum, drying and rehydration curves for maize (a yellow
dent variety). Isotherms for rice and maize determined
at 25°C, that for sorghum at 27-28°C. (Data from Gough
and Bateman, 1977).
*» 2.2 Macroclimate at Ibadan.
The climate of coastal West Africa depends on the annual move- ment of the Inter-Tropical Convergence Zone (I.T.C.Z.) - the meeting point of the dry continental (Saharan) air mass and the moister oceanic one. In the more southerly regions the northward movement of the
I.T.C.Z. and its return are marked by two distinct periods of heavy rain, in May - July and September - November, separated by a humid,
cloudy period of rather lower rainfall, in August/September (Figure 2.3).
Throughout this period temperatures vary daily between about 25 and 35°C
and relative humidity from 60 to 100% (mean 70 - 80%). During the months of December to March, when the I.T.C.Z. lies to the South,
the climate is dominated by the movement of dry air-streams from
the Sahara (the'Harmattan' ) which bring stronger daily cycles of temp- erature (20 - 40°C) and relative humidity (30 - 100% - mean 50 - 60%).
The typical daily cycles are illustrated in Figures 2.4a) and b). In more northern areas of West Africa the two wet seasons converge until
at about latitude 8° and above in Nigeria there is only a single wet
season.
In areas such as Ibadan, with a bi-modal pattern of rainfall,
two crops of grain can be grown each year. The first planted in April, benefits from the more prolonged and consistent rainfall of the first part of the wet season but must be harvested in August (during the 'short dry
season1) under conditions of high humidity and low insolation. The
second crop, planted in September and harvested in December or January, may suffer from drought in some seasons but ripens under conditions much more favourable to rapid drying, with lower daytime humidity and more
sunshine. These differences are exemplified by the climatic data for
the research site, covering the period of the current study (Figures
2.3 to 2.5). The contrast in the environmental conditions at the
times of the two harvests, and therefore in the background to the storage 12.
FIGURE 2.3 Climate at the study site, Ibadan : a) weekly total rainfall and b) mean daily solar radiation on a weekly basis for the period of the storage trials (August 1978 to July 1979). Maize was harvested in mid August ('Wet Season Harvest') and late December/early January ('Dry Season Harvest'). (Data courtesy of T.L. Lawson, Agroclimatologist, I.I.T.A.). FIGURE 2.4 Climate at the study site: daily cycles of air
temperature and relative humidity typical of a) Wet
Season and b) 'harmattan' conditions. (Data for 17-20th
October and 21-24th November 1978, respectively; trans-
cribed from F.A.O. A.R.S.C. recorder). 13. a) WET SEASON relative humidity s %
b> DRY SERSON relative humidity / % 14
40 dally temperature 35 - O O \ 30 o c. 3 +> 25 * a c_ ID Q. 20 £ O 15 •
i i i i t
100
* 80 \ X t 60 "O E J 40 o c 20 daily relative humidity
0 t i, Rug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
FIGURE 2.5 Climate at the study site: minimum, maximum and mean daily
temperature and relative humidity on a weekly basis for the
study period. (Data courtesy of T.L. Lawson, Agroclimatologist,
I.I.T.A.). 15.
25 r
20 •x
\ 15 o
£ C 10 (0 i- U) f j. observed m.c.. 5 • ...... predicted equilibrium tn.c.
0 j i i 1 1 1 1 1 » i 1 1 Rug Sep Oct Nov Dec Jan Feb Mar Rpr May Jun Ju 1
FIGURE 2.6 Comparison of moisture content observed in maize from cribs at Ibadan with 'predicted' equilibrium moisture content. Equilibrium values derived from daily mean relative humidity using an isotherm for white dent maize (from Gough and Bateman, 1977). 'Bars' on observed data represent the actual mean values for two replicate cribs (i.e. range). trials discussed, is of great importance to the development of the
insect populations.
The data on mean relative humidities through the year (Figure
2.5b,) may be used, with a standard equilibrium moisture curve for maize (Gough and Bateman, 1978), to plot the expected equilibrium
grain moisture content through the year. This may be compared with
the actual moisture content data obtained from the cribs (Figure 2.6).
It may be seen that the newly harvested grain rapidly approaches and
indeed falls below the 'predicted' equilibrium moisture content. Both histeresis and the tendency for higher wind speeds to occur during
the afternoon(when relative humidity is at its lowest) may have contri- buted to the apparent discrepancy between 'expected1 and observed
figures during the dry season.
2.3 Microclimate and Physical Conditions within the crib
The collection of data on the physical conditions within the cribs
was felt to be most important for interpretation of the biological data
and for any experimental investigations which might be carried out
later under controlled conditions. Particular instances will be dis-
cussed later (see §2.4 & §4.5), but at this stage it may simply be
noted that temperature and grain moisture content strongly affect the
reproductive success of storage pests (eg. Birch, 1945; Howe, 1956,
1960, 1962; Utida, 1971) and their behaviour (eg. Surtees, 1963a and 1965;
Amos et al.1967 & 1968). In addition to these two major parameters
(i.e. grain moisture content and temperature) it would seem likely that the
rate of air flow and the level of air relative humidity might be im-
portant variables in the crib environment. However, both are technically
difficult to measure and no attempt was made to do so in this study.
Considerable attention has been given to temperature and moisture distribution in bulk grain stores and to their practical implications
(e.g. review by Muir, 1973), but little information is available for maize cribs.
2.3.1 Grain Moisture Content
Insect sampling was based on the collection of samples of in- fested grain and in all trials sub-samples of grain were retained for determination of moisture content. An oven method, based on the
International Standards Organisation routine method (I.S.O., 1979), was used. The method is described fully in Appendix IV but, briefly,
it depends on heating a small sample of ground grain in an oven at
130°C and determining the resultant weight loss (which is assumed
to be equal to the water lost). Samples of higher moisture content
(above 17%) require a two-stage process in which some of the water is
driven off (and the weight loss determined) at a lower temperature.
Electrical resistance methods for measuring moisture content, using both the Marconi meter pressure cell and Reethorpe sensors (for measurements within cribs), were investigated but both proved unsat-
isfactory in the relatively moist conditions encountered in these trials
consistent results could not be obtained with the Marconi meter while
grain inside some of the Reethorpe 'probes* became mouldy.
Determinations of moisture content were made either on grain from
single cobs or on 'pooled' grain from several.. At harvest time the
variation in m.c. between cobs (and, indeed, in grain from different
parts of single cobs) was wide (Figure Z. 7a).Moreover the grain often
appeared to have a markedly different moisture content from the core
(Figure 2.7b), however techniques for determining the latter variable
are not well established and the method used here may not be entirely
reliable. As the grain moisture content approached equilibrium the 18.
8 samples from newly-harvested cobs
\
> « 4 u 4> 0
e ta 15 20 25 30 35 • * nom m.o.
2.0 r samples -from cobs In store
1.5
\
> * * ® 1.0 TJ
•+> o id 0.5
0.0 10 15 20 25 no an w • o • / %
FIGURE 2.7a) Variability in moisture content of grain and cores: intercob variation in grain moisture content showing greater variability in freshly harvested material (Data collected from several trials; storage samples were from material that had been in store for periods from 2 weeks to 10 months). core m.c- / %
FIGURE 2.7b) Variability in moisture content of grain and cores: b) relationship between grain and core moisture content; each • point represents determinations for an individual cob. Straight line is for grain moisture content = core moisture content. 20. inter-cob variation decreased, but then increased again in the later stages of storage due to uneven moulding and insect infestation of the cobs.
This variation in the moisture content means that, at a particular time, a variety of microhabitats are available to the insects, and indeed there is evidence that moister cobs are preferentially in- fested by some species (see §4.6). In practical terms, this variation leads to particular problems in the accurate estimation of weight losses
(see §3.5 iand Appendix V), which must be assessed on a dry-weight basis.
Long-term changes in moisture content were monitored by deter- minations at short intervals (2 to 4 weeks) on samples from the centre of each of eight cribs. In addition, samples were taken more rarely (1 to 2 month intervals), from 24 points in a single crib to investigate the possibility that drying might be uneven in different parts of the crib. Finally, uneven moisture distribution was more intensively studied over a short period, using 32 samples removed on each of 3 occasions from 3 cribs. The results of these trials are described briefly below but discussion of their biological implications will be left until the results of the associated insect sampling have been considered (§4.6 and 6.6).
Data from the long-term trials are presented in Figure 2.8. Details of the methods used are given in Appendix IV and of the overall crib treatments in Chapter 6. Plotted points represent means from each pair of cribs receiving the same treatment, based on determinations on subsamples from 3-5 cobs from each crib; 'bars' indicate the actual values obtained (i.e. range not standard deviation).
As already mentioned, the grain apparently dries to its equil- ibrium moisture content very rapidly, although in the case of the wet- season harvested material, this equilbrium level itself remains high FIGURE 2.8 Grain moisture content in samples from the centre
of cribs at Ibadan and Ilora (as indicated). Plotted
points are mean values for each pair of replicate cribs
with bars indicating means for each crib individually.
Data based on three oven determinations for individual
cobs, from each crib. 21.
25 UNRERTED CRIBS - Ibadan
N 20 o E C "5 15 c. a
10
25 r FUMIGRTED CRIBS - Ibadan
\ 20 o e c « 15 Y CD
10
25 r FUMIGATED CRIBS - Ilora
\ 20 o £ C
c«. 15 O)
10 j 1 u J 1 L Rug Sep Oct Nov Doc Jan Feb Mar flpr May Jun Jul for several weeks (until the onset of 'harmattan* conditions). Cobs used for all six 'wet-season' cribs were filled with maize from the same field and harvested over a period of only three days. Comparison of Figures 2.8) and b) indicates, however, that the fumigated grain was loaded at a higher moisture content; this was due to a slight build-up of moisture during the fumigation procedure (the material was fumigated with phosphine for four and a half days in hermetically sealed drums). The maize stored in cribs at Ilora Farm Settlement appears to have dried more rapidly than that at Ibadan and also remained at or near the minimum moisture content for a longer period. Ilora is only 35 - 40km north of IITA, however it lies in the 'derived savannah zone (while Ibadan lies within the current limits of the forest) and seems to have a distinctly drier climate.
The data from the (multi-point) long-term distribution samples are presented schematically in Figure 2.9, indicating the positions in the crib from which samples were drawn; the figures given are the . means of three determinations from each sampling point (carried out on samples from three randomly-selected cobs). Differences between one part of the crib and another are small, at most only 1-2%, but analysis of variance indicates that these differences are consistent at a particular time. A preliminary analysis (not presented), in- cluding the data from .all four sampling occasions and taking the 24 sampling points as separate 'treatments', confirmed the impression that the moisture distribution was markedly different on each occasion and, accordingly, the four samples were analysed separately. The sampling points were grouped factorially, as indicated in Figure 2.10, to allow different elements of the 'Position' effect to be separated; the results of the analysis of variance are summarised in Table 2.1. 23.
sample 1 (8/9/78) sample 2 (6/10/78)
yk. y y?.~y\ ^ yis.y yUy^ y y?.y yis.y y y'iG.y yxs.y y /is. y E/ | ^ ys.y ySa.
yii ,-y' yi?.y y'\ 1 ^ " y*\
I y^-yy i y*y /s,/ x
X | y^.y ysy
yA?.y y?.y y . yts.y yis.^ y\?.y y\?.y y I y~\g.y yi5 .y" y yu.y y?.y y y™-v y^-y y
sample 3 (22/11/78) sample 4 (11/4/79)
y y^.qy- yj.y y y*y y*y ' y*.y y-.y \ y y*-y .-- '"14 . S .s
y*y y\ y^y y[5-y- S
i y^-y y^y y' i y*y y* \y y \yI.?y y^>y y i \ys.y ys.y y
I y yi y y^y | ^ ysy y*-y y y2.y AI.AS | x yu.y ys.y' |y yiiy y\iy y*y y*-y
y^.y y*.y y y*y yu.y y yid.y yu.y y i y*y y*y y yis.y y' • y^.y yis.y y
FIGURE 2.9 Grain moisture content in different parts of a single crib on four occasions during the storage period (dates as indicated on figure). Each figure is the mean of three oven determinations from individual cobs. Samples 1 and 2 were taken during the humid wet season (after 2 and 6 weeks in store) sample 3 under harmattan conditions (after 3 months in store) and sample 4, after the onset of the following wet season (after seven months in store). 24.
upper
Rrtalysls of Variance Factor1al R level 1n ortb C2) B East-Heat (3) I outer C %exposure' (4) replications (3)
_ middle 3/ 7East
FIGURE 2.10 Design of factorial analysis of variance for moisture
content data from long-term trial: data from various
sampling points in the crib were grouped factorially, as
shown in diagram; data for each sampling occasion were
analysed separately. TABLE 2.1
Probabilities:
Sample 1 Sample 2 Sample 3 Sample 4
Source of variation df. (8/9/78) (6/10/78) (22/11/78) (11/4/7$)
Total 71
A top-Bottom 1 <0.001 0.15 <0.001 0.21
B East-West 2 <0.001 <0.001 <0.001 0.001
C exposure 3 0.15 <0.001 <0.001 <0.001
AB 2 0.66 0.33 0.07 0.08
AC 3 <0.001 <0.001 <0.001 0.01
BC 6 0.31 0.06 0.03 0.01
ABC 6 0.55 0.27 <0.001 <0.001
Sampling error 48
TABLE 2.1 Probability levels from 3-factor analysis of variance of
moisture contents from different positions in a crib, at
four different stages during the storage season.
(3 'factors' are different components of a 'position'
effect : design as in Figure 2.10).
Samples were taken after 2, 6, 12^ and 30^ weeks in store. Different factors seem to be operating on the four occasions.
Comparison of the analysis of variance with the raw data (Figure 2.9) suggests that on the first three occasions there was a strong East-
West gradient (though not always in the same direction), possibly imposed by the direction of the prevailing wind; on the the fourth occasion, at the beginning of- the following wet season, the dominant effect was a more uniform rehydration from all surfaces of the crib.
It should be noted in the former case that the prevailing wind may serve either to increase the apparent moisture content, if it carries rain, or to reduce it if the air relative humidity is low.
The short-term investigation was carried out over a six week period during the main wet season (of 1979) using material harvested
and stored during the previous dry season. Data on grain moisture contents was obtained from nine 32-point samples (i.e. on three occasions from each of three cribs) and an additional 64-point sample from each crib
as it was unloaded. The design of the sampling schedule will be discussed more fully in connection with the insect distribution studies which were based on the same samples (see §4.2). At this.stage it may be noted that in the analysis of the former series of samples the
sampling occasions appear as major blocks but that the inter-crib variation cannot be assessed (each 'sampling occasion' and each 'Time
of day' including one sample from each crib); this should not be a serious
problem so long as the 'crib' and 'time of day* interaction is not
significant. The sampling points were grouped differently for the two
analyses, as shown in Figure 2.11a) and b); the groups were chosen so
that further comparisons could be made to separate different elements
of the 'position' effect (as in the previous analysis). However,
this did not, in the event, provide significant additional information. 27.
a)
Rnalysla of Variance Factor1 a! R time of day (3) B position In orlb (16) (as shown) sampling occasions (3) as blocks minor reps. (2)
top Rnalysls of Varlanes Faotorlal fl Ieve1 In orlb (4) uppsr-m1d B Nsxposurs' (8) cribs (3) as blooks minor reps. (2) Touts r-mld
bottom
FIGURE 2.11 Design of factorial analyses of variance for moisture
content data from short-term trials:
a) pattern for successive determinations during the
course of the trial.
b) pattern for analysis of final determinations at com-
pletion of trial. 28.
TABLE 2.2
a) Anovar
Source of variation df, F ratio probability
Total 287
Blocks (sampling occasion)
A Time of d 2 8 .37 <0.001
B Positions 15 2 .44 0.004
AB 30 0 .34 0.999
Block error 94
Sampling error 144
;: moisture content / %
r - a.m. : 17.1
mid-day : 17.5
p.m. : 16.8
B Positions: East corners Upper 1. 18 .0 Lower 9. 17 .3
West corners 2. 17 .8 10. 17 .4
East faces 3. 17 .2 11. 16 .6
West faces 4. 17 .5 12. 17 .0
N/S faces (East) 5. 17 .5 13. 17 .1
N/S faces (West) 6. .17 .5 14. 17 .2
Interior (East) 7. 16 .9 15. 16 .5
Interior (West) 8. 17 .0 16. 16 .6
TABLE 2.2 Summary results of analysis: effects of time of day
and position in crib on grain moisture content
(Short-term distribution trial).
a) probability levels from analysis of variance
(design as in Figure 2.11a)).
b) treatment means. 29.
TABLE 2.4
a) Anovar
Source of variation df. F ratio probability
Total 191
Blocks (cribs) 2
A. Level in crib. 3 41.95 <0.001
B. Exposure 7 15.02 <0.001
AB 21 0.67 0.84
Block error 62
Sampling error 96
b) Treatment means (grain m.c./%)
A. Levels: Top 18.1
upper middle 17.2
lower middle 17.1
bottom 17.0
B. Exposure: East corners 17.4 West corners 17.8 East face 16.8 West face 17.6 South face 17.9 North face 17.0 Interior (East) 16.9 Interior (West) 17.0
TABLE 2.3 Summary results of analysis: effects of position in crib on grain
moisture content (termination of Short-Term Distribution trial).
a) probability levels from analysis of variance (design as in
Figure 2.11b)
b) treatment means. Each moisture content determination was carried out on a subsample
of pooled grain from three cobs drawn from each sampling point.
The data on which these analyses were based are given in Appendix
IV and a summary of the results of the analysis of variance in Tables
2.2 and 2.3. Both analyses indicate consistent differences in moisture
content at different levels within the crib and at different points within each level. The time of day at which the samples were taken
also appears to have a significant effect (Table 2.2). This is, ini-
tially, surprising, given the slow rate at which maize grains lose
and gain moisture, however, it may be that the differences are at
least partly due to superficially absorbed moisture, from rain and/or
dew.
2.3.2 Temperatures within the grain bulk.'
Temperature measurements were taken from the cribs during both
long-term and short-term distribution trials. A set of readings was
taken at the time of each insect sampling and additional readings were
taken to assess temperature changes through the day. Thermistors
were placed at different points within the grain bulk and readings
taken using a Telemax electrical thermometer. For the long-term
trial only seven thermistors were available and so these were arranged
to indicate the extreme conditions within the crib (i.e. near the
six surfaces and at the centre). In the short-term trials 33 thermistors
were used - 32 spaced regularly through the bulk and the last measuring
air temperature in the free space above the grain. Thermistors were
placed in contact with the cobs, to measure the grain surface temp-
erature, and even those in 'surface1 sampling positions were placed
within the grain bulk so that they could not be directly warmed by
the sun. 31. 21.Q 21 .0 26.5
20.5 s 20. 0 :5.0 y 2 1.0- -21.0 20.0 y •21 .0 19. 0 26. 0 27.0 •26.0 20.5 y
22.8 y 2 1 .0 27. 0
20. 0 13.0 03.00hrs (22/11/75) 26.5 07.3©hr s (22/11/78 3 11.00hrs C£2/11/78
30. 0 29.5 30.0
30.0 25. 0 30.5 / 30. 5 ^ 2 1.0- 29 .5 30.0 30.0- 29. 0 30. 5 30.0- •29.0 3 1.0 30.0 30. 5
30.0 29.5 15.3 0hrs (22/11/73) 30-0 13.45hrs (22/I 1/78) 17.30hrs C£2/11/73
23. 5 29.0 2 1.5
20.0 27. 0 20.0 / 22 .0 -24.0- 22 .0 26.5 •2 9.0 26. 0 20.5 2 1.0 19.0 s 25.0 22. 21.0
22. 0 2 4.0 01.00hrs (23/11/78) 18,5 £2.00h rs C22/11/73) 07.45hrs (£3/11/73
FIGURE 2.12 Changes m temperature at different points in a single crib
during a 24-hour period: Data for period
a) immediately preceding 3rd sample (long-term trial) under
harmattan conditions. 32. 25. 3 29.4
25 .5 23.2
25.8 23.8 29.5 30.0 •32.0 •28.s 0
29.0 31.0
26. 2 29. 1 12.00hrs CI 1/4/73) 08.08hrs (11/4/73) 29. 5 27.8 30. 1 30.5 33. 5 23 . 1 30.0- •29 .0 29 .5 •29.8 33. 0 29. 2 28.0- •2?. a 30.5 3 1.0 29. 3
30.8 31-5 20.00hrs (11/4/75) 29-2 16.00hr s Cll/4/79) 24.09hrs CI 1/4/79)
25. 0 25.2
6.2 25.2 y
26.4 25. 0 25 .5 26 . 4 •24.8 25.8 s / 23 .5 2 B . 2
27. 8 27.3 04.00hrs (12/4/73] 03.00hrs C12/4/79)
FIGURE 2.12 Changes in temperature at different points in a single crib
during a 24-hour period: Data for period
b) immediately following fourth sample (long-term trial)
under Wet Season conditions. 33. IS Tf\ \ OJ Is \ «-* W ID m in k » PI cj \ \ \ OJ OJ * > s: •3 \ • CD P7 o SI V s \ m \ CJ \ CO s s o V V s PJ \ s s
IS N x [\ IS IV s IS, a N \ 'V fs s
koc- Vi rr> r* \ \ 13 o © \ CD N \ \ \ OJ \ CO s. \ OJ \ \ OJ \ SI
K \ N- ^ K S IS \ k Is s \ \ \ X
VJ
s Q •n © ID \ \ s '35 13 \ CD \ CU \ \
FIGURE 2.13 Changes in temperature at different points in a crib
during a 24-hour period: data for 23rd February 1980,
during the dry season, but without 'harmattan1 conditions. The temperature data corresponding to samples three and four of
the long-term trials are given in Figures 2.12a) and b) . In both
cases the grain seems to be providing considerable insulation against
the extremes in the ambient temperature: in the former case against
the low night temperature characteristic of harmattan conditions and in
the latter against the high afternoon temperature. It should also be noted that the actual surface temperature" of cobs exposed to direct
sunlight will be considerably higher than the maxima recorded here
(from positions approximately 10cm from the surface of the crib). The
observations presented in Figure 2.13, from 32 points in a crib re-
corded in February, indicate a similar pattern to that shown in Figure
2.12b); again the largest temperature differential, of approximately
4°C, was recorded in the late afternoon.
The temperature gradients indicated here are low compared with
those encountered in shelled bulk grain stores, but, given the small
size and open construction of the cribs used in this study, it is perhaps surprising that there are appreciable gradients at all. In biological terras the insulating effect provided by the grain bulk
even in small cribs may well be significant in keeping the temperature
of most of the grain within a narrow range of the optimum for insect
development (c.27°C for several major pest species).
The temperature data from the short-term trials are set-out
schematically inEigura 4.11c. The data were analysed using the same
design as that used for the moisture contents. The summary results of the
analysis of variance and the basic design are given in Table 2.4, however,
it should be noted in this case that analysis of variance is not
strictly appropriate as the readings were, inevitably, collected from
single points in a systematic grid and so were not random samples from 35.
TABLE 2.4
a) Design of analysis (as for moisture contents Figure 2.11a))
2 Factors : A Time of day (3)
B Positions (16 - as before).
3 Blocks : Sampling occasions
2 Replicates
b) Anovar,
Source of variation df probability Total 287 Blocks 2 A - Time of day 2 <0.001 B - Positions 15 0.06 AB 30 <0.001 Block error 94 Sampling error 144
c) Treatment means (A x B interaction means) time of day: Positions: a.m. mid-day p .m. 1 upper East corners 23.8 26.1 27.8 2 West corners 23.0 25.9 28.0 3 East faces 24.5 26.2 27.4 4 West faces 23.2 25.9 27.7 5 N/S faces (East) 23.7 26.1 27.7 6 N/S faces (West) 23.7 26.0 27.7 7 Interior (East) 24.3 25.8 27.1 8 Interior (West) 23.9 25.8 27.3 9 lower East corners 24.3 26.4 27.8 10 West corners 23.1 26.1 28.3 11 East faces 24.9 26.2 • 27.8 12 West faces 23.3 26.0 28.7 13 N/S faces (East) 24.2 26.3 27.8 14 N/S faces (West) 23.9 26.1 27.7 15 Interior (East) 25.1 26.2 27.5 16 Interior (West) 24.7 26.1 27.4
TABLE 2.4 Summary results of analysis: effects of time of day and position in crib on grain (surface) temperature. a) outline design. b) probability levels from analysis of variance c) treatment means (each figure is mean of 6 determinations). 36.
the 'population' of possible readings within each sampling position.
This proviso apart, the results tend to support the obvious prediction
that the distribution of temperatures within the crib, as well as
their level, is markedly affected by the time of day.
It is of interest that comparable differences in both surface
temperatures and grain moisture content between East and West faces of cribs were noted in an earlier study at Ibadan (F.A.O. 1975), but not critically investigated.
2.4 Maize as a substrate for Insect development.
To complete the description of the environment in which the pest populations develop, the characteristics of the substrate need
to be briefly outlined. The grain moisture content and temperature have already been considered; in addition, the physical state of the grain and its nutritional characteristics are of great importance to the insects.
A particular batch of grain will have certain inherent character- istics which may be partly or wholly determined by heredity (i.e. varietal characters) and others resulting from the conditions under which the particular crop was grown (for instance, periods of drought
stress or nutritional deficiencies). Such characteristics in the case of maize include the nature of the endosperm (e.g. hard and vitelline in the case of 'flint' types, soft and floury in 'dents'), and its chemical composition (e.g. its lysine content), the nature of
the seed coat, and the number, size and form of the 'spathes' that cover the cob. These characteristics are known to have a very marked effect on the susceptibility of the maize to insect attack, (see,for instance, the summary by Dobie, 1977). These inherent features will be modified by any damage caused to the grain by the harvester (human or machine), by rodents and birds, by moulds and by the insects themselves. The intact grain is, to some extent, protected by the intact seed coat and cob sheaths (if present), and its hardness when dry confers resistance to some pests.
A limited range of agents (including some insect pests) will be able to overcome these barriers and their activity will in turn make the grain a suitable substrate for a much wider range of species. Damage begins in the field (§5.2) and will be continued in store at first mainly by the primary pest species (Sitophilus zeamais and Sitotroga cerealella in the cribs studied) and by rodents. The progressive increase in damage which occurs in store represents a significant change in the nature of the substrate. No attempt was made in this study to quantify these changes, except in as much as they are implied by the weight loss figures; a great increase in the proportion of 'holedf grains and in the quantity of 'frass' was however obvious in all cribs over the storage period.
Moulds are of particular importance to the progress of substrate degradation. Apart from the direct damage they cause to the grain, moulds may promote insect damage either by favourably altering the structure and nutritional status of the Substrate or by providing a supplementary source of food (Sinha, 1971). Fungal infection occurs in the field, involving both pathogenic species (e.g. Diplodia macrospord and Ustilago maydis) and others which usually accompany insect damage
(e.g. Fusarium moniliforme). In the well-ventilated cribs used for
this study there was little visible spread of moulds to undamaged grains and with the onset of dry-season conditions even damaged grains did not become affected. When more humid conditions returned at the beginning of the next wet season, extensive sporulation and dis-
colouration of grains was again observed on damaged cobs, especially
on those exposed on the surface of the cribs. Wallace (1973), con-
sidering mainly temperate conditions, describes a succession in the
community of fungal decomposers of grain: in the field, species of
Alternaria, Cladosporium and Helminthosporium are the most common but
in storage these are displaced by Aspergillus spp. and Penicillium
spp..
In assessing the importance of the various changes that occur
in the grain, it is important to recognise that only a small minority
of the insect species found in cribs are primarily adapted to a stored
grain environment, or even to seed-feeding. (The former group will
include, for instance, species that have become adapted to the ex-
ploitation of the 'natural' stores of rodents). The majority of species have 'moved' to grain stores from rather different habitats such as wood (Bostrichidae and Lyctidae), under-bark (Tenebrionidae and Silvanidae),
leaf litter and various other types of decaying vegetable matter
(Nitidulidae, Mycetophagidae). The various natural sources of 'storage
insects' have been reviewed by Linsley (1944). As will be discussed
later (Chapters 4 and 6), different features of a particular environment will be limiting for each of these diverse groups of insects. 39.
CHAPTER 3
SAMPLING TECHNIQUES
3.1 Introduction
The sampling of storage insects presents many of the same problems that are encountered in other branches of insect ecology: the insects are active, they may be unevenly distributed in space or time, their numbers need to be related to an appropriate unit of their environment and so on. The most significant problem particular to the crib en- vironment is that of access : material can only easily be removed from the top surface, while the insects infest the whole grain bulk.
Stratified samples may be collected relatively easily from stores of shelled grain by the use of hollow probes, of which various designs are available. In most, the grain and infesting insects are retained in a chamber (or chambers) within the probe while in others they are removed continuously via an aspirator tube running down its centre.
(Burges, 196o). A probe of similar design, the Iowa Corn Probe, is available for use in cob-maize stores, the outer sheath in this case bearing stout teeth which rasp the grain off the cores fin situ'; unfortunately this instrument has a number of drawbacks which make it unsui for quantitative sampling of adult insects (§3.3.1)'. The alternative is to remove whole cobs. However, in a maize crib the cobs are packed so tightly together that it is virtually impossible to withdraw even single cobs from the interior of the store. Cobs can be removed from up to c.30cm from the top surface, but many of the more active insects will be lost in the process.
Considerable attention is given in the existing literature to appropriate methods for selecting stores for sampling (for instance, de Lima (1975), Adams and Harman (1977), Drew.(1978))but relatively little to the problem of obtaining representative samples within a store. Most authors (e.g. Adams and Harman (1977), Pointel (1969)) have been content to take samples which mimic, or accompany, the consumption of grain as it occurs in a subsistence store (i.e. grain is removed at frequent intervals from the top of the store so that the grain is entirely 'consumed' by the end of the storage season).
De lima (1973), sampling from rather small, shallow stores, found that by reaching down 'as far as possible' into the cobs it was possible to remove cobs from as deep as the bottom of the store after only a few weeks of'consumption'. While such surface-sampling techniques may be adequate for many practical purposes (for instance for loss assessment surveys), they depend on the assumption that insect in- festation is essentially uniform at different levels within the crib.
There seems to be little evidence on which to base this assumption.
Samples can be taken from all levels of a crib at the time of unloading - and, clearly, cribs could be broken down after different periods of time to obtain information on the progress of infestation
(although this method does not seem to have been widely used, pre- sumably because of the quantity of materials required). Evidence from such studies on the uniformity of infestation is conflicting. Schulten
(1972) found'little stratification of damage' while Kockum (1953 and
1958) did find significant differences between damage at different levels - though the pattern was not uniform for the various treatments (in-
secticides) he used. Both Kockum (1953) and Pointel (1969) found differences in the levels of damage near the surface and in the interior of cribs.
The variety of crib designs and environments in which they are used is such that one might expect quite different patterns of insect 41. infestation in different localities. It is, however, clear that much more work is required to improve sampling techniques in general.
The assumptions on which particular methods are based need to be defined and then tested in a variety of locations to investigate the extent to which they are justified. In the remainder of this chapter,
the main objectives of, and constraints on, insect sampling in cribs will be set out and the particular techniques considered for use in this study will be discussed.
3.2 Insect Sampling : Constraints and Considerations
3.2.1. General Objectives
An acceptable storage method must, clearly,meet a variety of
social and economic requirements, but its technical success will be assessed primarily on the extent to which it is able to prevent damage
to the stored commodity. In some instances it may be sufficient to base the choice of storage method on loss assessment alone, but a more
rational strategy will involve the quantitative investigation of particular components of the loss, including that due to insects.
Work is urgently needed to relate the losses due to insects
to their abundance. This relationship is complex, depending as it
does on the biology, behaviour and dynamics of each species involved;
this question was only superficially considered in this study. The main concern here was to look at insect abundance itself and therefore
to assess the ability of various sampling techniques to estimate par-
ticular measures of abundance. Only a few of the trials went beyond
this to the application of sampling techniques to investigate questions
of practical importance - for instance, to study the effect of harvesting
practices on insect numbers and damage in store (Chapter 5). 42.
Particular attention was given to the study of dispersion patterns and variability at the habitat and microhabitat level and to changes in abundance related to short-term, daily cycles and long-term, seasonal cycles in the environment (Chapters 4 and 6).
The criteria to be used for judging sampling methods must be those applied in any branch of ecology (including repeatability, objectivity, quantifiable accuracy etc) however it was often not possible here to obtain independent estimates of particular population parameters and so, in- many cases, discussion of the merits and drawbacks of the various methods must be largely qualitative.
3.2.2 Choice of Sampling Universe.
The majority of insects found in maize cribs appear to remain closely associated with the grain throughout their life cycles. For many of the species the population level-in the crib may represent a dynamic equilibrium, involving the exchange of individuals with populations in the surrounding environment, but, on the whole, one
is dealing with species which are able to feed, reproduce and find
shelter within the sampling universe of the crib. The most obvious exceptions to this rule are some of the larger and more active ants, both phytophagous and predatory, which form colonies outside the
crib, but which forage within it. Probably several of the larger
species of Hymenoptera recorded from the cribs are only transitory vis-
itors from outside populations but these were never present in app-
reciable numbers. In general, one may reasonably hope to obtain a useful estimate of the effective population levels of both adults and
iirmatures by collecting samples only from the grain in the crib.
3.2.3 Insect Mobility
In collecting samples of infested grain one has, at first sight, 43. a direct estimate of the number of insects per unit of habitat or
substrate. The accuracy of this estimate will, however, be severely affected by the level of activity of the insects. The pest complex
in maize cribs includes species, at one extreme, which are highly vagile and easily disturbed (e.g. various Lygaeidae) and, at the other, those which are developing within individual grains (e.g.
the immatures of Sitophilus spp. and Sitotroga cerealella) which cannot escape at all. The level of activity of most species is affected by the ambient temperature and many will respond to physical shocks by flight or thanatosis.
A sampling programme based entirely on the collection of the
immatures of the primary pest species, combined perhaps with loss
assessment, could therefore be relatively easily carried out (using virtually ainy method that allowed retrieval of grain sample's). It
is arguable that such a programme would be adequate for many practical purposes. However, for this study it was clearly desirable to sample
from as much of the pest complex as possible. In an undisturbed crib
the majority of the insects feed and take refuge within damaged grains
or in the interstices between them. In practice it was found that, if
a cob is carefully picked-up and placed rapidly within a closed con-
tainer, the majority of insects associated with it may be collected;
if, however, the cob is 'jolted' or exposed to direct sunlight for more
than a.few seconds, insects will leave the cob in large numbers.
Methods had, therefore, to be evolved which allowed ready
access to the interior of the crib and with a minimum of physical
disturbance. Careful stacking of the cobs at the time of loading
was found to be necessary so that cobs could be removed singly (without setting- 44. off 1 avalanches'of cobs) and collection of insects was easier in the early morning when the low temperature made the insects less active.
The effectiveness of retrieval could not be quantified but it must be recognised that, despite all precautions, collection of insects probably was not equally effective for the adults of all species.
Moreover the retrieval of insects is markedly sensitive to practical details in sampling and to the care and dexterity of the sampler.
Standardisation would present a serious problem if the methods des- cribed here were to be used, for instance, as part of a more extensive survey, involving several collectors.
3.2.4 Sampling Units and Variability
Individual cobs represent the smallest sampling subunit that can be conveniently collected, but it is apparent that under normal circumstances inter-cob variation in the level of insect infestation is large. Single-cob samples were not taken on a regular basis, but examples taken at various times over the study period give an indi- cation of the distribution of most of the more abundant species from the initial infestation in the field through the first half of the storage period. In all cases for which sufficient data were available for analysis, chi-squared tests for over-dispersion showed variances to be significantly greater than means - i.e. distributions were clumped rather than random, normal or regular. Negative binomial distributions were found to give a good fit for most samples. Examples of the observed distributions with fitted negative binomials (using
Fisher's maximum likelihood method) are given in Figures 3.1, 3.2, 3.4 and 3.5.
The major pest species, Sitophilus zeamais, was found to become less strongly clumped with time in store (compare a) to c) in Figures
3.1 and 3.2) and, at a particular time, to be more ciumped when cobs FIGURE 3.1 Distribution of Sitophilus zeamais (adults) on maize
cobs stored 'in the husk' after a) 6 weeks, b) 10 weeks
and c) 14 weeks in store. Data are the numbers of cobs
with the degree of infestation shown, based on samples
of 30 cobs on each sampling occasion (10 from each of
three cribs) collected c. 30cm below the upper surface
of the grain bulk. 'Expected* distributions are negative
binomials, fitted using Fisher's maximum likelihood
method. s
o w iroquency froquoncy
© l\>
3 C 3 cr o
o
3 (I (I a) Ex p.d ist. Obs.d ist. k - 2.04 £ 4 c o D or c c a B-l 2-3 4-5 6-7 fl-9 lfl-11 13-13 14-15 16-1? 16-19 20-21 ?SS b) Exp.d 1 st. Obs.d i st. k - 2.10 >. 4 o c© 3 or o c <•• 2 r-C j: 0 4-T n-ll 12 —H ie-l» W-23 S*~ZT 28-11 tC-M 3f-«J» HB-^3 *4-*T 12-1$ >*» C) Exp.dlst. Obs.dist. k - 3.04 >» 4 0 c 3 o©r 1 <•- 2 a 0 i I- 9-4 P~f 1B-H I "I'll »-2* 11-IP 1B-U IP-M VJ-M "SP-nB qS-M fW-CT number of Insects • cob FIGURE 3.2 Distribut ion of Sitophilus zeamais (adults) on maize cobs stored without husks after a) 6 weeks, b) 10 weeks and c) 14 weeks. . Data presentation as in Figure 3.1. .47. slope - 1.38 fnteroept - 0.48 ® Oc (0 OJ o 0 a log (mean) FIGURE 3.3 Dependence of variance on mean for samples of Sitophilus adults from maize stored without husks. Data collated from various trials: sample size 1 - 10 cobs, taken at different stages in the storage season. Correlation coefficient for the regression : 0.95. \ 48. a) 10 Exp .d 1 st. Obs . d ist. 8 k - 2.47 >» u ©c cr o 0 0-3 4-? 3-11 12-13 IE-U 20-23 24-27 28-3 1 32-33 3B-33 >33 b) 10 Ex p.dls t. Ob s . d i s t. 8 k - 2.43 >» o 6 ©c 3 or S 4 <4- 2 T u 0-2 3-3 E-B 3-11 12-14 13-1? IB-2D 21-23 24-2E >2E No. insects / cab FIGURE 3.4 Distribution of emergences of major primary pests from.cobs stored without husks after five months in store : a) Sitophilus zeamais and b) Sitotroga cerealella. Data based in each case on forty samples of lOOg (one sample per cob); emergences scored after six days. were stored in their husks (compare Figures 3.1 and 3.2 at each level) The data from samples of different sizes and for different levels of abundance may be collated (as described by Southwood, 1978) to provide a plot of log (variance) against log (mean), as shown in Figure 3.3. The gradient of the regression is 1.38, corr- 2 — 1 38 esponding to the 'power' in Taylor's Power Law (i.e. S = 0.48 x * ), indicating that the underlying distribution of the insect is moderately aggregated and that an appropriate transformation of sampl0 e3 counts (to normalize the distribution) would be of the form i Z = x . Southwood notes that, for most purposes, data from 'slightly contagious' pop- ulations may be transformed satisfactorily by using square roots and . those from 'distinctly aggregated' populations by using logarithms. The distribution of immatures (as judged by emergences) was also clumped (Figure 3.4a) but in a number of examples (not shown) the negative binomial did not show a close fit. Insufficient data were collected to allow assessment of the distribution of the other major primary pest, Sitotroga cerealella, but immatures of this species showed a similar distribution (Figure 3.4b) to those of Sitophilus. Among the secondary pest species Cathartus quadricollis was like Sitophilus in being generally more strongly clumped in maize stored in the husk (Figure 3.5), but differed in becoming more clumped with increasing time in store. This aggregation reflects the concentration of Cathartus in the diminishing patches of sufficiently moist (and usually mouldy) maize grains. The commonest Tenebrionids, Palorus subdepressus and Gnatocerus maxillosus,were not sufficiently abundant in these samples for satisfactory assessment but their distribution appeared to be more clumped on maize without husks. Carpophilus spp. showed a similar (high) degree of clumping in both situations. All species were highly aggregated in field samples (k values for the negative binomial being less than one in most cases), both in samples taken immediately before harvest and a month earlier. Although the insect distributions have been described as 'clumped this term is not intended to imply the existence of a behavioural response to the presence of other insects. It is much more likely that the clumping reflects variation in the cobs (for instance in their moisture content) and results from their aggregation in favour- able microhabitats (as mentioned for Cathartus quadricollis, see also Section 4.7). This aspect is most important from the point of view of sampling : in some situations it may be desirable to sample from populations showing the full 'natural' range of variation. However, where the effect of only one particular factor (for instance, position in the crib) is of interest, it may be possible to reduce some of this extraneous variability by prior selection of more uniform cobs. Part of the variation is simply due to the fact that some cobs are larger than others. Accordingly, in reporting data from all trials a simple correction has been applied so that insect numbers are related to standard quantities of shelled grain at a specified moisture content Some further variation is attributable to genetic variability in the inherent susceptibility of the grain to insect attack. For example the material used for the initial trials here included a wide range of endosperm types from typical 'flints' to 'dents'. While such variability is inherent in some 'composite' varieties, such as those used here, more uniform selections within the variety can be chosen in advance. Finally, some variation will be attributable to difference in the physical state of the cobs, for instance, relating to their physiological stage at the time of harvest or to damage in the field. Where such conditions are visible at the time of loading the affected 51. a) Exp.d i st. . Obs.dist. 10 k - 0.77 >» 9 o ©c D zr © c. 4 0 a-a n-i* 19-19 2B-5« =3-« a-" «•-•• =M'4 "~aa " w No. insects / cob b) 12 Ex p . d i s t. Obs.dist. 10 k - 0.91 >» 2 0 ©c 1© 6 i. 4 0 n-i4 ia-)3 so-e* za-ca at-* ai-aa *a-*a M-a* aa-as >aa No. insect® / cob FIGURE 3.5 Distribution of Cathartus quadricollis adults on maize cobs after three months in store: a) cobs stored 'in the husk' and b) without husks. Samples collected as for Figure 3.1. cobs can be removed and the subsequent reduction in basic variability will make it easier to detect any 'treatment' effects. 3.2.5 Sample size in relation to the size of cribs. The variability shown by the populations to be sampled, even when the above measures have been taken to reduce it, is such that large samples are desirable in order to obtain population estimates with an acceptably low standard error. However, the number of cobs that may be collected for a particular sample is constrained by various considerations arising from the small scale of cribs. The cribs used for these trials each held about a half tonne of maize cobs. Larger cribs might have been desirable but their size was effectively determined by the availability of suitable material. Trials carried out at the study site (by other workers) indicated that large differences in insect infestation could be expected in cribs loaded only a few days apart (Boshoff, unpublished data). It was clearly desirable that the cribs to be used for this study should be loaded with maize of uniform origin and that loading should be com- pleted over as short a period as possible. In studying small grain cribs, there is a risk that the sampling programme itself may significantly deplete the pest populations - both directly, by removing insects and indirectly in that the 'disturbance' involved may cause them actively to leave. An half tonne of maize contains only about 2,000 cobs. Clearly, if say, 20 to 30 cobs are required for an adequate sample, repeated sampling may represent an appreciable drain on the population. The cobs removed may be replaced with infested material from elsewhere but there are problems in ensuring that the cobs brought in are truly comparable. To minimise active emigration it may be helpful to ensure that as little of the gram bulk as possible has to be disturbed in removing the sample and to leave parts of the bulk as 'refuges* which are not used for sampling and from which reinfestation of depleted parts may occur. There is also a problem with small grain stores that 'edge effects' may in fact affect the whole grain bulk. In the experimental cribs here, the maize cobs occupied a volume of approximately 90 x 90 x 140cms. Accepting for the moment the likely existence of some form of gradient in insect abundance from surface to interior, it is clear that any changes must occur over rather short distances and accordingly, if sampling is to detect such changes, the cobs must be collected from a comparably small sector of the crib. This too tends to conflict with the desire to collect large samples.. 3.2.6 Sample Size and Handling Time. The 'handling time' for a particular set of samples includes three main'components : the time required to collect the samples from the cribs, that needed to remove the insects from the grain samples (and to carry out any tests, such as moisture content determinations, that require the grain samples to be 'fresh') and finally the time taken subsequently to identify and count the insects collected. Of these, the last is the least critical. Although it is often desirable to have the results from a particular sample immediately (and, moreover, fresh samples are often easier to score than preserved ones), the insects can, in principle, be preserved in fluid for later attention. The time taken to collect the live insects is, however, critical to the success of sampling, and imposes severe constraints on the number and size of samples that may be taken. Firstly, it is important that samples should be collected from all comparable 'treatments' over a very short period of time. It has been noted that the retrieval of insects will be markedly affected by different environmental conditions,- such as one might encounter if samples were to be collected on different days or at different times on one day. If sufficient replicates are available this will not be important, however, if replication is limited (for instance by the supply of materials or time), it will be important to minimise such 'non-treatment' variation. Having collected the samples from the cribs, it is important to 'process' them as quickly as possible and, in practice, this should be completed within a few hours. Various undesirable effects occur in infested grain samples stored in closed containers : in moist or heavily infested grain, the build-up of carbon-dioxide., condensation and sometimes temperature can kill the insects or at least make them difficult to collect; the moisture content of the grain may be appreciably raised - which will be important if this is to be determined or if the material is to be retained to assess emergences; there may be inter- actions between the adult populations and immatures within the grain - for instance there may be a significant number of emergences over a period, or parasitism and predation may be intensified; many storage insects are capable of perforating and escaping from plastic, paper or cardboard containers. Finally, if material is to be returned to the crib, it is desirable to do this as soon as possible. The various possible methods for the extraction of insects from infested grain will be discussed in a separate section (§3.4). Whatever the method employed, the time required for this is considerable and represents the major practical limitation on the quantity of material that can be used in sampling. All the issues discussed in this chapter will arise again in considering the methods used for particular trials and in the imm- ediately following sections relating to basic sampling techniques. It must be recognised that, in all cases, the choice of sampling regime, and in particular the number and size of samples, represents a com- promise between the desire to estimate accurately population parameters and the constraints imposed by the habitat under study and the limited time and materials available. In a number of instances this compromise cannot be regarded as entirely satisfactory. 3.3 Assessment of Insect Sampling Techniques The field studies commenced in April (1978), approximately three months after the dry-season harvest, at which time six half tonne cribs of heavily infested maize were available for study. Initially a large number of samples were taken using the Iowa Corn Probe. A number of cribs were then emptied, in the course of which samples were taken for comparison with those obtained using the probe and to assess more generally the potential of such 'destructive* sampling. These preliminary investigations indicated serious short-comings in both methods. Accordingly a technique was developed which will be referred to as 'partially destructive' or 'replacement' sampling. This involved structural modification of cribs to allow cobs to be removed from, and replaced within, the grain bulk without unloading the whole crib. The major part of the material removed on a particular occasion would be immediately replaced in position in the crib while small sub- samples were retained. This method was employed, with progressive modifications, for most subsequent trials. Details will therefore be considered later, in the context of particular trials, but the general .56. principles will be set out here for comparison with the other two options considered. 3.3.1 Iowa Corn Probe The Iowa Corn Probe has, at first sight, a number of advantages as a sampling tool. i) The probe could be used to collect grain from any part of the crib; ii) no structural modification to the crib or changes in the wall material were required (the probe could be pushed through wire mesh or between palm slats); iii) grain could be collected from a crib filled in the normal 'haphazard' way (as compared with the ordered stacking required for replacement sampling - see §4.2); iv) all species, including active Hymenoptera and Heteroptera could be collected (though not necessarily quantitatively); and v) a large number of samples could be collected rapidly and with relatively little effort. In practice, however, the probe proved unsatisfactory. The probe collects too small a quantity of grain at each insertion while causing excessive disturbance to the insect population and damage to the grain. Each insertion of the prqbe collects only 20 - 30g of shelled grain and, although the wide 'catchment-area' of the sample should tend to reduce the effects of inter-cob variation, this is in- adequate to provide a quantitative estimate of population density. Figure 3.6, based on samples collected from a single crib indicates that the numbers of adult insects are not related to the quantity of grain collected by the probe. There is evidence that the number of insects collected by the probe is in some way related to insect abundance in as much as reasonable consistent results can be obtained. Table 3.1 shows the results of the analysis of variance of some of the data collected from four different cribs, sampling from sixteen different positions as shown in Figure 3.7a). .57. 