ECOLOGICAL AND PHYSIOLOGICAL ASPECTS OF AESTIVATION-DIAPAUSE IN THE LARVAE OF TWO PYRALID STALK BORERS OF MAIZE IN KENYA
in mi •»> ••• - OOOO 0086 promotor:dr .J.d e Wilde,hoogleraa r inhe t dierkundig deelva nd e planteziektenkunde. Inn $z.o /i 3.si
P. SCHELTES
Ecological and physiological aspects of aestivation-diapause in the larvae of two Pyralid stalk borers of maize in Kenya
Proefschrift terverkrijgin g van de graad van doctor ind e landbouwwetenschappen, op gezag vand e rector magnificus, dr.H.C.va n der Plas, hoogleraar in de organische scheikunde, inhe t openbaar te verdedigen opwoensda g 6 September 1978 des namiddags tevie r uur ind e aula van deLandbouwhogeschoo l teWageningen .
BIBLIOTHCE*
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STEU.TNCEN
I Doord egrot everscheidenhei d ind eaar dva nd eperiodiek erusttoestan dva n insektene nd emechanisme ndi ehieraa ntengrondsla g liggeni selk eklassifikati e vand erusttoestand ,gebaseer d opextern eekologisch efaktore n (tliiller)o fo p internefysiologisch everanderinge nbinne nhe tinsek t (Mansingh)gebrekki ge n daardoorbetrekkelij kzinloos . MilllerH.J . (1970)Nov aAct aLeopoldin a35 ,1-27 . MansinghA . (1971)Can .Ent .103 ,983-1009 . Ditproefschrift .
II Hetverdwijne nva nd ekutikulair epigmentati eal skriteriu mvoo rd ediapauz e dientme tvoorzichtighei d teworde ngehanteerd . Ditproefschrift .
Ill Konklusiesal sdi eva nHiran obetreffend ed elarval egroe iva n Chilo suppressalis end e IV Dekonklusi eva nChippendal ee nRedd yda td eindukti eva ndiapauz e ind e "southwestern cornborer " Diatraea grandiosella een"extremel ytemperature - dependentprocess "is ,waarbi jfotoperiod eee nondergeschikt ero lspeelt ,berus t oponvoldoend egegevens . ChippendaleG.M .an dRedd yA.S .(1973 )J .Insec tPhysiol .19 ,1397-1408 . V Debewerin gva nUsu ada te ree nkausaa lverban dbestaa t tussenhe toptrede n vandiapauz e ind emai sstengelboorde r Busseola fusoa engelijktijdi gvoor - komendeveranderinge n ind esamenstellin gva ndien swaardplan ti szuive r spekulatief. UsuaE.J . (1973)Ent .exp .& appl . 16,322-328 . VI Het toekennenva nee nkeuringscertifikaa taa nbepaald efruitgewasse ndoo rd e + . NAK-B isgee nenkel egaranti evoo rd elevensvatbaarhei dva ndi egewasse nindie n zei nhe tnajaa ri npakkette nworde naangebode ne ni sdu smisleiden dvoo rd e konsumentent. + NAK-B NederlandseAlgemen eKeuringsdiens tvoo rBoomkwekerijgewassen . VII Dediskrepanti e tussend eautomatisch evermeldin gva nd ema ni nhe tpaspoor t vanzij nechtgenot ee nd eonmogelijkhei d voord ema nzij nechtgenot e inzij n paspoort tevermelde ni see nsymptoo mva nd eopgedronge nonafhankelijk ero l vand ema ni nd ehuidig emaatschappij . Paspoort instruktieNederlan d 1952,art .23 . VIII Doord esterk einvloe dva n"tribalism "o pd emaatschappelijk estruktuu rva n velederd ewerel d landen,worde nta lva nontwikkelingsprocesse nernsti g bemoeilijkt. IX Debezware nva nKenyas eautoriteite n tegenhe tdrage nva nd etraditionel ekledi j doord eMasa izij nonjuis te nleide nslecht sto tonnodig eirritatie . X VeleNederlander s tonenplotselin gee nbete rbegri pvoo rhe t levensritmeva n volkereni ntropisch egebiede n tijdensee nhittegol f dantijden snormaa li n Nederlandvoorkomend etemperaturen . Proefschriftva nP .Schelte s Ecological andphysiologica l aspectso faestivation-diapaus e inth elarva eo f twoPyrali dstal kborer s inKenya . Wageningen,6 Septembe r1978 . Contents 1 GENERAL INTRODUCTION 1 2 THE INCIDENCEO FAESTIVATION-DIAPAUS EA SRELATE DT O CLIMATE 3 2.1 Introduction 3 2.2 Literature 3 2.3 Materials andmethod s 8 2.3.1 Rearingmethod s 8 2.3.1 Criterion fordiapaus e 9 2.3.3 Fieldexperiment s 10 2.3.4 Effects ofphotoperio d andtemperatur e 11 2.4 Results 12 2.4.1 Drought resistance as criterion fordiapaus e 12 2.4.2 Field experiments 14 2.4.2.1 Climate during fieldexperiment s 14 2.4.2.2 Seasonal fluctuations in larval andpupa l populations 15 2.4.2.3 Seasonal incidence ofdiapaus e 15 2.4.3 Effects ofphotoperio d and temperature 20 2.5 Discussion 22 3 THETIMIN GO FTH EPERIO DO F DIAPAUSE INDUCTION;SOM EBEHAVIOURAL , PHYSIOLOGICALAN DMORPHOLOGICA L ASPECTSO FAESTIVATION-DIAPAUS E 26 3.1 Introduction 26 3.2 Literature 27 3.3 Materials andmethod s 30 3.3.1 General 30 3.3.2 Behavioural studies 30 3.3.3 Physiological studies 31 3.4 Results 32 3.4.1 Construction ofrestin g sitean d spinningbehaviou l 32 3.4.2 Feedingbehaviou r 33 3.4.3 Physiologyo fnon-diapaus elarva e 35 3.4.4 Physiologyo flarva eenterin gdiapaus e 38 3.4.5 Morphologicalchange si nlarva eenterin gdiapaus e 43 3.5 Discussion 46 THEINCIDENC EO FAESTIVATION-DIAPAUS EA SRELATE DT OTH ECONDITIO N OFTH EHOS TPLAN T (MAIZE) 51 4.1 Introduction 51 4.2 Literature 51 4.3 Materialsan dmethod s 53 4.3.1 Handlingo fsample s 53 4.3.2 Analysiso fste mmateria l 54 4.3.3 Consumptionan dutilizatio no fmaiz estem s 55 4.4 Results 55 4.4.1 Diapausean dstag eo fmaiz e 55 4.4.2 Diapausean dchemica lcompositio nmaiz estem s 57 4.4.3 Compositiono fth emaiz este mdurin git snorma l development 59 4.4.4 Consumptionan dutilizatio no fmaiz e 60 4.5 Discussion 61 EFFECTSO FNATURA LAN DARTIFICIA LFOO DO NTH EINDUCTIO NO F AESTIVATION-DIAPAUSE 67 5.1 Introduction 67 5.2 Literature 67 5.3 Materialsan dmethod s 69 5.3.1 Larvalmateria l 69 5.3.2 Experimentswit hmaiz e 69 5.3.3 Experimentswit hartifica ldiet s 70 5.3.4 Studieso nth ephysiologica lconditio no flarva e 72 5.4 Results 72 5.4.1 Responseso flarva et oage dmaiz eplant s 72 5.4.2 Sensitivityo flarva et oage dmaiz eplant s 75 5.4.3 Larvalgrowt han dpupatio no ndiet s 77 5.4.4 Pigmentationan dphysiolog yo flarva eo ndiet s 78 5.4.5 Sensitivityo flarva et odie t 80 5.5 Discussion 83 HORMONAL INVOLVEMENT INAESTIVATION-DIAPAUS E 86 6.1 Introduction 86 6.2 Literature 86 6.3 Materials andmethod s 87 6.3.1 Juvenile hormone titre 87 6.3.2 Head ligatures and injections with 0-ecdysone 88 6.3.3 Experiments with JH-analogues 88 6.4 Results 89 6.4.1 Juvenile hormone titre during diapause induction, maintenance and termination 89 6.4.2 Effects ofhea d ligatures and/or B-ecdysone on diapausing larvae 90 6.4.3 Effects of JHA onnon-diapaus e larvae 91 6.5 Discussion 94 SUMMARY 97 SAMENVATTING 100 ACKNOWLEDGEMENTS 103 REFERENCES 104 CURRICULUM VITAE 110 1 General introduction Stemborer sar ebein gconsidere da smajo rpest so fman yGraminea eal love r theworl d (JEPSON1954 ,METCAL Fan dFLIN T1967 ,HIL L 1975).Al limportan t graminaceouscrop ssuc ha smaize ,millet ,rice ,sorghu man dsugarcan e- ofte n thesubsistenc efoo dcro pi ndevelopin gcountrie s- ma yseriousl yb eaffected . Inth etemperat eregion srelativel yfe wimportan tste mborer sar eknown .Ver y notoriousar eth esouthwester ncor nbore r Diatraea gvandiosella andth eEuropea n cornbore r Ostvinia nubilalis, bothPyralidae .I nth esubtropic san dth etropic s stemborer sar emuc hmor eabundant .Well-know ndestructiv eexample sar efoun d amongth eNoctuida ee.g .th emaiz ebore r Busseola fusoa (maize,sorghum) ,th e pinkstal kbore r Sesamia oalamistis (maize,sorghum ,millet ,rice ,sugarcane) , andth epurpl este mbore r S. inferens (rice,sugarcane )an damon gth ePyralida e e.g.th espotte dstal kbore r Ch.Ho partellus (maize,sorghum ,millet ,sugarcane , rice),th ecoasta lstal kbore r C. oriahalooailiella (maize,sorghum ,millet , sugarcane),th eric este mbore r Chilo suppressalis (rice,maize) ,th esugarcan e stalkbore r Eldana saacharina (sugarcane,maize ,sorghum )an dsevera l Tryporyza spp. (rice)(HIL L1975) . Thelife-cycl ean ddamag eo fal lborer si sver ysimilar .Normall yegg sar e laido nth eundersurfac eo fyoun gleave so rbetwee nlea fsheath san dstems .Afte r hatchingth eyoun glarva efee dactivel yo nth etende rleave sbu ta ssoo na sthei r sizeincrease sthe ybor eint oth estems .I nyoun gplant slarva eattac kth e growingpoin tan dcaus es ocalle d 'deadhearts' .I nolde rplant sth ecaterpillar s boreint oth emai nstem ,whic hsubsequentl yi shollowe dou tove ra considerabl e length.Plant sthu saffecte dhav ea poo rgrowth ,a reduce dyiel dan dar emor e susceptiblet owin ddamag ean dsecundar yinfections .Smal lan dwea kplant s usuallysuffe rmor efro mbore rattac ktha nhealth yplants .I ntropica lEas tAfric a wherecrop sar eregularl ygrow nunde radvers econdition s (unpredictablerainfall , poorsoils )thi sha softe nbee ndemonstrate d (COAKER1956 ,MATHE Z 1972,HIL L 1975). Insuc hcase sste mbore rdamag ema yb edisastrous .Whe nlarva ear efull ygrown , theystar tpreparin gfo rpupatio nb ycuttin ga nexi thol ei nth este mt oenabl e theemergin gmoth s toescape .Th e life cyclema yb e continuous inarea swher e suitable conditions forgrowt h ofth ehos tplan t arepermanentl ypresent .Usuall y however thecycl e isinterrupte db y acol do rdr y seasondurin gwhic hplan t