BIOLOGY AND POPULATION ECOLOGY OF THE MUSTARD BEETLE
Phaedon cochleariae FABRICIUS
by
Maria Rosa S. de Paiva, Licenciada in Biology (Portugal)
A Thesis submitted in part fulfilment of the requirements for the Degree of Doctor of Philosophy in the University of London.
Imperial College Field Station Silwood Park, Ascot, July, 1977 Berkshire. 2.
ABSTRACT
The biology and population ecology of the mustard beetle Phaedon cochleariae Pabricius were studied under laboratory and field conditions.
In the laboratory, the relationships between temperature and fecundity, longevity, weight cycle and food consumption of adults were investigated.
The food preferences of the adults were tested and related to the nitrogen content of four species of cruciferous plants.
The relationship between temperature and development was studied for all stages. The number of larval instars was inversely correlated with temperature. Development thresholds were found to be higher for the eggs and larvae than for the pupae.
Measurements and diagrams of internal reproductive organs at different
stages of maturity were made and could be used in assessment of ages of field
populations.
As an aid to the interpretation of mortality in a field population,
a laboratory population was set up and its fate was followed in the absence
of natural enemies. The highest mortality in the laboratory occurred in the eggs and last larval instar. Pupal mortality was very low.
The field population originated from reared adults, released onto
a crop of turnips in Spring 1974. This population was studied for the
following three seasons. Adults, eggs and larvae were sampled at regular
intervals, while the rate of pupation was estimated independently.
Mortality occurred in complete absence of parasitism, but predation
by carabid beetles and spiders was detected. Density independent factors 3. were the main causes of mortality. Thus, in 1974 and 1976, the normal sequence of life cycles was upset by extreme weather conditions. Popula- tion budgets are given for the three years of this study.
The behaviour of the adults was investigated both in an insectary and in the field. The ability of the beetles to fly, and some of the factors that influence dispersal were studied. Experiments with marked adults showed that movements were over a short distance and that dispersal by walking took place only under conditions of acute food shortage. 4.
CONTENTS
ABSTRACT
CONTENTS 4
INTRODUCTION 11
Geographical distribution of Phaedon cochleariae. 13
History of pest attacks in Britain 14
SECTION I - Biology of P. cochleariae 17
1. Life history 17
2. Separation of sexes based on weight and size 20
3. Methods of rearing 22
4. Effect of temperature on fecundity, longevity and
weight cycle of adults 22
4.1 Introduction 22
4.2 Materials and methods 24
4.3 Results 25
a) Effects of two temperatures on a single
variable 25
i) Fecundity 25
ii) Pre-oviposition, oviposition and
post-oviposition periods 25
iii) Longevity 27
iv) Mature weight 27
v) Rate of oviposition 28
b) Relations between pairs of variables at
a constant temperature 32
i) Longevity and fecundity 32 . 5. Page
ii) Longevity and mature weight 32
iii) Fecundity and mature weight 32
c) Relation between weight rise from emergence
to maturity and 33
i) Fecundity 33
ii) Longevity 33
d) Effect of weight at emergence on its increase
to maturation. 33
4.4 Summary and conclusions 35
5. Effect of plant species on fecundity, longevity
and weight cycle 37
5.1 Introduction to 5. and 6.1 37
5.2 Methods and host plants 38
5.3 Results 39
a) On mustard 39
b) On chinese cabbage 39
c) On Brussels sprouts 39
i) Old plants 39
ii) Young plants 39
5.4 Summary and conclusions 42
6. Experiments on food consumption by adults 43
6.1 Introduction (See 5.1) 43
6.2 Effect of plant species on amount of food
consumed 43
a) Methods and host plants 43
b) Results 43
c) Total nitrogen content of host plants 43 6. Page
e) Summary and conclusions 45
6.2 Effect of temperature on amount of food
consumed. 47
a) Methods 47
b) Results 47
c) Summary and conclusions 50
7 Effect of temperature on developmental rates of
immature stages and mortality 50
7.1 Aim of experiments 50
7.2 Experimental methods 51
a) Eggs 51
b) Larvae 51
c) Pupae 51
7.3 Analysis of results 52
a) Eggs 52
b) Larvae 58
c) Pupae 60
7.4 Summary and conclusions 60
8 Lower lethal limits of temperature 61
8.1 Developmental thresholds of immature stages 61
8.2 Survival of adults at low temperatures 62
a) Methods 62
b) Results 63
c) Discussion 63
8.3 Summary and conclusions 65 7. Page
9. Reproductive organs and sexual maturation 65
9.1 Aim of observations and experiments 65
9.2 Methods 66
9.3 Results and description of the
reproductive organs 67
a) Males 67
b) Females 68
9.4 Summary and conclusions 73
SECTION II - Laboratory studies on adult behaviour 79
1.1 Introduction to SectiOn II and Section III - 11. 79
1.2 Ability to fly 80
1.3 Effect of starvation on locomotory activity
and flight 80
1.4 Effect of density on dispersal 82
1.5 Effect of the quality of food on dispersal 8.3
1.6 Effect of the water content of soil on
locomotory activity 83
1.7 Summary and conclusions 86
SECTION III - Population studies 88
A - Laboratory experiments 88
1. Materials and methods 88
2. Population budgets 89
2.1 Introduction 89
2.2 Estimation of population parameters 93
2.3 Budget of a population in controlled conditions 97
2.4 Analysis of the budget data 97 8.
Page
Field experiments 101.
1. Description of the study area 101
1.1 Plot A 10.1
1.2 Plots B and C 103
2. Sequence of field experiments 104
2.1 1974 104
2.2 1975 104
2.3 1976 105
3. Sampling methods _106
3.1 Eggs, larvae and adults 106
3.2 Pupae 107
i) Estimation of the rate of pupation 107
3.3 Summary and conclusions 109
4. Methods of ageing the population 111
4.1 Examination of reproductive organs 111
4.2 Cuticular rings 111
4.3 Summary 111
5. Examination for parasitism 112
6. Predation 112
6.2 Arthropod predators 112
a) Field observations 112
b) Pitfall traps and sticky traps 113
c) Feeding trails in the laboratory 116
d) Field collections 116
e) Summary and conclusions 117 9.
Page
7. Estimates of field populations 121
7.1 Estimation of population parameters 121
a) Natality 121
b) Durations of immature stages 121
c) Survival rates and recruits to stages 122
7.2 Population budgets 133
a) Description 133
b) Analysis of the budget data 133
7.3 Summary and conclusions 135
8. Population patterns of distribution 138
8.1 Introduction 138
8.2 Type of distribution 139
a) Eggs 139
b) Young larvae 143
c) Old larvae 143
d) Adults 144
8.3 Summary and conclusions 144
9. Studies on dispersal 145
9.1 Use of marked adults 145
a) Home range 148
b) Rate of dispersal 148 10.
Page
9.2 Survey of adjacent areas 148
9.3 Invasion of a crop 149
9.4 Experiment on mixed cropping 149
9.5 Summary and conclusions 154
General Discussion and Summary 156
Acknowledgements 164
References 166
Appendices 176 INTRODUCTION
The mustard beetle, Phaedon cochleariae Fabricius (Coleoptera,
Chrysomelidae) is a pest of the family Cruciferae.
In the United Kingdom, during the first half of this century, it
has often been reported to be of economic importance, particularly to water-
cress growers. However, since 1960 it has been observed less frequently and
at levels below the threshold of economic injury.
Over the last decade, this decline has been accentuated to such
an extent that nowadays it is difficult to find the species out of doors.
No references to attacks in other countries, in recent years, could
be traced. Apparently, the decline of this species is not restricted to
Britain. One of the latest references where P. cochleariae is still con-
sidered as causing losses of economic importance, dates back to 1962 (publ.
1965). In this paper, Stepanova states that the mustard beetle, together
with nine other insect species "....are the principal pests of cruciferous
crops in the North-West of the Soviet Union.".
The aim of the present work was to understand the population
ecology of this beetle. It was expected that this investigation would
reveal some of the reasons for the reduction of its numbers.
The paucity of existing data on the biology of this species,
determined that a major section of this project was devoted to the study
of parameters such as fecundity and rates of development, under laboratory
conditions.
A culture of P. cochleariae was kindly supplied by the Insecticide
Department of Rothamsted Experimental Station.
The plants used in all laboratory experiments were grown in the 12. greenhouses of Silwood Park. Under these circumstances, outbreaks of aphids, especially Myzus persicae and Brevicoryne brassicae, were frequent and difficult to control. Several measures of control were tried such as spraying the plant with a 10% soap solution, but without success. During
October 1974, spraying the turnip plants with a nicotine solution, resulted in over 70% mortality of the adult beetles.
At this stage, help was sought from the Horticultural Department of
Reading University, who kindly offered a new batch of insects.
The field work extended for three seasons. Over this period, extreme weather conditions recorded during the Summers of 1974 and 1976, influenced the outcome of the experiments. The first season was cold and wet, in contrast to the last one, which was excessively hot and dry.
In the Spring of 1974, prior to the main studies on population
ecology, a small scale field trial was set up to observe the behaviour of
the adults.
Conflicting references were found in literature, regarding the
ability of this species to fly. Experiments were designed to assess the
means by which the invasion of crops is achieved and the potentiality of
P. cochleariae to disperse.
The mustard beetle has few natural enemies, the main one being the
tachinid Meiginia floralis. A survey of parasites and predators was con-
ducted throughout the project.
The botanical names quoted are reproduced from the Royal Horticultural
Society Dictionary of Gardening. For the Cruciferae used in the study of
food preferences, the commercial brand of seeds is also given.
In the Tables, the level of significance obtained for the statistical
tests performed is indicated by stars, according to the convention : *P<0.05,
**P<0.01, ***P<0.001. 13. Geographical distribution of Phaedon cochleariae
The mustard beetle Phaedon cochleariae F. is distributed throughout
Europe and Asia Minor (Weise, 1916). Although Schaufuss (1916) considers it as a Northern European species, its occurrence is reported in Morocco by Balachowsky (1958) and in Japan by Balachowsky and Mesnil (1936).
Fall (1929), says that it is "essentially of Northern distribution", also occurring in North America: Massachusetts, New York, Quebec, Ontario,
Minnesota, Manitoba, Alberta and Utah. Lindroth (1957) considers it as a doubtful case of unintentional introduction, that has now spread in the
North East of the United States and in East Canada, West of Utah and
Alberta.
In Europe, the distribution of P. cochleariae is given by Seidlitz
(1881) as stretching North to Finland and Sweden. In 1935, Munster mentions it as a Norwegian species, only present in the southeastern districts.
In Denmark it is associated with aquatic crops, such as Nasturtium
aquaticum and Roripa amphibia (Hansen, 1927). Everts (1903) mentions its
occurrence in the Netherlands. In Germany it occurs on Nasturtium amphibium
and N. palustre (Reitter, 1912).
In East Europe it is distributed over Czechoslovakia and Hungary
(Roubal, 1937-41). Seidlitz (loc. cit.) lists this species in his Fauna
Baltica and Fauna Transsylvanica, in both regions being "frequent and
sometimes noxious".
It is also present in Austria (Redtenbacher, 1858) and in Switzerland,
appearing "frequently in large numbers, in meadows " (Stierling, 1898).
Deville and Mequignon (1935-38), report the distribution of the mustard
beetle all over France and Bedel (1889-1901) makes special reference to its
presence in the Seine basin. According to Porta (1934), P. cochleariae
is distributed throughout Italy, while in Spain it is only present in the
North-West province of Galicia (Garcia-Tejero, 1962-63). 14.
The following section deals with its distribution in Britain. In
Ireland, this species is reported to occur both in Ulster and in the Irish
Republic (Johnson and Halbert, 1902).
History of pest attacks in Britain
Early papers, such as by Sharp (1910) report the occurrence of
P. cochleariae in the United Kingdom. A leaflet, published in 1912 by the Board of Agriculture and Fisheries states that it is distributed over
England, Scotland and Ireland, but "....complaints... come chiefly from the
East side of England.". Many acres of mustard are said to have been spoiled by the mustard beetle and some measures of control are indicated.
Roebuck (1916), reports that "...watercress beds on a Shropshire farm have suffered severely from the attacks of the mustard beetle...".
In a further paper (1929), he describes a mass migration observed in
Wainfleet, when the beetles invaded a watercress bed by means of walking.
Miles (1923) gives details of more attacks in the Fen district and recom- mendations of its control.
Thompson (1931 and 1932) refers to heavy losses of watercress in West
Glamorgan. He points out that such extensive injury had never been exper- ienced before. Control was attempted with Derris and Pyrethrum sprays. A further attack, recorded in South Monmouthshire, was controlled by flooding the beds. Edwards (1937) reports severe attacks on watercress, in South
Wales, during 1935 and 1936. Pyrethrum and Derris were again used, with some success.
An advisory leaflet (1950) from the Ministry of Agriculture, indicates dusting with D.D.T. and B.H.C. as the best method of controlling the beetles.
Smith (1951) emphasises the damage caused to crops of cabbage, mustard and
cauliflower and draws attention to the wild host plants of this insect. 15.
Weeds like Cardamine amara, Sinapsis arvensis and Raphanus raphanistrum act as alternative hosts and should thus be removed from the proximity of the crop.
pnd J ones References later than 1960, e.g. Jones/ (1973) and Ministry of
Agriculture, Fisheries and Food (1967) generally state that this insect had become uncommon, except on watercress. D.D.T. is openly recommended as an effective method of control.
Tables IA and 1B were compiled from the available records, between
1949 and 1970 (Ministry of Agriculture, Fisheries and Food). Its analysis show that, the total number of attacks recorded was much higher over the period 1949-59 than in the following 11 years (1960-70). The preferred target of this pest was watercress, with 18 attacks out of the total 32.
Furthermore, during the first period, the zones more heavily attacked were
situated in the East Midlands, while between 1960 and 1970 infestations
occurred mainly in the South West of England. This is probably a result
of changes in agricultural practice.
References to any attacks of the mustard beetle could not be obtained
for years later than 1970. Between 1973 and 1976, a search was carried out
for any outbreak of this pest in England. Several Advisory Centers were
contacted and watercress beds visited, without success.
Within the genus Phaedon, the species cochleariae Fabricius is
considered the most common. It seems that the decline in numbers of this
species, observed in the 1960's, is continuing in the 1970's.
1 6.
TABLE 1A
INTENSITY OF ATTACK TOTAL NO. OF ATTACKS Light Medium Severe Period 1949- 1960- 1949- 1960- 1949- 1960- 1949- 1960- Crop f time -59 -70 -59 -70 -59 -70 -59 -70
Watercress 5 2 2 2 5 2 12 6
Mustard 2 0 1 0 0 1 3 1
Cabbage 3 0 0 0 2 2 5 2
Others 0 0 0 1 1 1 1 2
TOTAL 10 2 3 3 8 6 21 11
TABLE 1B
NUMBER OF ATTACKS Period Area of time 1949-59 1960-70
South Wales 3 0
South West England II 6
East Midlands 9 4
West Midlands 4
Berkshire 2 0
Lancashire 2 0
TOTAL 21 11
TABLES IA and 1B - Number of attacks by P. cochleariae recorded
in Britain, between 1949 and 1970. IA - Type of crop and intensity of
the attack. IB - Number of attacks in separate areas. 17.
SECTION I - Biology of P. cochleariae
1. Life History
Phaedon cochleariae F. was previously known as Phaedon betulae L.
(Board of Agriculture and Fisheries, 1912). It is a small insect, 4 to 6mm long and 3 to 4mm wide that weighs between 5 and Ilmg. It is oval and black with a metallic blue sheen; the ventral side and appendages are also black.
A pair of apparently functional wings is present, covered by strong elytra.
There are no external characters for the distinction of the sexes. Never- theless, females are generally heavier and larger than the males.
Both the larval and the adult stages can cause considerable damage
to cruciferous crops. In England, this species has been described as having
two overlapping generations per year, although Hamnett (1944) found that
three generations were produced in South Wales.
The adults emerge from hibernation by late April or May, according
to weather conditions and start feeding on the leaves of the crop. Copula-
tion takes place almost immediately, followed by egg laying within three
days.
Eggs are laid individually or in small groups, in shallow depressions
made by the female in the leaf tissue, more frequently on the underside of
the leaves, along the veins. The egg is ellipsoid, with a smooth chorion
and measures between 0.6 and 1.0 mm in length and between 0.3 and 0.5mm in
width. It is pale yellow, soon after being laid, darkening progressively
until eclosion, when it is orange in colour. Oviposition extends over May
and June, the incubation period varying from seven to 18 days.
The larvae feed actively on the leaves throughout the larval period,
which may last between 14 and 25 days, and moult two or three times. They
are cruciform, brownish with a black head, with two rows of tubercles along
the body, from which yellow glands can be protruded. 18.
When the first instar larvae emerge, they measure about 1.5mm and they do not disperse. The second instar is slightly more active, each larva being about 2.5mm long, after the moult. During the third and fourth instars, movements of some individuals towards contiguous plants are likely.
Their size varies between 3.0 and 6.0mm. By the end of the last instar they stop feeding, become inactive and fall to the ground.
Pupation takes place in the soil, at a depth of 2 to 4cm (Miles, 1923) some of the pupae being enclosed in a cocoon made of earth, while others are unprotected. This is a particularly vulnerable stage to ground preda- tors, partly because it lasts from seven to 14 days and also due to the lack of a hardened pupal. : case.
The pupae are piano-convex and the dorsal surface is covered with brown bristles. They measure 4 to 5mm in length and 2 to 3mm across. The colour is bright yellow at first, gradually darkening to brown near emer- gence, when the antennae, mouth parts, eyes and tarsi become visible through the pupal cuticle.
The adults are soft and pale yellow upon emergence, but after a few hours the pigmentation of the exoskeleton is completed and the cuticle becomes hard and acquires its characteristic dark colour.
The first generation occurs between the end of June and the middle of August and the second between the end of July and September (Figure 1).
This one causes the most severe damage to the crops, both because its numbers are greater than those of the first generation and on account of
the phase of the culture, which is generally close to its flowering period.
These adults do not become sexually mature, but seek refuge for hibernation at the first low temperatures. They spend the Winter in the hollows of the stems, under bark or hidden in straw or stubble. V A
2nd
FIGURE 1 Diagram showing life history of P. cochleariae, in Britain
20.
2. Separation of Sexes Based on Weight and Size
In Section I, 9., the reproductive organs of 48 adult beetles,
24 males and 24 females were studied. Before the dissections, the weight and some external measurements of these insects were recorded.
Significant differences in weight, total length and maximum width were found between the two groups, when t - tests were performed (Table 2)
The frequency distribution of the three variables is shown in Figures 2A,
2B and 2C.
It can be concluded that, although there is no sexual dimorphism in this species, a fairly reliable estimate of the sex of an adult beetle can be based on its weight and size.
WEIGHT TOTAL LENGTH MAXIMUM WIDTH x 6.33 7.67 3.60 4.09 2.19 2.37 s 0.84 1.13 0.21 0.39 0.21 0.13 t 5.53*** 5.11*** 3.60** d 23 23 23
TABLE 2 - Means, standard deviations and significance of t tests,
comparing the weight, total length and maximum width of
48 adults of P. cochleariae (24 males and 24 females). 21.
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 5.4 5.9 6.4 6.9 7.4 7.9 8.4 8.9 9.4 9.9 10.4 2A Weight (mg)
12 11 10 00 9
7 >-6 a c3.) 5 car 4 it 3
2 1N
3.00 3t20 3.40 3.60 3.80 4.00 4.20 4.40 4.60 4.80 3.19 3.39 3.59 3.79 3.99 4-19 4.39 4.59 4.79 4.99 2B Total Length (mm)
1.80 1.90 2.00 2.10 2 20 2.30 2 40 2.50 2.60 2.70 1.89 1.99 2.09 2.19 2 29 2-39 2 49 2.59 2.69 2.79 2C Maximum Width (mm )
FIGURES 2A, 2B and 2C Frequency distribution of the weight, total length and miraum width of 48 adults of P. cochleariae (24 dd and 24 49). 22.
3. Methods of Rearing
The culture was kept in a constant temperature room at 25°C with a period of 16/24 hcurs of light, provided by four neon tubes of 20 watts each, placed 70cm above the bench. Relative humidity was not controlled, but fluctuated around 70%.
The adults were put into plastic buckets closed with muslin squares, in groups of 60 to 70, together with one potted turnip plant - Brassica napus cv. Green Tops (from Suttons) - which provided both food and oivposition sites.
The plants were renewed daily. Those with eggs were enclosed in celluloid cylinders with open tops. A day prior to the emergence of the larvae, the cylinders were removed and the plants were enclosed in muslin sleeves, tied at both ends with a piece of tape.
During the larval stage, a new turnip plant was inserted every day in each sleeve, following the method described by Way et al. (1951).
Pupation occurred inside the sleeves. The pupae were collected and transferred to a container with moist sterile peat, left inside an
emergence cage.
4. Effect of Temperature on Fecundity, Longevity and Weight
Cycle of Adults
4.1 Introduction
Many authors have stressed the importance of temperature upon
variations of insect fecundity, that is a measure of the total number of
eggs produced by a female (Southwood, 1966), and on the rate of oviposition,
i.e. the rate at which eggs are laid. 23.
It is known that for each species there is a range of specific temperatures, generally called the optimum, that maximise the rate of ovi- position (Park and Frank, 1948). But usually the temperature at which the largest number of eggs are laid is a few degrees lower than this one
(Atwall, 1955).
Most conclusions are drawn from laboratory work done at constant temperatures. Under field conditions, however, the insects are submitted to oscillations that may induce alterations in the birth rate (Bursell,
1974). These changes do not follow a linear relationship with temperature
(Dick, 1937; Donia, 1958), and the laws that rule them are not yet fully understood.
Investigations into the fecundity of P. cochleariae F. were carried
out by Way et al. (1951). They used turnip as the food plant and did their
studies at three different temperatures: 12°, 24° and 30°C. They concluded
that total fecundity did not vary significantly with temperature, although
the rate of oviposition increased proportionately with the rise in tempera-
ture. The life span at 30°C was reduced to almost one third of that at 12°C,
which was 124 days. Nevertheless the authors admit that their results could
be invalidated by the fact that they worked with batches of 25 adults each,
the proportion of sexes in each batch being unknown.
The temperature of 24°C is recommended for cultural procedures,
because it is close to the highest one to satisfy "...the requirements of
(1) relatively low mortality during development and (2) production of normal
full-sized adults."!
Further work on the fecundity of this species was done by Donia (loc.
cit.) using fluctuating temperatures. His experiment was carried out in a
greenhouse between the months of January and June, and oscillations from
15°C to 40°C were recorded. The results obtained show that fecundity was
much higher than the values indicated as maximum for this species, either 24. by Way et. al. (loc. cit.) or other earlier authors (Smith, 1951;
Hamnett, 1944).
4.2 Materials and methods
Data on fecundity, longevity and weight cycle of isolated couples of P. cochleariae were obtained at two constant temperatures: 20° and 25°C.
A period of 16/24 hours illumination was provided by four neon tubes of 20 watts each. Humidity was not controlled, but varied around 90% R.H., inside the tubes where the adults were kept.