140 r 120 + + £ 100 10 0 \ 0 80 4> ©O C - 60 40 10 15 20 25 30 sample uit. / g FIGURE 3.6 Scatter diagram for numbers of Sitophilus adults collected in each sample against the weight of grain collected in that sample, using the Iowa Corn Probe. Probe samples collected randomly from different parts of a single crib. .58. a) Rnalyata of vtrltno* Single Factor position* (16) as treatment® or Ibe (3 or 4) me blooke - top Rn« y1e 1 e of varleiiea Fmotorlal - middle R North-South (2) B Eiet-Weet (3) C bottom-top (3) - bottom treatment mean* teeted ve • 3-y»e yInteraction mid FIGURE 3.7 Design for analysis of the effect of position in the crib on the number of insects collected in probe samples. Diagrams indicate approximate positions in the cribs from which samples were drawn. a) samples collected from 16 points in 3 (or 4) cribs. b) samples collected from 18 points in one crib. .59. TABLE 3.1 Differences in adult insect abundance in probe samples from different positions in 3 cribs (Carpophilus) or 4 cribs (Sitophilus). Sampling positions as shown in Figure 3.7a). a) Probability levels from a single factor analysis of variance with positions as treatments (16) and cribs as blocks on data transformed loge Sitophilus Carpophilus Source of variation df. zeamais dimidiatus Total 63 0.01-0.025 <0.01 Positions 15 <0.0l <0.01 blocks (cribs) 3 error. 45 b) Treatment means - number of adult insects/50g fresh weight (arithmetically corrected from sample weight). Position Sitophilus Carpophilus 1 73 197 2 71 460 3 74 61 4 74 113 5 96 40 6 91 75 7 78 36 8 53 33 9 124 36 10 117 42 11 96 56 12 105 52 13 195 104 14 113 140 15 160 60 16 105 97 60. TABLE 3.2 a) Probabilities: Source of variation df. Sitophilus Carpophilus Sitophilus Sitotroga (adults) (adults) (emergences) (emergences) Total 17 A North-South 1 0.05-0.1 B East-West 2 <0.01 <0.01 C Bottom-Top 2 0.05-0.1 0.025-0.05 AB 2 0.01-0.025 AC 2 BC 4 ABC 4 b) Treatment means A North 82 43 2.1 . 3.4 South 89 . 35 1.7 2.3 B East 93 47 0.8. 3.0 Mid 61 19 2.7 2.7 West 103 52 2.2 3.5 C Bottom 80 45 • 0.7 1.0 Middle 87 36 1.3 2.3 Top 89 37 3.7 5.8 TABLE 3.2 Insect abundance in probe samples from different parts of a single crib (sampling positions as in Figure 3.7b). a) Probability levels from a 3-factor anovar, using the 3 major axes of the crib as factors (probabilities greater than 0.1 are omitted). Data were insects/sample (arithmetically corrected for sample size) for adults or number of insects emerging/sample over ten days; data transformed logarithmically for analysis. b) Treatment means (actual values): adult counts are -numbers of insects/50g. of grain, fresh weight (arithmetically corrected); emergences are numbers retrieved from 25g samples over the period 10 to 20 days after collection (figures for 0-10 days were severely affected by parasitism). Some sampling positions yielded higher numbers of insects than others, both for Sitophilus and Carpophilus spp. (although the pattern was different for the two species), but the figures were not consistent for all the cribs (and, indeed, the anovar indicated no significant 'position1 effect when all possible figures were included). Similar 'significant' differences between insect numbers in groups of samples (Table 3.2a) were found when figures were analysed for several samples within one crib (Figure 3.7b) or when subsequent emergences from the samples, rather than adult counts were analysed (Table 3.2b). While these results provided an interesting indication that insect distribution was non-uniform within the cribs and suggested that the probe might be useful in some circumstances where only a comparative index of in- festation was required, they clearly showed that the probe could not give sufficiently precise estimates of adult insect populations for use in this study. Initially it seemed possible that the probe might, nevertheless, be used to collect grain samples for 'breeding-out* of primary pests and for damage assessment, however, in these applications too it proved unsatisfactory. Considerable force is required both to insert the probe into the crib and then to rasp the grain off the cobs. This leads to four major problems : i) samples cannot be taken near the top of the crib as the weight of the cobs provides insufficient resistance against which to shell the grain; ii) large quantities of grain are shelled but not collected and so accumulate at the bottom of the crib; iii) both moist grains early in the season and badly damaged grain later on, are broken by the probe rather than simply shelled off the cob; and iv) the disturbance caused by the probe is considerable: The sensitivity of the insects to mechanical shocks has already been men- tioned; during probe sampling insects could be seen to leave the crib 62. in considerable numbers. Finally, although not of importance to this particular study, it was clear that the results obtained with the probe were markedly affected by the person taking the sample. An inexperienced operator tends to collect large numbers of insects (and quantities of frass) but little grain, and will also tend to obtain markedly inconsistent results. 1 3.3.2 Destructive Sampling of Whole Cribs The collection of samples at the time of unloading the crib (i.e. 'destructive sampling') has three obvious advantages: i) the size and origin of the sample can be precisely controlled and an appropriate selection procedure applied (for instance, it is easy to choose cobs in a precisely defined stratified random manner); ii) larger samples can be taken as 'depletion' is not a consideration; and iii) samples will be truly representative in that they will have re- mained undisturbed until the time of sampling. For the purposes of this study, however, destructive sampling presented three problems i) Adult insect counts could not be obtained from such samples. Even when cobs were removed a few at a time, with great care, appreciable numbers of insects were clearly falling from the cobs as they were removed thus increasing the apparent infestation in the lower cobs still to be sampled; ii) frequent sampling was required to monitor pest population increase and, if whole cribs had to be un- loaded on each occasion, this would have required prohibitively large quantities of material (it would be effectively meaningless to reload a crib and use it for a later sample); iii) the unloading of an infested crib causes a massive exodus of insects, inevitably affecting nearby cribs. Even when rapid-knockdown pyrethroid insecticides were used to .63. try to minimise cross-infestation, a marked increase in insect counts in nearby cribs was apparent after unloading. Destructive sampling remains the obvious choice for trials where the assessment of damage and hidden infestation will yield sufficient information. It may also be practicable to obtain adult counts in this way where cobs are stored in their sheaths (which markedly reduces the speed with which insects escape from the cobs). 3.3.3 Replacement Sampling The cribs to be sampled in this way required extensive structural modification. The crib was divided with partitions (horizontal and vertical) of galvanised 'chicken wire' (5" mesh) supported on light wooden lathes - (see Chapter 4.2 for details). Any of the sections so formed could be emptied of cobs, the remainder of the grain being supported by the wire partitions. Access was gained-via 'trap-doors' in one (or two) of the vertical faces of the crib, which had itself to be of wire (rather than the normal wooden 'slats' or palm-frond petioles). The cobs were marked, with a band of indellible ink, and those from separate sections retained separately so that all could be replaced in approximately the position from which they had been removed. Cobs retained on each occasion (for instance those used to estimate emergences and moisture content) were replaced with cobs from another crib that had been in storage for the same period. In the preliminary trial of this system, samples of five cobs were collected from each of 24 points. Initially adult insects were removed from intact cobs and the cobs replaced in their former positions; however, as infestation increased, this system became too slow and the grain had instead, to be shelled^nd sieved to remove the insects. This .64. in turn, meant that large quantities of cobs had to be brought in from another crib on each occasion but these cobs, though of similar age in store, would not have any physical attributes or the level of infestation characteristic of the positions into which they were placed. The method required considerable time and effort and so could not be very frequently repeated. Moreover the samples, though large enough to indicate that distribution was not uniform, did not give a satisfactory estimate of population density in absolute terms. The number of cobs to be collected from each position could not be in- creased without losing positional 'resolution1 (see 3.2.5), increasing the depletion effect and impossibly increasingly the handling time. It was concluded that separate trials should be conducted to monitor changes over time and to investigate distribution within the cribs. For the former, a small number of large samples could be taken on each occasion from one part of the crib; this could be repeated frequently and oh several cribs and would give an accurate estimation of one index of the population changes (i.e. only from one point). These results could be compared with those from less-frequent samples taken from many points in a crib which would indicate any major changes t in population distribution. For the 'sequential* samples the adult insects could be removed from the cobs without shelling and the cobs replaced; reinfestation should be rapid from the remainder of the undisturbed grain. Sampling in the distribution trials would be 'destructive' (i.e. samples would have to be shelled) but, because of the wide sampling interval, cobs introduced from the reserve crib would have a considerable period to 'equilibriate' to their new position before being used for sampling. The methods and modifications used in the various trials will be detailed in the subsequent chapters relating to them (i.e. "Succession Studies" in Chapter 6 and "Distribution .65. Studies" in Chapter 4). 3.3.4 Sampling to Estimate Recruitment It was decided at an early stage that the recruitment of the main pest species, Sitophilus zeamais and Sitotroga - cerealella, would be assessed only by scoring the emergence of adults and that no attempt would be made to sample the immatures of secondary pest species. It was felt that the extra information which could be gained would not justify the time required, in the former case to dissect the grains and in the latter simply to collect and identify the larvae. Two methods were considered for the sampling of the primary pests. One possibility was to plant uninfested (fumigated) cobs into the crib for a short period (say, one week) to allow eggs to be layed on them; the cobs could then be retrieved, all adults removed, and the cobs retained for at least fifty days to allow all the developing insects to emerge. The developing larvae would suffer competition only from other larvae of the same age and would not be subject to parasitism. The alternative was to collect cobs that had remained undisturbed in the crib for a long period and to retain these for a rather short period, say five days. The adults emerging over that period would represent an estimate of net recruitment. In this case the larvae would be subject to the 'normal' pressure of parasitism and competition except for the short period afte.r their removal from the crib. The former method was rejected mainly on the grounds that ovi- position on the newly introduced, uninfested cobs might well be very different from that experienced on the surrounding infested ones; the rate of oviposition of Sitophilus spp, at least, is known to be markedly affected by adult density. In practice, moreover, it proved difficult to obtain a satisfactory independent es timate of the rate of parasitism 66. in the crib and difficulties were encountered in retaining the samples for so long an emergence period: mould development on damaged grain was severe, plastic or card containers were readily perforated by emerging Coleoptera (especially Bostrychidae), and parasitism was often severe (presumably the parasitoids were introduced with the late instars and pupae of secondary pest species that had entered the sample during its exposure in the crib) . The method adopted was not without problems. Parasitism, especially of the late instars of Sitotroga, was at times severe and so the estimate of recruitment was very much dependent on the period over which emergences were scored (Table 3.3). Parasitism is also likely to occur during the assessment period; this could be largely avoided if emerging insects were removed each day, but this was precluded in this study by the time required. Despite these shortcomings, the method was felt to provide at least a satisfactory indication of the rate of recruitment for comparative purposes. 3.4 Extraction of Insects from Grain Samples. The method used to remove the insects from the maize varied somewhat, depending on whether it was to be replaced in the crib (in which case it could not be shelled) or, if not, whether the sample was to be- subsequently used for estimation of recruitment and/or moisture content. For samples which were to be replaced in the crib, the cobs were transferred, a few at a time, to a large plastic bag, inside which they could be knocked gently together, and the insects so dislodged collected in an aspirator. The main limitation on the speed with 67. TABLE 3.2 emergence period (days after collection). p (no diffs.) 0-10 10-20 20 - 30 Sitophilus 5.0 6.4 6.0 >0.5 zeamais Sitotroga 2.8 13.4 12.0 <0.001 cerealella parasitoids 6.9 2.8 0.7 <0.001 TABLE 3.3 Effect of time after collection -on numbers of insects emerging. Mean no. of insects emerging from ten lOOg samples (from individual cobs) in successive ten day periods after sampling, with probability levels from a single factor analysis of variance of the data transformed logarithmically, (cobs were collected from approximately 30cm below the surface of the cobs in Crib 25 - that used for the probe sample < investigation, Table 3.2). 68. 9UNLXGHT FIGURE 3.8 Arrangements used for the rapid extraction of insects from samples of a) shelled grain and b) cobs. Insects were retained in the collecting tube either by painting a band of 'Fluon' around the top (inside) or by adding alcohol. Funnels used were approximately 25cm diameter. When using solar heating (case b)), evaporation of alcohol (and con- densation on the perspex lid) could be reduced by standing the extraction funnel in a large jar of cold water. which the insects can be collected is their tendency to take refuge within damaged grains, where they may remain undetected for long periods. If the grain was warmed slightly, for instance by leaving the bagged sample in the sun for a few minutes, the insects became more active and so more easily collected; this had, however, to be carried out very carefully to avoid killing the insects or driving moisture out of the grain. If a light source was placed at the closed end of the bag during insect collection this both served to increase the general level of insect activity and to attract the actively flying species, in both cases making them easier to collect. The proportion' of insects which could be retrieved by this method was limited largely by the time available; it became increasingly difficult to collect the insects as the grain became heavily damaged. When the grain could be shelled,collection of insects was made much faster by the use of nested sieves (2.5mm and 0.8mm mesh). This afforded the added advantage of providing insect samples less con- taminated with frass, but a number of the smaller species (especially Cucujidae, Corylophidae and Scelionidae) were able to pass through the finer mesh and were then very difficult to separate from the debris. Sieving had to be used cautiously on samples to be used for estimation of recruitment as violent sieving can cause considerable mortality of immatures. Collection of insects from shelled grain was more efficient if the insects were sieved directly into a tube of alcohol via a large funnel (Fig. 3.8a)). This method could, however, only be used in samples showing little damage. In samples from late in the storage season the large numbers of dead insects in the grain would also be collected (and could not always be distinguished in the preserved .70. samples) together with quantities of frass; a second separation was then required, usitig wet-sieving or a kerosene flotation method. Tullgren futinels, suitably modified, have been recommended for the extraction of storage insects (Golob, Ashman and Evans, 1975). In practice, this method proved too slow to deal with the large quantities of grain that had to be processed for this study. A more convenient alternative, using sunlight as the heat source,was developed (Fig.. 3.8b)); this method proved much faster than the conventional Tullgren funnel but, of course, suffers from the same drawback of heating the grain that the sample cannot subsequently be used (except perhaps for damage assessment). 3.5 Damage Assessment Estimates of loss in quality and/or weight (in the stored grain) which can be related to economic lossy are vital to the development of rational pest control strategies. As previously mentioned, little attention has been given to the relationship between the level of insect populations and the damage they cause. In this study weight loss was monitored in parallel with all insect population studies to show how damage progresses over the storage period and how losses are distri- buted in the crib. In the absence of information on the contribution of individual species to the overall loss, these figures can be only imprecisely related to the observed insect populations; the data required for a more complete interpretation of the figures could, however, now be collected in laboratory studies. A variety of established methods are available for the estimation of losses in stored grain (Harris and Lindblad, 1978). However, all were rejected for the purposes of this trial on the basis of the time required to carry them out or their lack of precision. The method .71. moan final weight loos • * ProlImlnary Succession » * 4 Trial Trial » '' / / « 1—1 < f J unaampTod 31.1 o 34.0 o v—ni sampled 25.3 a 30.1 b • - e 'L / ' • » 'i i unaampled 28.1 b 25.0 a / / e analysis of variance source. . df P P total 59 R cribs I 0.51 0.14 B pos'n 2 <0.001 <0.001 R x B 2 0.53 0.10 error 54 FIGURE 3.9 Weight loss of grain for cobs from sampled and (adjacent) unsampled parts of a crib under more and less intensive sampling regimes: cribs in the Preliminary Trial were sampled six times in three months and those in. the succession trial six times in six months. Means (percentages, dry weight basis) are based on estimates for ten cobs in each sampling position in each of two cribs. For details of methods see Chapter 6. developed here is described in detail in Appendix V. It depends on the identification of individual cobs (numbered and*banded*with indellible ink) which are weighed at the beginning and end of the storage season and, in some cases, at intermediate times. Deter- minations of grain and core moisture contents are made in parallel, on comparable cobs, or on sections cut from the loss assessment cobs to allow corrections to be made for changes in weight due to loss or gain of water. The precision of the method depends largely on the inter-cob variation in moisture content : trials commenced at high moisture contents, soon after maturity, when variation is greatest, are less accurate than those begun when the grain moisture content is approaching equilibrium*. There o.s-also the possibility that some of the inaccuracy when grain moisture content is high is due to phy- siological processes in the grains producing real dry weight losses. In addition to information oh damage per se, loss assessment was also found to be useful as at least a crude check on the effects of the insect sampling procedures. In most trials, cobs for weight loss estimation were included in both sections of cribs that were to be used for insect sampling and in adjacent sections that were not. If the cobs in the sampled sections proved, at the end of the season, to have been damaged significantly less than those in the undisturbed sections, this would be strong evidence that the sampling had depleted the insect populations, or at least affected their pattern of distribution. This was found to have occurred in some trials (Figure 3.9). .73. CHAPTER 4 INSECT DISTRIBUTION WITHIN THE CRIB 4.1 Introduction The factors which influence the distribution of insects within bulks of grain have been intensively studied in the laboratory. Surtees (1964b) showed that, even in uniform darkened cubes of grain, each of the five species studied took up a characteristic three-dimensional distribution, which he describes as a 'dispersion pattern1. The re- sponses of several species to temperature and moisture content gradients and surfaces in small grain bulks have also been analysed (Surtees, 1963, 1965c; Amos, et al., 1968) and the effect on these responses of the condition of the insects and the presence or absence of light have been noted (Amos, 1968 and 1969). Surtees (1964c, 1965 a-c ). and others have shown how these reactions together will tend to result in aggre- gation of pest species in conditions favourable to them and particularly in patches of damaged grain. It is generally accepted that, in stores of bulk grain, insect infestations will be patchily distributed, and the implications of this for insect control and general store management have been widely discussed (see, for instance, Cotton and Wilbur, 1974). Insect movement in response to changing physical conditions in large-scale stores in the tropics have been described by Smith (1963), Graham (1970) and Prevett (1964) . Grain stored in small cribs will be exposed to a variety of changing environmental conditions and it may reasonably be assumed that the infesting insect populations will react similarly to the stimuli provided. This possibility, however, does not seem to have been critically investigated and has rarely been considered in the design .74. of sampling programmes for studies of crib stores. Uneven distribution of insects in small-scale maize stores has been implied in a number of observations. As mentioned previously (Section 3.2), Kockum (1953) and Pointel (1969) studying quite different types of cribs, both noted higher damage levels near the surface, while the former author also noted some vertical stratification. A *sumpf effect in stores of shelled grain (i.e. a limited area of very highly damaged grain at the bottom of the store) has been noted by various authors (e.g. Adams and Harman 1977). Direct evidence in terms of actual insect numbers is less common in the literature although it has often been reported that Sitotroga cerealella is only abundant on the surface of stores (e.g. Kockum, 1953, in the study noted above; Coyne, 1945; Salmond, 1957). The need for more quantitative data on insect distribution patterns has already been discussed (3.2.3) in relation to sampling methods and loss assessment. The methods used in this study to in- vestigate insect distribution are derived from those used by Surtees (1964a) in the laboratory: the grain bulk (in this case a complete half-tonne crib of maize cobs rather than a small cube of wheat) was subdivided so that it could be rapidly broken down and the insects from various parts collected separately; differences between the numbers from the different parts could then be investigated by analysis of variance (though this poses certain difficulties here which are dis- cussed in the following section). In addition, some effort was invested in estimation of the naturally existing gradients of temperature and moisture content (as described in Chapter 2) and grain damage. In the field it is likely that changes in distribution will occur not only in space but also in time. Successional changes in insect abundance over a period of several months were noted by de Lima (1978) in small maize stores in Kenya while daily cycles in the activity of several storage species have been noted in the laboratory (Barnes and Kaloostian, 1940; Amos et al., 1968), in fields of the growing crop and in stores (Riley, 1965; Ajibola-Taylor, 1971; Giles and Ashman, 1971). The possibility that such temporal effects might be reflected in changes in spatial distribution patterns was investigated both over the period of the storage season and over a matter of days at one time in the season. 4.2 Sampling and Analysis for Insect Distribution. Three trials were carried out using a similar basic technique. This involved partitioning the crib into a number of sections from which many samples could be removed, rapidly and with a minimum of disturbance to the grain bulk. The first trial was concerned prim- arily with developing the sampling technique and will not be described in detail. In the second trial samples were taken at widely spaced intervals to investigate any successional changes in the insect pop- ulation over the storage period. In the third trial samples were collected from the cribs at different times of day over a short period of time to investigate the possibility of daily cycles of movement within the crib. These trials will be referred to respectively as the 'Preliminary', 'Long-Term* and 'Short-Term Distribution Trials'. The. methods used for this series of investigations have already been outlined (Section 3.3.3) and the main problems that were encountered already discussed (Section 3.2). The cribs were structurally modified as shown in Figure 4.1 by the introduction of light partitions (horizontal and vertical) of J" galvanised mesh stretched on light wooden laths. Access was, in the a) b) arrangement for long term trial Host mid East ftno nitre trays vortical wtro arrangement for short term trial partitions lath'uitre floors West mH mE East O oobs for Inseot sampling oobs for lot rment unsampled oobs FIGURE 4.1 Hod1ftoatton of orlbs for Distribution Studies a) general view of ortb trap bags b) stacking of oobs 1n sampling tunnels first two trials, through only one (vertical) face of the crib; this was covered with wire mesh in which 'trap-doors' were cut so that cobs could be removed. In the third ('Short-Term') trial tunnels were accessible from two faces so that samples could be removed more easily and quickly. The palm frond slats that form the sides of a normal, unmodified crib were fitted to removable panels so that a consistent degree of shading and shelter from rain was maintained. It was clearly desirable, both from the point of view of the time and effort involved and of minimising disturbance to the insects, to unload as little of the grain bulk as possible when removing samples. Accordingly it was decided that the cobs in-half of the tunnels should remain totally undisturbed throughout the trial and would form a reservoir of insects from which the sampled tunnels would be rapidly reinfected; weighed cobs were included in all tunnels at loading so that at the end of the trial any general reduction in infestation pressure due to sampling could be assessed from the weight loss (Appendix V for methods). The tunnels to be sampled and to be- left undistrubed were allocated alternately"in successive layers, as indicated in Figure 4.1. This allowed variation in all three dimensions to be assessed, but resolution in the direction of the tunnels would be clearest. The cribs were orientated with the tunnels running East-West because it was assumed, a priore, that the most consistent directional influence in the environment would be provided by the sun moving in that direction. In the 'preliminary' and 'long-term* trials cobs in the tunnels to be used for sampling were loaded in shallow trays of 2mm galvanised mesh ('mosquito wire'). When sampling, after careful removal of a few surface cobs, the whole tray could be removed from the crib allowing immediate access to the interior sections; most of the insect pests were able to crawl through the mesh when moving normally but insects falling onto the tray when disturbed during sampling were retained at least briefly and could be collected in an aspirator. The main drawbacks of this system were that the mesh may well itself have affected insect distribution (because it impeded the movement of larger species while others tended to cling to it) and the tray collected 'extra' insects falling from cobs not intended for inclusion in the sample. In the short-term trial the improved access provided by the two removable sides made it possible to dispense with the trays. The stacking of cobs within a crib is important because it is likely to affect the rate of airflow through the crib and, thus, the microclimate at different points and the distribution of insects. In the storage system on which this study is based the cobs would normally be tipped into the crib at random, leaving considerable interstitial space. In the preliminary trial an attempt was made to simulate this in the loading of each tunnel but in practice this disorderly arrangement proved too unstable, the removal of one or two cobs causing 'subsidence' and immediate disturbance of the infesting insects. Subsequently the cobs were arranged regularly as shown in Figure 4.1; the cobs forming the 'stack' at each sampling position could be safely removed one at a time and, moreover, each cob in a particular position had a comparable degree of exposure to the surface of the crib. At loading particular attention was given to stacking cobs closely against the partitions so that the grain bulk was effectively continuous. The regular stacking of cobs may have reduced airflow and so accentuated differences between parts of the crib. The cobs removed on each sampling occasion were shelled imm- ediately and the adult insects collected for later determination. Grain .79. from all the cobs from a particular position was shelled together, mixed thoroughly and then subsampled (by 'coning and quartering') for estimation of moisture content (3 x lOg samples) and insect re- cruitment (3 x lOOg samples). Cobs taken as samples were replaced with ones which had been stored for the same length of time in a similar crib nearby; these would have been similarly damaged but the infesting population somewhat reduced by insects leaving the cobs during the transfer. Cobs so introduced were marked with indelible ink so that on subsequent occasions they would not be included in samples. In the preliminary and long-term trials samples of approximately lkg were taken (from each of 24 positions in the crib) during the early stages of the trial when insect numbers were low, falling to c.500g as insect numbers built up. In the short-term trial, for which samples were taken at a late stage of succession when insect numbers were high, four cobs were collected from each of 32 positions, pro- viding 300-400g of shelled grain. The size of samples taken, particu- larly when the insects were most abundant, was rather smaller than the ideal but this was dictated by practical considerations as discussed in Sections 3.2 and 3.4. The time required to handle larger samples 1 would have been prohibitive. The method for selecting cobs to be sampled within each position was slightly different in the two main trials. In both trials the top and bottom layers of cobs within each 'stack' (i.e. sampling position) were not used for sampling: many storage insects show thig- motactic responses which it was felt.might produce aggregations of insects adjacent to the partitions. The second layer of cobs (from the bottom) consisted of the marked and weighed cobs to be used for loss assessment and these also could not be used for insect counts. In the long term .80. trials the loss assessment cobs were weighed on each sampling occasion (to obtain a time-course of damage) so all the cobs above had to be removed. The cobs for the insect counts were selected at random from among these as they were removed (excluding any that had been intro- duced on the previous sampling occasions). The samples, then were effectively 'stratified random* samples (though considerably restricted). In the short-term trial it was felt that priority must be given to minimising disturbance to the crib. Accordingly on the first sampling occasion the top layer of cobs was carefully removed and those in the second layer collected; on the second occasion the top two layers were removed and third collected and on the third occasion three layers removed and the fourth collected. The cobs were also packed in 'envelopes' of flexible nylon netting (2|cm mesh), each containing four cobs, which could be removed and bagged quickly and with minimal loss of insects. The sampling was thus, in the latter case, systematic rather than random. Statistical analysis of the data from these trials presents a number of problems. As already mentioned, although the selection of samples in the long-term distribution trial did not differ seriously from a stratified random pattern, sampling in the short term trial (and for loss assessment in both trials) was systematic. For practical purposes this is perhaps not too serious: the main interest is in com- parisons between similarly selected samples (rather than an absolute estimate of insect numbers) and there is no reason to suspect a particular bias in this selection. (Milne,(1959) has pointed out that in most circumstances systematically collected data may safely be analysed as if it had been randomly collected). The distribution of insect numbers between samples was found to differ from normal in many instances (all groups tested showing over- FIGURE 4.2, Designs for analysis of effects of position in crib on insect numbers (Distribution Trials). a) Preliminary and Long-Term Distribution Trials - based on one crib in each case; in the Long-Term. Trial each sampling occasion was analysed separately; one sample from each position. b) Long-Term Distribution Trials (emergences) - three replicate samples from each position; (this pattern was also used in some cases for analysis of adult counts (unreplicated), testing treatment mean squares against the 3-way interaction M.S.) c) Short-Term Distribution Trial - based on 3 cribs, each sampled on three occasions at different times of day; one sample from each position. Figure 4.2 81. a) Preliminary 8» Long Term Distribution Trials (adults) ZL Rnalysis of Variance Factor1al R "exposure'(2) (interior-exposed) B East-West(3) minor replicattons(4) b) Long Term Distribution Trial (emergences) zp^l upper Rnalysis of Variance Factorial R vertical pos'n (2) B East-West (3) C "exposure'(4) lower minor repl1cattons(3) c) Short Term Distribution Trial Rnalysis of Variance Factor1al R (time of day - 3) B East-West pos'n (4) C vertical pos'n (8) Blocks (3) sampling occasions « /ly^mld H * X » X - X » Xm1d E Note: * Indicates unsampled sections .82. dispersion) but equally did not fit simple negative binomial dis- tributions (indeed one might expect, a priore, compound distributions). Simple logarithmic or inverse transformations did not consistently reduce deviations from normality so the data has been analysed as collected. Routine tests for homogeneity of variances, kurtosis and skewness were made to exclude from analysis populations showing extreme deviations, but given that the populations are in general non-normal, undue weight should not be given to actual probabilities and separations produced by the analyses. Factorial analysis of variance was used in both trials to in- vestigate components of the 'position1 effect and in the short-term trial to test for any effect due to the time of day. An alternative approach to the investigation of the effect of position was tried: this involved grouping the sampling positions into categories chosen on the basis of a prior knowledge of the insect behaviour (for instance grouping *top corners,''interiors' etc., following Surtees, 1964b) followed by a single factor analysis of variance, but this proved less informative in most cases. The basic designs used are set out in Figure 4.2; these had to be modified in each case, depending on the number of cribs • in the trial, the presence or absence of replication and so on, and that information will be set out alongside each set of results. In conclusion, it should be stressed that the statistical analyses are only to be regarded as a useful indicator of the various postulated effects, and that the formal problems in applying the techniques to this data are recognised. 4.3 Preliminary Distribution Trial The methods to be used for subsequent investigation of insect .83. TABLE 4.1 Effect of sampling position within crib on insect numbers for a) Sitophilus zeamais and b) Carpophilus dimidiatus. Probabilities are for the null hypothesis and figures in brackets are main effects means (no. insects/500g maize) Design is 2-way factorial as specified in Figure 4.2a). Note: i) No data on adult insect numbers were collected for sample ii) 1C. dimidiatus' includes all 'dimidiatus group' species - in this case mainly C. dimidiatus (s.s.) with a few C. pilosellus. a) Sitophilus 'zeamais' Effects Sample 3 Sample 4 Sample 1 p. P (x) P (x) GO 'Exposure' <0.01 0.02 0.05 (Exterior/Interior) (133-62) (317-222) (264-208) East/mid/West <0.01 0.06 0.02 (42-91-158) (203-294-309) (182-241-285) Interaction 0.29 0.48 0.73 b) Carpophilus 'dimidiatus' Sample 1 Sample 3 Sample 4 Exposure <0.01 <0.01 0.04 (Exterior-Interior) (142-62) (153-89) (262-197) East/Mid/West 0.09 0.85 0.07 (80-87-139) (116-129-118) (217-193-279) Interaction 0.37 0.50 0.68 distribution were tested using a single crib of heavily infested maize. The maize was initially harvested in January (i.e. during the dry season). The crib was emptied in May to allow it to be modified (as in Figure 4.1), the maize fumigated with phosphine to kill all infesting insects and then reloaded. The cobs were mixed before reloading, destroying any stratification that might already have developed. Samples were taken on four occasions in June and July. Only two species Sitophilus zeamais and Carpophilus dimidiatus were sufficiently abundant for their distribution to be assessed and the data for them is presented schematically in Appendix II. Both species tended to be more abundant in samples from near the surface of the crib than in those from the interior and the highest numbers were recorded in the corners. There was an increasing.^gradient in Sitophilus abundance from East to West while for Carpophilus, although numbers were also generally higher on the West, the pattern was. less regular. Factorial analysis of variance, taking the degree of exposure and East-to-West position of each sample point as the two factors (see Figure 4.2), also indicated this pattern (Table 4.1). The situation considered here was to a large extent artificial, involving recolonisation of already heavily damaged grain. However, the results indicated that the insects were adopting reasonably con- sistent patterns of distribution and that these could develop over a short period of time (i.e. after reloading in this case). The loss assessment figures, already mentioned in Section 3.5, also showed that the sampling regime was reducing insect numbers sufficiently to be reflected in reduced damage in the sampled sections. .85. 4.4 Long-Term Changes in Insect Distribution The long-term distribution trial followed the development of pest populations on maize harvested in August (i.e. during the humid 'small dry' season) and was carried out in parallel with the studies on succession described in Chapter 6. Practical constraints meant that only a single crib could be used for this study and the results of the preliminary trial indicated that samples should be widely spread to avoid depletion of the infesting populations. In the event, four samples were taken: the first and second during the second wet season, respectively two and six weeks after harvest, the third in late November soon after the onset of dry 'harm^ttan' conditions, and the fourth in April at the beginning of the main wet season. The ambient conditions on each sampling occasion were clearly quite different and were reflected by changing physical conditions within the crib (as described in-Chapter 2). The accompanying seasonal succession in the insect populations will be considered in detail later (Chapter 6), but at this stage it should be pointed out that very marked changes occur in the composition of the pest complex over the storage season, in addition to the changes in distribution which are the main concern here. Initial colonisation of the cribs is mainly by species that are primarily adapted to moist conditions such as Cathartus quadricollis and Monanus concinnulus (Silvanidae), and various species of Carpophilus (Nitidulidae). As the grain dries these species become less numerous while Sitophilus zeamais, the major primary pest species, rapidly increases; Sitophilus then remains abundant, and usually the dominant species, throughout the remainder of the practicable storage period (c. 6-9 months). Sitotroga cerealella, which is also potentially a highly damaging primary pest, occurs in large numbers for only a short period FIGURE, 4.3 Distribution pattern of Sitophilus zeamais at different stages of the storage season. (Long-Term Distribution Trial). a) Adults - no. insects/500g shelled grain @ 17% m.c. (Arithmetically corrected from actual sample size and grain moisture contents) b) Emergences - no. insects emerging during one week from lOOg samples of shelled grain (fresh weight) - data are means for 3 samples from each position. Samples were taken after the following times in store: sample 1 - 2 weeks sample 2 - 6 weeks sample 3 - 3 months sample 4 - 7 months 86. N. 0 IV X OJ X m DO \ \ rO O K X \ X OJ X XI 00 X X \ X X oa X \ [X X in' •3 XI x en l\ ca« \ 1 X X x S 1\ C£3 \ X X \ \ X rn ca \ \ 00 en \ f\ X a \ X X X \ L CO X X in \ \ \ \ X| en X X X %N X CD \ 0-1 \ CD X \ X X \ X X X ro D5 \ \ \ IX \ X oa X fixn L X \ X\ Hi X rt X X CD X V X X X tH \ c X X X IX CD X •D \ r- X \ -f X \ v \ X X rC on" X X CO x \ X in X \ X \t-\ • X X 'J3 ' r- X X X XCO X V X \ X CO X l"0 IN X X cn X r - a X C3 K \ X \ IN V. X \ X X X x \ k X in cn N X X X (D si- \ X \ [X X X in ru cn fx X X Xcn X IV X. \ X X X X on el in X X \ C\O X X \ in Xj X ro x r>. X X T X X (VI N \ r\i X in X X U"> \ IX m IX in \ V X X K X \ \ K X N\ 10 CO \ X X X oo xl 03 X\ \ X in X in X \ X 00 X X rf X l\ X X CJ cn \ K X XI K X E3 X X OJ XI CU >T) sr X X X X X La X |mX \ cr> PJ X X X X 00 X CO X \ \•—4 FIGURE 4.3 « )Sftophilus zoamals b) S. zoamala (adults) (emorgoncos) .87. TABLE 4.2 Results of factorial Analysis of variance for dispersion of Sitophilus zeamais in long-term distribution trial, a) adults and b) emergences. (Designs for analysis are given in Figure 4.2 a) and b), respectively). Figures are probabilities for the null hypothesis with main effects means in brackets. a) 'Effect1 Sample 1 Sample 2 Sample 3 Sample 4 P P P x P Exposure .95 .23 .04 .52 • (Outside/inside) (448/329) East/Mid/West. .29 .23 .50 .26 Interaction .87 .62 .51 .11 b) A Top/Bottom .05 .23 .73 ,44 (4.0/2.3)- B East/Mid/West .95 .17 .36 .07 (17/16/12) C Exposure .64 .01 .15 .21 (8.9/5.9/5.6/4.8) AB .80 .19 .31 <.01 AC .43 .02 <.001 .17 BC .78 .04 .84 .14 ABC .49 .81 .04 .23 at the end of the dry season and into the wet. Over the second half of the storage period, and particularly stimulated by the onset of the rainy season, there is a great increase in the variety and ^abundance of secondary pests and detritus feeders attacking the already damaged grain. Most abundant among these are Gnatocerus maxillosus, Palorus subdepressus and other Tenebrionidae, Cryptolestes spp. (Cucujidae) and Carpophilus spp. (Nitidulidae). The succession in the pest species is accompanied by changes in the parasitoid and predator species that depend on them. The data on all species recorded in the individual samples is given in Appendix II; only the distributions of the most abundant species can be discussed here. The distribution data for Sitophilus (adults and emergences) are given in Figure 4.3 and summary results of analyses of variance in Table 4.2. (The complete anovar tables for all significant species are given in Appendix VI). The adult counts suggest that colonisation and subsequent infestation by Sitophilus (samples 1 and 2 in Figure 4.3) are essentially uniform. There is some indication of aggregation near the surfaces of the crib on the second and third sampling occasion, but no sign of the East-West gradients noted in the preliminary trial (and subsequently in the short-term trial- §. 4.5), The emergences, although essentially uniform on the first sampling occasion, subsequently indicate some preference for positions on the surface (in some cases appearing as an 'interaction' effect in the analysis). On the fourth sampling occasion the emergences initially seem to suggest a gradient of increasing abundance from West to East. However, if parasitism by Choetospila elegans is taken into account (and assuming that Choetospila was mainly attacking Sitophilus) this is transformed into an East to West gradient, consistent with that found in the other trials. It may be noted that sampling for the preliminary and short-term trials was also carried out in the wet season, at a late stage in the succession. Sitotroga cerealella was only present in appreciable numbers at the time of the third sample and even then was not sufficiently abundant to reveal any clear dispersion pattern. It may be noted however, that this species here penetrated throughout the crib and, if anything, appeared more abundant within than on the surface (as compared with its poor penetration noted in the studies quoted in Section 4.1). The remainder of the significant pest species (for which the data are given in Figure 4.4a) - f)) show differences in detail but overall tend to show a preference for" surface (or corner), rather than interior, positions. This also seems to be true for the commonest anthocorid predators (Lyctocoris cochici in samples 2 and 3, shown in Figure 4.4h), and Scolopoides divareti in sample 4) which are pre- sumably attacking the free-living larvae of some of these secondary' pest species. The preference for more * exposed1 (i.e. surface) positions is reflected in the results of the analysis of variance for Cathartus quadricollis and Carpophilus dimidiatus given in Table 4.3; although the 'exposure' effect is not always statistically significant the treatment means for the surface positions are in all cases higher. Superimposed on this preference for surface positions several of the species show gradients in abundance from East to West. Carpophilus fumatus and, to a lesser extent, C. dimidiatus, Cathartus quadricollis and Monanus concinnulus tend to be more abundant on the East side in the earlier samples. In the later samples (3 and 4), however, the FIGURE 4.4 Distribution patterns of secondary pest species and natural enemies at different stages of the storage season (Long-Term Distribution Trial). a) Carpophilus dimidiatus (Col., Nitidulidae) b) C. fumatus c) Cathartus quadricollis (Col., Silvanidae) d) Monanus concinnulus ( " ) e) Gnatocerus maxillosus (Col., Tenebrionidae) f) Cryptolestes Spp. (Col., Cucuj idae) g) Choetospila elegans. - (Hym., Pteromalidae) h) Lyctocoris cochici (Het., Anthocoridae) Data are numbers of adult insects/500g shelled grain @ =7% m.c. (arithmetically corrected from sampled values). Samples were taken after 2 weeks (1), 6 weeks (2), 3 months (3) and 7 months (4) in store. .90. L. \ g> ro \ \ \ \ \ \ [\ \ OJ \ \ \J OJ \ \ 01 \ \ 00 L \ \ \ \ \ T \ \ \ \ A in \ \ \ \ \ \ \ •Nj \ \ \ \ ID \ tT \ \ \ \ l3 \ \ k ri- \ \ \ al \C O \ co \ \ \ \ \ \ \ \ co cuN \ \ \ \ Ol \ \ CD \ cn \ (71 \ \ \ \ \ \ iH \ \ \] \ \ \ N \ N \ \ \ \ \ K (\ \" cn pj K \ N |\I \ \ f\ CO CO \ ft \ \ \ \ \ cu \ K \ \ \ ft \ ft in \ Rl ft \ M \ \ rt" \ ft \ \ ft pj \ \ ft \ \ ft K \ LO \ T \ 00 ft \ 00 \ \ \ \ PJ \ N N \ \ N \ \ \ \ \ en' rs_ \ rv \ \ r>w \ oj \ \ K a 0J k f\ \ \ cn J \ \ \ \ \ \ Q Q T N K \ \r-l K \ \ \ \ \ \ CD \ NC O \ \ \ 00 \ in CD \ CO oa \ \ 00 \ \ in \ •J \ \ i3 00 \rt \ \ \ \ \ N cn \ [\ \ oa \ \ i—l CO N tv f\l \ \ \ \ N i p». \ \ \ \ 00 N \ \ fv \ \ \ R in \ \ \ \ -t \ i CD R \ rv- \ t\: OJ R \ C3 \ m \ \ \ •jj a \ f\ \ \ \ \ in" \ \ \ cn \ , i-i CD cu k \ \ \ \ \ \ FIG.4.<4 a) Carpophi lua dlmldlatua b) C. fumatua .91. X X X \ V \ X X X \ \ \ CD X X i \ \ ca X X \ \ \ OJ \ oi \ \ 1-t X \ X \ K X n \ \ ru \ \ cu \ \l \ -t- \ \ X r\i \l X r\i \J > \ )> v \ *—i OJ X X \ \-t X X, \ X X CD l\ \ \ X \ X X \ [\ X \ \ \ \ X X X \l \ X x X X X X \ X \ CJ \ \ \ Q. RlC O rf X OJ X \ V X •TJ X \ X X \ '.'1 [X. IXUS x \ \ \ X a? T N \ X \ X \ •N X X X X i-t \ \ m \ X 'Tl X oa X \ \ \ oo \ X G) \ \ 00 \ \ \ \ X \ X cn X ai K X \ PJ X CD LT7 \ CD ft Kl \in| \ X cn * \ X in \ \ \ CO \ in X Rl X IV- k rr \ \ [Y\ \ X \ \ f PJ N ru in \ \ N «—i [\ \ in X X \ \ HJ X 00 \ IX X UT cu 01 GT X \ OJ X C£l> X \ p- in X \\N m X in X X X X "X X•W-*> X x \ X 'M CO \ Tf ro X X \ XI C=JsJ ca K X m V. X rt X v X \ GJ X X \1 X X X X "t CO CD OT \ a \ tH X X X C\J N X CO OJ \ X \ X X CO X V \ X \ \ (u \ X X OJ * X. \ X Q. X X LO \ x CD X X CD X v"' X \ \ \ in \ \l X \ X K \ \ X X PJ X PJ \ X x \ \ \ \ X CO \ X X cn X PJ \ en in X X X X N X, ~T X \a \ 2 CO X X CVJ N x cn in Ln XEJ X -t- K X X p- X PJ x 1- X T xCD X XI X X XOJ X X X 00 X X X CO in X X X X X X * X X cn X X X •If X r\. X X CO XI X X \ X a x X cn \ rt £ \ X X X X X X ru X ca X •u \ X X X X X CD X in \ x X X X \ \ X FIG.4.4 o) Cathartus quadrtool l is cL) Monanus oonotnnulus 92. \ ft "ft f>x [ft 0) L> CD RW ft R ft ft ft ftM \ ft ft M M ft ft ft R Ift] CA 0 CU FT ft \ ft ft ft or CD ft ft T ft ft ft Ikl ft R ft ft ftl RV ft ft ft CD \ ft X ft ft ftl R \ ft ft ft \ R- CD ft ft lO ft ft 01 RR ft,R - ft ft ft, R- ft ft *T ft CD \ in \ ft F- ft \ ft \ ft N- ft CN ft ft \ £2. N \ \ cr*. ft Rl ft £ \ CD S rv- ft "f >T> \ V\ ft" CO \ R X ft R" Ift ft \ M R PJ LO ft \ K \ \ FT ft ft \ ft ft ca R M ft 1 ft OJ • ft R ft ft cn ft ft ft \ ft 00 ft 1 ft CM \ ft ft \ \C D ft R cn ft ft \ \ \ AI ft ft ft ro in \ CD ft ft ft ft LO \ ft cn ft CD R ft ft CD ft \ CO. ft, CO CD ft CO ft ft FT ft GT R FN- ft O ft ft ft <1> ' ft ft ft' ft \ OJ \ ft Q. ft ft \ ft ft ft R Rl Q. ft ft ft, ft EN cu ft ft ft R S ft ft \ CN ft LO CD \ ft Rl ft ft ftl ca ft ft \ ft. ft N PR^ \ \ \ \ ift V >—I ft \ \ \ V ft\ \ \ \ \ V \ K ft \ ft ft \ ft \ ft TT \ \ cu > ft ft R ft \ > \ ft ft \l ft. ft ft ft K ft ftl IM ft ft \ Ri ft ft ft ft ft ft ft ft \ \ ft T ft ft p—I \ ft CO \ ft ft ft \ ft \ OJ ft \ \ ft \ ftlOJ \ 1 V ft OJ \ rr \ \ ft \ \ ft, K \ < K ft \ ft N ft \ ft \ \ ft ft ft K ft ft ft ft ft V ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft R ft ft ft ft ft ft ftl ft ft ft ft ft ft ft ft ft ft ft ft ft ft a ft ft a £ ft ft ft ft ft ft n) ft ft ft \ ft ftlft ft \ ft ft \ ft FIG.4.4 o) Gnatocorus-maxtII o <3 us f) Cryptolastas spp. 93. FT X f\ X \ in E> \ i—§ S \ X \ \ \ K X, \ \ ™K \i CD X \C O \ \ \ X \ X 01 \ \ X \ \l \ m Si R cn cn \ \ \ i—i \ \ \ X X X >innJ X X \ X X \ X in \ k \ \ \i n X \ S OJ \ \ •H * \ \ \ \ <71 \ \ \ X \ \ CJ X \l •1; \ \ X N k X \ X ifl \i 13 \ X k] Q. \ \ X \ \ \ \rf' X X \ \ X \ X vi \ X \ X X ST X IS IX IX PJ X cn \ K ro X \ \ \ \ X \ \ \ IX in \ X pv X oa in X IV X o X © in \ \ X CD \ \ \ \ x \ rt \ \ X rr \ \ \ X iJ ro X \ X X PO jxl XI X X rj- \ N in \ \ X X .TT \ X 00 \ in \ CD \ cn Si •si \ CO X in X X \ \ X •V in \ X X si \ X X k X CM \ X CL X k X, kl X \ \ \ \ X ru X \ \ X in X in X X k X X X XX I _XI \ X \ X \ >—i (V n \ \ X \ ro \ \ X \ \ x X * X X \ X \ X CD \ X \ X X \ \ \ 00 X X X CO X X X X X X k X k X r-4 X X X Xm X X •f X X s X \ X X \ si X cn X in X x \ X IS) X \ X X X \ CD \ X X CM x \\ k X \ rr X CD x X CO \ to X \ \ X k \ X X kl X Ln a X \ > \ X \ X fx X X 0D ."5 >A \ X \ \ X X \ \ \ K \ \ \ \ IX \ X \ \ X \ X 1 X X cu X X X X X > \ X X X \ X X \ X X X X \ \ X X X nj « X \1 X X X X X s X X X X Ix s X X X, xl X \ X \ X CXI \ \ X X X x si X X X X X Of X X. X X X \ X V X X X a \ \ X X X X X X X X X X k X X X FIG.4.4 g) Chootosplla ologans h) Lyotooorts cochloi .94. TABLE 4.3 Results of Factorial Analysis of Variance for dispersion of a) Carpophilus dimidiatus and b) Cathartus quadricollis in long-term distribution trial. Figures given are probabilities for the null hypothesis with main effect means in brackets. Design is as given in Figure 4.2a); complete Anovar tables are given in Appendix VI. a) Carpophilus dimidiatus Effect Sample 1 Sample 2 Sample 3 Sample 4 P (x) P 'Exposure' 0.58 0.70 0.07 <0.01 (Outside/Inside) (11/10) (36/33) (33/24) (173/98) 0.07 0.24 0.25 East/Mid/West 0.06 (11.5/11.5/7) (46/28/30) (22/32/31) (165/129/114) 0.96 0.95 0.54 Interaction 0.25 b) Cathartus quadricollis Effect Sample 1 Sample 2 Sample 3 Sample 4 'Exposure' 0.16 <0.01 0.62 0.13 (Outside/Inside) (23/16) (87/38) (67/60) (76/46) East/Mid/West . 