growth isimpossible .Th e larvae thenente r diapause (called Ihibernation'whe n occurring during acol d season and 'aestivation'whe n inth edr y season) inside the old stems orstubble .O nretur no f favourable conditions,pupa edevelo p andth e emerging moths oviposit onth enewl yplante dhos tplants . Chemical control ofste mborer sha s oftenprove d tob e ratherunsuccesful . Best results are obtained inth eearl y season against theyoun g larvaewhic hhav e justhatche d from theegg s laidb ymoth swhic hha ddevelope d from diapausing larvae.Olde r larvaehav epenetrate d the stalks inwhic h they arewel l protected against insecticides.Th e durationo flarva l development,varie swidel ywithi n one population ofste mborer s and after themor e or lesssynchronou s development of the 1stgeneratio n attacking the crops,al l developmental stages ofborer s can soonb e foundwithi n one field.Fro mtha t time chemical control,unles s applied very regularly, is little effective (SCHMUTTERER 1969,HIL L 1975). Cultural controlo fste mborer s ismos t frequently aimed ata destructio n of thediapausin g larvae fromwhic h thenex t crop infestationoriginates .Uprooting , burning,ploughin g and flooding ofth eol d stems arewidel y adoptedmethods ,bu t only effectivewhe n applied ata large scale. Indevelopin g countriesman y individual farmers cultivate a largenumbe r ofsmal lplot s and such acommo n approach istherefor e difficult toaccomplish .Thi s isespeciall y sowhe nol d stems areutilize d e.g. inTanzani amaiz e stemswer e found tob euse d asbuildin g material (SWAINE 1957)an d inKeny a Iobserve d cutmaiz e stems asboundarie s of terraces onslopes . Iti s commonpractic e toabando nmaiz ean d sorghumplant s in the field afterharves t inKenya . Ifstem s arecu t (mainly for fodder)stubbl e is normally leftbehind .Al l these culturalpractice s increase the chances of survival fordiapausin g larvaedurin g thedr yseason . Aestivation-diapause ofste mborer s has oftenbee n referred to asa crucial link inth e life-cyclewhic h enables the insect toovercom e theunfavourabl e hot anddr y season (SCHMUTTERER 1969,HIL L 1975). Nonetheless,thusfa r almost all attentionha sbee n focused on thephas e ofth e insectwhic h isdirectl y doingth e damage andhardl y any toth ephas e fromwhic h thisdamag e initially results.Th e aimo fthi s researchwa s to fill this omission. Investigationswer e carriedou t on the factorswhic h induce,maintai n and terminate aestivation-diapause intw o tropical stemborers .A bette rknowledg e ofth e factors determining their seasonal activityma yultimatel y lead toa bette r controlo fthes e destructive insects* 2 The incidence of aestivation-diapause as related to climate 2.1 INTRODUCTION Diapause (hibernation)ha sbee nthoroughl ystudie dfo ra larg enumbe ro f insectsi nth etemperat eregion s (LEES1955 ,1968 ,DANILEVSKI I1961 ,BEC K 1968). Incontras tver ylittl eattentio nha sfocuse do naestivation-diapaus eo fth e tropics.Th epresen tresearc hexamine sou rknowledg eo fth eclimatologica l factor(s)tha tma yinduc eaestivation-diapaus e in2 specie so fPyralida ei nKenya . Theexperimenta lspotte dstal kbore r Chilo partellus (Swinhoe)an dth ecoasta l stalkbore r Chilo orichalaoailiella (Strand),ar emajo rpest so fmaiz ei nEas t Africa.A nunderstandin go fthi scrucia llin ki nth elif ecycl eo fthes einsect s maylea dt obette rtechnique so fcontro li nth efuture . Atth estar to fthi sresearc hi nKenya ,littl emor ewa sknow ntha nth e existanceo fa larva lrestin gstag ei nol dmatur ean dofte ndr ystalk so r stubbleo fth ehos tplan tlef ti nth efiel dafte rth egrowin gseaso n (NYE1960 , SCHMUTTERER1969 ,MATHE Z 1972).Hardl yan yinformatio ni savailabl eo nth e seasonalincidenc eo fth eaestivation-diapaus eo ro nth eenvironmenta lcondition s thatinduce sth earreste ddevelopment .I nthi spape rw ewil lconcentrat eo nth e roleo fclimat efactor si nth einductio no fdiapause .Th erol eo fth ehos tplan t willb edeal twit hlate r (chapter4) . 2.2 LITERATURE Criterion for diapause Themos tfrequentl yuse dcriterio nfo rlarva ldiapaus e ofLepidopter ai sth efailur eo fth ematur elarv at opupat ewithi na n arbitrarilydetermine dlengt ho ftim eafte rcessatio no ffeeding .Th ecritica l lengtho ftim esignificantl yexceed sth enorma lperio drequire dfo rpupation .Th e diapauseo flarva eo fth eEuropea ncor nbore r Ostrinia nubilalis (MUTCHMORan d BECKEL 1959,BEC Kan dHANE C 1960),th epin kbollwor m Peotinophora gossypiella (ADKISSONe tal .1963 ,KHALIF Ae tal . 1975),th eric este mbore r Chilo suppres- ealis (FUKAYA1967 )an dth esouthwester ncor nbore r Diatraea grandiosella (CHIPPENDALEan dREDD Y1973 )wa sdetermine di nthi smanner .Larva ear eusually - keptunde rdr yconditions ,withou tfood ,i nvial swit hmois tabsorben tfilter - paper.Sometime sthe yar eprovide dwit hth enatura lmateria li nwhic hdiapaus e takesplac ee.g .EL-SAYE Dan dRUSTO M (1960)an dHASSANEI Nan dGALA L(1969 ) suppliedfiel dcollecte dlarva eo f P. gossypiella withfragment so fcotto nfibr e topreven tcannibalis man dt ofacilitat eth econstructio no fcocoons .Suc hfibre s obviouslyca nno tb econsidere da sadequat efood .Th eus eo fthi smetho dimplie s thatdiapausin glarva ear ecapabl eo fsurvivin gstarvatio nan ddrough t (without pupating).Th equalit yo fdiapausin glarva et oresis tstarvatio nca nb eattribute d toth eusuall yhig hconten to fmetaboli creserve san dt oth ever yslo wexpenditur e thereofbecaus eo fth elo woveral lactivity .I nth etropic sresistanc et odesicca tioni so fgrea timportanc esinc eaestivatin glarva ear eusuall yexpose dt o extremelydr yconditions .Soli ddat ao nthi showeve rar erare .USU A (1974)demon stratedtha ta tal lrelativ ehumiditie sth epercentag eweigh tlos sb ynon-dia - pausinglarva eo fth emaiz este mbore r Busseola fusaa isa tleas tdoubl etha to f diapausinglarvae .Hi sexperiment swer ecarrie dou tnea rtherma ldeat hpoint .Bu t evena ta mor enorma ltemperatur eo f23° CCHIPPENDAL Ean dREDD Y (1972)foun dtha t bothfiel dan dlaborator ycollecte dmatur elarva eo f D. grandiosella (originally atropica linsect )whe nplace di nvial swit honl ymois tabsorben tpape rhav ea highrat eo fweigh tlos sunti lthe yecdys et oa nunspotte dfor massociate dwit h diapause.Thereafte rweigh tlos si sabou ttwic ea slow .Th eincrease ddrough t resistancema ywel lb ecause db ychange si nth erespirator y (intermittentopenin g ofth espiracles )a swel la sth ecuticula r (reducedpermeability )transpiratio n asha sbee nfoun dfo rman yothe rinsect s (LEES1956 ,BARTON-BROWN E1964 , CLOUDSLEY- THOMPSO N 1975). Fieldcollecte dlarva ehav eno talway sbee nteste dfo rdiapaus ei nth e absenceo ffood .KATIYA Ran dLON G (1961)provide dfiel dlarvd eo fth esugarcan e borer Diatraea saooharalis withpiece so fyoun gmaiz estem sdurin gth eperio do f (winter)diapaus edeterminatio nan dth esam emetho dwa sadopte db yUSU A(1970 , 1973)fo r B. fusaa toinvestigat eth eincidenc eo faestivation .I nbot hcase s larvaedi dactivel yfee do nth emaize ,althoug hamon gdiapausin glarva eth e feedingrat ewa sdistinctl ylower . ManyLepidopter alarva einhabitin gth etropic so ro ftropica lorigi noffe r -nex tt oth efailur et opupat ean dth edrough tresistanc e- a thir dwidel yuse d criterionfo rdiapause :a tth ebeginnin go fdiapaus ethe yloos eth ecuticula r pigmentationo fthei rpinnacul ian dtur nint oa nunspotte dmorph .Suc ha transi tionha sbee nobserve dfo r Diatraea lineolata (HYNES1942 ,KEVA N 1944), Sairpophaga (= Tryporyza) innotata (VANDE RGOO T1925 ,ROTHSCHIL D 1971), Coniesta ignefusalis (HARRIS1962) , B. fusaa (HARRIS1962 ,USU A 1970), Chilo partellus (GONCALVES1970 ,MATHE Z 1972,DELOBE L 1975b), Chilo orichalcociliella (MATHEZ1972 ,DELOBE L 1975a), D. saccharalis (KATIYARan dLON G1960 )an d D. grandiosella (CHIPPENDALEan dREDD Y 1972). Climatic factors inducing diapause Diapausei nth etemperat ean dsubtropica l climatesi sprimaril yinduce db yshor tday san dlo wtemperatures .Generall yth e criticaldaylengt hi sdependen to nth elatitud ewher eth einsec ti sfoun dan dth e incidenceo fdiapaus ei ninversel yproportiona lt oth eprevailin gtemperatur e (BECK1968) .Example so fborer sar eth eric este mbore r Chilo suppressalis (INOUYEan dKAMAN O1957 ,KISHIN O1969 )an dth eEuropea ncor nbore r Ostrinia nubilalis (MUTCHMORan dBECKE L1959 ,BEC Kan dHANE C1960 ,SKOPI Kan dBOWE N 1976). KATIYARan dLON G (1961)workin gwit hth esugarcan ebore r Diatraea saccharalis in Louisiana (USA)als oindirectl ysuggeste dtha tdiapaus ei nth elarva ei sinduce d byshor tphotoperiod ssinc epupatio nn olonge roccur sfro mOctobe r (duringwhic h monthth etemperatur ei sstil l"wel labov eth etreshol dfo rpupation" )an dsinc e diapausinglarva ewer ecollecte dfro mstem swhic hwer e"gree nan