University of Nigeria Research Publications
NPUMECH, Mercy Ngozi Author PG/M.Sc/90/9610 The Biology of Araecerus Fasciculatus DEG. (Coleoptera:Anthribidae) on Selected Tuber Title Products
Biological Sciences Faculty
Zoology Department
March, 1993 Date
Signature Signature
Ihe biology of Araecerus ~asciculatusDeG. (Co1eoptera:Anthribidae)on selected tuber products.
NPUMECHI, MERCY NGOZI (P~/M.3~/90/9610)
DEPARTMENT OF ZOOLOGY FACULTY OF BIOLOGICAL SCIENCES UNIVERSITY OF NIGERIA, NSUKKA.
MARCH, 1993, The biology of Araecerus fasciculatus DeG, (Co1eoptera:Anthribidae) on selected tuber products.
Being postgraduate research project report submitted in partial fulfilment of the requirement for the award of a Masters degree in Applied Entomology in the Department of zoology, University of Nigeria, Nsukka.
NPUMECHI, MERCY NGOZI (PG/M.Sc. /90/9610)
Supervisor: Prof. M.C. Eluwa CERTIFICATION
' r Npumechi, Mercy N. a pstgraduate student in the Department of Zo313gy an8 with the registration number PG/M.Sc./90/9610 hss satisfactorily completed the requirements for course and research>work for the degree of Master of Science in C Applied Entamology. The work embodied in this project report is .original and has not been submitted in Part or in full.for any other diploma or degree of this or any other University.
Supervisor: Head of Department: Prof. M.C.Eluwa Prof. M.C. Eluwa Depsrtment of Zo~logy, Department of Zo3logy, University of Nigeria, University of Nigeria, Nsukka. Nsukka. iii
DEDICATION
This work is dedicated to the Almighty and all those
who successfully achizve their goals in life by
., trusting God. ACKNOWLEDGEMENTS
I am grateful to my supervisor, Prof. M.C. Eluwa, for his unfailing attention and assistance during the research as well as for his constructive criticisms and patience in reading through the completed work.
My profound gratitude goes to Rev. (~rof.1E.U. Iheagwam, who if not for his encouragement and scholarly advice, the research would have been abandoned half way.
I am forever grateful to Dr. O.C. Agwu of the Department of Botany for sacrificing his time to take photographs of some of my specimens. I am also grateful to Bro. K. P.
Baiyeri for the computer analysis of some of my data.
I must not fail to thank my sister, Mrs. Bertha. 0.
Nkemere, for her moral and financial support and my parents, Mr and Mrs V. 0. Npumechi-Opara, for their understanding and support throughout the study period.
Lastly, I am equally grateful to all the academic and technical staff of Zo~logyDepartment for various helps rendered to me in the last two years.
Mercy. N. Npumechi
March 1993. ABSTRACT
The biol3gy of the pestiferous Anthribid beetle -
Araecerus fasciculatus DeG. was studied under laboratory conditions 3n the following tuber products: pot3t0, yam and cassava vsrieties - NR 8083, T,% 30572, NR 8212 and
TM3 91934. The head capsule width measurement 3nd direct cmnt of shed head capsules showed that -A. fasziculatus has 5 larval instsrs. The larval head capsule width ranged fr3m 0.23mm in the first instar larv~ieto l.Omm in the fifth instar larvae.
The developmental periods of the immature stages of -A. fasciculatus were inversely related to temperature. The corrzlation coefficient (r) was 0.435 for egg development and 0.948 3nd 0.974 for larval and pupal developments, respectively. The threshold tempsratures of development were 12.2'C f~rboth the egg and larvsl st3ges while that of the pup3 was 11.75"C. Development and survival to sdulth3od wore surer in larvae reared on intact dried tuber chips (potato - 86.7%, yam - 63.3%, NR 8083 - 60%,
TM3 30572 - 33.3%, NR 8212 - 23.3% 3nd TMS 91934 - 83.3%) than in those reared on flour of the tuber foods (potato flour - lo%, yam flour and zsssavs flour (TMS 91934)- ,.>3me unidentified prasitic insects and predatory mites wer2 recorded from the egg and larval stages of the beetle.
Beetles lived longest on potato chips and shortest on cassava variety - NR 8212. The high?stnunber of eggs was laid by adult females maintained on cassava variety -
TM3 91934 while the least was on cassava variety - NR 8212.
Fecundity rates of fertile females in most -3ses were high early in adult life, usually within .the first 21 days from date of adult emergence. Population build-up of the beetles was highest on TMS 91934 an3 lowest on
NR 8212. The beetle also preferred TMS 91934 for f2eding and oviposition.
Loss assessment of food chips was based on 2ercentage weight loss and physizal damage. Losses were signifisantly related to the insect's population. Percentage weight
Loss was highest in cassava variety TMS 91934 and lowest in NR 8212. The extensive damage caused to dried stored tuber chips was as a result of feeding by the prolong2d larval stages as well as by the adult beetles.
Infestation of unsterilized tuber/food chips in storage by -A. fasciculatus and other stored products pests was progressive and by the end of the 9 month study period, the food :hips were completely pulverized as a result of vii
the feeding activities of these insects.
Drying of tuber chips to 10% moisture content and below followed by their sterilization and st3rage in seal~d polythene bags completely protected zhips from insect sttacks for at least 9 months when the investigation was terminated. viii Pagz TABLE.'; OF CONTENTS Tit12 Page i
ii
Dedication iii
iv
v
Table of Contents viii
List of Tables xii
List of Figures xv
List a£ Platss xvii
Chapter One: Introduction and Literature &view
1.1 Introduction
1.2 Literature reviow
1.2.1 Araezerus fssciculatus DeS.
1.2.2 The adult beetle
1.3.3 The pups
1.2.4 The larva
1.2.5 The egg
1.3 Distribution
1.4 Occurrence on crDps and plant products
1.5 The reproductive biolagy of the beetle
1.6 Source of infestation and extent of damage
caused in stores Page 1.7 Enviromental faztors affecting the development of -A. fasciculatus on products 1.8 Control measures tak2n against -A. faszizulatus
Chapter Two: Msterials and methods 2A Procurement and prxessing of the food substrates. 2B Insezt culture and c~nditioning
.# 2.1 Life history 2.1.1 Copulation and miposition behaviour 2.1.2 Eggs 2.1.3 Larvae 2.1.33 Effect of food type on larval developnent 2.1.3b Determination of number of larval instars
(ik By direct rzaring and counting ~f shed head zapsules (ii) By head sapsule width measurements 2.1.4 Pupae
2.2 Effests of temperature on development 2.2.13 Egg 2.2.lb Percentage hatshability 2.2. lc Temperature-time curve and threshold
temperature for development of immature st2ges of A. fasciculatus 2.2.2 Larva
2.2.3 Pupa
2.2.4 Mean total develop-iental
period (Egg-adult)
Effezts of types of food substrates
and starvation on:
(a) Longevity of adults
(b) Fecundity of adult femsles
(c) Population build-up of -A.
fasciculatus
2.3-i Assessment of loss of commodities
Influence of food types and stqrvstion
on papulstion parameters
Ability af first instar larvae to
penetrate food ehips.
Preference of food substrates for
feading and oviposition. -A. fss~izulatusas a pest of dried stored tuber products.
Chspter Three: Results
3.1 ' Life history 40
3.1.1 Copulation and oviposition behaviour 40
3.1.2 Eggs 41
3.1.3 Larvae 47 Page
3.1.3a Number of larval instars 3.1.3b Effect of temperature regimen on larval development. 3.1.4 Pupae 3.2 Effects of typs 3f substrates and starvation on:
(a) Longevity of adults 60 (b) Fecundity of adult females 64 (c) Population build-up of -A. fasciculatus 72 3.2.i Assessment of loss of commodities 72 3.3 Influence of food types on population parameters 3.4 Ability of first instar larvae to penetrate food substrates. 3.5 Preference of f~odsubstrates for feeding and oviposition. 3.6 Parasites of immature stages of -A. fasciculatus in the laboratory 3.7 Araecerus fasciculstus as a pest a£ dried stored products.
Chapter Four Discussion and Recommendations 102
Reference s 112
Appendices 129 xii
LIST OF TABLES
TABLE Development of -A. fasciculatus $-_qgs.at_ constant and room temperatures Development and survival of immature stag2s of -A. fasciculatus- reared on chips and fl~urof various food substrates at room temperature Head capsule width measurements of -A. fasciculatus- larval instars. Development of A._ fasciculatus larvae at constant temperatures. Regression equations and threshold tempratures of development of immature stages of g, fasciculatus Development of -A. fasciculatus pupae at constant temperatures Percentage of mean total developmental period (egg-adult) occupied by each immature stage at constant temperatures. Mean longevity (in days) of & fasciculatus adults reared on various food substrates and when starved. xiii Page Anslysis of vsriance for the effects of substrates on the lonvevity of msted adult males and females. Analysis of variance for the effects of substrates and starvstion on .the lonvevity of unmsted sdult males and females.
Fecundity of females of -A. fasciculatus when resred on six different food substrates 2nd when stsrvzd. Anslysis of variance for the effects of substrates and starvation on the actual fecundity and populstion build-up of
-A. fssciculstus. Populati~nbuild-up of -A. fasciculatus when resred on six different food substrates and the extent of damage csused to the substrstes. 74 Age-specific survival and age-spezific fecundity rstes of adult -A. fasciculatus females reared on TM3 30572 chips. Age-specific survivsl and age-specific fecundity rstes of sdult -A. fascizulatrus femsles resred on yam chips. Age-spezific survivsl and age-specifiz
fecundity rates of adult -A. fascizulstus
femsles reared on 'I'M3 91934 chips. xiv
Page 9d. Age-specif ic survival and age-specif ic
fecundity rates of adult A. fasciculatus
females reared on potato chips.
9e. Age-specif ic survival and age-specif ic
fecundity rates of adult A. fasciculatus
£male3 reared on NR 8083 chips. 80
9f. Age-specific survival and age-specific
fecundity rates of adult A. fasciculatus
females reared on NR 8212 chips.
10. Influence of food type and starvation
of A. fasciculatus females on some
population parameters. 88
11. Ability of first instar larvae of -A.
fasciculat'us to penetrate food chips. 91
12. ~rgferred£333 substrate(s1 by -A.
fasciculatus for feeding and oviposition. 92 xv
LIST OF FIGURES
Page FIGURE
1. Percentage hatchability of A. fasciculatus eggs at constant temperatures.
2. Tempeprature-time curve and graphical determination of threshold temperature of development of egg stage of -A. fasciculatus. 49 3. Third larval instar of -A. fasciculatus 50 4. Frequency distribution of head capsule width of -A. fasciculatus larvae. 54 5. Temperature-time curve and graphical determination of threshold tempeprature of develo2aent of larval stage of
-A. fasciculatus. 6. Pupal stage of -A. fasciculatus 7. Temperature-time curve and graphical determination of threshold temperature of development of pupal stage of -A. fasciculatus. 8. Percentage of mean total developmental period (egg-adult) occupied by each
immature stage at constant temperatures. 66 93. Age-specific survival and age-specific Page
fecundity rates of adult feaales of -A.
fasciculatus reared on TM3 30572 chips 82
9b. Age-specific survival and age-specific
fecundity rates of adult females of -A.
fasciculatus r3ared on yam chips
9c. Ag2-specific survival and age-specific
fecundity rates sf adult females of -A.
fasciculatus reared on TMZ 91934 chips.
9d. Age-specific survival and age-specific
fecundity rates ~f adult females of -A.
fasciculatus reared on potato chips
92. Age-specif ic survival and age-spezif ic
fecundity rates of adult females of -A.
fasciculatus reared on NR 8083 chips.