0.08 <0.01 0.Q8 0.03 (28/14/18) (101/26/60) (69/39/82) (56/29/98) Interaction 0.29 0.06 <0.01 0.60 .95. TABLE 4.4 Results of factorial analysis of variance for dispersion of insects in Sample 4 (Long-term distribution trial) (Design is 3 x Factorial as in Figure 4.2b, but note that for the adult counts, in the absence of replication, treatment mean squares are tested against the three way interaction MS.). Figures are probabilities for the null hypothesis with main effects means in brackets 'Effects' ADULTS EMERGENCES Cryptolestes Gnatocerus Cryptolestes Choetospila pusillus maxillosus pusillus elegans Level (A) 0.01-0.025 >0.5 0.34 0.66 (Upper/ Lower (69/103) (8/9) (14/14) East/Mid/ West (B) 0.01-0.025 0.05 <0.01 <0.001 (71/71/117) (139/110/237) (5/8/12) (6/16/21) Exposure (C) >0.5 0.5 0.12 0.50 (11/8/9/6) (14/15/12/15) Interaction A and B >0.5 0.4 0.61 0.59 A and C >0.5 >0.5 0.25 0.82 B and C 0.01-0.025 >0.5 0.67 0.34 A, B and C - - 0.73 0.82 .96. west side is preferred both by Cathartus and by all three species that build up at this stage (Gnatocerus maxillosus, Palorus subdepressus and Cryptolestes pusillus), though not by Carpophilus dimidiatus. This East to West gradient is also indicated by the emergences of Cryptolestes pusillus, the only secondary pest species whose immatures were retrieved in sufficient numbers for their distribution to be assessed. The results of the analyses of variance for these last species in sample 4 are given in Table 4.4. It would be dangerous to draw general conclusions from the results of a limited trial, based on only four instances from a single crib. However, as far as they go, the results show a degree of internal consistency and generally accord with what is known of the behaviour of individual species from laboratory studies (as will be discussed later in this Chapter). On a practical level, the rather uniform distribution patterns shown by Sitophilus over most of the storage season suggest that the build-up of that species should be satisfactorily represented in more limited single-point samples (as used in the successional studies). The tendency of the secondary pest species to aggregate near the surfaces of the crib means, however, that fluctuations in the populations of these species may not be fully reflected in samples taken only from the centre of the crib. 4.5 Short-Term Changes in Insect Distribution The possibility of daily changes in insect distribution or abundance was investigated by intensive sampling over a short period of time. Samples (4 cobs from each of 32 points) were collected on three occasions from each of three cribs. The cribs were sampled in rotation over a period of approximately five weeks; this spread in sampling time represented a compromise between the desire to complete sampling quickly 97. a) Latin Square Rnovar CRIBS I II III Samp11ng occasion 1 p • m. mid. a. m« 2 a. m « p* m, mfd. 3 mid. a. m< p • m< b) Factorial Rnovar ^» ^ ^ Faotors R time of day (3) B posItlons-East/West (4! C posl tlons—"^vertical Blocks - <3) sampling occasions S 'X ». FIGURE 4.5 Experimental design and analysis for the Short-Term Distribution Trial: a) allocation of sampling times and sampling occasions in the 3 replicate cribs. Analysis of variance on this design was carried out on crib totals (ie. all sampling positions combines) for adults of major species. b) analysis for effect of time of day and position within crib on insect numbers. under uniform environmental conditions and the need to allow the insects to return to their undisturbed pattern of distribution between samples. Maize harvested in January was used for this trial and sampling carried out in June and July when the full complex of second- ary pests had developed. This time of year was chosen as offering an extended period of fairly consistent weather conditions. On each occasion one crib was sampled in the morning (07.00-08.00 hrs) one at mid-day (12.00-13.OOhrs) and one in late afternoon (16.00-17.00) (though not on the same day); cribs were allocated according to a latin square design (Figure 4.5a). Crib totals were analysed (on this design) to test for differences between times of day, _crib$. and. sampling occasions. Totals were then broken down factorially (Figure 4.5b)) to test for any consistent position .effect (i.e. distribution pattern) or interaction between time of day and positions (i.e. indicating insect movement within the crib). It should be noted that in this analysis sampling occasions have been used as major blocks but that inter-crib variation cannot also be separated. Inherent in this design there is the risk that a sampling occasion and crib interaction could mask or enhance a 'treatment' effect (i.e. of position or time of day). For practical reasons emergences could only be assessed for three of the nine samples and only two of the three cribs are represented; an analysis of these data for 'position' effects was carried out but the results cannot be regarded as properly representative: The data from all samples are included in Appendix II. The distribution patterns of the more important species are shown schematically in Figures 4.6 (adults) and 4.8 (emergences). The analysis of crib totals indicated significant differences only between totals for different sampling occasions (Table 4.5). , In .99. the case of Sitophilus zeamais and Carpophilus dimidiatus there was a progressive decline in numbers in all cribs over the three sampling occasions while for Cryptolestes spp. there was a considerable increase. For the two former species it is not clear whether the decline represents Jk a natural feature of the ecological succession (as is presumably the case for the increase in Cryptolestes spp.) or, as seems more likely, the decline is due to depletion and disturbance by the sampling itself. No differences are indicated either between cribs or for different times of day. However, it should be noted that this analysis is rather insensitive. In the factorial analysis of variance, by contrast, nine species out of the thirteen tested show a significant effect of time of day on insect abundance (assessed at 1% level; see Table 4.6); it should be noted, however, that Sitophilus zeamais, the most abundant species, was among those unaffected (Table 4.6a). Such differences could rep- resent real increases in the numbers of insects in the cribs at par- ticular times of day but,, on balance, it seems more likely that they reflect changes in the efficiency of the sampling technique under different environmental conditions. It seems unlikely that most of the species are sufficiently active actually to leave and return to the crib in appreciable numbers, though it should be noted that three of the species in question (the pteromalids Choetospila elegans and Cerocephala dinoderi and the anthocorid Cardiastethus pygmaeus, do fly strongly and are often observed in considerable numbers outside the crib. The treatment means (Table 4.6b)) show that for eight of the nine species which exhibit a 'time of day' effect the highest insect numbers were recorded at mid-day or in late afternoon when temperatures are highest and relative humidities lowest. It seems plausible that at these times many of the insects will avoid exposure to the unfavourable 100. TABLE 4.5 Analysis of crib totals from short-term distribution trial: Probability levels from Latin square anovar (Figure 4.5(a)). Species Source of Variation Sitophilus Sitotroga Carpoph. Cryptotestes Guat. Choe. zeamais cerealella dimid. spp. max. elegans Sampling 0.05-0.1 >0.1 0.05-0.1 0.05-0.1 >0.1 >0.1 occasion Cribs >0.1 >0.1 >0.1 >0.1 >0.1 >0.1 Time -of day >0.1. >0vl - - - - >0.1 >0.1 >0.1. ->0.1- ,. .101. Figure 4.6 (in part) a) Sltophllus zeamals (max. density - 808 insaota • 500g) b) Sitotroga osrealella (max. density ~ 58 Inseots / S88g) FIGURE 4.6 Distribution of adult inseote within orlbe (Short Tarsi Distribution Trial). Mean numbers of Inseots per 588g of shelled grain • 17X ot.o. In samples from 32 points In eaoh or lb (3 replloatee) at different times of day. The extent of shading within eaoh square Indloatee ths den- sity of Inseots in the samples from that position as a fraotlon of the maximum density for that epeolee (given In Individual oaptlone*. 102. Figure 4.6 (oontfnued) o> Ctrpophtlue dlmfdlatus (m«x .density - 198 fnseote • 388g) d) Grtttooerue omxtlToeue (ntx. denetty - 188 fneeote / 388g) e> Ptlorue eubdepreeeue (max. denetty - 289 tneeote / 588g> «.m ®id-d»y P • Rl* 103. Figure 4.6 (continued) •f )Crypto Testes spp- (max. density - 108 Insects ' 580g) »td-d»y p • Bl« 104. Figure 4.6 (oontlnued) h> Lyotooorle ooohlot (max. density " 10 tneeote / S00g> O Choetoeplle elegene (nmx. denelty " 30 Ineeote / S00g> J) CerooepheTe dlnoderl (mtx. denelty - IS Ineeote / 500g) eld-dey p.m. 105. Figure 4.7 Vertical 600 posItlons d 8 700 cd 1 cd 2 Vt 600 3 be 7 X a 500 +o> ab 3 ab 5 cn ab 4 400 o 6 c 300 200 - 2 3 East-West position FIGURE 4.7 Distribution of Sltophllus (Short Term Distribution Trial)i interaction plot shouting the effect of East-West position (factor B) and svert1oa1' position (faotor C) on adult abun- danoe (see fig. 4.5). Data are mean numbers of Inseots per 500g of shelled grain, based on nine samples from eaoh position. Separations are from a Newman-Keuls test (5% level). TABLE 4.6 Dispersion of adult insects within cribs: effect of time of day and sampling position on insect abundance (Short-term distribution trial) a) Probability levels from 3-factor analysis of variance as specified in Figure 4.5ti Source of Sitophilus .Sitotroga Carpoph. Gnato. Palor. Crypto. Typhaea variation zeamais cerealella dimid. max. subdep. spp. sterc. (No. of levels) A. Time of day (3) 1 0.68 <0.001 0.39 0.01 <0.001 0.001 0.90 B. East-West position (4) <0.001 <0.001 <0.001 <0.001 <0.001 0.05 0.002 C.f Vertical'position (8) <0.001 <0.001 •<0.601 <0.001 <0.001 <0.001 <0.001 AB 0.96 0.29 0.56 • 0.74 0.83 0.97 0.19 AC 0.64 0.05 0.98 0.89 0.01 0.89 0.54 BC <0.001 0.06 0.17 0.07 0.77 0.03 0.12 ABC 0.99 0.67 0.96 0.75 0.95 0.95 0.19 Litargus Choeto. Cero. Cardiast. Lycto. Scolopoides grain grain bait. eleg. dinod. sp. cGchici divareti m. c. temp. A 0.07 <0.001 <0.001 0.01 0.001 0.001 <0.001 <0.001 B <0.001 <0.001 <0.001 <0.001 0.66 0.03 0.03 0.002 C <0.001 <0.001 0.06 <0.001 <0.001 <0.001 <0.001 <0.001 AB 0.79 0.86 0.81 0.03 0.87 0.99 0.47 <0.001 AC 0.46 0.86 0.25 0.67 0.81 0.77 0.48 0.001 BC 0.20 0.92 0.67 <0.001 0.99 0.98 0.45 0.99 ABC 0.58 0.81 0.72 0.49 0.99 0.99 1.00 0.94 TABLE 4.6 b) Treatment means from factorial analysis of variance. Separation of means on the basis of Newman-Ketrls test (5% level) 1 Treatment1 Sitoph. Sitotr. Carpo. Gnato. Palqr. Crypto. Typhaea Species zeamais cereal. dimid. max. subdep. spp. sterc. Time of a.m. 11 a. 41 b 84 a 31 a day mid. 19 b 31 a 86 a 30 a p .m. 12 a' 38 ab 107 b 41 b East-West E 308 a 10 a 54 a 30 a 77 a 37 a 2.6 b position M.E. 380 b 13 a 49 a 34 a 87 ab 28 a 0.7 a M.W. 482 c 13 a 53 a 37 a 103 be 34 a 1.1 a W 538 d 20 b 76 b 47 b 105 c 37 a 1.2 a Vertical 1 470 cd 25 c 45 ab 25 a 21 a 34 a 0.3 a position 2 433 be 21 c 59 be 60 c 68 b 55 b 2.3 a 3 395 ab 15 b 54 be 45 b 76 b 33 a 1.6 a 4 327 a 15 b 29 a 30 ab 70 b 26 a 0.3 a 5 387 ab 11 ab 42 ab 32 ab 75 b 29 a 0.3 a 6 334 a 11 ab 66 c 36 ab 120 c 52 b 1.6 a 7 544 e 7 ab 102^ d " 40 ab 1-64 d 24 a 4.0 b 8 527 de 8 a 67 c 28 a 148 d 21 a 1.0 a Litargus Choeto. Cero. Cardia.. Lyctocor Scolo. grain. grain bait. eleg. dinod. sp. cochici divar. m.c. temp. Time 3 a 13 a 5 a 5 a 4 a 4 a 17.1 a 24.0 a 4 a 12 a 6 a 5 a 6 b 4 a 17.6 b ' 26.0 b 5 a 16 b 8 b . 7 b 4 a 7 b 16.9 a 27.7 c E-W 6 b 11 a 4 a. 4 a 4 a 7 a 17.3 ab 26.1 b 2 a 12 a 5 a 3 a 4 a 4 a 17.0 a 26.0 ab 2 a 16 b 8 b 3 a 5 a 4 a 17.1 ab 25.9 a 7 b 16 b 7 b 13 b 5 a 6 a 17.4 b 25.8 a Vert. 4 ab 10 a 5 a 10 b 2 a 4 ab 17.5 be 25.6 a 9 c 11 a 6 a 13 c 4 ab 10 c 17.7 c 25.8 ab 6 b 13 a 6 a 8 b 4 ab 5 ab 17.7 b 25.8 ab 2 a 13 a 5 a 3 d 3 a 3 a 16.8 a 25.9 be 1 a 13 a 5 a 3 a 3 ab 2 a 16.8 a 26.1 be 4 ab 13 a 7 a 4 a 4 ab 8 be 17.0 ab 26.2 c 4 ab 18 b 7 a . 3 a 8 c 7 abc 17.5 be 25.8 ab 3 ab 18 b 7 a 2 a 6 b 2 a 16.5 a 26.2 c 108. TABLE 4.7 Summary of adult insect distribution pattern (short-term distribution trial). Symbols indicate whether insect numbers increase (+) or decrease (-) within the crib in the direction specified. A blank indicates no discemable trend in that direction; symbols in parentheses indicate that trend is unclear or that analysis of variance indicates no significant differences. *Note that Sitophilus was more abundant at top and bottom and less abundant at the intermediate levels. Species CO CO CO CO P East to West North to South top to bottom + (-) + (+) + + + interior to surfaces V 109. Figure 4.8 (In part) a)Si tophi 1usNzeamai s' <432) <423) <433) b)Sitotroga cerealella FIGURE 4.8 Distribution of emergenoee (Short Term Distribution Trial). Numbsre of ineeote emerging In one week from eamplee of 108g of shelled grain. Extent of shading within eaoh square showe number of Ineeots in aaoh sample as a fraction of ths maxi- mum number recorded for that epeotee (ae Indicated In Indi- vidual oaptlone). Samples were oolleoted from orlb 2 on the third sampling oooaston (423) and from or1b 3 on the ssoond (432) and third (433) samp1ing oootstone. 110. Ffguro 4.8 (oontfnued) c>Cryptolestes spp. <432) < 423 > <433) d^Gnatocerus maxillosus <432) <423) <433) •^Palorus subdepressus ^ J? S s y Sis s s ^—^ T/ s y- s a s> ^ x s. y y ^ y y yjy v ^ s y ~7 1 IZ ^V y <432) <423) <433) 111. Ftgur* 4,8 (oontinuod) f) Choetospila elegans <432) <423) <433) g) Cerocephala dinoderi <432) <423) <433) 112. TABLE 4.8 Distribution pattern of emergences (short-term distribution trial) based on 2 factor analysis of variance. a) Probability levels, b) Treatment means with separations based on Newman-Keuls test (except column marked * where separations are based on Duncan's New multiple range test) c) Summary of trends : "+ " indicates increase, "-" decrease, in directions specied. Treatments Sitoph. Sitotr Crypt. Gnato. Palorus Choeto. Ceroceph. species zeamais cer. spp. max. subdep. elegans dinod. a) East-West <0.001 0.18 0.82 0.15 0.59 0.03 0.05 position 'Vertical* 0.01 0.65 <0.001 0.11 <0.001 0.01 0.13 position interaction 0.64 0.95 0.77 0.44 0.98 0.57 0.09 b) East-West 10.5 b 1.8 4.4 5.8 2.8 4.7 a 2.3 position 8.3 ab 2.0 5.0 6.8 3.0 4.6 a 2.4 7.7 a 2.8 4.7 8.7 3.3 5.5 ab 2.8 12.8 c 2.8 5.2 7.4 3.8 6.7 b 3.6 'Vertical* 9.2 a 2.6 7.2 be 5.3 0.9 a 3.8 a* 2.1 position 9.0 a 2.2 6.7 be 7.7 '2.4 ab 4.8 ab 2.1 8.7 a 2.1 5.3 abc 5.8 2.8 ab .4.8 ab 2.8 7.7 a 3.3 2.8 a 5.9 1.3 ab 4.1 ab 2.3 9.3 a 2.5 4.4abc 10.5 3.6 b 4.6 ab 2.8 10.8 ab 2.2 6.8 be 7.6 3.9 b 6.4 bed 3.7 13.3 b 2.7 3.3 ab 6.7 6.9 b 7.3 d 2.7 10.5 ab 1.6 2.1 a 8.2 3.8 c 7.2 cd 3.8 c) East to + (+) (+) (+) + + West North to South top to bottom + - + + (+) Interior to + + surfaces - 113. conditions by spending more time within damaged grains, or in the interstices between grains, in which situation they will be more readily collected in samples. Only three species (Sitotroga cerealella, Palorus subdepressus and Cardiastethus sp.) show changes in distribution with time of day (as indicated by the Time and Positions interactions, AB or AC, in Table 4.6a)). The interaction means, however, reveal that these do not represent insect movement from one part of the cribs to another. Rather, the time of day effects are only experienced, or are more strongly in evidence, in some sections of the crib; thus, for instance, « Card iaS te thuS" shows" a noticeable increase rn numbers~(in the afternoon) - only for samples for the west of the crib. . It should be noted that these effects too might be sampling artefacts. Turning to spatial distribution, it is evident from the results of the analysis of variance (Table 4.6) that, at the time of this trial at least, all species showed consistent, non-uniform patterns of dis- tribution within the cribs: both factors expressing position effects (B and C) in the analysis show significant differences for almost all species (0.1% or 1% level). It must immediately be pointed out, however, that the distributions cannot be described in terms of simple gradients along the two factors. Factor C in particular represents both vertical positions within the crib and, because the sampling tunnels are stepped alternately (see Figure 4.5b)), different degrees of exposure to the surface; any North-South trends cannot be properly tested, due to the design of the experiment. Both main effects and interactions have, therefore, to be taken into account to build-up a meaningful description of the distribution pattern; the trends in distribution have been summarised, as far as possible, in Table 4.7 but it must be recognised that this presentation involves a degree of simplification and (debatable) 114. interpretation. The analysis for Sitophilus zeamais shows highly significant differences (p < 0.1%) for both factors B and C and their interaction. There is a consistent increase in abundance from East to West, though the effect is stronger at the top and bottom of the crib than in the centre (Figures 4.6a) and 4.7). Emergences too show higher levels on the West than the East, but in this case the interior positions are lower, rather than intermediate (Figure 4.8a) and Table 4.8). The adults tend to be more abundant at the top and bottom of the crib than in the centre (Figure 4.6a) and separation of means Table 4.6b)). Sitotroga cerealella was only present in small numbers at the time of this trial and virtually disappeared during the course of it. This species, like Sitophilus, showed an increasing East to West gradient (both adults, Figure 4.6b) and Table 4.6b), and emergences* Figure 4.8b and Table 4.8); however the largest numbers in this case were found at the top of the cribs. Of the four common secondary pest species, the two Tenebrionidae, Gnatocerus maxillosus (Figure 4.6d,) and Palorus subdepressus (Figure 4.6e)), showed increasing gradients in abundance from East to West, though more erratic than in the case of Sitophilus. Carpophilus dimidiatus (Figure 4.6c)) was also more abundant in samples from the West than from the East but less abundant in interior samples. Cryptolestes spp., mainly C. pusillus, (Figure 4.6f) and, to a greater extent, the two commonest Mycetophagidae, Typhaea stercorea and Litargus balteatus, were markedly concentrated on the surfaces of the cribs, though patchily distributed. Both Palorus and Carpophilus were most abundant in samples from the bottom layer of the crib. Both of the common parasitoids, Choetospila elegans and Cerocephala 115. dinoderi (Pfceromalidae), showed consistently increasing gradients from East to West and from top to bottom for both adults (Figures 4.6 h) and i)) and emergences (Figures 4.8 j) and g)). Their distribution corresponded approximately with that of Sitophilus which is regarded as the main host of the former species; the biology of Cerocephala does not seem to be properly known. The two most abundant Anthocoridae, Lyctocoris cochici(Figure 4.6g)) and Scolopoides divareti, occurred rather erratically in the three cribs. They were most abundant in surface samples and their distributions followed most closely those of Carpophilus dimidiatus and Palorus subdepressus; the larvae of both of these species were subsequently shown in the laboratory to be suitable prey species for the Anthocorids. 4.6 Distribution of Losses within the Cribs. The methods used to assess weight loss have-been described briefly in Section 3.5 and are considered more fully in Appendix V. " For the distribution trials marked and weighed cobs were included at loading both in the sections to be used for insect sampling and in the undis- turbed parts of the crib. In the long-term trial those in the sampled sections were weighed (whole) on each of the four sampling occasions to provide an estimate of the progress of damage during the storage season. At the end of the trial all the loss assessment cobs (i.e. from both sampled and unsampled sections) were shelled and the weight loss assessed on the basis of the remaining clean, sieved grain. In the . short-term trial the loss assessment cobs were not exposed during insect sampling and only a single estimate of loss was made at the end of the trial when all cobs were shelled and weighed. For the long term trial losses were assessed on the basis of four replicate cobs at each of the forty-eight 'positions' in the crib and for the short-term trial on three cobs at each of the 64 positions (in each of three cribs). The crude weight losses observed have to be corrected for diff- erences in moisture content (both with time and position in the crib) so that they can be presented on a comparable dry weight basis. This presents considerable problems, as already mentioned in Section 3.5. The grain and core moisture contents had to be estimated at the beg- inning of the trial, and at intermediate sample points in the long- term trial, from cobs other than those actually used for loss assess- ment. Even at the end of the trial, when determinations could be made on subsamples from the loss assessment cobs themselves, the number of cobs involved meant that only a proportion could be tested individually. As a result there is an uncertainty in the moisture content correction for each cob. To simplify calculations, no attempt has been made to allow for this source of variation in the presentation or analysis of results. While this should not bias the overall results, the existance of appreciable inter-cob variation in moisture content" does mean that the estimates of loss for individual cobs are subject to errors of several percentage points. The estimated weight losses (dry weight basis) recorded in the long-term trial are presented schematically in Figure 4.9; no consistent weight loss was detectable by the time of the first sample (after two weeks in store), so these data have not been included. At the second sample, after six weeks1 storage, damage levels were still low; there is no clear pattern of distribution, although there is evidence of higher damage in some corner and surface positions. In the third and fourth samples, after three and seven months in store, respectively, there is clearer evidence of more serious damage to grain on the surfaces of the crib; however the small number of samples from the interior of the crib make it difficult to assess this critically. In the fourth sample there is evidence of vertical stratification with more damage to Figure 4.10 >5 .^8 y {/is .fi? u Sample 2 Sample 3 Sample 4 FIGURE 4.9 Progreee of weight loee In different parte of a elngle orlb (Long Term Dletrlbutlon Trial) Height loes of oobe (dry wstght baete) after elx weeke, three months and ssvsn months In store. Figures are meana of eetlmatee for four oobe In eaoh poeltlon and are oorreoted for moleture content ohangee with time in etore and poeltlon within the orlb. Figure 4.10 . 6/36. 5/44T0X42.5 /j? .3/36.4/59. 2/^2»9 CRIB 1 CRIB 2 CRIB 3 FIGURE 4.10 Distribution of weight loss within orlbs. (Short Term Distribution Trial). Final weight toes (dry weight basis) - figures are means of estimates from three oobs In eaoh position. 119. TABLE 4.9 a) Source (Name) df Sums of squares Mean square F Ratio F-Prob Total 575 21478.26 37.35 Blocks 2 2371.65 1185.83 A Top/Btm 3 2183.75 727.92 24.962 <.001 B South/Nth 3 497.09 165.70 5.682 .001 C West/East 3 1251.87 417.29 14.310 <.001 AB 9 339.52 37.72 1.294 .25 AC 9 1271.88 141.32 4.846 <.001 BC 9 548.90 60.99 2.092 .03 ABC 27 671.36 24.87 .853 .68 Block Error 126 3674.14 29.16 Sampling Error 384 8668.10 22.57 All F tests were formed-with the Block Error b) North 34 .4b East 32.4a Top 36.0c 32 .4a 31.9a 32.6b • 32.3 a 32.9a 30.7a South 33 .9b West 35.7b Bottom 33.7b TABLE 4.9 Summary results of analysis of variance: Effect of position within crib on grain weight loss. a) Summary anova table with probabilities for null hypothesis 'no differences between means'. b) Treatment means and separations on Newman-Keuls test at 5% level. Data were analysed as a 4x4x4 factorial design for the 64 sampling positions within the crib with three determinations (cobs) at each point (minor replications) and three cribs (blocks). 120. cobs in the top and bottom sections of the crib than to those in the middle two. In the top half of the crib at the time of the third sample, and more erratically at all levels at the fourth, samples from the West face of the crib tend to be more damaged than those from the East. There is no evidence of reduced damage in the parts of the crib from which insect samples had been collected (indicated by arrows in Figure 4.9). The data from the short-term trial are presented in Figure 4.10. None of the loss assessment cobs in this trial were disturbed in the insect sampling program and so all figures were included in a simple factorial analysis of variance foTL.ppsitjton.,effeotS., jthe factors1 being the three primary axes of the crib. The.results of the analysis are summarised in Table 4.9 with the main effect treatment means and separations from Newman-Keuls tests. The analysis, and implied null hypotheses, need to be interpreted with caution, bearing in mind the variation inherent in the moisture content corrections used. As in the long-term trial, the overall picture is of higher levels of damage on the surfaces of the crib, especially in the corners, and a tendency towards more severe damage on the West face. There is some vertical stratification, with the top layer being most damaged and the third layer least. It should be noted, however, that the trends are not uniform and that inter-cob variation is appreciable (approximately + 10% within positions). The contribution of various sources of loss (i.e. insects, moulds rodents, etc.) were not investigated quantitatively. There was visible evidence of higher levels of mould activity on the surfaces of the cribs in the form of much more extensive discolouration of grains (as noted in Section 2.4); there can be little doubt that the more severe losses 121. in the surface samples are attributable, at least in part, to this source. Higher levels of Sitophilus and several secondary pest species were, however, also noted in these positions and the increased numbers of insects will also have contributed, both directly and in interaction with the fungi, to the loss of grain. Rodents were present, and caused severe losses, in some of the experimental cribs but their damage was readily identifiable and was not a contributory factor in this trial. It may be noted that the estimates of loss provided by these figures, although high and representing in practice total loss of the grain, are well within the range recorded in various surveys of on-farm cereal storage in Africa (Hall, 1970). f 4.7 Species Interactions and Habitat Selection The data presented in the preceding sections have indicated that insect populations are not uniformly distributed within the crib and that the distribution patterns of individual species can be described, at least approximately, in terms of consistent 'preferences1 for par- ticular parts of the crib. This information is of itself important in its implications for sampling, whether this is directed towards assess- ment of losses or of insect infestation: surface samples cannot, in general, be expected to provide a good indication of the state of the grain in the entire crib. The more interesting question remains, however, of whether these observed distribution patterns can be inter- preted in terms of the behavioural responses of the insects to envir- onmental factors or to one another. Multivariate techniques have been used by Sinha and co-workers (1969, 1977 and 1980) to investigate the factors influencing the dev- elopment and distribution of infestation of bulk grain by insects, moulds and mites. In the current study quantitative data were not collected on a number of potentially crucial environmental and biological factors, 122. particularly relating to the type, of grain damage and to the development and distribution of fungal activity and mites. Given the limitations of the environmental data gathered and the manifest complexity of the infesting populations, it would be inappropriate here to attempt a similarly sophisticated interpretation of the maize crib ecosystem. Rather, attention may be drawn to a number of points of interest in- dicated by simple correlation and the kind of influences on insect distribution discussed in general terms. Data from the short-term distribution trial are summarised in the form of correlation matrices, comparing the abundance of the thirteen commonest insect species and levels of-grain moisture and total weight loss, in Table 4.10 and a schematic outline of the observed-environmental-gradients in Figure •• < 4.11. In order to simplify consideration of the correlation matrices (Table 4.10), all values of the correlation coefficient which do not differ significantly from zero at the 5% level according to a bivariate significance test (i.e. suggesting that the variables are uncorrelated) have been diagonally 'hatched*; in addition, some figures that are significant (at the 5% level) have been similarly 'eliminated1 where comparison with the corresponding values for the other two cribs indicate that correlation is not consistent. Attention may then be focussed on those variables showing consistent correlations, either negative (vertical hatching) or positive (left unhatched). The matrix has also been divided on the basis of the known biology of the insect species. Sitophilus and Sitotroga forming the first group (A - 'primary pests'), both have larvae that develop within an individual cereal grain and feed entirely on it. The second group (B - 'secondary pests') all have free-living larvae but are much more diverse in their feeding habits: some feed mainly on the grain but others are primarily detritus- FIGURE 4.11 Summary of trends in environmental factors (Short-Term Distribution Trial) (Means based on data from 3 cribs) a) Weight loss of grain (dry weight basis) (based on estimates for 3 cobs from 64 sampling points in each of 3 cribs - data in fig .4.10) b) Grain moisture content (fresh weight basis) . (based on determinations made at end of trial; one de- termination, based on pooled grain from 3 cobs, from -each of 64 sampling ponts in each of 3 cribs) c) Grain temperatures at different times of day (figures are means of 3 readings, taken on different ' days, at each point) (For details of methods see text and earlier full data). 123. *) weight loss • X 36.0 34.4 34.4 38.1 H 36.0 top 32.3 33.3 33.4 32.7 32.6 32.5 30.9 31.5 32.9 30.7 34.9 30.6 30.3 33.9 33.7 bottom N b) motsturs content / X 17.7 17.7 17.4 17.9 H 18.1 top 17.9 17.2 16.9 17.2 t7.2 18.0 17.1 16.7 16.8 17.1 17.9 16.9 16.7 16.9 17.0 bottom S -v N Figure 4.11 TABLE 4.10 Correlation matrices showing associations between insect species and with two environmental parameters, (data from Short-Term Distribution Trial) Each correlation coefficient is based on 96 samples - 32 sampling positions each sampled three times. Data for the three cribs have been analysed separately. Correlation coefficients not significantly different from zero (at 5% level) have been diagonally 'hatched' and those showing a significant negative correlation vertically 'hatched' (see text). Species in parentheses (T. stercorea and L.cocbici in CRIB III) were present only in very small numbers. Species have been classified as: A - primary pest species - B - secondary pest species. _ C - parasitoids (Hymenoptera, Pteromalidae) D - predatory bugs (Heteroptera, Anthocoridae). TABLE 4.10 CO CO 0) CO P 4-1 CO 3 CU r-l CO p r-l b0 •H 0 4-1 0 U o O P, P- 4-1 O 4-> • 4-> U £ cfl rH • H •H nJ C Ctf tn C/3 O U O CRIB I Sitophilus A 0.22 .32 Sitotroga Carpophilus B W////W. .39 .68 Cryptolestes .41 y//M. Gnatocerus 1 .21 Palorus 1 Typhaea Litargus Choetospila C Cerocephala Cardiastiethus D Lyctocoris Scolopoides mTC^ Wt. loss TABLE 4.10 (Continued) (0 u Scolopoide s Damag e Cardiastethu j Lyctocori s Choetospil a Cerocephal a Typhae a Litargu s Sitotrog a Cryptoleste s Gnatoceru s X Sitophilu s Carpophilu s Paloru s n t o M M M Sitophilus 1 .24 .67^^ .67 .32 .65 .47 .46 .23 %^ .33 .35 Sitotroga A 1 .28 .34 Carpophilus B 1 .27 .59 .69 .59 .30 .74 .49 .24 .54 .40 .45 .55 y Cryptolestes 1 .29%^ .20 .49 .37%^/ .54 .36 //M Gnatocerus 1 .38 .25 .42 .56 .41 .50 .34 .33 .35 .35 Palorus 1 .W'/Z/M .69 .56 JPBII .73 .26 VM V/to Typhaea 1 .39 W/& .60 .42 ' .31 .71 Litargus 1 .!*'///&, .34 .30 .58 Choetospila C 1 .56 //Mr, .^V/tt// .27 .43 Cerocephala 1 ////& .29 y/py,v m Cardiastethus D 1 '//J8&?//JW* .39 .38 Lyctocoris 1 .33 .37 Scolopoides 1 .26 M.C. 1 .44 Wt. loss TABLE 4.10 (Continued) CO CO Heteroptera. Considering first the mainly phytophagous species (groups A and B), it is noticeable that the dominant primary pest, Sitophilus, which one may assume to be the main agent of insect damage, is consistently pos- itively correlated with the two most abundant secondary pests, Palorus and Carpophilus. Sitotroga, on the other hand, although very slightly- correlated with Sitophilus (0.01 (strong) and Carpophilus (weaker). Both primary pests show a weak correlation with grain moisture content in two of the cribs and a similarly weak correlation with damage in all three. —It-may-be recalled that-both^Sitophilus and Sitotroga were more abundant towards the west of the crib and that Sitotroga, which was present only in small numbers, was concentrated strongly towards the top. As may be seen from Figure 4.11, the West and top of the crib tended to be moister, more damaged and, except in the late afternoon, cooler than the remainder (all of which may be associated with the observation that on eight of the nine sampling occasions the prevailing wind was from the West). It seems likely that the two species are favoured by, and are responding to, the same environmental conditions but that Sitotroga is being largely excluded by competition. Ayertey (1979, 1980) has shown that, at insect densities comparable to those found here, Sitophilus causes severe mortality to Sitotroga larvae developing within the grains and that this effect is more acute in already-damaged grain (Ayertey, 1979 and de Lima, 1978). The eggs (and newly-hatched larvae) of Sitotroga are also exposed to predation by insects and mites. These factors may be related to the low or 128. negative correlation coefficients that Sitotroga shows with several secondary pest species and to the observation that, although Sitotroga adult abundance in general increased from East to West, the rate of recruitment was rather low in North-West and South-West corner positions where grain damage and insect pest populations were highest. Turning to the secondary pest species there is a 'gradient' of associations: Palorus, at one extreme, is most closely correlated with Carpophilus, less so with Typhaea and Gnatocerus and not at all with Cryptolestes and Litargus; Carpophilus is correlated with Palorus and Typhaea and less with Gnatocerus and Litargus; Typhaea is most strongly strongly correlated with Carpophilus and Litargus and less with Gnatocerus, while only Gnatocerus and Litargus are correlated with Cryptolestes. The same associations can be seen in terms of the spatial distribution of the species, summarised in Table 4.7. All the secondary pests . except Palorus show a tendency to aggregate near the surfaces of the crib; Palorus, Gnatocerus and Carpophilus show gradients of increasing abundance from East to West while Palorus and Carpophilus are both abundant towards the bottom of the crib. If these observations are compared with the environmental data it may tentatively be suggested that Palorus is able to exploit the driest parts of the crib, Carpophilus is quite versatile infesting both dry and moister parts but preferring the latter, while the remaining species are largely confined to the moister surface conditions; Cryptolestes and Litargus are most strongly limited in this way, Litargus being moreover associated particularly with the most heavily damaged, mouldy areas. The two Preromalid parasitoids, Choetospila and Cerocephala, are correlated with one another, with Sitophilus, Palorus and, to a lesser extent, Carpophilus. This is consistent with the possibility that Choetospila is aggregating in areas where Sitophilus, its main host, is most abundant. (It may be noted that Choetospila was preseit at much lower densities than its host and that the rate of parasitisi was not high enough to depress the host population). Dinoderus was originally described as the host of Cerocephala, hence C. dinoderi, (Gahan, 1925) but Dinoderus was only occasionally recorded from the study cribs and then not in sufficient numbers to have supported the parasitoid population. Attempts to rear Cerocephala in the laboratoy on a variety of hosts proved unsuccessful. Among the Anthocorid predators, Scolopoides was uncorrelated with the primary pest species but correlated with all the secondary pests except Palorus; Lyctocoris was correlated with Sitophilus, Paltry s, Carpophilus and Typhaea while Cardiastethus was correlated with Sitotrg^r»ga and Litargus and more weakly with Sitophilus, Gnatocerus and Cryptolts * es. Cardiastethus was confined almost entirely to the top half of the crib especially the surfaces, Lyctocoris occurred throughout the crib but nymphs were found mainly near the bottom, while Scolopo'ides occurred and reproduced in surface samples at all levels. The distribution of these predators, in the crib then, provides strong evidence of some i degree of ecological separation between them even though, in the labcr atory, both Scolopoides and Lyctocoris were able to reproduce success- fully on cultures of all the secondary pests which were offered to ttenmz* (Carpophilus, Palorus, Gnatocerus and Cryptolestes). Cardiastethus was not reared in the laboratory despite several attempts with a varie~e=^;y of hosts. In conclusion it should be pointed out that the foregoing commenss imply an overly simplistic interpretation of insect distribution in relation to environmental conditions. Three additional and related considerations must be borne in mind. Firstly, conditions throughout the crib were, at the time of the study, quite favourable to insect L30. development and most of the phytophagous species were maintained quite easily in single species culture on similar grain and under comparable physical conditions in a nearby open-air laboratory. Second- ly, insect infestation was very heavy with total pest densities often exceeding one insect per grain of maize, implying intense competition both between and within species. Under these conditions (i.e. equable environment but high insect numbers) any full description of insect distribution should be formulated in terms of competitive exclusion under subtly differing conditions rather than simple preferences for a particular habitat. Thirdly, although the environmental conditions have been described in terms of large-scale gradients, on the scale of individual cobs the habitat was very heterogeneous: moi-sture and mould development in particular were" 'patchy* and the overall 'gradients' often reflected the changing prevalence of patches of more or less heavily damaged grain. The processes that determine insect distribution, such as microhabitat selection, competition for food, shelter and ovi- position sites, and the search for hosts or prey, were thus occurring on a structurally complex, heterogeneous substrate. The data discussed in this chapter were collected under only one set of environmental conditions and it would clearly be dangerous to try to generalise the conclusions too widely. The complexity of the situation revealed should, however, at least serve as a warning against an unduly simplistic approach to the analysis of stored grain ecosystems. 13L. CHAPTER 5 THE INITIATION OF INFESTATION 5.1 Introduction The previous chapter was concerned mainly with the spatial structure of and relationships within the insect community of the maize crib at a particular time. The next two chapters will consider in more detail the changes that occur in this community with the passage of time. This chapter will describe the initial infestation of the grain maturing in the field, the transfer of grain to and colonisation of the crib, and the influence of the preharvest in- festation and harvesting practice on the first stages of development of the storage insect community. The next chapter will then follow the successional changes in the pest complex that occur over the storage period. Traditional small farm stores are often situated near to or on the fields where the maize is grown. Where the grain is stored for long periods, for subsistence use, storage pests may readily move directly from infested stores to the new crop growing in the field. Infested stores have been recognised as the main source of infestation both in the U.S.A. (Blickenstaff, 1960) and Africa (Giles and Ashman, 1971) although other crops and natural reservoirs may be important sources for some species and in some situations (Schulten, 1976; Linsley, 1944). Many storage insects fly readily and Sitophilus zeamais, which seems to have been the species most extensively studied in this respect* can cover distances of at least 400 - 800 metres (Giles, 1969; Chesnut, 1972) . Sitotroga cerealella, too, can actively infest maize before harvest and this species was found to be more common in the field than Sitophilus spp. in several localities in Kenya (de Lima, 1978) and 132. Malawi (Schulten, 1972, quoted by Schulten, 1976; Dobie, 1974b). Field infestation by storage pests follows and is probably aided by, prior damage to the silks, sheaths and grain caused by 'earworms' - i.e. Lepidoptera larvae (Floyd, et al 1958; Comes, 1964; Starks et al. 1966). Secondary storage pests (Coleoptera may also be common on maize in the field : Schulten (1976; also quoting Giles and Leon, 1974) suggests that field infestation by these species may be low in the dry tropics but higher in more humid areas. Cornes (1964), working at Ilora, S.W. Nigeria, (a location also used in this study) recorded a succession in the pre-harvest infestation : the silks were damaged by (unspecified) Diptera and Heliothis armigera (Noctuidae); damage "to the ears, especially the tips, by Mussidia sp (Phycitidae) and Argyroploce (=Cryptophlebla) leucotreta (Olethreutidae) followed and finally the damaged cob apices and sheaths were invaded by Sitophilus zeamais, Cathartus quadricollis, Carpophilus spp. and other storage pests. Particular attention has been given to the role of the husks in protecting the cob in the field from infestation by storage pests. Schulten (1976), reviewing the storage of maize,cobs, noted the impor- tance of inter-varietal differences in extension of the husk over the tip of the cob (Eden, 1952a), the tightness of the husk (Freeman, 1955) and the number of sheaths forming the husk (Eden, 1952b). Damage to the sheaths by birds, rodents and Lepidoptera larvae may allow storage insects to enter otherwise well-protected cobs (Floyd et al. 1958; Freeman 1955; Starks.et al. 1966) and resistance to sheath-damage by Lepidoptera may itself be related to varietal characteristics (Starks and McMillian, 1967). In Africa too, poor husk cover has been associated with in- creased flight activity (Ajibola-Taylor, 1971) and infestation (Giles and Ashman, 1971) by storage insects in the field. 133. Storage of maize 1 in the husk', which is the traditional practice in many areas, may provide protection against infestation for at least the first part of the storage season, so long, as husk-cover is good as in most traditional varieties (Thorshaug, 1975; de Lima, 1978). The retention of the husks may reduce the effectiveness of admixed insecticides (F.A.O. 1980). However, Golob (1981) has shown that insecticides applied at appropriate levels to maize cobs in the husk can achieve satisfactory insect control while leaving very low re- sidues on the grain itself. As noted in Chapter 2, cobs to be stored in the husk may have to be allowed to dry to a lower moisture content before harvest, with the possibility of more severe field damage, (Thorshaug, 1975; F.A.O., 1980) and their'irate of drying in store may be slightly slower (Salmond, 1957; de Lima, 1978). It is difficult to obtain a good idea of the seriousness of- pre-harvest infestation both because infestation and damage are recorded in a variety of different ways and because the various farming practices in different areas mean that maize is not always harvested at a com- parable stage of maturity. Estimates of grain damage at harvest vary from 0.2% in local Malawi varieties (Reader, 1971) to over 10% in some localities in Southern Nigeria (Adesuyi and Adeyemi, 1970). Surveys in Southern Nigeria (Cornes and Riley, 1962; Comes, 1963 and 1964; Patel and Adesuyi, 1975) and in Kenya (de Lima, 1978) indicate that a wide range of values may be expected even under superficially similar conditions: De Lima (1978) found less than 5% in most localities but a few were as high as 10% and above. Little attention seems to have been given to investigation of the relationship between preharvest infestation and subsequent pest problems in store. Giles and Ashman (1971) found that a higher level of damage at harvest led to a more rapid increase in damage in store while Pointel (1969) observed a correlation between Sitophilus zeamais infestation after harvest with Lepidoptera damage in the field. An understanding of the relative importance of sources of infestation is clearly of crucial importance to the development of an appropriate insect control strategy. Grain placed in a crib after harvest will typically carry a t degree of 'hidden infestation* (i.e. immatures of primary pests dev- eloping within the grain) and a number of adults from the field pop- ulation (although a proportion will have left the grain during harvest and subsequent handling). To these insects will then be added any that were infesting the fabric of the store, or residues from the previous year's crop, and those that actively move to the store, either immediately after harvest or during the storage period; these latter may include insects from the field populations, from alternative agri- cultural or natural habitats and from already-infested stores. Im- portance has variously been placed on disinfestation of the fabric of the empty store (with the help of exposure to sunshine, smoking, or chemical insecticides), reduction or elimination of the pest population carried into store with the grain (by 'sunning' or fumigation prior to loading) and protection of the stored grain by admixture of persistent insecticides, synthetic or natural, at the time of loading or repeated applications of less persistant insecticides throughout the storage season (methods reviewed by: Pingale, 1963 and 1964; Hall, 1970; Hindmarsh, Tyler and Webley, 1978; F.A.O., 1980). The effectiveness of such measures, and so the stress to be placed on them in a pest control strategy, depends critically on the sources of infestation and the timing of any insect movement to the store. A comprehensive investigation of the relationship between pre- and post-harvest infestation was beyond the scope of the present study. 135. Limited observations were, however, made on the pre-harvest infestation of the maize to be used for storage trials: these were to investigate the species involved, their distribution and abundance, and their role in promoting damage. In addition, two experiments were undertaken to consider particular aspects of the relationship between field and storage infestation: one, the 'Harvesting-Practice Trial1, was con- cerned with the effects on the insect populations of, firstly, the timing of the harvest and, secondly, the removal or retention of the husks; the other, the 'Pre-Harvest Damage Trial* considered the persistent effects in storage of the damage caused in the field by insects and fungi. Some information on the source of colonisation of stores was also provided by the inclusion in the- long'-term 'Succession Studies' of cribs loaded with maize fumigated after harvest to destroy the field infestation; these data will be considered in more detail in Chapter 6. 5.2 Pre-Harvest Infestation Three surveys of field infestation were carried out: the first at the time of the wet season harvest of 1978 and the second and third prior to the dry season harvests of 1978/79 and 1979/80. Field samples were collected from the maize subsequently used for the long-term Distribution and Succession Studies, the Pre-Harvest Damage Trial and the Harvesting- Practice Trial, respectively. The maize for the first and third surveys was grown using mechanised zero-tillage methods (I.I.T.A., 1973) while that used for the second survey was grown conventionally (i.e. sown on tilled ground and hand-weeded). The maize varieties used were white 'composite' varieties, TZPB and TZB. In the wet season survey two fields of maize were sampled at the beginning of August during the week before harvest when the grain (in both cases) had a mean moisture content of approximately 30%. For the 136. second survey (in the 1978/79 dry season) the maize from a single field was sampled twice: the first sample was taken at the end of November, three weeks before harvest, at a grain moisture content of 57 _+ 8%, and the second the day before harvest, in late December, at a moisture content of 30 '+_ 6%. The intention in the third survey was to compare the effects on infestation of harvesting at physiological maturity of the grain with those of allowing the maize to dry some- what in the field before harvest in the traditional way. One field sample therefore accompanied the first harvest at 33 _+ 5% moisture content and the other the second harvest at 18 +_ 3% moisture- content. The methods used in this last trial will be discussed- further in Section 5.3. The procedure for selection of samples was slightly different in the three surveys, depending on the size and shape of the fields studied, but in all cases the intention was to obtain a 'stratified' random sample from the whole field. Transects were initially set, at regular intervals, perpendicular to the rows of maize as sown. The transects were then divided into subunits, each of a specified number of rows (namely the total number of rows, divided by the number of samples required); walking along the transect, one could then select a sample (one cob) from each subunit, according to pre-selected random numbers, simply by counting the number of rows crossed. In the first survey 25 cobs were picked along each of two transects in two fields, in the second survey ten cobs were picked along each of four transects on the two sampling occasions and in the third survey ten cobs were picked along each of six transects at the two harvests. In all trials cobs were snapped off and sealed immediately into individual plastic bags. In the laboratory the cobs were dehusked, 137. all insects collected and a subsample of grain taken for moisture content determination. No attempt was made to distinguish between insects associated with different parts of the ear - i.e. silks, husk, grain or core - but where damage or infestation appeared limited to a particular part this was noted. As the cobs were dehusked a note was also made as to whether the sheaths were 'open' at the apex, properly 'closed1 over the tip of the cob, or, if closed, whether the husks had been 'holed' by insects. After collection of the insects an approximate count was made of the number of grains on each cob damaged by insects and moulds; only damage to fully-formed grains was scored and where moulding appeared to have followed insect damage to a grain that damaged was attributed to insects. All samples from field trials had to be handled rapidly to avoid the excessive build-up of condensation and the perforation of sample bags by Lepidoptera larvae. Outline results indicating the degree of field infestation and damage are given in Table 5.1 and the abundance of the various insect species is summarised in Table 5.2. In comparing the results of the three surveys it may be noted that the wet season samples, the 'at harvest' sample of the 1978/79 dry season survey and the 'first harvest'sample of the 1979/80 survey were all taken at a comparable stage of the crop phenology - i.e. at grain maturity. The general picture provided by these data is of considerable infestation : only a single uninfested cob was collected in each of the first two surveys (i.e. two from a total of 180 cobs). However, in many cases the 'infestation' was of no economic significance, consisting of only small numbers of Coleoptera, often associated with the husk or silks rather than with the grain. At the time of harvest 52% of the cobs in the wet season samples and 68% in the first dry season survey showed less than ten grains damaged by insects (7% and 22% of cobs, t TABLE 5.1 Summary results of field samples: infestation by major pest groups, grainidamage and husk, cover. Mean no. grains/cob husk cover: Mean grain Cobs Percentage of cobs infested by: damaged by:, % cobs Survey m.c./% collected a)Lep. & Col. Lep. only Col. only Uninf. a) insects b) fungi intact holed open WET SEASON (1978) Field A. 29 50 56 16 22 2 16 48 Field B. 30 50 58 26 14 0 36 44 DRY SEASON 1. (1978/79) 1. 3wks.before 57 40 67.5 20 10 0 2 8 57.5 30 12.5 harvest. 2. at harvest 30 40 67.5 0 30 2.5 9 15 27.5 40 22.5 DRY SEASON 2. (1979/80) 1. First har- 33 60 48.3 8.3 35 8.3 N/D N/D 71.7 20 8.3 vest 2. Second 18 60 38.3 3.3 • . 53-3 5 N/D N/D 45 35 20 harvest u> 00 139. TABLE 5.2 Percentage of cobs infested by each species (or group). Figures in parentheses are mean numbers of insects/cob for the most abundant species. SPECIES WET SEASON 1 DRY SEASON 1. DRY SEASON 2. LEPIDOPTERA: (Field A) 3 wks. pre- harvest first second harvest harvest harvest Eldana saccharina } 70(2) 28 18 5 2 Mussidia sp. J 3 - i 28 15 Cryptophlebia leuc 1 75 (1. 2) 33 • 20 10 Pyroderces sp. 1 12 5 45 8 22 indet. 12 — 13 5 COLEOPTERA Sitophilus zeamais 28 - 45 (3. 5) 7 32 Carpophilus spp. 44 38 (1. 5) 35 (2. 3) 35 (1.2) 45 (2 .0) Brachypeplus spp. 8 8 30 28 13 ' Cathartus quad. 14 ., 55 (2.1). 78 (7. 5) 42 (1.0) 38 (3 .6) Mycetaea hirta 18 35 60 (2. 0 36 (2.4) 67 (1 .9) Litargus'varius' — 5 8 5 - Gnatocerus max. — — 25 - - Staphylinidae 16 23 23 18 10 other Coleoptera 6 - 38 12 10 Coleoptera larvae Nitidulidae 42 13 48 (2. 3) 20 (1.5) 17 . others N/D 10 75 (2. 7) 17 42 (1 • 2) HYMENOPTERA « Parasitoids N/D - 8 2 2 Formicidae N/D - 23 10 10 DERMAPTERA 24 63 (1 3) 45 23 17 . (add. and ny.) HETEROPTERA 2 5 10 2 3 (add. and ny.) DIPTERA N/D 20 N/D 10 - (larvae & pupae) BLATTIDAE N/D - 3 5 2 Other insects N/D - - 2 2 Spiders N/D 5 3 140. respectively, showed 110 visible insect damage to the grains). Using an approximate conversion, based on the mean number of grains per cob, the proportion of grains damaged by insects at the time of the wet season harvest may be estimated at c.3 and 7% (for the two fields sampled) and for the dry season harvest at c.9%; the corresponding figures for mould damage were 8-9% for the wet season harvest and c.3%- for the dry. It has already been noted (§2.2) that the distributions of insects in field samples closely followed the negative binomial distribution with low values of k (< 1.5 for most species) and this pattern was reflected in the figures for insect damage. Mould damage was similarly, or more strongly, 'clumped1: at the wet season harvest, for instance, 10% of cobs had been totally infested with mould (i.e. all grains visibly infected) while 20% showed no visible mould damage at all. The re- lationship between fungal development and insect infestation is complex and appears to depend both on the species involved and the timing of infection. Infection by Diplodia macrospora was usually primary (i.e. attacking cobs not previously damaged by insects or other agents) and, once established, tended to destroy the entire cob. This species accounted for all the cobs showing 'total infection* mentioned above. Cobs attacked by Diplodia usually had intact husks, the sheaths covering the tip of the cob and adhering strongly to the grain due to the vigourous growth of hyphae between. Such cobs were rarely infested with insects, with the exception of small numbers of Mycetaea hirta (Endomycidae), a species believed to feed mainly on fungi. Another primary pathogenic fungus, Ustilago maydis, was also recorded but only occasionally. Ustilago tended to cause severe deformation of the cob and husk and the resulting 'wet' rot was particularly attractive to Nitidulid beetles (Carpophilus spp; 141. Brachypeplus spp. and Urophorus humeralis). More limited damage was caused by Fusarium moniliforme (= Gibberella fujikuori) (probably in association with other species). Infection in this case appeared to be associated almost always with prior infestation by insects, especially Lepidoptera larvae. Fungal development was usually confined to the immediate vicinity of insect-damaged grains and often affected only the tip of the cob. More severe damage by these fungi occurred when the sheaths were open or damaged at the apex. The larvae of Carpophilus spp. and Cathartus quadricollis seemed to be mainly feeding in the grains already damaged by moulds although Schulten (1976) states that Cathartus can act as a primary pest (i.e. attacking undamaged grain) at moisture contents of 30% or above. Husk cover in the maize varieties used for these studies was near the average for 'improved' high-yielding varieties-(Olusanya, pers. comm.) with the sheaths completely closed over the tip of the cob in most plants. The results indicate that the proportion of cobs with intact husks declined markedly during field drying, with comparable increases in both husks perforated by insects and those that opened at the tip as they dried. It may be noted that in both dry season surveys the rate of infestation by Lepidoptera declined markedly between the two samples, reflecting emergence of the single generation of these species that is completed on the developing cobs. It is the late instar Lepidoptera larvae, especially Eldana saccharina and Mussidia nigrivenella, i that are mainly responsible for damage to the sheaths. It may be noted that both insect infestation and the proportion of cobs with 'open' husks were higher in the first dry season survey than in the second. Poor husk cover in maize is often associated with adverse conditions during growth (Quin, pers. comm.) and it may be relevant that the former crop 142. suffered considerable drought stress. Damage to husks by birds and rodents was not significant in the fields surveyed, although large flocks of weaver birds (Ploceidae) were at times observed feeding on maize fields on the research station. The Lepidoptera infesting maize cobs in the field are diverse in biology and in the damage they cause. Eldana saccharina is economically important mainly as a stem borer, invading the crop at or after tass- elling and continuing to develop in the maize plants until they are completely dry (Kaufmann, pers. comm.). The severe lodging that may be caused by infestation by this species is an important factor to be con- sidered in assessing the optimum time of harvest. Eldana larvae may invade the cobs at any stage, entry being via the tip or directly through o the sheaths, rather than via the stem (a point also noted by Cornes, 1964). Damage to the grain can be extensive: a single larva may move and feed superficially down one or two rows of grains..,along the length of a cob, causing little direct damage but exposing all the grains so affected to fungal attack and infestation by secondary pests. Mussidia nigrivenella appears to attack only the cobs (i.e. it is not a stem borer) but shows a similar pattern of damage. The late instar larvae often tunnel through the bases of a row of grains, finally pupating 'in situ', and similarly promoting the destruction of a large number of grains. Several larvae of the same size are typically found together. The dominance of these two species (present in approximately equal numbers) at the time of the wet season survey was responsible for the higher number of insect damaged grains recorded then. The other two common species of Lepidoptera, Cryptophlebia leucotreta and Pyroderces sp. (probably gossypiella), were almost in- variably found near the apices of cobs. The former was often found feeding on the silks or on immature grains, while the latter appears to 143. complete development within a single grain (and, for this reason, was probably under-recorded); the damage caused by both species is, acc- ordingly, much more limited. Damage to the cob apex and sheaths by Cryptophlebia appeared to be associated with some mould development but this was usually limited to the core. Cryptophlebia feeds on a variety of other hosts, especially fruits, and only attacks the maize at a high moisture content before maturity. Pyroderces infests later in the succession and many adults emerged in the crib after harvest, though they did not reproduce there. Pyroderces sp. has been found in large numbers on maize at harvest in Zaria, under much drier climatic con- ditions (Ayertey, pers. comm.,), and two species have been collected from maize in Cameronn (Bradley, pers. comm). The dearth ,of records of this species from other localities may be due to its being mistaken for Sitotroga cerealella, which is similar in size and form. Other Lepidoptera recorded in small numbers included Helio.this armigera, Sesamia calamistis and Busseola fusca, the first feeding usually on the silks and the latter two on grains or cores. The dominant Coleoptera in field samples were, as indicated in Table 5.2, Cathartus quadricollis, various Carpophilus species and Mycetaea hirta. Among the Carpophilus spp., C. fumatus was by far the commonest, followed by C. dimidiatus, with smaller numbers of C. zeaphilus, C. freemani,C. binotatus, C. hemipterus and C. obsoletus; the incidence of the Carpophilus species was erratic and highly clumped with the less abundant species sometimes occurring in large numbers on a single cob. There was no evidence of primary damage by any of these species but they undoubtedly contributed to losses by completing the destruction of grains previously only slightly damaged. Infestation by Sitophilus zeamais in the field was not severe, despite the proximity of infested stores to the sampled fields. It has 144. been shown that Sitophilus zeamais can oviposit successfully on maize with a moisture content as high as 60% (Giles and Ashman, 1971), but in this study no infestation was observed at this level. The data confirmed the reported preference of Sitophilus for cobs with open or damaged sheaths : cobs in these categories comprised 83% of those infested by Sitophilus as compared with 63% in the sample as a whole, in the first dry season survey and 79% as compared with 55%, in the second. A slight preference for drier cobs was also indicated in the second survey. Sitotroga cerealella was not recorded in any of the field surveys. The data from the second dry season.survey were analysed to investigate the possibility of uneven distribution of insects in the field. The field surveyed was rectangular, approximately 1.5 hectares in area, with a- larger area of maize fields to the North, a small patch of forest and a residential area to the East and plots of rice and carsava to the South and West. The nearest storage cribs (which con- tained infested maize) were 200 - 300m away to the South-East. Single factor analysis of variance was carried out on counts for all the common insect species, transformed ^og^o (X + 1), using first the transects and then the position along transects as 'treatments'. Only Mussidia nigrivenella at the time of the first harvest, and Sitophilus zeamais at the second showed any indication of differences in abundance between transects (p = 5% and 10%, respectively) or position along transects (p = 3% and 6%). Both species showed a progressive decline in abundance from North to South ('positions along transects') and from East to West ('transects'); proximity to the main area of maize fields and, for Sitophilus at least, to the infested cribs might have been the important factors in the two directions. No 'field edge effects' 145. as noted by Blickenstaff (1960) and Giles and Ashman (1971) were discernable but this may be due to the rather small size of the field surveyed. 