dsucculen tan d appearedt oconstitut ea satisfactor yfoo dsupply" .I nspit eo fthi sth eauthor s didno texclud ea foo deffec taltogether .I tshoul db ementione dher etha ti nth e tropics D. saccharalis wasno tfoun dt odiapaus e (KEVAN 1942).Anothe rinsec ti n thesout h ofth eU.S .o fwhic hdiapaus ei scontrolle dphotoperiodicall y isth e pinkbollwor m Pectinophora gossypiella. Hightemperatur eca nlargel ynullif yth e shortda yeffects ,whil eals ofoo d (ahig hfa tcontent )ha sa diapaus einducin g effectunde rshor tday s (ADKISSONe tal.1963 ,MENAKE Ran dGROS S1965 ,ANKERSMI T andADKISSO N 1967).Althoug hlarva eo fth esouthwester ncor nbore r Diatraea grandiosella -a noriginall ytropica linsec ttha trecentl ymigrate dint oth e southernU S- ente rdiapaus eunde rth einfluenc eo ftemperature sa shig ha s23 - 25°Can da shor tphotoperio d (12L:12D),itwa ssuggeste db yth eauthor s (CHIPPEN DALEan dREDD Y1973 )tha ttemperatur ewa sth emor eimportan tfacto ro fth etwo . Theirevidenc ewa sbase do nth eoverridin gimportanc eo ftemperatur efo rth e inductiono fdiapaus e (withoutrespec tt ophotoperio dn odiapaus ea tconstan t temperatureso f27-3 0C an d 100%diapaus ea t2 0C) ,an do nth eobservatio ntha t diapausei nth efiel di sinduce dwhe nnigh ttemperature sstar tfallin gbelo w 20C wherea sth edaylengt hi sstil ldiapaus eaverting .N ophotoperiodi ceffec t couldb erelate dt odevelopmen to fth elesse rcornstal kbore r Elasmopalpus lignosellus. Moderatelylo wtemperature ssignificantl yprolon gth edevelopmen t butthi sretardatio ncoul daccordin gt oHOLLOWA Yan dSMIT H (1976)no tb econsider eda sdiapause . Atlowe rlatitude sseason sdepen dles supo nchange si ndaylength .Tempera turean dothe rfactor se.g .moistur e (rain)an dchange si nth ecompositio no f thehost-plan twhic har eo fmino rimportanc ei nth etemperat eregion sten dt o playa majo rrol ei nth etropic s (chapter4) .Bu teve na tthes elatitude sphoto - periodca nb einvolved .Thi si sbes texamplifie db y Nomadaoris septemfasdata whichrespond st ophotoperio di na nare a (Tanzania)wher eth edifferenc ebetwee n thelonges tan dth eshortes tda yi sonl y 1hr .(NORRI S1965) .Howeve rothe r factorsar ereporte dt oinduc ediapaus eo rquiescenc emor efrequently . Pupaldiapaus eo fth eSuda nbollwor m Diparopsis watersi isi nCameroo n primarilydependen to ntemperature ;alternatin glo wnocturna ltemperature san d highdiurna ltemperature sdurin gth elarva llif einduc ediapaus e(JACQUEMAR D 1976).GALICHE T (1964)cam et oth esam econclusio ni nCha dbu th ethough ttha t theperio do ffluctuatin gtemperature sneede dt ob efollowe db ya perio do fver y hightemperature s (38C durin g6 hrs/day )afte rpupation .H eals omentione dtha t photoperiodi sno trelate dt oth einductio no fdiapause .Th eincidenc eo fdia pausei nlarva eo fth ewhit eric ebore r Rupela albinella inSurina mi snormall y verylo wthroughou tth eyea rbu tsuddenl yrise st o50 %o fth elarva lpopulatio n duringa perio do frelativel yhig htemperatures .Compare dt oth esam eperio do f otheryears ,neithe rfood ,dr yperio dno rrainfal lcoul db eindicate da sth e agentcausin gdiapause ;agein go fth ehos tplan tstimulate sdiapaus e (HUMMELEN 1974). InEgypt ,larva ldiapaus eo fth epin kbollwor m Peatinophora gossypiella seemst ob eprimaril yinitiate db ylo wtemperatures .Agai ncompositio no fth e food (cottonboll )whic hchange stoward sth een do fth eseaso nplay sa nim portantadditiona lrol e (EL-SAYEDan dRUSTC M1960 ,HASSANEI Nan dGALA L 1969). Resultso fPREVET T (1971)ar ever ysimilar :th eIndia nmeal-mot h Plodia inter- punatella collected fromPretori a (SouthAfrica )entere da pre-pupa ldia pausea ttemperature sbelo w2 0C .Tim erequire dfo rlarva ldevelopmen ta t17. 5C ismor etha n1 4x longe rcompare dt otim ea t30° Cbu tlarva efro ma strai n collectedi nKano ,Norther nNigeria ,develo ponl y3. 5x slowe ra tth elowes t temperature.PREVET Tconsidere dth edifferenc ei ndevelopmenta ltim ea tth etw o temperaturesa snorma lfo rth eNigeria nstrain .H esuggeste dtha tth ediapaus e factori sbre dou ti nstrain sinhabitin gwar mclimates .Th einfluenc eo fphoto periodwa sno tstudie dfo r Plodia norfo r Peatinophora althoughi nbot hcase s thelatitude s (South-Africa,Egypt )ar esuc htha ta neffec tmigh tb eexpected . Thespotte dstal kbore r Chilo partellus hasa distributio ni nsouther n • Asiafro mAfghanista ni nth ewes tt oThailan di nth eeas t(HIL L1975 )an di nEas t Africafro mSuda ni nth enort h (SCHMUTTERER1969 )t oMozambiqu e (GONCALVES1970 ) andMadagasca r (DELOBEL1975b )i nth esout h Theenvironmenta lstimul iwhic h leadt opreparation sfo rdiapaus eo fth elarva ear ehoweve rquit edifferent .I n NorthIndi alarva ed ono tpupat ebelo w13° C (BUTANI 1955).Als oobservation so f otherscientist sindicat etha tth ediapaus eo f C. partellus inSout hAsi ai s governedb ylo wtemperature s (PANTan dKALOD E1964 ,KHA Nan dKHA N1968 ,MOI Zan d QURESHI 1969). InEas tAfric ahoweve rw efin dles sagreement .I ti sno teve n clearwhethe rdiapaus eexist si nal lareas .I nMozambiqu efo rexample , C. partel lus developscontinuousl ybu tha s" alo wactivity "fro mMa yt oSeptembe r (GONCALVES1970) . INGRAM (1958)eve nspecificall ymentione dth eabsenc eo fa restingstag ei nUganda ,bu tals oh estate dtha t"th edevelopmen ti sprobabl y sloweddow ni nth edr yseason" .Whe nlate rNY E (1960)di dfin da fe waestivatin g larvaethi sincidenc ewa sattribute dt oth eextremel ydr yhos tplan ti nwhic h theywer elocated .Anothe rexampl eo fa continuou slife-cycl eth ewhol eyea r aroundwa sfoun di nSuda n"durin gth erain yseaso no runde rfavourabl econdi tionsi nirrigate dareas" ;larva ldiapaus eoccur si narea swit ha conspicuou s dryo rdea dseaso n (SCHMUTTERER 1969).Th emor esever edr yseaso ni nth eLak e Districto fTanzani awa shel dresponsibl efo rth epresenc eo faestivatin glarva e (NYE1960) .Fro mthes eexample si tappear stha tth ediapaus eo f C. partellus is afacultativ eon eonl yemergin gwhe nth eenvironmenta lcondition s- i nwhic h moistureseem st ob ecrucia l- deteriorate .Thi sma ywel lals ob eth ecas ei n Kenyawher eaestivatin glarva ear efoun dunde rsimila rcircumstance s (SCHELTES 1976).Th esituatio nseem st ob esomewha tdifferen ti nMadagasca rwher eagai n relativelylo wtemperature sar ethough tt ob eo fprim eimportanc ei nth edia pauseo f C. oriohaloooiliella (DELOBEL1975a )an d C. partellus (DELOBEL 1975b). Butagai nnex tt otemperatur eDELOBE Lmentione dimpoverishmen to ffood ,drough t andeve ndaylengt ha sfactor swhic hpossibl ystimulat eth eretarde dlarva l development. InNigeri aUSU A (1968,1973 )studie dth etemperatur eeffec to nth elarva e ofth emaiz este mbore r Busseola fusca. Therat eo flarva ldevelopmen twa s fastesta t28-30°C .Highe rtemperature s (32°C)wer elethal ,lowe rtemperature s (23°C)resulte di ndelaye dgrowt hwhic hhoweve rwa sno tregarde da sdiapaus eb y USUA.Th eonse to fdiapaus ewa sshow nt ob eprimaril yinduce db yth estat eo f maturityo fth ehos tplant .Earlie rSWAIN E (1957)an dSMITHER S (1959)ha d suggesteda simila rrelatio nfo rth esam einsec ti nTanzani aan dsouther n Rhodesiarespectively .They ,howeve rpai dmai nattentio nt oth emoistur econten t ofth eplant .Importan tevidenc et od os ocam efro mobservation stha t B. fusoa continuest odevelo pi nirrigate dmaiz efield sgrow nou to fseaso n (andi n tillerso fwil dgrasse san dsorghu mcontainin grelativel ymuc hwater )wherea s 7 thedevelopmen to fth elarva ei nnon-irrigate dfield sdurin gth edr yseaso n ceases.Als ofo rothe rtropica lste mbore rlarva ediapaus ewa sthough tt ob e primarilyinduce db yth ehos tplant :e.g . Tryporyza innotata (VANDE RGOO T 1925), T. inaertulas (ROTHSCHILD 1971), D. lineolata (HYNES1942 ,KEVA N1944) . Furtherdetail so nth efoo dconditio ni nrelatio nt odiapaus ewil lb epresente d inchapter s4 an d5 . 2.3 MATERIALSAN DMETHOD S 2.3.1 Rearing methods Thecolon ywa sstarte dwit hlarva ecollecte dfro mmaiz efield si nth e CoastalProvinc enea rKikambala ,Keny a (about4 °sout ho fth eEquator) .Althoug h twodifferen tspecie so f Chilo [C. partellus and C. oriehaleooiliella) occuri n thisarea ,onl y C. partellus wasreare d inth elaboratory .Thi sspecie si sno t onlyth emor eimportan ton eo fth etw oi nEas tAfric abu ti sals oa majo rpes t inSout hAsi awher e C. oriahalaooiliella isabsen t (HILL1975) .Larva ewer e rearedo na wheat-ger mdie t (afterCHATTERJ Ie tal . 1968)whic hwa sslightl y modifiedt oobtai nbette rmicrobia lcontrol .Th ecompositio no fth edie ti s giveni ntabl e1 . Within2 4hr so fhatchin gegg swer etransferre dt oa corke dglas stub e(dia meter2. 5cm ,lengt h7. 