9f. Agz-specific survival and age-specific!
fecundity rates of adult females ~f -A.
fssciculatus reared on NR 8212 chips. xvii
LIST OF PLATES
PLATE Page
1. Adult -A. fsscizulatus 2. Egg of -A. f~isciculatus. 3. Ecto-par~isite of the egg Stage
4. Ecto-parssite of the egg stage
5. Ezto-parasite of the larval stsge
6. Ecto-psrasite 3f the larval stsge
7. Extent of damage zsused to unsterilized
cassava chips stored for a psriod of 9
months by insect pests.
8. Condition of cassava chips sterilized
befc~restor~ige in sealed polythene bags
~ifter9 m~nthsstorsge period.
9. Characteristic emergence holes of ~idult-A. fasciculatus. CHAPTER ONE
INTRODUCTION AND LITERATURE REVIEW
1.1 INTRODUCTION
Cassava (Manihot sp.) continues to be a staple food for about 160 million persons, about 40 percent of the total population in sub-Saharan Afriea. Cassava ranks first among root crops in sub-Saharan Africa, with total produstion accounting for some 55% of all root and tuber crops [FAO, 19881. Its produstion inzreased 2.4% annually between 1965 -74 and 1975 -84; anly yam had a higher production level of 3.2% for the periods stated [Gebremeskel and 9yewole 1987; FAO, 19881. Hahn and Onabolu (1988) reported that by FAO projections and IITA experience, zassava will continue to be a vitally important crop.
Cassava can be made into csssava chips directly from tubers of low cyanide cantent or medium cyanide varieties csn be used for the sane zhips by passing cassava flour through a dough-making and frying process (IITA, 1987).
Cassava flour is also used in the baking industries
(IITA, 1988). A number of varieties sre available locally and are consumed as fufu, lafun, garri, amala, t3pioca and starch. Tubers from the sassava cultivars considered sweet can be eaten simply boiled or baked (Dufour, 1987). Ysms (Dioscorea sp) constitute a major staple food in s~utheasternNigeria (3korji. 1986) and have been ranked sezond only to cereals as the most importsnt food crop in West Afriza (Coursey 1967;3nwueme, 1987). White yam
(D. rotundata Poir) is the most widely grown and eaten cultivar in West Africa (3koronkw3, 1986). In Nigeris, ysm is consumed as fufu, fried chips, boiled yam and snsla. IITA, (1988) report2d that yaa fl~ur,espesially thst from -D. alsta, has been found a successful substitute for wheat flour even at s high flour substitu-tion rate in the baking industries.
According to IITA (1976) sweet potatoes (Ipomoea bstatas) are extensively grown snd eaten through~utthe tropics.
The crop has the potential t3 produce up to 43,000 kiloc3lories of energy per hectare per year. It is high in vitamin A-an essenti21 nutrient often lacking in diets, especially of children, in humid 2nd sub-humid tropical areas (Davidson --et al., 1972). IITA (1980) report23 that the starch zontent 3f some sweet potato is as high as 27.5%.
In addition to food uses, high yielding varieties with high starzh c~ntentare good for industrial purposes and animal feed.
The peeled and dried chips of cassava, yam and pot at^, from whizh the fl~uris derived, sre heavily infested and damaged by a number of stored products pests while in storage. One of suzh destructive Pests is
Araaserus fascizulatus (DeGeer).
1.2 LITERATURE REVIEW
1.2.1 ARAECERUS PASCICULATUS (DeS. 1775).
A. fasciculatus (DeG.) (Coleoptera: Anthribidae) is one af the insect species injuri~usto certain st~red products as well as some field crops. It has heen referred to under a variety of cammon names, for example, Coffee Bean Weevil (Back,1931), Coffee Berry
Borer (Usman, 1949), and Cocoa weevil (S~lomonand
Adamsanr1955). A. fasciculatus has been described as a serious pest causing severe destruction of dried cassava tubers, as well as other stored products
(Hill, 1990). However, available literature pertaining t3 description a£ the various stages and aspects of the bialogy of -A. fasciculatus are summarized as follows:
1.2.2 THE ADULT BEETLE
The adult beetle is dark brown to black in zolour, with light and dark brown pubescence. It is ovate or convex in shape. The adult is a fairly small beetle said to be robust and measures 2.5 - 4.5mm in length (Cotton, 1921 and Sayed, 1940). The antenna is 11 - segmented with the three apical segments distinctly larger than the other segments. The eyes are entire, without emargination. The baak is short and wide. Females are easily distinguished from the males by diffarenzes in the pygidium (caudal shield cavering the abdomen)(Halstead, , 1963). In males, the pygidium is verticsl, not distinstly visible darsally, whilst in the females it is inzlined and distinctly visible dorsally.
1.2.3 THE PUPA C3ttan (1921) dessribed the pupa as being whitish when first formed, with the zast larval skin clinging tightly to the last abdominal segments. The pupa measures 3.75 ta 4mm in length and 2mm in width. Tips of wings are pointed and terminate with a long, chitinized hook nearly reaching seventh abdominal segment. Metathoraeic legs extend well beyond tips of wings. Head is rounded and profusely supplied with hairs. ~eakis short and broad. Wings are armed with numerous hairs. Bach abdominal segment is armed with two rows of dorsal, and numerous lateral hairs. Seventh and eighth abdominal tergites are apparently fused together; the ninth segment bears two larg3 bilobed fleshy processes armed with numerous papillae. The tenth segment is ventral to the ninth.
1.2.4 THE LARVA
The larva as described by Cotton (1921) when matured measures 4.5-6mm in lenght. It is a white, f33tless, fleshy grub with body curved, wrinkled, and profusely covered with long hairs. The head is very pale straw in colour, with the anterior margin and inandibles slightly darker. Head is long~rthan broad and somewhat
~blongin shape. Mandibles are large, stout, triangular, with apex produced into an acute t~oth. Eyes are represented by a well defined black spot beneath the exoskeleton. The larva has ten abdominal segments.
The ninth is small while the tenth is reduced.
one t3 eight are each provided with n~onofore rliPgments spiracles . The spiracles on the eight Beginenr are locatad slightly more dorsal with air tub~spointing cephalad instead of dorsal.
1.2'. 5 THE EGG
Cotton (1921) reported that the egg is white, shinning, and ovoid in shape. Top is broadly rounded, bottom slightly inore pointed. The egg is about 0.56mm in length and 0.35mm in width.
1.3 DISTRIBUTION
The beetle was first described by DeGeer in 1975.
It is thmght to have ariginated in India (C~tton,1921) but is now virtually cosmopalitan (Mphuru, 1974). It is essentially a tropical and subtropical pest occurring in almast all the coffee and cocoa producing countries of Central America, Africa and Asia, within about 20'~
3rd 20"s of the equator. Child3rs and Woodruff (1980) reparted its occurrence in North and South Ameriza,
Australia, Eur~peas well as Africa and Asia. Its occurrence in the tropics and subtropical regions and in a few temperate locations has been reported by Hill
1.4 OCCURRENCE ON CROPS AND PLANT PRODUCTS -A. fasciculatus as reparted by Mphuru (1974); Childers and Woodruff.(1980) attacks a variety of crops both in the field and in starage in different parts af the world.
Though the insect has been considered primarily a stared products pest, reports of its occurrence on living plants or their fruits in the field have also been published
(Chil.ders and Wa~druff , 1980 1. Working around Ibadan, Nigeria, Adesuyi (1967) and Osuji (1980), identified -A. fasciculatus as one of the pests attacking stored yam chips and yam flour. Iheagwam (1986) reported -A. fasciculatus as a primary pest of stored yam tubers. Parker and Bo3th (1979) discovered
the pest on stored cassava chips in West Malaysia. -A. fasciculatus was reported by.Lin. (1976) as a serious pest of st3red maize, sweet potato and the medicinal
" herb-chiretta-(Liqusticum acutil3bum). In Japan, Nagano (1981) reported that the pest was found injuring garlic bulbs. The beetle has been observed attacking coffes berries in the field in Brazil (Abrahao and Bitran, 1973). Childers and Woodruff (1980) described the beetle as a primary pest of stored products including c~ffee, c3caab, nutmeg, maize, groundnuts, nut crops, spices, grains and dried fruits in the tropics.
U~DAreport of 1971 has it that there were records of this pest in a few healthy or dried oranges in Fl~rida, Louisiana and California between 1929 and 1944. During th2 late 1960s, a citrus gr3wer in Florida became increasingly cancerned abaut the excessive fruit drsp in his grove of oranges prior to harvest. Subsequent examination revealed the presence af coffee bean weevil immature stages in the fruit (Woodruff, 1972). Mphuru (1974) deszribed the beetle as one of the major
pests of stored coffee in India and Central America
an3 of stored cacao in West Africa. He further stated
that it attacks a variety of other stored products
including cassava (Manihot sp), sweet potato (Ipomoea
batatas), dried plantain (Yusa sp) and various seeds
and fruits.
" 1-5 THE REPRODUCTIVE BIOLOGY OF THE BEETLE
The biology of fasciculatus has been studied fairly
well in Southern America where it causes considerable
damage to harvested coffee (Mphuru, 1974). Autori
(1931) stated that the female oviposits in the coffee
berries, laying only one egg in each berry. The larva
hatchds in 6 to 9 days and feeds in the pulp for 10
to 15 days and within the seed for a further 25 to
30 days. The pupal period lasts 6-9 days. De Figueiredo
(1957) reported a shorter life history with development
from egg to adult lasting 30 to 45 days whilst,
acz~rdingto Bricenco-Iragorry (1940) the life cycle
on coffee lasts 56 days. Cabal Concha (1956) stated
that pairing occurs 4-5 days after emergence, females
ovipositing almost immediately, usually inserting
their eggs in the cxoa and coffeerbeans. The total number of eggs laid per female averaged 52 with an average ovipasition rate af 3 eggs per day. Eggs hatzhed in 5-7 days, the larval stage lasted 46 to 66 days at 28'~ and 80% relative humidity and the pre- pupal and pupal stages 1-1.5 to 8 days, respectively.
Sayed (1935 and 1940) noted that at 27'~ the male matures in 3 days and the female in 6 days after emergence, fertilization taking place at 6 days after emergence. The incubation period was 5 to 8 days at 27'~ at all humidities between 50 and 100 percent. The maximum number of eggs were laid when the relative humidity was high (80-100 percent at 27'C). On maize he noted that the life cycle at 27'~ varied .£ran 57 days at 60% RH to 29 days at 100% RH, the v3riation occurring only in the period spent as larvae. The pupa was the only stage which could survive humidities lower than 60%.;1 On maize, adults lived 27 to 28 days
at 50% RH 3nd 86 to 124 days at 90% RH. On cocoa, few lived more than 20 days at humidities below 80%.
In laboratory studies carried out in Brazil, Goncalves, --et al. (1976) reported that females became sexually mature 6 days after adult emergence and under conditions of high relative humidity, the duration of development was negatively correlated with temperature; 6 generatians were obtained in a periad of 333 days. Adult females
lived for 83-114 days; each pair of adults praduced
about 50 Qrogeny.Considerably lsrger numbers of adult
beetles emerged from groundnuts than £ram caffee beans
(both newly cured and those that have been in storage
for sDme time), maize grains or soy beans after the
parent adults hsd been provided with a choice between
these substrates for ovip~sition. Beetles kept without
food died within 15 days.