5.3 The Effects of Harvesting Practice on Infestation Current recommendations for the storage of maize 'on the cob' (F.A.O., 1980) differ most conspicuously from traditional practice in that the maize is harvested earlier (i.e. at physiological maturity), the husks are removed and the grain is treated with insecticide. The high moisture content of the grain at harvest means that only 'well- ventilated' cribs may be used for storage. The aim of the 'Harvesting Practice Trial' was to assess the effects of the first two factors (i.e. early harvest and removal of the husk) on the initial infestation in store. Assessment was based on counts of adult insects and emergences, grain moisture content and weight loss. The trial was not intended to show which practice was preferable in economic terms and no attempt was made to estimate the total crop losses involved. The maize from a single large plot was harvested in two parts, the first at physiological maturity (assessed visually on the basis of 'black layer' formation) and the remainder three weeks later. On each occasion half the maize was 'husked' (i.e. the husks removed) and half 'snapped' (i.e. the husk retained). Cobs were then sorted to remove those unsuitable for storage (see below) and stored in comp- artments in three cribs. Samples were collected from the field prior to each harvest, from the sorted piles waiting to be loaded into the crib and, at the time of the second harvest, from the maize stored in the crib since the first harvest. Maize from all treatments (i.e. early - & late-harvested, with and without husks) was then sampled after an additional one month and two months in store. Table 5.3 summarises 146. TABLE 5.3 Summary of Sampling regime for Harvesting Practice Trial. FIRST HARVEST Field sample 6 x 10 = 60 cobs adult counts (individual cobs) 23/11/79 moisture content( " " ) emergences (6 x 500g samples). Harvest .26/11/79 Sorting and Loading all cobs sorted into damage categories and scored. 27/11/79 12 x 5 .' snapped* adult counts (sample totals) 12 x 5 'husked': loss assessment = 120 cobs (24 x 1000 grains) SECOND HARVEST Field sample 6 x 10 = 60 cobs adult counts (individual cobs) 17/12/79 moisture content( " " ) emergences (6 x 500g samples) Harvest 19/12/79 Storage sample (from early-harvested material in crib) 6 x 20 'snapped' adult counts (12 sample totals) 19/12/79 6 x 20 'husked' emergences (12 x 500g shelled = 240 cobs grain) moisture content (12 x lOg subsample) loss assessment (12 x 1000 grains « Sorting and Loading all cobs sorted and scored. 20/12/79 6 x 20 ' snapped' adult counts (12 sample totals) 6 x 20 /husked' emergences (12 x 500g shelled = 240 cobs grain) moisture content (12 x lOg subsample) loss assessment (12 x 1000 grair FIRST STORAGE SAMPLE 20/1/80 Storage sample 6 x 20 'early snapped' adult counts (24 sample total 6 x 20 'early husked' emergences (24 x 500g grain) 6 x 20 'late snapped' moisture content (24 sub- samples) 6 x 20 'late husked' loss assessment (24 x 1000 grains) = 480 cobs SECOND STORAGE SAMPLE 18/2/80 Storage sample as for first storage sample. 147. FIGURE 5.1 Summary of sampling program from cribs (Harvesting-Practice Trial) Design: Lh Eh Ls Es Compartments allocated at random to the four treatments in pairs (as shown), so that each treatment is represented in the Lh Eh Ls Es top^and bottom of three cribs, (only one crib shown). Anovar: Ls Lh Es Eh Blocks (3) = cribs Treatments = 1) Position in crib (upper or lower half). Ls Lh Es Eh 2) Harvesting time (Early or late). 3) Husks (presence or absence' First harvest: E/L = Early/Late h h - s s h/s = husked/snapped All compartments loaded (as shown): h h s s Es and Ls with 'snapped* cobs Eh and Lh with 'husked* cobs s h s h s. h s h • Second harvest: samples Compartments originally allocated to 'Ls' and 'Lh' are emptied; Subsamples (20 cobs/section) are collected randomly from this material as it is unloaded, for comparison with 'pre-loading' samples. Ls and Lh compartments are loaded with newly harvested 'snapped' and 'husked' cobs, respectively. samples Storage samples Lh Ls^ Es^ First Storage Samples (subscript 1) 1 Ehl Lh2 Eh2 Ls^ ES2 Second Storage Samples (subscript 2) On the first sampling occasion sections in the Ls Lh Es, Eh2 top and bottom layers are emptied; on the second 2 2 i the sections in the middle layers are emptied. Ls.. Es^j Eh In both cases samples of 20 cobs/section are Lhl collected at random from the material as it is unloaded. the size, timing and purpose of all the samples collected and figure 5.1 the sampling programme from the cribs. Maize cobs were harvested directly into hessian sacks which were carried by the pickers and removed from the field as soon as full, the intention being to minimise the movement of disturbed insects to the remainder of the crop which was to be harvested later. Harvesters were spread out across the field, about 10 rows apart, and picked two rows at the first harvest and the balance at the second. Some maize for the storage trial was collected from each harvester so that all parts of the field were represented. . Alternate harvesters collected 'snapped' and 'husked' cobs: the former group simply broke off the ears whole, while the second group opened each ear on the plant and twisted off the cob, leaving the husks attached to the haulms. A time and motion study carried out on this harvest showed that 'snapped' maize could be harvested three times as fast as 'husked' maize, and that 'husking* on the plant, as here, was still significantly faster than the more traditional method of collecting * snapped' cobs and husking them later (Buchele, pers. comm.). Cobs were left in piles near to the cribs overnight before sorting, sampling and loading. The selection of cobs for loading was intended to simulate the normal practice of local farmers. Cobs that were severely damaged by moulds or insects, or any that were seriously malformed (due to poor pollination or physiological stress), were discarded. In addition, 'snapped' cobs with loose or open sheaths were also excluded. Although the selection (carried out by the author) was basically subjective, standardisation was improved by comparison with a set of 'acceptable' and 'unacceptable' (for storage) cobs used at both harvests. The numbers of cobs attributed to the various categories are given in Table 5.4. 149. TABLE 5.4 Selection of damaged and sound cobs for storage - Harvesting Practice Trial a) First Harvest b) Second Harvest Accepted for storage: Rejected as unsuitable: (i) stored (ii) excess ( i) open sheaths (ii) mould (iii)mal- o r insect damaged damaged formed a) SNAPPED No. 1080 235 129 35 41 % 84% 10% 3% 3% HUSKED No. 1140 869 96 155 68 % 86% 4% 7% 3% b) SNAPPED No. 536 136 237 51 174 % 60% 21% 4% 15% HUSKED No. 576 294 241 207 • 222 % 57% 16% 13% 14% a* 150. Although the overall intensity of selection was approximately the same for 'husked' and 'snapped' cobs, the composition of the 'rejects', and so, by implication, of those stored, was not identical.' This occurred because, in selecting snapped cobs, any with open or loose husks were rejected, irrespective of whether or not they showed visible insect damage. The larger number of cobs excluded for this reason was, however, balanced by the inclusion of more Diplodia infected cobs: these usually had closed sheaths and so snapped cobs infected with Diplodia were only noticed in the most severe cases where the sheaths as well as the grain had become discoloured. Cobs for the field samples were collected individually, as des- cribed in Section 5.2. For the pre-loading samples and those from the cribs, all cobs for a particular sample (10 or 20) were collected together.in a large plastic bag, husked (where necessary) and shelled inside the same bags. All adult insects were then sieved off and subsamples drawn from the pooled, mixed grain for estimation of emergences, moisture content and loss assessment. The cobs were stored in the sectioned cribs previously used for the distribution studies (Figure 4.1). Each section was carefully packed with stable 'stacks' of cobs, those in successive layers being laid perpendicular to one another, to form a single well-ventilated bulk. Each section could be unloaded separately, one cob at a time, and a sample of 20 cobs randomly selected. Two vertically-adjacent compartments were allocated randomly to each of the four treatments in the top and bottom halves of each of three cribs (see Figure 5.1). Insects could move readily from one 'treatment' to another through the wire partitions. Loss assessment was carried out on the basis of successive estimates of the mean dry weight of a thousand grains. A subsample of approximately 151. 500g was drawn from the mixed shelled grain from each replicate sample. This was heated, first at 60°C then at 90°C, for several hours to re- move excess moisture. A further subsample of 1000 grains was then counted out, weighed, and the moisture content determined to provide an estimate of the dry weight. Simple analysis of variance was used to compare the infestation and moisture data from field samples with those from the piles of cobs prior to loading and, at the time of the second harvest, with those from the cribs. Figures for the individual cobs collected in the field samples were pooled so that the data compared were based on the same number of cobs in each case. The selection procedure was, however, different in the three situations (i.e. 'field1, 'pre-loading' and 'in stdire') and so the comparison connot be regarded as entirely satisfactory. The two complete storage samples were analysed factorially (Figure 5.1) to separate the effects of time of harvest (early or late), removal or retention of the husks and position in the crib (i.e. upper or lower half). Samples were taken from different 'layers' of the crib on the two sampling occasions (see Figure 5.1) and so the data obtained should not be compared across sampling occasions. Counts of adult insects and emergences for most species showed 'over-disperison' and so these data were transformed (Log^) before analysis. Data comparing the numbers of insects in field samples, prior to harvest, with those from sorted cobs awaiting loading, 24 hours after harvest, are given in Table 5.5. There is no evidence that harvesting and selection have had any effect on the numbers of Sitophilus zeamais or Mussidia nigrivenella, but secondary pest pop- ulations have been affected :; Mycetaea hirta has been virtually eliminated from the post-harvest samples and Carpophilus spp. markedly reduced. 152. TABLE 5.5 Effects of harvesting on adult insect populations: comparison of adult insect numbers before harvest (field samples) and 24 hours after harvest (snapped and husked). Probability levels from single factor analysis of variance. a) First Harvest b) Second Harvest a) Mean number of insects/10 cobs: Species field samples snapped husked prob.(no diff.) Sitophilus 1.2 2.2 0.3 zeamais (1.6) (2.6) (0.5) Cathartus 9.5 4.0 9.8 0.21 quadricoll. . (3.8) (4.6) (8.7) Carpophilus 12.0 2.0 6.5 0.001 spp. (4.1) (2.5) (3.8) Mycetaea 22.0 0.3 1.0 <0.001 hirta (9.8) (0.5) (1.5) . Mussidia 6.2 8.5 3.2 0.12 nigriven. (6.1) (3.0) (2,2) b) Mean number of insects/20 cobs: field (3) snapped (6) husked (6) Sitophilus 13.7 12.2 9.5 zeamais (14.4) (14.2) (5.0) Cathartus 72.2 58 73 quadj-icollis (47.2) (42) (35) Carpophilus 39.7 5.2 7.7 spp. (5.1) (4.2) (5.9) Mycetaea 37.3 0.2 0 hirta (14.0) 153. TABLE 5.6 Effects of Early harvesting on insect populations. Comparison of mean moisture contents (a),emergent insects (b),and adult insects (c),from early-harvested maize (after 3 weeks in store) and late-harvested maize (24 hours after harvest and before loading); data from pre-harvest (field) samples are included in comparison of emergences. Probability levels are from a single-factor analysis of variance. Probabilities in parentheses indicate data showing non-homogeneous variances (Bartlett's Test); Figures in parentheses below means are atandard deviation. (a) Moisture content (%) Treatments Early harvested Late harvested (from crib) (freshly harvested) husked snapped husked snapped probabilities. 14.7 16.7 17.2 17.1 <0.001 (0.3) (0.5) (0.9) (0.4) (b) Emergences (no. insects emerging from 500g/4 weeks). Species early husked early snapped late husked late snapped field P Sitophilus 129 b 84 ab 91 ab 32 a 53 a o.oc zeamais (37) (42) (39) (36> (48) Cathartus 10 21 18 14 11 0.04 quadricoll (4) (8) (8) (4) (7) (c) Adult counts (no. insects/kg @ 15% m.c.). Treatments Species Early harvested Late harvested (from crib) (freshly harvested) husked snapped husked snapped probabilities Sitophilus 63.2 65.0 3.8 5.1 (<0.001) zeamais (21.4) (26.1) (2.1) (6.0) Carpophilus 5.5 3.0 2.2 3.1 0.21 spp. (3.3) (3.0) (1.7) (2.4) Cathartus 59.7 92.6 • 29.2 24.0 <0.001 quadricollis (31.7) (31.4) (14.0) . (18.3) Palorus 0.6 7.7 0.1 0.1 (<0.001) subdepressus (0.7) (3.2) (0.2) (0.2) Gnatocerus 0.6 1.3 0.0 0.0 maxillosus (0.5) (1.0) Mussidia 1.0 1.0 1.1 0.7 0.91 nigrivenella (1.0) (0.9) (1,1) (0.8) Pyroderces 0.4 1.0 0.9 1.1 (0.15) gossypiella (0.2) (0.8) (0.3) (0.8). Zeteticontus 1.7 0.3 0.3 0.1 (0.07) la evigatus (2.0) (0.5) (0.5) (0.3) It may be rioted that for both Cathartus quadricollis and Carpophilus spp. there is evidence of lower numbers, post-harvest, in snapped than in husked cobs, even though insects in the latter have suffered less * direct disturbance. It seems likely that the majority of these more active insects in fact left the cobs during harvest and that the figures reflect more rapid recolonisation of the exposed, husked cobs. The effects of early harvesting are indicated in the data collected at the time of the second harvest, presented in Table 5.6. The figures for grain moisture content (Table 5.6a) show that cobs stores in their husks (i.e. 'snapped') have dried at the same speed as those left in the field, but that cobs dehusked before storage have dried significantly faster. Insects emerged from the grain subsamples (Table 5.6b)) were collected four weeks after sampling and so mainly reflect oviposition at a time when the early harvested material was in the crib and the late-harvested still in the field. Differences are not clear-cut but there is some evidence that on the early-harvested husked maize re- production of Sitophilus has been the most successful and that of Cathartus the least. The figures for adult insect numbers (Table 5.6c)) indicate higher levels of Sitophilus, Cathartus, Palorus subdepressus and Gnatocerus maxlllosus on the early-harvested maize in the crib. It should be noted that the higher infestation on the maize in the cribs cannot, after so short a time, be due to higher recruitment but must be due to preferential colonisation. It is possible that some insects moved directly from the newly-harvested material to that in the cribs between the time of harvest and sampling. However, this cannot have been the case for the two Tenebrionidae, which were rare in the field, and seems unlikely to be responsible for the great difference in Sitophilus 155. TABLE 5.7 Effect of time of harvest and retention of husks on grain moisture content. Figures are means of single determinations from six samples (B each being the pooled grain from 20 cobs) with probability levels from a three-factor anovar (as indicated in Figure 5.1); after one month in store ('First Storage Sample1) and two months in store ('Second Storage Sample') - early- harvested material has had an additional three weeks in store. FIRST STORAGE SAMPLE Early Late X Husked . 14.9 | 15.0 15.0 A time of harvest 0.12 B husked/snapped 0.08 C position in crib 0.005 Snapped AB 0.02 15.3 | 15.0 15.1 AC 0.68 BC 0.31 ABC 0.31 x 15.1 | 15.0 SECOND'STORAGE SAMPLE Early Late X Husked 13.5 | 13.2 13.4 A time of harvest 0.03 B husked/snapped 0.90 C position in crib 0.01 Snapped AB 0.90 13.5 | 13.2 13.3 AC' 0.21 BC 0.37 ABC 0.37 X 13.5 | 13.2 156. numbers. Of the maize stored in the cribs, the snapped cobs were much preferred by Palorus and Gnatocerus and possibly slightly pre- ferred by Cathartus quadricollis. The first complete storage sample was taken four weeks after the second harvest (i.e. when the early-harvested maize had been in store for seven weeks and the late-harvested for four) and the second storage sample another four weeks later. By the time of the former sample all treatments had dried to effectively the same grain moisture content (and continued to dry uniformly thereafter) although consistent, very small differences were detectable on both occasions (Table 5.7). The probability levels from a factorial analysis of variance of the insect counts (transformed, Log^) are given in Table 5.8; where significant differences between treatment means are indicated the ~ actual-means are given in Tables 5.9 (adults) and 5.10 (emergences). Emergences from the second sample correspond approximately to oviposition at the time of the first sample while those from the first sample re- present oviposition over a more extended period between the second harvest and the first storage sample. The 'breeding-out* period for the first sampling occasion was long enough to allow some additional parasitism of Sitophilus in the laboratory. In order to provide a better approx- imation to the original pest distribution the figures for Anisopterom alus calandrae and Chcetospila elegans emergences have been added to those of Sitophilus. The data indicate that the retention of the husks has provided no protection against insect infestation. On the contrary, Sitophilus appears to have reproduced initially more successfully on the snapped maize (Table 5.10a), possibly due to its slightly.higher moisture content, and both adult counts and emergences indicate that the snapped maize was preferred by most of the secondary pest species. 157. TABLE 5.8 a) , ADULT COUNTS (FIRST STORAGE SAMPLE) Sitophilus Cath. Oryzae. Carpoph. Gnato. Pal. zeamais quad. mere. spp. max. subdep. A Early/Late 0.18 0.13 0.32 0.02 0.16 <0.01 B husked/snapped 0.27 <0.01 <0.01 0.92 <0.01 <0.01 C position in crib 0.37 0.20 0.05 <0.01 0.52 0.06 A and B 0.34 0.23 0.27 0.35 0.03 <0.01 A and C 0.57 0.95 0.91 0.87 0.05 0.09 B and C 0.01 0.02 0.65 0.11 0.57 0.95 A, B and C 0.85 0.03 0.70 0.73 0.61 0.67 b) EMERGENCES (FIRST STORAGE SAMPLE) Sitophilus Cath. Gnato. Anisopt. Choeto zeamais quad. max. cal. eleg. A Early/Late 0.07 0.57 0.05 0.25 B husked/snapped 0.58 <0.01 0.32 0.43 C position in crib 0.24 0.44 0.09 0.39 A and B <0.01 0.92 0.37 0.02 A and C 0.51 0.58 0.46 0.70 B and C " 0.02- 0 .33 - — <0.01 0.14 A, B and C ' 0.74 0.02 0.39 0.79 c) EMERGENCES (SECOND STORAGE SAMPLE) Sitophilus Cath. Gnato. Anisopt. Choeto. zeamais quad. • max. cal. eleg. A Early/Late 0.79 0.02 <0.01 0.82 0.61 B husked/snapped 0.82 <0.01 <0.01 0.32 0.96 C position in crib 0.73 0.38 . 0.56 0.60 0.84 A and B 0.30 0.09 0.87 0.58 0.84 A and C 0.95 0.32 0.73 0.78 0.53 B and C 0.40 0.66 0.84 0.33 0.29 A, B and C 0.63 0.29 0.49 0.70 0.45 TABLE 5.8 Effects of Time of harvest on insect infestation 1 1. Probability levels from analysis of variance - effects of time of harvest, removal of husks and position in crib on insect numbers. a) adult insects - first storage sample b) emergences - first storage sample c) emergences - second storage sample Data used were: a) numbers of insects/kg shelled grain @ 15% m.c. b) insects emerging from 500g grain fresh weight in 23 days c) insects emerging from 500g grain fresh weight in 8 days Data were transformed Log-n before analysis. 158. TABLE 5.9 Effects of time of harvest and removal or retention of husks on adult insect infestation (first storage sample). Figures are mean numbers of insects per kg of shelled grain at 15% m.c. (each figure based on six samples of 20 cobs). a) Cathartus quadricollis Husked Snapped Mean Early 155 426 290 Late. 126 259 192 Mean 140 1 342 b) Oryzaephilus mercator Early 1 5 3 , Late 1 1 4 2 Mean 1 1 c) Carpophilus spp. Early 21 20 1 19 Late 12 1 10 11 Mean 16 1 14 d) Gnatocerus maxillosus Early 6 3 0 1 Late 1 1 3 2 Mean 1 1 4 e) Palorus subdepressus Early 1 | 23 12 Late 1 3 2 Mean 1 13 159. TABLE 5.10 Effects on emergences of time of harvest and removal/ retention of husks at the time of a) the first storage sample and b) the second storage sample. Figures are mean no. of insects emerging from 500g (fresh wt.) of grain in a) 23 days and b) 8 days; figures are based on six replicates of each 'treatment*. a) FIRST STORAGE SAMPLE Sitophilus zeamais husked J snapped mean Early 174 | 309 241 Late "212 1 154 183 Mean 193 \ 231 Cathartus quadricollis i Early 3 1 11 7 Late 4 1 9 6 Mean 3 | 10 Anisopteromalus calandrae I Early 1.2 1 1.2 1.2 Late 0.9 0.4 0.6 Mean 1.0 | 0.8 Choetospila elegans i Early 0.2 0.6 0.4 Late 0.3 0.1 0.2 Mean 0.2 0.3 b) SECOND STORAGE SAMPLE Cathartus quadricollis htisked 1 snapped mean Early 7 I 19 13 Late 5 1 8 6 Mean 6 i 13 Gnatocerus maxillosus i Early 24 18 12 1 Late 6 1 12 9 Mean 9 1 18 160. TABLE 5.11 Effect of time of harvest on losses. Figures are mean dry weights of 1000 grains (standard deviation in parentheses) with probability levels from 3 factor anovar; after a) one month in store; b) two months in store. (Grain weight in grammes) FIRST STORAGE SAMPLE Early Late X Husked 234.3 248.4 241.3 A Time of harvest 0.005 (6.23) (15.5) B Husk cover 0.045 C (position in crib) 0.697 Snapped ABTime and Husk 0.438 217.9 240.7 229.3 AC 0.19 (17.3) (9.0) BC 0.99 ABC 0.78 X 226.1 244.5 SECOND STORAGE SAMPLE Early Late Husked 218.5 249.3 233.9 A Time of harvest <0.001 (7.8) (4.8) B Husk cover 0.29 C(position in crib) 0.37 Snapped ABTime and Husk 0.20 219.4 240.0 229.7 AC 0.10 (13.3) 1 (8.0) BC 0.98 ABC 0.74 218.9 | 244.6 161. The time of harvest seems to have had little persistent effect on Sitophilus infestation : despite the heavy initial colonisation of the early-harvested material, infestation was effectively uniform by the time of the first full storage sample. At the first storage sample Carpophilus spp. adults were more abundant on both types of early- harvested material while Palorus subdepressus was concentrated strongly on the early-harvested, snapped cobs. The data on emergences suggest that reproduction of both Cathartus quadricollis and Gnatocerus maxillosus was most successful on this material; it should be noted however that recruitment of these secondary pest species will not be accurately estimated by emergences from samples of shelled grain. The overall losses suffered in the various treatments could not be assessed because the baseline samples proved unsatisfactory, probably due to some loss of dry weight involved in the heat-drying of the early, high-moisture content samples. The data for the two storage samples, provide a comparative indication of performance, but there is a poss- ibility that the differences indicated are the result of differential selection at loading, rather than more severe losses in storage. Mean grain weight was lower in the early-harvested maize and for the cobs stored in their husks (Table 5.11a)). The inclusion of more Diplodia - damaged cobs in the selection of snapped cobs almost certainly con- tributed to their lower mean grain weight but there is no evidence for the spread of Diplodia infection in store (Table 5.11b)). . The im- portance of insect infestation cannot be assessed on the basis of this data. On the evidence of this trial and of the data quoted in Chapter 3, the storage of maize in the husk does not appear to reduce the level of storage pest infestation although the latter figures showed that serious 162. infestation is confined to a smaller number of cobs. The increase of primary pest species does appear to be delayed by leaving the maize in the field; however, this may not provide a net advantage if losses from other sources, such as lodging or bird and rodent damage, are severe in the field. Such factors may be expected to vary considerably from one locality to another. The dynamics of pest population increase in store will be discussed further in the next chapter but it seems that under the conditions of the study site, maximum equilibrium levels were reached so rapidly that little benefit could be expected over the period of the storage season from minor changes in initial conditions. 5^4 Persistent Effects of Pre-Harvest Damage ., . , . The experiment described in this section, the Pre-Harvest Damage Trial, was set up to investigate whether field infestation might be affecting storage pest populations indirectly by providing a more favourable substrate for their development at the beginning of the storage period. It was noted in Section 5.2 that reproduction of Silvanidae and Nitidulidae in the field appeared to be confined to grains already damaged by Lepidoptera and/or associated moulds; it seemed possible that this damage might continue to support secondary pest species in store until damage by primary storage pests provided an alternative substrate. It has also been shown that some grain damage may reduce mortality of first instar Sitotroga cerealella larvae by aiding their penetration into the grain (Ayertey, 1979). Sitophilus zeamais may oviposit preferentially on damaged grain. The grain for the Pre-Harvest Damage Trial was harvested in late December and all cobs were dehusked. Cobs were then selected which showed ho visible insect damage and an equal number which had suffered limited damage by Lepidoptera" and fungi. Heavily damaged cobs were not in- cluded, those selected in the 'damaged' group having no more than 15% 163. damaged grains. The cobs selected were not intended to be in any sense representative of the total population : the intention was to compare the effect of the presence of small foci of damaged grain on the infestation of otherwise sound cobs. The progress of infestation was assessed on the basis of samples taken before storage and after approximately one, two, three and four months in store. On each sampling occasion adult insect populations, recruitment, grain moisture content and weight loss were estimated. The cobs selected were divided into five groups of eighteen cobs of each type (i.e. damaged and undamaged). Two cobs were taken from each group to provide an estimate of the initial 'latent1 infestation. All adult insects were removed from these cobs and a file of grain removed along the length of each as a subsample for moisture content determination. On the 'damaged' cobs Lepidoptera attack and mould infection were mainly confined to the apices. To investigate whether . Coleoptera infestation was similarly limited the cobs were cut in half and the apical and basal portions caged separately. Emergences were scored after 10, 20 and 30 days. Of the remaining (16) cobs in each group, sections were cut from the bases of four and the core and grain moisture content determined separately from each. All cobs were then numbered individually with indellible ink and weighed. Each group of 16 cobs was packed tightly into a coarse netting bag (commercial onion bags) and the bags stacked in a suitably modified crib, in the arrangement shown in Figure 5.2, to form a single bulk. On each sampling occasion three cobs were removed from each bag. Two were sealed in a plastic bag and set aside whilst the third was weighed, a section cut off for moisture content determination, and the remainder replaced in the crib. From the former two cobs all adult a) vertical section b) plan views upper layer wire partitions unsamplsd cobs (hatohed) loose middle layer bagged sampled oobs (plain) 1-5 ^positions' C / D field damage lower layer C " clean • h D m damaged FIGURE 5.2 Rrrangement of material for Pre-Harvest Damage Trial a) vertical ssotlon through whole or1b b) plan view of sampled layers 165. insects were collected for later identification and scoring; the cobs were then shelled individually, the grain and core weighed, and subsamples taken from each for moisture content determination and estimation of emergences (from lOOg over 8 days). The difference between the weight of each cob when removed and its weight initially, when suitably corrected for moisture content changes, provided an estimate of the progress of weight loss. At the fourth (i.e. final) sampling occasion the four cobs from which sections had initially been cut for moisture content determination were also weighed, shelled, and their moisture content again determined. The overall dry weight loss could more accurately be estimated from the weight change of these cobs because their initial and final moisture contents were individually known. Collated data on adult insect numbers, recruitment, weight loss and moisture content are presented in Tables 5.12 - 5.15. The composition of the insect population was different on each of the four sampling occasions and so the data for each have been analysed separately. Differences between mean numbers of adult insects on damaged and undamaged cobs were tested using t-tests, but undue reliance should not be put on the results: the samples were collected systematically rather than randomly and the markedly uneven distribution of insects in the crib may have affected the sample variance. Recruitment samples were replicated and so these could be analysed factorially to separate the effects of grain damage and position within the crib. Recruitment data were transformed (Log^^(X +1)) before analysis. The data for progressive weight loss and moisture content changes have been analysed over all four samples, using sampling occasions, position in the crib and grain damage as factors in the analysis of variance. Emergences from the samples collected at the beginning of the 166. trial showed that initial infestation by both Sitophilus zeamais and Cathartus quadricollis was much heavier on the damaged cobs (Table 5.12). The numbers of Sitophilus emergences from basal and epical halves of the cobs were approximately equal but Cathartus emergences were higher from the apices. Emergences of Zeteticontus laevigatus, a parasitoid of Cathartus, closely followed the distribution of its host. Adult counts for all the common pest species indicate that the damaged cobs were more heavily infested throughout the four months of storage (Table 5.13). Mean numbers of Sitophilus zeamais, Carpophilus spp. and Cathartus quadricollis were higher on the field-damaged cobs on all four sampling occasions (although, in most cases not significantly so, on the basis of the individual t-tests). During the fourth month in store, at the onset of the wet season, several secondary pest species (Cryptolestes pusillus, Typhaea stercorea, Palorus subdepressus and Gnatocerus maxillosus) appeared in appreciable numbers; these species too, together with their Authocorid predators, preferentially infested the field-damaged cobs. Emergences of the primary pest species and their parasitoids were, however, not significantly different in samples•fro mdamaged and undamaged grain (Table 5.14). It is possible that differences were simply not detected, due to insufficient sample size, but it is also possible that less infested cobs (i.e. those that had not been damaged initially) were preferred for oviposition or that mortality of immatures was lower on these cobs. Recruitment of the secondary pest species again could not be assessed from these samples because of the loss of immatures during shelling and sieving. Summary results of the analysis of moisture content and weight 167. TABLE 5.12 Effects of field damage by Lepidoptera on initial infestation of maize by storage pests (Pre-Harvest Damage Trial) a) Probability levels from 3 factor analysis of variance: (Factor A : successive periods over which emergences were scored. Factor B : presence or absence of grain damage. Factor C : portion of cob (i.e. apical or basal half). ) Data were numbers of insects emerging over successive 10 day periods. corrected for sample size and transformed Log^. Source of Species : Sitophilus Cathartus Zeteticoutus Variation df zeamais quadricollis laevigatus A Time 2 <0.001 0.14 <0.001 B Grain damage 1 <0.001 <0.001 <0.001 C Tips/bases 1 0.27 <0.001 <0.001 t r~> AB 2 0.40 0.51 0.42 AC 2 .0.95 0.27 <0.001 BC 1 0.90 <0.001 <0.001 ABC 2 0.51 0.48 0.33 Sampling error 108 b) Mean number of insects emerging/50g shelled grain over 10 days. Undamaged damaged tips bases tips bases Sitophilus 0.7 0.4 5.9 4.2 zeamais Cathartus 0.5 0.4 6.9 1.5 quadricollis Zeteticoutus 1.0 0.3 6.4 0.6 laevigatus ... TABLE 5.13 Effects of field damage on subsequent infestation in store. Mean number of adult insects per 250g of shelled grain @ 15% after one, two, three and four months in store. Figures in parentheses are standard deviations, figures below each line are estimated values of the t statistic. Sampling Sampling 1 Sample 2 Sa;nple O J Sample 4 Occasion § G nd is rt 0) rta a) § 0) t>0 o Critical values of the t distribution (8 degrees of freedom) 5% : 2.3 . 1% : 3.4. i ON 00 TABLE 5.14 Effects of field damage on subsequent infestation in Store. Mean numbers of primary pests and their parasitoids emerging from lOOg of shelled grain in eight days after one, two, three and four months in store. Probability levels are for 2 factor analysis of. variance of the data transformed Log^CX + 1) . (For the Anovar the numbers of parasitoids emerging have been added to the numbers of the appropriate host to provide a better estimate of the underlying pest distribution) Sampling Occasion: 1 2 3 4 Sound or damaged: Clean damaged Clean damaged' Clean damaged Clean • damaged Species: Sitophilus 23.2 17.9 9.9 11.5 3.4 3.4 29.6 31.3 Sitotroga 1.6 1.8 3.0 3.4 9.4 7.4 22.0 17.4 Cathartus 0.3 0.2 0.1 0.2 0 0 3.7 2.7 An. cal. 0.6 0.1 0.1 0.1 0.2 0.1 1.7 1.0 Hab, cer. 0.3 0.1 1.5 2.6 , 2.4 2.6 0.5 0.4 Sito. Sitot. Sito. Sitot. ' Sito. Sitot. Sito. Sitot. Anovar. df zeam. cer. zeam. cer. - zeam. cer. zeam. cer. grain damage 1 0.05 0.28 0.39 0.93 0.46 0.90 0.23 Position in crib 4 0.04 0.34 • 0.65 0.67 0.70 0.33 0.81 Interaction 4 0.32 0.70 0.63 0.52 0.20 0.16 0.37 Sampling error 10 ON VO i 170. TABLE 5.15 Progressive changes in mean moisture content and mean dry weight loss over the storage period with probability levels from a three factor Anovar. Sampling occasions : (months in store) a) 1 2 3 4 Moisture undamaged 11.9 11.5 13.5 14.9 content % damaged 11.9 11.4 13.5 14.8 11.9 11.4 13.5 14.9 Weight undamaged - 9.7 14.7 22.1 loss % damaged - 10.7 14.9 26.2 - 10.2 14.8 24.1 b) Source bf moisture content weight loss p variation df P df A sampling,occasion 3 <0. 001 - 2 <0. 001 B grain damage 1 0. 11 1 0. 05 C position in crib 4 0. 13 . 4 0. 41 AB 3 0. 94 2 0. 17 AC 12 0 .01 8 0 01 BC 4 0..9 0 4 0 .10 ABC 12 0 .55 8 0 .12 Sampling error 80 30 TABLE 5.16 Final weight loss (four months in store) for maize damaged in the field by Lepidoptera (Pre-Harvest Damage Trial). Overall weight loss (final) %. a) Position in crib 1 2 3 4 5 X undamaged 18.5 21.9 18.4 20.4 18.2 19.5 damaged 20.0 17.5 27.6 23.2 16.7 21.0 X 19.2 19.7 23.0 21.8 17.5 I b) Source of variation df P A grain damage 1 0.13 B position in crib 4 0.01 AB 4 0.002 Sampling error 30 171. loss data are given in Table 5.15 and 5.16. The moisture content of the grain increased markedly over the third and fourth months of storage, approaching the tfet season. Although the moisture^content changes were different for the different parts of the crib (p = 0.01 for the 'sampling occasion X position' interaction) there was no difference between 'damaged' and 'undamaged'. The increase in weight loss over the season was also different for the various positions in the crib. There was some indication of higher weight loss in initially-damaged cobs in some parts of the crib but the overall difference in weight loss would not have been economically significant. The results of this experiment confirm the impression that the initial field damage to cobs is important for a considerable period in maintaining high populations of secondary pest species but has little effect on the primary pests (and so, apparently, on weight loss). Initial recruitment of pests was higher from field-damaged cobs. However, insects from this source may, as previously noted, contribute relatively little to the population colonising the crib. 5.5 Sources of Storage Infestation. i The studies described here confirmed in general terms the observations of workers in other countries regarding the importance of insect infestation in the field, particularly by Lepidoptera, in causing direct damage to the grain, promoting mould damage and .allowing the early establishment of storage insects. Under the conditions of the study the transfer of the field infestation with the harvested, grain appeared to be less important than active migration of insects in colonising the newly-stored maize. This was also confirmed by the succession studies, to be described in the next chapter, in which grain fumigated before harvest to eliminate all field infestation became, 172. within a few weeks, as heavily infested as material in nearby cribs that had not been treated. The separation of damaged cobs at loading and the storage of cobs in their husks had little effect on the damage ultimately suffered by the maize in store. In considering the im- plications of these results for improved storage strategies it is important to recognise the extent to which the experimental conditions differed from those found on local farms and the practical constraints imp- osed by particular farming systems. The incidence of various stem-boring Lepidoptera was found to be variable from one field to another on the study -site, was generally higher on the field station than on farmers' fields-.-outside> ^nd changed n , markedly through the year (Kaufmann pers. comm). Moreover, the storage of large quantities of maize on the field station over several seasons, • in connection with insecticide trials, may have produced locally high levels of storage pests. Against this it should be noted that levels of field and storage infestation recorded in this study were comparable to those found on local farms in some localities in Kenya (Giles and Ashman, 1971; de Lima, 1978) and Nigeria (Cornes and Riley, 1962; Comes, 1963, 1964). Poor store sanitation and similarly high levels of insect infestation were also noted in the current study on commercial farm settlements in the Ibadan area. The initial infestation of stored maize could be reduced by measures that directly reduce the field infestation, that lower the numbers of insects transferred with the harvest from field to store or that break the cycle of infestation from already infested stores to the new crop. Trials of insecticides to control Lepidoptera infesting cobs in the field have generally proved this method to be too expensive or 173. ineffective (Conies, Donnelly and Adeyemi, 1966). There is clearly some scope for resistance breeding to increase the inherent resistance of the grain and to improve the protection provided by the husk (Kirk and Manwiller, 1964; Starks and McMillian, 1967). The breeding of varieties with two smaller, better-covered ears has been proposed by Giles and Ashman (1971) as a means of maintaining overall yield. The general problem remains, however, that selection for longer husks will tend also to select for preferential development of other vegetative parts of the plant at the expense of the reproductive, and thus to reduce 'plant efficiency1 and yield potential (Quin, pers. comm.). The benefit from reduction of the initial infestation by fumigation or relatively short-lived insecticides (Rawnsley, 1968) or by the sep- aration and differential treatment of damaged cobs (de Lima, 1978) will be lost if active reinfestation of stores is significant. Clearly, the storage pests have a considerable capacity for movement from sources of infestation. It has been proposed that cross-infestation may be reduced by removing stores at least 800m from the nearest source of infection (Giles, 1969), but the handling of the crop involved would make this impractical for many local farmers. Measures directed at this point in the cycle of infestation can only be successful if combined with greatly improved sanitation in both field and store to reduce sources of reinfestation. Control measures directed against insects in infested stores would have to be taken long before harvest of the new crop if cross- infestation is to be prevented. Giles and Ashman (1971) have drawn attention to this problem, noting that Sitophilus zeamais is able to survive for long periods on newly pollinated cobs (until they are dry enough to allow successful oviposition), on crop residues buried in the field 174. and on dumps of maize cores left after shelling (Mossop, 1940). There are particular problems in preventing cross-infestation from old stocks of maize to new where the grain provides the main staple food. These possibilities and their associated problems will be con- sidered again later in the context of a wider discussion of control strategies. 175. CHAPTER 6 THE INSECT COMMUNITY : COMPOSITION AND SUCCESSIONAL CHANGES 6.1 Introduction Published records from a number of African countries (Cornes, 1965, 1967, 1968; Giles, 1965; Forsyth, 1966; Walker and Boxall, 1974; Haines, 1974; Walker 1979) indicate that a considerable variety of insects may at times be found in rural maize stores. There is, however, little quantitative data on the incidence or pest status of individual species in such stores. De Lima (1978), in an extensive study in Kenya, has considered the dynamics of Sitophilus zeamais and Sitotroga-cerealella under a variety of environmental conditions and insecticide treatments. He - also considered the succession of species-that occurred on small quantities of grain in experimental cribs and in the laboratory over a three and a half year period. In the latter studies Sitotroga and Sitophilus both increased rapidly during the first months of storage. Sitotroga then declined steeply to extinction while Sitophilus remained the dominant pest for more than two years. Secondary pest species, Tribolinum castaneum, Cryptolestes ferrugineus and Oryzaephilus sur- inamensis, Carpophilus dimidiatus, Rhizopertha dominica and Gnatocerus cornutus, appeared and became abundant in successive seasons as the grain became increasingly damaged. Cornes and Riley (1961), studying maize cribs in Southern Nigeria which had been initially treated with Malathion, observed a marked succession of species over a much shorter storage period. Sitophilus 'oryzae' (=S. zeamais)^ and Cathartus quadricollis were brought in to 1. Sitophilus oryzae and S. zeamais were for a long period considered to be 'strains' of a single species. Richards (1944) showed that the two strains were physiologically distinct and that progeny of crosses between them were sterile. The nomenclature of the two species in. the literature remained confused until settled by Kuschel (1961). 176. the cribs with the maize from the field; Cillaeus sp., Carpophilus dimidiatus and Khyzopertha dominiea appeared during the first month in store, Gnatocerus maxillosus and Tribolium castaneum during the second, third and fourth months, and Cryptolestes spp. and Araecerus fasciculatus during the fourth and fifth. The pattern of population changes was slightly different at the three localities studied, although in all cases the dominant pest, Sitophilus, increased to a peak after three to four months in store, declining slightly thereafter. At Ilaro the secondary pest species increased steadily over the storage period. However, at Ilaro Cathartus and Carpophilus reached a maximum in the second month of storage and then declined, while Gnatocerus reached a peak in the fifth, and last month in store.' - Data from large-scale shelled maize stores in Nyasaland (Salmond, 1957) showed some changes in"pest incidence over the storage season as did samples of shelled maize from local markets in Nigeria (Caswell, unpublished data). Successional changes in insect populations have been observed in bulk stores of other commodities both in temperate . conditions (wheat, studied by Coombs and Woodroffe, 1963, 1968, 1973; Sinha, 1974) and in the tropics (groundnuts, considered by Smith, 1963; Prevett, 1964). Laboratory studies on the environmental and nutritional re- quirements of storage insects and their reproductive potential can provide strong evidence of the likely ecology and pest status of particular species in real stores (Howe, 1963). It is difficult in such studies, however, to take account of the cyclically changing con- ditions (Howe, 1956a) interactions with other members of a potentially large pest complex, and dispersal behaviour to and from alternative environments which may be important in particular situations. Field workers, involved for instance in insecticide testing, have perhaps been too ready to accept 'conventional wisdom' and have felt it unnecessary to collect quantitative data on the incidence of particular species. In the absence of a clear understanding of the 'natural* factors limiting pest population growth the results of insect control studies may easily be misinterpreted. In the present study an effort was accordingly made to consider as many members of the pest complex as possible, including those which do not initially seem to be economically significant. To simplify discussion, only the incidence of the more abundant species will be described in this chapter. However, a complete list of the species identified, with notes on the taxonomy and previous records of species of particular interest, is given in Appendix I and collated data on the incidence of all species in Appendix III. 6.2 Treatments and Sampling Techniques Cribs for the Succession Studies were set up as indicated in Table 6.1. Maize of the white dent variety TZPB, grown at the IITA study site, was used for all cribs and that for the Wet Season trials came from a single field. The cobs were harvested at approximately 30% moisture content and all were dehusked. Fumigation (where in- dicated) was carried out in hermetically sealed drums using phosphine ("Phostoxin" tablets) for four and a half days. During fumigation the drums were kept in the shade to avoid excessive heating but slight fermentation nevertheless occurred. The cribs of fumigated maize at Ibadan were set about 100 metres away from the untreated ones, to reduce direct cross-infestation, and 178. the cribs for the dry-season harvest were subsequently sited c.15 metres from the untreated TWet Season* ones. The storage site was isolated from other grain stores but near to a store of yams and surrounded by fields of maize, cassava and cowpea. The cribs at Ilora Farm Settle- ment, near Oyo, were sited near to farmers' cribs that had been used for maize storage in previous seasons and which still contained some infested residues. There were maize fields on one side of the Ilora study site and a residential area, including maize stores, nearby. The cribs used were the standard half-tonne units used in pre- viously-described trials and were modified as shown in Figure 6.1a . The cobs to be used for insect sampling were packed inside a central tunnel of wire netting supported on wooden 'laths'. The sample cobs could be removed through a wire 'door' iii one of the vertical faces, - without disturbing the cobs in the remainder of the crib. Separate sets of cobs were designated for sampling of adult insects, of emergences and moisture content, and for loss-assessment. Those for adult insect sampling were placed in a flexible nylon netting 'trap bag' (2.5cm mesh), approximately in the centre of the crib, and the other cobs packed around them as shown in Figure 6.1b). The same cobs were « used throughout the trial for the adult counts, although the quantity of cobs in the sample in the wet season cribs had to be reduced from c3kg initially to c.lkg by the middle of the storage season (in order to keep the handling time for samples within reasonable bounds as the insect numbers increased). For the dry season cribs the sample was divided between three trap bags (per crib) which were collected and scored separately in an attempt to obtain an estimation of the population variances. In practice the samples proved too small, given the con- siderable inter-cob variation in infestation, to provide a useful FIGURE 6.1 Modifications to cribs used for the Succession Studies: a) general view showing structural modifications - 'cut-away* section shows construction of sampling tunnel; b) arrangement of cobs for sampling (note that cobs within the sampling tunnel were removed at frequent intervals but that loss assessment cobs in the 'unsampled* sections were only collected at the end of the experiment). 179. FIGURE 6.1 a) uf re meah (South face) wooden 1aths sampling tunnel wi re mesh b) unsampled E aooees to samples oobs for damage assessment mm cobs for adult insect s amp lee oobs for recruitment & m.o. samplee estimate and so the data were pooled. Three cobs were collected from each cob on each sampling occasion to provide individual subsamples for estimation of grain and core moisture content and recruitment. Moisture contents were determined using the routine oven method (Appendix IV) . Recruitment was assessed on the basis of the number of insects emerging from lOOg of shelled grain over one week under ambient conditions. Samples were kept during this week in gauze-topped containers in the shade of an open- walled shelter on the study site. Cobs removed from the cribs for these samples were replaced with cobs from below the top surface of the un- sampled remainder of the same crib. Introduced cobs were marked with indellible ink and were not subsequently used as samples them- selves until they had been in the centre of the crib for at least •three months. Weight loss (on a dry weight basis) was estimated, as in the Long- Term Distribution Studies, by repeated weighing of individually identified cobs (Appendix V), with an appropriate arithmetic correction for the changed moisture content on each occasion. Ten such cobs were included in the sampling tunnel of each crib. In all trials loss-assessment cobs, weighed only at the beginning and end of the experiment, were also included at loading above and below the sampling tunnel, 15 cobs in each position. These cobs, as described in Section 3.5, were in- tended to show, by comparison with those in the sampling tunnel, whether the repeated sampling had reduced insect populations as evidence by the weight loss. For the dry season trial the initial moisture content of each loss-assessment cob was estimated from a section cut from the base of the cob and in all trials the final core and grain moisture content were determined individually. Moisture content corrections for the intermediate sampling occasions and for the 'baseline' of the TABLE 6.1 Cribs ' treatment' locality Time of harvest/loading A & B untreated IITA, Ibadan August 1978 C & D fumigated IITA, Ibadan August 1978 initially E & F fumigated Ilora Farm August 1978 initially Settlement L & M untreated IITA, Ibadan January 1979 TABLE 6.1 Cribs on which Succession Studies were based. Letters designate individual cribs and are used to identify data in Appendix III. Cribs A - F are indicated as 'Wet Season' in the following figures, cribs L & M as 'Dry Season'. 