5cm )tha to nth ebotto mcontaine dabou t1 5m ldie twhic h wasslightl yloosene dfro mth etub ewal lwit ha needle .I nth efiel dnewl yhatche d Table1 Compositiono fth eartificia ldie tfo rrearin g Chilo partellus component weight (8) volume (ml) wheat germ 15.00 vitamin-free casein 17.50 glucose 11.50 Wessons'salt + 5.00 cellulose 2.50 vitamin fortificationmixtur e (Vanderzant)+ 7.00 ascorbic acid 1.70 aureomycin 0.18 methyl para hydroxybenzoate 0.75 agar 12.50 KOH AM 2.50 formaldehyde 10% 2.00 water 450.00 +Obtaine d fromNutritiona lBiochemica lCorporation ,Cleveland ,Ohio . larvae tendt ob egregariou swhil efeedin gi nth ehumi d environmento fyoun g rolled leaves.Th eminut e spacebetwee nth etub ewal lan dth edie tprove dt ob e an idealplac e foryoun g larvae.T opreven t larvaefro mcrawlin garoun di nth e tubewithou treachin gth ediet ,th etube swer eplace dupsid edow ntoward sa wea k light source (theearl y larval instarsar epositivel yphototropi can dnegativel y geotropic).Th e corkscoverin gth etube swer eprovide dwit ha hol ean dwer e lined withfin e stainless steelgauz et opreven tescape . Third instar larvaewer e transferredwit ha fin ebrus ht oa laye ro f1 cm dieti nhard-plasti cboxe s (11.5x 17. 5x 4 cm )wit hscreene d holes,wher e they stayed tillpupation .Th e dietwa schange d twicea week .Pupa ecollecte d fromth e dietwer epu to na tra ycontainin gmois t cottonwoo l andplace di na cylindrica l cage (diameter 15cm ,lengt h3 0cm )mad e froma plasti cdrain-pip ean dcovere d witha musli ncloth .Th ewall so fthi scag ewer e linedwit hcrease dwax-pape rt o provide suitableovipositio nsite sfo remergin gmoths .Eg gmasse swer ecu tou t daily fromth ewax-pape ran dtransferre d intoclose dplasti cboxe s containing moist cottonwoo lt omaintai nhig hhumidity .Al ltube san dboxe suse d forrearin g were soakedovernigh ti na 1 1sodiu mhypochlorit e solutionbefor euse .Th einsect - arywa smaintaine da ta temperatur eo f2 7+ 1.5°C,a relativ ehumidit ybetwee n 70an d8S' »an da 12L :12 Dphotoperiod .Rearin go f C. partellus inthi swa ywa s carriedou twithou t interruptiondurin g fiveconsecutiv eyear so rabou t4 0genera tions.Occasionall y fresh larvae fromth efiel dwer eadde dt oth einsectary-stock , but thiswa sdon eonl yt oreduc e thepossibilitie so fa ninadverten t selection thatmigh tmak e comparisonwit h thenatura l fieldpopulatio nunreliable . 2.3.2 Criterion for diapause Experimentswer eundertake nt oinvestigat e thepossibilitie st ous eth e "failuret opupat ecriterion "fo rdiapaus eo f Chilo partellus (see2.2) .Whe n aestivating larvaear esupplie dwit hfres h food (dieto rmaize )diapaus ei s rapidly terminated (unpublished observations).Th eus eo fdr yfoo do rn ofoo da t all (asdon e formos t insects)ma yhoweve rb eequall yunreliable .I tha softe n beensuggeste d thatdr yfoo d inducesaestivation-diapaus ei nste mborer s (HYNES 1942,KEVA N1944 ,SWAIN E 1957,WITHER S 1959,NY E1960) .Thi shypothesi s first neededt ob etested .W etherefor ecompare dth esurviva lan dth e lossi nbod y weightunde rdr ycondition so f5 0aestivatin g larvaean d5 0non-aestivatin g larvae.Th e aestivating larvaewer e collected froma maiz e fieldnea r Kikambala threeday sbefor eth e experimentwa s started.Judge d fromth epresenc eo f exclusively unspotted larvae andn opupa e overa perio do fmor e than2 months these larvaecoul dsafel yb eregarde da saestivating .Non-aestivatin g larvae,obtaine d from the ICIPEinsectary ,wer e2 0day sol dan di nth eearl y6t h instar (normallymale shav esix ,female s sevenlarva l instars). Sincelarva e regularlyhav et ob eobserve dt odetermin e their survivalth eeffec to fdisturbanc e (handling andremova lo fcocoon )wa sinclude di nthes e experiments.Thi swa s doneb ysubdividin gth e5 0aestivatin gan dnon-aestivatin g larvae intogroup so f 25larva eeach .Th eindividual so fon egrou pwer epu t intocorke d glasstube s (2.5x 7. 5an) . Larvaewer e takenfro m their tubetwic ea wee kan dthei r eventual cocoonwa sremoved .Th elarva ewhic hremaine dundisturbe d throughout theexperimen t were placed insmal l (1.5x 0. 5cm )cylinder smad efro m stainless steel small-meshgauze .Thes e larvaewer eweighe ddirectl y insidethei rcylinder san d survivalwa schecke db yobservin gmovements .Whe na ver y thickcocoo nmad e this observationimpossible ,a tin ywindo wwa smad ewit ha fin eneedle . Fieldcollecte d larvaewer eroutinel y suppliedwit hthei rnatura l "diapause environment",i.e .piece so fdr ymaiz e stemscontainin g 10-20%o fwater ,whe nth e presenceo fdiapaus ewa s investigated. Inorde rt ofin d thecritica l lengtho f timewhic ha larv aha st oexcee dbefor ei tca nb ecalle ddiapausin gw edetermine d deathan dpupatio no fnon-diapaus e larvaeo fdifferen tage s (at least5 0larva e ineac hag e group)i ndr ymaize .Fiel dcollecte d larvaesurvivin gi ndr ymaiz efo r a longerperio d than95 1non-diapausin g larvaed ounde rth esam econdition swer e consideredt odiapause .Thi s criterioni si nfac tbase do nth ecapacit yo fa n aestivating larvat osurviv edr yconditions .I nth efollowin gtex tan dfigure sw e will thereforerefe rt odorman t larvaefo rwhic hth e aestivationwa s established thiswa ya st o"larva eresistan tt odrought" .Thi si ncontras tt olarva efo rwhic h the losso fth e cuticularpigmentatio ni suse da scriterio nfo raestivatio n(se e 2.2). Thesediapausin g larvaewil lb ecalle d "unspotted,larvae" . All experimentsmentione dabov ewer ecarrie dou ti na constan t temperature room (25.0+ _1. 0C )wher ea relativ ehumidit yo f70-80 1an da photoperio do f 12L/12Dwa smaintained . 2.3.3 Field experiments Experimental fields Fieldresearc hwa s carried outa tth eCoas tAgricultura l Research Stationi nKikambala ,Coas t Province,Kenya .Th eexperimenta l fields fromwhic h sampleswer eobtaine dwer e sized 1000-2000m {\-\ acre)an dwer e plantedwit hmaiz e (Coast Composite). Sampleswer e takenfro mmaiz egrow nunde r twodifferen tconditions :a .maiz egrow ndurin gth ewe t season (April-August/ 10 September);Thes eplot swer esubjec tt oth enatura lweathe rconditions ,b .maiz e growndurin gth edr yseaso n (December/January-March/April);field swer eirrigate d twj.cea wee ka sindicate di nth eexperiment sconcerned . Sampling Sampleso flarva ean dpupa ewer ecollecte do nregula rweekl yintervals . Sampleswer ecollecte db yuprootin gon emaiz eplan tafte ra fixe dnumbe ro fstep s (dependingo nth enumbe ro fplant spresen ti nth efield )whe ngoin gthroug hth e rowso fplants .Sampl esiz ealway sconsiste do fa tleas t10 0stems/field .Stem s weredissecte dimmediatel yafte rcollectin gan dth enumbe ro flarva ean dpupa ei n eachste mwa srecorded .Usuall ywithi nth esam eda ylarva e (placedinsid emaiz e stemsfro mth esample dfield )an dpupa ewer esen tt oNairob ib ytaxi-cab . Observations Temperature,relativ ehumidit yan drainfal lwer erecorde ddail ya t aweathe rstatio nsituate di na nope nfiel dnex tt oth eexperimenta lfields .O n theda yo fsamplin gth egrowt hstag ean dth econditio no fth emaiz eplan twa s described.Th erol eo fth eplan ti nth einductio no fdiapaus ewil lb edescribe d later (chapter4 + 5).Th eanalysi so fth elarva lmateria l (ofwhic hi nthi schap ter onlyth ecuticula rpigmentatio nan dth eresistanc et odrough tar ementioned , buti nth enex tchapte r alsosom ephysiologica lcharacteristics )normall ytoo k placea tth eICIP Elaboratorie si nNairob iwithi n3 day safte rsampl ecollection . Thefigure so nth eseasona lchange si npopulatio nlevel san do nth eincidenc eo f aestivationwer ecombine dfo rth etw ospecie s Chilo partellus and Chilo oriahalaoailiella. Thisha dt ob edon ebecaus eth elarva eca nonl yb e distinguishedo nth ebas eo fdifference si nth epatter no fth ecuticula rspot s (MATHEZ1972 )whic hgraduall ydisappea ra sth elarva eente rdiapause .N o behaviouralo rothe rdifference srelate dt odiapaus ecoul db edetecte dbetwee n thetw ospecies . Forth edeterminatio no faestivation-diapaus eonl ylarva ewer euse dwhic hha d atleas treache dth efift hinsta r (determinedb yth esiz eo fth ehea dcapsule) . 2. 3. 4 Effects of photoperiod and temperature Thedevelopmen to flarva eobtaine dfro mth einsectar ywa schecke dunde r differentphotoperiodi can dtemperatur eregimes ,comparabl et oth enatura l environmenti nwhic hlarva elive . Todetermin eth eeffec to fphotoperio dthre egroup so f10 01s tinsta rlarva e eachwer esubjecte dt ophotoperiod so f 12j,1 2an d11 Jhr spe rda yrespectivel y ata temperatur eo f25°C .Foo dwa salway schange ddurin gth ephotophase . 11 Temperatureeffect so n1st ,3r dan d5t hinsta rlarva ewer eobserve dunde r a6 h r (>2 5C) : 18h r (25°C)thermoperiod .Th eteste dtemperature sdurin gth e 6h rthermoperio dwer e25 ,30 ,33 ,3 5an d37°C .Th ehig htemperature salway s coincidedwit hth ebeginnin go fth ephotophas eo fth ephotoperio dwhic hi n theseexperiment swa skep ta t12L:12D .Eac hexperimen twa sstarte dwit h 100-150 1st,50-6 03r do r35-5 05t hinsta rlarvae . Timerequire dfo rpupatio nwa srecorde dfo reac hexperiment .Experiment s werecontinue dunti l allsurvivin glarva eha dpupated .Larva edyin gdurin gth e observationperio dwer eno ttake nint oaccount . 