As mentioned before under I — 1., males and females cannot be distinguished externally with certainty, so the identification of a couple is done by watching copulation. However, pairing does not occur during the first days of adult life. If an experiment is to be initiated with recently emerged adults, groups of two have to be isolated at random, and the couples sorted out later.
Pairs of recently emerged adults, no older than 12 hours, were put into glass tubes containing moist peat and one freshly detached turnip leaf.
The tubes were labelled and closed with perforated corks. Assuming the sex ratio to be 1 : 1, the probability of having one male and one female per tube is one third. Therefore, to obtain a given number of results, three times that number of pairs had to be isolated initially. Aiming for the results of 20 couples, 60 pairs were transferred to a temperature controlled room at 20°C, while an equal sized batch remained at 25°C.
The insects were individually weighed at the start of the experiment, and this operation was repeated every day, until death. The leaves were renewed daily and when oviposition begun, the number of eggs laid per day, by each female, was recorded. These experiments were repeated and thus data relating to 40 couples were obtained. 25.
4.3 Results
a) Effects of two temperatures on a single variable
Columns I and II of Table 3 list the mean values and the standard deviations of the longevity, pre-oviposition, oviposition and post-oviposition periods, total fecundity, mean fecundity per female per day and average mature body weight, obtained at 20° and 25°C for 40 females. Column III contains the result of t tests performed to compare the variance of means, for each variable, at the two temperatures.
i) Fecundity
Both total fecundity and the mean fecundity per day were
significantly higher at 25° than at 20°C (P<.001).
The values obtained compare reasonably well with those given
by Way et. al. (1951): 300 eggs per female laid at 24°C. Smith
(1951) claims 300 to 400, while Hamnett (1944) gives a maximum of
100 eggs per female. Donia (1958), working with fluctuating tempera-
tures, between 21° and 28°C, obtained a much higher value for fecundity,
averaging 1,143 eggs per female.
ii) Pre-oviposition, oviposition and post-oviposition periods
The pre-oviposition period had an average duration of 12,3
days at 20°C, while at 25°C it lasted 7.7 days.
When a t test was performed to
compare the means a highly significant difference was seen (P<.001).
Previous work does not supply comparative values for these temperatures,
but Hamnett (loc. cit) observed in the field a pre-oviposition period
of 7 days and Donia (loc. cit.) gives an average duration of 6 days
for this experiment with fluctuating temperatures. 26.
I II III TEMPERATURE
20°C 25°C t
LONGEVITY r. 89.28 46.45
s 20.33 9.30 22.57***
PRE-OVIPOSITION x 12.33 7.65 PERIOD *** s 1.62 1.37 1 4 .7 5
OVIPOSITION x 47.40 34.63 PERIOD s 19.62 9.20 1 7.3 9 ***
POST-OVIPOSITION x 2.55 4.20 PERIOD s 1.20 4.69 1.25
FECUNDITY x 172.28 296.88
s 49.57 95.55 7.50 ***
MEAN FUCUNDITY x 2.38 8.91 pe r day s 0.49 2.60 1 5.3 6 ***
AVERAGE x 8.55 8.66 MATURE WEIGHT s 1.07 1.07 0.4 9
TABLE 3
COLUMNS I & II - Mean values and standard deviations obtained at 20° and
25°C for longevity, pre-oviposition, oviposition and post-oviposition periods, fecundity, mean fecundity per day and average mature body weight of 40 females of P. cochleariae.
COLUMN III - Results of t tests and levels of significance. 27.
Mean values for the oviposition period were 74.4 days at 20°C and 34.4 days at 25°C. The comparison of variances yielded a sig- nificant difference at a level of 0.1%. Similar results were repor- ted by Way et. al. (loc. cit.)
The duration of the post-oviposition period was directly related to temperature. Its mean value was 2.55 days at 20°C and
4.20 days at 25°C. The dispersion of this parameter is very high, especially at 25°C: s = 4.69. For this temperature, about 80% of the females studied lived only one to four days after the end of oviposition, but five insects survived over 10 days, and one of them
21 days, without laying eggs. These values are responsible for the comparatively high mean found. No specific references to the duration of the post-oviposition period exist in the literature. It is generally stated that when egg laying stops, the insects "...die soon afterwards." (Smith, loc. cit.). iii) Longevity
The suLamation of the number of days taken by the pre-oviposition,
the oviposition and the post-oviposition periods equals longevity.
Again, there is a significant difference for this variable when the
temperature is altered by 5°C. At 25°C, it is approximately reduced
to one half of its duration at 20°C, i.e. to 46.5 days from 89.3 days.
Figure 3 shows the frequency distribution of the longevity of
40 females at 20° and 25°C, in histogram form. At the lower tempera-
ture, the data are more widely dispersed. At 20°C the standard
deviation is 20.33, while at 25°C it equals 9.30.
iv) Mature Weight
No significant difference was found between the average
mature weights of adults living at 20°C and 25°C. Way et. al. (loc. 28. cit.), describe a negative relation between the temperature at which the culture was kept, and the weight of the adults produced. But in this case, since the first stages of the life cycle were reared at the same temperature (25°C), no such effect could be expected.
It may be concluded that the higher fecundity observed at 25°C, was caused by a direct influence of temperature upon the physiology of the females, and was not due to weight changes. v) Rate of oviposition
Figure 4, represents the average oviposition curves of 40 females,
at 20° and 25°C. In Figure 5, the rate of oviposition (eggs/female/day)
is expressed as daily percentage of the total oviposition.
At 20°C, four peaks are present in the oviposition period, the
second one being the highest, on the 20th day of the cycle, with 8.6 eggs
laid, equivalent to 4.8% of the total oviposition. From the other three
peaks, one occurred during the first five days, and two on the last 20
days, separated by an interval of three days. The egg numbers oscillated
around 1.5 per day, in the 24 days that elapsed between the two sets of
peaks. At 25°C, three major peaks can be distinguished. They are of
approximately 4 days duration and follow one another, decreasing steadily
throughout the cycle, their maximum values being 12.0, 10.4 and 7.7 eggs
per day.
Donia (1958) presents a graph where the daily average number of
eggs, laid by 24 females is plotted against days after emergence. Although
under his experimental conditions an extremely long oviposition period was
obtained (120 days), the curve shows a pattern comparable to the one
recorded at 25°C. In both sets of experiments an absolute maximum is
present, during the first fifth of the cycle, and the rate of oviposition
decreases constantly till the end of the period. 21- 2 0- 25 °C 1 19^
174 FA 20 °C 16- 15^ 14- 13- 12. cr 11- LL 10. 9 8. 7
5 4 3
a -35 46 - 55 66 - 75 06 - 95 106 - 115 126 -125 146 - 155
36 -45 56 - 65 76 - 85 96-105 116-125 136-145 Longavity (days)
FIGURE 3 Frecuency distribution of the longovity of 40 44 of P. cocbleariae, at 20° and 25°C. o—o 2 5 °C
c—o 20 *C
0 ra E
CI) 67
0
O . C.—
0 CJ ro CC
•""•••3---"ir••••••7•".•-'7 1-" 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 G5 67 69 Days
FIGURE 4 Average oviposition curves for 40 99 of P. cochleariae at 20° and 25°C.
5 00 o-o 25 °C 450 0 0-0 20 °C •4••• 400 c.:14Z 0 350
4•••• 3 00
cm 5 250
kl••• O 2 00
cc 1 50
1 00
050
1--1 9 11 13 15 17 19 21 23 25 27 29 3 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69
Days FIGURE 5 Rate of oviposition, expressed as percentage of total oviposition, for 40 99 of P. cochlec.riae t_O " 70° and 25°C. 32. b) Relations between pairs of variables at a constant temperature
Table 4 summarises the results obtained, when correlation co- efficients were calculated for three pairs of independent variables : longevity-fecundity, longevity-average mature weight and fecundity- average mature weight, at 20° and 25°C.
i) Longevity and fecundity
At 20°C, the females that lived longer laid more eggs, and
the positive correlation found between the two variables, was
significant at 0.01 level. But at the higher temperature of 25°C,
the metabolism was accelerated and the relation between longevity
and fecundity disappeared.
ii) Longevity and mature weight
For this pair of variables no significant correlation was
found at either temperature. These results agree with the work
of Donia (1958), who did not find any correlation between the
average mature weight and the duration of the oviposition period.
iii) Fecundity and mature weight
Finally, fecundity was tested against average mature weight.
At 25°C there was no significant correlation between the
two variables. Similar results were reported by Donia (loc. cit.).
At 20°C, however, the correlation coefficient was significant at
0.05 level and the setting of confidence limits to it, using the
modified z* transformation (Sokal and Rohlf, 1969) confirmed this
significance.
Since the larvae were all reared at the same temperature,
the weights of adults at emergence are approximately equal. Thus, 33.
the rapid maturation and increased fecundity observed at the
higher temperature (25°C), masks any effect of weight that was
apparent at 20°C. c) Relation between weight rise from emergence to maturity and
i) Fecundity
The percentage rise in weight, from emergence to maturity,
was determined for each female. It averaged 18.44 (±6.80)% at
20° and 20.16 (±6.13)7. at 25°C.
The analysis of Table 5 reveals that, at 20°C, fecundity
is positively correlated with the percentage rise in weight.
ii) Longevity
The correlation coefficient between longevity and weight
rise is also significant, at the same level, only for the lower
temperature (Table 5, II).
d) Effect of weight at emergence on its increase to maturation
The weight at emergence and the mature weight were correlated at
20° but not at 25°C (Table 5, III). Working with fluctuating temperatures,
Donia (1958) found a significant regression coefficient between the two
variables.
34.
VALUES OF r
20°C 25°C
LONGEVITY V FECUNDITY 0.70** 0.28
LONGEVITY V WEIGHT 0.24 0.23
FECUNDITY V WEIGHT 0.40* 0.08
df = n 2 = 38
TABLE 4 - Values and significance of the correlation co-efficients
calculated for the pairs of variables longevity-fecundity,
longevity-mature weight and fecundity-mature weight, for
40 females of P. cochleariae.
VALUES OF r 20°C 225 °C
I 7. Rise in weight - fecundity 0.79** 0.24
II % Rise in weight - longevity 0.49** 0.35
III Weight at emergence - average 0.44* 0.14 mature weight
df = n - 2 = 38
TABLE 5 Values and significance of the correlation co-efficients
calculated between: I and II percentage rise in weight,
from emergence to maturity and fecundity and longevity;
III weight at emergence and average mature weight, of 40
females of P. cochleariae. 35.
4.4 'Summary and Conclusions
The effect of two temperatures, 20° and 25°C, on the reproduction, life span and weight cycle of adults of P. cochleariae was studied.
Both fecundity and the rate of oviposition were significantly increased by the higher temperature. At 25°C, the average number of eggs laid per female was 296.9, that is 124.6 more eggs than at 20°C. The ovi- position curves showed four and three major peaks, respectively at 20° and
25°C. In both cases a maximum was present during the first fifth of the oviposition period.
The durations of the pre-oviposition and oviposition periods were
considerably reduced at 25°C, when compared with those at 20°C. They
were, on average, respectively 4.7 and 39.8 days shorter. The duration
of the post-oviposition period was slightly prolonged at the higher
temperature: it averaged 2.6 days at 20°C and 4.2 days at 25°C.
No significant difference was found between the mature weights of
the adults kept at 20° and at 25°C. Since all the insects originated
from larvae reared at 25°C, this was expected.
Within each temperature, the relationship between pairs of indepen-
dent variables was investigated. At 20°C, a positive correlation was
detected between longevity and fecundity, and between fecundity and
mature weight. But at 25°C such association was not observed. For
neither temperature were longevity and mature weight correlated.
At 20°C, the rise in weight, from emergence to maturity,
expressed as a percentage of the initial weight, was positively cor-
related with fecundity and longevity. A similar correlation existed 36. between weight at emergence, and mature weight. Again, none of these correlations were detected at 25°C.
37.
5. Effect of Plant Species on Fecundity, Longevity and Weight cycle
5.1 Introduction to 5. and 6.1
The aim of this experiment was to test the influence of different
host plants on the fecundity, rate of oviposition, longevity and weight
cycle of P. cochleariae.
Variations in the amino acid composition of the phloem are corre-
lated with the physiological state of the plant, which is determined in
part by its age (van Emden and Bashford, 1971). The nutrient condition
of the host plant is a decisive factor in influencing insectfecundity.
Working with adults of P. cochleariae, Allen and Selman (1955)
studied the effect of several mineral deficient diets on egg production.
They used leaves of watercress which were deficient in either nitrogen,
phosphorus, potassium or iron, and concluded that the lack of any of these
nutrients considerably reduced fecundity. But when different species are
used, the results are difficult to interpret, since distinctions must be
made between nutritional and non-nutritional effects. Some characteristics
of the leaves, such as colour, toughness, 11"riness and waxiness of the
cuticle are part of the mechanisms involved in "plant defence" (van Emden
and Way, 1973), which affect the capacity of insects to reproduce.
Tanton (1962) studied the effect of leaf toughness on the rate of
feeding, by larvae of the mustard beetle. He concluded that this factor
was responsible for a retarded rate of growth, of the larvae feeding upon
tougher leaves. The weight of the resulting adults was also affected.
Conflicting results were found by Gairn (1975), in an extensive study of
49 cruciferous species. Neither leaf toughness, nor succulence, appeared
to influence the host preferences of the adults.
The importance of chemostimulants, in the feeding of phytophagous 38. insects, was pointed out by VercShafelt (1910). Among them, mustard oils glucosides, were found to he essential to stimulate the larvae of Plutelia
(Gupta & Thorsteinson, 1960), P. cochleariae (Santon 1965) and many other insects. These compounds are particularly abundant in the family Cruci- ferae (Kjaer, 1959). However, the determination of the concentration of mustard oil glucosides in a plant tissue, is an elaborate process that lies outside the scope of this project.
Furthermore, plants that are acceptable to an insect species, can
contain toxic substances that will affect their development and fecundity
(Thorsteinson, 1953).
5.2 Methods and host plants
Pairs of recently emerged adults, no older than 24 hours, were
isolated in glass tubes, half filled with moist peat and closed with
perforated corks. All adults came from larvae reared on turnip. Four
groups of approximately 60 pairs each were isolated.
For the first group, a leaf of white mustard, Brassica alba, was
inserted in each tube. In the second set of tubes leaves of chinese
cabbage, Brassica cernua cv. Petsai, were used. The third group of adults
was fed on leaves of Brussels sprouts, Brassica oleracea cv. Gemmifera,
var. Irish Elegance. Finally, the fourth group was used as control and
fed on leaves of turnip, Brassica napus, var. Green Tops (Suttons).
The experiment with Brussels sprouts was later repeated, but this time
using leaves of younger plants, aged between four and five weeks.
The leaves were excised from potted plants, between eight and nine
weeks old, and renewed daily. With the same periodicity, the adults were
weighed individually and the number of eggs laid was recorded. The
means and standard deviations, calculated for each variable (M .-- 20) arc
shown in Table 6. Table 7 was constructed by comparing the results 39. obtained on these plant species, for longevity, fecundity and weight cycle of 20 females. The numbers express the results of t tests performed.
5.3 Results
a) On mustard
Using this host plant, the total fecundity recorded for 20 females
was significantly lower than the value obtained on turnip. It did not
differ from that observed on chinese cabbage, although the mean fecundity
per day was significantly lower, due to the lengthening of oviposition
period. The duration of the oviposition period was approximately equal
to that on turnip, and much longer than on Brussels sprouts.
b) Chinese cabbage
Comparing these data with the results obtained on turnip, only the
total fecundity and the mean fecundity per day vary at a significant
level, the values being lower in both cases. The differences encountered
between chinese cabbage and Brussels sprouts were highly significant for
all parameters, except for the duration of the pre- and post-oviposition
periods.
c) Brussels sprouts
i) Old plants
Using plants of this species, eight to nine weeks old, both
total fecundity and longevity were considerably reduced, when
compared with the corresponding values on turnip. In this experiment,
scars in the surface of the leaves were observed, made by attempts
to lay, without an egg being deposited.
ii) Young plants
When leaves of plants aged between four and five weeks were
used, the oviposition period, fecundity and mature weight were 40.
I II III IV CHINESE OLD BR. YOUNG BR. MUSTARD TURNIP CABBAGE SPROUTS SPROUTS
LONGEVITY x 42.30 48.25 39.35 43.40 46.45 s 7.71 6.20 7.16 6.16 9.30
PRE-OVIPOSITION x 6.85 7.30 8.00 7.80 7.65 PERIOD s 1.35 1.56 1.52 3.09 1.37
OVIPOSITION x 32.30 37.35 27.20 32.85 34.33 PERIOD s 7.45 6.81 6.54 6.21 9.20
POST-OVIPOSITION x 3.20 3.60 4.25 3.15 4.20 PERIOD s 2.40 2.74 2.95 2.40 4.69
TOTAL FECUNDITY x 244.20 220.20 117.05 156.90 296.28 s 38.88 53.28 25.67 38.59 95.55
MEAN FECUNDITY/ 3c 7.92 5.97 4.15 4.55 8.91 DAY s 2.02 1.44 1.08 1.48 2.60
AVERAGE MATURE x 8.50 •8.78 8.14 8.80 8.66 WEIGHT s 0.69 0.85 0.66 0.82 1.07
n = 20
TABLE 6 - Longevity pre-oviposition, oviposition and post-oviposition
periods, total fecundity, mean fecundity per day and average
mature weight, of 20 females of P. cochleariae, on different
host plants: mustard, chinese cabbage, young Brussels sprouts
(4-5 weeks old), old Brussels sprouts (8 - 9 weeks old) and
turnip, at 25°C. MUSTARD MUSTARD MUSTARD CH. CABBAGE CH. CABBAGE BR. SPROUTS BR. SPROUTS (Y) V V V V V V V TURNIP CH. CABBAGE BR. SPROUTS TURNIP BR. SPROUTS TURNIP BR. SPROUTS (0)
LONGEVITY 1.720 0.784 1.789 0.214 4.202*** 2.995** 1.918
PRE-OVIPOSITION PERIOD 2.142* 1.392 3.609*** 0.891 1.450 0.899 0.260
OVIPOSITION PERIOD 0.855 2.238* 2.301* 1.299 4.808*** 3.091** 2.802**
POST-OVIPOSITION PERIOD 0.894 0.417 0.647 0.528 0.233 0.435 1.294
TOTAL FECUNDITY 2.335* 1.627 12.205*** 3.304*** 7.800*** 8.182*** 3.845***
MEAN FECUNDITY/DAY 1.490 3.515*** 7.360*** 4.697*** 4.522*** 7.830*** 0.976
AVERAGE MATURE WEIGHT 0.590 1.552 1.686 0.426 2.660* 1.931 2.804**
TABLE 7 - Comparison of longevity, pre-oviposition, oviposition and post-oviposition periods, total fecundity,
mean fecundity per day and average mature weight on four host plants: mustard, chinese cabbage,
Brussels sprouts and turnip, using t tests, for 20 females of P. cochleariae 42.
significantly greater than for the older plants.
The interpretation of the differences observed could be based on the fact that the quality of the plant, especially the soluble nitrogen content, decreases sharply with age. Since this element is basic to protein synthesis, and thus to egg production, the fecundity of the insects would be expected to be reduced with the ageing of the host plant. Sim- ultaneously, the increase in leaf toughness could affect the feeding of the insects (Tanton 1962), as well as their ability to oviposit.
5.4 Summary and Conclusions
From this set of experiments, it seems that the best performance of P. cochleariae was achieved on turnip, as the host plant. Both mustard and chinese cabbage induced lower fecundity, that was still further re- duced on Brussels sprouts.
For the same plant species, a difference of four to five weeks in the age of the host plants, corresponded with a significant decrease in fecundity. Apart from variations in the nitrogen content of the plants tested (analysed in 6.2), other factors, relating both to the chemical and physical properties of the leaves are important (Wiggiesworth, 1965).
They can account for the differences in the fecundity and longevity of
this insect. 6. Experiments on Food Consumption by Adults
6.1 Introduction (See 5.1)
6.2 Effect of Plant Species on Amount of Food Consumed
a) Methods and host plants
When the set of experiments described under 5.was carried out,
another variable, the daily food consumption by each. couple, was also
measured. Each leaf, removed from a tube, was placed against a sheet of
millimetric paper; the portion of leaf tissue destroyed was marked on the
paper with a sharp pencil. These areas were later transformed into fresh
weight of plant material.
b) Results
Table 8, Columns I and II, show the average amount of food consumed
per couple, during the oviposition period, when fed on different host
plants.
Considering the total values (I), turnip was the preferred species,
followed by chinese cabbage, mustard and Brussels sprouts, in decreasing
order. The mean values per day fall into a similar sequence. On comparing
plants of the same age, the only significant difference found was for the
total food consumption, between turnip and Brussels sproats.
c) Total nitrogen content of host plants
The total N content of the leaves of the host plants, was determined
by the standard micro-Kjeldahl method. The leaves were excised, dried in
a freeze drier, ground to a powder in a ball mill and stored in a des
cator.
The leaf powder was digested with N-free sulphuric acid, in the
proportion of 0.06g to 2m1, and one selenium catalyst tablet. After five 44. I
FOOD CONSUMED / COUPLE NITROGEN INTAKE / COUPLE mg mg
Total PER DAY Total PER DAY
MUSTARD 682.49 21.30 17.21 0.54 (±189.01) (±3.88) (±4.76) (±0.093)
CHINESE CABBAGE 803.15 21.49 18.74 0.50 (±230.00) (±4.31) (±5.37) (±0.10)
BRUSSELS SPROUTS 727.40 22.26 39.55 1.21 (Young) (±174.07) (±16.80) (±9.46) (±0.91)
BRUSSELS SPROUTS 381.23 14.61 10.01 0.38 (Old) (±171.61) (±4.09) (±4.51) (±0.11)
TURNIP 952.81 27.51 37.32 1.08 (±183.20) (±3.08) (±7.17) (±0.16)
TABLE 8 - Means and standard deviations for the amount of food
consumed per couple, during the oviposition period, in
mg of fresh weight of leaf material (I & II) and corres-
ponding amounts of nitrogen intake (III & IV), for 20
couples of P. cochleariae 45 . hours, the sample was diluted to 100m1 with distilled water and a sub- sample taken for analysis in a Technicon mark 7 Autoanelyser. The results are given in Appendix 1-6. Table 8, Columns III and IV, show the total amounts and the daily mean values of nitrogen intake per couple, during the oviposition period.
The value observed for turnip is significantly higher than that for any other host plant, of the same age, but the maximum intake occurred on
the younger plants of Brussels sprouts.
No relationship was detected between the total amount of food con-
sumed per couple, and the total nitrogen content of the leaves of the host
plants. Although the correlation coefficient calculated for these two
variables was not significant, some degree of association between them can
be seen on Figure 6.
d) Summary and conclusions
Turnip was the host plant preferred by the adults of P. cochleariae.
The total nitrogen content of turnip leaves was higher than that of any
other plant of the same age. Total N content can be a misleading figure,
that might not reflect the nutrient state of the plant (ncNeil and South-
wood, 1977). However, in the present study, both the intake. of N per
couple, during the oviposition period, and fecundity, decreased in the
following order: turnip, mustard, chinese cabbage and Brussels sprouts.