182. wet season trials depended on the routine determinations made from the 'recruitment sample1 cobs. 6.3 The Abundance of Major Insect Groups and Changes in the Physical Environment The data presented in Figure 6.2 show the extent to which Coleoptera were numerically dominant in-the insect community in the study cribs. Lepidoptera (almost entirely Sitotroga cerealella) only became well established in the untreated cribs and, even there, were only abundant .for part of the storage season. Adult parasitoids were observed in the cribs from the beginning of the storage season and increased in abundance fairly steadily throughout. Heteroptera, including both- :M_ ~ predatory Anthocoridae and 'phytophagous1 Lygaeidae, became abundant in the early part of the storage season, declined sharply and then increased again in the final samples. When the Coleoptera population is broken down by families (Figure 6.3) it is apparent that, although Curculionidae (i.e. Sitophilus zeamais) formed the greater part of the insect population over most of the storage season, other families became abundant at times, their incidence following markedly different patterns. Nitidulidae and Silvanidae were present in large numbers in the early samples, declined to a different extent in the various cribs, and then increased again at the end of the trials (except at Ilora where the observations were terminated earlier). Tenebrionidae and Cucujidae showed a contrasting pattern, being rare ot absent at the time of harvest but increasing steadily over the storage season. Although there are marked differences in the ecological require- ments of some of the component species (as discussed later) the per- formance of the Coleoptera families may be broadly related to changes 183 10000 „ UNTRERTED CRIBS - Ibadan TOTRL INSECTS CoTeoptora <9 1000 \ 9 Paras tto Ids 0C. 1 100 Heteroptera c +» o o tt c 10 I 10000 _ FUMIGRTED CRIBS - Ibadan TOTRL INSECTS Colooptora w 1000 JC \ Parasttoids OC. | 100 c •»» .i" o 0 c 10 i ^ Hotoroptera K Lepfdoptera i • * 1 1 i 10000 FUMIGRTED CRIBS - Ilora TOTRL INSECTS !—i Coleoptera a* 1000 \ v c© I 100 +> t... .f Parasftofds ©o 5 10 1 Hotoroptora 1 J L Rug Sep Oct Nov Dec Jan Feb Mar Rpr May Jun Jul 184. 10000 UNTRERTED CRIBS - Ibadan Dry Season Harvested TOTAL INSECTS 1000 Coleoptera 100 Parasitoids • • I I Lepidoptera 10 f A I Heteroptera 1 J^I Rug Sep Oct Nov Dec Jen Feb Mar Rpr May Jun Jul FIGURE.6.2 Incidence of major insect groups through the storage season. Data are mean numbers (for 2 cribs) of insects per kg. of shelled maize at 13% moisture content (arithmetically corrected from observed weight and moisture content), transformed log . e Bars indicate actual values for two replicate cribs (i.e. range). Arrow on x -axis indicates time of loading. (Note: insect populations start from zero in fumigated cribs; initial populations were not critically determined for untreated cribs). 185. Rug Sep Oct Nov Dec Jan Feb Mar Rpr May Jun Jul 186. FIGURE 6.3 Seasonal incidence of major Coleoptera families Presentation of data as for Figure 6.2. FIGURE 6.4 Changes in grain moisture content through the storage season. Data are means of six determinations (3 from each crib) with standard errors. 187. 25 UNTREATED CRIBS - Ibadan Net Season 20 15 ^ ^ I--' 10 UNTRERTED CRIBS - Ibadan Dry Season 25 20 15 10 25 20 15 FUMIGATED CRIBS - Ilora % \ \ 10 \ 25 V 20 p. Aug Sep Oot Nov Deo Jan Feb Mar Apr May Jun Jul 15 10 188 25 UKTOERTEH CKlflB - Xbsdan 20 * \ A-r" 15 10 .r 0 i i i i i i « i i 25 FUHIGRTED CRIBS - Ib«d««l Hit Smon 20 * \ 15 A I 10 A -{ 0 25 FUMIGflTEB CRIBS - Ilora Hit Siuon * 20 s 15 10 5 .i" .i-i-r 0 Bug Sip Oct Nov Deo Jin Fib Mir Rpr May Juri Jut FIGURE 6.5 Increase in grain damage over the storage period. Weight loss of cobs (dry weight basis). Data are mean values for 20 cob& (10 from each replicate crib); bars in- dicate mean for each crib separately. in the physical environment. The changes in numbers of Nitidulidae and Silvanidae followed approximately the fall and rise in grain moisture content (Figure 6.4), dying out completely under the slightly drier conditions at Ilora. Cucujidae and Tenebrionidae, in contrast, increased throughout the dry period and on into the following wet season. The figures for weight loss (Figure 6.5) describe only one aspect of the changing condition of the substrate (as discussed in Section 2.6). However, from the known ecology of the species of Cucujidae and Tenebrionidae involved, which are characteristically pests of damaged or milled grain products, it seems likely that their increase may be related to increasing grain damage. 6.4 Incidence and role of individual insect species. 6.4.1 Primary Pest Species The data for Sitophilus adults are given in Figure 6.6. and for emergences in Figure 6.7. Adult populations in all cribs of Wet season maize increased rapidly for the first three to four months but much more slowly thereafter. The populations in dry season cribs reached a maximum within one month of loading and no further increase occurred until the onset of the new wet season. It is immediately apparent that initial fumigation failed to suppress adult population build-up. There is, indeed, some evidence that the initial rate of increase was faster in the fumigated cribs and that the level of the first 'plateau' was higher. No emergences were recorded in the samples from the fumigated material during the first month in store, indicating that the fumigation had successfully eliminated all developing immatures. Emergences in the unfumigated cribs reached a peak after 3-4 months, while the fumigated cribs showed peaks after 2-3 months and 4-5 months in store. 190. 10888 „ UNTREATED CRIBS - Ibadan Hot Season harvested Both seasons « 1888 J£ \ Co JO £ 3 188 C Dry Season harvested 4» o o e 5 10 • * 1 18888 FUMIGATED CRIBS - Ibadan fc Ilora Ibadan Net Season . ' ts 1888 JC i \• Ilora t e A I 188 •»» o o• / c 18 L i "7T7T Rug Sop Oct Nov Dec Jan Feb Mar Rpr May Jun Jul FIGURE 6.6 Seasonal incidence of Sitophilus zeamais (adults). Data presentation as for Figure 6.2. FIGURE 6.7 Seasonal incidence of Sitophilus zeamais and Sitotroga cerealella (emergences) Data are means of emergences during one week from 6 samples of lOOg each (3 from each crib), with standard errors. 191. 30 UNTREATED CRIBS - Ibadan Ha* Saaaon 20 A 10 SttophtTua / •*',4 -fc- + A XX^^ . » *' ^ * 1 .... I Bttotroga 0 i i UNTREHTED CRIBS - Ibadan Dry Season 30 20 1 H/D \ 1- St tophi 1us Sltotroga 10 H I I I I I I Ii H I j-— i » i 0 FUMIGRTED CRIBS - Ibadan 30 / \ i Sitophilus 20 / Y 7 I Sltotroga •, •••>•;' I r-fi, J » I L 10 FUMIGRTED CRIBS - Ilora 0 30 ^ ^ Sitophilue / i "f 20 / » I I 1 I I » I I I I Rug Sep Oot Nov Deo Jan # Feb Mar Rpr May Jun Jul 10 0 192. Without more detailed information these patterns cannot be inter- preted with confidence but it seems likely that the fumigation has produced semi-synchronous 'generations' while those in the unfum- igated cribs were more continuously overlapping. If this is the case, it is unclear whether the increase in the final samples represent a response to more favourable conditions at the beginning of the wet season or simply the emergence of a third population peak. It should be noted that adult populations remained high throughout the storage period and that egg production in Sitophilus zeamais is spread over . an extended period, though reaching a maximum during the second or third week of life (Dobie, 1974). Accordingly the 'peaks' in emergences must represent variation in oviposition orsurvivalof^ i-Temafeures..^atAei^.ihan the progeny of discrete generations. Oviposition by Sitophilus zeamais is known to be favoured by high grain moisture content and fall off sharply at a relative humidity between 60 and 70% on wheat, (Howe, 1952b),equivalent to 12-14% moisture content for maize. Such low moisture contents were reached in January and February in the study cribs. These adverse conditions cannot, however, have been responsible for the decline in emergences as this occurred earlier when conditions for oviposition and development were within the favourable range. The second 'peak' of emergences occurred in the fumigated material at a time when emergences from the unfumigated maize had already begun to decline, even though grain moisture content in the two treatments were almost identical. McFarlane (1978) has noted the adverse effects of periods of high temperature (in excess of 30°C) on the reproductive success of the closely related S. oryzae in some lowland localities in Kenya. Air temperatures did exceed 30°C for a short time on most afternoons during 193. the dry season in Ibadan (see Chapter 2). However, this can also be rejected as the major cause of reduced recruitment, given that all cribs at Ibadan were exposed to similar conditions yet showed 'peaks' at different times. Parasitoids which are known to attack Sitophilus spp. were present throughout the storage period (see 6.A.5 below). Life table analysis would be required to demonstrate conclusively that parasitism was not playing a significant role in limiting recruitment, but the very small number of parasitoids emerging in samples, especially during the early part of the storage season, suggests that they were not important. The major factor limiting Sitophilus populations appears to be its own response to crowding. Markedly reduced oviposition (and/or reproductive success as assessed by the number of progeny produced per female) have been noted in both Sitophilus zeamais and S. oryzae at densities similar to, or below, those observed in the study cribs at Ibadan (Birch, 1945; Khare and Agrawal, 1963; Dobie, 1974). The pattern of adult population increase in the cribs,, corresponds quite closely with that observed by Ayertey (1976) in crowded .laboratory / cultures of-S. zeamais. Ayertey, in the same study, observed that populations starting from a lower initial density reached a higher first 'peak' of abundance. There is some evidence, both from the present work and from a recent study in Malawi (Golob, unpublished data), that this effect also occurs in the field. In this study the fumigated cribs (i.e. starting totally uninfested) showed slightly higher adult insect numbers than the untreated ones after three months in store, while in Malawi Sitophilus populations in insecticide treated cribs (nkokwes) overtook those in untreated ones when the insecticide had . 194. broken down and the insects began to increase with the onset of the wet season. Oviposition by S. zeamais on previously uninfested grain has been shown by Dobie (1974) to be clumped rather than random. Without further information on the operation of this effect at various densities its importance cannot be evaluated. However, it could clearly affect the severity of density dependent mortality due to larval competition. In conclusion, mechanism appear to exist which could explain the observed changes in Sitophilus populations in terms of intra-specific interactions; changes in the environment may modify these effects but are probably not the primary cause of population fluctuations. Numbers of adult Sitotroga cerealella in the cribs are indicated by the curves for TLepidoptera' in Figure 6.2 and data for emergences are included in Figure 6.7. Sitotroga became abundant only in the untreated cribs, though appreciable numbers also appeared in the fumigated cribs at Ibadan at the beginning of the wet season. Sitotroga was recorded in samples from the cribs at Ilora but never became es- tablished there. Other Lepidoptera were recorded from the cribs but never in large numbers. Mussidia nigrivenella and Pyroderces sp. occurred at the beginning of the storage season, but did not reproduce successfully in store. Live larvae of Mussidia were found on maize that had been initially fumigated, indicating that considerable oviposition had occurred in the cribs, but most larvae appeared to become desiccated and died before completing development. Ephestia cautella (adults and larvae) and, occasionally, Plodia interpunctella (adults only) were found in the cribs later in the storage season. Both species were 195. easily maintained in single-species cultures on damaged grain under ambient conditions; their failure to become well-established in the cribs is thus probably due to competition or the activity of natural enemies. Emergences give a better indication than adult counts of the status of Sitotroga because the adult flies readily (and so tends to be under-recorded in cob samples) and because it lives only a few days. Although less abundant than Sitophilus in the cribs used for the Succession Studies, Sitotroga is clearly a potentially serious pest under similar conditions: in two cribs set up for a preliminary study and filled with traditional yellow maize varieties, Sitotroga became for a time the most abundant species in recruitment samples with up to 20 adults emerging per 50g of shelled grain in one week (mean of 10 samples from one sampling occasion). The population dynamics of Sitotroga are rather different from those of Sitophilus. Although the total number of eggs that may be laid is comparable, those of Sitotroga are laid over a much shorter period: 50% on the day of emergence and 90% within the first three days under laboratory conditions (Ayertey, 1976). Moreover, ovi- position is unaffected by the moth's own population density or that of Sitophilus. The factors affecting competition between Sitophilus zeamais and Sitotroga cerealella have been considered in some detail by Chestnut and Douglas (1971), Ayertey (1976, 1979, 1980) and de Lima (1978). Without more detailed information it would be pointless to speculate on the possible role of competition in limiting Sitotroga populations under the conditions of this study. It is of interest to note, however, that the increase in Sitotroga numbers observed in the final samples from the Ibadan cribs occurred under conditions which, from the studies 196. quoted above, might be considered very unfavourable to it, with high populations of Coleoptera and severely damaged grain. In the case of Sitotroga, the importance of natural enemies to limiting populations cannot be discounted: rates of parasitism appear to have been higher than for Sitophilus (see 6.4.7, below) and a mite, Blattisocius tarsalis, which is known as an efficient predator on Lepidoptera eggs (Graham, 1970; Haines, unpublished data) was often found, both in the cribs and phoretic on Sitotroga adults. 6.4.2 Secondary Pest Species ~ Coleoptera The contrast has already been noted (6.3) between the incidence of the Nitidulidae and Silvanidae, which were most abundant at the beginning and end of the storage season, and that of the Tenebrionidae and Cucujidae, which increased throughout. These general trends however, conceal considerable differences in the ecology of individual species. The Nitidulidae recorded included small numbers of Brachypeplus spp. (mainly B. pilosellus) and abundant Carpophilus spp. The taxonomy of Carpophilus spp; associated with stored products has been well established by Dobson (1954, and subsequent notes), but the detailed examination required to separate the species of the 'dimidiatus group' precluded their specific identification in later samples. Although many .Carpophilus spp. were recorded (see Appendix' I), only two were present in large numbers: C. fumatus, the commonest species in the field was initially the more abundant in store but died out after approximately three months (Figure 6.8), while C. dimidiatus appears better adapted to storage conditions and was present throughout the seaspn at Ibadan. C. fumatus reappeared in some cribs (for instance those used in the - FIGURE 6.8 Seasonal incidence of G3rpophilu^,^fi, (N,itidulidae). Presentation of data as in Figure 6.2.- 197. 1080 UNTREATED CRIBS - Ibadan Hit Ssuon Total CarpophITus 100 10 C.dlsldlatus 1 I C. funatus .1 • * ' * 1 • i i i 1000 UNTREATED CRIBS - Ibadan Dry Ssason Total Carpophilus 100 10 .1 •V « t t 1000 „ FUMICRTED CRIBS - Ibadan Tot a1 Carpoph11us 1O0 1000 FUMIGRTED CRIBS - Ilora 100 Total Carpoph11us 10 C.dlmldlatus C.-fumatus • * • • Rug Sep Oot Nov Deo Jan Feb Mar Rpr May Jun Jul FIGURE 6.9 Seasonal incidence of main species of Silvanidae (Data presentation as in Figure 6.2). 198. 1000 UNTREHTED CRIBS - Ibtdmn Hat Sauon 100 L — , f~ Cathartua quadrtoolIt* 10 I K.J- Monanua 1 I K- oonofnnulua Oryzaspht tua naroator .1 1000 UNTREATED CRIBS - Ibtdan Dry StMon 100 Cath.quad. 10 1 I .1 1000 FUMIGATED CRIBS - Ibadan 100 • Cath.qutd. 10 Oryz.msro. Monan.oon. \ 1 I ' f' " \ .1 \ 1009 FUMIGATED CRIBS - Ilor* 109 10 A, \ i' \ 1 • w- | Ctth.qutd. N 'r "-> / i Oryz.Mro. i A \ >r \ Honan.oon. .1 lL * • Aug Sop Oot Nov Dso Jan Fob Mar Apr May Jun Jul 199. Distribution Studies) late in the succession. C. pilosellus, although only occasionally recorded from the Succession Studies cribs, was re- corded in appreciable numbers on damaged grain in a preliminary trial. C. fumatus has been recorded from maize cobs in the field in Nigeria (Cornes, 1964) and Kenya (Aitken, 1975) and from stored maize in the West Indies (Dobson, 1959) . C. dimidiatus is known as a serious pest of dried fruits and has been recorded from cocoa, groundnuts, palm kernels (Dobson, 1954) and various cereals in Africa (Haines, 1974). Neither species is recognised as a significant pest of stored maize, although the large numbers present in the cribs at Ibadan must have contributed to the damage. The two commonest species of Silvanidae, Monanus concinnulus and Cathartus quadricollis, show patterns of incidence closely analogous to that of the Carpophilus spp. : "M. concinnulus was common only under the humid conditions at the beginning and end of the storage season (and never became established on the dry-season harvested material), while C. quadricollis, was present in-considerable numbers throughout (Figure 6.9). The increase in numbers which occurred in the fumigated cribs at Ibadan during December and January is surprising in a species normally favoured by more moist conditions but may reflect invasion of the cribs by insects driven from the fields by the dry season harvest. Both C. quadricollis and M. concinnulus have a worldwide distribution on a variety of commodities (Aitken, 1975) and C. quadricollis has been described as a field pest of maize by Cornes (1964) and Schulten (1976). Neither is usually considered to be a pest of stored maize but, as with the case of Carpophilus dimidiatus, Cathartus must have made some con- tribution to damage here. A third Silvamid, Oryzaephilus mercator, which is known as a common pest of oilseeds and their products from West Africa and elsewhere (Aitken, 1975), increased to some extent in the middle of the storage period (Figure 6.9) and was found in most cribs in small numbers late in the succession. Conditions would appear, on the basis of its biqlogy (Howe, 1956b),to be suitable for the development of 0. mercator and its failure to achieve pest status was probably due to competition with other secondary pests. The same may be true of Ahasverus advena, a . species often found on damaged grain where it feeds on both moulds and the grain itself (Woodroffe, 1962; Hill, 1964). Although fre-' quently recorded, Ahasverus never-became established in the study cribs. The vast majority of Cucujidae occurring in the cribs were Cryptolestes spp. (For incidence, see the curve for Cucujidae in Figure 6.3). Small numbers of Placonotus politissimus were recorded at the beginning and end of the storage season but did not become established in the cribs. Cryptolestes species can only reliably be separated on the basis of internal genitalia (Lefkovitch, 1962) and so the species were not determined in most samples. The limited number of determination that were made indicated that the population consisted almost entirely of C. pusillus with occasional C. ferrugjneus » This is in accord with the observation of Howe and Lefkovitch (1957) that C. pusillus is the dominant species worldwide in the humid tropics, probably due to a faster rate of increase under these conditions. Aitken (1975) notes that both species can be very serious pests of cereals and are able to build-up on grain that shows little initial damage. By the end of the storage period at Ibadan C. pusillus was the second most abundant species (after Sitophilus) in most cribs and was still increasing rapidly. Twenty species of Tenebrionidae were recorded from the cribs, including five species of Palorus and four of Tribolium. Palorus FIGURE 6.10 Seasonal incidence of main species of Tenebrionidae (Data presentation as in Figure 6.2). 201. 1000 UNTRERTED CRIBS - Ibadan Wet Sauon o» Gnatooarue max. JC 100 \ / %N • . • Palorue aubdapr . C9 0 n Trlbolfun oaat. e3 10 L C / 4> •O i c I A- / .1 Id UNTRERTED CRIBS - Ibadan (9 Dry Saaaon JC 100 N« c. 1. . I Pal .aub. 10 • Gnato.«ax, 4» o • V i L .1 1000 FUMIGATED CRIBS - Ibadan . .a Pal .sub • viv. x Gnato.nax. JC 100 \ T A N. Ay' K 10 3 Trfb.oaat. C -i 4» o e •• r/ » 11 c ! ij/N t/ 1 i i .1 -I • iii? 1000 FUMIGRTED CRIBS - Ilora _ Gnato.max. 100 E \ _ > Palor.aub. 9 tmo + ' /iTrlb.oaet . 10 3 C •» • " o c I' .1 t i i i i Rug Sop Oot Nov Doo Jan Fob Mar Rpr May Jun Jul 202. subdepressus and Gnatocerus maxillosus were both abundant, the former jtn- i creasing earlier in all the wet season cribs, and both appeared to reach a 'plateau1 during the dry seasofi (Figure 6.10). Tribolium castaneum was present in all cribs but did not become as abundant as P. subdepressus and G. maxillosus, while T. confusum was present in smaller numbers. Palorus subdepressus is well known as a 'minor pest' • of cereals and cereal products in humid tropical areas (Halstead, 1967a). However, the comparative insignificance of the Tribolium spp. is perhaps surprising : on the basis of laboratory studies of biology it has been suggested that Tribolium spp. are likely to be more successful than both Gnatocerus maxillosus (Aitken, 1975) and Palorus subdepressus (Halstead, 1967a). . , Competition between T. castaneum and T. confusum has been ex- tensively studied in the laboratory (e.g. Birch et al., 1950; Sokoloff and Lerner, 1967) but competition with other T.enebrionidae does not seem to have been considered. P. subdepressus is sometimes found under bark in natural habitats and is probably indigenous to West Africa (Halstead, 1967 a and b), while both P. subdepressus and G. maxillosus were found in the fabric of empty maize cribs on the study site. The comparative success of these species in the cribs may be due to the existence of significant source populations in the surrounding en- vironment. Halstead (1967a) notes that P. subdepressus is often found in association with Sitophilufi and that Sitophilus frass is a favourable diet for it. The accumulation of frass in the cribs may have been advantageous to P. subdepressus and may explain the greater abundance of this species at the bottom of the crib. Of the remaining Tenebrionidae only Palorus ficicola, Sitophagus hololeptoides, Palembus ivoirensis and Palembus ocularis occurred in sufficient numbers to suggest that they had become established in the 203. cribs. The records of Palembus spp. are of some interest in that Giles and Graham (unpublished) had previously predicted that one of the species, P. ocularis, could become a pest of maize. Araecerus fasciculatus (Anthribidae) was recorded from all cribs but was only common during the first half of the storage season. As mentioned earlier, Cornes and Riley (1961) recorded this species later in the succession on cribs treated initially with Malathion. Araecerus is important in West Africa mainly as a pest of cocoa and coffee but it was obviously also breeding successfully on maize at Ibadan. Boshoff (pers. comm.) noted considerable populations of this insect on cribs at Ibadan that had been treated previously with Pirimiphos-methyl ("Actellic", I.C.I.). Rhyzopertha dominica (Bostrichidae) is a major pest of cereals throughout the tropics but only occurred occasionally in.the^study cribs. It did, however, increase to become one of the more abundant pests in some cribs on the same site in which grain-drying was promoted by lighting a slow-burning fire below the platform (a traditional practice in the area to the South of Ibadan - See Figure 2.1). This is consistent with the suggestion that Rhyzopertha cannot compete with Sitophilus • under humid conditions, but replaces it in hotter, drier environments (Howe, 1958; Aitken, 1975). Finally, three species of Mycetophagidae were frequently recorded from the cribs. Litargus 'varius occurred only in the early part of the storage season while Litargus balteatus and Typhaea stercorea are both mould feeders that are recorded frequently from produce stored under poor conditions (Aitken, 1975) and the ecology of L.'varius*is probably similar. The taxonomy of this species is uncertain - see Appendix I. 204. 6.4.3 Predatory Coleoptera Several species of Staphylinidae, Carabidae and Histeridae were found in the cribs. The Staphylinidae occurred mainly at t^he beg- inning of the.storage period, Coenonica sp. being commonest in the field but rarely recorded from the cribs, while. Coproporus sp. and Oligota chrysopyga were comparatively common in store. 0. chrysopyga is known to be predacious on mites and, from the biology of closely related species, both Coenonica sp. and Coproporus sp. are also most likely to be pre- dators on small arthropods (Hammond, pers. comm.). Carabidae were found sporadically throughout the storage season.- Two species, Coptoderina laticollis and Catascopus senegalensls were recorded sufficiently fre- quently to be regardfed ^s -more-Irhan just 'accidental'-.-visi-tora to the - cribs. Histeridae were found mainly at a late stage in the succession and the commonest species was Platysoma castanlpes. None of the species was sufficiently abundant to be of any prac- tical importance as a predator on the grain pests and no attempt was made to investigate possible predator-prey relationships. 6.4.4 Heteroptera Four species of Anthocoridae, three Reduviidae and two Lygaeidae were frequently recorded from the cribs. Some Anthocoridae and Reduviidae are well known from stored products as predators on the larvae of Coleoptera and Lepidoptera and on mites. The potential of one of the species, Xylocoris flavipes, as a biological control agent has been widely studied (see, for instance, Jay et al., 1968; Awadallah and Tawfik, 1972; Le Cato and Davis, 1973; Press et al., 1974, 1975; Le Cato, 1976; Arbogast, 1978). One lygaeid, Aphanus sordidus, is well known as § damaging pest of groundnuts (Gillier, 1970) and has been recorded from cocoa, copra and sorghum (Haines, 1974). Lyctocoris cochici (Anthocoridae) and Mizaldus sp. (Lygaeidae) 205. built up rapidly in the cribs at the beginning of the storage season and then disappeared completely (Figure 6.11). From their close temp- oral association it seemed possible that the former was preying on the- latter. However, Lyctocoris did occur in some cribs in the absence of Mizaldus and, in later laboratory observations, Lyctocoris was never seen to attack live Mizaldus. (adults or nymphs) although it fed readily on the larvae of several Coleoptera, including Carpophilus dimidiatus, Palorus subdepressus and Lasioderma serricorne. Lyctocoris cochiciiand Xylocoris afer (Anthocoridae) both reproduced successfully on laboratory cultures of Coleoptera under ambient conditions but the latter species never became abundant in cribs. Cardiastethus sp. (probably always C. pygmaeus), Anthocoridae, was recorded in all cribs and became established for short periods in the fumigated cribs at both localities. Population 'peaks! occurred . during the first two months in store, during the dry season in the fumigated cribs and then, with the onset of the new wet season, in the cribs of dry-season harvested maize (Figure 6.11). This pattern of incidence does not correspond with that of any of the common Coleoptera pests and Cardiastethus was not observed to feed on any of the Coleoptera 1 immatures offered to it in the laboratory (though 'probing' of the substrate was observed). It seems likely that this species is attacking mites or psocids, whose seasonal incidence was not investigated. Scolopoides divareti occurred only in very small numbers at Ilora but in all Ibadan cribs became common during the second half of the storage season (Figure 6.11). In the laboratory it was observed to feed on larvae of Palorus subdepressus, Carpophilus dimidiatus and a variety of other Coleoptera and was easily maintained on cultures of these species (with repeated additions of the prey species). FIGURE 6.11 Seasonal incidence of main species of Heteroptera. (Data presentation as in Figure 6.2). 206. 1000 UNTREATED CRIBS - Ibadan Wet Season <9 JC 100 \ Mtzaldus sp. c. Soolopotdss dlvarstt i 10 Lyotooorfs 3 ooohfof C 4» O ¥rt .1 UNTREATED CRIBS - Ibadan Dry Stason JC 100 \ C9 . 1 10 Card f a. 3 C Lyoto.oo. 4* o h r Sool.dfv. ± .1 •*-7r i t FUMIGATED CRIBS - Ibadan 100 \ Lyoto.oo. c. Mtzald.sp. 1 10 3 C 4> o o• .« Sool.dtv, c ,/f V Ns V 't I y Card1astathua ap. .1 i L , , v * • . • 1000 I FUMIGATED CRIBS - Ilora a» JC 108 \ e t e 41 Mfzaldus sp. e 10 3 mr Lyoto.oo. C 4* o Card!aststhus sp, o» 1 c i 1/ i i Soolop.dlvar. \ i .1 \ Rug Sop Oct Nov Deo Jan Feb Mar Rpr May Jun Jul 207. Of the Reduviidae, adults and nymphs of Cethera musiva and Emesopsis nubila (Emesinae) were found only sporadically but Peregrinator biannulipes built up considerably, late in the succession in some cribs. In:the laboratory both Cethera and Peregrinator fed on tenebrionid and nitidulid larvae and were successfully reared on Tribolium castaneum, although development was very slow. Both Lyctocoris cochici and Scolopoides divareti appear to have a considerable reproductive capacity under crib conditions and are potentially important control agents of secondary pests although the rather brief appearance of each species in the succession suggests particular , ecological limitations. There -is evidence in the results of this •» study as to what the limiting factors might be. The role of the Lygaeidae is not clear. From the biology of related species they are likely to be phytophagous (sensu lato) rather than predatory and species of one of the genera (Dieuches) are common in leaf litter habitats (Deeming, pers. comm.). Neither Dieuches armatipes nor Mizaldus sp. was successfully maintained on maize (or Coleoptera cultures on maize) in the laboratory, although the former survived for « some time and oviposited, especially when provided with a source of moisture. Mizaldus sp. was observed to feed on dead (damaged) Coleoptera larvae, but these may simply have been a source of moisture. The eggs of D. armatipes were extensively parasitised by a scelionid, Telenomus sp. 6.4.5 Hymenoptera At least 28 species of parasitoids were collected from the maize cribs, although of these only 13 could be identified to species level. The incidence of the commonest species is shown in Figures 6.12 and 6.13. Adults of Anisopteromalus calandrae, Choetospila elegans, Cerocephala FIGURE 6.12 Seasonal incidence of main species of Preromalidae. (Data presentation as in Figure 6.2). 208. UNTRERTED CRIBS - Ibadan Hat Saaaon Choatoap 11a { aTagana \ 9 •C. Carooaphala dtnodart i ~ -- i3 10 C 4> Habrooytua oaraalal li o I I Rn f aopt a roaa 1 ua c btrAiI- oatandraa I UNTRERTED CRIBS - Ibadan Dry Saaaon j£CO 100 \ 9 •C. Choat.alag. I — * 3 10 h- — C Cero.dfno. 4> K o 1 Rnfao.oal. c V Habro.oar. Choat.alag, \ 0c 1 3 C 4» •O 9 C FUMIGRTED CRIBS - Ilora » 100 L \ (9L 0 Choat.aleg. 1 10 |— •— "f" * 3 C 4* Rnlao.oal• o o 9 C Cero.dfno. .1 Rug Sap Oot Nov Dao Jan Fob Mar Rpr May Jun Jul FIGURE.6.13 Seasonal incidence of various parasitoids. (Data presentation as in Figure 6.2). 209. UNTREATED CRIBS - Ibadan Hat 9>««on 109 \ m •c BsthylIdas 1 3 19 Zststloontus 3 C lasvlgatus 4> /' ^ I Eup*1 nus o urozonus r .1 iU UNTREATED CRIBS - Ibadan Dry Season JC 100 \ cm 10 Mssopotobus 4» O J BethylIdas 1 I £ Eup.uroz. .1 1 A FUMIGATED CRIBS - Ibadan 109 N BsthylIdas c Zststr.lasv. . I 3 19 C 4» O Eup.uroz. s. _ y 1 ' .1 J. Yt * 1009 FUMIGATED CRIBS - ITora » JC 109 . \ m c« Bsthyl Idas 1 10 . 3 C •> O Eup.uroz. •0 * r"" c *"'in Zstst.Iasv. i .1 Rug Sep Oot Nov Deo Jan Feb Mar Rpr May Jun Jul 211. it was thought to attack Nitidulidae (Noyes, identifier's comment). At Ibadan it was found to be attacking Cathartus quadricollis and, assessed on the basis of total emergences, achieved 30 - 40% parasitism at the time of harvest. Among the Bethylidae, Cephalonomia spp. are known to parasitise a variety of stored products Coleoptera, but especially Oryzaephilus and Cryptolestes spp. Their steady increase over the second half of the storage period is consistent with the latter species being the main host. Rhabdepyris zeae, which showed a similar progressive increase in abundance, is well known as a parasite of Tribolium spp. (Haines, 1974), but its host range does not seem to have been critically investigated and it may have been attacking one of the commoner Tenebrionidae here. Both Holepyris hawaiiensis (Bethylidae) and Bracon hebetor (Braconidae) are common pests of Phycitidae in tropical stores (Haines, 1974) and Antrocephalus mitys has also been associated with storage Lepidoptera in Africa and Asia (Boucek, identifier's comment). Ephestia cautella was, like the parasitoids, present in small numbers in most of the cribs and may have been the host species; there is, however, no particular evidence for this. Scelionidae of the genera Gryon and Telenomus were frequently re- corded from the cribs and were at times abundant. Scelionids were often .found in the eggs of Dieuches spp. in insect samples and, judging from this, the rate of parasitism appeared to be considerable. Telenomus sp. successfully reproduced on eggs of D. armatipes in the laboratory, but the parasite species could not be determined. The investigation of the suitability of parasitoids, especially Pteromalidae, for use as biological control agents against storage pests 212. was begun many years ago (see, for example, Cotton, 1923, on Aniso- pteromalus calandrae, and Noble, 1932, on Habrocytus cerealellae). Small-scale trials under both laboratory and ambient field conditions have indicated that, in confined environments,parasitoids can limit populations of both Sitophilus spp. and Sitotroga (Williams and Floyd, 1971; De Lima, 1978). However, studies of full-scale stores have in general shown that, although parasitoids were present and at times abundant, they failed to maintain the pest populations below the economic injury level (Kockum, 1953; Salmond, 1957; De Lima, 1.978) . In the current study no attempt was made to quantify the impact of parasitism and the recruitment samples were too small to assess properly the rate of parasitoid emergences. The results from such samples are difficult to interpret both because one cannot be sure of the species of the host with which an emerged parasite was associated and because of the difference in development time between parasite and host (which means that the parasites emerging in a particular unit of time will not be those associated with the 'generation' of hosts that emerges during that period). Taking the total numbers of hosts and parasitoids emerging and assuming 1 the separation of hosts discussed earlier, the rates of parasitism achieved here appear to have been of the same order as those observed by De Lima (1978), namely less than 5% for Sitophilus and usually less than 10% for Sitotroga. Higher'apparent rates of parasitism were recorded for Sitotroga in cribs other than those used for the Succession Studies and for Sitophilus in the final sample from the wet season cribs at Ibadan when total emergences of Sitophilus (for the four cribs combined) were 149, those of Choetospila 56 and those of Cerocephala 21. Although adult parasitoids were caught in all cribs from the fourth week of storage onwards appreciable numbers 213. of emergences were not recorded until after 2| months at Ilora and after more than three months at Ibadan. Several species of Formicidae were recorded but only two, Pheidole sp. and Myrmicaria sp., appeared in the cribs in significant numbers. Colonies were not formed in the cribs themselves. Foraging ants were observed to carry away fragments of grain and/or frass, dead insects and, occasionally, live insect larvae. In the period just after harvest Myrmicaria sp appeared to collect significant numbers of Mussidia nigrivenella larvae, but this was not examined critically. Graham (1970) noted the importance of predation by Pheidole megacephala on larvae of Epnestia cautella in a warehouse in Kenya, but there seems to be no information on the —general importance of predation by ants in rural stores. 6.4.6 Diptera Diptera were frequently collected from the cribs but were never numerous. The .most consistently recorded was Medetera sp. (Dolichopodidae) which was often seen in small numbers on the outside of the cribs. Larvae which probably belonged to this species were found in infested grain , samples and may have been predatory on immatures of the grain pests. The larvae of some Medetera species are known as predators on larvae and pupae of wood boring Coleoptera (Dyte, pers. comm.). Drosophilidae and Sciaridae were occasionally found, probably associated with the mouldy grain, and Phlebotomus sp (Phlebotomidae) were recorded in several samples from Ilora, where they may have been feeding on the rats which were often found in the cribs. 6.4.7 Psocoptera Psocoptera became abundant in the cribs but were difficult to census (mainly because of the time and care required to extract them from the grain) and most species could not be identified. Psoquilla marginepunctata 214. was by far the most abundant species and was sometimes seen to cluster on,the outside of the cribs in large numbers. Liposcelis sp. (possibly more than one species) was also common. Psocids are frequently recorded from stored products but little seems to be known of their role in storage ecology. Nineteen species have been found in stored products in Zaire (Badonnel, 1974). In the ck . laboratory Liposcelis bostryophilus has been shown to feed on the eggs of A Plodia) interpunctella (Lovitt and Soderstrom,. 1968) and of beetles (Williams, 1972; Shires, unpublished report) as well as a variety of plant materials. Williams (1972) reports 5% predation on eggs of an anobiid beetle in wood under natural conditions. Since Psoquilla marginepunctata has been recorded quite frequently from tropical stores (Hairies, identifier's comment), its biology would seem to merit investigation. 6.4.8 Other Insect Groups Metabelina abdominalis (Dictyoptera, Blatellidae) and Diaperasticus erythrocephala (Dermaptera, Forficulidae) were found in maize cobs both in the field and during the early part of the storage season. The former species reproduced in small numbers in the cribs. Spongovostox gestroi (Dermaptera, Labiidae) became quite abundant in some cribs (especially those used for the Short-Term Distribution Studies) on damaged grain late in the succession. Metabelina is presumably a scavenger but the Dermaptera may be wholly or partly predatory. 6.5 Other Arthropods As Haines (1974) has remarked, infestations of mites in tropical stores are probably more frequent than the few records in the literature might suggest. In the current study mites were observed on the maize from field samples and became abundant in store. Small collections of mites were made at various stages in the study using a paraffin extraction 215. process (Thind and Griffiths, 1979) but the large numbers in samples and the difficulty of identifying them meant that this could not be done frequently or quantitatively. This was an unfortunate omission in that mites may well have had important effects on the insect pest population via egg predation or parasitism. The most abundant species appeared to be Tyrophagus putrescentiae (Astigmata, Acaridae). This species has a cosmopolitan distribution in a variety of habitats, including many stored products where it appears to feed both on carbohydrates and moulds (Hughes, 1961). Other common mites were prostigmatans of the genera Tarsonemoides, Tydeus and Anystis and the me sostigmatans Proctolaelaps, Typhlodromus and Amblyseius. It is difficult to generalise on the ecological roles of mites because individual species are often very versatile, while closely related species may have totally different habits. It is likely, however, that the mesostigmatans at least were predators on-phytophagous (or mycetophagous) mite Carpophilus spp. caught in the cribs were frequently observed to be carrying Pseudotarsonemoides sp. (Prostigmata), a genus which has been \ found in association with bark beetles (Lynch, identifier's comment). On Carpophilus the mites were usually clustered along the soft membranes between selerites, but it is not clear whether they were ectoparasitic or phoretic; the mites were also found free on frass in samples. Pyemotes sp. (Prostigmata) was on one occasion found parasitising Sitotroga in a laboratory culture recently started from moths caught in the cribs, while Paracarophenax sp. (Prostigmata), another species that may well be an insect parasite, was found in at least two samples from the cribs. The frequent occurrence of Blattisocius tarsalis in association with Sitotroga and its possible importance has already been noted; this species was also found free in grain samples. 216. The effect of the mites in degrading the substrate must have been trivial in comparison with that of the insect pests. However, as Haines (1974) points out, in temperate climates mites can be of economic importance on stored produce and may become so in the tropics as insect control is improved. Small numbers of pseudoscorpions were occasionally found in the cribs. Pseudoscorpions are frequently recorded from stored products where they prey on mites (Champ, 1966), but in the conditions of this study they,were not common enough to have had any significant impact. Spiders were often present in samples from the cribs, but also in small numbers. Zelotes sp. (Aranea, Gnaphosidae) was frequently recorded but the majority of other species have not, as yet, been identified. 6.6 Vertebrates Rodents are one of the most important^ causes of losses in stores, both because of the considerable quantity of grain consumed' (up to 10% of body-weight per day) and the much larger quantity that is contaminated and damaged (Dyks tra, 1973). Rat guards were fitted to the study cribs but proved ineffective, especially at Ilora. No attempt was made to quantify losses due to rodents and cobs damaged by rats were not included in the loss assessment data below (6.10). The species usually noticed in the cribs was the multimammate rat, Mastomys natalensis. Birds did not appear to be a serious cause of loss from cribs although Laughing doves, Streptopelia senegalensis, were frequently seen feeding from the top surface of the maize. Agama lizards, Agama agama, and skinks, probably Mabuya sp., were frequently observed in the cribs. Examination of the faecal pellets of the former species indicated that its diet in the cribs consisted mainly 217. of ants, Myrmicaria sp., but included a small proportion of Sitophilus. 6.7 Grain Weight Losses The progress of weight loss for the wet season cribs has already been indicated (Figure 6.5). The considerable variation in the initial moisture content of cobs in this trial resulted in estimates of dry weight loss with large standard errors (not shown). As a result successive estimates of weight loss cannot be compared critically. The mean values (Figure 6.5) suggest, however, that-the weight loss over the .first two. months in store is comparatively small but rises steadily thereafter. The observation that weight loss continues to increase rapidly over the second half of the storage period, when reproduction of Sitophilus and > Sitotroga is comparatively low, provides at least circumstantial evidence for the importance of the secondary pests in continuing damage. "Hie final losses for individual cribs are given in Table 6.2. Differences between the four Ibadan cribs were tested using a single factor analysis of variance with each crib as a 'treatment1. There were sig- nificant differences between replicates (i.e. A vs. B, C vs. D) but the fumigation appeared to have had no effect. The Ilora cribs had to be tested separately because they were terminated after a shorter storage period. 'T' tests on these cribs and on the dry season cribs at Ibadan showed no significant difference (at 5%) between the replicate cribs. The dry season cribs suffered slightly greater damage than the wet season ones over a considerably shorter storage period. The faster rate of damage may be due at least in part to the higher rate of Sitophilus reproduction over a longer period in the dry season cribs, but the missing data points (Figure 6.7) make it difficult to assess this difference. The weight loss in the cobs placed outside the sampling tunnels could not be assessed for the wet season cribs because a number of cobs 218. TABLE 6.2 Crib Treatment Total time in store/ Final wt. loss/ s.d. weeks % A ) Wet season, untreated 38 22.5 a 3.8 ) B ) Ibadan 38 26.7 b 2.3 C ) Wet season, fumigated 38 27.9 b 3.6 ) D ) Ibadan 38 19.8 a 4.5 C N r- . E Wet season, fumigated C M 14.8 ) 6.7 ) r ^ ) ) N.S.D. F ) Ilora 16.4 ) 7.0 L ) Dry season, untreated 26£ 31.8. ) 4.6 ) ) N.S.D. M ) Ibadan 26£ 28.4 ) 1.5 TABLE 6.2 Mean loss in dry weight at the end of the storage period. (calculation assumes that weight loss in the core is negligible). 4 Single factor anovar indicated significant differences between means of cribs A - D (P<0.001). Separations are from a Newman - Keuls test with « = 0.05. Cribs E and F and cribs L and M were not significantly different on a t test at the 5% level. 219. TABLE 6.3 'Cribs' - a) 'levels' CRIB L CRIB M Mean above tunnel 33.3 34.6 34.0 (unsampled) + 4.7 + 3.1 inside tunnel 31.8 28.4 30.1 (sampled) + 4.6 + 1.5 below tunnel 25.9 24.0 25.0 (unsampled) + 3.5 + 2.2 b) Source of variation degrees of freedom probability, Total 59 Cribs 1 0.14 Levels 2 <0.001 Interaction 2 0.10 Error 54 TABLE 6.3 Weight loss in dry season cribs at termination: Effect of position/sampling. a) mean weight loss (jf standard deviation) on a dry weight basis for different positions in two replicate cribs. b) probability levels from a 2-factor analysis of variance, were severely damaged by rats and because in others the identification C u«"" numbers were obscured. Improved rat guards and a different marking system were used in the dry season trial. The results for this trial are presented in Table 6.3. The mean weight loss for cobs within the sampling tunnels is intermediate between the values for cobs immediately above and below (as compared with the results of the preliminary trial in which the sampled cobs showed a lower value - Section 3.5). This suggests that although there is a 'position1 effect, sampling at this intensity (approximately monthly) has not significantly reduced the insect population. The levels of weight loss recorded here represent very severe damage to the maize, although (as noted in Section 4.6) the data are within the range recorded in surveys of rural cereal stores (Hall, 1970). Grain in the condition reached at the end of the study would not normally be used for human consumption but might be fed to poultry. However, as Adams and Harman (1977) have pointed out, such figures for loss at the end of the storage season greatly overestimate the effective losses that occur in subsistence stores: in normal circumstances consumption of the grain would reduce the quantity left in the crib so that only a small proportion of the original total would be subject to the severe damage encountered over the latter part of the storage season. 6.8 Conclusions The occurrence of different patterns of incidence of insect species in the cribs with the passage of time demonstrates the need to consider both the detailed ecology of individual species and their interactions with other members of the insect community. The seasonal incidence of, say, Monanus concinnulus or Carpophilus fumatus, might have been broadly predicted from a knowledge of their requirement for a moist and/or mouldy 221. substrate, combined with the obvious climatic observation that there is a marked dry season at Ibadan. However, it is much less obvious, for instance, what factors might have enabled Cryptolestes pusillus and Gnatocerus maxillosus, species which are regarded as sensitive to low humidities, to increase almost throughout the storage period while Tribolium castaneum and T. confusum did not, despite their greater drought-tolerance and proven ability to eliminate other species of secondary storage pests in laboratory competition experiments. The evidence produced by this study is not sufficiently detailed to answer such questions with any confidence. It is not known, for instance, whether the increasing populations of particular secondary pest species were partly or wholly due to successful reproduction within the cribs or whether they reflected immigration from other habitats. There is, however, evidence that different species may be limited by quite different factors. The observation that Sitophilus reproduction'is apparently limited mainly by its own adult population density (rather than, say, unfavourable substrate conditions during the dry season) has particularly serious implications for control strategies: one may expect any breakdown of control measures to be followed by very rapid recovery of pest pop- « ulations as individual surviving insects are able to realise their full reproductive potential. Similarly, there is at least circumstantial evidence that a number of potentially serious pest species are present in the environment but are not achieving pest status due to competition. If control measures were to act selectively against existing pest species there is at least a possibility that they would be replaced by others. This phenomenon is well known from field crops, such as cotton, that are also subject to attack by a variety of insects, and there is some evidence that it has occurred on stored produce in Kenya (Graham, 1970). Interspecific differences in tolerance to insecticides are already well documented for storage pests (Champ and Dyte, 1976), but a similar outbreak of 'new* pests could occur if, for instance, cultural controls were successfully used to interrupt the cycle of Sitophilus infestation. The implications of these possibilities will be further considered in the discussion which follows. 223. CHAPTER 7 DISCUSSION:CHARACTERISTICS OF THE MAIZE CRIB SYSTEM AND IMPLICATIONS FOR CONTROL STRATEGIES Stored grain has been described as "a man-made ecosystem with relatively simple structure and non-regenerating food energy supply ...... Such an ecosystem is unstable and is composed of species with high growth and reproductive rates and low specialisation" (Sinha, 1973) . i Entomologists studying grain storage under commercial conditions are usually concerned with insect pests at low population densities developing on an abundant food supply. The rate of population growth may be constrained by harsh environmental conditions, especially by very low moisture contents and high temperatures, or the associated physical and physiological problems_of exploiting the food supply (i.e. dry, undamaged grain). Equilibrium population densities are rarely, if ever, attained. As Solomon (1953) has pointed out, although studies of storage pest population dynamics in the laboratory have shown a variety of crowding effects, the densities at which these effects become important are rarely achieved under good storage condit ions. They are encountered in practice only around 'hot spots1 or on limited grain residues left in empty stores. It is interesting to consider the extent to which the maize cribs studied here differ from such 'conventional1 stored grain systems. The features in common include the limited duration of the habitat (i.e. the length of one storage season) and the non-regenerating food supply. Although the insect populations reach high densities after a short period of storage, their development occurs in an environment of seasonally changing physical conditions and the insects are themselves progressively 224. changing the nature of their substrate: stable interactions between species and equilibrium population levels cannot, therefore, be expected. The insect community in cribs is remarkably diverse and, although some of this diversity is undoubtedly maintained by the inter- change of insects with other habitats, there do seem to be various features of the crib system which, from stability arguments, appear to favour the maintenance of; diversity. One such feature is the spatial heterogeneity of the substrate which is greater than that in bulk shelled grain. The variation in grain conditions from one part of the crib to another, imposed by the outside environment, and, at a smaller scale, the heterogeneity provided by small foci of damaged and mouldy grain have already been described. These provide a variety of microhabitats favourable to insects with different ecological requirements. Moreover' the storage of maize on the cob provides a structural complexity not encountered in bulk grain. Crombie (1946) showed that the provision of 1refuges1 (consisting of sections of fine glass tube) allowed Oryzaephilus surinamensis and Tribolium confusum to coexist on flour, by providing protection for the pupae of the former species. It may be imagined that in cobs of maize a variety of such refuges might exist and provide shelter for vulnerable stages such as eggs or pupae. The superficial similarity of many storage pests is perhaps mis- leading. There is an obvious difference between the requirements of primary pest species, whose larvae develop most successfully within intact grains, and those of secondary pests whose larvae feed mainly from damaged surfaces or on frass. Co-existence of two such contrast- ing species, Rhyzopertha dominica and Oryzaephilus surinamensis under laboratory conditions was demonstrated by Crombie (1945). However, within these broad groups a variety of more subtle differences exist in feeding habits, moisture content preferences and so on. The importance of such niche separation in allowing coexistence of com- peting species has been discussed by May (1975) . Another important condition for coexistence that is fulfilled, at least by Sitophilus, is that populations are limited more strongly by intraspecific effects than by interspecific ones. The strong inhibitory effect of high Sitophilus densities on its own reproduction may prevent it from eliminating other less numerous species over the duration of the storage period. It is possible to speculate that the activity of predators and parasitoids is contributing to the maintenance of species diversity, (see Hassell 1979). While these agents do not appear to be limiting Sitophilus populations they may be having a significant effect on the secondary pest species (between which competition is likely to be most acute). The mite Blattisocius tarsalis is known to be polyphagous (attacking the eggs of both beetles and moths), the three commonest Authocoridae were shown in the laboratory to attack a variety of Coleoptera larvae and the Bethylidae also appear from published records to show at least limited polyphagy. No information seems to be avail- able on the 'switching1 or aggregation behaviour of these species on mixed populations of hosts; however, given the demonstrated voraciousness of both the mites (Haines, unpublished data) and of Anthocorids similar to those found here (e.g. Jay et al. 1968), it seems at least plausible that the activity of natural enemies is contributing to the maintenance of diversity. 226. The picture of the storage community which emerges is one of considerable complexity. There appears to be a good deal of special- isation among the grain-feeding species while the consistency of the spatial distribution patterns and of the temporal succession observed suggests the existence of well-established relationships between species analogous to those found in co-evolved communities. Although a similar spectrum of Arthropod groups may occur in temperate stores (see, for instance, the food webs proposed by Sinha (1973), these systems are usually dominated by only one or two species. The greater species diversity in crib stores may be partly explained by the features discussed above in combination with more equable environmental conditions: in part- icular, the floury endosperm of the dent maize at a comparatively high moisture content provides a favourable substrate for a wide range of species. It is important to recognise, however, that the crib, unlike a closed bulk grain store, is an integral part of a farming system and, indeed, of a farming system that retains great ecological diversity by the alternation of crops with semi-natural 'bush-fallows'. It is widely accepted that traditional cereal varieties resistant to storage pests have evolved by a process analogous to natural selection over an extended period of time: only grains sufficiently resistant to withstand prolonged exposure to insect attack over thfe storage period remained viable and were propagated in the following year's crop. While there is little direct evidence that insect communities have been similarly selected in traditional agricultural systems this is at least a possibility. More- over the crib habitat is similar in several respects to the 'natural' food stores of other organisms in which some at least of the pest species probably evolved. 