In anather series of laboratory tests in Brazil, Bicran --et al. (1978) reported that when adults of -A. faszieulatus were confined with coffee beans, groundnuts, maize
grains, beans (Phaseolus) or sunflower seeds for a
perioi of 6 months, it was observed that the time
interval before the adults of the next generatian
emerged were 50-55 days for msize and groundnuts, 55-60
for coffee beans and 80-85 days for beans and sunflower
seeds. They also recorded that more adultls were
obtained from coffee, graundnuts and maize than £ram
beans snd sun£lower seeds.
In India, Kumar an3 Karnsvar (1986) observed that females
matsd 4-7 days and nales 3 days sfter emergence.. Mating
lasted 4-30 minutes and f~rmany females a second mating took place 3-4 days later.
Soans and Soans (1972) observed cannibalism ~f eggs and adults in adult beetles even when kept at l3w densities with abundant fo~d. The reasons for cannibalism were not clear.
1.6 SOURCE OF INFESTATION AND EXTENT OF DAMAGE
CAUSED IN STORES
Parker an3 Booth (1979) in their study in West Malaysia discovered. that insect infestation of stored cassava chips occurred during sun-drying and that up to 16%
reduction in weight due to insect feeding was recorded
after 2 months storage. Adesuyi (1967) while working
in Ibadan (Nigeria) observed that dried yam chips in
the m3rket were uninfested in October to March;
infeststion first bezame apparent in April, and reached
a peak in August. In India, Kumar and Karnavar (1986)
rep~rtedthat fresh stocks of cassava chips in December
to February were free of the beetles, but infestations
began in March. The stocks were fres of insects within
the spezified periods because af their very low moisture
contents (as a result of excessive dry weather conditions
prevailing at the said periods of the year) which made
them unattractive t~ the pest beetles. However, infesta,tions began with the coming of the rains
and subsequent increase in the moisture contents of the
products.
Bitran (1973) in his evaluation of the damage caused by -A. fasciculatus observed that a highly significant correlation was evident between the numbers of beetles in
..the samples of coffee beans, the percentage weight loss
and the percentage of damaged beans. He recorded that in
the most heavily infested samples, 35.5% to 67.8% of the
beans were damaged and the losses in weight ranged from
7.2% to 13.7%. Lin (1976) after rearing 3 pairs of adults
on maize, swees potato chips or chiretts for 5 months,
reported that the number of progeny produced was 136.2.,
176 and 136.7, respectively, and the loss of products was
estimated at about 22.6%, 31.4% and 26.6% correspondingly.
Nwana and Azodeh (1984) reported that yam chips parboiled
before storage are less susceptible to attach by -A. fasciculatus
than unparboiled ones. 1.7 ENVIRONMENTAL FACTORS AFFECTING THE
DEVELOPMENT OF A. FASCICULATUS ON PRODUCTS
Very little work has been done to determine the environmental factors which predispose various commodities to -A. fasciculatus attack (Mphuru, 1974). Sayed (1935) reported that A. fasciculatus develops best on food with high moisture c~ntentand at high temperatures. He further stated that far maize and nutmeg, the minimum length of the total life cycle varied inversely with relative humidity of the atmosphere. Cotterell (1952) also noted that -A. fasciculatus infestation is dependent on high moisture cmtent of cocoa during sun-drying; moisture contents between 17% and 20% proved attractive to oviposting females. He also noted that larval development was not completed in be2ns of 8% moisture zontent and below. Adesuyi (1973 a & b) noted that insect population increased with increase' in the moisture contents of the food stuffs.
Crowson (1967) speculated that -A. fascizulatus evolved
from a , rotten-wmd-boring habitat. Mphuru (1974) suggested that if the above speculation is accepted, then any environmental factor, such as high humidity, likely to predispxe materials to rotting would fav~ur the development of this pest. To this view, Back
(1931) indicated that -A. fasciculatus female lays its eggs only in the soft kernels of corn; subsequent breeding after harvest causes little damag2 since the corn is too hard. Cabal Conzha (195'6) noted that softer c~ffeeand c~ffeeof poorer commercial quality were the m~stsusceptible to the pest attack. Oei-Dharma
(1969) observed that during storage of nutmeg fruits
(Myristica fragrans), attack by -A. fasciculatus was usually preceded by mechanical damage by the fungus
Corynium sp.
Narasimhan (1987) noted that relative humidity greatly affected activity in the pest. Thus, at 50% relative humidity the beetle did not breed, but the generation times were 50-60 days and 35 days at 75%-80%and 85%-90%
relative humidities, respectively.
From the foregoing review, there is no doubt that the
anthribid beetle pest prefers materials with high moisture
content and preferably at the decaying or rotting stage
for feeding and breeding. The other imp~rtantfactor which affects the development 3f -A. fasciculatus is temperature. Puzzi and Pereira (1967) studying the rate of reproduction of the pest in Brazil, found that the life cycle at different times of the year was inversely rzlated to the mean monthly temperature. Under very warm conditions, high moisture content in coffee also increased the severity of attask by beetles. Solomon and Adamson (1955) recorded similar
" results and further establishment that the 3ptimum temperature for development at high relative humidity is 27°C.
1.8 CONTROL MEASURES TAKEN AGAINST A. FASCICULATUS Practice 3f good store sanitation has been suggested as ones of the most important ways of controlling this pest. Adesuyi (1967) stated that good store sanitation is essential for starage of dried yam chips in order to check insect infestatian. Proper drying of stored produce is also most important. In Nigeria, owing to imporved drying conditions the level of infestati~nby -A. fasciculatus has decreased drastically (Cotterell, 1952)- Fumigation has also been employed in the c~ntrolof the pest. In Nigeria, cocoa stores are normally fumigated using methyl bramide (2uereshi, 1966). In Brazil, fumigation of coffee using phosphine tablets was found to be effective against all stages of -A. fas:iculatus (Puzzi and Orlando, 1963 and 1964).
Subrahamanyan (1963) recommended the use of pyrethrum - for the treatment of monsooned coffee in India. In India too,D~T,Lindane or sevin had been used t~ impregnate jute bags used for storage of-Areca nuts (Nair --et al., 1970).
Bitran --et sl. (1978) faund malathion and tetrachlorvinphos effective in the treatment of stared coffee but warned against c3mmmercial use of the products since they were tried at high application rate of20 p.p.m and the residue levels had not besn determined.
Childers and Nigg (1982) evaluated the contact toxicity of 27 insecticides against the adult beetles. Ten of the compounds with LDJ5~in the range of 5.6 to 58.7 ug/g were found promising. The compmnds were azinphasmethyl, bendiocarb~ fenvalerate, permethrin, Phosmet, Sw35 651. csrbosulfan, phenthoate, oxamyl,
and methidsthign. Chacko and Bhat (1979) suczessfully
impregnated jute bsgs, used in the storage of coffee,
using emulsion zoncentrates of malathion and phoxin
(~olaton1.
Apart from the foregoing cultural and chemical remedies, Goncalvles --et al. (1976) observed the l3rvae of ., Anisopteromalus ealandrae parasitizing the larvas ~f
the pest beetle. An unidentified nematode was observed
attacking the immature stages while an unidentified
disease reportedly affected some larvae anti pupae of
the pest beetle. Otherwise, no natural enemies have
been found sufficiently effective to act as biological
control agents of the beetle. However, it is not
considered that the use of biological contra1 against
stored products pest is practicable (Mphuru, 1974).
-A. fasciculatus has sttained the status of a serious pest (Hill, 1990). As a result of the extent of
devaststion caused to stored products in general, and
particularly dried tuber produzts in storage, this
study was aimed at underst3nding ths biology of the
pest on the prduzts snd finding ways of reducing infeststion levels or if possible keep stored dried
cassava, yam and potato chips ss well as other stored
products completely free from -A. fasciculstus infsstation.
If this is achievd, it would go a long way in reducing
the extent of damage caused to these products ss well
" as loss incurred as a result of the damage. CHAPTER TWO
2.0 MATERIALS AND METHODS
Studies on some aspects of the biology of A. fasciculatus
(DeG.) were carried out on selected food substrates in the Entomology (Special) Laboratory, and the Pure and
Applied postgraduate Project Laboratory, Zoology
Department, University of Nigeria, Nsukka.
A. PROCUREMENT AND PROCESSING OF THE FOOD SUBSTRATES
Six types of food substrates were used in this study.
Four cultivars of cassava (Maniho-t sp.) tubers-TMS
30572, NR 8212, TMS 91934 and NR 8083 - were collected from Federal University of Agriculture, Umudike,
Umuahia, Abia state on the 24th of September, 1991.
Yam tubers of the species - Dioscorea r~tundata,the variety crommonly called Zak,and sweet potato (Ipomoea batatas) tubers were purchased from Nsukka market in
Enugu State of of Nigeria, on the 27th of September,
1991. These varieties of crop tubers were chosen because they are the common types whose products are widely stored and used in the present area of study, namely, Enugu and its neighbouring states. The said crop tubers were peeled, cut into chips measuring 2cm x lcm and sun-dried for a period of 1 week as is dane by local/commercia~ producers of tuber chips. The percentage moisture cantent of each of the tuber chips was determined using the indirect distillation (or drying) method described by Pearsan (1973). The methad involved determination of the initial weights of the substrates (weights after sun-
' drying) using Metler's balance, after which they were placed in the oven at 70°c for a total period of 2.5 hours. The substrates were weighed at 30 minute intervals until weights became c~nstant (i.e. no further difference in weight was observed). With the initial and final (canstant) weights of the substrates determined, their bercentage moisture contents were determined using the farmula: 100 x [Initial wt. of substrate-final wt. of substrate] ; [Initial wt. af substrate].
The percentage moisture contents of the substrates were as follaws: Potato chips-13.23% Yam chips-13.12%
I'M3 30572 chips-13.16% 'NR 8212 chips-13.31%
TYS 91934 chips-13.16% 'NR 8083 chips-13.34% The food substrates were put in palythene bags after being properly caaled and stored temporarily in tins with air-tight lids. The stored substrates were sterilized before use to ensure that they were not contaminated by unwanted insects and or their eggs.
The methad a£ sterilization described by Adesuyi (1973a) in which the chips were placed in the oven at 104Oc f~ra periad of 1 hour was used.
B, INSECT CULTURE AND CONDITIONING
The beetles used in the study were taken from a culture of -A. fasciculatus beetles raised in ths Laboratory at the University. Adult beetles were handpicked from dried cassava chips for sale but under storage at Orba market (some 5 kilometers away from the University).
The beetles were transported in a Petri-dish with perforated lid containing some pieces of cassava chips.
On return, 8 healthy and active beetles were placed in a plastic trough measuring 14cm x 8cm x 8cm stocked with 30gm ~f sterilized dried yam chips as food and covered with muslin clath held in postion with rubber band. The culture trough was kept on a shelf at laboratory temperatures fluctuating between 26Oc and 30°c (average
28'~) and relative humidity between 55% and 70% for ovip~sition,develapment and emergence of new adults. New adults started emerging 58 days later.
In order to condition the insects to the various food substrates planned for the study, first generation adults from the primary culture trough were used to establish specific beetle cultures. Each of the latter consisted of a glass trough, 19cm x 14cm x 14cm, containing about
" 50gm 9f each of the following sterilized substrates: yam, TMS 91934, NR 8212, TMS 30572, NR 8083 and ptato, chips. These were each supplied with 20 males and 20 females of aetive first generation adults. They were kept under labaratory canditians to multiply. Insects for the rest of the studies were drawn from the progeny, 3f these specific cultures.
2.1 LIFE HISTORY
2.1.1 Copulation and Oviposition Behaviour To study copulation and oviposition behaviours, ten (10) pairs of freshly emerged adults (each pair comprising of Dne male and one female) from each specific beet1.e i culture were each car 23
muslin cloth held in p~sitionby rubber band. The chips
were introduced because preliminary studies revealed that
female -A. fasciculatus rarely oviposited away from their
food substrates.