Brussels sprouts aged between four and five weeks, contained 'twice
the nitrogen of those eight to nine weeks old. The concentration of
soluble N in this species, appears to reach a peak between the 6th and the
8th week (van Emden and Bashford, 1971), after which there is a steady
decline with the plant ageing. Under the present conditions, this maximum
appears to have been reached before, or around the sixth week, since, in
the older plants the concentration of total N was already declining. The
amount of food consumed was twice as large in the young plants when compared 46.
1.10 .9.0
0.90 7.0 C c.) Keletonshi? b-tween 0.70. fecundity ail:: intake by 20 con;iles of 0-50 P. co,.hleal:iae, fed on 17 ditr_crc,nc :lost plaufs. 0.30
-1-0 0-10
turnlp mustard c cabbane Ir. sprouteu d)
7A.
15
1200 7B E: 1 000 7 r.: C) 800 reression C)- fecundity on =I- 600- Lure (TB)(7A) and food +, consumption on tem- perature (711), for 400 20 couples of P. cochteariae 200
—r- 15 20 25 T C 47. with the older ones, but fecundity was only slightly increased.
The variations encountered for total food consumption, were probably
linked with the relative abundance of phagostimulants in the leaves of the host plants. A survey of the occurrence of mustard oil glucosides, in the
family Cruciferae, is given by Kjaer (1959). Turnip is listed as contain-
ing six different glucosides, while only one (sinalbin) is present in
mustard. Data on chinese cabbage are lacking and the two varieties of
B. oleracea analysed contained a maximum of four of these compounds.
Tant.on (1965) and Cairn (1975), showed the importance of sinigrin in stimu-
lating feeding by larvae of P. cochleariae. The effect of other mustard
oil glucosides upon this species, still remains unknown and further experi-
mentation is required in this area
6.3 Effect of Temperature on Amount of Food Consumed
a) Methods
In this experiment the effect of temperature on daily food consump-
tion, by isolated couples of P. cochleariae was studied. 20 couples were
isolated at each of the following temperatures: 15°, 20° and 25°C. The
amount of turnip leaves consumed by these adults, was measured daily, using
the method described under 6.2; fecundity was also recorded. The turnip
plants used were eight weeks old.
b) Results
Analyses of variance were performed to test the effect of temperature
on these parameters. The results, in Tables 10A and B, show that there is
a significant effect of temperature on both variables (P<<0.001).
For each temperature, the weekly amount of food consumed per couple,
and the mean fecundity per female per week, expressed as percentages of
the totals, are given in Figures 8A and 8B. At each temperature, the 48.
TABLE 10A
SOURCE OF VARIATION df SS NS Fs
Among groups (t°) 2 468,339. 234,169.
Within groups 57 156, 216, 2,741. (error, replicates)
TOTAL 59 624,556.
TABLE 10B
SOURCE OF VARIATION df SS US Fs
Among groups (t°) 2 6,832,493. 3,416,246. 189*'::
Within groups 57 1,029,901. 18,063. (error, replicates)
TOTAL 59 7,862,395.
F = 7.83 s ,001 12,571
TABLES 10A & B Analyses of variance of the effect of temperature
on fecundity (A), and on the amount of food consumed
(B), by 20 couples of P. cochleariae (n = 20 ; a = 3).
19/ Co 40
18 20 17 15 16 15- 14 13 ) 12 11 10 ›- 9 c1 6 tr.
L-61 ra 5 4- 3 2-
11 El 13- .P eg%\ 0 1') / X d 12 11 \ / N.
me 11, 11 \ / 0, u 10J 1 % 9 ...,,,
ns \/ -..), __ 1 / \ ©G I s\ C Co 9 1 A \ , 0 -v 0 \ A d ‘,..,_ „.!: 7 \ z 'so 1 s Foo :■‘ t•-; ---;... '4, X X 1 ,o, A 6 I % b i , i , c,..:, I /, . ...Ai 1 ...salt ‘ -8 5. i / ‘ / A■ 1 ►k / k I— ...... A, .....Z \ / / -.0 \ / 4- 1 ..... ci i % .... A 3 1 4 X X -..0 % X I. ci" 2 i V I 4 1 1 l 0. ! 1 ..., i i . -1-----; 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 13 10
Time in Weeks
Fi'..,ureF. 3A and B - Weekly esLimata of the „i. couple
and fecundity per f.e.i':)(1e, as p2i-
centaes of f.he totals, for '2.) CG. of
Y. cochleariaa at 15°, 90°
50.
association between the two variables is detectable, from the parallel
oscillations of the curves. The correlation coefficient between fecundity
and food consumption was also highly significant (r = 1.00, 1'<0.01).
c) Summary and conclusions
Within the range of experimental temperatures 15° - 25°C (optimum
ti 24°C), it was found that, both the quantities and the rates of fecundity,
as well as of food consumed by the adults, increased with temperature (Fig- ures 7A and B). This pattern is recorded in the literature for many insect species,
e.g. Ephestia elutella (Waloff et al., 1948), Lygus hesperus (Strong and
Sheldahl, 1970), etc. There are, however, some exceptions such as that in
Tribolium confusum (Dick, 1937), in which low temperatures may cause an
augmentation of the rate of oviposition.
Stepanova (1962), working with the mustard beetle, concluded that,
although the food factor had some influence upon the reproduction of this
insect, temperature was the decisive factor in regulating its seasonal
cycles. Nevertheless, the complexity of the study of the food factor, as
was emphasised by Thorsteinson (1953), poses the question to what extent
can results obtained under a set of constant temperatures, be applied to
field populations (Bursell, 1974).
7. Effect of Temperature on Developmental Rates of Immature Stages
and Mortality.
7.1 Aim of Experiments
The developmental rates of eggs, larvae and pupae, as well as the
percentage of mortality within each stage, were studied over a range of
temperatures, between 11° and 30°C. These results were subsequently used,
in the population studies, as a basis for the estimation of the duration of
the different stages.
51.
7.2 Experimental Methods
a) Eggs
The difficulties of sustaining whole turnip plants at the unfavour-
able temperatures of 11° and 30°C, had to be overcome in the experiments
on the eggs and larvae.
The eggs were laid on potted turnips, by adults kept at 25°C.
Fresh plants were offered to the beetles and removed within five hours.
Leaves were searched and those with eggs were cut off, with a sharp scal-
pel. Groups of 20 eggs were transferred, with a brush, onto moist filter
paper lining petri dishes. Sets of five petri dishes (100 eggs), were o o o placed in constant temperature rooms, at 11°, 15 , 20 , 25 and 30°C.
The filter paper was kept moist by watering it with distilled water, twice
daily, if necessary. Simultaneously, eclosions were observed.
At 30°C the experiment was repeated at 100% R.11-, by keeping the
petri dishes inside desiccators, containing distilled water.
b) Larvae
The larvae used originated from eggs that hatched at 25°C, within
12 hours proceeding the start of an experiment. They were put in groups
of five, on the surface of a freshly detached turnip leaf, placed on moist
filter paper, inside a petri dish.
Sixty larvae were transferred to each of the following temperatures: o 15.o , 2020° , 2525° and 30 C (at 100% R.11.). The leaves were changed twice daily.
At the same time, the filter paper was watered and any moult of the larvae
was recorded.
c) Pupae
Sixty pupae, formed at 25°C, were transferred to each temperature
of 11°, 15°, 20°, 25° and 30°C, within five hours after pupation. 52.
Groups of five were placed inside glass tubes, half filled with moist peat, and closed with muslin and bored corks. The peat was kept moist by adding a few drops of distilled water, when necessary. Examin-
ations for emergence of adults, were carried out twice daily.
7.3 Analysis of Results
Table 11 shows the total values observed for the developmental
periods, in days, and the percentage mortality of eggs, larvae and pupae,
at different temperatures.
Theoretical values for the rates of development of eggs, larvae and
pupae were calculated by two methods, namely by using Davidson's logistic
equation (Davidson, 1944a) and by linear regression. Figures 9 and 10, A,
B and C, show the fitting of the logistic curves, and of the regression
lines, to the observed values for the three stages.
a) Eggs
For the egg stage, the lowest mortality (0.04) occurred at 25°C;
20°C was the second best temperature, with 20% of the eggs failing to hatch.
At 11°C and 30°C, mortalities reached 82 and 72% respectively, but in the
second temperature there was a small drop in mortality, to 62%, when the
experiment was carried out at 1007. R.H.
Data available from literature, for the incubation period of the egg
stage, generally refer to field conditions and are rather variable. They
extend from a minimum of five days, given by Roebuck (1928), up to 20
days, observed by Falcoz (1929), in the region of Lyon (France). Labora-
tory data were obtained by Way et al. (1951), at a constant temperature of
24°C. Their value of eight days diverges slightly from the 6.2 days recor-
ded at 25°C, under the present experimental conditions.
Figure 9A represents the temperature time and the temperature
53.
I II III IV
TEMPER- EGGS LARVAE PUPAE TOTAL ATURE oc a b a b a b a b
11 (±1) 16.60 0.82 12.30 0.15 (±1.02) (±1.74)
15 (±1) 14.20 0.35 31.40 0.75 9.50 0.07 55.10 0.38 (±0.83) (±1.56) (±1.23)
20 (±1) 8.60 0.20 15.60 0.53 6.80 0.04 31.00 0.24 (±0.51) (±1.02) (10.57)-
25(±0.5) 6.20 0.04 12.80 0.37 5.70 0.05 24.70 0.13 (±0.37) (±0.89) (±0,51)
30(±2.0) 5.00 0.72 4.90 0.06 (±0.23) (±0.46) 5.30* 0.62* 12.10* 0.47* 22.30 0.43 (±0.31) (±0.90)
a Mean development, in days
b Rate of mortality, in percentage
Experiments at 100% R.H.
TABLE 11 - Means and standard deviations for the development, in
days, of immature stages of P. cochleariae, and percentage
of mortality, at 11°, 15°, 25° and 30°C. =
CQ -0 10
t-+ E OML 03 O C=1 O
, 1 e3.0000 - .1376X 0.2643
5 6 7 8 9 10 15 20 25 30 35 Temperature CC)
9A EGGS
Figure 9A Observed points on the temperature-time curve (closed 973 and 9C circles) and on the temperature-velocity curve (open
circles) for the egg, (9A), the larvae (9B) and the
pupae (9C) of P. cochleariae 55.
-15
100 32.33 1.620 - 0.072X 1 + e 13
.11
9
7
5
3
1.620 - 0.072X 1 + e 1 0.3233 ci
0 15. 20. 25. 30. 0 C b3 4,ci 9n LARVAE co 1.1-1
39 y 4.406 - 0.272X 1 e
27
21
15
4.406 - 0.277X y = 1 + e 0.0843
25. 10. 15. 20. 30. T ° C 9c PUPAE
0 0.22 0
0.20
c 0.13 Figures 10 A, B and C 0.16 Linear regressions between the inverse of developmental time, and temperature for 0.14 the eggs (A), larvae (B) and pupae (C) of ri 0.12 P. cochleariae.
0.10
0.03
15. 20 . 25. .3 0.
10 A EGGS 0 .24 t,0 rc) 0.22
•H 0.20
0.18 jr-11
l 0.16 ta
men 0.14 lop e 0.12 dev f o 0.10
0.0E, y = 0.774 X — 3.471
0.06
23. 30. 30. 15. 20. 15. 20. 25.
T°P C 108 LARVAE 10C PUPAE 58. velocity curves, for this stage, calculated by the logistic equation. On
Figure 10A, the inverse of the developmental time is plotted against tem- perature, and a regression line was fitted to the data. The values pre- dicted by Davidson's equation are, almost always, close to the real values, with one exception : when the lower threshold of development is approached, at 11°C, there is a discrepancy of four days. For this stage, the regression line gives an acceptable degree of fitness (r 2 = 0.95). b) Larvae
As with eggs, the lowest mortality occurred at 25°C (37%), the highest value (75%) was observed at 15°C.
In this experiment, the number of moults experienced by the larvae varied between two and three. Table 12 shows the number and duration of the larval instars and the percentage of mortality within each instar, at the four temperatures. At 15°C, all the 60 larvae passed through four instars. At 20°C, 82% of the insects had four larval instars, while the remaining 18% only had three. At 25°C the order was reversed. The majority
(76%), went through three larval instars and 24% underwent a fourth one.
The same occurred at 30°C.
References in literature, relating to the number of larval instars of this insect, are scarce and always referred to field conditions.
Hamnett (1944) in South Wales recorded three instars, but Smith (1951) in
England and Balachowsky (1963) in France, observed four. As to duration,
few data obtained in the laboratory, under constant temperatures, are
available from the literature. The present results agree with the value
of 16 days obtained by Taylor and Bardner (1968) at 20°C, but are not in
accordance with the work of Stepanova (1962) who claims durations of 15
and 8 days, at 23.5° and 30°C, respectively.
The larval development is poorly described by the regression line
(Figure 10B). The logistic equation (Figure 9B) provides a closer fit TABLE 12 - Number and duration of the larval instars, and percentage of mortality within each instar, of 60 larvae of P. cochleariae, at 15°, 20°, 25° and 30°C. LARVAL INSTAR TOTAL NO. 1ST 2ND 3RD 4TH o ENTER- t c PUPAE DURA- ING DURA- NO. NO. NO. TION % MOR- INSTAR % MOR- DURA- % MOR- DURA- % MOR- DURA- % MOR- TION ENTER- ENTER- ENTER- OF TALITY TALITY TION TALITY TION TALITY TION TALITY (DAYS) INC ING ING STAGE
15 60 5.20 0.62 23 5.00 0.17 19 6.70 0.05 18 14.50 0.17 15 31.4 0.75 (±1.10) (±0.98) (±0.96) (±1.40) 24 3.67 0.03 23 5.14 0.00 23 15.60 (±0.70) (±0.85) 20 60 3.26 0.45 33 3.53 0.12 0.53 (±0.83) (±0.64) N 5 7.90 0.00 5 14.59 (±1.13) 9 2.40 0.00 9 5.20 0.00 9 13.10 (±0.36) (±0.92)
25 60 2.66 0.27 44 2.84 0.07 0.37 (±0.51) (±0.70) •/ 32 7.30 0.09 s";>. 29 12.80 (±1.78)
8 2.37 0.00 8 4.90 0.25 6 12.34 (±0.54) (±1.00) \\.4 27 30 60 2.43 0.18 49 2.64 0.20 0.47 (±0.63) (±0.64) 31 7.17 0.15 25 12.10 (±1.29) 60. although at 15°C a discrepancy of 4 days exists between the observed and predicted values. c) Pupae
The influence of temperature, on the rate of mortality of this stage, is less marked than in either the eggs or larvae. The values observed at o 15°, 20°, 25° and 30 C do not differ significantly. It could be argued that the pupae remained enclosed in a micro-environment, where the moist peat provided some protection, and thus were not exposed to the real external temperatures. However, since it was found that these temperatures did not depart from the room temperatures by more than ±1°C, this explan- ation is not plausible.
The effect of humidity, as was emphasized by Way et al. (loc. cit.), seems to be the most important factor in the survival of the pupal stage.
Provided the surrounding medium is kept moist, mortality of the pupae will be low. The above authors obtained six days for the development of pupae at 24°C, which is close to 5.7 days recorded at 25°C, in the present experi- ments.
Figure 9C, shows that, three out of the four observed values, fall on the curves originated by the logistic equation. The regression line
(Figure 10C) fits the data between the temperatures of 20° and 30°C, but fails to describe the process near the lower range of temperatures.
7.4 Summary and Conclusions
The values observed for the developmental period of the immature
stages of P. cochleariae are in accordance with those given by Zolk (1928):
60 and 47 days, respectively at 14° and I5.7°C.
The number of larval instars was not fixed, and appears to be
correlated with temperature. Hence, at 15°C, all the larvae had four 61. instars, while at 20°C only 82, and at both 25° and 30°C, 24% of the insects experienced a fourth instar. No references on this topic were found for P. cochleariae, but variations in the number of larval instars
have been reported for several species, in relation to different factors,
e.g. density (Takahashi, 1961), sex (Polania and Helgesen, 1973) and tem-
perature (Gruys, 1970).
The total mortality observed at 25°C was very low (13%), but it
more than trebled when the beetles were reared at 30°C (43%). This last
value coincides with the results obtained by Way at al. (loc. cit.). They
found that "....At 30°C the mortality was not excessive (42-489).".
It may be concluded that, from the temperatures selected, 25°C was the
most favourable one, for rearing this species in the laboratory. The
optimum lies between 20° and 25°C, probably very close to the higher tem-
perature.
8. Lower Lethal Limits of Temperature
It has long been established that different kinds of thresholds limit the reproduction and growth of insect populations, at both ends of
the scale of viable temperatures (see Birch,.1948; Hodson and Alrawy,
1958).
Since the present laboratory studies were aimed at the evaluation of the role of temperature in population ecology, and this species is
essentially of northern distribution, attention was directed to the lower
lethal temperatures. Experiments were made to find the "developmental-
hatching-threshold", as defined by Bursell (1974). At this temperature,
some development might take place, but it will not reach completion.
8.1 Developmental thresholds of immature stages
Cabinets of adjastable temperatures, with a 16/14 light hour regime
were used. It was seen that, at 9.0° (±1.°)C, the eggs did not hatch and
the larvae could not develop. Thus, the hatching - threshold of the eggs, 62. lies around 10°C, since eclosion at 11°C had been seen in previous tests. For the larvae, the temperature of 10.0°C (±1.°)C proved lethal. Temperatures between this value and 15°C were not available.
The developmental threshold for larvae is higher than for the eggs, and o is located between 11 and 14°C, most probably near to the first value.
For the pupae, the adult emergence-threshold was not pin pointed, but it lies below 7.5° ± 1.0°C.
If one extracts the theoretical values of the developmental zero, from Figures 10A, B and IL, by reference to the points where the lines cut
the temperature axis, unrealistic values are obtained. This is hardly
surprising, since development is not a linear function of temperature.
8.2 Survival of Adults at Low Temperatures
A set of experiments was designed to observe the effect of low
temperatures on the survival of the adult stage. This information was
considered to be relevant to interpreting overwintering mortality, in
field conditions.
a) Methods
Groups of five adults, between seven and 12 days old, were put
into glass tubes, closed with muslin and perforated corks, containing
moist peat and a turnip leaf. A 100 adults were transferred to each one
of the following temperatures: -2.0°, 0.0°, 2.5° and 5.0°C. Another
group was kept at 20.0°C as control. At this temperature, the adults were
leading an active life, feeding and ovipositing, hence the leaves were
replaced daily. No feeding occurred at any of the low temperatures, and
the insects spent the whole time buried in the peat.
The experiment lasted for 42 days. Samples of 10 adults were re-
moved 24 and 48 hours, and then every five days after the start of the
experiment. They were transferred to 20.0°C and records were made daily, 63. for two weeks, on the number of beetles alive and the time required by the females to resume oviposition. b) Results
The cumulative number of dead beetles, expressed as a percentage of
the initial number of adults, is plotted against time on Figure 11. Sur- vival was similar at all the temperatures above zero, and rarely exceeded
10%, even by the end of the experimental period. At or below the freezing
point, mortality had reached 100% in 17 days.
Figure 12 shows the time that elapsed, after removal from the low
temperature, until resumption of oviposition. After spending either seven
days at -2.0°C, or 12 days at 0.0°C, the females needed two weeks at 20.0°C
to recommence ovipositing. Those placed at 2.5°C generally took only one
week, irrespective of the time spent at low temperatures. In the females
exposed to 5.0°C, the period of preoviposition increased, between the first
and the last samples, from five to seven days.
c) Discussion
An explanation generally suggested for the mortality of insects at
low temperatures, is the formation of ice crystals in the body fluid and
subsequent disruption of cellular structures (Salt, 1961; Asahima, 1969).
According to Salt (1958a) crystallisation depends on a favourable molecular
orientation, which is greatly enhanced by low sub-zero temperatures. The
relation between duration of exposure and temperature is then an important
function (Bursell, loc. cit.), because the lower the temperature, the
higher the speed of the orientation process. This law can be invoked in
interpreting the results obtained.
The overwintering adults remain protected by a layer of soil, or
litter. Even when air temperatures drop below zero, soil conditions rarely
approach the freezing point. Besides, exposure to low temperatures for a
14
12
10
q.1 ---0 ,;...... „. j ..„,„ 0- .....0-- - -0-- - -0------..., .0.. .0 O / \ -... ,.-- CNI .••• Op .w m 4 or o. m ..." ›- cc .-• Cl 2 0.0 o o'.. Figure 12
Days at low 80 -2.0°C O.() ° C 2.5 ° C 0 ..... - 5.0 ° C 70 0— 20.0° C
60
''•50
ia ca E40 ti 4-. ca = E 30 Ca
20
10
•••••0-• — •-••• ...... ••• 0
1 2 7 12 17 22 27, 32 37 42 Duration of exposure (days)
Figure 11 Nortality of adults of P. cochleariae, exposed to low temperatures for variable periods of time.
Figure 12 Number of days, required by 9? of V. eochleariae to resume oviposition, after removal from low temperature.
65.
few hours a day, may have a different effect to continuous exposure to
these temperatures below zero. Alternating temperatures probably have
different physiological effects on survival of adults in the field.
d) Summary and conclusions
The threshold of development observed for the larval stage was
found to be higher than the egg hatching-threshold and the pupa emergence-
threshold. These values differ from the theoretical values calculated for
the developmental zero.
Stepanova (1962) givesthe temperature of 8°C as the lower limit
for the development of P. cochleariae. This value is 2° to 3°C below the
thresholds observed for the eggs and larvae, under the present experimen-
tal conditions.
The adults could survive exposures of several days to freezing
temperatures. The females resumed oviposition after spending one to two
weeks at 20°C. Prolonged exposures to low, positive temperatures, did
not affect the survival of the adults, nor the oviposition of the females.
9. Reproductive Organs and Sexual Maturation
9.1 Aim of Observations and Experiments
In this section, dissections of adults of both sexes were carried
out. Insects of different ages, ranging from emergence to senescence,
were examined. The changes observed in the physiological conditions of
their reproductive organs were recorded and measurements were taken, so
that any growth could be detected.
This study enabled the determination of the approximate age of any
insect from the field populations. By taking samples at random and making 66. dissections one could detect the emerging individuals of a new generation.
9.2 Methods
The beetles were taken from the basic culture, kept at 25°C. They were weighed individually and killed with ethyl acetate. The following external measurements were then taken: total length, abdominal length and maximum width. Dissections were carried out under a normal solution of
Nc Cl and measurements of the reproductive organs were taken with a micro- meter eyepiece.
In both males and females, the size of the fat body was recorded in arbitrary units, as follows: 1 - small, 2 - large, 3 - very large.
The measurements and observations included:
Males - Size of testes : length and width
- Number of lobes per testis (difficult to determine
and subject to error)
- Length of the vasa deferentia
- Length of each one of the three sections of the
ejaculatory duct
- Width of the proximal and distal ends of the
middle section of the ejaculatory duct
- Colouration of the aedeagus.
Females Length of the ovarioles
- Length and width of the oviducts
- Number of ovarioles per ovary
- Number of egg rudiments differentiated in each
ovariole
- Number of mature eggs
- Length and width of the vagina
- Size of the spermathecal gland 67.
- Colouration of the spermatheca
- Number of corpora lutea.