227. One might postulate that the inherent 'irritability1 of storage insects (Surtees, 1965), which would lead in small open stores to dis- persal, and the effects that reduce net fecundity at high densities (Solomon, 1953) are in fact adaptations which allow the insects to survive for an extended period on a strictly limited resource. In some tropical ecosystems plant production may be nearly continuous through the year: in such an environment a seed feeder, like Sitotroga cerealella, which is short-lived, quite strongly dispersive and which maintains a high rate of reproduction (even at high densities) can survive by moving from one habitat of limited extent or duration to another, saturating and destroying, each."-However, in.other tropical environments, especially the savannah regions that include or are • dominated by grasses (i.e. cereals), the productive phase is limited to a short pefiod of the year in which rainfall is concentrated. An -insect which depends on surviving for at least the several months of dry season in an accumulation of grain must possess mechanisms that will allow it to maintain its population without destroying the substrate. The strong intra-specific limitation of reproduction shown by Sitophilus may be an example of such an adaptation. Self regulating mechanisms may be found in other species but it is also possible that many storage species, especially those described as 'secondary* pests, depend for their survival under natural conditions on the slow rate at which they are able to attack dry, undamaged grain. Although they appear in the laboratory to have very high inherent rates of reproduction these would not normally be achieved on whole grain in the field: reproduction only becomes sufficiently rapid for these species to reach high populations when they are provided with an unusually favourable substrate (such as moist, dent maize). 228. Although these considerations may seem to be of largely academic ititerest they are in practice crucial to an understanding of the development of storage pest problems with changes in the agricultural system. Traditionally, only inherently resistant cereal varieties have been stored and natural protective structures such as pods (grain legumes) glumes (rice) and husks (maize) have been retained. Many cereal-dependent agricultural systems developed in areas where a dry period (or, at higher altitudes, a dry and cold period) of sufficient severity to slow pest attack followed after harvest. Additional protection may have been afforded to small quantities of grain by 'smoking* or by the addition of ash, sand or tbxic plant products. Under these conditions losses due to insects, may have been appreciable but they were-sustainable. In humid areas,, where losses to cereals would have-been too severe,- staple foods were provided mainly by root and tree crops. In some areas these conditions still prevail, but in others changing economic and social circumstances have resulted in considerable changes in agricultural practices. Increases in human populations and in the degree of urbanisation have resulted in an urgent need to increase agric- ultural production and in particular to change from subsistence farming to systems that produce a marketable surplus. This has been expressed in various ways but most importantly in the selection of new crop varieties in the extension of cereal production into more humid areas and in 'intensification' (in the sense that more land has been brought into production with a concomitant reduction of fallows). New varieties of cereals have been selected mainly for good agronomic characters and maximum yield at harvest. Although techniques for ident- ifying post-harvest resistance have been established and a considerable 229. body of information accumulated on existing varieties (Dobie, 1974, 1976) these have not widely been exploited in breeding-programmes. Plant breeders have apparently believed the extra investment of time and effort required for post-harvest screening of separate progeny to be unwarranted. Historically, agricultural communities were to some extent excluded from very humid areas by factors such as human disease or excessive pest and disease damage to field crops. It has only become feasible com- paratively recently to grow significant quantities of cereals and grain legumes in high rainfall areas. While devices such as the storage of partially fermented grain in water of the use of 'smoking cribs1 have enabled the preservation of small quantities of grain, these methods cannot" cope with significantly higher production, hence the attempt to introduce highly-ventilated cribs for natural-drying. -The disastrous levels of storage damage described from the experimental cribs at Ibadan indicate the problems that may be expected if additional pest control measures are not taken in these circumstances. The effect of intensification on storage pest problems does not seem to have been widely discussed. The biological system described here depends for its long-term stability on high mortality among the insects that disperse from stores. With intensification there is an •increasin gchance that dispersing insects will find a new crop or store on which they can reproduce successfully, leading to much increased endemic pest populations. The question then arises as to whether the techniques of crib storage and the accompanying crop production system can be modified to cope successfully with these problems or whether a fundamental change 230. in storage practices is required to return losses to an acceptable level. In the situation considered in this study the following features seem particularly important. Firstly, the pest species appear to have a considerable capacity for dispersal which is apparent at the time of colonisation of the cribs and may well be important during the course of the storage season (although this was not demonstrated directly) Secondly, conditions are adequate for rapid build-up of the major pest species for most of the storage period and such limit- ations as there are on population increase appear to be largely due to interactions within the pest community. There are also other potential pests present in the environment for which conditions appear favourable.but which are effectively excluded by competition. Finally, there~is circumstantial evidence that some~of the species which are potential storage pests have significant source populations in habitats not associated with the maize production or storage system. Insect control strategies could, in principle, be aimed at reducing the potential rate of pest increase in store, reducing the overall level of pest populations in the total environment or interrupting the cycle of infestation from store to field and back. To have any chance of achieving lasting improvement all three components would have to be pursued in parallel. In a crib there can be little or no control over temperature or humidity and the improvements in drying rates that can be obtained by modifying the structure are not sufficient in humid areas to affect significantly insect development. The substrate must therefore be made less suitable by increasing the inherent resistance of the grain. While 231. varieties as susceptible as that used in this study are widely used there can be-little chance of reducing endemic pest population levels: any breakdown of chemical or cultural controls will be followed by explosive recovery of pest populations. This does not necessarily imply a return to traditional low-yielding varieties but rather the selection of the less-susceptible improved cultivars. Resistance levels in currently available varieties are not sufficient to provide protection on their own under high pest pressure but would make a significant contribution to a wider strategy. There may be some potential for exploiting improved husk cover. Although that shown by the varieties used in this study was clearly ineffective in protecting the maize (affecting insect distribution but not overall population levels), other varieties can.be better. The penalties*of lower maximum yield, slower^ drying, the need to delay harvest and the greater total bulk to be stored are all factors that argue against the development of better-covered varieties for storage 'in the husk1. It remains possible, however, that the reduction of losses in store might outweigh these disadvantages. Possibly good husk cover is more important before harvest as a means of delaying the establishment of storage pests. While under current conditions this early infestation seems unimportant compared with direct cross-infestation from infested stores, it might become significant if other sources of pests can in the future be controlled. Certainly it seems important to exclude, those varieties which show high susceptibility to Lepidoptera in the field and those with a large proportion of open tips because of the severe direct damage they suffer in humid conditions. Biological control seems to have little potential in the immediate future. Natural enemies cannot be expected to maintain pest populations 232. below injurious levels under current conditions of massive pest in- vasion and rapid reproduction. If these adverse factors can be significantly reduced the prospects would be improved, but the evidence of these studies suggest that the hymenopteran parasitoids at least are slow in moving to cribs at the beginning of the storage season. Reports of successful biological control of storage pests (e.g. Le Pelley & Kockum, 1954; Le Cato et al. 1977) appear to have come only from 'closed* environments (i.e. warehouses) where there is little insect movement to and from outside habitats. The conventional chemical control methods involving the admixture of more or less persistent insecticidal dustsloading Q.f the crib appears to be still effective in some dry areas. In humid conditions, however, the rapid breakdown of the insecticide renders this method virtually ineffective. Moreover, insect resistance to the two estab- lished pesticides for this application, Lindane and Malathion, appears to be widespread (Champ & Dyte, 1976). Some success has been claimed for a system involving the repeated spraying of the outside of narrow cribs with pirimiphos-methyl or synthetic pyrethroids (F.A.O., 1980); using the former chemical, the economics are favourable and the method appears robust enough for use at the small-farm level. In principle, however, it seems ill advised to advocate the use of considerable quantities of insecticide in a situation where they can be at best only moderately effective. A total 'kill' is not obtained and there appears to be little residual action. The current study has indicated the speed with which populations of major pests may recover from low levels and the potential for recolonisation from outside sources under current conditions is considetable. While the use of insecticides on cribs in humid areas may be necessary in the short or medium term it must be combined with measures to reduce the general pressure of infest- ation. More information is also needed .on.the precise biological ef.fects... of pesticide applications on the insect populations. Various authors have proposed that the cycle of infestation from infested stores to the growing crop might be interrupted by ensuring that there is a distinct interval prior to harvest when no grain is held in store and when the fabric of storage structures can be properly dis- infested. Even if this were socially feasible, it seems unlikely to be effective, given the existence of source populations' of storage pests (and their considerable longevity) in Alternative* habitats. Proper crop and store sanitation would undoubtedly improve the situation and would be a crucial component of any control programme, but a real solution to the problem in terms of an—integrated pest management strategy cannot be expected until—a greater part of-the total environment can be controlled. Storage losses may be reduced by removing the grain to a more easily controlled environment such as a silo or warehouse. While small-scale silos have been successfully introduced in some developing countries, in others they have not been adopted because of high capital cost or the non-availability of materials, or, in humid areas, because of the recurrent cost of artificially drying the grain. In such areas there is also a considerable danger that subsequent moisture migration in the silo can lead to moulding and, potentially, total loss of the grain. Warehouse storage offers a more robust system, in which the drying requirement is less critical and in which pesticides are likely to be reasonably effective. Good pest control has been achieved, for instance, by application of pirimiphos-methyl to successive layers of bags stacked in warehouses (F.A.O. 1980). Cribs could play an important role in such a system by providing a cheap method of natural drying of grain prior to 234. warehouse storage. For the short period involved it might be pos- sible to avoid the "use of insecticides in the cribs altogether. JThe small size of individual farms in many developing countries means, however, that the introduction of more sophisticated storage tech- niques may require a change in social organisation, such as storage by 'collectives1 of farmers or by larger-scale marketing boards. In practice such systems have often proved difficult to introduce or operate. In conclusion, the immediate prospects for the use of cribs in humid areas do not appear favourable. Environmental conditions are ideal for storage pest development and changes in agricultural practices have resulted in excessive endemic pest population levels. In the face of this pressure of infestation, measures such as the use of insecticides on cribs are only a palliative and breakdown of the protection prbvided by them must be anticipated. Research is needed to investigage the ecology of rural storage systems in different environments and to identify points of weakness before further serious pest problems develop. Applied workers seeking to improve storage techniques must consider crib stores as an integral part of the particular farming system and must give more attention to the biological characteristics of the insect community which they are trying to control. Improved crop sanitation and genetically resistant varieties should be introduced to contain the immediate pest problem. However, significant reduction of storage losses cannot be expected without further major changes in agricultural systems and these changes may, for economic and social reasons, be very difficult to achieve. 235. APPENDIX I : An annotated list of species of insects and mites recorded from maize cribs at Ibadan and Ilora. Insects are recorded by Orders, according to systematic convention,but within Orders lower taxa are set out alphabetically. Field Store DICTYOPTERA (det. J.A. Marshall - C.I.E.) Blattellidae Metabel'ina abdominalis (Shelford) DERMAPTERA (det. A. Brindle - C.I.E.) Forficulidae Diaperasticus erythrooephala (Olivier) Labiidae Spongovostox gestroi (Burr) PSOCOPTERA (det. C.P. Haines - T.S.P.C.) Liposcelidae Liposcelis sp. Psoquillidae Psoqwilla marginepunctata Hagen HEMIPTERA (det. M.S.K. Ghauri - C.I.E.) (HETEROPTERA) Anthocoridae Cardiastethus pygmaeus Poppius 1 Lyotocoris cookici Delamar-Deponttevimme & Paulian 1 Scolopo-ides divaret'i Carayon . 1 Xytocoris (Proxylocorzs) afer (Reuter) 2 Lygaeidae Dieuches avmatipes (Walker) • 2 236. APPENDIX I : Continued. Field Store Dieuches sp. 3 Mizaldus sp. 1 Pachybrachvus sp. 3 Reduviidae Cethera mus-Cva (Germar) .2 Emesopsis nub-ila Uhler 2 Pevegrinatcp biannuli,pes Montrouzier 1/2 Tingidae Arushia sp. 3 gen. & sp. indet. 3 COLEOPTERA Anobiidae (det. C.P. Haines) Lasioderma serrioorne (F.) 2 Anthicidae (det. R.B. Madge - C.I.E.) Anbhious bottegoi Pic 2 Anthribidae . (det. C.P. Haines) Arae oerus fascLaulatus .Degeer 1/2 . Bostrichidae (det. C.P. Haines) Bo s tryc hop 1% tes comu tus (01 iv i er) 2 Di-noderus minutus (F.) • 2 Heterobostryohus brunneus (Murray) 2 'Rhyzopertha dominica (F.) 2/3 Xyloperthella erznitarsis (Imhoff) 3 Bruchidae (det. C.P. Haines) Callosobruchus maculatus (F.) 3 Carabidae (det. R.B. Madge) Catasoopus senegalensi-s Dejean 2 Coptoderina latircollzs (Lafevre) 2 Metallica aeneipennis (Dejean) 3 gen. &. sp. indet. 2 237. APPENDIX I : Continued. Field Store Cerylonidae (det. R.B. Madge) Elytrotetrantus sp. 2 Chrysomelidae (det. M.L. Cox - C.I.E.) Melixanthus sp. 3 Ciidae (det. R.B. Madge) gen. & sp. indet. 3 Cleridae (det. R.B. Madge) Korynetes analis (Klug) " 3 •Neorobia rufipes (Degeer) 2 Colydiidae (det. D.G.H. Halstead - M.A.F.F.) Microprius oonfusus Grouvelle 2 Pseudobothrideres oonradsi Pope 3 Corylophidae (det. R.B. Madge) Alloparmulus sp. 2 Arthrolips sp. ' ^ 2 Cucujidae (det. D.G.H. Halstead) Cryptolestes ferrugineus (Stephens) • 2 Cryptolestes pusillus (Schonherr) • 1 Cucujirius sp. 3 Mario.laemus sp. 3 Plaoonotus majus Lefkovitch 2 Plaoonotus politissimus (Wollaston) 2 Planolestes oorrtutus (Grouvelle) • 2 Curculionidae (det. D.G.H. Halstead) Cylas puncticoll'is (Boheman) 3 Pseudostenotrupis marshalli- Zimmerman 3 Sitophilus zeamais Motschulsky 1 Elateridae (det. C.M.F. von Hayek - C.I.E.) Aeoloides sp. 3 Cardiophorus sp. 3 Endomychidae Mycetaea hirta (Marsham) 1 2 APPENDIX I : Continued. Histeridae (det. S. Mazur - Inst. Ochrony Lasu Drewna, Warsaw) Diplostix mayeti (Marseu-1) Platysoma castanipes Marseul Teretrius pulex Fairmair Teretrius oylindricus Wollaston Hydrophilidae (det. E.A.J. Duffy - C.I.E.) Enochrus sp. Lyctidae (det. D.G.H. Halstead) Lyotus nr. africanus Lesne Minthea rugicollis Walker Mycetophagidae (det. D.G.H. Halstead) L-itargus batteatus Leconte L-itargus'var-ius' Typhaea steroovea (L.) Nitidulidae (R.M. Dobson - Glasgow University; C.P. Haines; R.B. Madge) Brachypeplus Igabonensia (Grouv.) Braohypeplus' pilosellus (Murray) Carpophilus binotatus Murtay Carpophilus dinridiatus (F.) Carpophilus freemani •Dobson Carpophilus fumatus Boheman Carpophilus hemipterus (L.) Carpophilus maculatus Murray Carpophilus marginellus Motschulsky Carpophilus obsoletus Erichson Carpophilus pilosellus Motschulsky Carpophilus zeaphilus Dobson Carpophilus sp. nov. Haptonchus minutus (Reitter) Lasiodaotylus sp. Urophorus humeralis (F.) Phalacridae (det. R.B. Madge) Litotarsus sp. Platypodidae (det. M.L. Cox) Platypus hintzi Schaufuss 239. APPENDIX I : Continued. Field Store Scolytidae (det. M.L. Cox) Hypothenemus obscurus (F.) 2 Xyleborus ferrugineus (F.) 3 Silvanidae (det. D.G.H. Halstead) Ahasverus advena (Waltl ) 3 Cathartus quadricollis (Guerin) 1 1 Monanus concinnulus (Walker) 1 1 Oryzaephilus mercator (Fauvel) 1/2 Parasilvanus faipairei (Grouvelle) 3 Silvanoprus frater (Grouvelle) 3 Silvanoprus linsidiosus Grouvelle 3 Silvanoprus longicollis (Reitter) 3 Silvanus .inarmatus Wo11aston 2 Stephylinidae (det. R.B. Madge) Atheta dilutipennis (Motschulsky) 3 Coenonica sp. 12 Coproporus sp. 3 2 Gabronthus Ibadalus Tottenham 3 Oligota chrysopyga Kraatz 2 Philontfrus peregrinus (Fauvel) 2 Tenebridnidae (det. D.G.H. Halstead) Alphitobius diaperinus (Panzer) 3 Alphitobius laewigatus (F.) 3 AZphitobius viator Mulsant & Godart .2 Gnatocerus maxillosus (F.) 2 1 . Gonocephalum simplex (F.) 3 Latheticus oryzae Waterhouse 3 Palembus ivoirensis (Ardoin) - 2 Palembu$ ocularis Casey '2 Palorus bobiriensis Halstead 2 Palorus carinicollis (Gebien) 2 Palorus cerylonoides (Pascoe) • 2 Palorus crampeli Pic 2 Palorus ficicola (Wollaston) 2 Palorus subdepressus (Wollaston) 1 Platydema sp. 2 Sitophagus hololeptoides (Castelnau) 2 Stomylus sp. 3 Tribolium anaphe Hinton 2 Tribolium castaneum Herbst 3 1 Tribolium confusum Jacquelin du Val 1/2 Tribolium semicostata. (Gebien) -3 240. APPENDIX I : Continued. Field Store Trogositidae (= Ostomatidae) (det. C.P. Haines) Tenebroides mauritanicus (L.) 3 (Ilora only) LEPIDOPTERA (det. C.P. Haines; J.N. Ayertey - I.A.R.; M.J. Cornes - N.S.P.R.I.) Cosmopterygidae Pyroderces sp. Gelechiidae Sitotroga cerealella (Olivier) Pyralidae Eldana sacckarina Walker Ephestia cautella (Walker) Mussidia Inigrivenella Ragonot Plodia inter puna tetla (Hubner) Tortricidae (Olethreutidae) CryptopKlebia leucotreta (Meyrick) DIPTERA (det. J.C. Deeming - I.A.R.; C.E. Dyte - M.A.F.F.) Cecidomycidae gen. & sp. indet. Dolichopodidae Medetera sp. Drosophilidae .2 gen. & sp. indet. Phlebotomidae Phlebotomus sp. Sciaridae Bradysia sp. 241. APPENDIX I : Continued. Field Store HYMENOPTERA Braconidae (G.E.J. Nixon & I.D. Gauld - C.I.E.) Apanteles sp. Braoon hebetor Say Chelonus sp. Phanerotoma sp. Bethylidae (Z. Boucek) Cephalononria formiciform-is Westwood 1/2 Cephalonomia sp. 1/2 Holepyris hawaiiensis (Ashmead) 2 Plastanoxus westwoodi (Kieffer) 2 Rhabdepyr-is zeae Turner & Waters ton 1/2 Ceraphronidae (N. Fergusson - C.I.E.) Aphanogmus sp. Chalcididae (Z. Boucek - C.I.E.) Antrocephalus crassipes Masi Antrocephalus nritys (Walker) Antrocephalus sp. Euchalci&ia sp. nr. microgastricidia Steffan Diapriidae (Z. Boucek) Triohopria Bp. Encyrtidae (J.S. Noyes - C.I.E.) 1/2 Zetet-icontus laevigatus (De Santis) Eucoilidae (Cynipoidea (J. Quinlan - C.I.E.) Rhoptromeri-s sp. 2 Eupelmidae (Z. Boucek) Bruohocida vuilleti Crawford 2 Eupelmus urozonus Dalman 1/2 Maoroneura sp. 2 Formicidae (B. Bolton - C.I.E.) Dorylus (Anomma) sp. .. 3 . Monomorium sp. (pharaonis-group) 2 Myrmicaria sp. ' 1/2 242. APPENDIX I : Continued. Field Store Odontomaohus troglodytes (Santschi) 3 Paohyoondyla senaarensis (Mayr) 3 Pheidole sp. 1/2 Tetramoriwn caldar-ium (Roger) 3 Ichneumonidae (I.D. Gauld) Allophrys sp. 2 Pteromalidae (B.R. .Subba Rao - C.I.E.) An-isopteromalus oalandrae (Howard) 1/2 ' Cerooephala d-inoderi, Gahan 1/2 Choetdsp'Lla elegans Westwood 1/2 Habroeytus oerealellae Ashmead 1/2 Mesopolobus sp. 1/2 Scelionidae (I.D. Gauld) Gryon sp. 2 Telenomus sp. 1/2 ACARINA ASTIGMATA (det. D. Griffiths -M.A.F.F.) Acaridae Tyrophagus putresoentiae (Schrank) PROSTIGMATA (det.' S. Lynch - M.A.F.F.) • Anystidae Anyst-is sp. Cheyletidae Cheletomorpha lepidopterorum (Shaw) Pyemotidae Paracarophenax sp. Tarsonemidae Tarsonemcrides sp. Pseudotarsonemozdes sp. 243. APPENDIX I : Continued. Tydeidae ITydeMs sp. CRYPTOSTIGMATA (det. D. Macfarlane - B.M. (N.H.)) Scheloribatidae Soheloribates sp. MESOSTIGMATA (det. S. Lynch & C.E. Bowman - M.A.F.F.) Ascidae Blatt-isoovus tarsalis (Berlese) Proctolaelaps sp. Typhlodromus sp. Phytoseiidae Ambtyseius sp. Note I : In cases where identifier's name is followed by "C.I.E.", specimens were identified through the Commonwealth Institute of Entomology identification service, although in some case the identifiers were British Museum (N.H.) staff. Other institutions abbreviated above are as follows- - T.S.P.C. : Tropical Stored Products Centre (0:D.A.), Slough; M.A.F.F. : Slough Laboratory, Min. of Agriculture; N.S.P.R.I. : Nigerian Stored Prodjcts Research Institute; I.A.R. : Institute of Agricultural Research and Training, Samaru, Nigeria; B.M. (N.H.) : British Museum (Natural History). Note 2 : Classification in right-hand columns: 1 : abundant or common species. 2 : frequently recorded species 3 : occasionally recorded (for further explanation - see below) The above list is not complete (a small number of Hymenoptera and Coleoptera remain unidentified) but includes all species that were freqently recorded. The numbers in the right-hand columns are intended to provide an indication of the status of each species in the insect community, both . 244. APPENDIX I : Continued. pre-harvest ('field') and in the cribs ('store'). The categories do not relate to particular levels of abundance or numbers of records but are based on a subjective assessment of the information collected in all trials over a two year period. In category one are all species that were sufficiently abundant to cause or contribute to significant grain damage; also included are those species (mainly predators and parasitoids) which, though present in smaller numbers seem likely to have played a part in the ecology of economically important species. Category 2 comprises those species which did not achieve pest status but which were recorded sufficiently regularly to indicate that they had become established on the grain (or were at least frequent visitors from nearby habitats). This category includes a number of species that are apparently well adapted to the stored grain environment and which might well achieve pest status under slightly different conditions. . Category 3 includes species recorded on only one or a few occasions. It should .be noted that several of the species in the first two categories only occurred in significant numbers during a limited part of the storage season and were rare or absent at other times. The notes which follow are intended to be complementary to the inform- ation given in Chapters 4, 5 and 6 which dealt with the distributipn and seasonal incidence of most of the major species. Taxa are considered in the order presented above. Records for many of the insect groups associated with stored products in West Africa have not been collated and so comments on possible new records below must be regarded as tentative. Useful lists or reviews including such records have been published by Forsyth (1966), 245. APPENDIX I : Continued. Cornes (1973), Haines (1974) and Aitken (1975). Heteroptera The abundance of Lyctoooris cochici and Scolopoides divareti. is of interest. Lyctoooris campestris and two species of Xyloooris have been recorded from stored products in Nigeria (Cornes 1973) but these two species recorded here do not appear to be well known (Ghauri, p.c.) and would seem to merit further investigation as potential biological control agents. Sootopoides seemed in laboratory culture to be more tolerant of _ . low humidity than Lyctoooris. Coleoptera Both Las-ioderma serrioorne (Anobiidae) and Araecerus fasciculatus (Anthribidae) are versatile storage pests known from a variety of commodities Both bred successfully on the maize variety used (i.e. a white 'dent* with a fluor^fendosperm) in single-species culture and appear to be potential pests. • Bastrichids, with the exception of Rhyzopertha, are usually regarded as more important for the damage they can do to the structure of the store than for that done to the stored commodity. In the experimental cribs, however, Bostryohoplites, Dinoderus and -Heterobostrychus all appeared to be feeding on the grain. Their large size and mode of feeding (moving along 'files' of grain, taking little material from each) meant that they caused considerable damage. Korynetes analis and Necrobia rufipes (Cleridae) are both recorded from Nigeria and the latter species is also known as a pest of copra and 246. APPENDIX I : Continued. animal products stored under poor conditions. In the maize cribs they were presumably acting as predators (see Aitken, 1975). Mioroprius oonfusus (Colydiidae) is widespread in Africa. It is usually found in association with bark- and wood-boring species but has been recorded from Nigerian groundnuts (Aitken, 1975). In the cribs it was presumably feeding on moulds. Corylophidae are known from rotting vegetation in natural habitats and their frequent occurence in the cribs probably also reflects the poor storage conditions. Among the Cucujidae, species of Cryptolestes other than C. pusillus and C. ferrugineus may well have been present but remained undetected due to the impossibility of examining critically more than a small fraction of the total collected. The frequent occurrence of Planolestes cornutus is of interest because previously it has usually been found in association with legume pods (Lefkovitch, 1962), and was 'indeed found in this habitat at the study site. Cylas puncticollis (Curculionidae) presumably strayed into the cribs from nearby fields of sweet potato while Pseudostenotrupis marshal'li, although recorded from various Nigerian stored products, is probably associated with palms- (Aitken, 1975) . Both Sitophilus zeamais and S. oryzae have been recorded from Nigeria and both can attack maize in single species or mixed populations. Only S. zeamais was recorded from the experimental cribs but the dissections necessary to distinguish the species were only carried out routinely during preliminary investigations: a small proportion of S. oryzae could thus have remained undetected,. but this seems'unlikely. 247. APPENDIX I : Continued. The four species of Histeridae recorded are of some interest. Various species of Caroinops are often found in stored products (including records from Nigeria - Cornes, (1973)) and Teretrius spp. are recorded as predators of wood-boring beetles (Aitken, 1975). These records from maize cribs, however, appear to be unusual. The last published record for Diplostix mayeti (as Carcinops mayeti) from stored produce appears to be from 1899 (Hinton, 1945; Halstead, 1969). Minthea rugicollis (Lyctidae) is found throughout the world attacking - especially wood and bamboo (Aitken, 1975). Maize seems to be an unusual substrate for it and it may have moved to the maize from the structure of the crib. Typhaea stercorea and Litargus balteatus (Mycetophagidae) are both well known from stored products in poor conditions but the frequent occurrence of a second Litargus sp. is of interest. The sp'ecies has not yet been determined and the name 'varius' used in the text (S6.4.2) appears to be invalid (Halstead,' p.c.)., Carpophilus species are frequently recorded in stored products, especially when these are damp or mouldy. C. binotatus, however, does not seem to have been recorded from this environment before although it was frequently recorded (in very small numbers) from the cribs. C. zeaphiZus was described from maize in Uganda (Dobson 1969) and has been found in cribs ih Kenya and Ethiopia (Haines, 1974). Its occurrence in the experimental cribs considerably extends the known distribution and adds to the evidence that it may be widespread in this habitat. 248. APPENDIX I : Continued. Hypothenemus spp. (Scolytidae) have been recorded from various other stored products and H. hampei is a pest of coffee. H. obscurus was quite common in the maize cribs and there appeared to be at least one other species present at times. The commoner Silvanidae have already been discussed (S6.4.2). The remaining species were only found occasionally and are probably 'accidentals1 from natural habitats, Alphitobius viator (Tenebrionidae) has on a few occasions been recorded in cargoes of African produce and has been -found in a maize- store in Ghana (Green, 1980). The other two Alphitobius species are more familiar, being cosmopolitan pests of cereal products in poor condition. Gonooephalum simplex is common in fields of cereals but rarely recorded from stores. Though found only occasionally in the cribs a considerable infestation was observed on a batch of rice at the study site that had b,een in store for a long period. Three of the Palorus species (P. sub- — depressus3 P. fioioola and P. cerylonoides) are familiar from stored products, although P. cerylonoides is mainly an Oriental species (Halstead, 1967). • Palorus bobiriensis3 P. carinicollis and P. crampeli have all been found in West Africa in natural habitats but have not previously been recorded from stored products (Halstead, pers. comm.). Tribolium anaphe is widespread in Africa and has previously been recorded in small numbers in stores in Nigeria (Howe, 1952), but T, semicostata (= T. giganteum) has not been found in stored products before (Halstead, pers. comm.). Lepidoptera .All the Lepidoptera recorded are well known from stored maize or from the field crop although, as mentioned in the text, the abundance Pyroderces 249. APPENDIX I : Continued. sp. at the time of harvest was unusual. Diptera Among the Diptera, Medetera sp. (Dolichopodidae) does not seem to have been found previously in stores (Dyte, pers. comm.) but other predatory flies, especially Scenopinus fenestrates (Scenopinidae), are commonly found in warehouses (Hinton & Corbet, 1975). Hymenoptera The commonly occurring Hymenoptera have already been discussed (S6.4.5). The Bethylidae and Pteromalidae recorded here are all well known from stored products as is Braoon hebetor. The incidence of more 'marginal1 species is, however, difficult to assess in the absence of a convenient published collection of records. Bruchocida Vuilleti, has previously been recorded from stored cowpeas and soya beans in Nigeria (Cornes, 1973) although not, apparently from maize. Aphanogmus sp. (Ceraphronidae) and Gryon and Telenomus spp. (Scelionidae) were all common or abundant at times in the cribsVbut do not seem to be mentioned in the recent stored products literature; the association of Telenomus sp. with eggs of Dieuohes (Het., Lygaeidae) has already been noted ( 6.4.5). Allophrys sp. (Ichneumonidae), which was recorded several times in small numbers, appears to belong to an underscribed species which has been collected from other localities in Africa (Gauld, pers. comm.); other Tersilochinae are known to be parasites of coleoptera larvae, especially Curculionidae and Bruchidae. Material of all the species listed above has been deposited at the Tropical Stored Products Centre (Slough) or, in the ca e of less common species, at the British Museum (Natural History)". 250. APPENDIX II : Collated Data - Succession Studies. Data given are numbers of insects collected on samples of cobs from the centre of cribs on successive occasions during the storage season. For details see Chapter 6. Data on insect numbers presented here have been corrected arithmetically to standard sample weights as indicated, using the sample data presented at the head of each column. Shelling indices were estimated from the initial and final observed values and assuming a linear change with time. Cribs were as follows: location treatment starting date Wet Season A Ibadan untreated 16th Aug. 1978 B C Ibadan fumigated D E Ilora fumigated 23rd Aug. 1978 F. Dry Season . L 'Ibadan untreated 8th Jan. 1979. M 'Time Scale' on data sheets is in days, starting at 1st August 1978 = 0 for the wet season cribs (A - F) and at 8th January 1979 = 0 for the dry season cribs (L - M). 251. SEQUENT IflL SAMPLES Crib A IITfi 1978 Wet Season Number of insects corrected to 1000 grams at 13 moisture content • Samp 1e 1 2 3 4 5 6 7 8 9 10 Time scale 30 44 58 72 180 128 176 204 233 292 Samp 1 e welght 5300 3175 2664 2638 2542 2219 1668 1358 1347 1265 Moisture content 19.5 17.0 17.0 16.5 15.9 14.1 12.0 12.0 12.2 13.9 Core moisture content 21.1 17.2 17.6 17.3 16.4 11.8 10.9 9.2 12.O 12.3 Estimated shelling 86 86 86 85 85 83 82 81 81 <56 Lasioderma ser^i cornt 0 0 0 0 + 0 0 0 0 0 Rraecerus fascicul-ins +• 0 1 1 + 1 0 1 0 2 Heterobostrychus brunneus 0 0 0 0 0 1 0 1 0 0 indet. Cory1ophidae. 1 0 0 0 0 0 0 ' 0 0 y C. pusl11 us 0 1 1 2 4 Placonotus politissimus 0 . 0 3 0 + indet. Cucujidae 26 134 261 165 91? total Cucujidae 0 1 5 2 4 26 134 261 165' 91? Si tophi 1 us sp. 8 121 222 480 502 574 1353 1849 1115 L. ?varius 1 + + 2 0 0 0 0 0 0 Typhaea stercorea 0 0 0 0 0 0 0 0 0 1 7 C. dimidiatus 11 22 32 26 33 13 9 8 C. fumatus 21 17 16 19 15 0 0 0 C. maculatus 0 • 0 0 0 0 0 0 C. pi 1ose11 us 0 0 1 0 0 0 0 0 Cf zeaphi1 us + ^0 0 0 + 0 0 0 indet. Carpophilus 53 213 total Ni t i duli dae 33 40 49 44 49 13 9 o 53 213 Hypothenemus sp. 0 0 0 0 0 2 0 0 1 2 Cathartus quadricollis 12 27 35 48 31 31 6 2 1 22 Monanus ?concinnu1us 5 14 6 6 9 4 1 0 1 Oryzaephilus rnercator 0 0 0 + 2 5 5 2 2 0 Silvanus inarmatus + 0 0 0 0 0 0 0 0 0 tot al S i1vanidae 18 41 41 54 42 41 13 4 4 24 Coproporus sp. 0 + 0 0 0 0 0 0 0 0 total Staphy 1 i ni dae 0 + 0 0 0 0 0 0 0 0 Gnatocerus maxillosus + 0 1 0 + 7 11 153 28 122 P. fi c i col a 0 0 0 0 0 0 0 8 1 4 P. subdepressus + • 0 3 7 10 40 40 37 89 Tribolium castaneum 0 1 + 0 + 3 6 6 0 20 T. confusum 0 0 0 0 0 0 0 3 1 " lo total Tenebrionidae + 1 2 3 8 20 57 210 67 245 indet. Coleoptera • 0 0 0 0 0 1 0 0 0 0 TOTAL COLEOPTERA 62 1*30 220 329 534 606 786 1S37 1344 2537 Sitotroga cerealella + + 2 3 4 14 6 5 4 TOTAL LEPIDOPTERR ADULTS + + 2 3 4 14 6 5 4 9 Cardiastethus sp. + 1 0 + . 0 0 1 0 1 1 Lyctocoris cohici 1 3 S 5 13 12 0 0 0 0 indet. Anthocorid nymphs 1 2 12 .16 13 1 0 0 1 0 Peregrinator biannulipes 0 -0 0 0 0 0 0 0 0 5 indet. Emesinae 0 + 0 0 0 0 0 £1 ' 0 0 P. biannulipes nymphs 0 0 0 0 0 0 0 .4 49 tot predatory Heteroptera 1 4 8 5 13 12. 1 0 1 £ tot pred Heteropt. nymphs 1 2 12 16 13 i 0 0 5 49 Mizaldus sp. 0 + * 1 14 : 9 4 1 0 0 0 indet. Lygaeid nymphs + 2 20 2 . 37 v -V 0 0 0 0 indet. Heteroptera 0 0 0 0' + 1 0 1 0 o tot phytophag Heteroptera 0 + 1 14 9 4 1 0 0 tot phy'o Heteropt nymphs + 2 20 2 37 2 0 0 0 0 TOTAL HETEROPTERA 1 5 9 • 19 22 17 1 1 1 f TOT HETEPOPT NYMPHS 1 3 32 18 51 3 0 0 5 4 9 TOTAL DIPTERA 0 0 0 + + 0 G 0 0 0 Br acon hebetor- 0 0 0 + 0 0 0 0 0 0 indet. Chalcididae e 0 • 0 0 0 0 0 0 0 Rhabdepyris zeae 0 0 0 0 0 1 3 2 Ci 16 i ndet. Bethy1i dae 0 0 1 0 5 8 4 1 26 total Bethylidae 0 0 + 1 0 6 1 1 5 10 42 Zeteticontus laeuigatus I 2 -5 6 0 0 0 0 0 0 Eupelmus urozonus O 0 + 0 + 1 4 ? 0 4 Anisopteromal us calandrae 0 1 + 1 2 i 4 0 2 Cerocephala dincderi 0 0 0 0 0 i? 4 5 j 3. Cnoetospiia elegans 0 0 + + 5 25 19 31 29 215 •Habrocy t c e.real e 1 1 ae 0 0 C 0 0 0 12 19 4 4 Mesopolobus sp. 0 0 0 0 0 0 0 0 1 4 to' Pt-• roma= l i dae 0 1 1 2 s 26 37 55 4-y 25 :• Gr yOn sp. 0 0 0 0. 0 0 0 0 1 Tfi J e nofiius -p. 0 + O 0 0 0 0 0 0 0 i ndr t. Hyr» noo'e . er a 0 r- o * o •1 0 0 0 0 TOT HYMEHOPT FAr'ASITES 1 -- 3 * 6 . 9 8 '52 6 3 50 305 TOT HYMENC'PT FORMIC I DAE 0 . O 0 0 0 0 0 0 0 ' " 1 TOTAL PSOCOPTERR • + £ 2 adu It Blattidie 0 + j . i? 0 0 0 0 IJ 0 TOTAL DIC TYC'PTERR 0 • + 0 0 0 • 0 0 0 i' 0 TOTAL IHSECTR 1'3S 2 ; * ?60 619 1 9 O 7 1 393 i 'C OTHEP ARTHROPOD* 0 + • 1 4 ft 1 r< SEQUENT IRL SAMPLES Crib B IITA 1973 Wet Season ftDULT CO JUTS Number of insects corrected to 1800 gra ms at 13 'IIOI • jr e ont S fi r. Sample 1 2 3 4 5 tf. 7 3 C. ly Time scale 30 44 53 72 100 128 1 76 204 2 22 281 Sample weight 4700 3 170 2 585 2543 2423 2 365 15 24 12 124? 1 193 Moisture content 19.0 16.9 1 6.9 16.4 15.8 1 3. 3 12 8 1 1 . 6 11.5 13.? Core moisture content 19.9 17.2 1 7.9 17.5 16.3 11.6 10 . Ct 8 . 9 11.6 12.5 Estimated shelling v. 86 86 85 85 84 81 S 0 SO ct Lasioderma serricorne 0 1- 0 0 0 0 0 0 1 3 Araecerus fasciculatus 0 l 1 2 1 1 0 0 1 0 indet. Corylophidae 1 l 0 0 0 0 0 0 0 0 C. pus i11 us 0 + 0 1 1 16 152 Placonotus po1itissimus + + + 0 0 0 0 indet. Cucujidae 1 74 1 76 r 5i* total Cucujidae • l • 1 1 16 1 -•2 174 176 S i t oph i1 us sp. 16 63 139 244 457 596 14 68 24 47 1350 Platysoma castanipes 0 0 0 0 1 0 0 0 0 0 Lyctus brunneuj 0 0 0 0 0 0 1 0 0 >5 L. ?uarius 1 l 1 1 0 0 0 0 0 0 Typhaea stercorea 0 0 0 0 0 0 0 0 0 24 Brachypeplus ?gabonensis + 0 0 0 0 0 0 0 0 y C. dimidiatus 15 27 23 50 33 23 6 C. fumatus 21 31 36 33 25 0 0 indet. Carpophilus 0 107 296 total Hi t i dul i dae 36 58 59 83 58 23 6 0 107 2 91 Hypothenemus sp. + 0 0 0 1 0 0 2 0 Cathartus quadricollis 17 30 34 30 29 49 42 0 0 2 5 Monanus ?concinnu1us 7 16 7 5 5 4 2 0 0 0 Oryzaephilus mercator 0 1 0 + 2 8 1 0 0 0 total Si 1 wan i dae 23 47 41 36 35 61 4 5 0 0 25 Gligota chrysopyga 0 0 0 0 1 0 0 0 0 0 total Staphylinidae 0 0 0 0 1 0 0 0 0 0 Gnatocerus maxillosus 0 + 0 0 1 3 30 81 41 147 P. f i c i col a 0 0 0 0 0 0 2 3 2 Ci P. subdepressus •4- 3 3 2 10 Q 30 13 oc- 105* Sitophagus hoioleptoides 0 0 0 0 0 1 0 0 0 0 Tribolium castaneum 0 • 0 + 0 2 6 5 2 16 T. confusum 0 " 0 0 0 0 0 0 0 2 3 total Tenebrionidae + 3 3 3 11 14 63 • 1 02 72 271 indet. Coleoptera 0 0 0 0 0 0 0 1 0 >3 TOTAL COLEOPTERA 78 176 245 371 565 711 i:"4 0 2724 1710 235'? Sitotroga cerealella 0 0 1 1 11 24 16 1 2 5 Eldana saccharma + 0 0 0 0 0 0 0 0 0 TOTAL LEP.I DOPTERA RD'JLTS + 0 1 1 1 1 24 16 1 2 5 Lyctocoris cohici 1 6 9 13 14 1 0 0 0 0 Xyltjcorjs afer • 1 0 0 0 0 0 0 0 1 indet. Anthocorid nymphs 1 8 18 29 3 1 0 0 0 0 P. biannulipes nymphs 0 0 0 0 0 0 0 i3 1 r> HA 78 16 • ' 0 0 0 0 0 0 2 8 1 C o HA 78 16 nymphs . 0 0 0 0 0 0 1 . 0 2 oc tot predatory Heteroptera 2" 7 9 13 14 ' • 1 2 3 1 c q tot pred Heteropt. nymphs 1 s 1 3 29 8 1 i 0 3 91 Mizaldu^ sp. 0 • 1 3 10 6 * 5 0 0 0 0 indet. Lygaeid nymphs 1 4 32 27 26. 9 1 0 0 1 indet. Heteroptera 0 + 0 0 0 0 0 1 0 0 tot phytophag Heteroptera 0 1 3 10 6 5 0 0 ' 0 0 rot phyto Heteropt nymphs 1 4 32 2 7 26 Ct 1 0 0 1 TOTAL HETEROPTERA 2 8 12 2 5 1 ? £ 2 9 1 59 TOT HETEROPT NYMPHS 2 12 50 56 34 10 2 0 3 9 2 TOTAL DIPTERA 0 0 -> 0 0 0 0 0 0 0 Bracon hebetor 0 0 0 + 0 0 0 0 0 0 Rhabdepyris zeae 0 0 0 0 1 2 4 4 10 1 0 i ndet. Bethy1i dae • 0 1 1 1 1 2 0 1 12 total Bethylidae + 0 1 1 2 2 6 4 : I 22 Zeteticontus laevigatus 1 1 2 4 0- 0 0 0 0 0 Eupelruus ur'ozonus 0 + 0 + 2 4 2 2 2 2 An i sopt erorn al us calandr-ae 0 2 + + 1 3 2 0 0 0 Cerocephala dinoderi 0 0 0 0 0 5 1 0 1 27 Choetospila clegar.s 0 1 2 1 2 11 1 9 40 1 14 Habrocytus cerealellae 0 0 0 0 0 1 8 f 1 0 Mesopolobus sp. 0 0 0 0 0 0 2 0 0 1 t ot. Pt eromal i d ae • 0 3 2 2 2 1 9 21 1 3 42 1 42 Telenomus sp. 0 + 0 0 0 0 2 0 0 indet. Hvmenoptera 0 0 • .0 0 0 1 0 0 0 TOT HYMENdPT PARASITES 1 5 6 9 6 26 .c 1 r y, 1 65 •total psocoptera 13 17 20 adult Elattidae 1 0 + 0 . 1 .j . 0 0 0 0 TOTAL BlCTYGPTERfi 1 0 + 0 0 0 0 TOTAL IN2ECTA SI. 129 268 6 1 r.67 j 2 0 1 • 2 ~ = i 1 7.2 2 j 5 2 9 1 OTHER ARTHROPOD* ' . - y 1 2 0 * 1 253. SE01JEN.T 1A.L SAMPLES .... Crib C I I T A 1973 l-Jet 3sa=ori HDULT COUNTS Number of insects corrected to 1000 grams at 13 -moisture content Samp 1e 1 2 1 0 Time scale 30 44 1 00 128 176 204 23 3: Samp 1e ueight 4975 3094 !534 2426 2321 :iS9 1345 124 5 1106 1142 Moisture content 20.5 17.9 16.7 16.1 14.0 1 12.2 11.5 14. l Core moisture content 22.2 19.3 19.4 18.7 17 l; 11.9 12.1 12.9 Estimated shelling ': 86 86 85 85 82 30 Araecerus fasciculatus 1 2 + 2 2 2 I 0 0 0 Dinoderus minutus 0 0 0 0 1 0 l •J 1 0 Het. erobost rye hus brunneus 0 0 0 0 0 1 0 0 1 0, indet. Carabidae 0 + 0 0 0 0 0 0 0 0 indet. Corylophidae 1 1 0 0 0 0 0 0 0 0 C. pus i11 us 0 0 1 0 2 21 216 Placonotus politissimus 0 0 0 1 0 0 0 indet. Cucujidae 243 176 625 total Cucujidae 0 0 1 1 2 21 216 248 176 625 Sit oph i1 us sp. 5 31 66 139 526 990 2426 4120 194 2 2333 L. ?varius 0 0 + 0 0 0 U 0 0. 0 Mycetaea hirta 0 + 0 0 0 0 0 0 0 0 Typhaea stercorea 6 0 1 0 0 0 0 0 0 25 B. ?pi1osel1 us + 1 + 1 0 0 0 0 0 0 C. dimidiatus 17 56 64 50 59 46 2 5 C. f r e e m an i 1 + 0 1- 0 0 0 C. fumatus 46 33 36 30 1 1 1 0 C. pi 1ose11 us + 0 0 0 0 0 0 C. zeaphi1 us 0 0 + 0 0 0 0 indet. Carpophilus 32 48 24 9 total N i t i du1i dae 64 90 01 81 71 47 25 3 2 48 249 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 1 Ahasuerus advena 0 1 2 0 1 0 0 0 0 4 Cathartus quadricollis 14 40 33 69 53 183 27 1 131 31 1 1 1 Monanus ?concinnulus 2 12 42 28 14 11 1 0 0 1 Oryzaephilus mercator 0 0 + . 2 3 11 3 5 0 4 total Silvanidae 17 53 77 99 71 205 275 136 31 1 19 Oligota chrysopyga 0 1 1 0 0 0 0 0 0 0 total Staphylinidae 0 1 1 0 0 0 0 0 0 0 Alphitobius sp. 0 0 + 0 0 0 0 0 0 0 Gnatocerus maxillosus 0 0 • 0 2 6 43 344 58 169 Palembus iuoirensis 0 0 0 0 0 ' 0 0 0 0 1 P. ocularis 0 0 0 0 0 0 1 0 0 0 P. fi c i cola e 0 0 0 0 0 0 0 1 2 P. subdepressus 8 1 . 0 0 9 32 259 302 222 4 97 Sitophagus ho 1o1eptoides 0 0 0, 0 0 1 5 0 0 1 3 Tribol.ium castaneum 0 + 2' 3 1 12 18 1 1 4 5 T. confusum 0 0 0 0 0' -e 0 1 0 total Tenebrionidae 0 1 3 3 1 1 51 2 h & • fr : 21 7 6 33 indet. Coleoptera 0 0 0 0 0 0 I 0 0 0 TOTAL COLEOPTERA 87 1S1 :5i 324 632 1317 3270 5194 2436 4 0 3 9 Sitotroga cerealella 0 0 0 0 0 0 0 1 0 0 E. cautella larvae 0 0 0 0 0 0 0 0 0 1 TOTAL LEPIDOPTERA ADULTS - 0 0 0 - 0 0 0 0 1 • 0 0 Cardiastethus sp. •f 3 4 4 0 0 . 3 0 0 Lyctocoris cohici 0 1 4 6 14 2 . 0 . 0 0 0 indet. Anthocorid nymphs .0 2 8- 28 13 0 0 . 0 ' 0 0 Cethera musiva 0 0 0 0 0 0 1 0 0 Peregrinator b'annulipes . 0 0 0 0' 0 ,0 0 0- 1 IS indet. Emesinae 0 + 0 1 0 'O 0 0 0 1 P. biannulipes nymphs 0 0 . 0 . 0 0 0 0 0 23 -f HA 78 16 0 0 0 0 0 0 0 0 0 1 tot predatory Heteroptera •f 4 8 10 14 2 4 0 1 20 tot pred Heteropt. nymphs 0 2 8 28 13 0 0 0 3 76 Dieuches ?armatipes 0 0 • 0 2 3 0 0 0 0 Mizaldus sp. 0 0 + 0 0 2 0 0 0 0 indet. Lygaeid nymphs 0 1 0 0 2 23 0 0 0 4 indet. Heteroptera 0 0 0 0 • 0 1 0 0 0 0 tot phytophag Heteroptera 0 0 1 0 3 5 0 . 0 r- tot phyto Heteropt nymphs 0 1 0 0 2 23 0 0 0 4 TOTAL HETEROPTERA + 4 9 10 1 7 4 0 1 20 TOT HETEROPT NYMPHS 0 4 8 28 15 23 0 2 3 79 TOTHL DIPTERA 0 0 0 0 0 0 0 e 0 Rhabdepyris zeae 0 0 0 0 0 1 5 10 is' 74 i nde t . Bet. hy 1 i dae 0 0 0 1 0 . 1 1 a 21 106 total Bet hy1i dae 0 0 0 1 0 2 6 • 19 39 180 Zeteticontus lae^igatus 0 + 3 1 1 2 0 0 0 0 Eupelmus urozonus 0 0 0 0 1 4 2 0 1 0 Anisopteroma'us calandrae 0 0 + 0- 1 3 5 2 1 1 Cerocephala dinoderi 0 0 0 0 0 0 3 '4 2 3 .3 Choetospila e1egans e " 0 0 0- 1 2 28 54 4 T 264 Habrocytus cerealellae 0 0 0 0 0 0 0 , 1 0 - Mesopolobus sp. 0 0 0 0 0 • 0 0 » ''0 1 4 tot Pteromalidae 0 •0 •f 0 2 6 3 6 6: . 5 3 303 TOT HYMENOFT PARASITES' 0 4 . 2 3 14 4 3 >, 0 93 4 ; TOT HYMENOFT FORMIC 11AE 0 T 1 3 - 2 r> 2 1 TOTAL P-SOCOFTEFA 0 10 2 1 5 3 ' aault Blatti o 0 0 0 0 0 0 • 0 ij TOTAL DI C'TYOF TERh • 0 0 0 0 0 0 0 0 0 TOTAL I MSEC T A - 1 : ! : 6 5 34 1 705 i: 41 3 3 1 9 25S 1 4^47 OTHER ARTHROPODA 0 2 0 4 2 • = • 3 14* SEQUENTIAL SAMPLES Crib D IITA 1978 t-J • t= Seas or. ADULT CO'JNTS 254. Number of insects corrected to 1000 qrami 1 3 mo l 11 -jr e c oni ;ri' Samp 1e 1 6 10 T i r» e scale 30 44 100 1 28 176 Sample weight 4650 2591 2180 2125 204 9 12 4 0 1 1 55 1 144 1 4 Moisture content 19.4 1 7. 317. 2 16.4 16.1 13.8 12.8 12.1 11.6 14.1 Core moisture content 20. 8 19.0 17.8 17.8 17.2 12.3 11.9 9.4 12.4 13.1 Estimated shelling *: 36 86 36 85 84 81 81 Araecerus fasciculatus + 2 2 2 2 3 0 0 0 Dinoderus minutus 0 0 1 0 0 1 0 1 C) indet. Corylophidae 1 4 0 0 0 0 0 0 0 0 C. pus i11 us 0 0 0 1 18 148 Placonotus politissimus 1 0 0 0 0 0 0 i ndet. Cue uj i dae 336 8 3 44; total Cucujidae 1 0 0 1 2 18 148 3 26 33 442 S i t oph i1 us sp. 4 36 75 172 629 1350 2O03 1839 1590 2035 Lyctus brunneus 0 0 0 0 0 1 0 0 0 L. ?varius 0 1 0 0 0 0 0 0 0 0 Mycetaea hirta + + 0 0 0 0 0 0 0 o Typhaea stercorea 0 0 0 0 2 1 0 0 0 1 B. ?pi1osel1 us 2 0 0 0 0 0 0 0 o C. di mi di atus 11 38 61 59 84 62 C. fumatus 51 42 32 1 1 35 0 C. p i1ose11 us + 0 0 0 0 0 C. zeaphi1 us 2 0 0 1 0 0 indet. Carpophilus 30 21 87 40.5 Lasiodacty1 us sp. 0 + 0 0 1 0 0 0 0 0 t ot al Ni t i duli dae 66 80 93 71 119 62 30 21 37 405 Hypothenemus sp. 8 0 0 0 B 0 3 0 0 0 Ahasverus advena 0 + 0 0 0 0 0 0 0 Cathartus quadricollis 22 31 55 103 41 88 127 73 9 5 105 Monanus ?concinnu1us 1 6 30 20. 23 ' 14 1 0 1 4 Oryzaephilus mercator 0 0 2 1 3 T !> 22 2 3 total Silvanidae 23 37 87 125 67 114 149 75 96 120 Oligota chrysopyga 0 1 2 2 0 0 0 0 0 0 total Staphylinidae 0 1 2 2 0 0 0 0 0 0 Gnatocerus maxillosus + 0 1 1 2 9 86 419 51 34? Palembus ivoirensis 0 0 0 0 0 1 1 3 2 0 P. oculari s 0 0 0 0 e 1 7 1 •> P. fi c i col a 0 0 0 0 0 0 0 2 1 P. subdepressus 1 + 0 2 13 34 205 193 116 403 Sitophagus ho 1oleptoides ' 0 0 0 0 0 0 2 3 0 Tribolium castaneum 1 0 1 0 1 7 22 o 3 T. c onf usum 0 0 0 0 0 0 0 1 0 2 indet. Tenebr.i oni dae 0 £ 0 0 1 0 0 0 0 total Tenebrion 1dae 2 1 + 1 18 53 322 631 177 7&( indet. Coleoptera 0 0 0 0 1 0 0 1 0 TOTAL C0LE0PTERA 97 • 162 261 •375 839 1601 2656 2905 2034 jo 3 (j Sitotroga cerealella 0 0 1 , 0 0 0 0 1 2 C. leucotreta larvae 0 0 1 0 0 0 0 0 0 total Lepidoptera larvae 0 0 1 0 0 . 0 0 0 0 TOTAL LEPIDOPTERA ADULTS 0 0 1 0 0 -0 0 1 Cardiastethus sp. .+ + 1 0 2 0 4 1 Lyctocoris cohici 1 6 21 . 16 10 9 0 0 0 O indet. Anthocorid nymphs + 5 27 30 4. 3 0 0 0 0 indet. Emesinae ' 0 1 1 0 0 0 0 0 . £ 1 P. biannulipes nymphs 0 0 0 ' 0 0 0 0 0 0 5 indet. Emesinae nymphs • 0 0 0 0 0 • 0 0 0 0 . 1 HA 78 16 0 0 ' 0 . 0 0 0 0 12 1 tot predatory Heteroptera 1 8 22 16 12 * 9 4 14 3 tot pred Heteropt. nymphs + 5 27 30 4 3 0 0 0 Dieuches ?armatipes 0 0 0 1 1 0 0 0 0 0 Mizaldus sp. 0 0 0. 0 0 2 0 0 0 0 indet. Lygaeid nymphs 0 2 0 0 0 9 0 0 0 (k tot phytophag Heteroptera 0 0 0 ' 1 1 2 0 0 ,-i 0 tot phyto Hetenopt nymphs 0 2 0 0 0 9 0 0 y o TOTAL HETEP0PTERA 1 8 22 16 13 11 4 14 3 \ TOT HETEROPT NYMPHS + 7 30 4 13 0 0 0 c* Bracon hebetor 0 0 \o 0 0 .0 0 0 0 1 Rhabdepyris zeae 0 0 0 £ 1 J i = 0 0 0 * If indet. Bethylidae 0 0 0 0 0 0 6 2 3C total Bethyli dae 0 0 0 0 0 0 12 .5 12 45 Zeteticontus laevigatus 0 0 7 6 2 3 0 0 0 0 Eupelmus urozonus 0 0 0 1 ' 2 3 4 1 0 4 Anisopteromalus calandrae 0 + 1 i 1 5 1 0 0 1 Cerocephala dinoderi '0 0 0 0 0 2 10 4 =: 20 Choetospila elegans c : 0 0 0 1 Number of insects corrected to 1000 grams at 13 moist ore :on*«nt Sample 1 2 3 4 5 6 7 3 Time scale 37 52 65 79 107 1 3 6 183 212 Sample weight 4419 3875 2278 2242 2125 19 64 1361 13 09 Moisture content 19.3 16.7 15.6 16.2 13.4 1 1 . 9 11.3 11.7 Core moisture content 21.5 18.5 16.3 16.9 12. 7 10 . 2 ci # 9 • ? Estimated shelling ^ 87 86 85 85 84 8 3 82 81 LasiOderma serricorne 0 0 1 2 0 0 1 0 Araecerus fasciculatus 1 2 5 1 2 5 0 0 indet. Corylophidae 1 0 0 0 0 0 0 0 Cryptolestes ferrugineus 0 0 0 1 C. pus i11 us 1 0 2 6 Placonotus politissimus 1 + 0 0 Planolestes ?cornutus 0 0 0 0 0 0 0 1 i ndet. Cucuj i dae 18 51 96 514 + 2 7 51 96 515 total Cucujidae 1 . 18 Si tophi 1 us sp. 87 114 135 308 869 9 8 0 1427 S O 3 Platysoma castanipes 0 0 0 0 0 0 O 2 L. 'wariui 1 0 0 0 0 0 0 0 Typhaea stercorea . .. . 0 + 0 2 1 2 0 0 C. d i m i d i at us 1 4 8 5 6 2 0 0 C. fumatus 4 16 -> -> 0 0 0 0 indet. Carpophilus 0 0 0 0 1 0 0 0 tot al Ni tidulldae 5 19 16 1 1 7 2 0 0 Ahasverus advena 0 + 0 0 0 0 0 0 Cathartus quadricollis 8 16 31 20 Q 1 4 0 Monanus ?concinnulus 0 + 1 1 1 2 0 0 Oryzaephilus mercator 0 0 0 0 3 1 0 0 total Si 1 vani dae 8 16 31 20 12 5 4 0 Coproporus sp. 0 + 0 0 0 0 0 0 Oligota chrysopyga 0 0 0 1 0 0 0 0 \ot-al St aphy 1 i ni dae 0 + 0 1 0 0 0 0 Alphitobius sp. 0 0 1 0 0 0 0 0 Gnatocerus maxillosus 0 + 0 3 1 1 1 1 157 P. ocularis 0 0 0 0 0 Q 3 2 P. f i c i c o 1 a 0 0 0 0 0 1 4 4 P. subdepressus 3 8 12 13 34 81 114 112 Tr i bollurn cast aneum 2 1 1 2 • 9 16 1 1 13 T". c onf usum 0 0 0 0 0 0 0 3 total-Tenebrionidae 5 9 13 17 44 9? 1*4 2 291 indet.Coleoptera 0 0 1 0 0 1 0 O TOTAL COLEOPTERA J 08 162 253 368 954 1 145 1670 1616 Sitot-roga cerealella 0 0 1 0 0 0 0 0 TOTAL LEPI-DOPTERA ADULTS 0 0 1 0 0 0 0 0 Cardiastethus sp. • 1 2 3 1 0 0 5 Lyctocoris cohici • 0 2 7 16 4 0 0 indet. flnthocorid-nymphs • 0 2 0 18 3 0 0 0 indet. Emesinae ' 0 0 1 0 0 0 0 0 HA 78 16 0 0 0 0 " 0 2 0 0 tot predatory Heteroptera 1 2 5 7 16- 8 0 5 tot pred Heteropt. nymphs 0 2 0 18 3 0 0 0 Dieuches ?arr«a ti pes + + 0 1 0 2 0 0 ?Dieuches sp. 0 3 1 0 O 0 0 Mizaldus sp. 0 0 10 15 3 0 0 indet. Lygaeid nymphs 1 1 10 30 15 1 0 0 C tot phytophag Heteroptera + 3 -> 11 15 0 0 tot phyto Heteropt nymphs 1 1 10 30 15 1 0 0 TOTAL HETEROPTERA 1 5 12 18 31 13 0 5 TOT HETEROPT NYMPHS 1 3 10 43 18 1 0 0 tot Diptera larvae 0 0 0 0 0 2 0 0 TOTAL DIPTERA 0 0 3 0 0 0 0 0 i ndet. Bet hyIi dae 0 0 0 0 0 2 4 16 total Bethylidae 0 0 0 0 0 2 4 16 Zeteticontus laeuigatus 0 1 0 3 0 1 0 0 ej Eupelmus urozonus 0 + 0 2 4 1 3 Ar. i sopt eroma.l us calaridrae 0 1 2 3 3 2 10 2 Cerocephala dinoderi 0 •0 - 0 0 0 1 2 0 Choetospila elegans 1 3 2 5 7 16 12 : 4 tot Pteromalidae 1 4 3 8 ' 10 1? 24 16 Telenomus sp. • 0 0 0 2 4 2 2 0 indet. Hs'menopt er a 0 . 1 3 2 0 8 13 0 TOT HYMENOPT PARASITES. 1 7 6 IS 18 2 3 : 1 34 TOT HYMENOPT FORMICIDAE + 0 1 0 0 0 e 0 TOTAL FSOCOPTERA 3 2 14 adul t E I at t i dae ' 0 0 0 0 1 1 o 0 TOTAL DICTYOPTERA 0 0 0 0 1 1 ij 0 TOTAL INSECTA 110 •1.74. 275 4 02 1 0 0 3 '1 i S7 1-700 '1635 SEQUENTIAL SAMPLES Crib F 11 ora 1978 Uet Season Number of insects corrected to 1008 grams at 13 rn o is t ur e content Samp 1e 1 2 3 4 5 • 6 7 3 Time scale 37 52 65 79 107 136 183 212 Sample weight 4856 4258 2227 2172 2050 1885 1322 1 262 Moisture content 18.9 16.9 15.6 16. 0 13.5 11.7 11.3 11.3 Core moisture content 28.6 18.3 16.7 16. 7 12.6 10.2 10. 1 10.5 Estimated shelling '/. 86 86 85 85 84 83 81 80 Lasioderma serricorne 0 8 0 1 8 0 2 0 Araecerus fasciculatus 1 3 6 € 5 1 0 0 Heterobostrychus brunneus 8 8 0 0 0 1 0 0 indet. Corylophidae 1 0 1 1 0 0 0 0 C. pusi11 us 1 1 3 2 Placonotus politissimus 1 1 0 0 Planolestes ?cornutus 8 8 0 0 0 0 0 2 indet. Cucujidae 20 54 230 489 totarl Cucujidae 1 2 3 2 20 54 230 491 Si tophi 1 us sp. 48 69 162 309 &72 849 2259 1567 Litargus balteatus 8 8 8 0 1 0 0 0 Typhaea stercorea 8 1 2 1 5 2 3 1 B. ?pi1osel1 us + 8 8 0 0 0 0 0 C. di mldi atus 2 2 8 4 7 1 0 0 C. fumatus 8 5 8 3 0 8 0 0 C. pi 1ose11 us + 1 8 0 . •1 0 0 0 total Ni t i dulidae 11 8 16 7 8 1 0 0 Cathartus quadricollis 9 17 23 10 3 1 4 2 Monanus ?concinnu1us • 8 7 2 0 8 0 0 Oryzaephilus mercator 8 8 8 0 1 2 2 1 total Silvanidae 9 17 38 11 4 3 r 3 Gnatocerus maxillosus 8 8 1 0 1 1 5 152 P. ocularis 8 0 8 0 0 1 0 2 P. fi c i col a 8 8 8 1 1 1 5 7 P. subdepressus 3 4 4 15 47 36 153 115 Tribolium castaneum 1 1 1 3 4 8 21 51 T. confusum 8 8 8 0 0 8 5 9 total Tenebrionidae 3 5 6 18 52 47 189 336 i ndet.Coleopt era 8 8 1 0 8 0 1 1 TOTAL COLEOPTERA 66 185 228 356 965 959 2689 2399 Cardiastethus sp. 8 1 4 2 0 0 4 0 Lyctocori3 cohici 8 8 2 5 16 2 8 0 indet. Anthocorid nymphs 8 8 0 1 1 0 0 Cethera musiva 8 8 0 0 *1 0 0 0 Hfl 78 16 8 .0 8 0 0 1 3 0 tot predatory Heteroptera 0 1 7 7 16 3 6 0 tot.pred Heteropt. nymphs 0 8 0 1 1 8 • 0 Dieuches. ?armatipes 1 1 8 2 1 1 8 0 ?Dieuches sp. 8 2 6 1 1 0 • 8 0 tlizaldus sp. 8 1 6 9 15 1 8 0 indet. Lygaei-d nymphs + 3 20 ' 1-? ' 1 8 0 indet. Heteroptera 8 8 1 0 <3 0 8 0 tot ph'ytophag Heteroptera 1 4 12 12 18 2 8 0 tot* phyto Heteropt nymphs • 3 20 19 . 1 0 0 TOTAL HETEROPTERA 1 5 19 19 34 4 6 0 TOT HETEROPT NYMPHS + 3 20 21- • 2 0 • 0 TOTAL HOMOPTERA 0 0 1 0. 0 0 0 0 tot Diptera larvae 8 0 0 0 0 . 4 0 0 TOTAL DIPTERA 8 0 5 0 0 0 8 0 indet. Bethylidae 8 0 0 0 0 2 12 25 total Bethyl1dae 8 0 0 0 0 2 12 £. -' Zeteticontus laevigatus 8 0 1 1 • 1 0 0 0 Eupelmus urozonus 0 • 0 1 •y 3 5 2 finisopteromalus calandrae ' 0 0 2 1 1 4 8 4 Cerocephala dinoderi 8 0 0 0 0 2 2 2 Choetospila elegans 8 1 3 2 4 10 22 1 8 Habrocytus cerealellae 8 0 0 8 0 0 0 1 Mesopolobus sp. 8 8 0 0 1 0 0 0 c tot Pteromalidae 0 1 4 •J 16 32 25 Gryon sp. 0 0 8 0 1 0 0 0 Telenomus sp. 0 1 3 1 3 1 1 0 i ndet.Hymenoptera 0 0 1 1 0 0 0 1 TOT HYMEN0P"f PARASITES 0 2 8 4 11 27 49 53 TOT HYMENOFT FORM I CI DAE + 0 0 1 0 0 0 0 TOTAL PSOCOPTERA + 2 16 adul t B1 at. t i dae 0 0 1 0 0 0 0 0 TOTAL DICTYOPTERA 0 0 1 0 8 0 0 0 TOTAL INSECTA 67 1 12 261 380 1010 990 2745 2452 OTHER ARTHROPuDA + 0 0 0 0 1 4 0 sequential samples Crib L IITfl 1979 Dry Season ADULT COUNTS Samp 1e 1 2 3 4 5 6 Time scale 26 43 7 2 106 172 186 Sample weight 1369 1532 1545 1492 1 337 1305 Moisture content 12.5 11.3 12.6 13.3 1 5.4 15. 5 Lasioderma serricorne 0 0 0 0 1 2 indet. Corylophidae 1 0 0 0 0 0 indet. Cucujidae 5 1 1 3 12 40 total Cucujidae 5 1 1 8 12 40 Si tophi 1 us sp. " 440 335 551 129 375 581 Mycetaea hirta 0 0 0 0 3 1 Typhaea stercorea 0 0 0 1 0 0 C. pi 1osel1 us 1 1 2 2 6 6 C. succisus 0 0 0 0 0 2 indet. Carpophilus 14 20 38 12 51 56 total Nitidulidae 15 21 40 14 57 64 Hypothenemus sp. 6 0 0 0 1 0 Ah'asverus advena 0 0 1 0 0 0 Cathartus quadricollis 117 7 2 0 0 4 Monanus concinnulus 0 e 0 2 1 2 total Si 1 vanidae 117 7 -3 2 1 6 Gnatocerus maxillosus 13 11 5 12 2 10 P. fi c i col a 0 0 0 0 0 2 P. subdepressus 0 1 0 0 16 27 Sitophagus hoioleptoides 0 0 0 1 3 0 Tribolium castaneum 1 1 0 2 2 4 total Tenebrionidae 14 13 5 15 23 43 TOTAL COLEOPTERA 592 377 &00 169 473 737 Sitotroga cerealella 0 0 2 1 19 11 Mussidia ?nigrivene11 a 0 0 1 0 0 0 indet. Lepidoptera larvae 0 0 0 0 2 1 total Lepidoptera larvae 0 0 0 0 2 1 TOTAL LEPIDQPTERfl ADULTS ' 0 0 3 1 19 11 Cardiastethus sp. 2 0 0 1 14 2 Xylocorls afer 0 0 0 0 2 2 indet. flnthocorid nymphs 2 0 0 1 7 0 Peregrinator biannulipes 0 0 0 0 1 0 P. biannulipes nymphs • 0 0 0 0 0 2 Scolopoides divareti 1 0 0 0 0 1 S. divareti nymphs 0 0 0 1 0 1 tot predatory Heteroptera 3 0 0 1 17 5 tot pred Heteropt. nymphs •2 0 0 2 7 3 Dieuches ?armatipes 0 0 0 1 2 0 indet. Lygaeid nymphs 2 0• 0 0 2 0 tot phytophag Heteroptera • 0 0 0 1 2 0 tot phyto Heteropt nymphs " 2 0 0 0 2 0 TOTAL HETEROPTERA "V 3 0 0 2 19 5 TOT HETEROPT NYMPHS 4 0 0 2 - 9 3 TOTAL DIPTERA 0 0 0 1 0 0 Bracon hebetor 0* 4 0 0 . 0 0 indet. Braconidae • 0 0 . 