2.4 RESULTS 2.4.1 Drought resistance as criterion for diapause Thesuitabilit yo fdrough tresistanc ea sa criterio nfo raestivation-dia pausewa sinvestigated .Experiment swer ecarrie dou tt ostud ysurviva lan dlos s ofbod yweigh to faestivatin gan dnon-aestivatin glarva eunde rdr ycondition s andt oevaluat eth eeffect so fdisturbanc eo nth elarvae . Fig.1 show stha t3 0day safte rth eexperimen twa sstarte dalmos tn onon - diapausinglarva eha dsurvive dwherea s60 1o f theundisturbe ddiapausin glarva e " 100 i DIARAUSING LARVAE UNDISTURBED DIARAUSING LARVAE DISTURBED 2-WEEK • NON DIARAUSING LARVAE UNDISTURBED NON DIAPAUSING LARVAE DISTURBED 2* WEEK Fig.l.Effect so fdrynes s anddisturbanc eo nth esur vivalo fdiapausin gan dnon - diapausinglarva eo f Ckilo partellus. Eachgrou pcon tained5 0larva ewhe nth e TIME AFTER START EXPERIMENT ( DAYS I experimentwa sstarted . 12 100 >DIARAUSIN G LARVAE UNDISTURBED . DIARAUSING LARVAE DISTURBED 2" WEEK >NO N DIARAUSING LARVAE UNDISTURBED . NON DIARAUSING LARVAE DISTURBED 2«WEEK Fig.2.Effect so fdrynes s anddisturbanc eo nth elos s ofbod yweigh t(mea n +_S.E. ) ofdiapausin gan dnon-dia - pausinglarva eo f Chilo partellus. Eachgrou pcon tained5 0larva ewhe nth e TIME AFTER START EXPERIMENT ( DAYS I experimentwa sstarted . werestil lalive .Disturbanc ereduce dsurviva lo fbot htype so flarvae .Th e effectwa showeve rmor eobviou si naestivatin glarvae ,especiall yafte r3 0days . By9 0day sal ldiapausin glarva etha tha dbee ndisturbe dtwic ea wee kdied .B y contrastabou tSO Io fth eundisturbe dlarva ewer estil laliv eafte r9 0days . Similarresult swer eobtaine dfo rth eeffec to fdrynes san ddisturbanc eo n thelarva lweigh to fdiapausin gan dnon-diapausin glarva e (fig.2.).Weigh t decreasedrapidl yimmediatel yafte rlarva ewer eexpose dt odryness .Thi sdecreas e wasslowe rfo rth ediapausin glarva etha nfo rnon-diapausin gones .Afte r3 0day s allsurvivin gnon-diapausin glarva ewer ereduce dt oabou t30 %o fthei rinitia l bodyweight .B ytha ttim edisturbe ddiapausin glarva edroppe dt o50 1o fthei r originalweigh tan dundisturbe dlarva et o751 . Althoughth eresult ssho wtha t2 0day sol dnon-diapausin glarva ewer eno t capableo fsurvivin gdr yconditions ,thi si sno ttru efo rlarva eo fal lages . Fig.3 show sth erelatio nbetwee nlarva lag ean ddeat ho rpupatio n (theopposit e ofsurvival )o ndr ymaize .Youn glarva eles stha n1 4day sol dalway sdi ewhe n rearedo ndr ymaiz estems .Thereafte rth epercentag epupatio nincrease swit h larvalage .Fig .4 show sfo rth esam eexperimen tth etim eneede dfo rth elarva e todi eo rpupate .Th elonges ttim ewhic ha larv acoul dsurviv e (withoutpupatin g ordying )wa s7. 5+ 0. 6day s (mean+ S.E. ) (fig.4.).Thi swa swhe nlarva ewer e2 1 daysold .Th euppe rconfidenc elimi t( p= 0.05 ,studen tt-test )fo rthi sdistribu - 13 Fig.3. Relation betweenag e and development oflarva e of Chilo partellus indr ymaiz e stems. Each LARVALAG E( DAY S] age group consists of50-15 0 larvae. tion is15.1 1 days. Thus, ifa larv a survived indr yste man da t2 5C (when disturbed biweekly)fo rmor e than 15day s itwa sconsidere d tob ei ndiapause . 2.4.2 Field experiments 2.4.2.1 Climatedurin gth efiel dexperiment s Theclimati ccondition s (rainfall,relativ ehumidit yan dmaximu man dminimu m temperatures)showe dver ysimila rfluctuation sdurin g 1973,197 4an d197 5(fig . 5-8). Rainswer efrequen ti nJun ean dcontinue ddurin gpar to fJuly .Afte rtha t perioddr ycondition sprevaile dbu twer einterrupte doccasionall yb yrain . Relativehumidit ywa ssomewha thighe rdurin gth erain san dthereafte rtha ndurin g periodso fdrought .Decrease si nhumidit ywer eusuall yaccompanie db yincrease s intemperatures .Normall yrain sbega ni nearl yApril ,bu ti n197 4th erain sonl y startedo nth e25t ho fMay . Fig.4.Relatio nbetwee nag ean d longevity (averagenumbe ro fday s +_S.E. )o flarva eo f Chilo partellus indr ymaiz estems .Eac hag egrou p LARVALAG E consistso f50-15 0larvae . 14 2.4.2.2 Seasonal fluctuation inth e larvalan dpupa l populations Fluctuations inth e larval andpupa lpopulation s of Chilo inth e experimental maize fields during thegrowin g seasons of 1973, 1974an d 1975 areshow n in figures 5A,6 Aan d 7A.Fo r irrigated fieldswher emaiz ewa s growndurin g thedr y seasons of 1974an d 1975 dataar egive n in fig. 8A.Seasona l andyearl y variationswer e considerable.Th epopulation s showed somesimilarit y during the wet seasons of 1973an d 1974 (fig.5 Aan d 6A)afte ra ninitia lpea k inth enumbe r of larvaeearl y inth e growing season. "{1-2month s aftersowing ,ther ewa s a rather rapiddecreas e inth e larvalpopulatio n to levels of abouthal fth e previous size oreve n less. Thereafter thenumbe r of larvae remained quite constant during aperio d of at least 2month s afterwhic hnumber s dropped ton o more that 10-20 larvaepe r 100stem s atth een do fth eexperimenta lperiod . Resultso f 1975 (fig.7A )wer e different: asecon d larvalpeak ,highe r thanth e previous one,occurre d about 7>\month s after themaiz ewa s sown. Crops grown later inth e (rain)seaso nha d ahighe r initial larval population thancrop s grownearlier : in 1973th ehighes tpea k of larvae inmaiz e sown 21Apri lwa s 67 larvae/100 steins;i nmaiz e sown4 Jun e 126 larvae/100steins . In 1974ther ewer e 68 larvae/100 stems inmaiz e sown 23Apri l and 98larvae / 100stem s inmaiz e sown 20June . Pupae almostcompletel y disappeared atth een d of the growing season.A t that timequit ehig h levels of larvae (obviouslyenterin g diapauseo r indiapause ) could stillb e found.Occasionall y pupationo fdiapausin g larvae tookplace .Thi s however couldusuall yb e related to rains (1973,fig .5) . Fig. 8Ashow swha thappene dwhe nmaiz ewa s irrigated during the dryseason . In 1974irrigatio nwa s only continued tillth een do fJanuary . The larval population initially increasedbu t collapsed soonthereafter .Afte rmid-Marc h hardly anypupa ewer e found. In 1975 the irrigation tookplac enearl y throughout the observations.Thi s resulted ina nextremel yhig h larvalpopulatio ndensit y (anaverag e ofmor e than 5 larvae/stem) anda continuou spresenc e ofpupae . 2.4.2.3 Seasonal incidence ofdiapaus e The incidence ofaestivation-diapaus e inmatur e larvae collected fromth e fieldwa s usually determinedb ybot h observing the cuticularpigmentatio n and the drought resistance.A nexceptio n is 1973whe ndiapaus ewa s merelybase do nth e losso f cuticular spots. Results concerning thedormanc y during thewe t season in 15 Z Z 120- 1973 LU LU ,iu 1 go 100- o o la 80- fig 60- fefe ^^ ,~ yw 40- ZnZ ->n. • • MAIZE SOWN 21/4/73 o» MAIZE SOWN 4/6/73 100-1 o CL z z < ce s §0 30 X LU 28 < cr 26 M 24- < ce 22- LU • 20 UJZ l —I— 1/6 1/7 1/8 1/9 1/10 1/11 DATE Fig.5. Seasonal fluctuations of Chilo stalk borers in twomaiz e fields sown on different dates during thewe t season of 1973 inrelatio n to the climate. A. Total number of larvae andpupae . B.Percentag e aestivating larvae. 16 • y*"^"***^*r*''* •• ?*•« ^ D" MAIZE SOWN 23/4/74 o» MAIZESOW N 20/6/74 w 100 < -I 80 Oh >- -80§d5 -70 zO£g -6 02 i E x s: a. £ 20- 1JO UJT2 i. JJ. . ; 2 0 i r i 5aP 30-] <°- 28- 26- P 24- < cc 22- WW Z Q. 20- LU Z —r~ 51 1/6 1/7 1/8 1/9 1/10 1/11 1/12 1/1 DATE Fig.6. Seasonal fluctuations of Chilo stalk borers intw omaiz e fields sowno n different dates during thewe t season of 1974i nrelatio n toth eclimate . A. Total number of larvae andpupae . B.Percentag e ofaestivatin g larvae. 17 1975 MAIZE SOWN 25/4/75 E 50 i "l 90 •. • • 80 d 40- • • 70 z -60 3 z i < 20- i as L. b.. I Li-. • -4• LI -i 1 1. L . . Ill 30 n 28 S| 26-| 5< 24- LU 2222 51 20 LLj [~ —I— —I UJ Z 1/10 5z 1/6 1/7 1/8 1/9 1/11 DATE Fig.7. Seasonal fluctuations of Chilo stalk borers ina maiz e field during the wet season of 1975 inrelatio n to the climate. A. Total number of larvae and pupae. B. Percentage aestivating larvae. 1975 MAIZE SOWN 4/12/73 MAIZE SOWN 19/11/74 UJ inn-. M00 <> < o rr ® < 80- •80 co a: _j n LU Q i—n i- 60- •60 UJI- f> $ (i - z(/) 40" -40 < _> " 20- 20 1 1 1 \^&. e n ^ J o 20- o UMIDIT Y (% ) m. ) RELATIV E < I EA N (9.0 0 a m IRRIGATION 10- o 2 0 an d 3.0 0 p So" 32- WEEKL Y M 30- < 5: 28- UJ w 26 24 51 22 • • • $ < 10/1 1/21— 1/3 1/4 1/1 1/2 1/3 1/4 DATE DATE Fig.8. Seasonal fluctuations of Ckilo stalk borers in twomaiz e fields during the dry seasons of 1973 and 1974 in relation to the climate.Th emaiz e fields were irrigated twice awee k over indicated period. A. Total number of larvae andpupae . B. Percentage aestivating larvae. 1973, 1974an d197 5 aregive n infig . 