9.3 Results and Description of the Reproductive Organs
a) Males
The male reproductive organs consist of two pale yellow oval shaped
testes, situated dorsally, between the first and the third abdominal seg-
ments. Each testis measures 0.90 (±0.09)wm by 0.60 (±0.08)mm, and is
divided into several lobes, enclosed in a common sheath. Their number is
difficult to determine, but varies around 9-10. One thin vas deferens,
approximately 1.32 (±0.08)mm long, emerges from each testis. Around the
middle section of each vas deferens is a single heart shaped vesicula
seminalis, whitish and lined internally with a chitinous cuticle. A very
long (P-17.0mm) and coiled accessory gland joins the anterior end of each
vesicula seminalis.
The vasa deferentia unite in the third segment to form the ejacula-
tory duct, which is divided into three sections. The first section is
tubular, slightly thicker than the vas deferens, about 1.24 (±0.11)mm long;
the second is much dilated and surrounded by muscular structures, measuring
1.07 (±0.21)mm; the third section is a very thin tube, about 0.77 (±0.11)mm
long, that enters the middle part of the aedeagus. The aedeagus is chitin-
ous and measures about 0.8mm.
Appendix 1-9. a) includes the measurements and observations on
dissections of males of different ages.
The males are generally referred to in literature as being fully
mature at the time of emergence and no changes in their reproductive organs
have been described (Donia, 1958). In the present study, however, a change
was noted in the middle section of the ejaculatory duct, of males of differ- 68. ent ages. The distal end of this section was much wider than the proximal
end, in the males over 5 days old. In the younger ones, the two extremities
showed only a small difference in diameter.
The ratio between the width of the proximal and distal ends was
worked out. Its value was close to 0.5 for the older males and approached
0.7 or 0.8 in the ones up to 4 days old. The insects were divided into two
age classes: up to 4 days old and over 6 days old. The 5 days old males
were discarded, as they were considered to be in a transitory period. A t
test showed a significant difference between the two classes (Table 13).
The amount of fat body also varied with age. It was bigger in the
recently emerged males than in the mature ones, but increased again in the
senescent ones. Observations of the aedeagus showed that its colouration
was lighter, in the males up to two days old, than in the older ones.
A drawing of the reproductive organs of a mature male (10 clays old)
is given - Figure 13. Figure 14 shows in detail, the middle section of the
ejaculatory duct of a two days old and of a 10 days old male.
b) Females
The female reproductive organs consist of two ovaries, situated
ventrally, each one made of a variable number of acrotrofic ovarioles, gen-
erally 11 or 12, rarely 10. In a mature female each ovary measures approxi-
mately 1.9mm. The oviducts are tubular and about 0.90mm long. The vagina
is relatively long, almost of the same length as the oviducts. The sperma-
thecal duct, which is long and coiled opens into the dorsal middle region
of the vagina.
The spermatheca is a U-shaped, sclerotised structure, the basal arm
being shorter than the apical one. The two arms are linked by crossed
muscles, that run between them. There is a large spermathecal gland, about
69.
Age classes:
X - Males up to 4 days old
X1 - Males over 6 days old
Ratios xl
0.81 0.62 0.68 0.45 0.67 0.69 0.67 0.48 0.80 0.50 0.63 0.50 0.83 0.57 0.78 0.48 0.68 0.54 0.63 0.64 0.58 0.56 0.83 0.52 t = 4.51**
df = 11
Table 13 t test on the ratio of proximal/distal width of the
middle section of the ejaculatory duct, in males of
different ages. 70.
1. Testes
2. Collation sheath
3. Vas deferens
4. Accessory gland
5. Vesicula seminalis
6. Vas deferens
7. Proximal ) 8. Middle ) Section of the ejaculatory duct 9. Distal )
10. Aedeagus
FIGURE 13 Reproductive organs of a mature d (10 clays old)
of P. cochleariae E E o ,. - 72.
15A
I5B
Figures 15A and B - Middle section of the ejaculatory duct of an
immature (2 days old) and a mature (10 days
old) male of P. cochleariae. 73.
0.7mm long, which can be divided into two halves: the proximal half is tubular and the distal half forms a club.
Appendix 1-9. b) shows the measurements and observations on dis- sections of females of different ages. The growth of the ovarioles is the most obvious change observed.
A linear regression was calculated between the age of the females, in days and the size of the ovarioles (and ovaries), in run - Figure 15.
It was concluded that, at 25°C, the growth of the ovarioles is completed around day four, after which only individual variations, due to body size, were found.
The amount of fat body present increased from day one to day four,
and decreased when egg laying started. In the senescent females it was
generally abundant. In the mature females a small corpus luteum was
visible in the calyx of each ovariole. It became more obvious in the old
females.
Drawings of the reproductive organs of an immature and a mature
female are given in Figures 16 and 17.
9.4 Summary and Conclusions
A brief description of the reproductive organs of P. cochleariae
was given by Cholodkovsky (1919). Donia (1958) presents more detailed
work, which includes a study of the growth of the ovaries. His findings,
in general, agree with the present ones.
In conclusion, examination of the reproductive organs of an adult
beetle provides a basis for an estimation of its age. In males the relevant
observations are the shape of the middle section of the ejaculatory duct,
the amount of the fat body and the colouration of the aedeagus. In the 74. females, the size of the ovarioles is the most important feature.
It is possible to distinguish an immature female from a mature and a senescent one. The males could only be identified as immature (under five days old) or mature (six days or older). Age of older insects could not be distinguished. INDIVIDUAL VARIATIONS, AFTER MATURITY HAS BEEN REACHED OVARIES Y= 12.34 + F49 X r 2= 0.95 2.00 -o - - 1.80 o- Figure 15 Linear regres- so-
) 1.60. sions showing the m — 0,
(m 1.40 relationship between the s ie 1.20
length of the ovaries, Ovar d and the length of the n 1.00 a les
ovarioles, and age, in io
r 0.80 OVARIOLES
Females of P. cochleariae Ova 0.60- Y= 8.05 +1.74X r 2=1.00 0.40
0.20
-10 0.5 1. Ags cf 9 (days) 76.
1. Terminal filaments
2. Ovarioles
3. Oviducts
4. Vagina
5. Spermathecal duct
6. Spermathecal gland
7. Spermatheca
8. Ripe egg
FIGURES 16 and 17 Reproductive organs of an immature
(3 days old) and a mature (12 days
old) 9 of P. cochleariae
7$ SECTION II - Laboratory Studies on Adult Behaviour
1.1 Introduction to Section II and Section III - 11
During the course of this study an adult beetle was never seen to fly, although the insects are equipped with fully developed wing muscles and apparently functional wings.
There are some references in the literature to invasion of crops in Spring, which is achieved by walking (Roebuck, 1916 & 192a). Others state that the beetles fly "...perhaps for some considerable distance..."
(Ministry of Agriculture, Fisheries and Food, 1950, 1967). However, the same publications recommend control against attacks on watercress by the flooding of the beds. Thompson (1932) refers to the success achieved with this practice. Apparently the beetles do not fly, even from flooded fields.
The sampling of adults in the field proved to be difficult and subject to error, due to the behaviour of the insects, which is affected by the weather conditions. On sunny days the adults generally sit on leaves, but at the slightest disturbance, they fall to the ground and are not easily seen. If the weather is dull or windy, the beetles go into the soil, around the plant roots. Laboratory observations showed that there is a relationship between the water content of the soil and the tendency of the adults to bury themselves.
In this section some experiments were designed to study the behaviour of the adults in relation to their locomotory activity. 80.
1.2 Ability to Fly
Ten adults, between two and five days old were used. The insects were immobilised by low temperature and each one fixed to the head of a
pin, by its prothorax, with a drop of Durofix. Care was taken not to restrain the elytra. The pin was stuck into a piece of cork, and the
Durofix allowed to dry for one hour. The pin was inverted and the
insect brought back to its normal position - Figure 18, I and II.
A gentle air stream was directed towards the beetle and its move- ments watched for five minutes. The experiment was first carried out at room temperature ( 20°C) and repeated at 25°C.
Under no circumstances were rhythmic movements of the wings observed, which could have been interpreted as attempts to fly. Occas- ionally the elytra were lifted, but the second pair of wings remained folded. It was thus concluded that none of the adults tested dispersed by flying.
1.3 Effect of Starvation on Locomotory Activity and Flight
The relation between locomotory activity and starvation, as well as the ability to fly were tested in the following experiment.
A two months old tunip plant was enclosed in a celluloid cylinder, open on top and painted internally with fluon, to prevent the insects from crawling out. Enclosing it was a similar but larger cylinder, containing four turnip plants, of the same age as the central one. A replica of this arrangement (A) was set up nearby (B). Figure 19 is a diagram of this arrangements. V .
adult Durofix pin
cork
I II
Figure 18 - Experiment 1.2, to test flight ability of adult
P. cochleariae
A 6
Figure 19 - Set up used in experiments 1.3, 1.4 and 1.5 for
the study of dispersal. 82.
The experiment was carried out in an insectary, during the first half of July 1975. Temperatures oscillated between 11° and 24°C, with a mean of 17.5°C. Inside the central cylinder of (A), 10 adult beetles under five days old, were released. Simultaneously, 100 adults were released in (B). Observations were carried out for two weeks.
After 11 days in (A) and two days in (B), insects had consumed the inner plants. However, no adult was found on any of the outer plants, even --long after -the exhaustion- -of the—food .supply.- The beetles remained--- around the roots of the turnip, many buried in the soil and immobile for most of the time. Probably this behaviour prevented desication. The majority of the insects survived a 12 day period of starvation, at the end of which mortality was only 35%.
In several insect species it seems that locomotion is closely related to feeding and starvation. Green (1964) and Dethier (1969), in their studies of the blowfly, and Lambert (1972), working with the desert locust, found that the animals with empty guts always tended to be more active than the fed ones. To the contrary, the adults of P. cochleariae showed a marked decrease in activity, when deprived of food. They did not use their wings, even when starved.
1.4 Effect of Density on Dispersal
The influence of a high density on dispersal was studies, in the apparatus described in experiment 1.3.
This time the inner surface of the central cylinders was not painted,
and the insects could disperse towards the outer plants by welking. During
this experiment, temperatures fluctuated around 21°C, with a minimum of 12° 83. and a maximum of 28°C. The number of beetles found outside the central container was recorded twice daily. The results are shown in Columns I and II of Table 15.
The insects behaved similarly in (A) and (B), irrespective of their density. The large majority remained on the turnip where they had been released until it was consumed. Then the beetles moved to the outer plants, by walking up the walls of the central cylinder.
1.5 Effect of the Quality of Food on Dispersal
This experiment was planned to assess whether poor quality of food, together with high density, could stimulate dispersal.
The preceding experiment was repeated, the only difference being in the age of the plants used. The control turnips were five months old, while the outside ones were young plants, 1.5 months old. During this period temperatures ranged from 12° to 30°C, with a mean of 22°C. The results are shown in Columns III and IV of Table 15.
It was concluded that senescent plants did not alter the behaviour of the beetles.
1.6 Effect of Water Content of the Soil on Locomotory Activity
The following experiment was planned to see if the activity of the adults and their ability to bury themselves was related to the water content of the soil. 84.
I II III IV EXPERIMENT 1.4. EXPERIMENT 1.5.
Day after No. beetles released release in inner cylinder 10 100 10 100 No. beetles in outer cylinders
1 0 1 0 1
2 0 3 0 3
3 2 59 . 1 15 -
4 2 68 1 47 --
5 2 91 2 71
6 3 93 2 85
7 3 95 2 86
8 3 85 2 93
9 3 96 2 93
10 5 96 2 93
11 6- 96 3 96
12 8-- 96 6- 96
13 9 96 6-- 97
14 9 96 9 98
15 9 96 9 98
- Most plant eaten
-- Plant completely devoured
TABLE 15 . Results from experiments 1.4 and 1.5 showing the influence
of density (Columns I and II) and of the age of plants
(Columns III and IV) on dispersal by adults of P. cochleariea 85.
SOIL CONDITION IN RELATION TO ITS WATER CONTENT:
DRY 110 ml of water / 1 kg of soil -sand mixture
MEDIUM WET 220 ml of water / 1 kg of soil -sand mixture
WET 330 ml of water / 1 kg of soil -sand mixture
MEDIUM Time of Condition DRY WET Observation of Soil WET
10 a.m. 5 3 2
11 7 5 3
12 5 2 3
1 p.m. 8 4 1
2 6 2 2
3 6 4 3
4 7 3 3
5 6 4 3
6 8 5 4
7 6 3 2
x 6.4 3.5 2.6
1.07 1.08 0.84
t = 10.47 *** t = 2.59 *
df = 9 df = 9
TABLE 16 Results from experiment 1.6 - effect of water content of the
soil on locomotory activity of the adults of P. cochleariae 86.
Sieved sand and soil compound previously dried at 100°C for 24 hours, were mixed in the proportion of 1:2 by volume. Variable volumes of water were added to the mixture, to produce a dry, medium wet and wet soil.
These are shown in Table 16.
The experiment was performed in the laboratory, with temperatures varying around 19°C. In a cage with three walls of perspex and three of muslin, two large pots containing the dry soil were placed. A pot with a turnip plant was also introduced, but its soil surface was covered with cardboard. At 9 a.m. 30 adult beetles of different ages were released inside the cage. The number of beetles that buried themselves in the soil was recorded every hour. After five hours the soil mixture was replaced by a recently prepared one, to minimise any effects of evaporation.
Similar experiments were performed with medium-wet and wet soils.
Table 16 shows the results of these experiments. The average number of beetles found buried at each time interval was 6.4, 3.5 and 2.6 respec- tively. These values differ significantly from one another.
It appears that more beetles bury themselves in the dry than in moist soil. The stimuli that lead to this activity remain unknown and may involve reactions to the water content of the soil, to humidity, light, gravity or to combinations of all or some of these factors.
1.7 Summary and'Conclusions
The behaviour of the adults was studied in an attempt to understand the factors that influence locomotory activity and dispersal, or induce flight. 87.
The most striking observation was that flight could not be induced, even in starved individuals. The locomotory activity of the starved in- sects was lower than that of the fed ones. When an alternative source of food was available nearby, dispersal took place by walking, but only after the consumption of the immediate food plant. This pattern of behav- iour remained unchanged, even when the quality of food was poor.
The water content of the soil influenced the proportion of insects that buried themselves in it, and possibly the time that the insects spent buried in the soil.
Most of these conclusions were further confirmed by field observa- tions. 88.
SECTION III - POPULATION STUDIES
A - LABORATORY EXPERIMENTS
This experiment was set up to study the changes in a population of P. cochleariae under. controlled conditions.
The aim was to obtain estimates of mortality in the absence of unfavourable conditions of weather and of natural enemies. The values obtained could aid in the interpretation of field data.
1. Materials and Methods
Two cages, each with three sides made of perspex and three of muslin, were set up side by side, on a laboratory bench. A regime of
16/24 hours light was supplied by four neon tubes, placed 20 cm above the cages.
The temperature fluctuations were recorded in a thermograph, previously calibrated.
Fresh turnip plants were offered to 200 adults, that is approxi- mately 100 ovipositing females, confined in buckets, in the same room.
The plants were removed after 5 hours, and those bearing a significant number of eggs were placed in the above described cages. On day 7, a total of 1,500 eggs was obtained. The adults were discarded and the fate of this egg population was followed to its adult stage.
Fresh turnip plants were introduced in the cages, so that an excess of food was always present. No pots were removed, until the end of the experiment. Sampling was carried out at three day intervals.
All tile eggs, larvae and adults were counted. The pupae were estimated by taking small samples of the soil compost, used in the pots, with the help of a glass tube, having a diameter of 2.5cm. On each sampling 89. occasion 10 samples were taken; the total number of pupae was calculated by measuring the area available for pupation (A) and dividing it by the sampled area (a), which equalled 49.1 cm2.
2. Population Budgets
2.1 Introduction
Life tables or budgets help to interpret changes in populations.
The term budget was proposed by Richards (1961) to describe a special type of age—specific life table, where the actual absolute populations at different ages are listed, and the action of mortality factors is recorded.
The parameters needed to construct a population budget can be estimated by different methods. They are based on certain assumptions, basically that the daily survival rate is constant, within each stage, and that all instars are sampled with equal efficiency. Each of the methods available presents particular constraints and advantages.
One of the earliest is Richards and Waloff's first method (1954).
It can only be used on populations where each stage has a well defined peak in numbers. Richards and Waloff's second method (Richards, 1959;
Richards et. al. 1960; Richards and Waloff, 1961; Southwood, 1966) requires an accurate estimate of both the numbers of insects entering the first stage and of the stage duration; also, samples should be taken at regular intervals of time.
The method proposed by Dempster (1961) may be used if the same stages of successive generations do not overlap. It requires that the rate of entry to stage one is known, and a large number of population
samples should be taken, to produce reliable estimates (Southwood, 1966). 90.
Kiritani and Nakasuji's method (1967) necessitates that samples
are taken at regular intervals of time, until all instars have disappeared
from the population. The number of insects entering the first stage must
be known.
A method presented by Manly (1974.) has some advantages over the
previous ones. In common with Richards and Waloff's first method it
does not require that the durations of the stages be known, or the samples
taken at regular intervals of time. Moreover the numbers entering stage
one need not be known although this knowledge provides a control. A
basic assumption is that the time of entry to stages follows a normal
distribution.
Considering the requirements and restrictions of each method, it
was decided to analyse the data relating to field populations of
P. cochleariae by using Richards and Waloff's second method and the Manly
method.
For the laboratory population, Richards and Waloff's first method
was also used. It consists of plotting the regression of the logarithms
of numbers of an instar, together with the total of individuals in the
subsequent instars, after the peak, with time. The projection of this
line to day 0, will give an estimate of the total number of individuals
that entered the stage. If Yt is the population present on day t
P is the peak population and o S is the fraction of the population which survives to the end of the
unit time,
t Y = P S (1) t o and
log Yt = log Po + t log S (2)
when t = the day when the stage started 91 .
Y = the number of animals that entered the stage. t
The analysis of the laboratory data, using this method, is shown
on Figures 21 A, B, C and D.
Richards and Waloff's second method requires that the total number
of individuals entering a stage (P ) is known, as well as the duration of o the stage (a). The total number of insects in any one stage, taken in all
samples (N) is given by the expression
a a N = P j t d t = P (S - 1) o ✓o S o (3) loge S
where S = the fraction of the population that survives per unit of time.
Sa can be substituted by the term U, and so
N= a P U - 1 or N U - 1 (4) o log U a P e o loge U
A table (U - 1) / loge U was used for values of U from 0.01 to
0.99. Since the value of N is known, the U is read off the table, a P o which corresponds to the stage survival Sia.
One of the requirements of this method is an accurate estimation
of the duration of stages, since differences of only half a day may
account for large error in the calculation of mortality. (Richards et.al.,
loc. cit.).
Manly's method assumes that the time that insects enter a stage follows a distribution, with frequency function f (x). The constant daily survival rate is ems, where -60- is the age specific death rate. Thus, the probability of an individual being alive at time t- is
*(t-x) e , where x is the time of entry to the stage. 92.
The expected number of insects in a stage is
N t =Mr t e(t-x) f (x) dx (5) -0°
being M the total number of insects entering the stage.
If the entry to the stage is assumed to follow the normal frequency
distribution, then
_1 f (x) = (2x) 3 exp. {- (x - P)2 /6".2} (6)
which replaced in (5) gives
(t-p*) / (2.701 exp(-i x2) dx N = M* (7) t ,r -00
where
M* = exp{--(p + 0 G2) } M (8)
and
P* (9)
being p the mean entry time to the stage and 6" the standard deviation
about this mean.
If, for each stage, data are collected over at least four sampling
occasions, yielding four values of t, the unknown parameters M,
and -G- can be estimated.
Forastageq,thespecificsurvivalS is estimated by iq M q+1 Mq and the-duration aq by q+1 - q
A Fortran computer programme was used to fit equation (7) to the data. The adjustment was based on the principle of the least squares,
estimated by the modified Gauss iterative procedure (Osborne, 1969). 93.
2.2 Estimation of Population Parameters
The data obtained for the laboratory population are given in
Table 17. Figure 20 shows the population trends.
Inaccuracies in the estimation of the pupal stage are apparent, resulting from the small'number of samples taken. However, a compromise had to be reached between sample size and the damage caused to the micro- environment, by the removal of soil.
Throughout the experiment, temperatures fluctuated between 17° and 21°C, with a mean of 19°C.
The parameters needed to estimate the number of recruits to each stage, by Richards and Waloff's second method, were calculated as follows: the durations of stages were extracted from the equations referring to the temperature - time curves (Section I, 7).
The rate of oviposition was known for a set of constant temperatures
(Section I, 4 and 6.3). A linear regression of the rate of oviposition on temperature was calculated, and the relevant values were extracted from it.
Table 18 shows an estimate of the numbers entering each stage (P.) and of stage survival (Sia), obtained by three independent methods: 1 -
Richards and Waloff's first method 2 - Richards and Waloff's second method, 3 - Manly's method. The last two methods also provide a value for thP.daily survival (Si).
It can be seen that the more realistic estimates are the ones given by the first method. Figure 21, A, B, C and D show the fit of the regres- sion lines to the data.
A value for survival greater than 1.0, was obtained for the old
larvae, both with the second and third methods. This is probably due to 94.
Young Old Day Eggs Pupae Adults TOTAL Larvae .Larvae
1 561 561
4 1,350 1,350
7 1,500 1,500
10 520 870 1,390
13 182 904 63 1,149
16 90 595 264 985
19 282 515 30 827
22 163 558 64 785
25 50 551 154 755
28 389 345 7 741
31 200 459 42 701
34 69 355 249 673
37 5 176 451 632
40 40 553 593
43 12 601 613
46 611 611
TABLE 17 Estimates, at intervals of three days, of a laboratory
population of P. cochleariae 95,
1500
1400. 4----4 adults i eggs 1300. 4,_---le young larvae 0 o old larvae 1200. . pupae
1100
1000.
CI) 900.
LLI 800. CO
2 700. = 2 600.
500.
400
300-
200.
100.
I . r . • 1 7 13 19 25 31 37 43
DAYS
Figure 20 Changes in the laboratory population of
P. cochleariae.
96.
Young Old Eggs Pupae Adults Method Estimates Larvae Larvae
1 P. 1,489. 1,087. 1,000. 703. 611. 1
S.4 0.73 0.92 0.70 0.87 1
P. 1,500. 1,080. 674. 674. 649. 2 1
a S. 0.850 0.798 >1.0 0.974 1
S. 0.965 0.948 1.0 0.995 1
3 P. 1,497. 1,596. 841. 997. 721.
a S. >1.0 0.527 >1.0 0.723 1
S. 0.999 0.997 0.938 0.907
TABLE 18 Number of recruits entering a stage (Pi), stage survival
(S.a) and daily survival (S.). for a laboratory population 1 of P. cochleariae, estimated by :
: 1. Richards and Waloff's first
method.
2. Richards and Waloff's second method.
3. Manly's method. •
97. an underestimation of the larval population
The fit of the values obtained by the Manly method to the data is shown on Figure 22.