0 3 0 0 indet. Bethylidae 0 0 0 1 4 1 total Bethylidae 0 0 0 • 1 4 1 Zeteticontus laevigatus 1 0 0 0 0 1 Eupelmus urozonus 0 ' 1 2 2 1 1 Anisopteromalus calandrae 0 0 1 2 3 1 Cerocephala dinoderi 1 0 0 4 7 5 Choetospila elegans 14 0 6 19 15 24 Habrocytus cerealellae 0 0 1 1 0 0 Mesopolobus sp. 0 0 0 2 1 2 t ot Pt eromali dae 15 0 8 28 26 32 Gryon sp. 0 0 0 0 4 o indet.Hymenopt era 0 0 0 0 2 0 TOT HYMENOPT PARASITES lb 5 10 34 37 37 TOT.HYMENOPT FORM ICI DAE 0 0 0 e 0 5 TOTAL PSOCOPTERA 1 4 31 47 160 135 indet Labi\dae adults 0 0 0 0 t- 0 TOTAL DERMAPTERA 0 0 0 0 2 0 TOTAL INSECTA 611 382 613 207 550 795 OTHER ARTHROPODA 0 1 3 .10 7 7 SEQUENTIAL SAMPLES Crib M 11TR 1979 Dry Season ADULT COUNTS Sample 1 2 3 4 5 6 Time scale 28 43 72 106 172 186 Sampl e. we i ght 1593 1564 1569 1525 1374 1355 Moisture content 12.7 12.4 13.4 12.8 15.0 17.0 Lasioderma serricorne 0- 0 0 0 0 2 indet.Cucujidae 2 0 1 17 36 total Cucujidae 2 0 1 2 17 36 Si tophi 1 us sp. 262 323 365 185 376 683 Mycetaea hirta 0 0 0 0 1 1 Typhaea stercorea 0 0 0 2 0 0 B. pi 1osel\us 0 0 0 0 0 2 Carpophilus binotatus 0 e 0 0 2 0 C. fumatus 0 e 0 0 1 1 C. pi 1osel1 us 0 I 3 0 8 12 C. zeaphi1 us 0 e 2 0 0 0 indet. Carpophilus 4 27 26 19 36 118 Lasiodactyl us sp. 0 e 0 0 0 1 total "Nitidulidae 4 28 31 19 47 134 Hypothenemus sp. 1 0 0 0 0 0 Ahasverus advena 0 1 0 0 0 0 Cathartus quadricollis 179 11 3 0 1 2 Monanus concinnulus 0 0 0 1 1 9 total Si 1vani dae 179 12 3 1 2 1 1 Gnatocerus maxillosus 6 4 5 1 1 2 15 P. fi c i col a 0 e 0 0 0 2 P. subdepressus 0 0 0 1 21 9 S'itophagus hoi ol eptoi des 0 6 0 0 1 0 Tribolium castaneum 0 0 0 0 0 2 i ndet.Tenebri oni dae 0 0 0 0 0 1 total 'Tenebri oni dae 6 4 5 12 24 29 TOTAL COLEOPTERA 454 367 405 221 467 896 Sitotroga cerealella 0 0 0 6 32 11 Plodia interpunctel1 a e 0 0 0 2 1 .indet. Lepidoptera larvae 0 0 0 0 . 3 0 total .Lepidoptera 1arvae . 0 - 0 0 0 3 0 TOTAL LEPIDOPTERA ADULTS e 0 0 6 34 12 Cardiastethus sp. e 0 0 3 7 10 Lyctocoris cochici I 2 0 0 0 • 0 indet. Anthocorid nymphs 0 0 0 0 4 5 P. biannulipes pymphs 0 0 0 0 6 3 Scolopoides divareti 0 0 0 0 4 1 S. divare.ti nymphs 0 0 0 0 2 1 tot pr>datory Heteroptera 1 2 0 3 11 1 1 tot pred Heteropt. nymphs 0 0 0 0 12 9 Dieuches ?armatipes 0 0 0 1 0 . 0 indet. Lygaeid nymphs 0 1 0 0 0 1 tot phytophag Heter.optera 0 0 0 1. 0 > 0 tot phyto Heteropt nymphs 0 1 0 0 0 1 TOTAL HETEROPTERA 1 2 0 4 11 1 1 TOT HETEROPT NYMPHS . 0 1 0 0 12 10 TOTAL DIPTERft 0 0 0 0 0 1ndet. Bethy1i dae 0 1 0 0 3 5 total Bethy1i dae 0 1 0 0 3 5 Zeteticontus laevigatus 2 0 0 0 0 1 Eupelmus urozonus 0 1 2 4 0 1 Anisopteromalus calandrae 0 0 1 2 3 1 Cerocephala dinoderi 0 1 1 2 3 5 Choetospila elegans 1 1 2 12 24 25 Habrocytus cerealellae 0 0 0 5 2 0 Mesopolobus sp.' 0 0 0 7 9 6 tot Pteromalidae 1 4 23 41 37 Gryon sp. 0 0 0 2 5 3 Telenomus sp. 0 0 0 0 1 0 TOT HYMENOPT PARASITES 3 4 6 34 50 47 TOT HYMENOPT FORMICIDAE 0 0 0 0 2 1 TOTAL PSOCOPTERA 3 5 8 58 129 105 TOTAL INSECTA 453 •373 411 267 564 . 967 OTHER ARTHROPODA 1. 0 1 1 1 5 11 259. APPENDIX III : Collated Data - Distribution Studies Data presented are as follows Preliminary Distribution Trial 260 (Sitopilus and Carpophilus adults only) Long-Term Distribution Trial sample 1 8/9/78 adults 261 sample 2 6/10/78 it 262 sample 3 22/11/78 ii-- 263 sample 4 11/4 /79 ii 264 (cribs were loaded 25/8/78) samples 1 & 2 emergences 265 samples 3 5 4 it 266 Short-Term Distribution Trial (dates as indicated on"individual sheets) adults 266-284 emergences 285-287 Details of the sampling programme are given in Chapter 6. 260. F:R EL I.N I.NftR V . D-I S.Tft J B U T.I 0 H IR I H L Adult counts: D it t a. c o r r ~ •; T. •= d •t, n u n. b .= r o f i n s500 g fresh grain i t ophi 1 u s z € aTi 5 i s arpoph i 1 us d i m 1 d 1 it us U~T' N \ 'vt l \ \ 1- '71 CI PJ \ CD" \ '71 r- \ rO r._ \ \>S>.I\ \ \ in\ C3 \ 01 \ rt 'Ti O. \ GJH <7) m \ N r-v 03 \ K in> m\ \ in PJ \J OJ \ W or P> rtrH •7>' cry- ru Q u K rl cn \ ru \ m in V m \ N \ro \ p- CD \Tf CD- xfU \ o>, CT> tT i \• -v \ \ .•71 03 j' ca rvj K •10 \ V E>| oa fsv. LI* •11 '1 t \ _ U1 V* oi\ Q. ; l£* \ \ — • ro •TO\ rN PJ \ \ \j ' * \ ru \ mi \ A * \ % J lii N r- \ m s P-T t koj VI \ iv C0-. \ f-'J \ ,\ OJ ,RV \ in \ "T \ \ OJ"- \ \ % ai Kfc , T cn LD \ \ \ m rr \ * \ *T in \PJ \ N-'i \ \ •j3 m •"V 03' CO OJ i m in \ y— \0J \ (r» rv. \ \ INV D •OJ > —> , \ J t 0JN OJ CO f'OJ % I'D \ 1 K \ ^ \ ••1 s-.-. CO a EN CD N OJ • . Lu VJ N u> QCT ; V \ 'T* (£> a T r_ 03 K •71 CZ3 v kon \ CEJ \ \ fN- 0J -t\ ,03 \ iM \ \ LD CD \ 03 •f\j ,0J VJ V 'T> r. 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O •— —> 0 O — O — • Z S MI 2. — <9 0) 'II "1> 3 = - c^ a* Sample 1 - emergences from lOOg in 1 week Sample 2 - emergence s from 100g in 1 week (.Figures are means of three samples; » denotes mean <.5> (Figures are means of three samples; * denotes in e an <. 5) position 12 3 4 5 6 pos i t i on 1 2 3 4 .5 6 Sitophilus sp. 2 3 4 9 4 3 Si tophilus. sp. 3 4 4 4 7 5 other minor pest spp. 2 * * 2 2 1 other Minor pest spp. 4 8 2 * * 1 parasitoids 0 u 0 * 0 0. parasiioids 0 0 0 * 0 0 jjos i t l on 9 10 11 12 pos » ti on 7 8 9 10 11 12 Sitophilus sp. 3 2 4 3 6 5 Si tophilus sp. 16 8 10 8 7 5 other minor pest spp. 2 1*10 2 other minor pest spp. 3 1 3 2 5 2 par ii 11 o i ds 0 0 0*01 parasitoids 0 * 0 0 0 0 i)Oi 11 l on 13 14 15 16 1? 18 position 13 14 15 16 17 18 2 2 •f. i tophi I us sp. 3 2 5 3 Si tophilus sp. 5 6 3 9 7 3 other hi i nor p« spp. 1 * 2 1 3 * other minor pest spp. 3 3 2 7 2 2 p at" as 11 o i ds 0 0 0 1 1 1 parasitoids 0 0 0 0 0 0 pos11 i on 19 20 21 22 23 24 position 19 20 21 22 23 24 Sitophilus sp. 1 3 1 . 1 1 3 * Si tophi 1 us sp. 10 3 3 7 other minor pest spp. • • * 1 » 6 8 • other minor pest spp. 2 1 I 2 2 paras11 o i ds 0 * 0 0 0 2 1 parasito i ds * 0 0 * 0 0 ro Ln LONG-TERM DISTRIBUTION TRIAL LONG-TERM DISTRIBUTION TRIAL Sample 3 - emergences from lOOg in 1 week Sample 4 - emergences from lO0g in 1 week (Figures are means of three samples; * denotes m e an < .5) (Figures are means of three samples; * denotes mean <.5> pos i t i on 1 2 3 4 5 6 position 1 2 3 4 5 6 Si tophilus sp. 14 14 ' 7 16 12 17 Cryptolestes spp. 12 2 4 9 3 10 Cathartus quadricollis * 1 1 1 * 1 . Si tophi 1 us sp. 13 24 13 20 17 18 Sitotroga cerealella 13 14 13 12 12 5 Gnatocerus maxillosus 6 4 8 10 8 3 other minor pest spp. 0' 2 1 2 1 1 Choetospila elegans 21 16 9 25 15 7 parasitoids 1 2 # * * 0 other minor pest spp. 4 1 3 6 2 5 paras i t o i ds 3 3 1 5 1 • pos i t i on 7 •8 9 10 11 12 pos i t i on 7 8 9 10 11 12 Si t ophi1 us sp. 16 19 25 18 19 18 Cathartus quadricollis * 0 0 2 0 1 Cryptolestes spp; 18 11 6 6 8 2 Sitotroga cerealella 8 9 4 10 18 8 Si tophilus sp. 9 14 16 12 25 10 other minor pest spp. ' 2 • 1 2 2 2 2 Gnatocerus maxillosus 6 4 5 6 6 3 paras i to i ds 1 .2 1 2 .1 0 Choetospila elegans 25 14 2 14 15 3 other minor pest spp. 4 4 4 4 5 2 parasi toi ds 4 2 1 1 2 # pos11 i on 13 14 15 16 17 18 position 13 14 15 16 17 18 Si» ophi1 us sp. 1 1 13 13 12 1 1 Cat hart us quadricollis 1 * 0 0 * 1 Sitotroga cerealella 5 1 1 1 11 6 4 Cryptolestes spp. 15 13 7 14 10 7 other minor pest spp. 0 2 1 4 * * Si tophi 1 us sp. 14 17 30 5 10 23 • 2 par as i t o i ds • 2 * 0 * Gnatocerus maxillosus 5 5 7 7 4 6 Choetospila elegans 19 18 4 25 13 8 other minor pest spp. 3 3 3 7 3 4 pos i t i on 19, 20 21 22 • 23 24 paras i t oids 1 1 1 1 0 1 Sitophilus sp. 17 27 . 19 15 17 19 30s i t i on 19 20 21 22 cl i 24 Cathartus quadricollis 1 1 1 * 0 1 Sitotroga cerealella 6 5 6 12 lu 5 other minor pest spp. 2 2 1 * 3 3 Cryptolestes spp. 11 7 5 8 8 3 p arasi t o j ds .* 2 ' 0 2 0 Sitophilus sp. 16 1 1 12 13 10 16 Gnatocerus maxillosus 8 5 5 5 7 3 Choetospila elegans 19 18 6 16 19 Cl other minor pest spp. 4 2 5 3 3 b paras i't o i ds « 2 * 1 * 267. DISTRIBUTION TRIFiL IV Crib 1 sample 1 >3/7/79 p.m. ii r temp. : 31 '.C Sample 1 2 3 4 5 6 7 8 9 10 1 1 14 16 grain temp./ 'c 12 1 3 15 28. 1 28.2 27.9 28.0 29. 1 28. 8 28. 7 23.6 2?. 2 28. 7 28.2 28. 3 gr ai n m. c . s 2.9. 0 28.5 27. 8 28. 2 17. 1 16.7 16.6 16.6 17.3 16.9 16.3 17.0 17. 1 17.3 17.3 17.3 17.2 16.5 16.4 16.4 '3 298 362 387 342 337 242 294 34 1 292 396 337 337 sample wt. 319 405 367 352 3 119 113 121 126 107 96 129 1 1 1 107 135 103 135 97 95 1 1 1 127 Lasioderma serricorne 1 2 0 0 2 4 1 0 e 0 0 0 0 0 ftraecerus fasciculatus 0 0 1 0 0 1 0 0 0 0 1 2 1 0 0 Dinoderus minutus 0 1 1 0 0 0 0 0 0 0 0 G 0 1 0 0 . 0 Heterobostrychus brunneus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Microprius confusus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Pseudobothrideres conrad. 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 indet. Corylophidae 0 0 0 0 1 0 0 12 2 0 0 10 0 0 0 0 Cryptolestes spp. 59 7 0 9 39 59 13 21 37 7 25 8 Placonotus spp. 14 15 10 3 0 0 0 1 0 0 1 6 0 0 0 0 0 Planolestes cornutus 1 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 Si t ophi1 us sp. 0 0 446 398 31 1 217 586 274 229 163 281 225 193 :oo 271 335 >00 206 indet. Histeridae 0 0 0 0 1 0 0 0 1 0 0 0 0 0 * 0 0 Lyctus nr africanus 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 Litargus balteatus 18 2 1 6 8 1 v 9 23 2 13 0 L. wari us' 22 5 1 0 2 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 Typhaea stercorea 0 1 0 1 0 9 1 1 13 1 0 4 0 0 0 0 Brachypeplus ?gabonensis 0 0 0 0 0 0 0 0 . 0 0 0 0 1 0 0 0 B. pi 1osel1 us 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. d i m i di at us 56 62 32 33 87 51 14 32 38 50 28 C. fumatus 104 53 67 32 20 23 16 13 6 28 10 3 2 5 C. hemipterus 4 3 4 3 4 4 1 0 0 0 0 0 0 0 0 0 0 0 C. obsoletus 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 Lasiodacty1 us sp. 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 1 0 0 0 0 2 0 0 1 0 . 0 0 1 2 " 3 Monanus concinnulus 1 0 3 2 3 1 1 0 1 0 0 0 1 3 0 0 Oryzaephilus mercator 7 0 4 5 1 1 0 0 0 0 .0 • 0 0 0 0 0 0 Silvanus inarmatus 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 Gnatocerus maxillosus 0 0 0 0 0 26 20 18 6 98 43 18 34 44 Palembus ivoirensis 87 53 49 30 47 20 17 0 0 0 0 0 1 . 0 0 0 0 0 P. ocularis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Palorus bobiriensis 1 0 0 0 0 0 0 1 1 11 3 0 0 0 0 0 P. c ar i n i c o11i s 3 1 0 0 0 0 0 0 0 1 0 . 0 0 0 0 . 0 P. cerylonoides 8 0 0 0 0_ '0 0 0 0 1 0 0 0 0 0 0 P. fi c i col a 1 0 0 0 0 '0 0 0 1 10 8 2 0 P. subdepressus 58 4 18 0 1 0 0 " 6 2 2 7 37 23 18 9 30 Pal orus crampe1i 120 .23 31 51 44 0 0 0 0 1 0 0 0 0 Sitophagus hoioleptoides 0 0. 0 0 0 0 0 0 0 0 0 • 0 0 0 0 Tribolium castaneum 0 0 0 0 1 0 0 0 0 0 9 1 • "1 .1 1 T. conf usum 12 0 1 3 0 0 0 0 0 0 1 2 0 0 0 Tri boli um sp. 0 0 0 O 0 1 0 0 0 0 0 0 0 0 0 Platydema spp. 0 1* 0 0 0 0 . 0 0 •0 0 0 0 0 0- 1 Latheticus orvzae 2 0' 0 0 0 0 ' 0 0 0 0 0 0 0 0 0 p Sitotroga cer-=alella 0 0 0 0 18 25 10 3 30 11 21 .,8 • 0 Cardiastethus sp. ". 9 *8 12 8 16 1 1 1 13 5 2 4 8 10 Cardiastethus sp. nymphs 3 0 0 0 3 0 . 0 0 9 4 . 0 0 1 Lyctocoris cochici 0 0 0 1 1 1 2 4 1 2 0 0 L. cochici nymphs 12 2 ' 4 4 1 0 1 ' 5 0 1 2 . 0 0 Xylocoriis afer 1 0 0 3 0 " ' 0 0 1 1 0 0 1 2 X. afer nymphs 0 1 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 1 C. musiva nymphs 0 0 ' 0 0 0 0. 0 0 0 0 0 0 0 0 P. biannulipes nymphs 0 0 0 0 0 0 0 0 0 0 0 0 0 Scolopoides divareti 1 2 0 4 • 0 0 3 2 0 •0 19 2 0 0 S. divareti nymphs 8 1 1 4 1 0 4 2 .0 0 13 4 0 1 Dieuches armatipes 0 1 0 0 0 0 0 0 0 0 0 0 0 D. armatipes nymphs 0 1 0 0 0 0 0 0 0 0 0 0 0 Mizaldus sp. 0 0 1 0 0 0 0 0 0 0 0 0 0 Mizaldus sp. nymphs 0 0 0 0 0 1 1 1 0 0 0 0 2 indet. Heteroptera 0 0 0 1 0 0 0 0 0 0 0 0 0 indet. Bethylidae 0 0 1 0 0 0 0 1 0 0 0 1 Zeteticontus laevigatus 0 0 0 0 0 0 0 0 0 0 1 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 0 0 finisopteromalus calandrae 1 0 0 0 0 0 0 0 ' 0 0 o 0 Cerocephala dinoderi 5 5 5 • 3 5 0 6 5 0 10 4 Choetospila el'egans 2 11 5 5 11 • 12 •A 8 14 10 12 Habrocytus cerealellae • 0 0 0 • 0 0 0 0 0 or 0 . O Mesopolobus sp. 0 1 0 0 0 0 0 0 0 0 1 indet;" Sce1ionidae 1 0 0 6 0- 1 0 • 4 0 0 0 indet Labiidae adults 0 0 0 0 1 ' 0 0 .1 1 'ndet Labiidae nymphs 1 0 .0 2 '3 2 c. • .3 14 268. Sample 17 IS 19 20 21 22 23 24 , 25 26 27 28 29 30 31 32 grain temp 'C 30.2 23. 2 28. 1 28.0 29. 9 28.8 28.9 29.0' 29.7 23.0 28.3 2 8. 0 31.0 28. 3 28.3 28.7 grain m.c. 16.8 16.8 16.6 16.3 16.9 16.6 lb. 1 16.5 16.5 17.0 17.6 17. 1 16.6 16.8 16.4 15.3 sample ut. (grain)/ <3 337 384 410 323 402 316 430 323 3 30 367 3 5 9 312 4 05 352 390 453 sample wt. (cores)/ 9 1 11 120 133 104 145 116 114 105 131 124 137 104 1 13 123 116 1 13 Lasioderma serricorne 0 2 0 1 1 1 0 0 0 0 0 0 0 0 0 1 firae-erus fasciculatus 1 1 0 1 3 0 1 2 1 0 0 0 0 1 0 1 Din: .-r-us minutus 0 0 0 0 1 0 0 1 0 0 1 0 0 0 0 1 Heter strychus brunneus 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 Micropr us confusus 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 1 Pseudob:thrideres conrad. 0 0 0 0 0 0 0 1 0 0 0 0 '0 0 0 0 indet. Cory?ophidae 1 0 0 0 0 0 0 0 0 0 1 . 2 0 0 0 0 Cryptolestes spp. 23 33 5 10 35 76 25 36 25 9 4 10 3 t 4 3 Placonotus spp. 0 0 0 1 0 0 0 2 1 0 • 0 0 0 0 .0 1 Planolestes cornutus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Si tophilus sp. 295 362 }92 204 269 328 288 218 364 318 425 304 373 ' 426 360 342 indet. Histeridae 0 0 0 2 0 0 1 2 1 0 0 0 0 0 0 0 Lyctus nr africanus 0 0 0 0 4 0 0 1 2 0 0 0 1 0 • 0 0 Litargus balteatus 3 0 0 5 2 5 1 6 r 3 2 7 x 6 1 0 1 L. var i us' 0 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 Typhaea stercorea 0 1 0 1 0 7 2 5 2 1 5 1 1 0 0 2 Brachypeplus ?gabonensis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 B. pi 1osel1 us 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 C. dimidiatus 91 47 54 23 95 85 68 70 142 95 102 . 112 90 75 _49 77 C. fumatus 1 1 3 0 7 7 1 2 6 3 1 5 5 2' r 4 C. hemipterus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. obsoletus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lasiodacty1 us sp. 0 0 0 0 0 0 0 1 1 0 3 1 0 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 2 1 0 2 3 0 1 4 2 1 1 2 0 0 0 0 Monanus concinnulus 1 1 0 1 4 0 0 2 4 0 10 5 1 1 1 0 Oryzaephilus mercator 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Silvanus inarmatus 0 0 0 0 0 0 0 0 0 0 0 0 0 .0 0 0 Gnatocerus maxillosus 23 .57 19 20 40 48 17 45 47 1 1 54 20 1 1 29 • 10 1 1 Pal embus ivoirensis 0 • f0 0 0 0 0 0 0 0 0 0 0 0 0. 0 0 P. ocularis ' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Palorus bobiriensis 0 1 0 0 2 3 1 2 2 0 0 1 2 0 1 1 P. carinicollis 1 0 0 0 1 0 0 1 0 0 0 0 '0 0 0 0 P. cerylonoides 0 • 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 P. f1c i col a 4 0 0 1 4 26 5 45 15 4 5 2 7 0 2 0 Pi subdepressus 53 83 47 26 103 104 35 62 98 85 158 56 23 "97 65 81 Palorus crampeli 0 -0 0 0 1 1 0 2 0 0 1 0 0 0 • 0 0 - Sitophagus hoioleptoides 0 0 0 , 0 0 0 0 0 0 0 1 . 1 0 1 0 0 Tribolium castaneum 1 5 0 0 5 2 1 1 6 2 9 3 1 2 1 0 T. confusum 0 , 0 0 0 0 0 0 0 0 2 0 0 0 0 0 " 0 1 Tribol.ium sp. 0 0 0 0 0 • 0 0 0 1 0 0 0 0 0 0 0 PIatydema spp. '0 0 0 0 1 0 0 0 0 0 0 2 0 0 0 0 • Latheticus oryzae 0 '0 0 0 0 2 1 0 0 0 0 0 0 0 -0 0 Sitotroga cerealella 14 8 4 9 4 9 4 1 1 6 o 13 3 2 6 Cardiastethus sp. 2 . 0 2 0 2 'l •0 2 • 1 0 2 1 0 1 0 Cardiastethus'sp. nymphs 2 0 0 0 4 '0 0 0 0 0 0 0 0 0 0 0 Lyctocorig cochici 5 8 1 6 1 6 3 4 6 . 7 14 9 7 ' 5 5 8 L. cochi c i nymphs 0 1 0 2 5 5 1 2 1 2 •6 3 0 1 0 3 r Sample 1 2 3 4 5 6 7 8 9 10 1 1 1 2 13 14 15 16 grain temp./ 'C 23. 8 23. 8 25.? 23. 9 26. 1 26.0 26. 2 26.2 26. 0 26. 1 26. 1 26. 1 26. 2 26. 1 26.0 27. 0 grai n m. c . / 16.8 16. 3 16. 1 16.8 17.4 16.9 15.9 15.8 16. 9 18.2 17.6 13. 1 17.0 Is. 2 15.9 15. 9 sawple wt. Lasioderma serricorne 0 1 1 2 1 0 1 0 0 •-k 0 0 0 0 0 A. 0 firaecerus fasciculatus 0 0 0 0 2 0 0 1 0 i 1 1 0 0 0 0 Dinoderus minutus 0 0 0 0 1 2 3 2 0 .0 0 1 1 0 0 0 indet. Bostrichidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Carabidae 0 0 0 0 0 0 0 0 1 • 0 0 0 1 0 0 0 indet. Corylophidae 0 2 1 2 5 0 0 1 0 0 0 0 P 1 0 0 Microprius confusus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cryptolestes spp. 7 9 4 7 12 10 7 22 36 's 3 7 4 3 5 24 Placonotus spp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Planolestes cornutus 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0' Si tophi 1 us sp. 563 335 226 234 456 441 267 304 303 310 270 246 266 267 162 172 indet. Histeridae 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Lyctus ?africanus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Hinthea rugicollis 0 0 0 0 0 0 0 0 4 0 0 0 0 0 1 0 Litargus balteatus -4 3 1 1 12 3 6 7 1. -0 1 0 0 0 0 3 Typhaea stercorea 1 0 1 0 1 1 4 3 0 0 1 1 0 0 1 0 B. ?pi1osel1 us 0 0 a 0 0 0 0 0 0 0 0 0 0 0 0 0 Carpophilus binotatus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 £ . d i m i d i at us 52 34 33 43 67 49 39 70 85 56 36 31 47 21 12 5 C. hemipterus 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 C. obsoletus 0 1 0 0 1 0 0 0 1 0 0 0 1 0 0 0 Lasiodactylus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 0 0 0 0 5 0 0 0 2 1 2 1 0 0 1 1 Monanus concinnulus 1 0 - 0 0 6 4 0 2 •2 1 1 0 -> 0 1 0 Oryzaephilus mercator 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 11 4 12 8 20 27 14 11 20 18 16 11 17 25 1 1 10 Pal'embus ivoirensis — 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Palorus bobiriensis 1 0 0 0 e 0 0 0. 3 0 1 2 2 0 0 0 P. cari nicol 1i s 1 0 0 0 1 0 1 1 1 0 0 0 0 0 0 1 P. cerylonoides 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 P. ficicola 0 0 0 1 2 4 4 5 14 6 0 3 0 0 0 0 P. subdepressus 3 3 2 2 16 22 25 21 '46 44 32 23 25 26 24 19 P. crampeM 0 0 0 0 ' 0 2 . 0 0 0 * 0 0 0 0 0 0 0 Sitophagus hoioleptoides 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Tribolium confusum 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Tribolium castaneum • 0 1 1 0 0 1 0 0 2 1 0 2 ' 0 2 0 0 indet. Coleoptera 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sitot'roga cerealella 36 53 21 31 45 25 37 24 43 12 17 "16 28 Q 32 9 Cardiastethus sp-. 16 3 1 2 18 8 4 4 6 0 , 1 0 2 2 0 1 Cardiastethus sp. nymphs " 4 0 • 0 1 3 3 1 0 0 -0 1 0 1 0 0 0 Lyc tori s.cochi c i 0* 2 0 2 7 2 2 4 5 1 4 3 3 2 4 6 L. cochici nymphs 0 0 0 0 1 0 0 8 1 0 0 1 . 0 0 ' 0 0 Xylocori s afer ' 0 1 1 1 •0 1 5 0 0 0 - 0 1 • 0 0 0 1 Cethera musiva • 0 0 1 0 0 0 0 0 0 « 0 0 1 0 0 0 0 Cethera musiva nymphs 0 0 0 0 0 0 0 0 0 0 ' 0 1 • 0 0 0 0 indet. Emesinae nymphs 0 0 - 0 0 • 0 0 0 0 0' 1 0 0 0 0 0 0 Scolopoides divareti 0 0 0 0 0 0 0 1 2 0 ' 0 0 0 0 0 0 S. divareti nymphs 0 0 0 0 0 0 0 0 0 0 0 . 0 0 0 0 0 Dieuches armatipes 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 2 Dieuches sp. nympfts 0 1 4 0 0 0 1 1 0 0 1 1 1 0 1 o Mizaldus sp. 1 1 0 2 1 2 0 0 4 4 2 1 2 1 0 Mizaldus sp. nymphs 0 0 0 0 0 0 0 0 1 1 5 3 2 2 2 4 indet. Heteroptera 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 Bracon hebetor 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 indet. Chalcididae 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 i ndet. Bet hy1i dae 0 0 0 0 0 0 3 0 0 0 0 0 0 0 1 0 Zeteticontus laevigatus 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 2 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 flnisopteromalus calandrae 0 0 0 0 . 0 0 0 0 0 1 0 0 1 0 0 0 Cerocephala dinoderi I 2 1 I 0 1 7 . 0 4 3 4 0 2 2 3 0 Choetospila 'elegans 5 9 . 10 1 6 8 5 5 7 11 8 3 7 2 10 1 Habrocytus cerealellae 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 Mesopo.lobus sp. 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Seelionidae 1 0 - 0 • 2 1 1 . 0 1 1 0 0 0 . 0 0 0 . • 0 indet" Labiid'ae adults 0 2 0 1 0 0 1 0 0 0 0 0 0 0 0 0 indet Labiidae nymp.bs 0 0 1 1 ' 2 0 0 4 ; & 0 1 0 0 0 0 0 270. Sampl* 17 18 19 28 21 22 23 24 25 26 27 28 29 30 31 32 gr *i n t emp. / ' C 26. 1 26. 8 26.2 26. 2 26. 2 26. 1 26.3 26.9 26. 8 25.9 26. 0 26. 0 26. 0 25. 9 26.2 26. 2 gr*i n m.c. / X 17. 7 16. 7 16.8 17. 1 18. 3 17.7 17.3 17.4 17. 2 17.4 17.8 17.6 17.3 16.5 15.9 16.2 sample ut.(grain)/ g 417 349 357 354 352 315 294 412 354 356 318 329 353 323 365 347 sample ut. (corn)/ g 122 116 117 122 118 112 139 109 110 144 122 143 136 129 108 104 Lasioderma serricorne 2 0 0 0 1 0 0 8 0 0 0 0 0 0 1 0 flraecerus fasciculatus 2 ' 0 0 0 1 0 0 3 1 1 0 1 2 2 0 1 Dinoderus minutus 0 0 0 . 0 0 1 2 1 0 0 0 0 0 0 0 0 indet. Bostrichidae 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 indet. Carabidae 0 0 0 0 1 - 0 0 0 0 0 0 0 0 0 0 0 indet. Corylophidae 0 0 0 0 0 1 0 0 0 0 1 6 0 0 0 1 Microprius confusus 0 0 0 0 0 ' 0 0 1 0 0 0 0 0 0 0 0 Cryptolestes spp. 15 11 11 6 21 13 18 22 9 5 1 1 13 6 6 2 1 1 Placonotus spp. 0 0 0 0 0 . 0 0 0 0 0 1 0 0 0 0 0 Planolestes cornutus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sit ophi1 us sp. 323 313 260 182 207 217 283 294 458 391 395 353 622 417 411 210 indet. Histeridae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lyctus ?africanus 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 Minthea rugicollis . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 0 0 0 1 2 0 0 4 1 0 0 r 1 0 0 2 Typhaea stercorea 0 0 0 1 1 0 0 2 1 2 2 14 0 0 0 0 B. ?pi1osel1 us 0 0 0 0 - 0— 0 0 0 0 0 0 1 0 0 0 0 Carpophilus binotatus 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 C. di mi di at us 67 34 11 29 89 34 36 50 97 106 86 86 107 43 54 40 C. hemipterus 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 C,. obsoletus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lasiodacty1 us sp. 0 0 0 0 0 0 0 1 0 0 2 1 0 0 0 1 Cathartus quadricollis 0 0 1 0 2 1 0 0 2 0 1 5 2 0 1 0 Monanus concinnulus 2 0 0 0 2 2 0 0 0 2 2 6 1 0 0 1 Oryzaephilus mercator 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Gnatocerus maxillosus 29 19 18 13 ' 15 12 17 13 35 1 1 52 28 40 26 21 11 Palembus ivoirensis 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 Palorus bobiriensis 0 . 0 0 0 2 1 1 0 3 0 0 0 0 0 0 0 P. c ar i n i c o 1 1 i s - 0 0 0 0 0 0 0 0 0 0 1 2 0 0 0 0 P. cerylonoides 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 P. fi c i col a 0 1 2 0 1 2 2 3 3 3 1 4 ~2 1 0 0 P. subdepressus 34 22 36 36 64 59 27 78 103 47 42 86 96 52 47 53 P. crampeli 0 e 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 Sitophagus ho 1o1eptoides 0 2 0 2 0 . l 0 2 1 0 4 0 3 1 - 1 - 8 Tribolium confusum 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Tribolium castaneum 1 1 " 0 1 2 0 0 4 6 7 1 4 2 3 5 1 indet. Coleoptera 0 0 0 0 0 -1 0 1 0 0 0 1 0 0 0 0 Sito-troga cerealella 23 19 9 9 24 5 7 14 17 10 10 10 15 14 19 7 Cardiastethus sp. 2 0 0 1 7 1 0 0 3 1 2 1 1 0 0 2 Cardiastethus sp. nymphs 0 0 0 0 .0.0 0 0 0 0 0 0 0 0 0 0, Lyctoris cochici 6 3 4 4 5 3 2 4 9 10 5 12 7 3 9 5 L.- cocljici nymphs 0 0 2 2 4 "V 1 1 3 2 3 10 . 2 0 1 Xylocoris afer 0 0 0 0 0 0 0 2 1 0 0 1 0 0 0 0 Cethera musiva 0 0 0 1 0 0 0 • 0 1 0 0 0 " 0 0 •0 0 Ceth'era musiva nymphs 0 0 0 0 0 0- 0 2 1 1 0 1 1 0 0 1 indet. Emesinae nymphs 0 0 0 0 0 0 0 0 0 >0 0 0 0 - 0 0 . 0 Scolopoides divareti 0 0 0 0 1 ' 6 1 ' 1 1 0 0 1 0 0 0 0 S. divareti nymphs- 0 0 0 1 '3 0 0 2 0 1 0 0 0 0 0 0 Dieuches armatipes 0 2 ' 0 0 1. <3 0 1 0 0 0 0 0 0 1 0 D.ieuches sp. nymphs 0 3 5 6 1 1 •2 8 0 0 0 0 0 1 11 23 Mizaldus sp. 3 1 1 0 0 0 2 1 3 0 2 4 2 1 0 Mizaldus sp. nymphs 0 4 2 7 2 1 1 0 1 0 •3 1 1 2 0 0 indet. Heteroptera 0 0 0 0 0' 0 0 0 0 0 0 0 0 0 0 0 Bracon hebetor 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Chalcididae 0 1 0 ' 0 0 0 0 0 0 0 0 0 0 0 0 0 i ndet. Bet hy1i dae 1 0 0 0 0 0 1 0 1 0 0 0 0 3 0 0 Zeteticontus laevigatus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 flnisopteromalus calandrae 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 Cerocephala dinoderi 5 2 3 2 6 2 4 1 9 6 1 0 5 1 5 4 Choetospila elegans 7 5 5 4 12 4 3 7 1 1 14 13 9 15 14 13 14 Habrocytus cerealellae 0 0 0 0 0 0 0 0 1 0 0 0 0 3 0 1 Mesopolobus sp. . 1 1 1 0 0 0 0 0 1 0 1 0 0 0 0 1 indet. Scelionidae 0 1 0 0 0 0 1 0 8 0 1 0 0 0 0 0 indet Labiidae adults 0 0 . 1 1 0 0 0 0 0 0 0 4 ' 1 0 3 0 indet Labiidae nymphs 1 0 0 0 0 0 0 .0 1 1. •1 11 1 0 . 0 2 271. DISTRIBUTION TRIML IV Crib 3 sample 1 18/7/79 morning air temp: 22.8'C Samp 1e 1 2 3 4 5 6 7 8 '9 10 11 12 1 3 14 15 1* grain temp./ 'C 23. 1 23.2 23. 6 24.8 22. 8 23. 1 23. 3 23. 2 23. 1 23. 9 24. 2 23.8 22.9 23. 8 24. 5 25. 0 grai n m.c.• % 18. 1 17.4 18. 1 21.3 19. 1 18.7 20.7 22. 3 17. 9 17.5 18. 6 19.9 17. 7 16.8 16.2 lc. 4 sample wt.(grain)/ g, 293 388 283 401 413 252 430 292 335 309 263 230 344 250 328 412 sample wt.(cores)/ g, 183 182 91 130 134 84 121 111 109 91 90 105 121 86 107 1 10 Lasioderma serricorne 1 0 0 0 2 0 0 0 3 0 2 0 0 3 0 0 flraecerus fasciculatus 0 0 0 0 I 1 0 1 1 0 0 1 1 0 0 0 Dinoderus minutus 0 0 0 0 0 0 1 0 0 0 4 1 0 0 1 0 Heterobostrychus brunneus - 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 El ytrotetrantus sp. 0 0 8 0 0 0 0 • 0 0 0 0 2 0 0 0 0 indet. Corylophidae 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Pseudobothrideres conrad. 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Cryptolestes sp. . 1 12 10 1 1 6 17 36 24 17 1 9 3 3 0 0 10 ?Placonotus spp. 0 0 0 2 1 0 5 9 0 0 0 0 0 0 0 0 flpion sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Si tophi 1 us sp. 392 417 258 263 445 •261 282 217 397 259 223 247 358 205 210 204 ihdet. Histeridae 0 0 0 0 0 0 8 0 8 0 0 0 1 0 0 0 Lyctus ?africanus 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 Litargus balteatus 1 1 2 3 1 0 9 6 2 0 6 4 0 0 0 L.Vvar i us' 0 0 0. 0 0 0 0 0 0 0 0 0 0 ' 0 0 0 Typhaea stercorea - 0 0 0 0 0 0 0 4 O 0 0 4 1 0 0 " 0 Brachypeplus pilosellus 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 Carpophilus dimidiatus 36 23 46 38 53 25 78 43 58 20 58 38 44 11 17 13 C. fumatus 2 1 3 2 3 1 7 1 1 0 2 2 0 0 1 0 obsoletus 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Lasiodacty1 us sp. 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Hypothenemus sp. 0 0 8 1 0 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 2 1 2 0 0 1 3 0 0 1 0 0 1 0 0 0 Monanus concinnulus 1 0 8 2 0 0 0 5 0 0 3 2 0 1 0 0 Oryzaephilus mercator ' 0 0 8 0 0 0 0 0 0 0 0 1 0 0 0 0 i ndet. Si 1 wani dae 0 0 8 1 0 0 0 0 0 0 0 0 0 0 0 0 indet. Stapl^yl i ni dae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 13 10 13 44 15 10 84 111 30 14 21 31 14 43 12 22 Palembus ivoirensis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Palorus bobiriensis 0 0 1 0 0 1 0 2 0 0 0 0 0 0 0 0 P. car i ni c ol 1 i s 0 0 0 0 0 2 1 3 1 0 0 0 1 0 0 0 P. fi c i col a 0 0 1 1 0 1 2 11 5 1 4 1 0 2 1 0 P. subdepressus . 4 2 3 1 9 29 18 9 35 16 20 14 30 64 46 16 Sitophagus hoioleptoides 0 0 0 0 0 0 8 0 0 0 0 0 . 0 0 0 0 Tribolium castaneum 1 0 1 0 0 0 3 1 10 2 0 3 0 3 1 1 T. confusum 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 Pyroderces sp. 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Sitotroga cerealella 37 13 14 5 31 19 7 5 13 7 6 7 7 13 13 1 1 Ephest i a c aut e11 a 1arvae . 0 0 0 1 0 0 1 0 0 0 ' 0 0 0 0 0 0 Cardiastethus sp. 6 1 1 2 4 5 2 . 3 0 1 1 2 .1 0 • 0 0 Lyctocoris cohici • v 0 0 0 0 0 0 0 ' 0 0 0 0 0 0 0 . 0 0 Xy1oc or i s afer 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. flnthocorid nymphs . 0 5 3 2 1 2 3 0 0 I 0 2 . 0 . 0 ' 0 0 Cethera musiva 0 • 0 0 0 0 0 0 0 0 0 1 0 0 ' 0 0 0 Cethera musiva nymphs 0 - 0 0 0 0 0 0 0 . 0 - 0 0 l' 0 0 0 0 Peregrinator biannulipes 0 0 ' 0 0 0 0 0 0 0 0 * 0 .0 0 0 0 Peregrinator bi. nymphs' 0 0 0 0 0 0 0 0 0 0 1 0 0 1 ' 0 Scolopoides divareti d 1 2 0 0 1 •4 12 1 0 2 2 0 ' 0 0 0 S. divareti nymphs 0 •0 2 2 0 1 1 5 0 0 1 3 0 0 0 0 Dieuches armatipes 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 Dieuches sp. nymphs 0 0 8 '0 0 0 0 0 0 0 0 0 0 1 3 Mizaldus sp. 0 1 0 0 0 1 0 0 4 1 3 0 1 0 1 0 Mizaldus sp. nymphs 0 I 0 0 0 2 0 0 1 5 3 0 3 8 3 indet. Heteroptera 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Bracon hebetor 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Braconidae 0 0 0 0 0 0 0 0 0 0 0, 0 0 0 0 indet. Chalcididae 0 0 0 0 0 0 0 0 0 0 0 0 •0 1 0 0 i ndet. Bet hy1i dae 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 Zeteticontus laevigatus 0 0 0 0 1 0 1 0 0 0 0 1 0 0 1 Q Eupelmus urozonus 0 0 0 0 0 0 0 0 0 • 1 0 0 0 0 0 finisopteromalus calandrae 0 0 0 0 0 0 0 0 0 0 0 0 ' 0 0 0 0 0' Cerocephala dinoderi 2 4 1 1 3 1 2 1 6 0 3 0 1 2 0 1 Choetospila elegans 2 1 6 1 1 10 3 2 18 2 8 •5 4 0 Habrocytus cerealellae 0 8 0 0. 2 0 0 0 0 • 0 0 2 0 0 0 0 Mesopolobus sp. 0 0 0 0 . 1 0 0 1 0 0 0 0 0 0 . indet. Scelionidae G 0 0 0 0 0 0 0 4 0 6 0 0 . .' 0 0 4 2 indet Labiidae adults 0. 0 0 0 1 0 4 • 0 0 0 0 0 3 0 indet Labiidae nymphs 0 0 0 0 0 • 2 3 0 1 -. 0' .0 1 5 1 1 1 ' 6 5 1 0 0 Samp 1« 17 18 19 20 21 22 23 24 25 26 27 28 29 grain temp.-' 'C 23. 1 24. 4 25. 1 25. 1 22.8 23.4 24.0 23. 1 3. 1 23.8 24. 1 24. 1 23. 2 grain m.c./ v. 17.5 IS.4 16.2 17.9 18.5 17.4 17.4 17.7 7.5 17.2 17.4 19.3 17.1 sample wt. Lasioderma serricorne 1 0 0 0 0 0 1 1 0 0 0 0 0 firaecerus fasciculatus 1 0 0 0 2 0 0 0 1 1 0 1 0 Dinoderus minutus 0 0 0 0 0 0 0 0 0 0 0 0 0 Heterobostrychus brunnrus 0 0 0 0 0 0 0 0 0 0 0 0 0 Elytrotetrantus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Corylophidae 0 0 0 2 0 0 0 0 0 0 0 0 0 Pseudobothrideres conrad. 0 0 0 0 0 0 0 0 0 0 0 0 0 Cryptolestes sp. 13 4 0 41 11 35 26 37 4 2 3 0 *i ?P1aconotus spp. 0 0 0 0 0 0 0 0 0 0 0 0 0 flpion sp. 0 0 0 0 0 0 0 0 0 0 0 1 0 Si tophi 1 us sp. 292 258 247 277 424 317 235 254 392 323 325 300 593 indet. Histeridae 0 0 0 0 0 0 0 0 0 0 0 0 0 Lyctus ?africanus I 0 1 0 1 0 0 0 0 0 0 .0 1 Litargus balteatus 1 0 0 0 1 2 0 9 2 0 0 x 1 1 L. vari us" 0 0 0 0 0 0 0 0 0 0 0 1 0 .Typhaea stercorea 0 0 0 2 0 0 0 2. 0 0 0 4 - 0 Brachypeplus pilosellus 0 0 0 0 0 0 0 0 0 0 0 1 1 Carpophilus dimidiatus 25 32 7 61 55 61 43 72 87 39 56 93 70 C. fumatus 0 1 0 2 1 5 1 1 1 1 0 0 0 ,C. obsoletus 0 0 0 0 0 0 0 0 6 0 0 1 0 Lasiodacty1 us sp. 0 0 0 0 1 0 0 0 1 0 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 1 0 0 0. 0 0 1 Cathartus quadricollis 0 1 0 0 0 0 2 0 0 0 2 0 0 Monanus concinnulus 1 0 0 0 1 1 0 1 1 2 1 2 1 Oryzaephilus mercator 0 0 0 0 0 0 0 0 0 0 0 0 0 i ndet. Si 1vani dae 0 0 0 0 0 0 0 0 • 0 0 0 .1 0 -indet. Staphylinidae 0 0 0 0 0 0 0 0 0 0 1 1 0 Gnatocerus roaxillosus- 40 18 22 71 18 42 50 47 41 16 23 »22' 26 Palembus ivoirensis 0 0 0 0 0 0 0 0 0 0 0 0 0 Palorus bobiriensis 0 0 0 0 0 0 0 0 0 0 1 0 0 P. carinicollis 0 0 0 0 0 0 0 0 0 0 0 0 0 P. fi c i col a 0 0 0 3 12 1 5 9 2 1 1 '"I 0 P.^subdepressus 37 18 19 34 54 62 53 53 56 42 35 33 52 Sitophagus hoioleptoides 2 4 0 2 0 0 1 1 0 0 1 1 ' 0 Tribolium castaneum 4 7 2 0 8 2 3 10 3 1 5 1 1 T. confusum 0 0 0 0 0 1 0 0 0 0 0 0 • 0 Pyroderces sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 Sitotroga cerealella 7 11 13 10 20 9 9 9 6 3 6 2 5 Ephestia cautella laruae 0 0 0 0 0 0 0 0 0 0 0 0 ' 0 Cardi^stethus sp. 2 0 0 0 5 0 - 1 1 1 •1 0 0 1 Lydjtocoris cohici 0 1 •0 1 0 0 0 0 0 1 0 2 0 Xylocoris afer 0 0 0 5 0 0 1 1 0 0 0 0 0 indet. flnthocorid nymphs ' 0 0 0. 1 3 2 0 2 1 • 0 1 . 0 0 Cethera musiva 0 0 0 0 0 0 0 '0 •0 0 0 1 0 Cethera musiua nymphs 0 0 0 0 0 0 1 0 0 v 0 0 0 0 Peregrinator Mannulipes 0 1 0 0 0 •0 0 1 0 0 0 0 0 Peregrinator bi. nymphs 0 2 0 0 0 0 0' 0 0. 1 •1 0 0 ScolofJoides divareti 0 0 0 0 1 1 2 3 ' 1 1 1 0 0 3. divareti nymphs 0 0 0 0 ' 0 2 1 0 1 0 0 1 0 Dieuches armatipes 0 1 2 1 0 0 2 0 0 1 0 0 0 Dieuches sp. nymphs 0 0 3 • 5 0 0 5 2 1 0 0 0 0 Mizaldus sp. 1 1 1 1 0 3 0 0 0' 0 0 0 3 Mizaldus sp. nymphs 5 1 2 2 0 4 1 2 £ 2 1 1 0 indet. Heteroptera 0 0 0 1 0 0 0 0 0 0 0" 0 0 Bracon hebetor 0 0 0 1 0 0 0 0 0 0 0 0 0 indet. Braconidae 0 0 0 0 0 0 1 0 e 0 0 0 0 indet. Chalcididae 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Bethylidae 1 0 1 0 0 1 0' 0 0 0 0 0 0 Zeteticontus laevigatus 0 0 0 2 0 0 1 0 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 0 0 1 finisopteromalus calandrae 0 0 0 0 0 0 0 0 0 1 0 0 . 0 Cerocephala dinoderi 3 3 2 4 8 7 5 3 1 4 3 2 yj Choetospila elegans 13 9 2 4 2 15 11 5 4 12 ? 1 12 Habrocytus cerealellae 0 0 . 0 0 0 0 0 1 0 0 0 0 0 Mesopolobus sp. 0. . 1 0 0 0 1 0 0 0 0 • 1 0 0 indet. Scelionidae 1 0 0 5 1 3 1 0 0 0 1 0 indet Labiidae adults 1 0 0 1 0 0 0 • 2 1 1 ' 0 0 0 indet Labiidae nymphs 0 0 0 1 2 0 0 6 0 0 0 • 1 0 273. DISTRIBUTION TRIAL IV Crtb 1 sample 2 9/8/79 morning air temp: 22.9'C Sample 1 2 3 4 5 6 7 8 : 9 10 11 12 13 14 15 16 grain temp./ 'C 23.3 23.8 24.0 24. 2 23. 0 23. 6 23.6 24. 0 ; 23.2 24. 0 24. 2 24 . 0 23. 1 24. 6 25. 0 25.2 grai n m.c./ X 18.2 17.5 17. 4 17.5 19.0 17.7 17.0 17.3 | 18. 1 17.8 17.9 18.5 18. 1 17.5 16.6 16.5 sample wt.(grain)/ 9- 206 226 288 218 275 209 209 251 J 213 254 258 177 215 266 299 193 sample wt.(cores)/ 9• 90 88 83 67 106 91 96 87 92 111 94 73 90 84 92 69 Lasioderma serricorne 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0. . firaecerus fasciculatus 0 0 0 0 0 0 0 1 3 0 1 1 0 1 0 0 Dinoderus minutus 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 indet. Corylophidae 4 0 0 3 2 2 1 12 0 3 3 3 r 4 0 1 0 Microprius confusus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cryptolestes spp. 62 9 2 7 18 37 24 28 14 9 1 1 17 12 10 8 13 PIaconotus spp. 0 0 0 0 0 0 0 2 0 0 0 1 0 0 0 0 Cucujinus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Si tophi 1 us sp. 255 208 149 134 277 174 85 109 199 405 168 122 166 279 164 60 indet. Histeridae 0 0 0 0 1 0 8 0 0 0 0 0 9 0 0 0 Lyctus ?africanus 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 4 0 1 0 3 3 0 9 8 1 7 5 4 2 1 0 Typhaea stercorea 0 - 0 8 0 2 2 0 1 0 0 1 1 0 0 0 8— B. p i1ose11 us 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0 0 C. d i m i d i at us 35 9 19 21 65 14 16 21 24 26 21 21 26 23 12 14 C. fumatus 20 20 13 0 20 22 4 4 2 1 3 24 7 0 0 4 C. hemipterus 0 0 8 1 0 0 0 0 0 0 0 0 0 0 '0 0 Lasiodacty1 us sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Hypothenemus sp. \ 0 0 0 0 1 . 0 0 0 0 1 0 0 0 0 0 0 Cathartus quadricoliis 0 0 0 0 1 0 0 1 0 1 0 3 0 0 0 0 Monanus concinnulus 6 1 1 0 1 0 1 4 1 2 2 1 1 1 0 0 Oryraephi1 us mercator 0 0 0 0 0 0 0 0 0 0 0 0 0 0" 0 0 Coenonica sp. 0 0 0 0 0 0 0 I 0 0 0 0 0 0 0 0 Coproporus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 25 13 9 10 46 35 26' 17 51 15 11 12 14 27 1 9 Palorus bobiriensis 0 0 0 0 5 2 0 2 0 0 0 1 0 2 1 0 P. carinicollis 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 P. cerylonoides 0 0 0 1 * 0 0 0 0 ' 0 0 0 0 0 0 0 0 P. fi c i col a 3 1 0 3 12 1 7 5 5 1 3 6 0 0 1 0 P. subdepressus 18 14 14 11 31 40 29 21 49 33 35 21 26 63 36 38 _ P. crampe1i 1 0 0 . 0 1 0 0 1 - 0 0 0 0 0 0 0 0* Sitophagus hoioleptoides 0 0 0 ' 0 0 0 0 . 0 0 0 » 0 0 0 0 0 0 Tribolium castaneum 2 1 0 0 2 0 1 1' 1 - 0 1 0 0 3 0 0 T. confusum 0 0 0 0 0 1 0 0 0 0 0 0' 1 0 0 0 Platydema sp. 0 0 0 . 0 0 0 1 0 0 0 0 0 " 0- 0 0 0 indet. Coleoptera 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Pyroderces sp. 0 0 0 . 0 0 • 0 0 0 0 0 0 . 0. 0 0 0 0 Sitotroga cereaTella 10 3 4 4 9 2 4 2 4 7 4 • 3 . ? I" 3 3 Cardiastethus sp. 19 2 0 1 10 5 4 2 12 0 3 1 9 * 0 0 1 Cardiastethus sp.-nymphs 15 1 2. 1 7 ' 1 1 2 2 0 3 0 • 4 3 0 0 Lyctocoris cochici 3 1 0 2 3 3 4 3 3. 2 4 l' 4 0 2 0 Li cochici nymphs 4 3 1 9 7 3 5 8 6 v -3 13 4 0 3 3 4 Xylocoris afer 0* 1 0 0 0 0 0 0 0 0 0 0 0 0 0 n X. afer nymphs 0 0 0 0 • 0 0 ' 0 0 • 0 0 . 0 0 0 0 0 0 " Cethera musiva 0 0 0 2 0 0. 0 0 0 0 0 0 0 0 0 1 . indet. Emesinae 0 0 0 0 0 0 0 0 0 ' 0 .0 - 0 - 0 8 0 0 C. musiva nymphs 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 P. biannulipes nymphs 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 Scolopoides divareti 5 0 0 6 1 0 3 1 4 e. 1 •y 3 3 1 2 3 S. divareti nymphs 3 0 0 5 3 0 0 1 0 1 0 2 0 1 0 0 Dieuches arm. nymphs 0 0 0 0 0 1 • 0 ' 0 0 0 0 0 0 0 0 0 Mizaldus sp. 6 0 1 2 3 0 0 0 2 0 0 0 1 0 1 1 Mizaldus sp. nymphs 2 0 0 3 1 0 0 1 0 1 2 1 2 0 £ 0 indet. Bethylidae 0 0 . 0 0 0 0 0 I 0 0 0 0 0 0 0 0 flnisopteromalus calandrae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 2 Cerocephala dinoderi 6 7 4 1 3 0 1 4 8 ".1 1 2 ^ 0 3 Choetospila elegans - 9 4 8 5 6 3 5 4 11 7 2 9 13 3 10 Mesopolobus sp. 0 0 1 0 0 0 0 •0 0 0 0 0 0 0 1 1 indet. Seelionidae 0 0 0 0 0 1 1 1 0' 0 0 0 0 •0 . 0 indet Labiidae adults 0 0 ' 0 0 0 0 0 1 0 •0 0 2 0 0 0 0 indet Labiidae nymphs 0 0 0 0 0 0 0 1 1 1 2 1 0 0 0 0 274. Sample 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 grain temp./ 'C 23.2 25. 1 25. 3 25.2 23.2 24.5 25.0 25. 0 23. 5 24. 1 24. 2 24. 3 23.8 25. 0 25. 0 25. 0 grai n m. c . / '/. 17.3 17. 1 17. 2 16.9 18.3 17.6 16.3 16.6 18.0 17. 8 17. 7 17.3 17.4 16.5 16. 2 16.2 sample ut.(grain)/ g. 307 240 237 314 249 228 260 216 238 237 256 291 306 306 205 sample ut.(cores)/ g. 34 98 80 105 68 82 82 66 100 77 94 30 183 83 102 j < Lasioderma serricorne 0 0 1 0 2 2 0 0 0 0 0 0 0 ' 0 0 0 flraecerus fasciculatus 0 1 0 1 0 0 0 0 0 1 0 0 0 0 0 0 Dinoderus minutus 0 0 0 0 0 0 0 1 0 0 1 2 0 0 0 0 indet. Corylophidae 1 1 0 0 1 1 0 7 1 0 1 6 . 1 0 0 0 Microprius confusus 0 0 0 0 0 0 0 1 0 0 0 3 0 0 0 0 Cryptolestes spp. 12 11 9 14 25 69 16 22 18 1 1 2 17 9 12 7 1 1 Placonotus spp. 0 0 0 0 0 0 1 1 0 0 0 12 0 1 0 1 Cucujinus sp. 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 Si tophilus sp. 236 208 181 296 143 207 90 22 200 304 259 224 339 304 indet. Histeridae 319 113 0 0 • 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Lyctus ?afr i canus 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 Litargus balteatus 4 1 0 2 1 2 1 2 2 2 2 11 4 0 0 4 Typhaea stercorea" 0 0 0 1 1 * 1 " 0 2 2 7 0 11 0 0 0 2 • B. pi 1ose11 us 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. dimidiatus 49 26 22 34 29 52 " 11 35 42 33 41 39 43 46 20 C. fumatus 50 0 3 0 6 2 13 0 15 1 3 1 47 0 1 1 3 C. hemipterus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 t-asi odac ty 1 us sp. 0 0 0 0 0 0 1 0 0 0 2 3 0 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 0 0 3 0 0 . 0 2 Cathartus quadricollis 0 0 0 0 1 0 0 1 1 0 0 1 0 0 0 0 tlonanus concinnulus 4 1 0 1 2 1 0 0 1 2 6 4 5 0 0 0 Oryzaephilus mercator 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Coenonica sp. $ 0 0 0 0 1 0 0 0 0 0 0 4 0 0 0 0 Coproporus sp. 0 0 .0 0 0 0 0 0 0 0 0 1 0 0 0 0 ' Gnatocerus maxillosus * 8 11 ' 15 9 11 23 11 10 13 11 18 26 9 1 7 12 7 Palorus bobiriensis 1 1 0 0 0 2 3 1 0 0 0 1 0 2 0 0 P. carinicollis 0 0 0 0 1 1 0 0 1 1 1 0 0 0 0 0 . P. cerylonoides 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 P. ficicola 2 2 1 2 6 7 1 1 12 6 2 7 0 0 0 • 0 P. subdepressus _ 37 39 29 - 33 85 74 37 44 116 79 56 . 63 44 82 38 69- - P. crampe1i 0 0 0 0 ' 0 0 0 0 0 0 0 0 0 0 0 0 Sitophagus ho 1oleptoides 1 0 - 0 0 0 1 0 0 0 1 1 0 0 1 0 0 Tribolium castaneum 1 0 1 0 3 4 1 0 5 2 0 6 3 2 0 0 T. confusum 0 0 0 0 0 0 0 •0 0 0 0 0 0 0 0 0 PIatydcma sp. 0 0 0 0 0 0 0 r 0 1 1 0 0 0 1 0 indet. Coleoptera 0 0 0 ' 0 . 0 0 0 0 0 0 1 1 0 0 0 0- Pyroderces sp. ' 1 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 Sitotroga cerealella 5 " 7 5 1 6 3 3 ' 3 . 2 2 . 4 1 0 0. 1 3 Cardiastethus sp. 1 0 1 1 1 .0 0 2 . 1 0 c. 1 r> 0 0 0 Cardiastethus sp. nymphs 1 0 0 0 0 0 1 . 2 0 0 • 0 • 1 2 0 0 • e Lyctocoris cochici 2 2 0 3 1 7 4 2 6 6 4 7 4 1 4 2 L. cochici nymphs 3 9 0 8 5 • 8 9 2 27 * 26 28 17 7 7 9 16 Xylocoris afer 0 0 0 0 0 1 0 2 0 0 0 0 0 0 0 0 X. afer nymphs 0 ' 0 0 0 ' 0 0 0 1 0 0 * 0 0 0 0 0 0 ' Cethera musiua 1 .0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 - indet. Emesinae- 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 C. musiua nymphs 0 0 0 0 0 .0 0 0 • 0 0 0 2 0 0 0 0 P. biannulipes nymphs 0 0 0 •1 0 0 0 0 0 1 0 0 0 0 0 0 Scolopoides diuareti 1 0 0 2 5 10 3 4 4 e. 0 8 0 0 1 1 S. divareti nymphs 1 0 1 0 2 .15 2 8 3 I 0 7 1 1 1 1 Dieuches arm. nymphs 1 ' 2 i 0 0 1 0 0 1 0 tf! 0 0 0 4 4 Mizaldus sp. 0 o 1 1 ' 0 2 0 0 0 0 0 0 0 1 4 0 Mizaldus sp. nymphs 0 I 0 1 0 0 0 1 1 0 4 0 0 0 1 0 indet. Bethylidae 0 0 0 1 1 0 0 0 1 I 0 0 0 2 0 0 flnisopteromalus calandrae 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cerocephala dinoderi 5 4 2 2 4 5 • 1 5 0 6 1 . 1 6 f 0 Choetospila elegans 5 7 12 7 6 8 4 3 14 12 1 1 7 3 14 12 6 Mesopolobus s'p. 1 2 0 0 0 0 0 0 0 0 0 0 0 0 indet. Seelionidae ' 0 0 0 0 0 1 ' 0 0 0 0 o- •0 0 0 0 0 indet Labiidae adu1ts 0 e 0 0 0 0 0 0 1 0 0 1 0 0 1 0 indet Labiidae nymphs 0 0 1 0 0 0 0 0 0 0 1 2 1 '3 0 0 0 0 DISTRIBUTION TRIAL IV Crib 2 sample 2 6/8/79 p.m. air temp.: 29.3'C Samp 1e 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 grain temp,/ 'C 27. 0 26.8 26. 6 27. 0 27. 9 27.5 27.7 27. 9 27. 5 27. 2 27. 2 27. 2 27. 9 27.1 27.0 27.2 grai n m. c . / 17.6 17. 1 17.3 17.4 18.0 17.5 17.3 17.3 17.6 18.0 18. 1 17.7 17. 1 16.9 17.1 16.5 sample wt.(grain) / g. 229 277 350 277 192 220 257 241 131 185 312 234 266 211 270 232 sample wt. (cores) / g. 85 110 88 87 80 102 103 96 60 74 94 34 81 71 35 73 Lasioderma serricorne 1 1 0 1 0 0 0 0 0 0 0 0 0 1 1 1 flraecerus fasciculatus 0 0 0 0 0 1 0 0 1 0 0 0 • 1 0 0 0 Dinoderus minutus 0 0 0 1 0 0 1 1 0 0 0 1 ' 0 0 0 1 indet. Corylophidae 0 0 0 1 4 1 2 1 1 1 4 0 1 b 0 0 3 Cryptolestes spp. 27 24 3 13 23 15 15 23 23 19 6 35 ' 12 6 10 9 Si tophi 1 us sp. 349 360 254 166 244 251 196 186 172 191 164 123 268 184 114 30 indet. Histeridae 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Lyctus nr.africanus 1 0 0 0 0 0 0 . 0 0 0 0 0 0 1 0 0 Minthea rugicollis 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 Litargus balteatus 5 2 0 0 5 7 9 2 1 2 0 4 2 1 0 2 Typhaea stercorea 0 0 0 0 1 1 0 2 0 0 0 0 0 0 0 1 B. p i1ose11 us 0 0 1 0 0 0 0 0 0 0 0 . 0 — 0 0 6 - 0 C. dimidiatus 34 28 30 14 25 26 39 22 17 11 21 8 23 6 11 14 C. f umat us 15 .18 13 4 9 5 13 1 1 1 0 5 6 2 0 4 C. hemipterus 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Lasiodactylus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 0 0 0 0 0 0 2 0 0 0 0 0 1 0 0 0 Monanus concinnulus 0 0 0 2 4 2 0 1 3 0 1 2 1 4 d 0 Cryzaephilus mercator 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Si 1vanoprus sp. 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Coenonica sp. 0 0 0 0 0 0 0 a 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 15 20 20 5 28 25 15 39 16 11 21 • 6 19 8 9 6 Palorus bobirviehsis 0 0 0 1 0 0 0 0 0 0 0 0 2 0 0 0 P. cerylonoides 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 P. f i c i c o 1 a 2 0 0 1 0 1 4 6 4 6 7 2 2 0 o 0 P. subdepressus 5 4 8 8 16 31 51 31 24 38 20 17 20 20 36 15 P. crampeli 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 Tribolium castaneum 0 0 1 2 1 1 0 2 0 0 3' 0 0 2 0 3 T. confusum . * 0 0 0 0 1 2 0 0 . 0 0 0 0 " 0 0 0 0 Sitotroga cerealella 15 , 10 9 15 7 8 7 0 6 • 7 6 5 10 3 10 13 Cardiastethus sp. " 17 5 3 5 22 11 1 2 7 1 2 1 ,2 0 1 4 O Cardiestethus sp. nymphs 7 0 0 1 5 3 3 4 3 0 3 1 0 0 ' 0 Lyctocoris cochici 1 0 1 • 0 1 0 0 1 0 1 2 1 2 ? 0 1 L. cochici nymphs' 1 1 3 2 2 5 5 5 5 4 0 1 0 5' 1 1 Xylocoris afer 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 2 Cethera musiva 0 0 ' 0 0 0 0 0 0 0 0 0 0 n. 0 0 0 0 C. musiva nymphs 0 0 0 0 • 0 0 0 0 2 0 1 0 ' 0 0 0 1 P. biannulipes nymphs ef 0 0 .' 0 1 0 0 0 0 0 .0 0 0 0 . 1 0 Scolopoides divareti 0 0 1 0 0 3 0 • 8 0 1 1 1 3. 0 1. 0 S. divareti nymphs - 0 0 0 0 0 1 0 3 1 x 0 0 0 1 0 0 0 Dieuches arm. nymphs 0 0 1 0 0 0 0 0 1 1 0 0 • 0 ' 0 • 0 0 Mizaldus sp. l 0 0 0 0 .0 0- 1 1 0 1 • 0 . 0 0 0 1 Mizaldus sp. nymphs 0 2 0 0 1 3 0 0 6 ' 3 n 2 0 1 1 indet. Chalcididae • 0 0 0 0 0 0 0 0 0 0 0 0 0 , 0 0 0 i ndet. Bethy1i dae 0 0 0 0 0 0 2 0 1 0 0 1 1 0 1 2 leteticontus laeuigatus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 • 0 0 0 0 0 0 0 1 0 1 Cerocephala dinoderi 3 5 1 2 4 3 4 4 4 2 3 2 1 5 6 Choetospila elegans '6 7 3 6 9 1 6 2 4 5 5 7 10 e 6 5 Habrocytus cereal el la* 0 0 0 0 0 0 0 0 0 0 0 0 0 o 1 0 Mesopolobus sp. 0 0 0 0 0 0 0 0 1 1 0 0 0 o 0 0 i ndet. Seeli oni dae 0 0 0 1 1 0 0 0 0 0 1 0 0 I 0 1 indet Labiidae adults 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 indet Labiidae nymphs 0 ' 0 I 0 1 C. 0 0 0 0 0 0 1 0 0 0 V-": - " t; Sample 17 18 19 28 21 22 23 24 25 26 27 28 29 30 31 32 grai n temp./ 'C 27. 9 27.3 27. 3 27. 8 28. 1 28.8 28.8 28.0 27.2 27.0 27.1 27.1 27.8 27.3 27. 3 27. 8 grain m.c./ 16.9 17.2 17.2 16.8 17.6 17.3 16.8 16.6 17.2 18.8 17.7 17.7 17.0 16.6 16.7 16.4 sample wt.(grain) / g. 275 241 254 264 228 261 268 241 177 220 241 ' 223 238 216 244 254 sample wt. (cores) / g. 67 84 93 99 79 183 74 94 62 94 82 80 72 72 100 78 Lasioderma serricorne 0 1 0 0 0 0 1 0 1 0 0 0 0 0 1 0 flraecerus fasciculatus 0 0 0 0 0 . 0 0 1 0 1 1 0 0 0 0 0 Dinoderus minutus 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 indet. Corylophidae 0 0 0 1 1 2 1 -9 2 1 2 1 1 0 0 -> Cryptolestes spp. 14 18 21 14 9 39 20 11 8 13 20 13 31 10 6 16 Si tophi 1 us sp. 292 179 230 117 177 166 142 132 236 301 261 227 394 247 280 161 Indet. Histeridae 0 8 0 0 0 0 0 0 0 0 0 0 . 0 0 0 0 Lyctus nr.africanus 0 8 0 0 0 0 0 .0 0 1 0 0 0 0 0 0 Minthea rugicollis 0 8 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Litargus balteatus 1 8 8 0 0 1 I 6 0 0 2 0 3 0 0 2 Typhaea stercorea 0 8 8 0 2 0 0 2 3 1 1 1 0 ' 0 0 0 B. pi 1osel1 us 0 8 * 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. dimidiatus . 26 12 19 14 37 21 20 37 36 41 61 35 55 20 20 30 C. fumatus 0 0 0 0 0 0 0 3 0 1 2 1 1 1 0 1 C. hemipterus 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Lasiodacty1 us sp. ~ a 0 0 1 1 0 0 - 0. 0 2 1 0 " 0 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 0 2 0 1 1 4 0 0 0 0 Cathartus quadricollis 0 0 1 0 0 0 0 0 0 2 0 3 1 0 0 0 Monanus concinnulus —i 5 0 0 1 2 0 0 5 7 7 5 2 1 0 2 Oryzaephilus mercator 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Si 1vanoprus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Coenonica sp. 0 0 0 0 0 0 0 l 0 0 0 0 0 0 0 1 Gnatocerus maxillosus 29 23 7 2 1 18 15 10 9 19 12 9 15 12 12 12 Palorus bobiriensis 0 0 0 0 0 1 0 0 0 0 0 0 0 0 2 0 P. cerylonoides 0 0 0 0 0 1 ' 0 0 0 0 0 0 0 0 0 0 P. fi c i col a 1 2 0 1 3 5 1 4 6 7 3 1 0 0 0 0 P. subdepressus 27 35 25 17 30 54 45 51 50 88 91 67 94 70 92 75 P. crampeli 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 Tribolium castaneum I 2 0 0 0 • 1 1 2 1 5 4 2 2 2 1 0 T. confusun 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0- 0 Sitotroga cerealella 2 2 . 7 3 • 11 5 2 4 1 1 1 7 3 0 3 1 Cardiastethus sp. 10 3 0 0 4 3 1 3 1 2 1 0 4 0 0 2 Cardiestethus sp^_nymphs 1 0, 1 0 0 0 0 . 1 2 1 1 1 0 1 0 1 Lyctocoris cochici 2 0 0 3 4 1 1 2 1 4 2 1 0 2 5 . 2 L. cochi c i nymphs 5 6 3 2 * 8 0 2 7 25 22 18 20 8 7 4 6 Xylocoris afer 0 0 0 2 0 0 0 0 • 0 0 0 0 0 0 0 .1 Cethera musiva 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 1 C. musiva nymphs 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 P. biannulipes nymphs 0 0 0 0 0 0 .0 .0 1 0 0 0 0 0 0 0 Scolopoides djvareti 1 0 0 0 3 1 0 . 1 . 0 2 0 2 5 0 • 0 1 S. divareti nymphs. . 0 0 0 0 0 2 0 •V4 0 0 1 1 3 0 ' 2 0 Dieuches arm. nymphs 1 0 0 0 0 0 3 0 1 0 0 0 0 1 1 1 Mizaldus sp. 2 1 0 1 1 2 • 0 0 1 2 2 " 1 4 0 0 0 Mizaldus sp. nymphs 1 2 0 1 1 1 1 2 0 0 1 0 3 4 1 0 indet. Chalcididae 0 0 0 0 0 0 0 0 0 - 0 0 ' 0 0 1 0 . 0 i ndet. Bethy1i dae 0 2 0 0 0 0 0 '2 ' 0 ' 2 1 0 0 1 0 3 Zeteticontus laevigatus 0 0 ' 0 0 0 1 0 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 .0 0 0 0 ' 0 0 0 0 0 0 0 0 Cerocephala dinoderi 5 1 2 I 2 5 0 1 •4 9 0 7 4 2 4 3 Choetqspila elegans 13 6 4 3 5 9 4 9 12 9 12 9 16 7 8 5 Habrocytus cerealellae 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Mesopolobus sp. 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 indet.. Scelionidae 0 0 0 1 0 1 0 1 0 1 1 0 0 1 1 0 indet Labiidae adults 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet Labiidae nymphs 0 0 0 0 1 0 0 1 0 0 0 2 0 0 0 0 DISTRIBUTION TRIAL IV Crib 3 sample 2 1/8/79 mid-day air temp.:26.9' C Sample 12 3 4 5 6 7 8 9 10 1 1 12 13 14 15 1 6 grain temp./ 'C 25.2 25.2 25.2 25.5 25.5 25. 8 25. 8 25.8 25.8 26. 0 26. 0 25 .9 25.5 25. 8 25. 9 26. 2 grai n m. c . / *; 16.7 17.9 18. 8' 20. 8 18.5 17.5 17.9 20.2 17.0 17.2 18. 2 18 .9 17.0 16.4 17.4 17. sample wt.(grain) / g 229 180 214 259 192 386 203 216 246 255 276 1 79 286 229 308 9 sample wt.(cores) / g 93 80 76 96 81 107 81 62 80 107 94 79 102 56 107 ; 6 Lasioderma serricorne 0 1 0 2 1 0 2 0 1 0 0 1 1 0 1 0 flraecerus fasciculatus 0 0 0 1 0 0 0 0 0 0 2 0 0 0 0 0 Dinoderus minutus 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 indet. Corylophidae e. 1 0 1 2 13 6 3 3 3 3 3 3 ,1 0 0 0 Cryptolestes spp. 9 15 12. 16 36 18 33 23 19 32 1 1 8 6 13 31 20 Placonotus spp.. 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 Si tophi 1 us sp. 283 312 322 198 293 287 191 161 215 296 216 137 239 189 219 1^2 indet. Histeridae 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 Lyctus nr. afr i*canus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 0 0 0 1 13 1 0 6 0 3 3 5 2 0 1 0 L.s vari us' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Typhaea stercorea 0 0 0 0 2 . 1 0 2 0 0 ? 0 0 0 0 0 B. p i1ose11 us 0 0 I 0 0 0 0 3 0 0 0 0 0 0 0 1 C. dimidiatus 17 17 11 6 13 14 12 19 29 31 17 6 19 12 16 4 C. fumatus 0 0 0 0 1 1 0 0 1 2 0 0 2 1 0 0 C. hemipterus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. obsoletus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lasiodactylus sp. 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 indet. Scolytidae 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Hypotheneinus sp. 0 0 0 1 2 0 0 0 0 0 0 0 0 0 0 1 Cathartus quadricollis 1 1 0 1 2 1 0 0 1 2 1 0 0 0 0 1 Mohanus concinnulus 0 0 1 1 1 0 0 0 0 1 1 1 0 0 0 2 indet. Staphy1inidae 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 5 7 • 13 16 49 3 15 18 24 35 16 10 13 19 22 Palorus bobiriensis 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 P. carinicollis 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 P. cerS>l onoi des 0 0 0 0 0 0 0 1 0 0 • 0 0 0 0 0 0 P. fi c i col a 1 0 0 1 3 3 0 1 2 2 1 4 0 0 0 0 P. subdepressus 6 .5 6 14 52 33 30 20 26 41 19 10 10 53 55 28 Sitophagus hoioleptoLdes 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 _ Tribolium castaneum 1 0 0 1 3 0 0 0 0 3 .0 1 0 2 3 0 Platydema sp. 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 indet. Coleoptera 0 0 0 • 0 0 0 1 0 0 0 0 0 0 0 0 0 Pyroderces sp. 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sitotroga cerealella 13 11 29 5 25 8 8 6 14 17 5 5 11 8 3 6 Cardiastethus sp. 13 0- 3. 6 7 1 2 2 5 6 6 7 3" 1 1 2 Cardiastethus sp. nymphs 2 2 - 1 . 2 8 0 1 1 5 4 4 2 9. ' 0 1 . 1- Lyctocoris cochici 0 0 0.. 0 0 0 0 0 1 . 2 0 0 0 0 1 0 L. cochici nymphs 0 0 0 0 0 0 0 0 . 0 1 0 0 0 0 0 0 Xylocoris afer 0 • 2 . 0 0 0 0 1 0 0 0 0 0 0 0 J0 . 0 X. afer nymphs 0 0 0 •0 0 0 1 0 0 0 0 0 0 0 0 0' Peregrinator biannulipes 0 0 0 0 0 0 0 0 0 - 0 0 0 0 0 1 0 P. biannulipes nymphs 0 0 0 ' 0 1 0 0 0 1 0 0 0 *1- 0 1 0 C." musiva nymphs 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Scolopodes divareti 0 1 1 ' 2 9 3 4 3 2 0 1 1 1 0 0 9 - S. divareti nymphs 3 0 0 4 • 10 2 40 4 1 1 0 0 1 0 1 1 Dieuches armatipes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 D. armatipes nymphs 0 0 0 0 0 0 0 0 0 0 o 0 0 0 3 1 Mizaldus sp. 0 0 0 0 2 0 3 2 1 5 5 2 0 2 0 Mizaldus sp. nymphs 2 0 0 1 1 0 2 1 1 4 2 2 1 c. 9 1 indet. Chalcididae 0 1 1 0 0 0 0 1 0 0 O 0 0 0 0 0 indet. Bethylidae 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 Cerocephala dinoderi 3 3 3 1 2 8 1 1 1 7 4 1 4 3 2 0 Choetospila elegans 8 6 4 6 3 6 5 4 9 5 8 2 16 7 3 8 Habrocytus cerealellae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Mesopolobus sp. 0 0 0 0 0 0 0 0 0 1 0 0 0. 0 0 0 indet. Scelionidae 0 0 1 1 4 1 1 0 2 0 0 1 3 0 0 ' 0 1 indet Labi i dae 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 indet Labiidae nymphs 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 Samp 1e 17 18 19 28 21 22 23 24 25 26 27 23 29 30 31 32 grain temp./ 'C 25.8 26.3 26. 2 26. 1 25.8 26.3 26. 2 26. 1 25.8 26.0 26. 2 26.2 25. 9 26. 1 26. 5 26. 0 grai n m. c . s V. 16.7 16.4 17.4 13.8 16. 9 16.5 16.7 17.9 17.0 17. 1 18. 1 IS. 6 17.0 16.3 13.4 16.1 sample wt.(grain) / g 254 215 268 297 229 315 191 316 261 & 3 & 199 166 303 244 244 34 1 sample wt.(cores) / g 77 93 75 69 91 110 77 119 84 83 81 69 1 1 1 93 74 104 Lasioderma serricorne 1 8 8 0 0 0 0 8 0 0 0 0 0 0 0 flraecerus fasciculatus 1 8 8 0 0 8 0 0 0 0 0 0 1 0 0 0 Dinoderus minutOs 8 8 8 0 1 8 0 0 0 0 0 0 0 0 2 0 indet. Corylophidae 8 8 8 0 1 8 0 4 0 0 4 1 •0 0 Cryptolestes spp, 27 16 19 6 29 38 14 39 9 5 11 3 5 9 16 5 Placonotus spp. 8 8 8 0 8 8 0 0 0 0 0 0 0 0 0 0 Si tophi 1 us sp. 259 246 237 228 181 290 127 233 325 356 349 227 416 357 210 293 indet. Histeridae 8 8 8 0 ' 8 8 0 0 0 0 0 0 0 0 0 0 Lyctus nr.africanus 8 8 8 0 1 8 8 0 0 0 0 0 0 0 0 0 Litargus balteatus 8 8 1 3 5 1 4 0 1 2 1 1 2 0 4 0 s L. uar i us' 8 8 8 0 8 8 8 0 0 1 0 0 0 0 0 0 Typhaea stercorea .1 8 8 0 8 1 8 2 1 0 0 0 0 0 7 0 B. p i1ose11 us 8 8 1 1 8 8 8 0 0 0 0 0 0 0 S " 0~ C. d i m i di at us 19 13 23 15 38 44 9 38 44 26 39 43 47 23 54 14 C. fumatus 1 8 1 8 8 2 8 2 0 * 8 1 0 1 0 1 0 C. hemipterus 8 8 8 0 8 8 8 0 0 0 0 1 0 0 2 0 C. obsoletus 8 8 8 0 8 8 8 0 0 0 0 1 0 0 0 0 Lasiodacty1 us sp. 8 8 8 0 0 1 8 0 0 0 0 2 0 0 0 0 indet. Scolytidae 8 8 8 0 0 8 8 0 0 0 8 0 • 0 0 0 0 Hypothenemus sp. 8 8 8 0 1 1 8 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 8 1 8 1 0 0 0 0 0 1 0 0 0 8 0 0 Monanus concinnulus 8 8 2 2 1 1 0 1 1 0 2 0 0 1 7 0 indet. Staphy1inidae 8 8 8 0 0 8 0 0 8 0 0 0 0 0 2 3 Cnatocerus maxillosus 9 19 8 9 9 15 12 14 24 10 34 7 16 8 .17 13 Palorus l>obiriensis 8 8 * 8 1 0 8 0 1 0 1 1 0 1 0' 0 0 P. carinicollis 8 8 8 0 2 1 0 0 2 0 0 1 0 0 0 0 P. cerylonoides 8 8 8 0 0 0 0 8 0 0 0 0 0 0 0 0 P. f i c i col a 8 8 8 1 3 5 3 14 8 2 1 • 3 0 0 0 '0 P. subdepr.essus 33 58 51 60 40 67 64 67 49 40 47 40 44 75 102 53 Sitophagus hoio^eptoides 8 8 8 0 0 8 0 8 0 0 0 0 0 . 1 0 0 - Tribolium castaneum 2 2 3 0 5 3 2 2 5 7 { 0 3 1- 1 4 P*latydema sp. 8 8 8 0 0 8 0 8 0 0 ' 0 1 0 0 • 0. 0 indet. Coleoptera • 8 8 0 0 0 8 .0 8 0 0 0 0 0 0 0 O Pyroderces sp. 8' 8 8 0 1 8 8 0 0 0 0 0 0 0 0 0 Sitotroga cerealella 18 4 9 3 9 7 8 5 O 4 . 4 0 3 3 7 Cardi astethus sp. 2 8 8 0 6 8 2 4 7 1 2 2 6 1 0 " Cardi astethus .sp. nymphs 2 8 8 0 1. 1 8 4 2 0 • 0 0 2 0 1 1 Lyctocoris cochixi 8 1 8 0 0 " 8 8 0 0 ' 2 1 0 0 0 8 L. cochici nymphs 8 2 2 1 0 1 1 0 1 2 5 1 0 2 4 1 Xylocoris afer. 8 8 8 0 0 •8 8 I 0 0 . 0 1. 0 0 1 0 X. afer nymphs 8 8 8 0 0 0 8 1 0 0 0 1 0 0 1 0 Peregrinator biannuli.pes 8 8 8 0 0 1 . 8 0 0 > 0 0 0 0 1 1 0 P. biannulipes nymphs ' 8 8 8 0 0 0 1 0 1 . 0 0 0 0 0 0 0 C. musiva nymphs 8 8 1 0 0 0 8 0 1 0 0 . ' 1 0 0 1 0' Scolopodes divareti' 3 8 1 X 3 4 7 3 0 0 2 0 " 0 4 0 " S. diuareti nymphs 1 1 8 1 0 8 8 4 . 1 0 . 2 3 1 0 0 0 Dieuches armatipes 8 8 8 0 0 8 8 1 0 0 0 0 0 0 0 0 D. armatipes nymphs 1 8 8 0 0 8 0 1 1 0 0 .0 0 0 >J 2 Mizaldus sp. 1 1 2 3 1 1 1 2 1 2 0 1 0 1 2 1 Mizaldus sp. nymphs 4 1 4 0 3 2 2 0 1 0 1 0 0 10 1 indet. Chalcididae 8 8 8 0 0 0 8 0 0 0 1 0 0 0 0 0 indet. Bethylidae 1 8 8 0 1 1 2 0 1 0 1 0 0 0 4 1 Eupelmus urozonus 8 e 8 0 0 0 8 0 0 0 0 0 0 0 0 0 Cerocephala dinoderi 4 7 3 0 4 10 6 1 5 • 6 4 1 5 4 ~> 4 7s Choetospila elegans 9 13 3 2 10 3 8 8 8 4 2 6 4 15 Habrocytus cerealellae 8 1 8 0 0 0 0 0 0 0 0 0 0 0 0. 0 Mesopolobus sp. 8 8 2 0 0 0 0 • 0 1 0 0 1 0 0 0 U indet. Scelionidae 8 8 8 0 0 0 0 0 0 0 2 0 0 1 1 0 indet Labi i dae 8 8 8 0 0 0 0 0 0 1 0 0 0 0 0 0 indet Labiidae nymphs 8 8 0 1 0 0 0 0 4 0 0 0 0 0 0 1 279. DISTRIBUTION TRIAL IV Crib 1 samp 1e 3 22/8/79 mid-day air temp.:26.2'C Samplc 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 grain temp. / 'C 26. 1 26. 8 26.8 26.2 26.2 26.8 26.2 26. 7 26.8 26. 0 26. 2 26. 1 26. 3 26.0 26. 0 26. 1 grain m.c. / 19.8 18. 1 18.2 18.2 19.5 18.0 17.8 17.9 19.0 18.5 18.3 18.6 18.6 17.9 17.4 17.3 sample wt. (grai n> ' 9 248 127 251 204 169 242 273 274 231 248 221 234 245 232 247 sample wt. (c ores > ' 9 89 78 182 81 73 77 98 73 94 90 69 89 98 80 102 72 Lasioderma serricorne 2 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 flraecerus fasciculatus 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 Bostrychoplites cornutus 0 0 0 0 0 0 0 0 0 0 0 0 © 0 0 0 Dinoderus minutus 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 Heterobostrychus brunneus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Necrobia rufipes 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Microprius confusus 0 0 0 0 0 0 0 0 0 0 0 3 0 1 0 0 Pseudobothrideres conrad. 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 indet. Corylophidae 1 1 0 0 0 0 0 4 4 • 0 0 0 2 1 1 0 Cryptolestes spp. 42 7 11 22 10 45 15 25 11 12 21 31 28 16 9 23 Placonotus spp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Si t ophi1 us sp. 172 120 106 76 105 105 126 98 "258 162 86 58 122 148 114 53 indet. Histeridae 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 Lyctus ?africanus 0 0 0 0 0 0 1 8 8 1 0 0 0 0 0 0 Minthea rugicollis 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Litargus balteatus 7 2 1 5 3 1 0 2 6 3 0 5 4 0 2 0 Typhaea stercorea 0 0 0 0 0 0 1 8 0 0 0 4 0 0 0 0 B. pi 1ose11 us 0 0 0 0 1 0 0 8 0 0 0 0 0 0 0 0 C. di m i di at us 19 7 6 12 17 17 8 23 30 16 13 17 18 6 6 9 C. fumatus 37 7 3 2 3 15 12 16 4 0 6 13 8 3 6 9 Lasiodacty1 us sp. 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 0 0 1 0 0 0 0 0 1 9 1 1 0 0 0 0 Monanus concinnulus 1 1 1 1 1 0 1 1 7 1 1 3 3 1 1 0 Gnatocerus m&xillosus 20 6 12 9 36 18 13 15 30 20 17 14 29 13 13 4 Pal embus ivoirensis 0 ' 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Palorus bobiriensis 1 0 0 1 0 1 0 • 0 2 0 0 0 0 0 0 0 P. carinicollis 0 0 1 0 1 0 0 0 0 0 '0 0 0 0 0 0 P. ficicola 3 1 0 1 6 2 1 2 7 • 2 . 