5B, 6Ban d7 Brespectively . Infig . 8Bdr y season results areshown . When considering thecuticula r pigmentation, iti s striking that only very little unspotted larvae couldb efoun d during therain y period ofth eyear . These observations include thebiweekl y irrigated maize field during thedr yseaso n of197 5 (fig. 8).Whe n rainsha dpassed , nearly always anuninterrupte d gradual increase innumber s ofwhit e larvae followed.Th e only exceptionma yb e197 3(fig . 5)wher e inth efirs t sown crop temporarilyn o further increase inunspotte d larvae occurred from 8Augus t till 5September .• This period was characterized bya hig h rainfall. When thepercentage so f aestivating larvae areconsidere d (determined bymean s ofthei r potentialt o resist drought) itca nb esee n that 20-25°* aestivation mayalread y bepresen t during arain y period (1974 and1975 , fig.6 an d7) .Bu tagai n themos t drastic increases occurred when rains were rare orabsent .N ocorrelatio n between other climatic factors andth eincidenc e ofdiapaus e couldb efound . Diapausewa s observed both during the"wet " season with average minimum andmaximu m temperatures of21 °an d27° C respectively andrelativ e humidities upt o88° 6 (1975, fig. 7).Bu ti tals o occurred during thedr yseaso n when minimum temperatures were about 23°C, maximum temperatures 32°C andth erelativ e humidity was about 10%(1974 , fig. 8). 2.4.3 Effects of photoperiod and temperature Effects of photoperiod When larvae were reared throughout larval lifea t photoperiods which areclos e tonatura l conditions inKeny an oeffec to nth e rate ofdevelopmen t wasfoun d (table2) . Table 2.Effec t ofdifferen t photoperiods onth erat e ofdevelopmen t oflarva eo f Chilo partellus from first instar larva topup a ata constant temperature of2 5C . photoperiod number ofsurvivin g number ofday s required larvae forpupatio n (mean+ S.E. ) 12J L 11J D 51 32.2+ 1.4 12 L 12 D 45 33.9+1. 1 HiL 12J D 39 33.7 +1. 3 Effects of temperature Theeffect s oftemperature s onlarva l development were determined. 20 Thetes ttemperature sapplie di nthi sexperimen twer ederive dfro mth einterna l temperatureso fmaiz edurin gsunn yday san di na fiel di nwhic hpre-diapaus e larvaewer eabundant .Thes edat awer eobtaine dwit hthermocouple sconnecte dt oa recorderwhic hprinte dth etemperatur ea t \ hrintervals .A perio do fa tleas t 24hr swa scovered .Result sar egive ni ntabl e3 . Maximumtemperature swer e 35-36C .W etherefor euse d3 7C a sth euppe rlimi ti nou rexperiments .Lowes t temperaturesi nstem swer earoun d2 0C .Sinc ethes etemperature sar eonl y occurringdurin ga perio do f1- 2hr sjus tprio rt osunris ean dsinc eth e temperaturedurin gth eres to fth eevenin gan dnigh ti sclose rt o25°C ,w euse d thelatte ra sth efixe dnigh ttemperatur ei nth eexperiments .Th elengt ho fth e thermoperiod (6h r"high "temperature :1 8h r2 5C )i srathe rarbitraril ybu t stillreflect sth eaverage sme ti nth efiel d (table 3). Arelatio nbetwee nth edegre eo fdesiccatio no fa maiz eplan tan dit s internaltemperatur ewa ssuspected .Sinc eth emaiz estem si ntabl e3 ar eroughl y groupedtogethe raccordin gt othei rwate rcontent ,th eindividua lrelatio n betweenmoistur econten tan dtemperatur ei ssomewha tmasked .A close rexaminatio n ofindividua lstem s (notshow nhere )reveale dtha tsuc ha relatio ni sno tapparent . Whenw eloo kint oth eeffec to fth edifferen tthermoperiod so nth e developmento fth elarva e (fig.9 )i ti sclea rtha ttemperatur edoe shav ea n influence.Th edevelopmen twa sfastes twhe ntemperature swer e30-33° Cdurin gth e 6h rperio do fth e6:1 8 (25C )thermoperiod .Whe nlarva ewer eexpose dt olowe ro r highertemperature sdurin gthi speriod ,ther ewa sa clea rincreas ei nth etim e requiredfo rpupation . Table3 .Temperature s inth einterio ro fmaiz estem slocate d inthre edifferen t experimentalfield swit hpre-diapausin g anddiapausin g larvaeo f Chilo partellus. date no. waterconten t meannumbe ro f hourswit h meantemperature s of ofstem s thefollowin g temperatures in° C(range ) stems (range) 25°C 25-30°C 30°C early 4 77.7- 84. 7 14! 2 7j 26.2(19. 6- 36.0 ) Aug. 74 2 67.6- 69. 9 15 11 26.0(19. 1- 35.3 ) 3 67.5- 74. 6 14 2 8 26.8 (22.1- 33.5 ) mid 6 71.7- 79. 5 13 3 8 27.3(19. 7- 35.4 ) Oct. 74 21 a • 1s t instar larvae 3rd instar larvae 5t h instar larvae ¥ Fig.9.Tim erequire dfo rpupatio n (means+ S.E. )o f Chilo partellus 25 30 33 35 37 °C (6hrs/day ) larvaea tdifferen ttemperatur e + + + + 25 25 25 25 25 °C (18hrs/day) regimes.Number srefe rt olarva e TEMPERATURES remainingafte rpupatio no rdeath . 2.5 DISCUSSION The experimentso ndrough t resistanceo flarva e showed that aestivating larvaear emor e capableo fsurvivin gdr yenvironmenta l conditionswithou t food thannon-aestivatin g larvae.Thi s capacityca nno tb eexplaine db yth elarge r sizean dweigh to fth edorman t larvaea tth estar to fth eexperiments ,becaus e heavynon-diapaus e larvaewer e foundt odi e(o rpupate )o ndr ymaiz ewherea s small diapause larvaewer e found capableo fsurvivin g longdr yperiods .I ti s more likely thatth eincrease d drought resistanceo faestivatin g larvae iscause d by their reducedmobilit ywithi n theirrestin g sitesan db yphysiologica l changes sucha sincrease d fatcontent ,depressio no fth emetabolis man da resistanc et o desiccation. Inthi spape r some evidencefo rdrough t resistance isgiven .Durin g adr yperio d thebod yweight o fnon-diapaus e larvae decreasedmor e rapidlyan dt o lowervalue s that thato fdiapaus e larvae.Thi s decrease should largelyb e contributed todesiccation .Non-diapaus e larvae containedo nth eaverag e 10-151 moremoistur e thandiapaus e larvae.Th edifference s inweigh t decreasehoweve r weremuc h largeran dca ntherefor e onlypartiall yb eexplaine db yth edifferen t initialmoistur e contents.Change dpropertie so fth ecuticl e and/or inth e 22 transpirationthroug hth espiracle sprobabl yals ohav eplaye da role .Weigh t losscoul dhav ebee ncause db yth eexpenditur eo fmetaboli creserves .Non - diapauselarva erequir emor eenerg ysinc ethe yar emobil ean dhav ea relativel y highmetabolism .Diapausin glarva ehav ereduce denerg yrequirements ,althoug h thespinnin go fa ne w"diapaus echamber "whic hwa sinvariabl ydon emus thav e affectedth ereserves .Thi sma yexplai nwh yeve nundisturbe daestivatin glarva e lostmuc hweigh tdurin gth efirs tte nday so fexposur et odryness .Durin gthi s period25 %o fth ebod yweigh twa slos tbu tthereafte rth eweigh twa srathe r constantan donl ywen tdow nfo ranothe r 10°sdurin gth enex t8 0days .I nth efiel d decreasei nbod yweigh ti sprobabl yeve nles ssinc eaestivatin glarva ear ebette r protectedinsid ea dr ymaiz este mtha ninsid eth egauz eo fth eexperiments . Disturbedaestivatin glarva eappeare dt ocontinu elosin g weightunde rdr y conditions. Beforedrough tresistanc ecoul db eapplie da sa criterio nfo raestivation - diapausei twa snecessar yt omak esur etha tdrough t (drymaize )neve rca ninduc e diapausei nnon-diapaus elarvae .Wit ha biweekl ydisturbanc e (neededfo robserva tionan dessentia lfo rth efina lcritica lnumbe ro fday swhic ha larv aha st o survivebefor ei tca nb econsidere da saestivating )thi sturne dou tt ob eth e case.Al lnon-diapaus elarva eeithe rdie do rpupate d (oftenprecociously )unde r dryconditions . Duringth ewe tseaso ni nth eCoas tProvinc eo fKenya ,a larg evariabilit yi n thesiz eo fth elarva lpopulatio ni nth edifferen tyear san dals odurin gon e seasoncoul db edemonstrated .Simila rvariation swer eals ofoun di nth esam e regionsb yL ACROI X (1967)an dMATHE Z (1972).Th eaverag enumber so flarva efoun d inth epresen tresearc h (40-60larvae/10 0stem si n197 3an d197 4an dabou t10 0 larvae/100stem si n1975 )wer ea tleas thal fa slo wa sth elevel sfoun db yth e authorsmentione dabove .Peak si nth elarva lpopulatio nwer efoun d11- 2month s afterth esowin gdat eo fth emaiz ewhic hi si nagreemen twit hth edat ao fMATHEZ , andperhap sals owit hthos eo fL ACROI Xwh oobserve dth efirs tlarva eo nmaiz e always20-2 4day safte ri twa ssown .I nspit eo fthi sh einvariabl yfoun dth e firstpea ko flarva ei nth ebeginnin go fJune ,independan to fth esowin gdat eo f maize (inhi sexperiment searl yan dlat eApri lan dearl yJune) .Th eresult so f thispape rar eno tfull ycomparabl esinc emaiz ewa sonl ysow na tth een do fApri l andi nJune . Therei sn odoub ttha tth efirs tpea ko flarva efoun di nth eearl ysow n(en d ofApril )maiz efield srepresent sth eprogen yo fth ediapaus egeneration .L ACROI X camet oth esam econclusion .A secon dpea ko flarva elate ri nth eseaso nwa s 23 usuallyfoun db ybot hL ACROI Xan dMATHEZ ,an di nm ymaiz efield spopulation s tendedt ofluctuat esimilarl yalthoug hth e2n dpea kwa sno talway sa sdistinc t (excepti n 1975).A