2.3 Budget of a Population in CONTROLLED CONDITIONS
Finally, a budget was constructed, based on the estimates obtained by the first method. The following columns were considered:
• age interval
1 number surviving, at beginning of stage, in column x x
d number dying within the age interval, in column x x
L = (1 + ) / 2 = number alive between age x and x x 1x4-1 age x + 1
T = L + L +....L = number alive beyond age x x x x1 xn T e x = expectation of life
100 = mortality within x qx
x 1 d L T e 100 x x x x x qx
Eggs 1,489. 402. 1,288. 4,148. 2.79 27.0
Young Larvae 1,087. 87. 1,044. 2,860. 2.63 8.0
Old Larvae 1,000. 296. 852. 1,816 1.82 29.6
Pupae 704. 93. 658. 964. 1.37 13.2
Adults 611. 611. 306. 307. 0.50 -
Table 19 Budget of a population under controlled conditions 2.4 Analysis of the budget data From the analysis of this table, it is apparent that the heaviest mortality occurred in the egg stage (27.0%) and in the old larvae (29.6%).
Thus, the critical phases for this species, in the absence of natural enemies and unfavourable weather factors, seem to be at egg hatching and 98.
3.20. A Eggs y = 3.17299 - 0.00987 r = -0.935
Young Larvae y = 3.03621 -0.00603X r = -0.975
0 10 15 20 25 30 35 40 45 10 15 20 25 30 35 40 17 da ys 21A 21B E = =
Old Larvae Pupae O'J 0 y = 3.00202 - 0.00506 y = 2.84797 - 0.001377 r = -0.915 r = -0.952
A
40 42 44 4$ da ys 21C 21D
Figurc 21 Linear regressions (Richards and Waloff's first method)
fitted to the data for the laboratory population of
P. cochleariae
-C > 0 -1 N rr
. - aio • - • •
ohs. est. 1500 1350 1390 1028 1149 1024 627 673 741 755 785 985 593 561 632 00 701 00 613 ra 611 Os
• 1014 1001 786 984 938 966 855 560 636 712 355 916 487 418 + +
+ •
+ • -1•• • • • + • • 4- • + + + • obs. est. 785 967 593 827 632 673 741 755 859 611 870 701 613 11 C
w)-4
CIO 529 626 671 749 780 833 636 805 830 712 823 578 817 0 + • aET IEDILIDOO .+ • • + + go uo-prindod . • • -I- + • + Laolvioqui aq iog
'potilatu krurx aql 2u-pn obs. est. 264 558 200 389 515 551 69 63 5
sa put. 635
en paleurp tu
‘sant 459 595 566 259 278 63 11 81 II paniasqo ' • + . + • + +
ohs. est. 154 176 459 355 345 64 70 12 30
437 352 190 183 355 66 13$. 61 15 100. pupation.
The mortality factors acting within this generation were separated in Table 20. Column I shows the apparent mortality, that is the number of insects dying, as a percentage of the numbers entering the stage. The real mortality (Column II) is the percentage dying within a stage, in relation to the initial recruits to the stage. This factor allows for the comparison of population factors within the same generation and the values are additive. The indispensable (or irreplaceable) mortality (Column III), is that part of the generation mortality that would not occur, should the factor in question be removed from the life system (Southwood, 1966), assuming that these factors are density independent.
I - II III APPARENT REAL INDISPENSABLE STAGE MORTALITY MORTALITY MORTALITY
Eggs 27.0 27.0 22.3
Young larvae 8.0 5.8 5.1
Old larvae 29.6 19.9 26.9
Pupae 13.2 6.3 9.3
Table 20 Comparison of mortality factors within one generation
of a laboratory population of P. cochleariae
101.
B. FIELD EXPERIMENTS
1. Description of the study area
The present work was carried out on a piece of land referred to
as South Lodge Field, situated on the south side of Silwood Park, near
Sunninghill, Ascot, Berkshire.
From this field, three sites called plots A, B and C were chosen
for the population studies. Figure 23 shows their relative positions
and immediate surroundings.
1.1 Plot A
Plot A was the only one used in 1974 and 1975. It was approximately
a square, measuring.20m by 18m. Tt was enclosed on the North, West and
South sides by hedges that were, at the time of the experiments, 2m high.
The North hedge was of Thuja; the South and West sides were delimitated
by a species of Escallonia, with some wild Prunus trees intermingled in it.
In April 1974 a crop of turnips, Brassica napus , cv. Green
Tops (from Suttons) was established from seed. This consisted of 29 rows,
spaced at intervals of 65cm. When the turnips reached an average height of
14.6cm (±6.8cm), with a mean of 4.5 (±2.3) leaves, they were thinned out.
About 62 plants were left in each row; the total number of turnips in the
field was 1,776.
During the following Winter, the land was ploughed and cleared of
the old crop. In the Spring of 1975, a new crop was introduced. This time
1,036 plants were left after thinning, in 28 rows, each one of 37 turnips.
In 1976 the procedure adopted was different from the previous years. The
field was not cleared and the sowing of the new crop was carried out in
between the last season's rows. ••.•••••••••••••• OQ Pmus s lvestris co cD
I E< >W R th PLOT C el ree
ati R9 N ve pl
ot 5.6 posi
s n1 us ti
ed 20 44- pio 4—pi o i ns n
a empty land
nd Escallonia sp. th i e fi R1
mmedi .. lq
eld 16m
at e x e pe s ri urro me PLOT A i undi nt m :
s R 74' > R9
. P20 n gs
of P LO 6.7 th
e _ P1,--- marinus officinale Thu a shrubs _SIVIACP"e4 ROAD 103.
A strip of empty land, 3m wide, separated plot A from the nearest
crop. During 1974 wheat (Triticum aestivum) and during 1975 peas (Pisum
sativum), were cultivated on the adjacent site.
1.2 Plots B and C
Two additional plots, B and C, were used in 1976 for the population
studies. Plot B was a small patch, measuring 7m by 8m, lying on the East
of Plot A. On the North it was bordered by a low hedge of Rosmarinus
officinalis that separated it from the nearby road. It contained nine rows
of turnips, each one with 20 plants.
Plot C was 16m South of plot B and had the same dimensions. The
land that separated them was left uncultivated, but was cleared of weeds.
On the West, plot C was protected by cypress trees (Chamaecyparis lawsoniarA)
Ten m further South, the bottom of Lodge Field is delimited by a row of
Pinus sylvestris.
A mixed culture of turnips and dwarf African marigolds, Tagetes
erecta, was set up in plot C, forming nine continuous rows. The odd rows
consisted exclusively of turnip plants; the even rows had half of each
crop.
All the plots were surrounded by a metallic fence, to protect the
crops from rodents.
The weeds that grew amongst the turnips were difficult to control.
The more abundant species were Trifolium repens, Lolium perene, Crataegus
monogyna, Poa pratensis, Urtica dioica, Ranunculus repens, Holcus lanatus,
Taraxacum officinale. During 1974 and 1975 they were pulled out at regular
intervalz. In 1976 a weed killer was used, known commercially as Gramoxone, which is a liquid formulation of Paraquat. Three applications were made at
intervals of about 30 days; the dilution was 1/45.
104.
2. Sequence of field experiments
2.1 1974
On the 31st May, 1974 the crop of turnips in plot A, was artificially
infested with laboratory.reared adults of P. cochleariae. 700 insects,
under five days old, were separated in groups of six and released on every
19th plant, starting with plant one of the first row. Another batch of
102 marked adults was released in the central area of the plot to study
dispersal. Care was taken to choose a dry day and the operation was per-
formed shortly before sun set.
Adverse weather conditions, with heavy rainfall and low temperatures,
accounted for high adult mortality and delayed egg hatching. This necessi-
tated the release of another 200 insects on 18th June. Therefore, the total
number of adult beetles introduced was 1,002.
Observations were carried out daily, until the first larvae were
seen and subsequently at three days intervals. The fate of this population
was followed to its pupal stage. However, no adults emerged and there was
no second generation. A survey of predators was initiated and parasitism
was also investigated.
2.2 1975
No overwintering adults emerged in the Spring of 1975 and a
re infestation with reared insects was necessary. On the 21st May, 1,554
adults were released. This cohort was firmly established and two genera-
tions emerged, the second having larger numbers than.) the first.
Besides the repetition of the experiments carried out in 1974,
other methods were used for the study of dispersal, such as the survey of
adjacent areas. Also, sticky traps were set up in the plot, in an attempt 105. to survey flying predators and to check upon the flying ability of
P. cochleariae.
The adults of the second generation entered the overwintering stage on the last days of September.
2.3 1976
To avoid disturbance of the overwintering adults, plot A was not cleared from the preceding year's crop. Instead, the new turnips were sown amongst the rows of old plants.
A study of dispersal, under a regime of mixed crops, was planned for plot B, which was installed 3m from plot A. Both plots were sown simultaneously, but since plot B had been ploughed, the turnips developed faster on this site. Consequently, when the first adults emerged at the beginning of May, the plants on plot A were still very small and the beetles invaded plot B. But the insects that emerged later, found suitable food and remained on plot A.
The fate of these two slightly unsynchronised cohorts was followed by regular sampling. Two generations were present, but unlike 1975, the numbers in the second were smaller than those in the first. Abnormal weather conditions continued throughout the summer and the extreme drought and high temperatures, influenced the survival of the beetle population.
The experiments planned for plot B, were finally carried out in plot C, where 300 marked adults were released. The effect of the non-host crop on the movements of the beetles was studied.
106.
3. Sampling Methods
3.1 Eggs, larvae and adults
During the course of this work, the population of P. cochleariae
was sampled at intervals .of three days; the sampling unit was a turnip
plant, in which all leaves were inspected.
The eggs, larvae and adults were counted on the plants, care being
taken to cause a minimal disturbance to the environment. The first and
second larval instars were recorded together as "young" larvae, while the
third and fourth instars were counted as "old" larvae. In this way,
potential errors arising from visual observations were minimised.
The count of both eggs and larvae present no problem. Both stages
remain exposed on the leaves and the activity of larvae is very small
and does not interfere with the counting. The counting errors were thus
negligible (<0.05).
Assessing the number of adults was more difficult, as they are easily
disturbed and fall off the leaves, on approach of an experimenter. Thus,
both the insects sitting on the plant and those seen on the ground nearby
were counted. The activity of the adults is known to be positively correl-
ated with the amount of sunshine and negatively with the wind speed and
rainfall. The water content of the soil also plays a part in their mobility
(Section II, 1.6). Relatively large errors are to be expected in estima-
tions of the population of adults.
In 1974 and 1975, 100 plants from plot A were inspected on each sampling
occasion. From the practical point of view, this number was the largest that
could be dealt with on one day. Therefore, in 1976, when the population
studies were carried out in the two areas, A and B, only 50 samples were
taken from each one of them. 107.
During the first two seasons, sampling was carried out according
to the following pattern: on alternate rows, either three or four turnips
were examined, up to the total of a 100. From each row, the plants were
not picked at random, but chosen in such a way as to avoid repetition on
consecutive sampling, dates.
In 1976 however, plot A consisted of 28 continuous rows of turnips,
showing some patches of irregular growth due to competition. Hence, each
plant could not be considered as a discrete unit. Instead, a squared frame
of wire, of 0.Im2 was used as a sampling unit. Starting from one of the
corners of the plot and progressing along the rows, the frame was dropped
at random, once or twice on each row and up to a total of 50 times. All
the eggs, larvae and adults enclosed by the frame were counted in one
sample. Another group of 50 samples was taken from plot B. Since there
were nine rows of plants, either six or five turnips were examined on
alternate rows.
3.2 Pupae
The sampling of pupae was attempted, in 1974, by taking soil cores
with a wire-worm cylinder, each sample having an area of 75ciand depth of
5cm. But the process of inspecting the soil was extremely time consuming
and only a meaningless number of pupae was found. Although the sample
units were increased up to 40, the method still proved ineffective.
It was then decided to adopt other procedures to assess separately
the rate.of pupation in the field and the effect of natural enemies.
i) Estimation of the rate of pupation
To estimate this, plants bearing fourth instar larvae were
enclosed in celluloid cylinders, open on top and with a muslin sleeve attached to the bottom. The sleeve covered the soil around the plant and 108. enabled the recovery of the pupae. This method excluded ground predators and birds, but some predation, especially by Opilionidae and Araneido was still possible. The effect of parasites was not reduced.
In 1974 the rate of pupation was calculated for the only generation present. During both 1975 and 1976, the experiment was repeated for the two annual generations. All the pupae recovered were incubated at 25°C.
It was found that under 5% of the adults failed to emerge, but no parasites were found.
Table 21 shows the total number of plants and larvae used in each experiment (Columns I and II), the percentages of larvae found dead and the ones that disappeared (Columns III and IV), the percentage of pupae recovered and of .adults that emerged when these were incubated at 25°C
(Columns V and VI). The lowest rate of recovery occurred in 1974, and the highest in the second generation of 1975. These findings coincide with the subsequent number of adults counted in the field, which was very low in 1974 and the largest seen in this study is the second generation of 1975.
I II III IV V VI GENER- NO. OF NO. OF % DEAD % LOST % PUPAE % ADULTS YEAR ATION PLANTS 4TH INST. LARVAE LARVAE RECOV- EMERGED LARVAE ERED AT 25°C
1974 1st 9 40 52.5 20.0 27.5 84.6
1975 1st 18 200 24.5 13.0 62.5 94.4 2nd 16 200 20.5 11.5 68.0 95.6
1976 1st 12 100 27.0 9.0 64.0 92.2 2nd 10 50 34.0 12.0 54.0 88.9
TABLE 21 - Estimation of the rate of pupation of P. cochleariae for
1974, 1975 and 1976. 109.
3.3 Summary
On each sampling occasion, i.e. at three days intervals, all the leaves of 100 turnip plants were examined. The eggs, larvae and adults were counted and their total numbers, in the field, were calcu- lated.
Sampling errors might result from the pattern of adult behaviour.
The calculation of the number of pupae was based on estimations of the rate of pupation. Again, inaccuracies are likely to occur.
Figures 24 A, B and C are photographs of eggs (A), a last instar larva (B) and an adult (C), obtained in the field, and of the type of damage caused to the turnip leaves. 110.
•• N~-11 ***"., B
4 C 1
Figures 24 A, B and C Photographs of eggs CA), one 4th instar larva
(B) and one adult (C) obtained in the field, and of the
type of damage caused to the turnip leaves. 4. Methods of Ageing the Population
4.1 Examination of Reductive Organs,
It is possible to distinguish tenerat from mature adults of both sexes (see 1-9). Senescent females could also be distinguished.
This method was used, throughout the field experiments, to identify the emerging adults of the new generations.
4.2 Cuticular Rings
An attempt was made to age the population by observation of the cuticular rings (Neville, 1963a). This method depends on alternate de- position of rings of resilin and chitin, which in some insects, can be observed in sections of the hind tibiae, under crossed polaroid filters
(Neville 1963c).
Sectioning of the hard, minute hind tibiae of P. cochleariae proved difficult and moreover no obvious pattern of deposition of layers could be distinguished or identified with daily growth. The problem of chitin deposition is probably influenced by factors other than the circadian rhythm of the insect and may need further investigation.
4.3 Summary
The only reliable method found to age field populations, was the dissection of some individuals and examination of their reproductive organs.
This method has the disadvantage of removing insects from the population.
To cause the minimum of disturbance, only a small number was removed and the estimation of the percentage of insects of the new generation is thus not accurate. Besides, the age of the beetle cannot be pin-pointed; the females were separated into three age groups - under five days old, between five and
30 to 40, older than 30 to 40 days. The males were separated into the first 112.- two groups only.
The examination of cuticular growth layers was not successful.
The failure was due to the structure of the endocuticle of this species, which differed from the normal pattern, observed in the majority of the
Exopterygotes (Neville, 1975).
5. Examination for Parasitism
A search for parasites of the mustard beetle was carried out, over the three years of field experiments.
Periodically, groups of eggs were collected from the field and taken to the laboratory, where they were incubated at 25°C. The ones that failed to hatch were observed under a binocular microscope.
Larvae, pupae and adults were also collected and dissections were made, but no parasitism was found at any stage of the project.
6. Predation
The effect of predators on the population of P. cochleariae was assessed by visual observation, by exclusion techniques and by observations of feeding trials in the laboratory.
6.1 Arthropod Predators
The principal natural enemies of P. cochleariae are among the
Arthropods, especially the Arachnida and certain orders of Insecta, such as
Coleoptera and Dermaptera. a) Field Observations
When field samples were taken, predation by spiders was frequently 113.
observed. The adults, and sometimes the larvae of P. cochleariae were
seen trapped in the webs. At other times, the predators were seen hand-
ling the beetles. Among the arachnid species, Pisaura miriabilis Clerk,
Philodromus sp. Araneus quadratus Clerk, and Araneus sp. have
been observed feeding upon the mustard beetle.
An experiment was conducted to estimate predation on the pupal
stage. 50 pupae, recently formed in the laboratory, were taken to the
field and buried individually, at the depth of 2 to 3 cm. They were dis-
tributed all over the field and their positions were marked.
Observations were made after five and eight days. Since the
duration of the pupal stage at the time of the experiment, was calculated
at 8.6 days, the pupae that were missing after five days were presumed to have been eaten, or carried away by predators. Sometimes only a part of the pupa was eaten, and traces of predation were evident. Pprhaps the first form of predation was due to birds, or arthropods of large size, and the second one to the ground predators of a smaller size.
Table 22 shows that 10% of the pupae failed to emerge and 24% of the adults died after emergence. Those insects were later dissected and
30% of them were attacked by fungi. The causes of mortality of the other
70% remained unknown. Predation accounted for 22% of pupal mortality:
10% had disappeared and 12% were partially eaten by arthropods.
b) Pitfall Traps and Sticky Traps
A survey of the potential predators was carried out, with the help of pitfall traps. In 1974, pairs of glass tubes, half filled with a 10% formalin solution, of the type described by Luff (1964) were used. 20 pairs were distributed throughout the experimental area (Figure 25). During both 1975 and 1976, another type of pitfall trap was used. It consisted of plastic jars with perforated floors, having a diameter of 10 cm, that were 114. buried in the soil up to the rim. A grid of metal was placed inside the jar, to allow for the separation of large and small animals, thus minimi- sing canibalism. The top third of the inner surface of the trap was painted with fluon, to prevent the arthropods from crawling out.
In 1975, 20 pitfall traps were placed in plot A. In 1976, only 10 were distributed over this patch, and 10 others buried in plot B (Figures
25, b and c).
During 1975, 10 sticky traps were set up in plot A, to survey flying predators and check upon the ability of the adults of P. cochleariae to fly. They were made of celluloid cylinders of 15 cm diameter, covered with greaseproof paper spread with Stictite. ,These traps were pinned to wooden stakes, at a height of lm above the ground level and their distri- bution is shown in Figure 25 b. Hcz•Tsver, insects belonging to families of potential predators, such as Neuroptera and Heteroptera were not caught in significant numbers.
Initial No. of pupae : 50
Causes of mortality
1 Disappearance 10
2 Traces of predation 12
3 Dead pupae 10
4 Dead adults 24
Attacked by fungi (as % of 4) 30
5 Total mortality 56
TABLE 22 Pupal mortality in the field. 115.
Plot A
IV
• • S . o • •• %CI . . • • 0 • • : 4 •••• NI- W • E o. 25A •• n
t • . •• 1 . ► N . •• Plan .. :• 00 — • , • o •• t . , i 1 ,,40 Row 1 5 9 15 21 25 29
Pitfall Traps: .• Pair of tubes O Jar
• Sticky traps C./ O • e • 0 O 0 A 0
0 0
no. • t 0 0 A 0 25B • 0 A
Plan 0 0 A 0 0 A I I I 101 I I I
Row 1 4 7 10 13 16 19 22 25 28
0
Plot B s 0
ou 0 0 inu t n 0 25C co 0 in
t 0 ts CO 0 0
Plan 0 I I ' o' I I I I 1 35 7 9 Row 1 4 7 10 13 16 19 22 25 28
Figure 25, A, B and C Distribution of pitfall and sticky traps in 1974, 1975 and 1976. 116. c) Feeding trials in the Laboratory
The pitfall traps used in 1975 and 1976 allowed for the capture of living Arthropods. Most of the species trapped were tested in laboratory feeding trials, to detect those that would feed on P. cochleariae and compare their relative efficiency, at various prey densities.
The experiments were carried out at room temperature, under a regime of 16/24 hours light. Temperatures fluctuated between 17° and
24°C, with a mean of 20.5°C. All potential predators were previously starved for 48 hours.
In a set of trials, Carabid beetles were tested for either 7 or
14 days. The Carabid was placed inside a plastic dish of 10.5 cm. diameter, containing a thin layer of moist peat, and closed with a muslin square. At the beginning of the experiment either 4, 8 or 12 larvae, pupae or adults of P. cochleariae were placed inside the dish. In the experiments with pupae, these were buried under the peat, and the poten- tial predator introduced afterwards. The prey numbers were checked at
12-hours intervals, and the initial number kept constant.
The daily consumption rate of predators, in the absence of alter- native prey and being the searching area constant, is given in Table 23.
Table 24 indicates other insect species that were observed in the laboratory, to feed upon P. cochleariae, although the rate of prey consumption was not determined.
d) Field collections
Records of the seasonal variation of the species of Carabidae and
Staphylinidae caught in the pitfall traps, during the three years, are given in Appendices 111-6. Their numbers account for over 90% of the total catches. The dominant species were Harpalus rufipes, Leistus 117. spinibarbis, Pterostichus madidus and Bembidion lampros. Figure 26 shows the fluctuation in the numbers of six of the more abundant species.
Although in 1974 the pitfall traps were only set up in July, the corrected totals for several species were higher than in the following years, whereas in 1976 the lowest catches were recorded.
e) Summary and Conclusions
Few birds were seen visiting the experimental area, hence it was concluded that the natural enemies of P. cochleariae should be among the
Arthropods.
Arachnidae were observed, in the field, handling adults and larvae
of the mustard beetle.
Pitfall and sticky traps were set up to survey any potential
predators. Over 90% of the species caught in the pitfalls belonged to
the families Carabidae and Staphylinidae. Some larvae of Coccinelidae
and Dermaptera were also trapped. Feeding trials in the laboratory
revealed that most of these species are effective predators of P.
cochleariae. Only a meaningless number of potential predators was caught
with the sticky traps.
Ground predators accounted for 22% of the pupal mortality.