The experimental set-ups were each watched for about
3 minutes every two hours from 6am to 8pm for the first
14 days and records kept of copulation and miposition
behavisurs. The duration of copulation was the time
- from the engagement of the genitalia of the male and
female beetles to the time of disengagement. These
beetles were then reared till death to determine their
longevity.
2.1.2 EGGS
To abkain eggs of -A. fasciculatus, 6 - day to 8 - day, old cmditioned adult females were confined on ample
quantities of appropriate food substrates in Petri-dishes
cavered with muslin cloth. This is because females of
this age range were known, from preliminary results, to
be fully laying. The food substrates were dissected for
eggs after exposure to the said females for about 18
hours. To dissect the substrates for eggs, each substrate
was held between the fingers of b~thhands and br~ken
along the lines of weakness naturally created in them
by the probing astivities af egg- aying females. with 4 is!J; + 1 .,,-.tRwiera LIZFLW,Y the help of a mounted needle, the crust of the chip rxind the delicate egg was carefully l~osenedand the latter
tipped onto a filter paper in a clean petri- dish. In
all, 15 eggs were observed.
The colour of the eggs was noted when freshly laid and
as embryoniz development progressed. The shape was noted
and the size determined by measuring the distance between
the p~lesand across the centre, using a binocular
microscope fitted with an occular micrometer at a
For inzubati~n,half of the bottom of a Petri-dish was
lined with f~lded(double) filter paper while moist pad
of cotton wool in plastic bottle cap 3cm3 was stood in the
other half. Newly laid eggs realized as above were placed
on the dry filter paper using a spatula and the Petri-dish
was then zovered. This arrangement provided the eggs
axple huinid atmsphere (but not contact with water) in
which to develop. Each Petri-dish was plazed on a wooden block stood in an enamel trough (29cm x 19cm x 8zm) half - filled with water in order to prevent ants from eating up
the eggs. Each experimental set-up was kept on a shelf
in the laboratory for observation. The cotton wool in
the incubation chamber was remoistened once every other day and the eggs inspected daily until they hatched. Lsborat~rytemperatures were monitored with a thermohygrograph placed near the eggs and records of hatching kept accurately. Parasitized eggs were detected by dissections and any incriminated organism was recorded.
2.1.3 LARVAE 2.1.3a Effect of Food Type on Larval Development The larval developmental period of -A. fasciculatus was determined by rearingthirfy (30) day-old first instar larvae (derived from the laboratory hatched eggs) on each of the fo~dsubstrates. Whole chips (sterilized) were used for this experiment. To stimulate what obtains in nature, each larva was carefully introduced into an artifiicial puncture (made with fine sca!pel) on sDme 4g of the particular food substrate under test. The treated chip was then enclosed in a pair of Petri-dishes and left on the Laboratory bench for observation. Any larva that failed to penetrate the chip within 24 hours of introduztion was rem~vedand replaced with a new hatchling.
To monitor the duration ~f larval stage effectively, sample dissection of the artificially infested chips was made once a week from week 4 to week 6. Thereafter inspections were made daily until pupation and observations carefully recorded. Obvi~uscases of larval parasitism were also not2d.
2.1.3b Determination of number of Larval Instars
(i) By direct rearing and counting of shed head capsules To obtain the number of larval instars, tnirty (30) hatchlings of -A. fasciculatus were reared singly on cassava flour inside the experimental chambers. This procedure made it possible for shed larval head capsules to be obtained easily by sieving. Each shed head capsule was removed and put in a labelled specimen bottle using a fine camel hair brush. At pupation, the number of the shed head capsules recovered from each chamber was recorded and this indicated the number of larvsl instars. The pupae realized were reserved for other studies.
(ii) By head capsule width measurements In all, 270 larvse at vari~usstages of development were used in this study. Larvae were killed in 70% alcohol 2nd their head capsules measured at the widesc point.
All the head capsule ~iidthmeasurements obtained were used for a frequency distribution histogram with larval frequenzy on the ordinate and the head capsule widths on the abscissa. It was assumed that each major peak indicat~dan instar. 2.1.4 PUPAE
The pupal development of -A. fasziculatus was studied using pupae of known ages derived from larvae reared in section 2.1.3a. Fully formed pupae were sieved out of the flour of the respective food substrates on day one and placed on filter paper laid in clear plastic Petri-dishes (zovered) for observation. The experimental dishes were kept on shelf at temperatures fluctuating . between 26O~and 30°c and humidities betwsen 55% to 75%, the said environmental factors being recorded on a thermohygrograph also kept on the shelf. Observatian was maintained on the pupae throughout development and up till adult emergence. The results were arranged according to the food substrate fed upon by relevant larvae,
Adult beetles derived from the foregoing rearing exercises were wed for lon~vit,y,fecundity and other biolagical studies.
2.2 EFFECTS OF TEMPERATURE ON DEVELOPMENT 2.2:la Egg The incubation period and percentage hatchability of the eggs of A. fasciculatus were determined at 7 constant temperatures. Sixty (60) freshly laid eggs, obtained in the usual way, were set up in Petri-dishes (experimental chambers) as describsd in 2.1.2 above. Dated 2nd labelled zhambers were inserted in thermost2tizally controlled refrigerated incubators set at 7 selezted zonstant tsmperatures to develop. The constant temperaturs regimen wsre 15°C +-
30"~+- 0.5"C, 33OC +- 0.5OC and 35°C +- 0.5"C. Although humidity inside the Petri-dishes was not measured, it was presumably high throughout egg development since the zott~n~301 in each zhambsr was renoistened every ather day until termination of th? experiment. Records of hatchings were kept.
2.2.15 Percentage Hatchability
The t~talnumber of eggs (out of the sixty inzubated) that hatch4 at each temperature regimen was noted. The number of eggs that hatched when converted to a persentag? of ths total number 3f eggs inzubated gavs the percentage hatchability of the eggs at each zonstant temperature. Temperature-time curve and threshold temperature for development of immature staqes of A-fasciculatus. To obtain the course of the temperature-time curve, the observed times of development of each immature stage were plotted against temperature. The rate of development of each immature stage at each temperature regimen was determined as a reciprocal of time of development multiplied by 100 to give the average percentage development in one day and plotted against temperature. The threshold temperature of development of each immature stage was estimated graphically by extending the regression line until it intercepted the temperature axis. The point
D£ interception was taken to represent the threshold temperature of the immature stage in question.
2.2.2 LARVA
D~velopmentof the larvae of -A. fasciculatus was also studied at 5 constant temperatures namely, 20°C +- 0.50Cf 25'~ -t 0.5'~, 28'~ +- 0.5'~, 30°C+- 0.5'~ and 33'~ +- 0.5Oc. Thirty (30) day-old first instar larvae derived fr~mthe eggs incubated at the corresponding constant temperatures in2.2.la were used in this experiment. Each larva was carefully introduced into an artificial puncture (made with fine SE~\~~=-) on some 49 of sterilized q9q3 91934 cassava chips. The treated chip was then enclosed in a pair of Petri-dishes supplied with moist pad of c~tton 3 wool in plastic b~ttlecap (3cm ). Dated and labelled chambers were returned to the incubators. To maintain high humidity, the cotton waol in each chamber was remoistened every other day until termination of the experiment.
. To monitor the duration of larval stage effectively, sample dissecti~nof the artificially infested chips was made once a week from week 2 ts week 3 of the larval development. Thereafter inspeztisns were made daily until pupatian. Observations and readings were carefully recorded. The threshold temperature wa3 determined as already described in section 2.2.1~.
2.2.3 PUPA The pupal development of -A. fasciculatus at 5 constant temperatures namely, 20°C +- 0.5"~~25OC +- 0.5"~, 28°C +- 0.5"~~30°C +- 0.5"~and 33°C +- 0.5"C was also studied. Pupae derived from larvae reared at the corresponding constant temperatures in 2.2.2 were used in this experiment. Fully formed pupae were removed
from the food substrates on the first day and placed on filter paper laid in clear plastic Petri-dishes and covered. The chambers were supplied with moist pad of cotton wool in plastic bottle cap. The chambers were dated and labelled and returned to the incubators. The cotton wool in each chamber was rem~istenedevery other day. Observation was maintained on the pupae up till adult emergence. Readingswere carefully recorded. The threshold temperature of development was also determined . as described in 2.2.1~.
2.2.4 MEAN TOTAL DEVELOPMENTAL PERIOD (EGG-ADULT) From the results of the rearing experiments rep~rtedin 2.2.1, 2.2.2 and 2.2.3, the mean total developmental period (egg-adult) at each temperature regimen as well as the percentage of the mean total developmental period for each immature stage at each temperature regimen, was calsulated.
2.3 Effects of types of food substrates and starvation on:
(a) Lonqevity of adults The longevity of unmated beetles was determined by canfining ten (10) of each sex of newly emerged individuals with food in separate Petri-dishes as described in section 2.1. The dishes were placed on the shelf for daily observati~nuntil death of the beetles. The longevity of mated males and females was computed from records of individual beetles used for the oviposition experiments reported in section 2.1.1.
The longevity of the beetles when starved was also determined. The beetles (28 males and 30 females! were isolated on emergence and kept without food,each sex in sepsrate ktri -dishes covered with muslin cloth. Dated and labelled .. Petri-dishes were left on the shelf for daily observation and records kept accurately till all the beetles died.
The lmgevity 3f adults in each case was obtained as the time from adult emergence until its death.
(b) Fecundity of adult females (i) Mated Females The fecundity of mated females reared on the different food substrates was determined. The data were obtained from mated females treated as described in section 2.1.1.
To determine the number of eggs laid per female per day and the 'actual fecundity of a female, a piece of each food substrate was submitted to an ovipositing female at a time and replaced aftor every 24 haurs inside the Petridishes. The chips :recciver& daily after passible oviposition, were dissected carefully for eggs as described in 2.1.2.
The eggs thus laid daily by each female of known age were collected, counted and recorded against the age until either oviposition stopped or the female died 'naturally'. The insects ware dissected at death and the number of eggs found in the ovary counted. The number of the latter was then -. added to the number of eggs actually laid in arder to obtain potential fecundity of any one female.
( ii ) Unmate3 Females The fecundity of unmated females was also determined by isolating females in the usual rearing Petri-dishes stacked with food immediately on emergance and dissecting them at death to record the number of any unlaid egg.
(iii) Starved Females The fecundity of starved adult females was determined from mated females isolated on emergence and kept without food in covered Petri-dishes; these females were also dissected at death and the number of any unlaid eggs counted. The results of the fecundity ~f mated and unmated females as well as that of starved females were used to assess the effect of mating and starvation on ovipssition. (c) Population build-up of A. fasciculatus
To determine the population build-up of -A. fasciculatus on each of the food substrates used for the studies, 2 males and 2 females of freshly emerged adults from each specific beetle culture were confined in empty jam bottles
(500em3) and provided with 30g of corresponding sterilized chips. Eazh jam bottle was covered with muslin cloth held in position by rubber band. Each set-up was replicated 10 times thus giving a total of 20 females per feeding stuff. The set-ups were labelled and placed on the shelf in the experimental laboratory with temperatures fluctuating between 25'~and 30'~and humidities between 75% and 80% (read from thermohygrograph next to the jars) for a period of 7 weeks. The number of adult beetles emerging daily from each chamber was recorded and the emergents moved into new chambers for other possible tests until emergence stopped. The total number of beetles recovered from each food substrate was recorded and the mean found.