3 5 •0 0 0 0 P. subdepressus 25 10 17 15 34 39 24 29 70 • 72 41 51 63 76 36 31 P. c rampe1i 0 0 0 0 0 0 0 0 0 1 . 0 0 0* 0 0 0 Sitophaflus hoi oleptoides 0 a 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Tribolium castaneum 0 I 1 0 2 0 1 1 0 0 1 1 0 0 0 . 0 T., confusum 0 0 0 0 0 1 0 0 0 0 0 0 0 1 1 '0 Stomylus sp. 0 0 0 0 . 0 1 0 0 0 0 0 •' 2 . 0 0 0 0 Latheticus oryzae 0 o 0 0 0 0 0 0 0 0 0 0 0 0 : 0 0 indet. Coleoptera • '0 0 0 0 0 1 0 - 0 0 0 0 1 0 0 0 * 0 Sitotroga cerealella 8 7 15 5 7 1 3 .3 10 12 2 2 5 7 5 • 2 Cardiastethus sp. 14" 1 1 - 1 7 - 1 0 4 3 0 3 7 6 1 •0 1 Cardiastethus sp. nymphs 9 0 0 0 0 0 0 0 1 0 0 1- 2 1 o 0 Lyctocoris cochici 6 -3 3 . 3 5 4 2 1 4 10 2 7 2 4 2 3 •5 L. cochici nymphs 2 2 1 9 2 4 1 5 10 5 8 1 3 5 1 Xylocoris afer 0 0 0 0 0 0 0 0 0 0 0 0 0 " 0 0 0 X. afer nymphs 0 0 0 0 0 0 0 0 • 0 0 0 0 . 0 0 0 0 P. biannulipes nymphs 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 0 Scolopoides divareti 3 1 0 0 6 6 0 i 1 1 2 1 16 4 3 1 3 S. divareti nymphs 3 1 0 0 2 4 2 . 4 16 3 0 10 3 3 0 1 indet. flnthocoridae 0 0 0 1 2 0 0 0 0 0 0 0 0 0 0 0 indet. flnthoc. nymphs 0 0 0 1 0 0 0 0 0. 1 0 0 •0 0 0 0 D. ?armatipes nymphs 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 Mizaldus sp. 2 0 0 0 1 1 2 2 0 1 0 ' 0 1 1 0 Mizaldus sp. 0 0 0 0 1 0 1 0 1 1 0 0 0 0 2 1 i ndet. Bethyli dae 0 0 0 0 0 2 0 0 0 1 0 0 0 1 0 1 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 1 0 finisopteromalus calandrae 1 0 0 0 0 0 1 0 0 0 . 0 0 0 • 0 0 0 Cerocephala dinoderi 3 1 2 2 1 4 3 2 5 0 0 4 2 3 2 3 Choerospila elegans 1 3 4 1 1 6 3 9 3 5 " 8 £ • 3 6 6 6 Habrocytus cerealellae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Mesopolobus sp. 0 0 0 0 0 0 0 0 0 1 0 0 " 0 0 0 0 indet. Scelionidae ' 0 0 0 0 0 0 1 1 . 0 0 ' 0 0 0 0 0 . 0 indet Labiidae 0 0 0 1 0 0 0 1 0 0 • 0 0 0 •0 0 0 indet Labiidae nymphs 0 0 • 0 1 0 0 . 0 0 . 0 0 0 1 1 • 0 0 Samp 1e 1? 18 19 20 21 22 23 24 25 26 27 28 29 30 31 grain temp. / 'C 26.3 26.0 26. 126. 7 26.8 26.5 26. 6 26.8 26.0 26.0 26. 5 26. 2 26. 126 . 126 . 2 26 grain m.c. s V. 17.8 17.6 17.2 17.4 18.9 18.2 17.4 17.9 13.3 18.3 18.4 IS. 7 18.5 17.9 17.0 1 7 sample wt. (grain) • g 285 266 297 302 278 245 264 216 sample wt. (cores) • g 269 299 222 243 219 253 263 2 105 88 86 1 12 87 82 76 104 123 89 71 90 72 SI 83 1 Lasioderma serricorne 0 2 0 0 1 0 0 0 0 0 0 0 0 0 0 1 flraecerus fasciculatus 1 1 0 0 2 0 1 0 2 1 1 1 0 0 1 1 • Bostrychoplites cornutus 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 Dinoderus minutus 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 Heterobostryehus brunneus 0 0 0 0 0 0 0 0 0 Necrobi a rufi pes 0 1 0 9 0 0 0 0 0 0 0 0 0 0 0 6 . 0 0 0 o 0 0 0 Microprius confusus 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 >3 Pseudobothrideres conrad. 0 0 0 0 0 0 0 0 0 Indet. Corylophidae 0 0 0 o 0 0 0 0 0 0 1 0 0 0 0 1 1 2 4 I 1 0 0 Cryptolestes spp. 23 22 6 15 19 24 16 26 16 Placonotus spp. 11 12 16 23 14 • 12 t £ . 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 Si tophi 1 us sp. 189 204 206 98 178 146 104 77 261 198 127 172 372 206 209 1 17 indet. Histeridae 0 0 0 0 0 0 0 0 0 Lyctus ?africanus - 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0— Minthea rugicollis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 1 0 0 2 1 1 0 4 • 4 3 0 13 10 0 0 3 Typhaea stercorea 0 0 0 0 0 0 0 0 2 B. pi 1osel1 us 1 1 0 10 & 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 C. dimidiatus 35 10 24 16 20 22 9 36 42 22 33 45 39 33 19 34 C. fumatus 3 1 1 . 7 6 23 20 37 LasiodactyI us sp. 4 20 13 1 10 0 1 3 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 Hypothenemus sp. 0 0 e 0 0 0 0 0 0 0 1 0 0 0 0 0 Cathartus quadricollis 0 0 l 1 2 1 0 0 0 0 Monanus concinnulus 1 1- 0 0 0 1 0 0 0 0 5 1 0 3 .4 0 4 1 Gnatocerus maxillosus 2 7 0 0 15 25 17 13 34 11 13 15 18 8 9 23 17 9 7 7 Palembus iuoirensis 0 0 0 0 e 0 0 0 0 0 0 0 0 Palorus bobiriensis 1 0 0 0 0 1 0 2 1 1 0 0 0 2 0 1 0 0 P. carinicollis 0 0 0 0 0 0 1 0 3 0 0 P. f i col a 0 0 0 0 0 2 0 . 0 1 3 1 • 3 2 11 2 4 3 4 1 1 0 P. subdepressus 59 83 47 33 124 103 69 47 P. crampeli 146 83 59 110 80 75 56 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sitophagus ho 1o1eptoides 0 0 0 0 • 0 6 -1 0 ' 1 1 3 0 0 0' 1 0 Tribolium castaneum 1 0 1 1 0 1 1 0 1 1 T. confusum. 3 5 2 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Stomylus sp. 0 0 0 0 0 0 0 1 1 0- O 3 0 0 0 0 Latheticus oryzae 0 . 0 0 0 0 0 0 0 0 0 • 0 1 indet. Coleoptera 0 0 0 0 0 0 0 0 0 '0 0. 0 0 0 0 0 0 0 0 0 Sitotroga cerealella 7 . 3- 1- 1 5 2 4 € 1 . 2 2 0 2 4 4 3 Cardiastethus sp. 0 0 .0 0 1 0 1 6 0 1 . 4 Cardiastethus sp. nymphs 0 5 0 0 1 0 0 0 0 0 0 • 0 • 2 0 0 1 " 0 1 0 0 1 Lyctocoris cochici •5 . 4 3 3 3 4 2 2 13 L. cochici nymphs 10 r • 10 12 6 7 10 4 3 9 4 2 4 4 2 12 / 12 8 14 6 8 6 Xy1oc or 1s .afer 0 0 0 0 0 0 0 0 0 , 0 0 2 0 0 0 ' 0 X. afer nymphs 0 0 0 0 0 0 0 1 0 P. biannulipes nymphs 0 0 0 0 0 0 0 0 • 0 0 • 0 0 •0 0 . 0 0 0 0 0 0 " 0 1 Scolopoides diwareti 1 2 0 2 5 4 6 11 4 1 1 1 1 S. divareti nymphs 5 3 0 0 0 0 3 5 3 0 5 6 . 0 0 • 3 2 0 indet. Rnthocoridae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 c indet. finthoc. nymphs 0 0 0 0 0 0 0 0 ' 0 0 0 0 0 0 D. ?armatipes nymphs 0 0 0 0 1 2 0 0 2 0 1 1 ' 1 rj Mizaldus sp. 0 0 0 1 1 3 0 2 0 0 2 2 1 0 1 5 0 2 4 3 1 Mizaldus sp. 0 1 6 0 1 1 5 0 1 i ndet. Bet hy1i dae 0 3 0 1 4 0 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 finisopteromalus calandrae 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Cerocephala dinoderi 8 9 0 2 0 0 1 1 2 3 Choetospila elegans 5 1 4 9 3 0 6 12 6 4 5 6 5 2 ". 8 4 10 6 o Habrocytus cerealellae 3 10 10 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Mesopolobus sp. 0 0 1 0 0 • 0 0 0 1 indet. Scelionidae 0 0 0 0 0 0 O 0 0 0 0 0 0 0 ' 0 0 0 0 .0 . 0 0 0 o i ndet Labi i dae 0 0 0 0 0 0 0 0 1 indet Labiidae nymphs 0 0 0 0 0 0 >3 1 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 DISTRIBUTION TRIAL IV 13/8/7 ai r t emp 23.0'C Crib 2 sample 3 9 morning • : Sample 1 2 3 4 5 6 7 8 9 18 1 1 12 13 14 15 16 grain temp. • 'C 23. 5 23.7 23.8 23.7 23.8 23 5 23.6 24. 1 23. 1 23.8 23.5 23. 4 23. 1 24.2 24. 7 25. 0 gr ai n m.c. / 17.5 16.6 15.9 16.6 17. 1 16 7 16. 1 16.6 16.2 16.6 15.7 16.8 16.5 16.0 15. 9 15.3 2 -p 9 sample wt. (grain) ' 9 277 385 268 278 285 338 289 224 295 289 264 179 247 306 251 sample wt. (cores) ' 9 93 187 74 98 82 184 93 99 93 98 94 75 71 68 92 89 Lasioderma serricorne 0 0 0 0 0 0 0 1 1 0 2 0 0 1 \ o 0 Araecerus fasciculatus 8 0 0 0 1 2 0 2 1 1 0 0 .0 0 0 0 Dinoderus minutus 8 0 0 0 0 0 0 0 0 0 0 0 0 0 .0 0 Heterobostrychus brunneus 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Rhyzopertha dominica 8 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 Microprius confusus 8 0 0 0 0 0 1 0 0 0 0. 0 0 0 0 0 indet. Corylophidae 1 0 0 0 0 0 1 4 1 • 2 1 0 1 2 0 0 Cryptolestes spp. .. 18 16 4 6 22 44 40 37 21 24 13 17 14 8 35 14 Si tophi 1 us sp. 273 242 144 81 229 219 136 114 225 165 223 103 273 170 154 145 indet. Histeridae 8 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 Lyctus ?africanus 8 1 0 0 0 0 0 0 2 0 0 0 0 0' 0 ~ Minthea rugicollis 8 0 0 0 1 0 0 0 1 0 0 8 0 0 0 0 Litargus balteatus 2 2 0 0 • 0 2 0 3 1 1 1 0 3 0 0 0 Typhaea stercorea 1 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 Brachypeplus ?gabonensis 8 0 0 0 0 1 0 0 0 0 0 0 1 0 i 0 B. p i1ose11 us 8 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 C. dimidiatus 31 18 21 12 23 32 23 17 18 45 27 8 10 4 6 7 C. fumatus 15 12 6 4 6 7 6 1 1 2 1 0 0 0 1 0 indet. Carpophilus 8 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Lasiodactylus sp. 8 0 0 0 0 0 1 • 0 0 0 0 0 0 '0 . 0 1 Hypothenemus sp. • 8 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis . 8 0 0 0 0 0 3 1 1 0 1 0 0 1 " 0 0 Monanus concinnulus 1 2 0 0 2 0 0 2 3 4 4 2 3 0 0 i indet. Staphylinidae 8 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Alphitobius sp. 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 17 25 11 5 37 36 24 28 23 30 20 5 16 36 22 2 Palorus bobiriensis 0 0 0 0 0 0 0 8 0 0 0 0 0 • 0 i 0 P. carinicollis 8 0 0 . 0 0 0 1 0 0 0 0 0 0 0 .0 0 — P. c er.y 1 onoi des 1 0- 0 0 0 0 0 0 1 0 0 0 0 0 0 0 P. f i c i col a 0. 0 0 '0 2 4 0 7 4 5 5 *0 2 0 1 1 70 67 36 34 P. subdepressus 6 13 11 5 62 66 27 29 28 63 •J »' 2$ P. crampeli 0 0 0 0 1 • 0 0 0 0 1 0 0 0 0 0 0 Sitophagus ho 1o1eptoides 0 0 0 0 0 0 • 0 0 0 0 0 0 0 1 1 0 Tribolium castaneum 0 3 0 0 0 0 0 1 3 4 0 0 1 1- 4 0 Vlatydema sp. 0 0 0 0 0. 0 0 0 0 0 0 0 0 0 - 0 ' 0 indet. Coleoptera 0 0 0 0 0' et 0 ' 0 0 0 0 0 0 0 0 Sitotroga cerealella 7 1 2 . 4 7 6. 4 .5 6 1 4 j 3 4 4 3 . Cardiastethus sp. 12 0 1 2 13 8 . 5 11 12 3 6 0 2 0 0 2 Cardiastethus sp. nymphs 5 2 • 0 1 4 2 2 1 4 ' 1 1 0 1 0 0 * 0 Lyctocoris cochici 0 0 0 - 3 2 3 2 6 2 > 1 5 1 1 2 2. • 1 L. .cochici nymphs 5 7 1 1 8 5 8 4 4 7 5 7 1 o 6 4 Xylocoris afer 0 0" 0 0. 8 . 0 0 1 0 ' 0 0 1 . 0 o' 0 , 0 Cethera musiva 0 0 0 0 0 0 0 0 1 0 0 0 ' 0 0 0 0 " P. biannulipes nymphs 0 0 0' 0 0 0 8 0 0 0 0 0 0 0 0 0 ' Scolopoides divareti 0 0 0 1 2 3 6 3 4 0 0 0 1 0 3 1 S. divareti nymphs 2 0 1 0 0 0 5 16 1 0 0 0 0 0 . 0 2 D. ?armatipes nymphs 0 0 0 0 0 0 0 0 "0 0 0 1 0 0 0 0 Mizaldus sp. 5 0 0 0 6 1 1 1 0 0 2 0 2 0 1 ? Mizaldus sp. nymphs 1 0 1 1 0 1 1 3 1 1 1 0 3 1 7 1 i ndet. Bethy1i dae 0 0 0 0 0 0 0 0 0 1 2 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 Ani sopteromal us calandrae 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 Cerocephala dinoderi 1 2 1 0. 3 6 4 0 7 6 1 0 4 3 1 1 Choetospila elegans 7 6 3 2 10 4 7 7 9 5 .5 5 15 11 8 3 Mesopolobus sp. 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 in'det. Seel i oni dae •1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 indet Labiidae nymphs 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 282. Sample 17 13 19 20 21 22 23 24 25 26 27 28 29 30 31 grain temp. / 'C 23. 0 24.8 25.0 24.8 23.0 24.0 24. 5 25. 0 23.2 23. 7 23. 2 24. 0 23.5 24 . 5 25. 0 24 . s grai n m. c . s V. 15.6 15.2 15.5 15.4 16.2 15.6 15.4 15.2 16.0 17. 1 16.S 16.2 15.6 15.2 15.0 15.3 sample wt. (grain) • g 190 387 309 286 196 345 332 234 265 298 229 171 252 316 336 sample ut. (cores) / g 74 98 107 97 88 105 95 73 92 116 95 88 106 96 Lasioderma serricorne 3 0 0 0 0 0 2 1 0 0 1 0 0 0 0 0 Araecerus fasciculatus 1 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 Dinoderus minutus 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 Heterobostrychus brunneus 0 0 0 0 0 0 0 0 0 • 1 0 0 0 0 0 0 Rhyzopertha dominica 0 0 0 1 0 0 2 8 0 0 0 0 0 0 0 Microprius confusus 0 0 0 0 0 0 0 8 0 0 0 0 0 0 o indet. Corylophidae 1 0 0 0 1 1 0 8 0 3 3 1 0 1 1 Cryptolestes spp. 12 11 24 27 23 52 44 22 21 ' 17 28 18 15 3 13 20 Si tophi 1 us sp. 181 297 199 168 166 211 178 186 303 313 260 138 399 362 240 167 " indet. Histeridae 0 0 0 0 9 2 8 0 0 0 0 0 0 8 0 0 Lyctus ?africanus 8 0 0 8 0 0 0 0 0 1 0 0 0 0 0 1 Minthea rugicollis 8 0 0 8 9 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 0 0 0 1 3 0 0 0 1 0 2 0 0 1 Typhaea stercorea — - -- - - 8 - 0 0 8 0 0 0 1 0 -4 2 2 2 0 0 - 1 ' Brachypeplus ?gabonensis 0 0 0 8 0 0 1 0 1 0 0 0 0 0 0 o B. pi 1osel1 us 0 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0 C. dimidiatus 36 21 6 18 17 43 32 26 50 56 52 28 38 29 •? C. fumatus 0 0 0 3 3 7 1 2 3 3 0 0 2 0 1 1 indet. Carpophilus 0 0 0 0 0 0 1 0 2 0 0 1 0 1 0 1 Lasiodactylus sp. 0 0 0 8 0 0 0 0 1 1 1 0 0 0 0 1 Hypothenemus sp. 0 0 0 8 1 0 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 0 0 1 0 1 3 1 1 0 0 1 0 2 1 0 0 Monanus concinnulus 4 0 - 0 0 3 2 1 0 5 12 8 4 4 2 indet. Staphy1inidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Alphitobius sp. 0 0 0 0 0 0 0 0 0 0 8 1 1 0 0 o Gnat'ocerus maxillosus 22 26 23 8 36 19 14 12 • 27 34 23 11 33 14 31 1 2 Palorus bobiriensis 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 1 o P. carinicollis 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 P. cerylonoides 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 P. ffcicola 1 0 0 0 4 11 7 0 . 8 0 5 1 2 0 0 0 P. subdepressus 41 45 44 51 44 97 103 40 113 105 72 114 126 1 Q2_ P.. crampelu V ._75 0 8 0 0 ' 0 0 0 0 0 0 0 0 0 0 0 0 Sitophagus hoioleptoides 4 1 8 0 0 0 0 1 0 0 0 0 0 0 0 0 0 Tribolium castaneum 0 4 0 0 2 1 4 0 6 1 1 1 4 1 0 0 Platydema sp. • 0 . 8 0 0 0 0 0 \ 0 . 0 0 0 0 0 0 indet. Coleoptera o 0- . 0 0 0 0 0 0 0 0 0 0 ,0 0 0 0 1 Sitotr'oga cerealella 7 3 6 5 1 6 3 3 0 3. 1. 1 7 3 3 Cardi asteth'us sp.- 6 1 0 1 0 2 1 1 1 . 2 . 0 X 3 0 0 Cardiastethus sp. nymphs 0 - 0 0 0 0 0 ' 0 . 0 0 a. 0 0 i 0 0 0 Lyctocoris cochici 0 3 2 0 1 5 5 3 3 2 4 3 3 L. cochi c i nymphs 2 ' 13 12 ' 7 6 5 8 14 • 29 . 22 28 12 .6 9 9 1 2 Xylocoris afer ' 0 0 0 2 0 0 0 0 1 0 • 0 1 • 0 0 0 1 Cethera musiva 0 0 0 0 0 0 0 0 0 - 0 Q 0 0 0 0 0 P. biannulipes nymphs 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 Sco1opoides.divareti ' 2 2 • 0 • 2 •5 5 10 5 2 5 1 2 0 0 1 S. divareti nymphs 0 0 0 0 0 5 8 5 ' 2 3 2 * 1 0 1 0 0 - D. ?armatipes nymphs 0 1 0 0 0 8 0 0 0 0 0 G • 1 . 0 0 Mizaldus sp. 0 1 2 3 0 8 2 0 0 0 0 2 4 0 2 1 Mizaldus sp. nymphs 0 2 5 0 0 1 0 0 1 1 0 0 0 0 o i ndet. Bethy1i dae 0 1 0 1 0 0 0 0 0 1 0 1 1 1 1 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 I 0 0 0 0 i3 -finisopteromalus calandrae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o 0 Cerocephala dinoderi 0 1 2 0 2 4 3 2 3 3 •y 0 10 4 4 Choetospila elegans c 12 6 3 2 6 8 6 8 11 13 9 10 12 5 Mesopolobus sp. 2 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 Indet. Scelionidae 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 indet Labiidae nymphs" 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 DISTRIBUTION TRIAL IV Crib 3 sample 3 28/8/79 p.m. air temp.:28.2'C Sample 1 2 3 4 5 6 7 8 I 9 10 11 12 13 14 15 16 grain temp. / 'C 27.-0 27.0 26.9 27.0 27.0 26.8 27.0 27.5 27.0 27.0 27.2 27.4 27.2 26.7 26.4 26.8 grai n m. c. / 'A 16.9 17.1 16.7 16.3 17.3 17.4 17.0 16.7 17.0 16.9 17.3 17.0 17.3 16.4 15.9 16.0 sample wt. (grain) / g 208 21.3 218 230 177 138 204 276 255 159 264 301 234 296 314 264 sample wt. (cores) / g 98 67 91 99 75 73 73 87 117 63 100 96 83 90 103 82 Lasioderma serricorne 0 1 0 1 0 . 0 0 0 0 1 0 0 0 0 0 2 flraecerus fasciculatus 0 0 0 0 1. 0 0 1 4 0 0 1 1 1 0 0 Bostrychoplites cornutus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Dinoderus minutus 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 indet. Corylophidae 0 0 0 0 3 1 2 0 0 0 0 I 1 0 0 0 Cryptolestes spp. 22 12 31 62 28 34 56 21 15 6 23 31 20 16 25 52 Placonotus spp. 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 Pseudostenotrupis sp. 0 0 0 0 1 0 0 a 0 0 0 0 0 0 0 0 Si tophilus sp. - g2 178 180 117 113 184"" 102 153 215 131 160 218 201 158 159 32 indet. Histeridae 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 Litargus balteatus 3 1 1 1 10 0 1 4 x 4 0 0 2 1 0 0 0 L. warius' 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 Typhaea stercorea 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 Brachypeplus ?gabonensis 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. di mi di atus 12 10 16 13 20 19 11 24 22 14 7 12 13 8 9 12 C. fumatus 0 13 4 11 8 5 2 20 0 1 2 6 0 0 1 0 Hypothenemus sp. 0 0 0 0 0 0 0 2 0 1 0 0 0 0 1 0 Cathartus quadricollis 0 0 1 0 ' 0 0 1 0 2 0 1 0 0 0 0 0 'Monanus ?concinnulus 0 0 0 0 1 1 0 1 1 0 4 1 3 0 0 1 Oryzaephilus mercator 0 0 0 0 "0 0 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 9 11 7 11 29 5 31 11 24 9 25 12 18 16 16 14 Palorus bobiriensis 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 P. carinicollis 0 0 0 0 3 0 1 0 0 0 0 0 1 0 0 0 P. cerylonoides 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 P. ficicola 0 1 0 1 1 0 3 1 7 1 0 3 2 0 0 0 P. subdepressus 26 20 17 32 74 - 33 49 33 95 37 48 36 56 67 33 22 Sitophagus ho 1o1eptoides 0 8 0 0 0 0 0 0 0 1 0 0 0 0 1 0 Tribolium castaneum 0 0 " 0 0 0 1 3 1 1 1 2 0 1 3 1 0 PIatydema sp. 0 0 1 0 0 0 0 0 0 0 0 0 0 - 0 0 0 Sitotroga cerealella 7 10 8 11 8 3 1 3 15 3 6 3 5 7 4 6 Cardiastethus sp. 8 6 1 2 13 7 1 3 17 1 7 9 2 2 2 4 Cardiastethus sp. nymphs 4 2 0 0 • 1 - 0 0 0 6 4 4 2 5 1 0 2 Lygtocoris cochici 1 1 1 1 & 2' 2 3 0 0 1 2 0 0 0 0 L. 'coch»ic i nymphs 1 0 . 1 0 0 "v 0 1 0 1 1 0 1 2 0 0 0 Xylocor.is afer 0 0 0 0 0 0 0 0 0 . 0 0 1 0 0 0 0 X. afer nymphs 0 e 0 0 0 0 0 0 0 0 0 2 '0 0 0 0 Peregrinator biannulipes 0 0 0 0 0 0 * 0 0 0 0 0 0 0 0 0 0 P. biannulipes nymphs 0 0 0 0 0 .. 0 0 0. 0 ~ 0 1 0 0 • 0 0 Scolopoides diuareti 0 6 6 8 23 11 ll' 23 8 4 0 5 5 1 1 8 4 S. divareti nymphs ' 3 2 16 30 37 31 43 16 4 1 10 6 17 3 9 indet. flnthocoridae 5 0 0 '0 1 0 0 0 0 2 0 8 0 1 0 indet. finthoc. nymph 0 0 0 3 1 1 0 0 0 0 0 0 0 0 0 0 0 D. ?armatipes nymphs 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Mizaldus sp. 0 1 2 5 4 2 3 3 3 4 3 2 4 0 7 Mizaldus sp. nymphs 2 3 3 8 3 1 1 2 1 3 6 4 3 12 4 i ndet. Bethyli dae 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 flnisopteromalus calandrae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cerocephala dinoderi 2 3 2 0 8 4 1 0 4 3 3 2 5 7 4 Choetospila elegans 3 10 5 6 7 8 3 4 10 5 9 3 8 7 11 Habrocytus cerealellae 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Mesopolobus sp. 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 i ndet. Seeli oni dae 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 indet Labiidae adults 0 0 0 0 0 0 0 0 0 0 0 0 0 0 " 0 0 284. Sampie 17 18 19 20 21 22 23 24 25 26 27 23 29 30 31 :;2 grain temp / 'C 27. 4 26. 4 26.8 27.3 27. 4 27.3 27.3 27.9 27.2 27. 0 27. 2 27. O 27.9 27. 0 27. 0 27. 2 grain m.c. / 16.4 16.2 15.6 15.6 16.9 16.2 15.9 16. 1 16.5 16.5 16.6 16.6 16.7 16.3 16.0 16.2 sample wt.. Lasioderma serricorne . 0 0 1 0 0 1 0 0 0 0 1 0 0 1 0 0 flraecerus fasciculatus 0 0 0 0 2 0 0 1 1 1 1 2 1 0 1 0 Bostrychop1ites cornutus 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 Dinoderus minutus 0 0 0 0 0 1 0 0 0 0 0 2 0 0 0 0 irfdet. Corylophidae 2 0 0 2 3 0 0 0 o 0 2 1 0 0 0 2 Cryptolestes spp. 29 12 22 54 39 31 26 50 29 9 27 10 10 9 20 26 Placonotus spp. 0 0 0 0 1 0 0 0 0. 0 0 0 0 0 0 0 Pseudostenotrupis sp. 0 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 Si tophi 1 us sp. 211 167 180 142 202 172 153 77 324 283 267 159~ 305 271 191- 1 l"o' indet. Histeridae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 1 0 0 0 4 3 1 8 1 0 0 3 2 0 1 0 L. war i us' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Typhaea stercorea 0 0 0 0 1 0 0 2 1 0 0 0 0 0 0 0 Brachypeplus ?gabonensis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. di mi di atus . 15 8 2 6 22 21 20 24 39 1 1 39 17 20 8 15- 9 C. fumatus 1 0 0 0 0 1 1 0 5 1 2 0 0 0 1 0 Hypothenemus sp. 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 Cathartus quadricollis 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 Monanus ?concinnulus 1 0 0 0 2 0 0 0 5 2 5 2 2 0 0 0 Oryzaephilus mercator 0 0 0 0 0 0 0 1 0 2 0 0 0 0 0 0 Gnatocerus maxillosus 17 6 26 15 34 21 13 12 32 19 19 9 6 15 20 9 Palorus bobiriensis 0 0 0 0 0 1 1 0 1 0 0 0 0 0 1 0 P. carinicollis 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 P. eerylonoi des 0 0 0 0 0 0 1 0 0 0 0 0 0 0- 0 0 P. He icol a 1 0 0 0 11 3 2 3 25 2 2 3 4 0 0 0 P. subdepressus . . JL08 24 79 61 _ 90 137 89 62 199 202 140 54 183 100 . 146 _ 102 Sitophagus hoioleptoides 1 0 0 0 0 0 0 0 • 1 0 0 0 • 0 0 0 0 Tribolium castaneum 1 1 4 1 0 1 0 4 15 1 3 2 3 1 4 1 Platydema sp. 0- 0 0 . 0 0 0 0 0 .0 0 0 0 0 0 0 0 Sitotroga cerealella 8 2 8 5 5 5 3 3 5 6 4 1 2 4 1 4 Cardiastethus sp. 11 1 0 . 2 16 3 2 0 13 1 3 0 5 0 0 0 Cardiastethus sp. nymphs - 5 1 0 1 2 0 0 0 1 2 " 2 0 3 0 0 0 Lyctocoris cochici 1 • 2 1 0 1 0 1 0 1 4 0 1 •0 2 • 2 3 L. cochici nymphs • v1 1 2 1 1 0 0 . 0 2 3 0 '4 0 O . 0 0 Xylocor i s afer 0 0 0 1 0 0 0 e 0 0 2 0 0 0 0 1 X. afer nymphs 0 0 0 1 0 1 0 0- 0 0 0 2 . 0 . 0 0 3 Peregrinator biannulipes 0 ' 0 0 0 0 0 0 0 0 0 1 0 0 ' 0 0 1 P. biannulipes nymphs .0 . 0 0. 0 0 0 0 0 - 0 ' 0 0 o" 0 1 0 1 Scolopoides divareti 6 1 3 4 9 8 6 7 19 9 * 15 .9 3 0 3 4 S. divareti nymphs 12 0 0 5 12 4 10 28 15 2 14 5 2 5 1 ( indet. finthocoridae 1 ' 0 0 0 . 0 0 0 1 0 0 0 0 0 ' 0 0 • 0 indet. flnthoc. nymph 0 0 0 0 0 0 0 2 0 0 0 . 0 0 0 0 0 D. ?armatipes nymphs 0 0 0 0 0 0 0 0 0 0 3 1 0 0 0 2 Mizaldus sp. 2 2 1 2 1 2 3 0 2 1 0 0 0 1. J •p Mizaldus sp. nymphs 1 1 4 5 2 0 3 0 0 5 0 0 4 3 1 1 indet. Bethylidae 0 0 0 1 0 0 1 1 0 0 0 0 0 2 0 flnisopteromalus calandrae 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Cerocephala dinoderi 3 7 3 3 3 6 7 4 8 8 3 6 7 9 8 1 Choetospila elegans 6 1 6 2 10 8 7 5 10 7 10 7 18 11 11 3 Habrocytus cerealellae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Mesopolobus sp. 0 1 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 indet. Scelionidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet Labiidae adults 0 0 0 1 0 0 1 0 0 • 0 0 0 0 0 0 0 DISTRIBUTION TRIAL IV Crib 2 sample 3 emergences from lO0g grain / one week Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 grain m.c. / X 17.5 16.6 15.9 16.6 17. 1 16.7 16. 1 16.6 16.2 16.6 15. 7 16.8 16.5 16.0 15.9 15.3 Lasioderma serricorne 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Araecerus fasciculatus 0 0 0 0 0 0 0 0 2 0 0 0 1 0 0 0 Dinoderus minutus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Rhyzopertha dominica 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0 0 Cryptolestes spp. 6 0 2 9 9 5 4 4 10 4 6 2 4 2 5 4 Si tophilus sp. 9 3 3 6 11 7 6 9 15 3 8 13 Q 5 3 8 Lyctus ?africanus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Litargus balteatus 0 0 0 0 0 1 0 0 8 0 8 0 <0 0 0 0 C. ditnidiatus 4 1 8 1 2 0 0 2 0 0 0 0 0 0 0 0 C. pi 1osellus 0 0 0 0 0 1 1 0 0 0 0 0 1 0 8 0 Hypothenemus sp. 0 0 0 0 2 1 1 0 0 0 0 0 1 0 0 0 Monanus ?concinnulus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 indet. Siluanidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 Gnatocerus maxillosus ' 12 1 1 3 3 5 11 13 21 1 1 1 1 4 7- 9 1 6 6 Palorus bobiriensis 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 8 P. ficicola 0 0 8 0 0 0 2 2 0 1 0 0 0 0 0 8 P". subdepressus 0 0 8 0 9 4 0 0 3 3 0 2 0 4 2 " "0— Tribolium castaneum 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 Sitotroga cerealella 1 0 1 2 2 5 3 1 1 1 4 2 7 5 2 2 Rhabdepyris zeae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 i ndet. Bet hy1i dae 0 0 8 1 0 0 0 0 0 0 1 0 0 0 0 8 Cerocephala dinoderi 2 0 4 1 3 2 3 2- 1 3 3 1 0 2 2 1 Choetospila elegans 5 3 8 1 11 «j 8 3 6 4 2 2 7 7 3 0 Mesopolobus sp. 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 0 .indet. Scelionidae 0 0 8 0 0 1 8 2 0 0 0 0 0 0 0 0 Samp 1e 17 18 19 20 21 22 23 24 25 26 - 27 ' 23 29 -30 31* 32 ~ grain ID. c. s X 15.6 15.2 15. 5 15.4 16.2 15.6 15.4 15.2 16.0 17. 1 16. 3 16.2 15.6 15.2 15.0 J 5. 3 J Lasioderma serricorne 0 0 0 0 0 0 1 0 ! 0 ' 0 0 0 0 0 0 8 Araecerus fasciculatus 0 0 0 0 0 0 8 0 i 0 •0 0 0 0 0 0 8 Dinoderus minutus . 0 0 0 0 0 " 0 8 R ! ' 0 0 0 0 0 0 0 0 Rhyzopertha dominica 0 0 0 0 0 0 8 I 0 0 0 0 0 0 ••0 0 Crypt blest as spp.' 4 2 5 6' 1 12 12 6 3 4 5 - S 7 0 3 & Si tophi 1 us sp. 10 4 7 5 10 10 12 9 ! 9 8 14- 14 10 . 8 3 7 Lyctus ''africanus 0 0 0 0 0 0 8 0 ! '0 1 0 0 0 0 0 0 Litargus ba.lt eat us 0 0 0 0 ' 0 0 8 0 ! 0 0 '0 0 1 0 • 0 0 ~ C. di m i d i at us 0 0 0 0 0 3 0 0 3 1 0 1 2 2 0 C. pi 1osel1 us 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 Hypothenemus sp. 1 0 0 0 0 0 0 8 0 ' 0 0 0 0 0 0 0 Monanus ?concinnulus 0 0 0 0 0 0 0 0 0 0 2 1 0 0 0 1 indet. Silvanidae 0 0 0 0 0 1 0 0 0 0 0 - 0. 0 0 0 0 Gnatocerus maxillosus 9 9 15 6 5 5 4 0 8 7 2 4 10 6 4 6 Palorus bobiriensis 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 9 P. ficicola 0 0 8 0 0 2 0 1 0 0 0 2 0 0 0 0 P. subdepressus 0 2 2 1 3 6 2 1 * 5 1 3 3 4 e. 3 Tribolium castaneum 0 0 0 0 0 1 1 0 1 0 1 1 0 1 0 • 0 Sitotroga cerealella 1 1 0 1 3 1 2 1 5 3 0 1 • 3 0 0 Rhabdepyris zeae 0 0 0 0 0 0 0 0 0 0 0 0 1 2 0 0 i ndet. Bethy1i dae 0 0 0 0 0 0 0 8 0 0 0 0 0 0- 0 0 Cerocephala dinoderi 3 3 2 1 2 7 5 . 1 2 1 0 2 4 1 ,1 Choetospila elegans 4 6 2 3 4 2 5 3 6 6 0 9 9 5 1 6 Mesopolobus sp. 0 0 2 0 0 0 0 8 0 0 •0 0 0 0 . 0 0. indet. Scelionidae 0 ' 0 0 0 0 0 0 1 0 0 0 0 ' 0 0" 0 0 DISTRIBUTION TRIAL IV Crib 3 sample 2 emergences from 100g grain / one week Samp 1e 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 grain m.c / 'A 16. 17.9 18.8 20.8 18.5 17.5 17.9 20.2 17.0 17.2 13.2 18.9 17.0 16.4 17.4 17.3 Lasioderma serricorne 0 0 0 0 0 0 0 0 0 1 0 0 0 8 0 0 flraecerus fasciculatus 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Dinoderus minutus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 Cryptolestes spp. 2 3 3 5 2 5 6 1 4 4 3 3 0 0 1 2 Si tophi 1 us sp. 17 5 4 18 10 9 13 9 9 11 4 10 13'' 9 10 8 C. dimidiatus 1 1 0 0 0 1 1 0 4 0 0 0 0 0 0 0 C. pi 1osel1 us 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Hypothenemus sp. 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 Monanus ?coneinnulus 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 Gnatocerus maxillosus • 3 4 7 3 9 5 7 3 9 9 4 e. 6 14 5 4 P. fi c i col a 0 0 0 0 0 0 0 0 1 1 0 0 2 0 0 0 0 P. subdepressus 0 0 0 0 0 0 1 2 0 6 3 1 1 1 0 0 Tribolium castaneum 0 0 0 0 0 0 0 0 0 1 £ _0 0 0 0 0 Sitotroga cerealella 4 3 1 1 3 1 0 4 5 2 0 1 7 2 2 2 indet. Chalcididae 0 0 9 0 0 0 0 0 0 0 0 1 •0 0 0 0 indet. Bethylidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 flni sopt eromal us calandrae 0 0 0 0 0 0 0 0 • 0 0 0 0 0 1 0 0 Cerocephala dinoderi 2 2 0 1 2 0 . 2 1 4 2 1 4 2 4 1 0 Choetospila elegans 4 2 1 1 5 5 2 3 9 5 3 4 2 2 3 2 Mesopolobus sp. 0 1 0 0 0 0 0 0 0 0 0 0 0 2 0 0 Samp 1e 17 18 19 20 21 22 23 24 25 26 27 23 29 30 31 32 grain m.c. / 16.7 16.4 17.4 18.0 16.9 16.5 16.7 17.9 17.0 17.1 1S.1 18.6 17.0 16.3 18.4 16.1 Lasioderma serricorne 0 0 0 . 0 0 • 0 0 0 0 0 • 0 0 0 • 0 ' 0 0 flraecerus fasciculatus 0 0 0 ' 0 •0 0 0 1 0 0 0 ' 0 . 0' • 0 0 0 Dinoderus minutus 0 0 0 0 0 0 0 0 0 • 0. 0 0 0 O 0 0 Cryptolestes spp. 4 * . 0 5 3 6 4 12 6 3 " 5 3 3 0 0 0 0 Si t ophi1 us sp. 19 9 10 20 10 11 12 18 12 13 12 23 12 6 14 C. dimidiatus 1 0 0 0 0 1 1 1 1 0 0 0 1 0 " 0 0 C. pi 1ose11 us 0 0 0 0 0 0 1 0 0 0 . 0 0 0 1 1 1 Hypothenemus sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Monanus ?concinnulus 0 0 0 0 0 0 0 0 0 0 • 1 0 8 0 0 0 Gnatocerus maxillosus 13 13 18 5 6 15 9 10 1 6 4 6 10 8 6 P. ficicola 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 P. subdepressus 2 6 7 1 5 2 4 .8 2 4 - 5 6 1 2 6 4 Tribolium castaneum 0 2 2 0 0 0 2 0 0 0 0 0 0 1 0 1 Sitotroga cerealella 7 2 1 1 1 0 0 2 0 2 7 3 1 5 0 0 indet. Chalcididae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Bethylidae 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 1 0. 0 0 0 0 o flnisopteromalus calandrae . 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 Cerocephala dinoderi 4 2 • 2 2 7 2 2 1 1 4 2 5 9 2 1 5 •p Choetospila elegans 5 3 4 3 13 8 4 5' . 7 10 10 8 a 2 10 Mesopolobus sp. 0 1 0 0 0 0 0 1 0 1 0 0 0 1 • 0 0 DISTRIBUTION TRIAL IV Crib 3 sample 3 emergences from 100g grain / one week Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 grain m.c. 16.9 17.1 16.7 16.3 17.3 17.4 17.8 16.7 17.0 16.9 17.3 17.0 17.3 16.4 16.0 Araecerus fasciculatus 0 0 1 0 0 8 0 1 0 1 1 1 2 0 0 0 Dinoderus minutus 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 1 Cryptolestes spp. 16 19 14 7 12 13 13 6 8 9 5 6 3 5 2 5 Si t ophi1 us sp. 11 4 18 12 8 6 6 14 7 6 1 1 7 16 3 4 4 Lyctus ?africanus 0 0 0 0 8 8 0 0 0 0 1 0 0 0 0 0 Typhaea stercorea 0 1 0 0 8 8 0 0 0 0 0 0 0 0 0 0 C. dimidiatus 1 3 0 0 1 8 0 0 0 1 0 2 1 0 0 0 C. fumatus 0 0 0 0 0 8 0 0 0 0 0 1 0 0 0 0 C. pilosellus 0 0 1 0 0 8 0 0 0 1 0 0 0 1 0 0 C. zeaphi1 us 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Monanus ?concinnulus 0 0 0 0 0 1 0 0 0 0 0 0 2 0 0 0 Gnatocerus maxillosus 4 6 2 5 8 3 4 3 5 2 3 2 2 8 2 8 Palorus bobiriensis •- 0 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 P. ficicola 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 P. subdepressus 4 0 5 2 3 2 7 l 4 5 3 4 4 2 0 2 P. indet 0 0 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 Sitophagus hoioleptoides 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Tribolium castaneum 1 0 0 0 1 0 0 0 0 0 2 0 0 0 1 0 Sitotroga cerealella 4 6 4 4 0 4 1 2 1 4 4 0 1 1 5 3 Rhabdepyris zeae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 indet. Bethylidae 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 Anisopteromalus calandrae 1 0 0 0 1 0 0 0 0 '0 0 0 0 0 0 0 Cerocephala dinoderi 1 5 6 1 4 2 ' 2 2 7 1 2 5 7 r 1 0 Choetospila elegans 4 8 . 6* 3 7 4 3 2 i 2 8 4 8 8 9 1 5 Mesopolobus sp. 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 —ar Sample 17 18 19 20 21 22 * 23 24 25 26 27 28 29 30 * 31 32 .grai n m. c . / v. 16.4 16.2 15.6 15.6 16.9 16.2 15.9 16. 1 16.5 16.5 16.6 16.6 16.7 16.3 16.0 16.2 * Araecerus fasc i cu l.atus 1 0 0 0 0 0 0 1 1 0 5 3 0 0 • 0 Dinoderus minutus 0 0 0 0 0 0 i 0 0 0 0 0 0 0 0 Cryptolestes spp. 11 4 3 6 • 7 6 6 4 2 1 0 5 3 3 Si tophi fus sp. . 16 £ 6 10 13 6 11 19 14 16 3 13 Lyctus ?africanus 0 11 11 1 1 & 0 0 0 0 0 0 • 0 0 •0 0 0 0 0 Typhaea stercorea 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. d i m i d i at us 0 0 0 0 ' 1 . 1 1 0 0 4 0 0 1 0 C. fumatus 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C. pi 1osel1 us 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 C. zeaph i1 us 0 0 0 0 0 0 0 0 0 0 0 0 0 Monanus ?concinnulus 0 1 3 0 0 8 0 0 0 0 0 0 0 0 0 0 0 Gnatocerus maxillosus 15 6" 11 6 24 5 6 8 18 7 Q 8 19 Palorus bobiriensis 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 P. ficicola 0 1 0 0 0 0 0 3 0 0 0 0 0 0 0 P. subdepressus 5 5 5 7 6 3 0 19 14 1 1 1 1 2 1 8 P. indet 0 0 10 0 0 0 0 0 0 0 0 1 0 0 0 0 Sitophagus hololeptoides 0 0 0 0 0 . 0 0 0 1 0 0 0 0 0 0 Tribolium castaneum 0 0 1 0 0 0 0 0 0 0 1 0 1 0 Sitotroga cere'alella 2 8 5 1 5 3 5 3 2 3 3 • 0 Rhabdepyris zeae 0 0 0 0 0 0 0 0 0. 0 1 0 0 indet. Bethylidae 0 0 1 1 • 1 0 1 0 0 1 1 0 0 Eupelmus urozonus 0 0 0 0 0 0 0 0 0 0 0 0 0 Anisopteromalus calandrae 0 "0 0,0 0 ,-0 0 0 '0 •0 0 • 0 0 Cerocephala dinoderi 2 3 3 6. 3 4 . 2 2 3 7 3 4 Choetospila elegans 7 '9 5 4 3 13 10 •3 6 12 Mesopolobus sp. 0 1 1 3 0 0 O 0 0 a 0 0 0 288. APPENDIX IV : Methods for estimation of moisture contents of grain and cores. The method used for estimation of grain moisture content was based on the International Organisation for Standardisation routine reference method (I.S.O., 1979). Briefly, this specifies that a sample of cereal (larger than 5 g) should be ground (maximum particle size specified), weighed accurately, heated in a well-ventilated oven (minimum ventilation specified) at 130-133°C for 2 hours (90 mins. for flours), cooled in a desiccator and then reweighed. The moisture content of that sample is then given by the change in weight according to the formula: m.c. = (m - raj x 100 o 1 m o where mQ is the initial sample weight (after grinding) and m^ the final weight after drying. Samples of moisture content, higher than c. 17% are 'preconditioned1 (i.e. dried as whole grain) for 7-10 minutes before being allowed to cool and then treated as above. The moisture content in this case is given as m.c. = (m - mj m„ + m - m x 100 o 1 J 0l 50 m m 2 o where m^ is the sample weight before preconditioning and m^ the weight after preconditioning and before grinding. Because of the large number of determinations required for this study the possibility of simplifying the method was investigated, with a view to speeding up the" handling of samples while retaining sufficient accuracy and repeatability. Practical constraints were also imposed by the type 289. APPENDIX IV : Continued. of grinders and the small size of desiccators available. Initially the possibility of heating whole grains was considered. However samples did not reach 'stable weight1 within a reasonable time (Fig. IV .1). Indeed, by the end of the period, whole grain samples had lost more weight than equivalent ground samples (which had reached stable weight), indicating that in the former some loss of dry matter had occurred. A suitable powered gravity-feed knife mill was not available for routine use but one was obtained briefly for initial 'calibration1. Results from samples ground on this mill were compared with those from a hand-operated plate-mill and from an electric knife mill without a gravity- feed system (similar to a domestic coffee-grinder). The hand-mill produced samples of coarser grade than that specified in the I.S.O. method, but was fast and convenient to use. The electric mill produced a very'fine flour but left a small numbfer of large fragments: increasing the grinding "time did not reduce these fragments but resulted in heating of the sample * Samples from this mill had to be sieved before drying and it was felt that this process might bias the results-by preferentially selecting flour ^endosperm (the fragments removed being from the hard vitelline part). The moisture content estimates for five samples (from the same grain) ground on each of the three types of mill and heated for 120 minutes did not differ significantly on a single factor analysis of variance at the 5% level. Samples ground on both the hand and routine electric mills reached stable weight in approximately the same time (Fig. IV .2), despite the-coarser grain of the former samples. The hand mill was therefore 290. APPENDIX IV : Continued. chosen for routine use as being more convenient to use. Allowing samples to cool in a desiccator before weighing did not discernably affect the estimate of dry weight (possibly because the top-pan balance used was too heavily 'damped' and/or not sufficiently sensitive to be affected by the convection currents generated by hot samples). It was concluded that samples could be weighed immediately on completion of the drying period (i.e. hot) without a serious loss of precision. Other conditions specified in the I.S.O. method (regarding the oven, measuring tins and sample density) were adhered to. Separate determin- ations on samples from well-mixed, pooled grain usually differed by less than 0.2% which was felt to be sufficient accuracy for the purposes of this study. There appears to be no generally accepted standard for the determin- ation of the moisture contents of cores of maize cobs. An estimate of this was, however, required'for the estimation of weight loss of whole cobs (see Appendix V) as .there is evidence that the core moisture content may differ considerably from the grain moisture content of the same cob, especially at high moisture contents, early in the storage season (see Fig. 2.7b)). A mill capable of grinding cores was not available and so the possibility of drying whole cores or transverse sections was investigated. •The bulk of the core consists of pith which was sufficiently porous to allow rapid water loss. Cores from maize in the cribs (i.e. at low. moisture content) reached their stable weight within one hour.while cores 291. APPENDIX IV : Continued. from freshly harvested maize appeared to lose most of their water content within four hours (Fig. IV .3), although there was a continuing slight loss of weight (possibly dry matter) thereafter. Sections of cores reached dry weight slightly faster than intact cores but the time difference was not sufficient to warrant the extra time required to cut them up (and label them) .. No independent method of estimating core moisture contents was available.. -However, the readiness with which heated cores reached a (more or less) stable weight suggested that this method could provide an estimate of core moisture content sufficiently accurate for the purposes of this study. 292. 37 *[ whole grains - high moisture content a 36 • \ ¥ 4* * X GO © 35 I 3 0 * 4» O 34 +• ' •* •*.*: ± > •."l. ^ •.. •. ,x •i i i i I 33 1 t . . . « t . . » t e 68 122 tee £40 Time / minutes 37 whole grains - low moisture content +.•* • • 03 36 \ 4> x u> * . ^ -.V... + .. "5 35 3 A 4> o 34 go ' ' ' « « • ' * ' —I— I II 1 I I I I I 8 68 188 188 248 Tim® a minutes FIGURE IV.1 : Drying curves for lOg samples of grain heated in a ventilated oven @ 130"C. (Total weights include weights of tins). The grain moisture contents (determined from ground samples were 32.4% (high) and 16.1% (low). 38 - ground samples - hand mill 37 v 4 • I: * T* • • Jp . • « . *• *• *. •. % '•f'. s s •.'.•. s •, ». \ ', \ t l i t l i I » i i • i. i i I i I l B 60 120 160 240 Time / minutes 38 ground samples - electric mill V +. •+• < • > • J. •+ ..+• i .. i i i i i i i i i 0 60 120 160 240 300 Tlmo / minutes FIGURE IV.2 : Drying curves for lOg samples of ground maize heated in a ventilated oven @ 130*C. Initial grain moisture content was 16.1%. 294. whole cores - high moisture content 1———4 1 j H -4 1 1 + •4 1 1 1 L. 180 240 300 360 420 480 Time /'minutes 40 r whole cores - low moisture oontent 35 09 \ 30 3 t®. 25 o o. -1 1 H 20 > 1 1 I ^Vf + 15 8 68 128 168 248 888 368 428 468 Time / minutes FIGURE IV.3 : Drying curves for whole cores heated in a ventilated oven at 130*C. Estimated initial moisture contents were 47+2% (high) and 11+1% (low). 295. APPENDIX V : Methods for estimation of dry weight loss of grain. A method was required which would provide an indication of both the progress of damage through the storage season and of its distribution in the cribs, over a wide range of moisture contents. Methods.based on weighing standard volumes or counting and weighing fixed numbers of grains were found to require too much time or sampled material if they were to achieve sufficient precision. The grain was inherently variable necessit- ating heavy replication but, as discussed in Chapter 3, it was felt to be unsatisfactory to remove from the cribs large quantities of grain which would then have to be replaced from a different source. The method used here involved the identification of individual cobs which were weighed at harvest and, in some cases, at intervals during the storage season. At the end of the season each cob was again weighed, shelled, and the core and sieved grain weighed separately. The cores usually^showed no visible insect damage during storage: itJwas therefore- - assumed (see below) that they had suffered no loss of dry matter and so, with a suitable correction for moisture content changes, their final weight could be used to estimate, by difference from the total cob weight, the initial weight of grain. The difference between this estimate of initial weight (corrected to dry weight) and the final observed grain'weight (similarly corrected) would be the estimated weight loss: estimated initial dry weight of grain (Gdwt^): Gdwt. = Tot. - (Cwt _ x 100 - Cmc. ) 100 in in f in 100 - Cmcf (100 - Gmc. ) m where Tot. = initial fresh weight of whole cob. in Cwt^ = final .fresh weight of core. Gmc. = initial grain moisture content, m 296. APPENDIX V : Continued. Cmc. = initial core m.c. in Cmc^ = final core m.c. estimated final dry weight of grain (Gdwt^) Gdwtf = Gfwtf x 100 (100 - Gmcf) where Gfwt^ = final fresh weight of grain. Gmc^ = final grain moisture content. The overall loss (dry weight basis) is then: Loss = Gdwt. - Gdwt- m f Gdwt. in The final grain and core moisture contents can be determined directly but there are difficulties in estimating the initial values. In the first trials of this method the initial figures were estimated from determinations on separate cobs drawn at random from the same population. However, at the high initial moisture contents (25-30%) encountered in these trials, sample variances were often equal to or greater than the means (Fig. 2.7 a)): the uncertainty in the estimate of dry weight of individual cobs was then of the same order as the total weight loss that could be expected over the storage period. Although the estimated mean dry weight loss (for a sample of, say, 10 cobs) might well have been close to the real value, the sample variance would reflect mainly the uncertainty in the moisture content correction rather than the variation in damage levels. A better estimate of the initial moisture content was provided by taking subsamples from the cobs individually at the beginning of the trial. APPENDIX V : Continued. Sections could readily be cut from the cobs using secateurs, to provide a core sample, and a ring or longitudinal file of grains shelled from the cob, to provide a grain samples. (Loose grains along the cut edges were stabilised with a small quantity of plastic glue). The relationship be- tween the moisture content of such subsamples and that of the remainder of the cob was not examined critically. The limited number of determinations made indicated that the regression for the relationship was significant but that, for core samples especially, variation was considerable. (This may have been due to the uneven uptake of free water by cores exposed at the tip by poor husk cover in the field). Given that the core accounted for only about 16-20% of the fresh weight of a cob, it was concluded that this system reduced the uncertainty in the moisture content correction sufficiently for the dry weight loss to be satisfactorily estimated. In order to test*the assumption that the core did not lose any dry weight, bare cores (i.e: with the. grain removed) were included in one storage trial. The cares were weighed at the beginning and end of the season. The initial moisture content was estimated from a section (approx. 20-30% of the whole core) cut from the apex or base and the final from the whole remainder of the core. No significant dry weight loss was detectable over the four month storage period but the uncertainty in the moisture content estimation (as above) was considerable and the result cannot be regarded as conclusive. In conclusion it would seem that the general method described here could, if suitably refined, be used satisfactorily in a variety of situations to estimate weight loss and especially in situations where the initial moisture content of the maize is nearer equilibrium. 298. APPENDIX VI : Collated Analysis of Variance Tables. Summary tables are given for the results of the analyses of variance which were quoted in Chapter 4v. Long-Term Distribution Trial (adults) 299-300 Short-Term Distribution Trial (adults) * 301-303 „ ,, „ (emergences) 304 Species and sampling occasions are specified by individual tables. Sitophilus zeamais sample 1 Source (Name) df Sums of Squares Me an'Square F F at i o F-Prob Total 23 2783.77 .121.03 A Exposure 1 . 49 . 49 . 0O4 . 9524 B East-West 2 351.41 175.71 1 .321 .2915 AB 2 38. 15 19.07 . 143 . 3674 Samp Ii ng Error 18 2393.72 •132 9.8 - K^me ) df Sums of Squares Mean Square F R at i o F-Prob Total 23 16288.23 708.18 A Exposure 1 1065.54 1065.54 1. 550 .2290 B East-West 2 2185.15 1092.57 1 . 590 .2313 AB 2 666.81 333.41 . 485 .6234 Sampling Error 18 12370173 "687.26 sample 3 « Source (Name) df Sums of Squares Mean Sfquare F Rat i o F-Proo Total 23 149323.23 6492.31 A Exposure 1 28666.31 28666.31 4. 958 . 0390 B East-West 2 8423.48 4211.74 .729 . 4963 AB 2 8169.73 4084.86 .707 . 5065 Samp 1i ng Error 18 104063.71 5781.32 sample 4 Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 23 2409047. 14 104741.18 - A Exposure 1 38527.37 38527.37 . 420 .5249 B East-West 2 267709.19 133854.60 1. 461 . 2583 AB 2 453451.53 226725.76 2. 474 . 1 124 Sampli ng Error - 18 1649359.05 : 91631.06 Cathartus quadricollis sample 1 Source (Name) df Sums of Squares Mean Square F Rat i o F-Prob Total 23 3963.29 .172.32 A Exposure 1 289.59 289.59 2.093 . 1652 B East-West 2 813.72 406.96 2. 940 .0785 AB 2 369.23 184. 61 1.334 . 2382 Sampling Error 18 2490.76 133.38 sample.2 Source ^Name> df - Sums of Squares Mean S"quare F Ratio F-Prob Total- 23 61686.76 2682.03 A Exposure 1 14334.01 14334/01 14.184 .0014 B East-West 2 22303.59 111.51.79 11.035 . OO07 AB 2 6858.93 3429.47 3. 394 .0562 Sampling Error 18 18190.22. 101Q.57 sample 3 Source (Name) df Sums of Squares Mean Square F Rat i o F-Prob Total 23 47744.56 2C75.85 A Exposure 1 332.60 332.60 .254 .6204 B East-West 2 7657.02 3828.51 2. 924 . 0795 AB 2 16189.39 8094.70 6. 183 . 0090 Sampling Error 18 23565.55 1309.20 sample A . _ Source (Name). df Sums of Squares Mean Square F Rat I o F-Prob . Total 23 67074.33 2916.28 ,- A Exposure 1 • 5557.31 5557.31 2.492 .1319 B East-West 2 19084.29 9542.14 4.27S . 03O2 .AB ' 2 2285.52 1142.76 .512 . 6076 Sampling Error 13 40147.21 2230.40 Carpophilus dimidiatus sample 1 Source (Name) df Sums of Squares Me an Square F Rat i o F-Prob Total 23 337.22 14. 66 A Exposure 1 4. 35 4. 35 .319 . 5791 B East-West 2 86.52 43.26 3. 176 .0659 AB 2 1.16 .58 . 042 .9535 Samp 1i ng Error 18 245^28 13.62 sample 2 Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Tot al 23 5669.65 246.51 fl Exposure 1 32.98 32. 98 . 143 . 7093 B East-West 2 1475.56 737.78 3.208 . 0643 AB 2 21.76 10.88 .047 .9539 Sampli ng Error 18 4139.35 229.96 sample 3 Source (Name) df Sums of Squares Mean Square F Rat i o F-Prob Total 23 3877.95 168.61 A ' Exposure 1 578.19 570.19 3. 847 . 0655 B East-West 2 453.12 226.56 1. 529 .2437 AB 2 186.58 .93. 29 . 629 .5442 Samp 1i ng Error 18 2668.85 148.22 sample 4 Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 23 121375.13 5277.18 A Exposure 1 33675.38 33675.30 9. 185 .0072 B East-West 2 18756.62 5373.31 1.467 .2569 AB 2 18946.23 5473.11 1. 493 .2513 Sampli ng Error 18 65996.98 3666.50 Gnatocerus maxillosus sample 3 . Source (Name) df Sums of Squares Mean Square F. Rat i o F-Prob Total 23 761.57 33. 11 A Exposure. 1 7. 15 7. 15 , . 208 - •6536 B East-West 2 73.81 36.91 1. 074 .3625 AB 2 62.87 31.03 . 903 .4229 Samp 1i ng Error 18 618.54 34.36 sample 4 Source (Name) df Sums of Squares Mean Square . F Rat i o F-Prob Total 23 53928.32 2344.71 A Exposure 1 105.35' 105.35 .082 .7785 B East-West 2 11186.38 5593 ^ 19 4.329 •- . '?292 AB 2 19382.42 9691.21 7.502 .0043 Sampling Error 18 23254.17 • 1291.98 Cryptolestes spp. • sample 3 Source (Name) df Sums of Squares Mean Square F R at i o •F-Pro b Total 23 752.85 32.73 A Exposure 1 18. 39 10. 39 . 288 . 5978 B East-West 2 33.81 16. 90 . 469 .6330 AB 2 68.80 30 . 00 .833 . 4510 Sampli ng Error 18. 648.65 36. 84 sample 4 Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 23 264765.40 11511 .-54 A Exposure 1 •2833.56 2033.56 .6432 B East-West 2 70371.73 35185.37 3.340 ."0408 AB 2 27447.41 1372-3.71 1. 498 . 2502 Sampling Error 13 164912'. 69. 9161 ."82 301. .Adults, (STDT) . Sitophilus zeamais Source (Name) df Sums pf Squares Mean Square F Ratio F-Prob Tot al 287 8059464. 60 28081. 76 Blocks 2 673520. 59 336760. 30 R a. m./m/p.m 2 9656. 61 4828. 30 . 393 .6757 B East-West • 3 2289760. 15 763253. 38 62 . 103 -.0000 C Pos i t i ons 7 1684024. 44 240574. 92 19 . 575 .0000 RB 6 18967. 27 3161. 21 .257 .9559 AC 14 142890. 73 10206. 48 .830 . 6354 BC 21 680546. 00 32406. 95 2 .637 . 0003 RBC 42 224980. 92 5356. 69 .436 .9990 Block Error 190 2335117. 88 12290. 89 otroga cerealella Source (Name) df Sums of Squares Mean Square F Rat i o F-Prob Total 287 48235. 26 168. 07 Blocks 2 5889. 56 2944. 78 R a. m./m/p.m 2 3765. 68 1882. 84 21 . 778 .0000 B East-West 3 3661. 72 1220. 57 14 . 113 . 0000 C Pos i t i ons 7 9701. 91 1385. 99 16 . 025 -.0000 RB 6 643. 58 107. 26 1 .240 .2875 AC 14 2082. 88 148. 78 1 .720 . 0544 BC 21 2840. 14 135. 24 1 .564 . 0618 RBC 42 3216. 93 76. 59 .886 .6717 Block Error 190 16432. 85 86. 49 pophilus -dimidiatus Source (Name) .df Sums of Squares Mean Square F Rat I o F-Prob Total 287 367008. 61 1278. 78 B1ocks 2 62618. 47 31305. 24 R am/m/pm 2 1097. 76 548. 88 . 941 . 3920 B East-West 3 33133. 65 11044. 55 18 .936 ..0000 C Posi t i ons 7 122175. 49 17453. 64 29 . 924 -.0000 RB 6 2848. 34 473. 39 .812 .5621 AC 14 2921. 24 208. 66 . 358 . 9844 BC 21 16053. 28 764. 44 1 . 311 . 1721 RBC 42 15356. 01 365. 62 . 627' .9628 Block Error 190 110820. 36 583. 27 Gnatocerus maxillosus Source (Name) d.f Sums of Squares - Mean Square F R at i o F-Prob Total 287 184856.82 644 . 10 Blocks 2 3556.21- 1778 . 1 1 R a.m./m/p.m 2 .4704.22 2352 . 11 4. 738 .0098 B East-West 3 11780.66 3926 .89 7. 910 . 0001 C Positions 7 31326.91 4475 .•27 . 9.01 4 . 0000 RB 6 1731.44 288 .57 531 . 7450 AC 14 3929.13 280 .65 565 .8895 BC ' 21 16100.44 766 .69 1. 544 .0672 RBC 42 17397.68 41-4 .23, 834 .7528 Block Error 190 94330. 1.3 496 .47 * Paloru"Sourcs e subdepressu(Name/ df s Sums of Squares Mean Square F Ratio F-Prob Total 287 1392492. 32 4851.,8 9 B1ocks 2 261474. 85 130737.,4 2 R am/m/pm" 2 31433. 08 15716.,5 4 8. 577 .0003 B East-West 3 38241. 71 12747.,2 4 6. 957 .0002 C Positions '7 571790. 30 81684.,3 3 44. 573 -.0000 RB 6 5068. 89 844.,8 2 461 .8365 RC 14 57566. 81 4111,,9 2 2. 244 .0077 BC 21 29167. 09 . 1388,.9 1 . 758 .7675 RBC 42 49593. 76 1180,, SO . 644 .9536 Block Error 190 348155. 83 1832,.4 0 yptolest£La_spp. Source (Name) df Sums of Squares Mean Squar £ F R at i o F-Prob Total 237 203844. 86 710. 26 Blocks 2 28516. 46 14258. 23 R a.m./m/p.m 2 6580. 91 "3290. 45 6. 940 . 0012 B East-West- 3 3723. 99 1241. 33 2. 618 .0523 C Positions 7 40215., 16 * 5745. 02 12. 116 . 0000 RB 6 641., 18 106. 86 . 9682 RC • 14 3702.,8 2 264. 49 '553 . 394 9 BC 21 17435.,5 1 830. 26 1. 75.1 .0265 RBC 42 12937.,8 9 . ' 308.0 5 650 .9506 Block Error 190 90090., 93 474. 16 302. Source (Name) df Sums of Squares Mean Squar e F Rat i o F-Prob Tot al 287 3227.32 11. 25 Blocks 2 39.88 19. 90 R am/m/pm 2 1.84 . 92 . 103 . 9026 B East-West 3 143.57 47. 86 5 . 338 . 0015 C Positions 7 418.85 59. 84 6 . 674 . 0000 AB 6 79.85 13. 31 1 . 434 . 1855 RC 14 1 15.37 8. 24 .919 . 5392 BC 21 265.62 12. 65 1 .411 . 1169 RBC 42 458.96 18. 93 1 .219 . 1875 Block Error 198 1783.45 8. 97 Litargus balteatus Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 287 18938. 41 38. 11 Blocks 2 44. 01 22. 01 R am/m/pm 2 151. 75 75. 88 2.,67 9 .0712 B East-West ' 3 1372. 32 457. 44 16., 153 . 0000 C Positions 7 1638. 31 232. 98 8.,22 4 . 0000 RB 6 88. 54 14. 76 ,521 . 7919 AC 14 395. 31 28. 24 ,997 . 4579 BC ' 21 753. 70 35. 89 1.,26 7 .2016 RBC 42 1121. 79 26. 71 , 943 .5750 Block Error 198 5388. 68 28. 32 Choetospila elegans Source (Name) .—rtf Sums of Squares ' Me4n"Square F Ratio F-Prob Tot al 287 16504.,8 3 57.,5 1 Blocks 2 272.,7 4 136.,3 7 fl am/m/pm 2 742.,8 1 371.,4 0 7., 769 . 0006 B East-West 3 1428.,3 8 476., 13 9., 960 . 0000 C positions 7 2264.,8 6 323.,5 5 6.,76 8 . 0000 RB 6 124.,3 8 28.,7 2 , 433 . 8560 RC 14 484.,4 3 28., 89 ,604 .8596 BC 21 595.,3 7 28.,3 5 ,593 .9201 RBC 42 1589.,3 2 37.,8 4 ,792 .8136 Block Error 190 9882.,6 3 47., 80 Cerocephala dinoderi Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Tot al 267 6562.,7 2 22., 87 Blocks 2 215.,0 4 107.,5 2 fl am/m/pm 2 360.,0 5 180.,0 2 9,, 984 . 8001 B East-West 3 ' • 978.,8 2 326.• c. •r18 .,89 5 . 0000 C pos i t i ons 7 248.,7 3 35.,5 3 1.,97 1 .0610 RB 6 53.,4 2 8.,9 0 ,494 . .8125 RC 1-4 314., 15 22..4 4 1..24 4 .2463 BC • 21 ; 318.,8 3 • 15.. 18 , 842 .6655 ABC 42 647.,8 2 • 15..4 2 ,855 .7203 Block Error 190 3425.,86 - 18.,8 3 - Cardiastethus pygmaeus . _ Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 287 20766.,7 4 72., 36 B1ocks 2 881.,4 0 400., 78 A am/m/pm 2 259.,8 4 129.,9 2 .4,,52 1 .0121 B East-West 3 5136.,0 7 1712.,0 2 C positions 7 4029.,5 6 575.,6 5 20., 031 . 0000 AB 6 426.,4 3 71., 07 2.,47 3 . 0251 AC 14 321.,6 6 22.,9 8 , 799 . 6691 BC 21 3135., 40 149.,3 0 5., 195 . 0000 ABC 42 1196., 04 28., 48 , 991 . 4946 Block Error 190 5460,.3 4 28..7 4 Lyctocoris.. cQchici. Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Tot a] 28.7 6764. 15 .23.57 Blocks . 2 392. 17 196.09 fl am/m/pm 2 294. 73 147.37 6. 662 .0016 B East-West 3 - 35. 45 11.82 . 534 .6594 C positions _. 7 ' • 1022.,2 4 146.03 6. 602 ,. 0000 FIB 6 55.,7 3 9.29 . 420 .8652 RC . " 14 205., 16 14.65 .662 . 8083 BC 21 142.,4 6 6.78 .307 .9987 pBC ' ' . 42 413,,1 6 • £.84 .445 .9987. B1 ock Error " 190 4203,. 04 '22.12 303. Scolopoides divareti Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 287 18698.45 65 12 Block % 2 3121.38 1568 65 fl am/m/pm 2 737.83 368 51 7. 884 .O012 B East-West 3 475.95 158 65 3.815 . 8312 C poslt ions 7 2127.66 383 .95 5. 777 . 0000 RB 6 31.44 5 24 . 100 . 9964 RC 14 516.27 36 88 .781 . 7719 BC 21 528.12 25 15 . 478 .9753 ABC 42 1156.22 27 .53 . 523 . 9927 Block Error 198 9996.46 52 .61 grain moisture content Source (Name) df Sums of Squares Mean Square F Rat i o F-Prob Total 287 294.,7 5 1..0 3 Blocks 2 13.,5 3 6.,7 7 fl am/m/pm 2 23.,0 4 11..5 2 13 . 906 . 00O0 B East-West 3 7.,6 3 2.,5 4 3 .869 . 0291 C positions 7 53.,4 9 7,.6 4 9 .226 . 0000 AB 6 4.,6 9 .78 . 944 .4651 • AC 14 11.,3 3 ,81 . 977 .4787 BC 21 17., 67 , 84 1 .816 . 4462 ABC -•42 6.,0 2 • - - . 14 . 173 1.0000 Block Error 190 157.,3 7 ,83 grain temperature Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 287 807.80 2.81 Blocks 2 9.59 4. 79 A am/m/pm 2 681.79 340.89 B East-West 3 4.42 1.47 5. 206 . 0018 C positions 7 13. 19 1.88 6.659 . 0000, AB 6 24.72 4. 12 AC 14 18. 64 .76 2.686 .0013 BC 21 1.74 .08 . 294 .9991 ABC 42 7.95 . 19 '.669 .9381 Block Error 198 53. 76 .28 i> emergences (STDT) Sitophilus zeamais Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 95 1797. 24 18. 92 Blocks 2 192. 52 96. 26 A East-West 3 378. 86 126. 29 10.410 . 0000 B Position 7 254. 66 36. 38 2.999 . 0089 AB 21 219. 05 10. 43 . 860 . 6390 Block Error 62 752. 15 12. 13 - Sitotroga cerealella Source (Name) df Sums of Squares Me an Square F Ratio F-Prob Total 95 . 354. 50 3. 73 Blocks 2 15. 75 7. 88 A East-West 3 20. 50 6. 83 1 . 675 .1815 . B Pos i t i on 7 20.5 0 2. 93 .718 .6571"' AB 21 44. 83 2. 13 . 523 . 9497 Block Error 62 2S2. 92 4.,0 8 Cryptolestes spp Source (Name) df Sums -of Squares Mean Square F Ratio -F-Pr„ob Total 95 1347.,9 9 14,. 19 B1ocks 2 196.,0 2 98,.0 1 A East-West 3 9,.4 5 3,. 15 .301 . 8248 B Pos i t i on 7 328..5 7 46,. 94 4. 482 . 0004 AB 21 164,.6 4 7,. 84 . 749 . 7663 Block Error 62 649,.3 1 10,.4 7 - -- Gnatocerus maxillosus Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 95 1976 .63 20 .81 Blocks 2 1 .31 .66 A East-West 3 106 .54 35 .51 1.827 . 1515 B Position 7 240 .29 34 .33 1.766 . 1 104 AB 21 423 . 12 20 . 15 1.036 . 4369 4 A Palorus _ subdepressus % !.... Source (Name) df ' Sums of Squares Mean Square F Ratio F-Prob Total 95. 1054.41 11.10 B1ocks ' • 2 165.81 82. 91 A East-West 3 15.61 5.20 • .640 5921 B Position 7. 291.82. 41.6? 5. 127 , 0001 AB 21 76.97 3.67 .451 ,9775 Block Error 62 504.19 8. 13' Choetospila elegans Source (Name) df Sums of Squares Mean Square F Ratio F-Prob Total 95 882. 24 9. 29 B1ocks 2 65. 40 32.,7 0 A East-West 3 67. 78 22.,5 9 3.,10 9 . 0327 B Position 7 157. 99 22*., 57 3 ,• 10 5 .0071 AB 21 140. 47 6., 69 , 920 • .5676 Block Error 62 450. 60 7., 27 •rocephala dinoderi Source (Name) df Sums of Square « Mean Square F Ratio F.-Prob Total 95 391. 49 4. 12 Blocks 2 43. 90 21. 95 A East-West 3 24. 36 ' ; 12 2\68 6 . 054 1 B Pos i t i on 7 . 35; 91 5. 13 1. 697 . 1263 AB 21 99. 89 • 4. 76 1. 573 . 0863 62 187. 44 . • 3. 02 B1 ock. Error \ Acknowledgements This research project was sponsored by the Tropical Products Institute (Overseas Development Administration) under the London University 'Public Research Institutes' scheme. Field work was carried out at the International Institute of Tropical Agriculture, Ibadan, with the co-operation of the F.A.O. /Danida African Rural Storage Centre. I would like to express my gratitude to Dr C.P. Haines, who set the project in.motion, and to Dr W.H. Boshoff, project leader at the African Rural Storage Centre, who was generous in making available research facilities and materials and, at a personal level, in providing advice and encouragement. Special thanks are also due to Mr Peter Egbele and Mr Victor Udoh for their good humoured assis- tance with the field work. Among the many friends and colleagues who have given me practical and moral support during the course of this study, I am particularly indebted to Dr T. Kaufmann, Dr Kamil Vanek, Dr Pat Matteson and Ms Deborah Elton. My thanks ate also due to Mrs Maureen Robiiison and Mrs Margaret Clements for their . help in preparing ani typing this thesis. Finally, I would like to express my warmest and most.sincere thanks to Prof Michael Hassell and Mr Philip Dobie for all that they have contributed in practical help, advice and encouragement. 306. REFERENCES ADAMS, J.M. & HARMAN, G.W. (1977). The evaluation of losses in maize stored on a selection of small farms in Zambia with particular reference to the development of methodology. Report G.109, T.P.I., London. ADESUYI, S.A. & ADEYEMI, S.A.O. (1970). A comparison of Malathion, i •• Iodofenphos and Bromophos for the control of insect infestation on maize in cribs. Nigerian Stored Prod. Res. Inst.3 Ann. Rep. 1970: 39-46. AITKEN, A.D. (1975). Insect Travellers. Vol. 1. Coleoptera. Technical Bulletin No. 31, H.M.S.O., London. AJIBOLA-TAYLOR, T. (1971). 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