44-4 0 4-1 118. 0 0 >1 0 0 3-4 id 4J • r-1 ..••■ PREY TYPE 0 W P 0 Species of 41:3 0 0 P., Predator gr4 CTI 14 tt z 44 'V P1 LARVAE PUPAE ADULTS
7:./day s x/day 7s/day
Carabus 4 7 5.43 0.55 4.71 0.40 violaceus 3 8 7 6.86 0.65 5.57 0.62 12 - 7 8.71 0.76 6.43 0.56
Leistus 4 7 0.62 0.44 1.14 0.43 0.86 0.33 spinibarbis 4 8 7 0.91 0.53 1.57 0.52 1.29 0.54 12 7 1.23 0.82 1.86 0.67 1.71 0.62
Loricera 4 14 1.07 0.07 0.21 0.03 pilicornis 4 12 14 1.64 0.13 0.29 0.15
Pterostichus 4 7 1.53 0.84 2.86 0.86 2.50 1.03 madidus 5 8 7 2.76 0.65 5.50 1.53 4.64 1.21 12 7 3.42 1.43 7.57 1.92 5.71 1.52
P. melanarius 4 14 2.04 0.71 3.43 0.62 3.76 0.55 3 8 14 2.51 1.40 6.19 0.65 6.21 0.65 12 14 4.32 1.05 6.57 0.87 7.29 1.83
Luara apricaria 6 4 7 0.43 0.51 0.14 0.06 12 7 1.29 0.42 nal 0.35 darpalus 4 14 0.43 0.22 1.29 0.22 1.14 0.19 rufipes 10 8 14 0.79 0.33 1.64 0.16 1.43 0.29 12 14 1.07 0.72 2.00 0.38 1.86 0.40
H. aeneus 4 14 0.52 0.27 1.00 0.34 0.50 0.21 8 8 14 0.64 0.42 1.23 0.28 0.79 0.23 12 14 0.57 0.28 1.56 1.02 1.29 0.41
TABLE 23 Mean daily consumption rate of Carabid predators,
supplied with different densities of prey : larvae,
pupae and adults of P. cochleariae, in laboratory
feeding trials. 119.
PREDATOR TYPE OF PREY EGGS LARVAE PUPAE ADULTS
Coleoptera Carabidae Leistus spinibarbis
Bembidion lampros
B. femoratum
Agonum dorsale
Amara montivaga
Staphylinidae
Philontus sp.
Occipus sp.
Coccinellidae
Adalia bipunctata L.
Coccinella septempunctata L.
Propylea quatuordecimpunctata
Dermaptera
Forficula auricularia L.
TABLE 24 Results of feeding tests of different insect predators,
supplied with P. cochleariae. 120.
YEAR 74 N= 344-8
75 N= 24
I • 11 Fri-1 rfl l 76 N= 19 ta f to % o s d a sse Harpalus rufipes Pterostichus melanarius re N = 53+24 74 N = 28+11 exp
s, 101 N= 65 ap 10- N=63 75 l tr l 20- fa N = 76 76 N= 97 it
20 p r-i .
in Pterostichus madidus Amara apricaria 74 ht ug 2 N = 72+75 N =12+8 ca rs be m 7T-71 F-71 . Nu 3 N = '47 N= 19 20 75
11■■•■•■ n 20- r- N= 56 76 N =9 1 -1-1 f 1 1 M .1 A A S M J JL A Leistus spinibarbis Carabus violaceus
Figure 26 Seasonal variations in the abundance of six species
of Carabidae
N = total catch in the season -121.
7. Estimates of field populations
The data for the seasonal fluctuations of the field populations of
P. cochleariae are given in Appendices 111-7, A(1974), B (1975) and C (1976
plots A and B).. The numbers represent estimates of the total populations
in the field. On each sampling occasion, the counts were multiplied by a
constant factor, equal to the number of turnips, divided by the number of
samples taken (i.e. number of turnips sampled).
Figures 26, 27, 28 and 29 show the population trends for the three
years. In both 1974 and 1975 the sampling dates were numbered from the
day when oviposition started. In 1976, the emergence of the overwintering
adults marked the beginning of the season. There is a de-synchronisation
of about one week between the two study areas, reflecting the early
invasion of plot B by the first insects that emerged.
7.1 Estimation of population parameters
a) Natality
The number of females present on the field was estimated as half of the adult counts, on each sampling occasion. These values were plotted against time and the number of females present on each day, read off from the graph. Time units of six days were considered, over which the mean daily temperatures were taken and a mean calculated for each time unit.
Fecundity was estimated for each time interval and natality obtained by multiplication of the number of females by fecundity. Fecundity was estimated on the basis of laboratory experiments (Section I, 4. and 6.)
b) Durations of immature stages
From experiments on parasitism and predation, eggs, larvae and 122. pupae, recently formed in the laboratory, were taken to the field.
The durations of these immature stages under a regime of fluctuating
temperatures were found to be, on average, respectively 2.0days, 3.0days and 1.8 days shorter than under the corresponding constant temperatures.
As for the estimation of natality, the same six-days units were consid- ered and durations calculated over these periods.
From the analysis of the data for the three years, it can be seen
that there was a delay in egg hatching at the beginning of all seasons.
The inspection of the temperature records revealed that the limiting factor was the occurrence of low minimum temperatures. The first larvae were only noticed when these temperatures remained consistently above 10°C.
c) Survival rates and recruits to stages
Table 25 shows an estimate of the numbers entering each stage (Pi), of the stage survival (Sia) and daily survival (Si) of the field popula- tions, using two independent methods: Richards and Waloff's second method (2) and Manly's (3), already described under section III, 2. .
Direct estimations of numbers were made by a sequence of 3-days sampling. When calculations grossly departed from this sequence, they were considered to be either over- or under-estimates. Regarding the estimate of recruits to each stage, the numbers forecasted by Richards and Waloff's method are, in general, under-estimates, while Manly's method almost always gives over-estimations. On several occasions the two values predicted are rather close, e.g. 1974 and plot B, 1976, but on others gross disparities were obtained (e.g. 1976, plot A).
For the pupal stage, survival values greater than 1.0 were obtained, in some years. This is the result of inaccuracies in estimating the number of pupae.
Figures 30 and 31 show the observed and estimated values, obtained by the Manly method, for the 1975 populations. ._ _ _.. Adults x 10-2 Eggs •♦ Young larvae 1974 - x 10-3 o—o Old larvae ..--A Pupae
13 19 S M ' 43 49 55 M 97 73 79 DAYS
Figure 26 Population trends of P. cochleariae in 1974 (Total numbers in the field) .___. Adults x 102 2o- Eggs .--. Young larvae 1 3 co __.0 Old larvae x10 1915 A—A Pupae
15
10.
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 97 103 109 1 5 121 127 DAYS Figure 27 Population trends of P. cochleariae in 1975 (Total numbers in the field).
1976 125. PLOT A
8
7
6
5
4
3
CI)
2
X IC 2 eagle I, PLOT 13 larv.• _3 °Nam() ; X 10 o,PuPaes,
Figure
28 B
16,11
13 5 25 31 37 43 49 55 61 67 13 79 65 91 97 103 109 15 121 127 DAYS
1 9 7 6 t0TAL
_2 411 4. - - -e eagdultsg s x 10 13.. _ 3
NIP *---0 young larvae i x 10 _ 0-----0 old larvae p,____ 10. pupae _I
CCI . 4. 'A • 7_ , ,. 1 N I )it t % 4. Z + / % % 5- Ilt.. I4.. -+1 41 .4... / % % ..A"...*....4 -4. / 4% 3- 10 \% - / 4
121 127 I 7 13 19 25 31 37 43 49 55 61 67 73 79 85 97 103 109 115
'0 A Y S
Figure 29 Population trends of F. cochleariae in 1976 (Total numbers in the field : Plots A & B)
ohs. est. 174 122 G PG rt rr cr M 171 • 0' 0".4 H• 11 n M M rt CM 265 218 4. rt H• G cn G 416 357 + • —:C..0117)16- 1 Ws-Jrt rt '1:3 cr H• l.n V "a 590 541 + • )--, M M OQ Cl• CD PI 111 '0 M 0 637 756 •+ a fil Pi 0 0 I—. 4 r••0 m '`•C P3 0 1150 981 + • 0 MID 1—.° 11P3 El 5 po: 03 rt fti M M 1272 1187 + • .--. rt. I-.• rt 0'3 l'i 0 1-' • 0. C 1473 1347 obs. est. Jo oOoom + * o a. cr a. DT 1494 1443 105 112 = 0 rt 1- obs. est. O hh 1-h M 1:13 599 574 HI 0 0 1466 1470 = •+ 25 32 •+ 11 0 1:1. h 1445 1436 = 784 849 • + 61. 62 • 4 p. 1275 1359 . + 735 817 • + 161 165 •+ obs. est. t 1132 1255 • + 729 755 •+ 315 264 + • 8 48 • + 976 1141 • + 671 697 •+ 364 348 •+ 53 64 •••• 950 1026 636 644 •+ 416 394 + • 93 84 +• 939 917 547 595 • + 310 403 + 113 106 4-• 937 618 647 549 + • 298 389 . + 159 128 + 905 728 652 507 + 311 367 • + 135 151 • + • 769 548 604 456 + 343 343 = 114 171 + 635 577 552 433 + • 367 320 + 158 188 • + 553 513 507 399 + • 374 298 + • 205 200 4.
437 458 437 369 9- • 358 278 + • 233 207 + • 346 406 346 341 - 320 259 + • 228 208 + • 304 361 304 315 •+ 304 242 + • 210 203 199 321 199 290 • + 199 225 • + 180 193 • + +- 155 288 155 268 • + 155 210 . + 160 • + 163 Z54 • + 13Q 163 248 • + 163 196 • + 163 a ,r, OQ a. c 138 221 • 4 tn 138 229 • + 138 183 • + 138 145 •+ •t1 a) 133 201 135 211 • + 135 170 • + 135 127 + • m -• 0 ft) 144 179 ° 144 190 • + n 144 159 • + y 0 144 109 + • .1 a as
obs. est. 36I 316 136 814 1600 1576 4-• obs. est. 2270 2359 .4- 50 79 •+ 3015 2937 + • 155 145 = 2915 2599 4- 275 241 + • 2503 2643 •+ 333 365 -+ moo 2291 • 4- 436 505 -4- P1 1817 1945 638 - + Oo 4- 575 00 1749 1642 + • 814 742 • + 1414 1386 + - p 147 799 + 1255 1169 4- 245 803 - + 1063 986 4-- 743 759 = 849 832 = 654 682 • + 680 101 = 575 590 .4. 607 592 = 532 495 + • 462 499 • + 432 408 -I- 355 421 -+ 355 332 4- 292 355 -+ 292 269 +• 273 299 . 273 216 + • 43 253. + 0 43 174 +
03 obs. es t. 145 181 •+ 320 359 580 616 985 923 +• 1265 1219 +- obs. est.
1503 1436 + • 33 51 •+ 1480 1531 • + 71 87 •+ 1377 1503 • + 95 137 Sunox 1399 1397 249 198 sq 1243 1226 It, 277 264 + •
sAa +. -a 305 324 -+ a 1095 1057 fD 968 199 + • 378 370 809 760 + • 384 392 680 641 +. 370 3118 607 540 + - 362 360 462 455 307 316 355 384 •+ 265 263 -1-• 292 323 -+ 246 210 + • 273 273 227 162 230 • + 43 122
obs. est.
p-o rt rt cr e .4 130 99 + • a' a- %4 co H- al a) f-r ao (.4 135 124 + • u n rt 1-, 0 — o — NI a.. pi PI nu n 'o 0 m a to 125 143 • + m 0' •••.1 a. rt M us c.■ I-• to Z ..4 150 169 • + CD 00 133 0. ''' aaq P3 'CI a/ 0 175 115 • +
s ••••• "0 ID 4-4 P3 0 0 93 a.. P3 0 rt cr p—• 4.< 180 193 • + m • a El 0 03 li 03 03 rt uz IP 03 03 01 210 192 + • 1 rt 1.• rt 173 II or• 0 0- < a. 0 o o m ID 193 184 + •
00 0 fa. a' Ca. = 0 •• ft 170 183 P3 03 o3-11 M H. 0 . N 175 147 + dmvs o 0 a. ti a> 190 123 + ai a. s els 0 15 99 •112 129.
OLD YOUNG PUPAE ADULTS YEAR GENERATION METHOD ESTIMATE EGGS LARVAE .LARVAE
1974 1st P. 18,703 4,555 3,794 1,373 600 a 0.362 2 S.1 0.220 0.833 0.437 0.907 S.1 0.890 0.984 0.907 P. 20,397 6,448 6,150 1,410 1,003 a 3 S.1 0.316 0.954 0.167 0.711 - S. 0.955 0.945 1 0.923 0.949 0.803
1975 1st P.1 29,644 5,929 3,148 1,306 1,299 a 0.741 2 S.1 0.200 0.662 0.995 i S 0.818 0.942 0.931 0.998
P.1 27,488 9,846 6,915 6,484 1,864 a 3 S. 0.359 0.702 0.938 0.288 S.1 0.962 0.973 0.933 0.931 0.764
7,218 6,828 2,034 2,034 2nd P.1 30,583 a 0.576 >1.0 2 S.1 0.528 0.973 0.903 >1.0 S.1 0.847 0.995
P. 48,515 29,530 20,185 18,228 7,042 a 3 S. 0.609 0.684 0.903 0.386 0.945 0.929 0.857 0.705 S.1 0.945
P. 1,888 1,120 1,032 914 A1976 1st 1 16,890 a S. 0.118 0.593 0.921 0.886 2 1 0.923 S.1 0.766 0.990 0.987
P.1 14,793 12,616 8,699 4,083 607 a 3 S.1 0.853 0.690 0.469 0.149 S. 1 0.958 0.904 0.903 0.920 0.99
Continued TABLE 25 130,
YOUNG OLD YEAR GENERATION METHOD ESTIMATE EGGS PUPAE ADULTS ...... LARVAE .LARVAE
A1976 3,206 596 575 2nd P.1 8,808 2 S.a 0.364 0.484 0.964 >1.0 1 S. 0.881 0.886 0.996 >1.0
P. 116,197 10,164 10,056 7,038 3,045 1 a 3 S. 0.628 0.989 0.700 0.433 1 Si 0.997 0.887 0.803 0.841 0.944
P. 8,174 932 527 182 182 B1976 1st 1 a 0.565 0.345 >1.0 - 2 S.1 0.405 0.916 0.859 >1.0 S.1 0.749
B 1976 1st P. 7,333 2,646. 1,224 655 655 a 0.360 0.463 0.535 1.000 3 S.1 S. 0.939 0.830 0.947 0.962 1
P. 5,000 765 350 175 175 B1976 2nd 1 2 a 0.458 0.500 >1.0 S.1 0.153 S. 0.791 0.912 0.917 >1.0 1
2,841 1,062 537 647 B1976 2nd P.1 5,908 3 S.a 0.514 0.505 1.000 1 0.480 0.937 0.945 S.1 0.934 0.905
TABLE 25 Number of recruits entering a stage (Pi), stage survival
(S.a) and daily survival (Si), for the field populations of P. cochleariae, estimated by : 2 - Richards and
Waloff's second method. 3 - Manly's method. A 76 A 76 TABLE 26 1975 1974 1975 2nd. 2nd. 1st. 1st. 1st.
Generation 3 2 2 2 2 Young Pupae Old larvae Eggs Eggs Pupae Adults Young Pupae Young Young Old Eggs Pupae Adults Young Old Eggs Adults Adults Pupae Old larvae Old Adults Eggs larvae larvae larvae larvae larvae larvae larvae larvae x 29,644. 30,583. 18,703. 16,890. 4,555. 3,148. 3,794. 5,929. 6,828. 1,373. 2,034. 7,218. 2,034. 3,206. 1,306. 8,808. 1,299. 1,888. 1,032. 1,120. lx 600. 914. 575. 596. 575.
23,715. 23,365. 15,002. 14,148. 2,421. 2,781. 4,794. 1,842. 5,602. 2,610. dx 761. 773. 390. 768. 118.
88. 21. - - 7. - O. O. 100qx 78.0 63.8 80.0 46.9 56.3 58.5 16.7 76.4 70.2 88.2 40.7 51.6 63.6 11.4 0.5 0.0 5.4 7.9 3.6 0.0 - - -
Continued... >1.000 0.220 0.200 0.437 0.362 0.833 0.995 0.415 0.531 0.946 0.298 0.236 0.593 0.118 0.886 0.921 0.964 0.364 0.484 1.000 Sx 131. - - - 132.
0 a) o a) .1-4 r4 C) 4-1 tdJJ td rrl 1J cb 0.13 G.) 0 •r1 cd 4-1 4-1 (1) GJ o >4 c.D Z4-144 x. lx dx 100qx Sx
Eggs 7,333. 4,687. 77.0 0.330 Young larvae 5,646. 1,422. 78.4 0.216 B 76 1st. 3 Old larvae 1,224. 569. 46.5 0.535 Pupae 655. 0. 0.0 Adults 655.
Eggs 5,908. 3,067. 52.0 0.480 Young larvae 2,841. 1,759. 48.6 0.514 B 76 2nd. 3 Old larvae 1,062. 525. 49.5 0.505 Pupae 537. 0. 0.0 Adults 520. - - -
TABLE 26 Budgets for the field populations of P. cochleariae, over
three consecutive years. 133.
7.2 Population Budgets
a) Description
Population budgets were constructed for each of the three years, using the estimates obtained by the method that provided a more realistic approach to the observed values - Table 26. The columns correspond with those in Table 19.
b) Analysis of the budget data
The role of different factors can be evaluated from information on several consecutive generations, or by simultaneous observations of several distinct populations.
1974
From the population budget for this year it is apparent that high
mortality was seen throughout the cycle. The eggs and the last
larval instar were particularly vulnerable, with mortalities of
78.0 and 63.8% respectively. Only one generation occurred, which
died out in its pupal stage.
The explanation of this phenomenon probably lies in an interaction
of factors, basically the combination of low temperatures and heavy
rains, during July and August, and the occurrence of a large number
of predators throughout the season. Under these conditions, the
washing down of the larvae was certainly the main cause of mortality
and this was observed on some sampling occasions.
Mean temperatures in July and August were, on average, 2° to 3°C
lower than in 1975 and 1976. This extended the pupal period, which
is highly vulnerable to predators. Previous experiments (Section 134.
III, 6) indicated that 22 % of pupal mortality was normally due to predation. Although the survey of natural enemies was initiated only in July, certain species of Carabidae, such as Harpalus rufipes, Lonicera pilicornis and Pterostichus melanarius were more abundant than in the next two years.
1975
After an experimental reinfestation, the population was well established and its numbers were the highest recorded over the three years.
Both the first and second generations suffered the heaviest losses in the egg stage. Under laboratory conditions a 27.0% mortality had been observed for this stage, and may be considered as due to ster- ility or failure to hatch, i.e. to physiological reasons. The remaining percentage of deaths was probably caused by the interaction of two main factors: desiccation of the developing embryos and destruction by predators.
The numbers of the second generation were higher than those of the first. The adults entered hibernation on the last days of September.
1976
The Winter season of 1975-76 was a mild one, with temperatures rarely reaching the freezing point. Thus, considering the results from laboratory experiments (Section I, 8.2) the survival of the overwintering insects would not have been seriously affected.
The first generation of 1976 suffered a heavy mortality in the- egg stage, on both study areas, but higher on plot A. Egg samples were examined in the laboratory and it was concluded that desicca- tion was a major cause of mortality. Since plot A had not been 135. cleared from weeds, the turnip plants were surrounded by vegeta-
tion that helped to sustain a certain degree of humidity. The
fact that this plot is shaded by surrounding hedges also protected
the eggs from some insulation.
The high temperatures and the drought that occurred in Summer
1976, were probably responsible for the low numbers of Arthropod
predators. Hence, predation was not an important mortality factor,
at least in the first generation. During the month of September,
the catches of predators increased slightly.
A small second generation, apparently non-overlapping with the
first, was present in early September. However, it did not reach
completion, since no adults emerged. The cause of this phenomenon
is not clear, but a sharp fall of temperature occurred in September,
by the time the larval instars were developing.
7.3 Summary and Conclusions
Comparing the laboratory to field populations (Table 27), one notes
that:
1. Real mortality, from egg to adult in the laboratory was equal to
59% whereas in the seven field populations examined it fluctuated between
91 and 96%.
2. In the laboratory the heaviest mortality occurred in the eggs and
old larvae, i.e. the critical or the most susceptible phases of life
history of this beetle are presumed to be at the stage of embryonic dev-
elopment and hatching and at pupation.
Whereas in the laboratory egg mortality was equal to 27%, in
5/7 field generations it exceeded 75%, and in two it was equal to 52 and
64%. 136.
APPARENT MORTALITY
1974 1975 1976 A 1976 B Laboratory 1st. 2nd. 1st. 2nd. 1st. 2nd.
Eggs 78.0 80.0 76.4 88.2 63.6 63.9 52.0 27.0
Young larvae 16.7 46.9 5.4 40.7 51.6 19.4 48.6 8.0
Old larvae 63.8 58.5 70.2 7.9 3.6 46.5 49.5 29.6
Pupae 56.3 0.5 0.0 11.4 0.0 0.0 0.0 13.2
REAL MORTALITY
Eggs 78.0 80.0 76.4 88.2 63.6 63.9 52.0 27.0
Young larvae 2.7 9.4 1.3 4.6 29.6 19.4 29.8 5.8
Old larvae 11.7 6.2 15.7 0.5 0.2 7.8 8.9 19.9
Pupae 3.7 0.0 0.0 0.7 0.0 0.0 0.0 6.3
TOTAL 96.1 95.6 93.4 94.0 93.4 91.1 90.7 59.0
TABLE 27 Apparent and real mortalities of eggs, young larvae, old
larvae and pupae on field populations (1974, 1975, 1976)
and in the laboratory. 137..
As suggested above, in the field,developing eggs are subjected to extremes of weather conditions and to predation, possibly by Coccinellids.
In the laboratory 30% of the population died at pupation, whereas in 5/7 field generations death at this stage varied between 47. and 70.%.
As said above, this excess of mortality is probably due to predators, mainly carabid beetles. In 1976, late larval and pupal mortality in both generations, was extremely low, as were the numbers of predators, especially in the first generation. Favourable conditions of temperature, probably also helped survival in the first generation. 138.
8. Population Patterns of Distribution
8.1 Introduction
The spatial distribution of a species, at a certain time, is the
result of all the interactions between the species and its environment,
including any intraspecific ones. Thus, an investigation at this level is
important, both in the study of the behaviour of the species and in the
understanding of the complex relationships of the ecosystem.
The degree of association among the individuals of a population can
be expressed by indices, based on the sampling data. The pattern of dis-
tribution is obtained by comparing the data with the theoretical distribu-
tions. In general, aggregation or contagiousness is considered when the
variance between unit counts is greater than the mean. If the opposite is
true, the population presents a tendency towards under dispersion or regular
distribution, while a mean equal to the variance would point to a random
distribution.
In this chapter, a computer program TOPFIT was used to analyse the
field data of the population of P. cochleariae over the three years. This
program calculates indices of dispersion and fits up to 10 frequency dis-
tributions to the observed values (Robles, 1969). Out of these, six
distributions were selected, as the more likely ones to yield appropriate fits, namely the binominal, Poisson, Thomas double Poisson, Neyman type A 139.
and the negative binomial distributions.
The stages of life history were treated separately, but no data
were available for the pupae. Different sampling occasions, throughout the
seasons, were considered, taken from six arbitrarily defined major periods:
a - the interval of time during which numbers were building up, until the
b - peak of the first generation. c - decrease after the peak day. d, e,
f - corresponding periods for the second generation. Table 28 summarises
the results obtained, for eggs, larvae and adults. Examples of the distri-
bution of the three stages are given in Figures —A, —B and C, using the data from 1975.
8.2 Type of Distribution
a) Eggs
For the egg stage the Neyman A distribution generally provided the
best fit to the data. This implies that the variance between samples was greater than the mean number of individuals, and that the distribution could be either a bimodal or a unimodal one. From the biological point of view, the implications are that the eggs were laid in randomly distributed clumps, whereas the individuals, in the clumps, followed an independent distribution, which could be either Poisson, geometric or logarithmic
(Elliot, 1971).