nexplanatio nma yb eth egrea tvariabilit yo fth efactor s whichar edeterminin gth erat eo fdevelopmen ta ttha ttime .Th efirs tgeneratio n couldstil ldevelo prathe rsynchronousl ybecaus eo f1 )th esimila rstartin gpoin t ofth edevelopmen t (afterterminatio no fth ediapause) ,2 )th epresenc eo fver y nutritivefoo d (youngmaize )o ffairl yconstan tqualit yan d3 )th eoptima lweathe r conditions (rain).Al lthes efactor sbecom emor ean dmor evariabl ea sth eseaso n proceeds.I nparticula rth emaiz eplant sshowe dlarg eindividua lqualitativ e differencesdurin gthei rdevelopmen t (seelate rchapte r 4).Moreove rw eobserve d that Chilo larvaevar yconsiderably ,eve nunde rconstan tenvironmenta lconditions , inthei rtim erequire dfo rpupation .Afte rth esecon d"peak "th enumbe ro flarva e graduallydecreased .Sinc epupatio nwa sstil lextremel ylo wo rabsent ,i tappear s likelytha tth edeat hrat eo fdiapausin glarva ewa srathe rhigh . Afairl ylo wlarva lpopulatio nwa sfoun di n1974 .Thi sma yb eexplaine db y thever ylat estar to fth erain yseaso n (25May )wherea sth emaiz ewa salread y sowno n2 3April .A simila robservatio nwa smad eb yMATHE Z (1972).N ofurthe r relationbetwee nseasona lpopulatio nfluctuation san dclimat ecoul db e demonstrated.Crop sgrow nlat ei nth erain yseaso nwer emor eheavil yinfeste d thancrop splante dearlier .Th emos tobviou sreaso ni so fcours etha tth enumbe r ofmoth swhic hstar tth einfestatio nha sincrease denormousl ycompare dt oth e previousgeneratio no fmoth swhic horiginate dfro mth ediapausin gpopulation . Youngmaiz eals ooffer smor eattractiv eovipositio nsite stha nmor ematur eplant s (INGRAM1958) . Thepupa lpopulatio ndecrease ddurin gth edr yperiod sfollowin gth erain y season.I fpupatio noccurre d latei nth eseaso ni tcoul dofte nb eassociate dwit h temporaryrainfall .Thi smean stha tdrough ttend st opreven tan drai nt ofavou r pupation.Thi sseem st ob econfirme db yth eexperiment sdurin gth edr yseason .A s longa sirrigatio ntoo kplace ,pupa ecoul db efound .Som etim eafte rcessatio no f theirrigatio nhowever ,pupa ebecam erare . Theincidenc eo faestivation-diapaus e inth efield ,whethe rthi si sbase do n thecolou rchang eo fth elarva eo ro nit sincrease ddrough tresistance ,coul dno t beassociate dwit han yclimati cfacto rothe rtha nrain .Absenc eo frai nseem st o providea stimulu sfo rdiapause .Sinc ei twa sshow ni nthi spape rtha tdiapaus e canno tb einduce db ydr yenvironmenta lcondition salone ,th elac ko frai nmus tb e perceivedb yth este mbore rthroug hsom eothe rmediu msuc ha sth ehos tplant .A relationbetwee nth eincidenc eo fdiapaus ean dth econditio no fth eplan tha s oftenbee nsuggeste dfo rman yste mborer s (VANDE RGOO T1925* ,HYNE S1942 ,KEVA N 24 1944,SWAIN E1957 ,SMITHER S1959 ,NY E1960 ,USU A 1973,DELOBE L1975b )an dals o seemst ob eimportan tfo r C. partellus. Thissubjec tcertainl ydeserve sattentio n infuture . Ina neffor tt oseperatel yanalys eth edifferen tenvironmenta lcomponent si n thefield ,th einfluenc eo fphotoperio dan dtemperatur eo nth elarva ldevelopmen t wasstudie dunde rcontrolle dcondition si nth elaboratory .Photoperiod si n Kikambalarang efro m1 1hr san d5 0minute si nJun et o1 2hr san d1 8minute si n December.Wit hth edifferenc eo fonl y2 8minute sbetwee nth elonges tan dth e shortestda yi ti sno tsurprisin gt ose etha tn oeffec to fphotoperio dcoul db e detected.Th erol eo fphotoperio dca nhoweve rno tb eneglecte daltogether .I t maystil lb etha tdiapaus ei sinduce db ya shor tdaylengt h (whichi spermanentl y presenti nth eequatoria lregions )bu ttha tit seffec ti scounteracte db ydia pausepreventin gfactor so fa stronge rnature ,e.g .rain ,hostplan ti nful l growth.Onl ywhe nthes efactor sar eabsen tand/o rothe rdiapaus einducin gfactor s comeint oeffect ,shor tda yinfluenc ema yb efelt .Experiment swit hlon gday - length- althoug hirrelevan to nthes elatitude s- ar erequire dt oge ta conclusiveanswer . Temperaturesonl yha da ninfluenc eo nth evelocit yo fdevelopment ,no to n thedevelopmen titself .Evidenc etha ttemperatur ei sno tlikel yt opla ya crucia l rolei nth einductio no faestivation-diapaus ewa si nfac talread yprovide db yth e observationtha tdiapausin glarva ewer efoun dsoo nafte rth elon grain s(August , 21-27°C)a swel la sdurin gth edr yseaso n (March,23-32°C) .Furthe rsupportin g evidencei sprovide dfro mexperiment swit hthermoperiod sfro mobservation stha t larvaedevelope dfastes ta tthermoperiod so f6 hr s3 0C :1 8hr s25° Can d6 hr s 33C :1 8hr s25°C .Mea nda ytemperature sar eunde rthes econditon s2 6an d2 7C respectivelywhic hi sequa lt oth eaverag efiel dtemperatures ,measure da tth e momenttha tlarva ewer ediapausin go renterin gdiapause .Whe nlarva ewer ereare d underthermoperiod swit hhighe ro rlowe rmaximu mtemperature sth erat eo f developmentwa sslower .But ,th eretardatio nrepresente da nover-al lslo wdow n indevelopmen trathe rtha na stag especifi cdevelopmenta lrest . 25 3 The timing of the period of diapause induction; some behavioural, physiological and morphological aspects of aestivation-diapause 3.1 INTRODUCTION Inth epreviou schapte rI investigate dth erol eo fclimat ei nth einductio n ofaestivation-diapaus eo flarva eo fth espotte dstal kbore r Chilo partellus (Swinhoe)an dth ecoasta lstal kbore r Chilo oriohalooailiella (Strand).Th e principaloutcom eo fthi sstud ywa stha tth eincidenc eo faestivatio ni nthes e insectsca nno tb eassociate dwit han y climaticfacto rothe rtha nrain .Dr y environmentalcondition sstrongl yretarde dlarva ldevelopment .Tw ocriteri awer e usedt oidentif yaestivatin glarva ei nfiel dcollecte dmaterial :disappearanc e ofth ecuticula rpigmentatio nan dth eincrease ddrough tresistanc eo frestin g larvae.Th esecon dcriterio nwa sbase do nth efailur eo fa dorman tlarv at o pupate (ordie )withi nth etim elimit swhic har enormall yse tfo rnon-diapausin g larvaeunde rdr yenvironmenta lcondition si ndesiccate dpiece so fmaiz estems . Whenaestivation-diapaus e isdetermine dthi swa yi ti sver ylikel ytha tonl y ultimatereaction st oth efactor(s )whic har etriggerin gth ediapaus ear e observed.Thu sonl ylarva ewhic hhav ealread yentere ddormanc yar econsidere d andno tlarva ewhic har epreparin gfo rdiapause .Suc hobservation syiel donl y roughinformatio no nth ediapaus einducin gfactor(s) .I fw ewan tt okno wthes e factor(s)mor eprecisel yi ti snecessar yt oexamin elarva edurin gth epre-diapaus e periodwhe nthe yperceiv eth etoke nstimul ileadin gt oth eentranc eo f aestivation-diapause. Thepresen texperiment swer edon efo rtha tpurpose .Behavioura l (constructiono f restingsite ,spinnin g ofcocoon ,feeding),physiologica l (ecdysialfrequency , respiration,wate rcontent ,fa tcontent ,hear trat ean dtesticula rdevelopment ) andmorphologica l (cuticularpigmentation ,widt ho fhea dcapsule )change sdurin g bothth epre-diapaus ean dth ediapaus eperio dwer estudied . 26 3.2 LITERATURE Manyinsect schang ethei rbehaviou rwhe ndiapaus einducin g factorsbecom e effective.The yofte nstar tlookin gfo ra suitabl eplac et oovercom eth eoncomin g unfavourable.conditions .Th elarva eo fth erice-bore r Scirpophaga (= Tryporyza) innotata movewithi n3- 4week safte rharves tt oth esubterraneou spart so fth e ricestem swher ethe yaestivate .I fdrough ti sver ysever ea cocoo ni smad e(VA N DERGOO T 1925).Tunnel so fa smuc ha s1 0c mdee pma yb ecu tou ti nth eroot s (LI1961) .Similarly ,larva eo fth esouthwester ncor nbore r Diatraea grandiosella hibernatei na nexcavatio ni nth ebas eo fth emaiz estal kbelo wgroun dleve l (CHIPPENDALEan dREDD Y 1974).Th elarva eo fth e3r dgeneratio no fth eGurdaspu r borer Bissetia steniellus (insuga rcane )suddenl yrevers ethei rnorma lnegativ e geotropicbehaviou ra tth eonse to fdiapaus e (ATWAL1967) . InSouth-Afric ath e pre-diapauselarva eo fth emaiz este mbore r Busseola fusaa alsomov et oth elowes t partso fth estem ,bu tsuc ha behaviou rwa sno tfoun di nSouthern-Rhodesi a (SMITHERS 1959),Ugand a (INGRAM 1958),Tanzani a (SWAINE1957 )o rNigeri a (HARRIS 1962),wher ediapausin glarva ecoul db efoun di nan ypar to fth estem .Thi swa s alsoth ecas efo r Chilo partellus and Chilo oriahaloooiliella inEas tAfric a (MATHEZ 1962,DELOBE L 1975aan d1975b )an dfo rth esugarcan ebore r Diatraea saaaharalis inTrinida d (KEVAN 1944).Sometime sdiapaus elarva eoccup yspecia l structures:inNigeri a thelarva eo f B. fusaa constructa chambe rfro mfras skep t togetherwit hsil kinsid ethei rfeedin ggallerie s (HARRIS1962) .Diapausin g larvaeo fth ewhit eric ebore r Rupela albinella spina "protectiv ecylindrica l paperlikeenvelope "(VA NDINTHE R 1962).Larva eo f Tryporyza inaertulas and T. innotata forma "stron gsilke ncocoon "i nol dric estubble s (ROTHSCHILD 1971). Inth