The resulting mean total FI progeny gave the population build-up of the beetle on each of the food substrates. 2.3(i) Assessment of loss of commodities
T3 2ssess loss caused by -A. faszieulatus to dried tuber crop (food) under storage, the apprently und2maged rem2ins
(i.e n~treduzed to powder by beetles) 3f the chips used for the foregoing experiment 2.3(c), was extracted and ridden of all powdery matt2r using clean zoarse camel hair brush. Each intact ehip was further broken and any remnant food powder shaken out. The now clean pieces were re-weighed to constant weight (see section 2.0 (A)).
The weight of the remnant chip was substrated from the initi3l wzight of 30gm of the zhip. The difference so obt3ined, divided by the initial weight of 30gn, multiplied by 100 gave the percentage weight loss for e2ch af the food substr2tes attributable to the activities of the revelavt number of beetles alone.
2.4 Influence of food types and starvation on population parameters.
From the data -obtained from section 2.3(b) age-spezif ic surviv2l and age-specific fecundity tables were constructed for the females reared on each of the foA substrates.
The survival rate (1x1 and fecundity r3tz mx) were determined. [x represents the ago in days of the females; lx represents the proportion of females surviving at the b5ginning of age class x sxpressed as a fraction of an initial population of 1 (i.e 100% survival) while mx represents the numbe'r of living female eggs laid per female in each age interval using the sex ratio of 1:ll
With Ix and mx determined, the following were calculated:
(i) Net repreductive rate (Ro) = the number of times
a population will
multipy per generation
(ii)Cohort generati~ntime(Tc) = the mean age of mothsrs
in a coh~rtat the birth
of female offspring
(iii) Capacity for increase(rc) = The number of tim~sa
population multiplies
itself per time unit
= E Log e Ro]/Tc
2.5 Ability of first instar larvae to penertrate food
-$ubstrates To study the ability of first instar larvae to penetrate
the experimental root crops chips, groups a£ twenty-five
(25) newly hatched first instar larvae were confind onta some whole chips of the usual cassava, yam and potato materials in Petri-dishes covered with muslin. cloth.
The experimental chambers were labelled and kept on the shelf in the laboratory. Each set-up was carefully inspected once daily and the number of larvae that had successfully penetrated or bored into the chips, as well as the number found dead, apparently unable to dig in was recorded. The aim of this particular aspect of the study was to establish why the adult females 3f -A. fasciculatus ovip3sit within their food rather than on the surfaces of the chips as is the case in some other stored products bettle pests like Tribolium castane~m;- Lasioderma serricorne, and Dinoderus porcellus.
2-6 ---~keference sf food sustrates for-- feedinq and,
The preferred food substrate(s) for feeding and oviposition by adults 3f -A. fasciculatus, ~as/weredetermined in the laboratory. A glass trough (29cm x 19cm x 19cm) was partitioned int~six equal compartments using appropriate pieces of w3od measuring 9cm x 3cm x 3cm. Fifty gm wcight of chips of each of the six food substrates
[described in section 2.0 (A)] were put int3 each of the
experimental compartments and labelled. Fifty males fifty females of freshly emerged adult beetles (from cultures described in ssztion ~.O(B))were introduced into the trough and zovered with muslin 213th held in position by rubber band. The set-up was replicated 10 times and left on the shelf in the labgratory for a period of 6 weeks. At the end of the 6 weeks duration, the experimen- tal chips of each food substrate were rid of beetles and transferred into a clean jam bottle whose mouth was then zovered with muslin 210th held in positi3n by rubber band. These chambers were labelled and left an the labc~r?tory bensh until adult emergence. Daily emergences wzre carefully recarded ag3ins.t appropriate food substrates until emergenze st~pped. The total number of adults that emerged from a11 the replicates of each food substrate was c~mpute3and the aesn found.
2.7 A. £as ' The effects of starage techniques and state af stored products on levels of infestation by A. fasciculatus wzre als3 studied in the laboratory.
About 20kg of cassava chips dried up to 8% moisture
sontent (using the method described in 2.Q._A) were divided into two lots. One lot (unsterilized) was put into two jute sacks, their mouths were tied up with twine
and the sacks left on the shelf in the laboratory. The
second lot (10kg) of the cassava chips was sterilized
st 104°C for 1 hour and cooled. This portion was again
divided into two parts of about 5kg eazh. One part was
put in two polythene bsgs (approx. 2.5kg each), their
mouths were tied up with twine and the bags left on the
laboratory bench. The other part was put in two jute
" sacks, their mouths were tied up with twine and the bags
left on thz shelf too. The bags were untied briefly and
the chips inspected once every week for the presence of
any insects thrmgh a perid of nine (9) months. The
condition of the chips was recorded.
In this particular aspect of the study, chips were stored
in the jute sacks as is usually done by commercial
produeers of tuber chips and in polythene bags (personal
idea) in order to establish the effects of storage
techniques on levels of in£estation. 40
CHAPTER THREE
RESULTS
3.1 Life History
3.1.1 C~pulationand Ovipositi~nbehaviour
During caplation, the m3le mounts the fem3le 3lm~st at right angle and such that their abd~minaltips (i.e their genitalia) touched. Engagement of the genitalia was intermittent, each engagement peri~d lssting 3-10 minutss. Out 3f 10 rezorded observati~ns, the average engagement period was 50.2 -+ 5.49 minutes (range 45 - 60 minutes).
The age 3t which mating occurred v3ried aaangat adult males an3 females. Generally, 3dult beetles (PLATE 1) mate3 from d3y 4-7 after emergence. Observations revealed that sexually immature females ware not receptive t3 males' advances and in most cases, the males reached sexual maturity 1-3 days earlier than the females. Mating occurred both at night and in the day. Oviposition commenrjed some 24 - 48 hours after first nating.
The pre-oviposition period ranged from 6-8 days £ram adult emergence. The female usually bored holes into the f003 substrates to deposit its eggs. The hales were made with the beak. The female, after.making the hole (usually 1-2mm deep) plased its ovipositar inside the hole. When it had deposited its egg (one per hale), it reconstitutsd chewed £333 material into a hard ball snd used it to plug the ovip~sitionhole. The aversge oviposition time (i.e the time taken to deposit one egg) was 8.6 +- 1.17 minutes (range 7-10 minutes). Ovip~siti~n ocsurred b3th in the day and at night. Often, the male staod behind the female as it oviposited. It wss not clear whether the male distracted or stimulated the female by its action.
3.1.2 Eggs
Eggs (PLATE 2) were white, shinning, ovoid to spherical in shape and were almost indistinguishable from the fa33 substrate when newly laid, the crop tubsr chips used being all dirty white. Each egg measured on the average,
0.53mm +- 0.03mm in length and 0.31mm +- 0.02mm in width
(n = 15). As embryonic 3evelopment progressed, the zolour of the egg first -changed to cream and finally t3 PLIATE 1 : Adult -A. fasciculatus X6 straw just bef3rc eclosi~n. Th3ugh the eggs were n3t measured ss embry~niedevelapment progressed, there was n3 glaring change in size. Fully d2vel~pe3eggs were usually uniform in c~lour,but dark brawn at the anterior end which marked the pcsition of the mandibles of the devel~pingembryo.
At the lsbsratary temperatures fluctuating between 25°C and 30°C and saturated atm~sphere3f the incubati~n chambers, eggs hatched in 5.13 -+ 0.44 days (range 4-6 dsys), (Table 1). Percentage hatchability was ss high as 91.7%.
Egg development at the respective constant temperatures is summarized in Table 1. At the extreme temperatures of 15"~and 35"C, eggs did not hatch. However, partially formed embryoes were evident through the egg shori3n. Eggs developed fastest st the fsvourable higher temperature a€ 30°C to 33"C, devel3pmental time being 3-4 days than at 20°c whsre they t33k 9-12 days to hatch. At the constant temperatures, the highest percentage hstch 3f eggs ozcurred at 28'C'(85%) and 30°c(83.3%), respectively. When percentage hatzhability is represented graphically, the optimun temperature rmge for development 3f the eggs fell between 25°C and 30°C (Fig. 1). PLATE 2: Egg of -A. fasciculatus m mrl . * 0 0 N m m
* * I I 0 m m
b wN * I 0 0 +I + I 40 mrl mm
m b I * 0 m mwrl
OPO mm
www0 0 0
omm m m m FIG 1. % hatchability of -A. fasciculatus eggs at constant temperatures. The thresh3ld teayerature of development [ i .e that temperature above which the rate of development begins to become perceptible (Shelford, 1929) in Iheagwam and
Eluwa (1983gof the eggs as determined by extrapolati3n from the regression line of percsntage rate of development against ten~araturewas found to be 12.2"~(Tabls 5, fig. 2). The r-value (correlation coefficient) of
0.435 and R-sq of 18.92% indicate that the relationship between temperature and rate of development is not perfect.
3.1.3 Larvae
The nswly hatched larva (Fig.3) was apodous, tiny and uniformly white except for the mandibles which were brown in colour. On the average, it measured 0.81mm +-
0.05mm in length and 0.58mm +- 0.02mm in disneter st the widest point, (n = 15). With age its head zapsule graduslly turned dark brown and the body cream. The soft-bodieilarvs is covered with numerous fine hsirs.
The developmental psri3ds of the immature stages of
-A. fasciculatus whose larvae were resred on the different food substrates in this study st the ususl fluctusting temperatures of the lsboratory are summarized in Table 2. For larvae, the mean developmental time rsnged fr3m 44.3+3.99- days on Potato chips to 54.9 +- 5.01 days on c3ssava (NR 8083) chips. Larval devel~pmenttsok longer
in flours, the mean range being 62.0 -t 3.61 d3ys an potato to 73.5 +- 6.36 days for yam and cassava materials.
Percsntsge survival to adulth~odwas generally higher in larvae reared on intact chips (being 23.3% and 86.7%
" for NR 8212 and pot3t3, respestively) and lower in th~se reared on flour of the relevant foods (10% for potato flmr and 6.7% for casssva and yam flour, respectively). r - value = 0.435
= 18-93.5:
Temp (OC)
FIG. 2 Tempersture tine zurve (e-0-o) and graphical determinsti~n3f threshold
temprstura of dav?l2pnent (3-a-3) of Fig. 3: 3rd Instar Larva of -A. fasciculatus (Dorso - Lateral view) X 40 Table 2. Developmentand survival of immature stages of -A. fasciculatus reared on chips and flourof various food
No. of larvae reared 30 30 30 30 30 30 30 30 30 No. surviving toadult 26 19 18 10 7 25 3 2 2 U1+' % survival to adult 86.7 63.3 60 33.3 23.3 83.3 10 6.7 6.7
Meantimeoflarval 44.3k3.9954.8k2.9 54.9S.0153.2k2.9753.9S.3750.7S.5762.Ofi.6173.5S.3675.5S.36 devt. [days] k SD Range of larval devt. 37-53 41-60 44-62 48-58 47-64 41-57 58-65 69-78 71-80 [days] Mean timeof pupal 5.550.51 5.550.56 5.550.51 5.950.32 5.7S.49 5.550.51 6.350.58 6.550.71 6.5S.71 devt. [days] k SD
Range of pupal devt. 15-6 15-6 15-6 15-6 15-6 15-6 16-7 16-7 16-7 I
Meantotaldevtalperiod59k4.46 66.6s.07 68.3s.8765.9s.6466S.92 65.1S.5474.7K3.2286S.66 88S.66 [egg - adult] [days] fSD
Range of total devtal 5 1-68 57-7 1 59-72 60-71 . 62-77 56-73 71-77 82-90 84-92 period [days] 3.1.3s Number of larval instars Direct caunt of shed head eapsules realized £ram breeding chambers in whizh larvae were reared singly on cassava flaur, gave five (5), *his suggesting that -A. fasciculatus has 5 larval instars.