Under some circumstances, e.g. in the second generation, 1976, when the numbers in each sample were low, besides the Neyman A, the double
Poisson distribution also fitted the data. Since both distributions are similar, there is little change in the biological implications, the only one being that the individuals, inside the clumps, are also randomly distributed. 140. EGGS Sampling period
a before 1st generation peak
b 30 1st generation peak day
11■■ 70• C after 1st generation 60. peak
50•°"°'
ency u eq fr
e 50D d iv t before 2nd generation
la peak Re
20' e 2nd generation peak 100 day r-,
f after 2nd generation peak
• 1 6 11 16 21 21 11 36 41 46 51 56 61 66 71 76 11 16 91 5 10 15 24 25 36 35 41 45 511 55 SO 115 79 75 SO 55 90 >
32 A Frequency classes
Figure 32 A, B and C Examples of the distribution of eggs (A), young larvae (B) and adults (C), of P. cochleariae, on 100 turnips, sampled throughout the season of 1975. . 141.
70 YOUNG LARVAE ADULTS a soti
b
20 ency u freq e iv t la Re
e
1
RCS
1 11 11 15 21 215 31 36 41 45 51 1 2 3 4 5 I 7 11 I 10 0 5 19 15 211 25 30 35 40 4S 511 > Figure 32 § Frequency classes 32 C 142.
SAMPLING a CCASION 1ST GEN. .: /21 2ND GEN. STAGE YEAR PEAK PEAK
1974 4 ' * 4 4 - 1975 4 4 * 4 • EGGS 3,4 * 1976A 4 4 4 4 3,4 3,4 1976B 4 4 * 4 4 3,4
1974 3,4 4 4 - YOUNG 1975 3,4 4,5 5 4 4 4 LARVAE 1976A 3,4 3,4 3,4 3,4 3,4 3,4 1976B 4 4 3,4,5 * 4 3,4
1974 3,4 4 4 - - - OLD 1975 3,4 4 4 4 5 4 LARVAE 1976A 3,4,5 2,4,5 * 3,4 3,4,5 2 1976B 3,4 3,4,5 * 4 3,4 3,4,5
1974 3,4,5 1975 3,4 3,4 3,4 3,4 3,4 3,4 ADULTS 1976A 3,4,5 3,4 3,4 3,4 1976B 3,4,5 4,5 3,4,5 3,4,5
TYPE OF DISTRIBUTION
Binomial 2 Poisson 3 Double Poisson 4 Neyman A 5 Negative Binomial No data available Numbers too small, or too large, for 3 and 4 to be fitted
TABLE 28 Distribution of the Eggs, Larvae and Adults of P. cochleariae
in the field, before, during and after the occurrence of the
peak numbers of the first and second generations. 143.
b) Young Larvae
For the young larvae, the most fitting distribution (19 times, out
of 21) was again the Neyman A, followed by the double Poisson, which fitted
on 10 occasions.
The Neyman A distribution was first described for the dispersion of
larvae, hatching from random clumps of eggs (Neyman, 1939). The present
case is thus a suitable one, showing that the activity of the first larval
instars is very low and the insects tend to remain in the site of emergence,
in the absence of competition. The double Poisson distribution is less
skewed than the Neyman A (Anscombe, 1950), and in samples with a smaller
variance, as in days after the peak, it also gives a good fit.
c) Old Larvae
Basically, the old larvae show the same pattern, but on five out of
20 occasions the negative binomial distribution, together with the previous
two, fitted the data, while at the peak of the second generation, 1975, it
provided the only good fit.
The negative binomial distribution has been widely used to describe different patterns of aggregation in insect populations (e.g. Richards and
Waloff, 1961; Harcourt, 1965). Although several models can be fitted to
this unimodal distribution, sometimes arising from divergent hypotheses
(Bliss and Fisher, 1953), they imply the existence of contagiousness if the value of K is found to be small (Southwood, 1966). This was true of the present observations where K varied around 0.5, indicating a strong aggregation of the larvae.
The closeness to the Poisson distribution of the last sampling occasion of 1976, on plot A, is unexpected. But the meaning of this is not the presence of a truly random distribution. Instead, it reflects the very low 144. numbers in the sample and the consequent reduction of the degrees of free- dom.
d) Adults
Once again it is either the Neyman A or the double Poisson distri- bution that fits the data. Hence, the interpretation must be similar to the one given for the larval stages.
It appears that the adults tend to remain in small clusters through- out their lives. Since the present populations were small, this type of behaviour could be advantageous to mating. In 1974 and 1976 the numbers were so low that no analyses were possible on several sampling occasions.
8.3 Summary and Conclusions
Considering all the stages, the Neyman A distribution was the one
to fit the data on most occasions.
The eggs are laid individually, but form clumps, as the females
make extensive use of the available oviposition sites on each plant, before
moving to a contiguous one.
The activity of the first and second instar larvae is very low, and
although the last instar is potentially more mobile, in the absence of
competition the insects will not disperse.
Adult behaviour also shows a gregarious pattern, which seems to be
a characteristic of this species.
145.
9. Studies on Dispersal
9.1 Use of Marked Adults
An attempt was made to measure and describe the type of dispersal
of P. cochleariae, by using laboratory reared marked adults, in two experi-
ments carried out in 1974 and 1976.
A standard procedure was followed to mark the insects. They were
immobilised by putting them at 0°C, for two to three minutes. A small
drop of celluloid paint was then applied to one of the elytra, care being
taken not to touch any suture. The insect was kept in a small container
until the mark was dry, and transferred afterwards to a rearing bucket
with the other marked beetles. The batch remained under observation, at
room temperature, for three days prior to release. Any deficient insects
were discarded. The adults used in both experiments were about one week
old.
In 1974, 102 beetles, split into groups of six, were released in the
central area of plot A, between rows 13 and 16, on plants 28 to 32 (Figure
33). Observations were carried out daily, for five days following the
release, and every three days afterwards.
In 1976, four groups of 200 insects each, marked with different
colours (yellow, blue, green and red) were released in separate areas of
plot A. The field was arbitrarily divided into eight sections, measuring
two metilzs each, designed to provide a spatial scale, as a substitute to
the plant numbers of previous years. (Figure 35).
Observations were carried out at three-days intervals. Dispersal
took place on a small scale, the most distant position of any insect from
the site of release being only one row, or one section. There was no
interchange of individuals, between the four cohorts, and thus the rate of
population interchange could not be measured. 146.
ROWS 11 12 13 14 IS 18 17 11 • • • • • . . • .
. • • • . so . • • • • • • • • • • . . • • . • • • •
MINIMUM AREA = 5.73 m2 RANGE LENGTH = 3.9t m
Figure 33 Central area from plot A, showing the release of marked
adults (R) a- their outermost positions observed.
D=
N
10 13 14 19 22 25 21 31 DAYS after release
Figure 34 Relation between rate of dispersal and time after release.
d distance of the observation point of each insect, from the release point N total number of insects observed on each occasion 147.
ROWS 1 3 5 7 9 11 13 15 17 19 21 25 27 ----H)"
VIII I 1 1 1 3 4 3 3 Y Y g g VII e e r r 2 2 1 1 2 e e 1 1 o o . n n w w 5 6 VI 5 3
V
IV
III 3 4 1 3 3 b b 1 r r II 1 3 u1 u e e 2 e e d d 3 4 6 3 I
• 1 1 1 1 • e •
FIGURE 35 PLOT A (1976), showing the release of the marked adults
and their dispersal 148. a) Home range
The extreme positions of all marked adults observed in 1974 is shown in Figure 33. Joining up these points, the home range for this species, that is the area over which the insects forage, search for mates and rest (Southwood, 1966) was calculated. The minimum area method was used (Odom and Kuenzler, 1955) and the value obtained was 5.73m2.
Although this is not an accurate method, it can give an approximate estimation of the area over which the insects engage in trivial movements.
The range length, that is the distance between the most widely separated observations (Linsdale, 1946) was 3.91m. This measure is con- sidered as being useful for species which have a short range of movement
(Southwood, loc. cit.).
b) Rate of dispersal
The relation between the rate of dispersal and time after release was calculated, using an index devised by Clark (1962):
E (d2 )
where d is the distance of•the observation (or recapture) point of an individual, from the release point and N = total number of animals observed (or recaptured) on each sampling occasion. In Figure 34 , D was plotted against time after release. It can be seen that the rate of dis- persal rase during the first week, the insects showing maximum activity around day 8, after which it fell off to a fairly constant level.
9.2 Survey of Adjacent Areas
During the field season of 1975 the land adjacent to plot A was sown with peas, which are not a host crop of P:'650i1datiae. 149.
Aiming at detecting emigration, potted turnip plants were placed
among the peas, at logarithmic distances from the border of plot A (Figure
36. It was thought that any beetles leaving the turnip field would land
on the cruciferous plants available nearby. However, although the adja-
cent area was monitored throughout the season, no beetles were found on
these plants.
9.3 Invasion of a crop
In 1976, plot B was invaded by adults that overwintered in plot A.
This provided data for the study of dispersal, in relation to the distance from the point of emergence.
Three arbitrary unit areas were considered in plot B, consisting of
rows 1 to 3 (I), 4 to 6 (II) and 7 to 9 (III), as shown in Figure 37 .
On each sampling occasion, the adults and eggs were pooled in each unit
area. Logarithms of these numbers were plotted against the distance, bet-
ween the middle row of each unit and the border of plot A (Figure 38).
These curves indicate a sharp fall-off in density, of both adults and eggs, with the distance.
Figures 39 A and B, show the relation between the percentage of the total numbers of adults and eggs, sampled in the three unit areas and time.
The first adults that invaded plot B did not disperse uniformly over the whole crop; this tendency to remain on the third unit, which was the closest to plot A, was accentuated when more insects arrived, possibly pointing-to the gregarious tendency of this species. Two weeks after the invasion began, the percentage of adults found on unit III was 74%, com- pared with 18 and 12% respectively, on units II and I.
9.4 Experiment on Mixed Cropping
In 1976, dispersal was studied under a regime of mixed crops in 150.
Dm
Figure 36 Disposition of turnip plants in the area adjacent
to plot A, to survey migrant insects. 151.
PLOT B PLOT A rows 1 3 S 7
•■••• •■•=11 ■ID 411■1. ■•• ■11.. 0 V Figure 37 Invasion e r of plot B by over- w a
.1■•• •••••• mm1. •••■• ======*:= OWN. n u wintering adults t I e t from plot A. r s ==: n
L J L- I J L. 111 J units
3 . ADULTS
0 2 G
N EGGS U M B
E 1 R S
5 4 3 2 m Distance from each unit of plot B to plot A,
Figure 38 Fall off in the numbers of eggs and adults of P. cochleariae in plot B, with distance from plot A. Figure 39AandBRelationshipbetween number ofadults(A)andeggs 39 A 39 B (B) ineachsamplingunit,andtime. Numbers in each unit, as % of total 60 - s 2 0- 40 - 4 0... 20 8 0- 6 0- o —
MIN _ Days afteremergence 7
— 10 41k, I
■ EGGS 13 ADULTS IIIIIIIII1
— 16
sr' 19
„AD 22 I III 152.
153.
PLOT C 1976 PLANTS * 1 3 5 7 9 11 13 15 17 19 111,.■■• OOOOOOOOOOO . . . • • . .
$
4, 4, = 4•111111■•ccl O = El
..- • -S • .. • • .
4—
Figure 40 Experiment on mixed crops, showing the dispersal of
adults of P. cochleariae, from the central row. 154. plot C. the design of this experiment is shown in Figure 40 . Nine rows
of plants were established on this patch. The odd rows had 20 turnips each,
and the even ones had 10 turnips plus a barrier of a non host crop, namely
dwarf African marigolds.
On the 7th July, the turnips had reached an average height of 15cm
(±4.7cm), and the marigolds averaged30cm (13.2cm).4 300 adult beetles were
released onto the central row (R5), in groups of 15/plant. The beetles,
aged between one and two weeks, were previously marked with a drop of
cellulose paint. In this way, immigration of adults from either plot A
and B would have been detected.
Observations were carried out on one and two days after the release,
and every 3 days afterwards. During the first two weeks no dispersal
occurred. On the third week after release, one beetle was seen on plant
17 of row 6 and two others on plants 3 and 5 of row. 4. Two weeks later,
a few insects dispersed towards rows 3 and 7, but in both instances they
were seen sitting on the plants adjacent to the turnips of rows 4 and 6,
not on the side of the marigolds.
Ten of the adults found outside the central row were dissected.
They were all mature adults, six being females and four males. The size
of the sample was small but these results indicate that the sexes disperse
at an equal rate, in contrast to what is often seen in many other insect
species (Johnson, 1966). The maximum number of adults (13) counted away
from row 5, occurred during the seventh week after release.
9.5 Summary - and'Conclusions
In this Chapter attempts were made to understand the types of
movements of this species. Both trivial and migratory movements were
investigated. Williams (1958) defines migration as "...movements deter-
mined by the insect itself...so as to result in a change of habitat." 155.
Southwood (1962) refers to trivial movements as those restricted to the animal's habitat, but the distinction between the two types is a matter of relative thresholds, as pointed out by Kennedy (1961).
Using marked adults, the home range was calculated for the mustard beetle and found to be a narrow one, in comparison with other non-flying insects (Greenslade, 1964). These experiments led to the conclusion that this species has low locomotory activity, when food is available "ad libidum". A directional movement, from plot A to B was only detected in conditions of food shortage.
The introduction of a non-host crop acted as a barrier, thus confir- ming previous findings (Section II) that dispersal takes place by walking and demonstrating the inability of the adults, in the population studied, to fly. 156.
GENERAL DISCUSSION AND SUMMARY
The present work originated from an attempt to understand the population ecology of Phaedon cochleariae Fabricius, which used to be a pest on several Cruciferae of economic importance, but has been steadily declining over the last decades, almost to the point of extinction.
The geographical distribution of the mustard beetle is linked with the Palaearctic region, although it has been introduced to some southernmost regions (Lindroth, 1957).
The decrease in the number and intensity of attacks by P. cochleariae, in Britain, results from changes in the agricultural practices, such as the adoption of cement beds for growing watercress and a widespread use of insecticides.
The three sections of this thesis deal with the biology, the behaviour of the adults and population studies of P. cochleariae.
Detailed discussions and summaries are given within each section.
The more important results are now briefly discussed and the main con- clusions pointed out.
SECTION I - Biology of P. cochleariae
1. The typical life history of this beetle, in Britain, is illustrated and described. Two overlapping generations normally develop between May and October, but the occurrence of a third one has been reported (Hamnett,
1944), while during the first season of the present study only one generation occurred. 157.
2. The lack of external sexual dimorphism is a hindrance to experiments requiring isolation of adults of a specific sex. External measurements and weights were taken and it was concluded that the females are, on average, heavier and larger than the males.
3. The rearing of the beetles presented no problems and could be carried out at high densities per plant.
4. A decrease in temperature of 5°C reduced the fecundity of this species (117. at 15°C, 182. at 20°C and 328. at 25°C). The rate of ovi- position was also reduced whereas the duration of the pre-oviposition, oviposition and post-oviposition periods was significantly prolonged.
The weight cycles of the adults at 20° and 25°C did not differ significan- tly. The results obtained are in general accordance with a previous work by Way et. al. (1954).
In this species, temperature is probably the key factor in the regulation of fecundity and in these experiments, the highest number of eggs was laid at 25°C.
5. From an experiment where four species of cruciferae were tested, turnip plants emerged as the host plant prefeAd by the adults. Fecun- dity was higher on turnips than on any other species tested, while on
Brussels sprouts both fecundity and longevity were the lowest recorded, probably due to some of the physical properties of the leaves, such as toughness, which impaired feeding and egg laying.
6. Fecundity was related to the amount of food consumed and to nitrogen intake on different host plants, by isolated couples of P. cochleariae. This association is recorded in literature for several 158. insect species (e.g. Smith and Northcott, 1951).
On the same host plant, i.e. turnip, the amount of food consumed was largely influenced by temperature.
7. The developmental rates of immature stages and mortalities, were studied at temperatures between 11° and 30°C. The values predicted by the logistic equation were close to the observed ones. The theoretical values for the developmental zero, calculated by linear regressions, were much lower than the ones obtained experimentally.
Adults emerged from pupae kept at 7.5°C, while the minimum tem- peratures required by the eggs and larvae to complete development were above 10°C.
The larvae had either three or four instars and this variation appears to be related to temperature, the number of moults increasing at lower temperatures. The lowest mortality was recorded at 25°C, for'all stages, which is a temperature close to the optimum for this species.
At 30°C, desiccation becomes an important source of mortality for the eggs and larvae, whereas for the survival of the pupae a moist pupation medium is crucial.
8. The' survival of the adults was not affected by prolonged exposures to low temperatures above zero, or by short exposures to the freezing point. After such exposures the females resumed oviposition after spen- ding one to two weeks at 20°C. Since ground temperature, where the adults overwinter, rarely falls below 0°C, theoretically their survival in the field should not be seriously affected by this factor. 159.
9. Changes with age, in the reproductive organs of males and females were detected and illustrated. These allowed for the separation of the adults, into two or three age classes and separation of overlapping generations. In the females, the growth of the ovaries was measured; in the males a swelling of the middle section of the ejaculatory duct was seen to occur with maturity.
SECTION II - Studies on adult behaviour
1. Conflicting references are found in literature, regarding the ability of P. cochleariae to fly. Inspite of possessing developed wing muscles, the beetles cannot be induced to fly.
2. Several attempts made to induce flight resulted unsuccessful.
Adults were seen to die from starvation, when food which was available nearby could have been reached by a short flight.
3. In the laboratory dispersal took place only under conditions of acute food shortage, by means of walking. A high density of insects per plant or poor quality of the immediately available food did not stimulate dispersal.
4. A certain association was detected between the water content of the soil and the readiness of the adults to bury in it. The beetles showed a tendency to hide more often in dry, as opposed to wet, soil.
5. Field experiments on dispersal confirmed most of these laboratory findings. 160.
SECTION III - Population Studies
A - Laboratory Experiments
1. The study of a population of P. cochleariae under controlled conditions was carried out in the laboratory, for one generation, starting with 1,500. eggs.
2. Estimates of recruits to a stage and survival rates were calculated by Richards and Waloff's first and second methods, and by the Manly method. The first method yielded the more realistic estimates and a popu- lation budget was constructed, based on these values.
3. The total mortality, from egg to adult, observed in the absence of unfavourable weather conditions and natural enemies, was 59%. The critical phases were at egg hatching and pupation, respectively with
27. and 20.% mortality.
B - Field Experiments
1. During 1974 and 1975 population studies were carried out in one
area of 300 m2 (plot A). In 1976 two additional sites from the same field, were used. (Plots B and C). Plot A was surrounded by hedges and this
might have had a beneficial effect upon the survival of the 1976 population.
A crop of turnips was planted from seed, each Spring.
2. In 1974 and 1975 the populations originated from artificial infes-
tations, with laboratory reared insects. In 1976 the previous year's
overwintering adults were established in plots A and B, and the fate of
the two populations was followed throughout. 161.
3. The seasonal fluctuations of the populations were detected by
sampling, at three days intervals. The estimation of the numbers of
pupae and adults presented practical problems and may be inaccurate on
several sampling occasions.
4. The population was aged by dissecting and examining the reproduc-
tive organs of samples of adults. The sex ratio was found to be approx-
imately 1:1.
5. No parasitism was detected at any stage of the project.
6. Since few birds were seen visiting the study areas it was concluded
that the main predators of P. cochleariae are among the Arthropods. The
catches in pitfall traps showed that carabid and staphylinid beetles were
particularly abundant in 1974, while their numbers decreased in 1976.
Feeding trials in the laboratory revealed that most of the species of the
two families of beetled, were efficient enemies of the mustard beetle.
In the field, predation by arachnids, upon adults and larvae, was observed.
The pupal stage was vulnerable, with 22% of mortality due to predation.
7. The duration of immature stages was on the average 2 to 3 days shorter under field conditions than at the corresponding laboratory con- stant temperatures. Natality was estimated on the basis of laboratory experiments on fecundity and of a 1:1 sex ratio. Independent estimates of the rates of survival and of recruits to stages were assessed by
Richards and Waloff's second method and by the Manly method and population budgets were constructed. The population trends over the three years showed marked differenced. In 1974 only one generation occurred, which died out in its pupal stage; two overlapping generations were seen in
1975, the numbers in the second being the largest recorded in this study; 162.
in 1976 the second generation was a small one, and no adults were seen.
The egg to adult mortality for the field populations fell between 91.%
and 96.%, the highest in 1974 and the lowest in 1976. But since inac-
curacies are likely to occur in the estimation of the pupal and adult
stages, these values are probably, underestimates. On the average,
mortality of the eggs exposed in the field was 40% higher than in the
laboratory. The difference was attributed mainly to desiccation of the
embryos and predation by coccinelids.
In 1974, larval mortality was caused by heavy rainfall. The pupal
disappearance is certainly linked with the large numbers of predators.
In 1976, both pupal mortality and the numbers of arthropods trapped were
the lowest recorded. The climatic conditions in May and June have been
shown to influence the outbreaks of this pest (Ozols, 1932), the most
favourable ones being temperatures between 14.5 and 16.5°C and precipi-
tation between 2 and 7 cm. These ideal conditions have not been observed
during the present study. However, it might be concluded that meteoro-
logical factors played an important role in the direct and indirect,
control of the population of P. cochleariae.
8. The pattern of distribution of the eggs, larvae and adults was
investigated, by fitting the data to several theoretical distributions.
It was concluded that the Neyman A distribution was adequate for the eggs and larvae, on most sampling occasions. This indicates that the eggs are laid iu clumps, randomly distributed, and that the larvae have low mobility.
The adults also showed some tendency towards aggregation. These findings are in accordance with the conclusions from the studies on behaviour.
9. Field studies on dispersal of P. cochleariae were carried out, using marked adults. The home range of this species was found to be narrow. 163.
Migrant insects were not detected, although a survey of the adjacent areas was conducted, but the invasion of a contiguous crop (plot B) by overwintering adults was observed, under conditions of critical food shortage. When a barrier of a non—host crop was introduced, the adults did not disperse beyond it. This species has a low rate of mobility and early statements found in literature (Miles, 1924; Roebuck, 1917) referring to the invasion of crops achieved by walking were apparently confirmed. 164.
ACKNOWLEDGEMENTS
I am grateful to Professor T.R.E. Southwood for the facilities
provided at Silwood Park.
I wish to express my gratitude to Dr. N. Waloff, my supervisor,
for her encouragement, interest and guidance throughout the construction
of this thesis.
I am indebted to Professor M.J. Way for useful suggestions and
criticism.
I am grateful to Dr. V. Brown and to Ms. L. Ridout for reading
and criticising parts of this manuscript.
My thanks are due to Dr. P. Needham, of the Insecticide Department,
Rothamsted Experimental Station, and to Dr. H.F. van Emden, of the
Horticultural Department, Reading University, for supplying the insect
cultures.
I acknowledge the advice received from Drs. G. Murdie and M. Birley
on the use of the computer programmes.
I would like to thank Ms. M. Gratwick, of the Plant Pathology
Laboratory, Harpenden, for making available unpublished information;
Mr. I. White for the identification of the Carabidae and Staphylinidae
and Mr. A. Broodbank for help with the nitrogen determination.
I am extremely grateful to the Estacgo AgronOmica Nacional, Portugal, for granting me paid leave to carry out this research. In particular, I wish to thank Dr. G. Magalhges Silva, of the Entomology Department, for his constant interest and encouragement throughout this work. I am also indebted to Dr. J.C. Contreiras, of the Plant Physiology Department, for his encouragement. 165;
I gratefully acknowledge Calouste Gulbenkian Foundation for the award of a scholarship and especially Dr. D. de Castro and Ms. M.A. Silva for their interest in this project.
I thank Mrs. J.A. Kent for typing this manuscript.
Finally, I wish to thank all my friends without whose unfailing support I would not have been able to carry out this work. 166.
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ANSCOMBE, F.J. (1950). Sampling theory of the negative binomial and
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ASAHINA, E. (1969). Frost resistance in insects. Advances in Insect
Physiology, 6: 1-49.
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Determination of the total nitrogen content of the leaves of the host plants used in 1.6., by the micro-Kjeldahl method.
HOST PLANT P.P.M. OF NITROGEN NITROGEN CONTENT (pgN/mg material)
1ST. 2ND. 1ST. 2ND. MEAN MUSTARD 15.000 16.250 24.167 26.250 25.209 (±1.473)
CHINESE CABBAGE 14.000 15.000 22.500 24.167 23.334 (±1.179)
BR. SPROUTS 37.000 29.250 60.833 47.920 54.377 (4-5 WKS OLD) (±9.131)
BR. SPROUTS 17.000 15.500 27.500 25.000 26.250 (8-9 WKS OLD) (±1.769)
TURNIP 26.000 22.000 42.500 35.833 39.167 (±4.712)
CONTROL (BLANC) 0.500 0.833
Calculation of the total N content (ex. for mustard)
15.000 P.P.M. (mustard) - 0.500 P.P.M. (blanc) = 14.500 P.P.M.
There are 14.500 g of N in 106 g of water
There are X g of N in 102 ml of water 1
X = 1.450 mg of N/100 ml water 1
1.450 mg N are contained in 60.0 mg of plant material
X mg N are contained in 103 mg of plant material 1
X = 24.167 mg N/mg plant material 2
177.
APPENDIX 1-9 a)
MALES AGE (days) 1 2 3 4 5 10
WEIGHT (mg) 5.8 6.2 7.3 6.4 6.0 7.0
TOTAL LENG 3.50 3.57 3.81 3.66 3.86 3.71 ABD LENGTH mm 2.80 2.68 2.92 2.97 2.54 3.10 MAX. WIDTH 2.03 2.17 2.29 2.12 2.73 2.20
FAT BODY 3 2 1 2 1 1
NO. LOBES/ L 9 10 10 9 TESTIS R 8 9 8 8
L .800 .960 .995 .876 .779 .780 VAS DEFERENS .860 .970 1.006 .905 .840 .761 .540 .530 .721 .503 .532 .642 E R .500 .550 .684 .487 .49L .620 rii 1.400 1.352 1.430 1.410 1.193 1.410 T VAS DEFERENS 1.387 1.348 1.421 1.392 1.210 1.395 [EJACULATORY 1.310 1.193 1.293 1.344 1.281 1.190 DUCT 1.200 .700 .940 1.270 .924 1.105 3 .825 .661 .750 .794 .750 .744
DIAMETER PROXM. END .214 .180 .182 .320 .230 .420 (2 EJ. DUCT DISTAL .173 .150 .142 .200 .140 .241
Colour AEDEAGUS 1 1 2 2 2
Measurements of the reproductive organs of males of
P. cochleariae 178.
APPENDIX 1-9 b)
AGE (days) 1 2 3 4 5 10
WEIGHT (mg) 8.0 6.7 10.0 8.9 7.5 8.6
TOTAL LENGTH 3.82 3.79 4.26 4.63 4.28 4.11 ABD. LENGTH 2.95 2.88 3.35 2.99 3.00 3.27 MAX. WIDTH 2.41 2.34 2.59 2.41 2.41 2.51
FAT BODY 2 2 2 1 2 1
NO. OVARIOLES/ L 12? 11 11 11 11 10 OVARY CR 11 10 11 11 11 11 N0. EGG RUDIMENTS/,--L 0 1- 2 1 2 3 2- 3 2- 3 2 3 4 OVARIOLE ---R 0 1- 2 2-3 2- 3 2- 3 3-4
L TERMINAL L .640 .523 .600 .615 .521 .457 E FILAMENTS R .673 .497 .514 .603 .476 .486 N .862 .935 1.342 1.416 1.484 1.429 OVARIOLES -"=:::::::: G., LR .854 .918 1.428 1.388 1.663 1.514 T 1.000 OVIDUCTS L 1.142 .834 1.000 .740 .635 H R .975 .882 .914 .786 .583 1.143 M VAGINA .894 .975 .857 .880 .700 .602 M SPERMATHECAL GLAND .696 .784 .857 .795 .848 .725
W I D OVIDUCTS L .145 .138 .229 .231 .267 .514 R .163 .146 .257 .197 .294 .343 H VAGINA .287 .266 .314 .326 .786 .438 MM
NO. RIPE EGGS 0 0 0 0 7 6
CORPORA LUTEA 0 0 0 0 0 1
COLOUR SPERMATBECA 1 1 1 2 2
Measurements of the reproductive organs of females of
P. cochleariae
APPENDIX 111-6 a) 179.
1974 JULY AUGUST SEPTEMBER TOTAL FAMILY CARABIDAE Tribe CARABINI Carabus violoceus Linnaeus 2 2 1 3 1 1 1 1 12
Tribe NEBRIINI Leistus spinibarbis Fabricius 3 1 4 24 40 72 Leistus fulvibarbis Dej 1 1 3 5 Nebria brevicollis Fabricius 2 3 1 6
Tribe NOTIOPHILINI Notiophilus rufipes Curtis 1 1 1 3
Tribe LORICERINI Loricera pilicornis Fabricius 5 1 3 4 5 4 2 1 2 27 Clivina collaris Herbst 2 1 1 2 1 3 3 13
Tribe TRECHINI Trechus quadristriatus Schank 1 1 1 2 1 6 Trechus obtusus Erichson 1 1 1 4
Tribe BEMBIDIINI Asaphidion flavipes Linnaeus 14 8 5 5 6 5 4 5 1 53 Bembidion lampros Herbst 6 2 7 5 3 4 3 1 2 2 35 Bembidion femoratum Sturm 4 3 1 2 1 11 Bembidion quadrimaculatumLinnaeus 3 2 5 9 10 8 4 5 5 2 53
Tribe PTEROSTICHINI Pterostichus madidus Fabricius 3 2 5 9 10 8 4 5 5 2 53 Pterostichus melanarius Illiger 3 3 5 6 2 1 2 34 Abax parallelepipedus Piller & Mitterpacher 1 2 1 2 6 Calathus piceus Marsham 6 4 3 2 2 3 3 1 24 Calathus fuscipes Goeze 4 2 1 2 3 12 Calathus melanocephalus Linnaeus 3 1 1 2 1 2 3 1 2 15 Agonum dorsale Pontoppidan 2 1 1 1 3 8 Agonum mulleri Herbst 1 1 2
Tribe AMARINI Amara aulica Panzer 1 1 1 3 Amara Montivaga Sturm 1 1 2 1 5 Amara apnicariaPaykull 2 2 3 5 9 5 1 1 28 Amara equestris Dufschmid 1 1 1 1 3 7 Amara communis Panzer 3 1 2 1 6 Amara sp. 1 1 1 3
Tribe hARPALINI Harpalus rufipes DeGeer 37 40 55 74 87 50 20 5 4 2 375 Harpalus aeneus Fabricius 7 3 5 21 3 1 21 Harpalus sp. 1 1 2
Tribe LEBIINI Metabletus foveatus Fourcroy 1 1 2
APPENDICES 111,-6 a, b and c Records of weekly catches of
Carabid beetles, in 20 pitfall traps. 180. APPENDIX III-6 b)
1975
MAY JUNE JULY AUGUST SEPTEMBER TOTAL
C. violaceus 1 1 2 3 2 1 3 2 2 1 1 19 L. spinibarbis 27 29 18 5 3 4 1 1 1 10 13 20 14 97 L. fulvibarbis 4 2 3 2 1 2 2 16 N. brevicollis 2 1 1 4 8 N. rufipes 2 3 7 2 2 1 1 2 1 1 3 25 L. pilicornis 1 6 17 2 5 1 3 4 2 4 1 1 47 C. collaris 2 2 1 3 8 2 1 1 1 1 22 T. quadristria- 1 1 1 4 2 1 10 tus T. obtusus 4 1 1 2 2 1 8 A. flavipes 5 1 1 2 1 1 11 B. lampros 24 53 75 11 47 18 7 15 12 17 5 22 4 7 5 322 B. femoratum 9 18 23 7 17 5 6 4 5 6 3 18 7 6 3 7 6 150 E. quadrimacu- 3 7 20 4 11 1 2 1 1 1 1 52 latum P. madidus 2 2 3 1 5 7 9 1 3 1 3 9 6 5 7 11 6 2 83 P. melanarius 1 1 1 2 1 1 1 3 5 2 2 1 2 1 24 A. parallel - 1 3 1 1 2 1 9 pipedus C.pi.221.is 1 1 1 3 C. fussipes 1 2 1 -3 1 2 6 7 16 14 12 6 3 37 C. malenocepha- 1 1 1 1 1 1 1 3 1 1 1 13 lus A. dorsale 2 2 1 2 3 3 1 14 A. mulleri 1 1 1 1 4 A. aulica 1 1 1 1 4 A. montivaga 1 3 5 3 1 1 1 3 1 1 2 22 A. apricaria 3 3 4 2 1 2 2 2 1 4 1 7 10 10 7 3 1 2 65 A. equestris 1 1 1 1 3 3 2 1 13 A. communis 1 2 2 3 2 1 1 12 A. sp... 2 5 3 4 5 4 3 3 1 2 3 5 4 2 2 1 49 H. rufipes 2 5 4 1 6 3 7 8 2 14 10 38 37 49 31 23 17 3 261 H. aeneus 2 3 5 2 1 3 2 6 14 5 4 1 2 1 51 A. RE. 1 1 2 4 M. foveatus 1 5 2 1 2 6 6 5 2 2 1 1 34 181. APPENDIX 111-6 c)
1976
MAY JUNE JULY AUGUST SEPTEMBER TOTAL
C. violaceus 1 2 1 2 2 1 9 L. spinibarbis 7 11 4 2 2 8 4 5 3 6 4 56 L. fulvibarbis 1 1 2 1 1 6 N. brevicollis 2 2 1 1 1 1 8 N. rufipes 4 5' 4 1 2 2 18 L. pilicornis 9 10 14 12 6 5 2 2 3 63 C. collaris 1 2 1 4 T. quadristria- 1 2 3 1 7 tus T. obtusus 1 2 2 5 A. flavipes 2 2 1 1 6 B. lampros 39 41 28 14 17 15 2 7 12 175 B. femoratum 7 10 9 6 4 2 4 2 3 5 4 56 B. quadrimacu- 8 5 3 4 1 1 22 latum P. madidus 1 2 6 4 2 2 3 10 12 5 14 9 6 76 P. melanarius 1 1 1 3 5 4 2 2 19 A. parallelo- pipedus 1 2 1 1 1 1 7 C. 2iStRE 3 4 3 1 1 4 2 2 20 C. fiscipes 1 1 2 2 3 1 1 2 3 5 4 25 C. malanocepha- 1 1 1 3 lu s A. dorsale 1 1 1 2 1 2 1 1 10 A. mulleri 1 1 1 3 A. aulica 1 1 2 5 A. montivaa 2 3 2 5 6 4 1 24 A. apricaria 5 6 9 3 4 1 2 2 5 13 17 10 8 4 8 97 A. equestris 1 1 1 1 - 4 A. communis 4 3 3 3 4 2 2 21 A. sp.. 2 2 2 1 1 2 1 11 H. rufipes 2 2 2 3 8 22 71 31 11 7 5 4 168 H. aeneus 2 1 1 4 2 2 2 4 4 3 3 28 H. sp.. 1 3 2 2 8 M. foveatus 1 2 4 3 2 12 182. APPENDIX 111-6 d)
1974
JULY AUGUST SEPTEMBER TOTAL
FAMILY STAPHYLINIDAE
SUBFAMILY OMALIINAE
Anthobium Samouelle 2 2 4 Omalium Gravenhorst 1 2 3
SUBFAMILY STENIAE
Stenus Latreille 1 1 1 3
SUBFAMILY STAPHYLININAE
Philontus Stephens 1 3 2 6 Gabrius Stephens 1 1 2 1 1 6 • Occipus Samouelle 1 1 8 3 13
SUBFAMILY TACHIPORINAE
Tachyporus Gravenhorst 2 2
SUBFAMILY ALEOCHARINAE
Atheta Thompson 3 2 2 7 Aleochara Gravenhorst 3 13 20 16 18 70
APPENDICES 111-6 d and e Records of fortnightly catches of
Staphylinid beetles, in 20 pitfall traps. 183.
APPENDIX III-6 e)
1975 AND 1976
MAY JUNE JULY AUGUST SEPTEMBER TOTAL 75 76 75 76 75 76 75 76 75 76 75 76
SUBFAMILY OMALIINAE
Anthobium 1 1 3 2 1 6 2 Omalium 1 1 1 1 1 3 2 3 7
SUBFAMILY STENINAE
Stenus 1 1 2 3 1 2 2 8 4
SUBFAMILY STAPHYLININAE
Philontus 1 1 4 2 8 2 3 5 16 10 Gabrius 1 1 1 I 2 2 4 Occipus 1 2 3 2 3 2 6 6 2 3 18 12
SUBFAMILY TACHYPORINAE
Tachyporus 1 1 1 1 3 2
SUBFAMILY ALEOCHARINAE
Atheta 2 3 4 3 2 8 7 4 10 6 4 7 4 2 44 22 Aleochara 7 5 10 23 5 3 12 6 3 13 11 4 8 23 20 11 8 125 47
184. APPENDIX 111-7 a)
1974
YOUNG OLD DATE DAY EGGS PUPAE ADULTS TOTAL LARVAE LARVAE
2/6 1 497 462 959 5/6 4 5,577 551 6,128 8/6 7 6,038 391 6,429 11/6 10 6,127 302 6,429 14/6 13 7,850 497 8,347 17/6 16 7,974 355 8,329 20/6 19 8,454 2,486 320 11,260 23/6 22 9,164 6,252 284 15,700 26/6 25 5,808 7,896 301 249 14,254 29/6 28 5,364 2,890 479 373 9,106 2/7 31 4,937 2,131 1,332 106 391 8,897 5/7 34 12,752 1,812 2,557 231 497 17,849 8/7 37 7,530 2,717 3,552 408 266 14,473 11/7 40 6,145 2,859 2,273 1,652 249 13,178 14/7 43 6,500 4,032 2,451 1,065 284 14,332 17/7 46 6,180 3,783 2,504 551 107 13,125 20/7 49 3,588 2,161 1,794 391 53 7,987 23/7 52 4,529 2,220 1,758 799 88 9,394 26/7 55 1,971 1,847 1,723 515 88 6,144 29/7 58 1,883 1,332 1,421 551 71 5,258 1/8 61 1,758 1,012 1,030 586 53 4,439 4/8 64 1,012 444 675 497 36 2,664 7/8 67 888 213 533 320 0 1,954
13/8 73 710 107 195 178 18 1,208 16/8 76 515 124 • 53 0 692 19/8 79 178 18 18 0 214
APPENDICES 111-7 a, b, and c Seasonal fluctuations in the
abundance of the field populations of
P. cochleariae
APPENDIX 111-7 b) 185.
1975
YOUNG OLD DATE DAY EGGS PUPAE ADULTS LARVAE LARVAE TOTAL
25/5 1 1,753 614 2,367 28/5 4 2,671 585 3,256 31/5 7 4,193 544 4,737
3/6 10 5,947 595 6,542 6/6 13 6,925 635 7,560 9/6 16 11,592 444 12,036 12/6 19 12,822 403 13,225 15/6 22 14,848 363 15,211 18/6 25 14,001 1,058 383 15,442 21/6 28 8,739 6,764 252 403 16,158 24/6 31 6,663 7,288 614 231 423 15,219 27/6 34 5,443 5,786 1,623 575 302 13,729 30/6 37 4,062 4,173 3,095 1,522 333 •13,185
3/7 40 3,074 3,095 3,085 2,913 302 12,469 6/7 43 3,165 2,218 3,256 2,903 323 11,865 9/7 46 3,951 2,389 1,986 3,064 212 11,602 12/7 49 2,923 3,518 1,401 1,865 343 10,050 15/7 52 2,550 3,437 1,774 1,320 433 9,514 iiii7 55 1,865 2,631 2,308 1,663 665 9,132 21/7 58 837 1,864 2,107 2,167 877 7,852 2417 61 464 1,341 1,704 1,986 1,210 6,705 27/7 64 3,629 796 1,260 1,603 1,371 8,659 30/7 67 6,965 1,724 927 1,189 1,522 12,327
2/8 70 12,902 3,226 474 877 1,492 18,971 5/8 73 17,035 5,342 696 444 1,431 24,948 8/8 76 20,462 8,366 1,562 655 1,310 32,355 11/8 79 16,632 9,979 2,772 1,472 1,462 32,317 14/8 82 10,080 11,290 3,528 2,611 1,391 28,900 17/8 85 7,056 10,019 4,183 3,316 1,361 25,935 20/8 88 5,140 8,084 4,838 3,931 1,452 23,445 23/8 91 3,528 5,897 5,695 4,546 1,310 20,976 26/8 94 2,379 4,133 5,746 5,352 1,361 18,971 29/8 97 1,613 3,326 4,637 5,403 1,260 16,239
1/9 100 958 2,218 3,730 4,355 1,512 12,773 4/9 103 403 1,562 2,722 3,508 1,764 9,959 7/9 106 1,058 2,066 2,560 1,814 7,498 10/9 109 756 1,714 1,945 2,117 6,532 13/9 112 302 1,260 1,613 1,945 5,120 16/9 115 907 1,189 1,714 3,810 19/9 118 504 857 1,764 3,125 22/9 121 101 484 1,814 2,399 25/9 124 91 1,512 1,603 1976
EGGS YOUNG LARVAE OLD LARVAE PUPAE ADULTS TOTAL DATE DAY A B Total A B Total A B Total A B Total A B Total A B Total
15/5 1 43 43 43 43 18/5 4 76 76 76 76 21/5 7 340 340 193 90 283 193 430 623 24/5 10 655 655 276 68 344 276 723 999 27/5 13 1,274 1,274 304 115 419 304 1,389 1,693 30/5 16 883 1,339 2,222 359 108 467 1,242 1,447 2,689
2/6 19 2,870 2,333 5,203 359 130 489 3,229 2,463 5,692 5/6 22 4,306 2,347 6,653 442 104 546 4,748 2,451 7,199 8/6 25 5,189 4,018 9,207 497 191 688 5,686 4,209 9,895 11/6 28 10,543 2,567 13,110 608 608 635 151 786 11,178 3,326 14,504 14/6 31 11,564 2,106 13,670 626 626 22 22 497 137 634 12,061 2,891 14,952 17/6 34 7,093 2,084 9,177 607 929 1,536 205 205 359 158 517 8,059 3,376 11,435 20/6 37 6,679 1,789 8,468 1,104 954 2,058 349 349 18 18 318 119 437 8,101 3,229 11,330 23/6 40 6,265 1,624 7,889 1,601 1,015 2,616 856 536 1,392 187 187 276 108 384 8,998 3,470 12,468 26/6 43 2,594 853 3,447 2,705 353 3,058 1,270 558 1,828 320 320 166 151 317 6,735 2,235 8,970 29/6 46 1,187 392 1,579 2,042 133 2,175 1,628 346 1,974 828 346 1,974 221 137 358 5,685 1,501 7,186
2/7 49 980 302 1,282 1,669 1,669 1,821 191 2,012 1,214 515 1,729 248 90 338 5,932 1,098 7,030 5/7 52 773 274 1,047 1,297 1,297 2,015 54 2,069 1,393 317 1,710 276 97 373 5,754 742 6,496 8/7 55 496 220 689 966 966 1,518 1,518 1,573 176 1,749 221 126 347 4,747 522 5,269 11/7 58 524 234 758 331 331 883 883 1,960 50 2,010 248 112 360 3,946 396 4,342 14/7 61 580 432 1,012 759 759 1,711 1,711 220 148 368 3,270 580 3,850 17/7 64 635 756 1,391 635 635 1,463 1,463 193 133 326 2,926 889 3,815 20/7 67 444 612 1,056 331 331 856 856 193 115 308 1,824 727 2,551 23/7 70 580 864 1,444 552 552 359 122 481 1,491 986 2,477 26/7 73 773 1,332 2,105 428 428 386 115 501 1,587 1,447 3,034 29/7 76 966 2,088 3,054 304 304 414 162 576 1,684 2,250 3,934
Continued APPENDIX 111-7 c)
1976 (Continued) APPENDIX 111-7 c)
EGGS YOUNG LARVAE OLD LARVAE PUPAE ADULTS TOTAL DATE DAY A B Total A B Total A B Total A B Total A B Total A B Total
1/8 79 1,573 2,610 ,4,183 386 140 526 1,959 2,750 4,709 4/8 82, 2,374 2,268. 4,642 469 137 606 2,843 2,405 5,248 7/8 85 2,733 1,555 4,288 443 443 496 130 626 3,229 2,128 5,357 10/8 88 3,091 1,584 4,675 248 468 716 47 47 524 119 643 3,863 2,218 6,081 13/8 91 8,225 1,282 9,507 386 814 1,200 122 122 524 101 625 9,135 2,319 11,454 16/8 94 9,577 774 10,351 883 734 1,617 469 187 656 43 43 552 86 638 11,481 1,824 13,305 19/8 97 7,741 623 8,364 1,214 673 1,887 579 310 889 115 115 579 83 662 10,113 1,804 11,917 22/8 100 5,906 331 6,237 1,546 486 2,032 690 407 1,097 442 176 618 497 68 565 9,081 1,468 10,549 25/8 103 4,195 252 4,447 2,125 288 2,413 911 342 1,253 690 292 982 718 50 768 8,639 1,224 9,863 28/8 106 2,042 241 2,283 2,070 230 2,300 966 277 1,243 911 382 1,293 580 36 616 6,569 1,166 7,735 31/8 109 2,001 187 2,188 1,629 112 1,741 1,090 209 1,299 934 320 1,254 552 40 592 6,206 868 7,074
3/9 112 1,960 155 2,115 1,187 1,187 1,214 76 1,290 966 263 1,229 524 29 553 5,851 523 6,374 6/9 115 1,463 126 1,589 856 856 580 43 623 1,214 194 1,408 276 43 319 4,389 406 4,795 9/9 118 1,297 72 1,369 138 138 580 72 652 193 36 229 2,208 180 2,388 12/9 121 952 54 1,006 359 29 388 110 11 121 1,421 94 1,515 15/9 124 607 607 138 138 83 83 828 828 18/9 127 386 386 386 386