The frequency distribution of pooled larvae head capsules (Fig. 4) showed 5 main peaks indicating 5 larval instars - as well. The peak and the range 3f head capsule measurements f3r the various larval instars is shown in Table 3. The head capsule measurements ranged from 0.225-0.325mm in the first instar to 0.925-1.0mm in the fifth instar, thus sonfirming that the first instar larva described earlier was decidedly small.
3.1.3b Effect of temperature reqimen on larval development. At favourable constant tsmperatures of 20°c, 25"~,28Oc, 30°C and 33°C used, duratian af lz~rvaldevelopment of -A. fasciculatus decreased with increase in t-mpr-tur- (Table$). Thus, mean time of development was longest at 20°c [52.3 +- 4.26
days] and shortest at 33OC [22.7 -t 1.70 days]. Similarly,
percentage rate 3f development was inversely related to temperature, being 1.91 and 4.41 at 20°C and 33"~,respectively. The threshold temperature f3r larval development as determined graphizally was 12.2"C [Table 5, Fig. 51 The r-Value (correlation coefficient) of 0.948 and R-sq value of
89.87% indicate that there is a perfect relationship between temperature and the rate of development.
3.1.4 Pupae The pupal stag= was preceded by a pre-pupal stage which lasted
1-3 days depending 3n the prevailing temperatures. It was distinguished qorpholqie3lly from larval stage by first becoming somewhat slender [i.e the larvs l3osing its fleshy naturel'and finally reducing in body length through contraction ofthe segments. The pre-pupal stage was quiescent, especially just before pupation..
ITable 5. Regressionequati3ns and threshold temperatures:ofdevelopment 1of- immature stages ?f -A. fasciculatus
Stage 3f development Regression equation Temperaturethresh313 deg. C
4Cfl Larva Y = -2.197 + 0.212X 12.2
- Pupa Y = -16.415 + 1.302X 11-75 PaL k7 r - value = 0.948 60-. R - 3q. = 89.97% - 6
50.- - I;
P" - 4
C - 3
2D .- - a
I0 '- -I
0 - r I 6 m I J~&Z 15 W 25 30 3'5 Temp -+ FIG. Ternp2rature - time curve ba-a ) an3 grsphizsl det2rmin2tion of thr~sb3Ld t?npzr.sture of d..v?Lop=nt (0-3-0) of L3rvsl stage of A.- faaciculstus. The pupa was of the exarate type [i-e. the appendages are
free of any secondary attachinent to the body.] [Fig. 61.
It was white when newly formed but gradually became cream
in colour with age. At this stage, the points shawing the
position of the eyes and the beak were quite distinct at
the anterior end. The colour finally zhang~dto light
brown, even more praminently about the head and thoraciz
regions. The areas corresponding to the positians of the . wings on the ventral side were distinztly black. When
fully formed, the pupa of -A. fasciculatus had a characteristic
bulbous attachment 3f the last larvsL skin at its pasterior
tip. The pups, unlike the pre-pupa, had greatzr power of
movement, snd resdily wriggled vigorously when disturbed.
At theblaboratory tem2eratures fluctuating between 25°C and
30°C and humidities between 55% and 75%, mean dev~loprnsntsl
periods of ?upae whose larvae were fed on the differenk-. tuber chips vsried only slightly, ranging from 5.5 +- 0.51 to 5.9 +- 0.32'days [Table 21. Adult beetles took slightly longer [6.3 -+ 0.58 to 6.5 +- 0.71 days] ta emerge from pupae whase larvae were reared solely on flour of the zorresponding
food substrates [Table 21.
AT the favourable constant temperatures of 20"~~25'~~ 28"~~
30°C and 33"C, and humid atmosphere of covered Pstri-dishes, pupal develgpmental period was agsin (see results for 2gg and larva) inversely related t3 temp~rature (Table 6). Thus
the mean times of development were 10.54 +- 0.54 and 4.0 +- 0 at 20°C and 33"C, respectively. From this experiment, the threshold temperature for pupal development
determined graphizally was 11.75OC (Table 6 and fig. 7).
The r-value of 0.974 and R-square value of 94.87% indicate that there is a perfect relationship between temperature and . the rate of devolopment.
The pooling of the mean 3evelopmental periofis of the three immature stages of -A. fasciculatus at the cmstant tsmperatures used in thz study shows that the pupa
consistently took longer than the egg stage while the larval
period d3minatsd some 2/3 3f the insect's developmental
period from egg to adulthood (Table 7; Fig. 8)
3.2 Effects of food substrates on: (a) Longevity of Adults
The longevity of unmated and mated beetles maintained on each bf the six different food chips and that of starved individuals are summarized in Table 73. Analysis ~f varianse showod some levels of significant differences in the longevity 3f adults fed 3n each 3f the food materials FIG. 6 Pupa ~f -A. fasciculatus (ventral view) X 40 Table 6. Devel~pnentof -A. fasziculatuspupae at constant temperatures
I Temp. deg. C No. ~f obser- Mean duration Range of 8 rate 3f vations 3f development development developmen [days]-+ SD [TI time [daysI [100/Tl r - value = 0.976
R - 3q. = 94.87%
Temp. (OC)~
FIG. 7: Tempersture - time curve (0-0-0) and graphi-31 determinstian a£ thrsshold
tempsr3ture 3£ dzv5lapnent (0-3-3) oE
pupal SC~CJ~3f -A. fasizuL3tus. as against when they were starve3 (Table 7b and 7c).
In general, fed beetles lived longest on potato =hips than on any other tuber chips used. Secondly, unmated individuals lived l~ngerthan their mated counterparts.
Starved beetles did n~tmate because they were too weak to mate after the normal 4-7 days pre-mating;period.
'b) Fecundity of adult females.
Fesundities ~f adult females of -A. fasciculatus maintained on the vsrious food substrates or starved are shown in
Table 8a. Fecundity v~~riedwidely between 8.7 +- 0.92 for chips of NR 8212 zassava variety and 51.0 -t- 6.36 on the
TMS 91934 variety.
Indeed Anova (Table 8b) confirmed that there were significant differenses (P = 0.05) in the mean numbsr of eggs laid by grDups of females maintained on the different food substrates.
At death no eggs wore recovered from ths ovaries 9f the fertile females maintained on any of the food ships. Mated but starved adult females did not lay eggs in their lif3timc nar wErP ova rez~vsredfrom their ovaries at death. In this species, therefore, food must be vital for egg format ion.
Table 7a. Mean longevity [range in brazketsl [in days] of A_ fasciculatus adults 1 I
I reared on various food suQstrates and when starved.
TMS 91934
Unmated females
Dash [-I stands for not applicable since starved adults did not mate. L. I Table7b. Analysis of variance f3r the effects of substq3tes 3n the longevity of mteds adult males and femles of -A. fasciculatus. I Substrates Longevity of mated dult females Longevity of mated adult [in days ] ' males [in days1 NR 8212 22.00 a 24.20 a
Yam chips 24-20 ab 27.90 ab
TMS 91934 27.10 ab 30.40 bc
I Potato chips 30.70 c 32.90 c * * * Means not f3llowe3 by the same letter[s] along the column are significantly - different (P = 0.05) as determined by Duncan's New Multi~leRange Test -Y 09'ZSI P OS'ES sa~yz oq~qod I
I I 9 OP'TE I a(4 01'92 E808 NN 1 t 1 1
-ppp
ci 06'OE 9 08'22 ZLSOE SW& I Table 81. ~ecunditv of 1 fmd substr ates and w
Potato observa- tions
post ion period + SD [days]
1 Total no. of eggs
Rmge of loe gs laid f esundity ~actuaiJ + ISD-
3f unlaid eggs at death
I 1 1 I I I ?re stands' for not a$plicaSle 1 1 I
Fed.but unrnated females, like the mated but starved
females, did n~tlsy eggs throughout their life time.
When they were dissected at desth, mssses of mature
eggs were discovered in their ovaries. Thus, copulstion
seems a necesssry stimulus to induce oviposition.
(c) Populstionba~~in cul atus on substrates
Results of the population build-up of -A. fasciculatus
. reared on the variogs experimental tuber chips sre shown
in Tsble 8c.
An~3(Table 8b) showed significsnt differences(P=0.05)
in themeans of the number of adults that ultimately emerged
from the original 20 females placed on each of the food
substra$es. Cssssva vsriety TMS 91934 gave the best result
(mean t~tslof 104.7 -t 7.29 beetles), followed by potato (mean t~talof 71.1 +- 4.23 bsatles) than the other food chips.
3.2 (i) ~ssessmentof loss of commodities
Results on the extent of dsmage and loss caused by the
feeding stsges of -A. fasciculstus t~ food chips are 3lso
sh3wn. in Table 8c. Results sh~wthat the greatest damage was done to cassava
variety TMS 91934 and the le3st to sassava variety
NR 8212. The percentage weight loss in fo~dchips
ranged betwzzn 11.6% in NR 8212 chips and 29.5% in
TVS 91934 chipst
It is evigent from the r~sultsthat -A. faszizulatus beetles . cause varying degrees of damage to stored foods, dam3ges
being related to the numbers of beetles present in
the substrates.
Influence of food types on population parameters. .-- Results on the influence of £903 types on age-specific
scrvival and age-specific fesundity rates of females of
-4. fasciculatus are pr3san~4 in fibl2~9a-f and Figs 9a-f while those on net reproductive rate (Ra), gan2ration
time (Tcr) and capacity for increase (rc) are shown in Table 10.
Fecundity rates (Figs 9a-f) 9f females in most cases were
high early in adult life, usually within the first 7-14
days; The rate of oviposition fell gradually with age, the
fluctuating fecundity rates thus manaifesting erratiz
peaks throughout ovipostion period. Table 8c. Population build-up of A-fasciculatus when reared on six different food substratps and the,extent of qamaqe caqsed to the qubstrates. 1 1 I 1 I
Pgtat~ chips Yam chips NR 8083 NR 8212 TMS 91934 TMS 30572 chips chips chips chips
No. of replicates 10 1s i3 10 10 10
Total no. 4 of adult IP emergents 711 617 590 221 1047 405
1 Mean no. of adult emergents -+ SD 71.1+4.23- 61.7+3.95- 59.0+3.30- 22.1+2.96- 104.7+7.29- 40.5+2.99-
Mean % wt. loss in feed stuff 20.4 19 17.7 11.6 29.8 16.3 Generally, adult fenales spent about half their lifetime oviposting but st LTS0 (i.e the time when only 50% of the population were alive) only few continued to lay eggs.
The survivorshi@-curv~sfor this species (Figs 9a-£1 showed that 100% of the population remained alive for 6-16 days depending on food varieties provided. Beyond these points, survival rates begsn t3 diminish gradually
(ss s result of sgeing snd death), and formed plateaux at some age class intervals indicating that fall in survival rates wss not continuous. The net rzproductive rate, generation time, capacity for increase snd LT varied in females resred on different 50 food substrstes. Net reproductive rate and capacity for increase for females maintained on casssvs variety TMS 91934 were superior t3 those of femsles reared on the other food chips while the generation time and of females maintained on potato chips were superior LT 50 to those of ~thersreared on the other food chips. On the other hsnd, all the population parameters studizd were most inferior in females maintained on casssvs vsriety NR 8212. %ble 9a- Agespecific su~cvival agespecific f:-mdity rates qf adult A, fasciculatus
females reared on TMS 30572 1 I I I I I
Age in d3ys [XI hrvival T~talNo. Mean No. of Fecundity rate Female births rat2 [ 1x1 of eggs laid eggs laid 2 3D egqs/day [mxl [lx.Mx] 1-49 Lmture stages 50-57 Pre-mi-. position stage 58 1 13 1.3+0.48- 0.65 0.65 - I Table 9b. Age-specific survival and age-specific fecundity rates of adylt 1 A. fasciculatus females reared on Yam chips 1 1
A92 in days [XISurvival Total No. Me2n No. of Fecundity rate Female births rate Clxl of egqs laid eqqs laid SD eggs/&y[.%] [lx.~~] 1-48 Irmuture staaes2 8 1 49-55 Pre-ovi- I I position stag2 56 1 l9 1.9+0.74- 0.95 0.95 Table 9c. Age-specific survival and age-specific fecundity rates of adult A. fasciculatus-- females reared on TMS 91934 I 1 1 Age in days [x] Survival Total No. Mean No. of Fecundity rate Female births rate [ 1x3 of eggs laid eggs laid + 3D eqgs /day [ MX] [lx.Mxl 1-46 Imture stages 47-52 Pre-~vi- position stage 53 1 35 3.5k0.71 1.75 1.75 54 1 36 3.6t1.27 1.8 1.8 55 1 43 4.321.06 2.15 2.15 5 6 1 -41 4.1i1.52 2.05 2.05 57 1 48 4.821.32 2.4 2.4 58 1 4 2 4.2i0.63 2.1 2.1 59 1 39 3.9L0.88 1.95 1.95 60 1. 37 3.7k1.16 1.85 1.85 -- 61 -- -- 1 - 32 3.2L1.23 1.6 62 1 - 27 1.6 2.7L1.25 1.35 1.35 63 1 27 2.720.82 1.35 1.35 64 1 26 2.650.84 1.3 65 0.9 27 1.3 3.0L0.87 1.5 1.35 66 0.9 15 1.67L0.99 0.835 67 0.8 14 0.7515 1.75+0.71- 0.875 0.7 Table 9d. Aqe-specific survival and age-specific fecundity rates of adult A, fasciculqtus femaleq reared on potato chips I
I I 1 A92 in days Ex] 3urvival Total No. Mean No. of F2zundity rate Feile births rate [lX] off eqqs laid eqgs laid f 3D eggs/*y [Mxl [lx.Mxl 1-42 mture stages 43-50 Pre-3vi- position stage 51 1 33 3.3+0.68- 1.65 1.65 ---- Table 9e: Age-specific survival and aqe-specific fecundity rates
of adult A, fasriculatus femaJes reared on NR 9083 I I I I Ags in days [XI 3urvival Total NO. Mean No. of Fezundity rate Feiile births rate [lXl of eqgs laid eggs laid 2~ eggs/day [Mxl [lx.Mxl 1-49 Immature stages 50-56 Pre ovi- ~ositionstage 57 1 23 2.3k0.82 1.15 1.15 5 8 20 2.020.94 1 1 5 9 1 19 1.9+0.88 0.95 0.95 60 1 24 2.4L3.7 1.2 1.2 61 19 1.940.88 0.95 0.95 62 1 20 2.0i0.67 1 1 63 1 14 1.420.7 0.7 0.7 64 10 1.0+0.82 0.5 0.5 65 1 8 0.840..79 0.4 0.4 66 9 0.9-+0.9,9 0.45 0.45 67 0.91 9 1.0+0.5- 0.5 0.45 Table 9f. Age-specific survival and age-specificfecundity rates of adult
A, fasciculatus females rearedon NR 8212 1
Age in dsys [XI SurvivsL 13ta~ NO. Mean N3. of Fecundity rate Female births rate [ax] of eggs Laid eggs laid +SD eggs/day [MxI [lx.LX I - -. 1-49 Imature stages 50-57 Pre-3vi- postion stage 5 8 1 11 1.1+0.32- 0.55 0.55 82
In crrZ u m14 d cnQ) crr + In C .0- .+- In 0 .-n > 9 !! L
u m i r) m ffl (0 (D
Table 10, Influence of food type and starvation on some population parameters of A. fasciculatus females. I I I I I I I P~pulati~n Yam Potst9 TMS NR 8083 NR 8212 TMS .C.txv~~ior Parxneters chips shi?s 91934 chi~s chips 30572 t chi~s Ne wprduet ive. t 10.5 --- rate [Raj 18.75 25.5 10.86 4.39 6.65
Generation time 62.09 57.8 59.39 62.82 63.71 63.44 --- [Tcl [days]
- -- ~ -- - ~ ~ Capazity far 0.0379 0.0507 0.0545 0.038 0.023 0.0299 --- increase [rcl
LTp;k*n days 1 26 30 26 26 20 24 --- - - 3.4 -Ability of first instar larvae to penetrate tuber-chips . - fisults of studies on the ability of first instar larvae
to penetr3te dry tuber chips are summarized in Table 11.
In general, first instar larvae were not efficient' in
boring into their £003 chips. Only some 22.67% of larvae
(n=25) used succeeded in penetrating the chips in 4 to 6
days. The successes were 32% for cassava, 20% for yam
snd only 16% for p~tatochips. 3n the other hand, when
incisions were msde on the f~odchips and the larv3e
plsced directly in them, more larvae bored into the
chips and in shorter times.
The inefficiency 3f the first instar larvae to b~reinto
thz food chips could probably be the reason why adult
fenales bored h~lesinto the food chips to deposit their
eggs, sinze this would aff3rd the first instar larvae
the opportunity to continue boring and feeding on hatching.
3.5 Preference of f d substrates for 'feeding and oviposition-- . . The results of the preference tests on food substrates for
fesding and oviposition by adult females of -A. fasciculatus
3re sh~wnin Table 12.
The means of the number of adults that emerged from each
f3od chips when -50 females were left with choice of
substrates for feeding and oviposition was highest in
TMS 81934 (mean t~talof 132.3f3.30 beetles), foll3we3 zlcsely by potsto zhips (Yesn tots1 of 101.7+4.45- beetles)
while the least number of sdults wss recorded from NR 8212.
The fast that this result is cDnsistent with results on
p~pulsti~nand fecundity studies suggests thst cssssvs
variety TMS 91931 snd potst3 chips are better substrates
than 3thsrs.
" 3.6 Parasites of immature staqes of A. fasciculatus in the laboratory
In the lsboratory, eggs and lsrvse c~f -A. fasciculstus
left to devel3p in covered Petridishes were attacked. by
a number 3f wsrssites.
Plates 3 and 4 show Ecto-psrssites of the eggs while plstes
5 2nd 6 show Ezto-psrasites of the larvse. The sgg-
psrasites (two types) were unidentified wingless insezts
while the IsrvalpsrasiteS were unidentified mites. In
either sssz, the parasites were found attachsd firmly to
their hosts and required considerable force frm mmnted
pin to dislodge them. Psrssitized larvae were observed
t~ bzc9me less sctive at first ~nlyto die in sbc~ut1-2
days. Parssitized eggs shrivelled up as saon as they
apprently got suckad up by the psrssites. Wle 11. Ability of first instar larvae g£ A. fasciculatus to penetrate food chips Potato chips Yam chips Cassava chips Tot.31 no. of larv2e introudceii 25 25 25
-- Total no. of larvae - that penetrated ' 4 5 8
% 3f the larvae that ponetrate3 16% 20% 32%
M=an time[in days] +- SD 5.25+0. 43 5.0+0.63 5.1+0.84 taken to penetrate [ 5-6 I [z-61 [z-61
- - 1 I I -- Note: Range 3f time [in brackets] [days] taken to penetrate the substrates Table 12. Preferred food substrate[sl by A. fasciculatus for feedingand
Oviposition. I I I I I I
T~taln3. of adults emerging 1017 665 1323 444 217 818
Wan na. of adults emerging 1 -. 1 1 -+ SD 101.7+4.45 66.5c5.58- 132.3+3.3- I44.4+3.24 - 21.7+2.18- I81.8+2.94 - 3.7 Ataecetus fasciculatus as a pest of dried stored products Results frcm laboratory studies on the effects of storsge techniques snd state of stored proudcts on levels of infestati~nby -A. fasciculatus revealed that -A. fasciculatus, amongst other pests, is responsible for the damage and loss of dried stored proudcts. The other pests encountered during periodic31 examination of the stored food chips, (both sterilized snd unsterilized chips stored in jute sacks), include Tribolium csstaneum, Dinoderus distinctus, Lasioderma sericorne, Sitophilus zesmais and Palorus subdepressus, (as identified by Dr. J. Allotey of Department of Biological Sciences, Rivers State University of Science and Technology, P.H), which were numerous in number.
The nsture of dam3ge caused to stored cassava chips (not gterilized before storage in jute sacks'arid sterilized but stored in jute s~c~s-)by -A; f~sciculatusin conjunction with the other 2est.s when stored for a period of 9 months
(Ostober, 1991 - August, 1992) is shown in plate 7. Plate 3: Ecto-parasite of the Egg stage of
-A. fasciculatus, Plate 4 Ecto-parasite of the Egg stage of
-A. fasciculatus. Plate 5: Ecto-parasite of the larval stage of -A. fasiculatus. Plate 6: Ecto-parasite of the larval stage of -A, fasciculatus. Infeststion, however, was first noticed in the unsterilized chips in the jute sscks, 9 weeks before it Segan in the sterilized chips contained in jute sacks. This result suggests that the unstsrilized chips may have been aontsminated st the time of storage or its unsterilized state made it more prone to infeststion than the sterilized chips. Studies also revealed that chips dried to 10% moisture content 2nd sterilized for one hour at 104OC can be stored successfully (in polythene bags with their mouths tied firmly) for upwards of 9 months with~utthe slightest infestation ss illustrated in plate 8. plate 9 sh~wsthe characteristis emergence holes of adult -A. fssciculatus and the characteristics of produzts infested with -A. fssciculstus.
it must be aentioned that -A. fasciculatus was encountered esrly in this study 3n ships of cassava varieties :TMS 91934 and NR 8083 during the sun-drying 3f my tuber chips. Plate 7: Extent of damage caused to unsterilized cassava chips stored for a period of
9 months. Plate 8: Condition of cassava chips sterilized
before storage in polythene bags after 9
months storage period. Plate 9: The characterisitc emergence holes of
adult -A. fasciculatus. CHAPTER FOUR
DISCUSSION
The percentage rate of development in the immature stages 3f -A. fsssiculatus w3s directly pr~portionslto temperature. This finding is in agreement with the observations of Messenger (1964), H3we (1967) and Thomas (1980). Sinse ., rate of development is gaverned by the effect 3f temperature Dn the speed ~f actim of enzynes (Hunter-J3nes, 1970 1, it coulfi be that as temperatures decreased t3 the lower thresh~ld,the rate 3f enzyrnatis action also decreased and ss temperatures rose t3 the higher threshold. and beyond, enzyme break-down occurred with the attendant arrestment ~f development and resultant death in some cases. This possibly explains why development of immature
stages 3f -4. fasciculatus was unrealistic beymd temperature
Limits of 20°Ct0.50C- (minimum)and' 33OC+0.5OC)- maximum.
The thresh~ldtmpsrskure ~f development of the egg (12.2"C),larval (12.2OC) and pupal (11.75"C) stagos DE -A'. fasciculatus as determined graphically were lower than th3se rezorded in same tropizal species such as the cassava mealybug Phenacocsus manihoti Mat-Ferr (14'~in Eggs - 20"~in first instar larva) (Iheagwam and Eluwa, 1983), snd the yam moth-Dasyses r~~osella(~gg-15.3~~, Larva-19:4"C, Pupa-15.0°C) (Iheagwam and Ezike, 1989) but higher than thst recorded in a temperate species, the cabbage white£ ly -Aleyrodes pr~letella ( 10°C in
Egg-10.lZ°C in inktar 'io larva ) ( Iheagwam 1978 ) . Ths threshold temperature of development of immature stages of -A. fssciculatus, however, is the same as the thresh~ld temperatures of development of some species noted to be worldwide in distribution such as the Acrididae - Melanoplus bivittatus Say.(Church ind Salt, 1952) and the locust Locusts m.- gallics Remsudiere (Uvarov, 1966). This finding perha93 explains why the pest is fairly worldwide in distribution (Mphuru, 1974; Hill, 1990). The r-value (correlation coefficient) of 0.435 snd R-square vslue of 18.92% indicate thst the relationshio, between temperature and rate of development in Egg is not perfect. However, no reason hss been found for this type of rzlstionship. The r-vslue of 0.948 and R-squsre value of 89.87% for larval development snd r-value of 0.974 and R-square value of 94.87% for pupal developnent indicate that there is a perfect relationship between temperature snd the rste of dev?lopment, which is in agreement with existing facts. The favourable constant temperatures for the developnent of the immature stages of -A. fasciculatus ranged between 20°C and 33°C. Andrewartha and Birch (1954) noted that the range of temperatures favourable to any particular species is related to the prevailing temperatures in the place where the organism usually lives. Since the tem- peratures prevailing in most parts of Nigeria at different times of the year rarely fall beyond 20°C or rise abmz 33"C, ., this beetle in nature, should be able to thrive at all times of the year, except when disturbed by factors other than temperatures, such as non-availability of food or relative humidity or moisture content of foods. At the constant temperatures, the highest percentage hatch of eggs occured at 28°C (85%) and 30°C (83.3%), respectively, suggesting
that the non-lethal fluctuating temperatures of 25°C - 30°C (percentage hatch of 91.7%) is perhaps, the more favourable and natural condition for the species.
Fed beetles lived longest on potato chips than on any other tuber chips used in this study. This result is not surprising since potato contains significant ammnt of protein, minerals, vitamins, amino acids and potassium which are lacking in the ~therfood chips (Davidson --et al., 1972). Unmated beetles lived longer than their mated counterparts.
Sifick energy is needed f3r aztivities in living things, it is obvi~usthat mated beetles, whish eventually oviposited, dissipated some energy during reproduction whizh had been saved in their unmated an3 non-laying zounterparts and probably prolonged their life span.
Anava sh~wedthat there were significant differences
(P=0.05) in the mean number of eggs laid by groups of females maintained Dn the different food chips. This result is expected since the different f3od chips varied in their nutrient zompositions (Davids,~n--et a1, 1972;
Baquar and Oke, 1976; and 4sadu --et sl., 1988), as well as in their cyanogenic contents, in the case of cassava vsrieties (Bolhuis, 1954; Dufour 1983 and 1985; Rosling
1987; Hahn and Onabolu, 1988). ObviDusly quality of food has a major influence on the survival and fecundity of some insects is have been rezorded in the sycamare aphid-
Drepanosiphum platanoides Schr. (Norris, 1934; Emden, 1964;
Sokoloff , 1972; Dixon, 19731, the viburnum whitef ly,
AleurDtrachelus jelinekii Frauenf. (S~uthwoodand Reader,
1976), the greenhouse whitefly-Trialeurodes vaporariorum
West (Hussey 2nd Gurney, 1959) and the v3riegated grasshopper-Zonocerus varieqstus L (~heagwam,1979). Mated but starved females did not lay eggs in their life time nor were there ova resovered frorn their ovaries at death. This situstion zould be explained in terms like "alimentary castration" or "nutritions1 castrati9nM which is common with insects that fee3 in their adult stage as wsll as thase whose egg maturation in progressive as seen in the blowfly-Phorrnia reqins (Rasso and Fraenkel, 1954). Fog3 therefore, must be vital for egg 5ormstion in females of -A. fas~iculatus. Fed but unmated females, like mated but starvod females, did not lay eggs throughout their lifetime When they were dissected at death, masses of matur2 eggs were discov9red in their ovaries. Thus, copulatian seems a necessary stimulus to induce miposition. This observation had long been made in some insects such as the blowfly-Lucilis cuprina (Mackerras, 1933), the artichoke plume moth-Plstyptilia cardiudactyla (Bragg, 1970) and the yam moth-Dssyses ruqosells (Ihesgwam and Ezike, 1989). At death n9 eggs were rezoverd from the ovaries of fertile females maintained on any 9f t5e faod chips suggesting that, in nature, the s~eciesdepasited a11 her eggs in her life time. Population Suild-up of -A. fascizulatus was highest on csssava variety TMS 91934 and potato ships than the other fgod chips. This beetle prcbabLy. thrives better on suitable but safter substrates. Similar observatian wss made by Bitran --et al. (1978), where a higher number of the beetle-A.- fasciculatus wss rezorded £ram coffee, groundnut and maize than from beans and sunflgwer seeds. In the same manner, female beetles preferred
TMS 91934 and potato chips to other substrates for feeding and ovipastion whizh could also be attributed t~ their physizal properties as well as their nutrient quality -A. fasciculatus had earlier showed this preference behsviour 3s rep~rtedby G3nealves --et al. (1976), where the Seetles preferred groundnuts and coffee to maize and s,3+beans.
In the study of some population parameters, the net reproduztive rate and capacity f3r increase were highest in adult beeties maintained on TM3 91934.. Tnis implies that it will be easier and safer to handle the other
c3sssva varieties in terms 3f storage thanl.l-P~s' 91334,
The .generation time was shartest in adult beetles maintainod on potato chips while Ln5,0,~~~lgngest in beetles reared on potato chips too. These results are in no doubt attributable to the nutrient quality ~f potato chips as a substrste whi-h had esrlier been mentioned.
It will be most appropriate, theref~re,t~ breed the beetle Dn p~tatochips when there is need to multiply it for bi~logicalstudies sinze the rearing can be azhi5ved in a shorter time. parasitoids in the beetle-A.- fasziculatus had been reported by a number of auth~rs. These include Aasnteles araeceri bred from -A. fasciculatus (Wilkinson, 1928); upe elm us jsvae as a parasite of the beetle in the pods of Tephrosia
(Ferriere, 1940), two species of mites-Cheyletus sp. and
M~ni5ziellasp. preying on the eggs of -A. fasciculatus
(Cabal Conchs, 1956); and sn unidentified nematode ss parasite ~f eggs, larvse and pupae of the beel-te
The above reports on parssites are from natures, It is therefore surprising that parasites invaded the immature stsges in the present study since the tuber chips used were sterilized and covered up inside Petri-dishes.
The feeding stages of -A. fssciculstus cause varying degrees ~f damage to dried stored tuber chips. Since the highest l3ss of 29.8% occurred in cssssva chips, vsriety TM~91934, sust3ining 104.7 boetles while the least loss of 11.68, was resorded from cassava v2riety
NR 8212 with 22.1 beetles, losses in these sommodities seemed directly related to the number of adult beetles emerging from 3r present in the eomm~dity. This
3bservation is in line with the findings of Azodeh [I9861 and Okoronkwo [1986] who reported that losses in commodities sre significantly related to the insect population.
Since sterilized dry tuber =hips stored in polythene bags
[tied up1 lasted for 9 months and pxsibly more without being infested by -A. fascizulatus, handling and storage techniques play a major role in the control of infestation of stoied tuber chips.
There is reason to believe that the 2xtsnsiv.e dsmsge to the dried tuber chips during storage [pulverization] is aggravated by the long dur2tion of the larval stage [about
2/3 of the insect's developmental period from egg to sdulthood] coupled with the fact that adult beetles
[unlike their Lepidopteran c~unterwartslalso feed.
Badly damaged chips were neither fit for human consumption not f3r industrial uses. Such chips could only be used in feeding pigs [Flour miller - Personal communication]. RECOMMENDATION
In the last 20. years, at lesst, there hss been flourishing
lqsal trade in yam an3 cssssva tubers [abviously 13221
staples] between the producing centres of the ni3dle belt
af Nigeria snd the consuming populations, especially of
the South E2,stern States. For reasDns of ease of handling
and distribution, these tubers [cassava in psrticularl are
largely marketed 3s dry chips inside assorted bags. Whole
, 3rie3 tuber chips or their "flour" sre therefore a commDn
sight =n the open markets, market stores and the like in
these S~uthernStates. Because gf ?oar storage facilities
an3 conditions, snd the peo~le'slow rsting [rather erroneously]
for casssv3 =hips as foad item, losses [unqusntifie3]
inrjurred principally through the aztivi-ties of -A. fascizulstus
on dried tuber chips within the said trade zones csn now
be discribed as alarming an3 perhaps call for serious
attention. Bssed on the findings of the present study
and svailable ..Literature, the foll~wingrecommendations
are made ss a contribution to the effective management of -A. fasciculstus and other beetle pests of stored dry tuber chips. 1. Since infestati~nwith beetles commence3 during
the prazess of sun-drying of rsw tuber chips, it wguld
be &great advsntsge to dry products to very low
moisture rjqntznts [LO% and bel~wland sterilize
adequately [by hesting to about 100°C for about - - 111
1-2 hours] before storage.
2. sterilized cammercisl products should be securely tied up and stored in wholesome polythene bags rather than in synthetic sacks or jute bsgs [as is currently the prqcticel which sre essily perforated by these beetles. In~xpensivepolythene bags sre todsy msnufactured in lozal zottsge industrisl centres of this cguntry.
3. Bulk supply dealers should be educated on and encmrsged to maintsin clesn [hygienic] stores thrmgh among other measures, spraying walls, floor 2nd corners with sa$e and appropriate insecteides when necessary. REFERENCES
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A p~tentialnew pest of citrus in Florida
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Consum. Serv. Div. Plt Ind. Entom~l. Circ. No. 117,2pp. Appendix I
Standard deviation
The standard deviati~nof a set of N numbers X1, X2, X3,...... Xn is demonstrated by S and is def ined by
Where X reprasents the deviations of each of the numbers XI from the mean X. Thus S is the root mean square of the deviations from the mean 3r, as it is sometimes called, the root mean square deviati3n.
Appendix V. Analysis of variance for the longevity of adult unmated females reared on variars food sustrates 1 I I -- - I Smrce of Degree of Sum of Pkan squares Varisnce F V3riance F variation [svl freedom [%I squsre [ssl [Ms 1 [cslsulatedJ [Table] [p =0.05] Treatments 6 11835.486 1972.581 9.31 0
I I I Error ! 6 3 1 13348.8 1 211.8857 ! t
I I F-LSD = tx/2 [Error diff.] x Sj I I
e relationship between
Parameter Estimate Standard Error T-Value Pr~b.Level
Intercept 4.3243 20.8794 -0.255 0.80888
1 I I Linear Model : Y1= 3 + bx I
I 1 Correlation Cogfficient [r] = 0.43455 R-squsred = 18188%
I I 1 I 1 I IStsndar3 Error of Estimate = 13.333 Appendix IX. Regression analysis to determine the relationshipbetween I
temperature and 8 rate of larval development I I I I I 1 I I Parameter Estimate Standard Error I T.Vslue I Prob. Level I
I Interreot -2.19721 1.13398 -1.9376 0. b4806
I I I I ine ear~odgl 1 Y = a + bx
I Correlation !coefficient [r] j = 0.947825
R - Sauared =189.84% I I I I Standard Error of Estimate = 0.40897 I Appendix X: Regression analysis to determin&-the relatiKsKp I between Temperature and % rate of pupal development 1 Parameter Estimste Standard Error T. Value Prob. Level
Intercept -16.4145 4, 63985 -3.53772 0.03843
I Linear Model i Y = a + bx I I I Correlation cdefficiant [r]' = 0.97582 [ I I
1 1 I 1 1 3tsn3srd Error of Estimate = 1.673% t