etemperat eclimate shibernacul aar eofte nconstructe de.g .b yth eEuropea n cornbore r Ostrinia nubilalis (BECKan dHANE C 1960).Th ediapaus ecocoo no fth e codlingmot h Carpooapsa pomonella isno tonl ythic kwalle dbu teve nha sa differentshap ecompare dt oth ecocoo no fnon-diapausin glarva e (HANSENan d HARWOOD1968) . Aftera restin gsit ei sselecte dan dprepared ,movement san dfeedin g activityar eabsen to rgreatl yreduced .Pre-diapaus e T. innotata larvaesto p feedinga ssoo na sth esubterraneou sste mpart sar ereache d (VANDE RGOO T1925 , ROTHSCHILD 1971).Onc elarva eha dstarve dfo rsevera ldays ,eve nfres hfoo di s nolonge raccepte d (VANDE RGOO T1925) .Th esam ewa sobserve dfo r C. suppressalis byFUKAY Aan dMITSUHASH I (1961),bu tearlie rKOIDSUM Ian dMAKIN O (1958)ha d demonstratedreduce dfeedin gb y C. suppressalis ondrie drice-stra weve ndurin g 27 hibernation.A cessatio no ffeedin go fdiapausin glarva eo f C. oriohaloooiliella and C. partellus inMadagasca rwa sobserve db yDELOBE L (1975aan d1975b )bu ti n India (PANTe tal.1959 )an di nKeny a (MATHEZ1972 ) C. partellus larvaecontinue d feedingdurin gdiapause ,eve nthoug ha ta ver ylo wlevel .Larva eo f Diatraea lineolata onlyfee di nth eearl ystage so fth erestin gperio dbu thardl ya tal l duringlate rstage s (KEVAN 1944).Thi si sals oth ecas efo r Coniesta ignefusalis (HARRIS 1962).Diapausin glarva eo f 0. nubilalis arecapabl eo fchewing ,bu td o notinges t (BECKan dHANE C 1960).Reduce dfeedin gwa sobserve dfo r D. sacoharalis duringth ewinte ro nwar mday s (HOLLOWAYSe tal .1928 )an di nth elaborator y (KATIYARan dLON G 1961).Als o B. fusaa (HARRIS1962 ,USU A1970 )ha da reduce d feedingactivit ywhe ndiapausing .Althoug hth elarva ementione dabov ear e relativelyinactiv edurin gdiapause ,the yinvariabl yar eactivate dwhe ndisturbe d inthei rdiapausin gsites .Observe d"feedin gactivities "afte rsuc ha disturbanc e weresometime sbelieve dt ob eassociate dwit hrepai ro rreconstructio no fth e diapausechambe re.g . 0. nubilalis- (BECKan dHANE C1960 )an d B. fusaa (SMITHERS 1959,HARRI S 1962). Thephysiologica lstatu so fdiapausin ginsect sha sbee ninvestigate db y numerousscientists : Supernumerarymoult shav eofte nbee nreporte ddurin glarva ldiapaus ee.g .fo r T. innotata (VANDE RGOO T 1925), D. lineolata (HYNES1942 ,KEVA N 1944), D. saoohavalis (KATIYARan dLON G 1960), C. partellus (MOIZan dQURESH I 1969,MATHE Z 1972,DELOBE L 1975b), C. oriohalaoailiella (DELOBEL 1975a), B. fusaa (USUA1970 ) and D. grandiosella (CHIPPENDALEan dREDD Y 1972).Th estationar yecdysi si softe n notaccompanie db ygrowt he.g . D. lineolata (KEVAN 1944), D. saoohavalis (KATIYAR andLON G1961 )an d D. grandiosella (YINan dCHIPPENDAL E 1974). Insectsi nearl ydiapaus eofte nten dt ob eheavie rtha nnon-diapausin gindividuals . Thiswa sth ecas ewit hlarva eo fth epin kbollwor m Peotinophora gossypiella (ADKISSONe tal.1963 )an d D. grandiosella (YINan dCHIPPENDAL E1974 )an dwit h pupaeo fth ecabbag ewhit ebutterfl y Pieris rapae (KONO1970) .Suc ha weigh t increasei susuall yexplaine db ya prolonge dlarva lfeedin gperiod ,whic hi squit e normalfo rinsect senterin gdiapaus e (ANDREWARTHA 1952). Areduce drat eo frespiratio n (reflectinga reduce drat eo foveral lmetabolism )i s aver ygenera lqualit yattribute dt odiapausin ginsects .I tha sbee nobserve di n diapausinglarva eo f C. suppressalis (FUKAYA 1951), 0. nubilalis (MUTCHMORan d BECKEL1959 ,BEC Kan dHANE C1960 ,LYNC He tal .1972) , Carpoaapsa pomonella (HANSENan dHARWOO D1968 ,HAYE Se tal .1972) , D. grandiosella (YINan dCHIPPENDAL E 1974)an d B. fusaa (USUA1974 )an di ndiapausin gpupa eo f Heliothis zea and H. viresoens (PHILLIPSan dNEWSO M 1966)an d P. rapae (KONO197Q) .ADKISSO Ne tal . 28 (1963)measure di nadditio nt oth erat eo foxyge nconsumptio nals oth erat eo f heartbea to fhibernatin glarva eo fP . gossypiella. Bothwer econsiderabl ylowe r comparedt onon-diapausin glarvae . Wateran dfa tconten to fdiapausin ginsect shav eals obee nfrequentl yinvestigated . Usuallyther ei sa reductio ni nwate rconten tan da nincreas ei nfa tconten twhe n insectsente rdiapause .Thi si sver yobviou si nlarva eo fP . gossypiella (SQUIRE 1940,ADKISSO Ne tal . 1963), D. gvandiosella (CHIPPENDALEan dREDD Y1972 ,REDD Y andCHIPPENDAL E1973 ,YI N andCHIPPENDAL E 1974)an d B. fusaa (USUA1973) . Differenceswer eles sdistinc ti n C. supressalis (FUKAYA1951 )an dcoul dno ta t allb eassociate dwit hdiapaus eo flarva eo f C. pomonella (HANSENan dHARWOO D 1968)an dpupa eo f H. sea and H. viresaens (PHILLIPSan dNEWSO N 1966). Alas twell-know nphysiologica lchang eoccurrin gi ndiapausin ginsect si sth e retardedgrowt ho fth egonads .Th evolum eo fth efollicl ean dth eteste so f C. suppressalis remainedsmall ;spermatid sar eno tforme dsinc emeiosi so fth e spermatocytesdoe sno ttak eplace .Als odevelopmen to fth eovarie si nfemal e diapausinglarva ewa sarreste d (MOCHIDAan dYOSHIMEK I 1962).A standstil li n spermatogenesisresultin gi na comparativel ysmal ltesticula rvolum ewa sals o observedi nmal ediapausin glarva eo f 0. nubilalis (BECKan dHANE C1960 , CLOUTIERan dBEC K 1963), D. gvandiosella (ALEXANDERan dCHIPPENDAL E1973 )an d P. gossypiella (ADKISSONe tal .1963 )an dpupa eo f C. pomonella (HANSENan d HARWOOD 1968), H. zea and H. viresaens (PHILLIPSan dNEWSO M 1966). Lacko fth epigment si nth ecuticula rpinnacul iappear st ob ea commo n morphologicalchang eonl yi ndorman tste mbore rlarva eo ftropica lorigin .Suc h achang eha sbee nreporte dfo r D. Uneolata (HYNES1942 ,KEVA N 1944), T. innotata (VANDE RGOO T1925 ,ROTHSCHIL D 1971), C. ignefusalis (HARRIS1962) , B. fusaa (HARRIS1962 ,USU A 1970), C. partellus (GONCALVES1970 ,MATHE Z1972 , DELOBEL 1975b), C. oriahalooailiella (DELOBEL 1975a), D. saoaharalis (KATIYAR andLON G1960 )an d D. grandiosella (CHIPPENDALEan dREDD Y 1972).Onl yi nth elas t caseth etransitio nwa sstudie dmor eclosely .I nCHIPPENDAL Ean dREDDY' swor k (1972)i twa sfoun dtha t"immaculation "i nthes elarva emos tfrequentl yoccurre d after (stationary)ecdysis .Ecdysi swa saccompanie db ya reduce drat eo fweigh t lossan da nincrease dcold-hardiness .Th eauthor ssuggeste dtha tchange si n hormonetiter s (particularlya lo wtite ro fecdysone )ma ypreven tth etannin go f thecuticle .Other se.g .KATIYA R (1960)an dUSU A (1970)attribute dth echange s incuticula rpigmentatio no flarva e (of D. saoaharalis and B. fusaa respectively) toth econditio no fth elarva lfood .Thi so fcours edoe sstil lno texclud e endocrineinvolvement . 29 3.3 MATERIALSAN DMETHOD S 3. 3.1 General Observationso nth ebehaviou ro fnon-aestivatin gan daestivatin g larvaewer e carriedou tbot hi nth efiel dan di nth elaboratory .Fiel dobservation swer edon e inexperimenta lmaiz e fieldso fth eCoas tAgricultura l Research Stationi n Kikambala,Coas tProvince, Kenya .The ywer emor eextensivel ydescribe di nth e previouschapter . Aestivating larvaerequire dfo rth eexperiment si nth elaborator ywer eobtaine d fromKikambal aan dth etim eo fdiapaus e initiationwa sestimate db yusin gth elos s ofcuticula rpigmentatio no fabou t 501o fth elarva lpopulatio na sth estartin g pointfo rdiapause .Non-diapausin g larvaewer eobtaine d fromth einsectary-stoc k bredo nartificia ldie t (chapter2 ,tabl e1 )a ta temperatur eo f2 7+ 1. 5C ,a relativehumidit ybetwee n 70-851an da 12L/12 Dphotoperiod . 3. 3.2 Behavioural studies Thepositio nan dconstructio no fth eaestivatio nsite swer eonl yobserve d directlyi nth efield .Later ,spinnin gwa sstudie dmor eclosel yi nth elaborator y with2 0day sol dnon-diapausin g larvae (early6t hinstar )an ddiapausin g larvae whichha dbee ndorman tfo ra tleas ttw omonths .Al llarva ewer eplace di nsmal l stainless gauzecage s (1.5x 0. 5cm) . After fourday sth ecag ewa schecke dfo r thepresenc eo fa cocoon .I fa cocoo nwa sfound ,a visua ldiscriminatio nwa smad e betweena thi ncocoo n (larvavisibl e inside)an da thic kcocoo n(larv ano tvisible) . Feedingbehaviou ro fdiapausin g larvaeo ndr ymaiz e (normalfiel d situation) was studiedwit h larvaetha tha drecentl yentere ddiapause .Dr yweight swer e recordedfo rfras s (thisinclude sfaece spellet san dth e"diapaus echamber" ) producedb yundisturbe d larvaeafte rperiod so f3 days ,3 month san d8months . These figureswer ecompare dwit hweight sobtaine dfo rlarva edisturbe d twicea weekb yopenin gthei rstem .A ttha ttim efras swa scollecte dan dth eaffecte d stemwa sreplace dwit ha whol e stem.Th e accumulatedweight so f"used "maiz ewer e recorded after 1, I5,2 ,2 \ and3weeks .Larva ewhic hdie do rpupate dwithi n these3 week swer eno tinclude di nth edata . Feedingbehaviou ro nmois t foodwa sinvestigate dwit h 23-27day sol dnon - diapausinglarva e (mid6t hinstar )an dwit h field-collecteddiapausin g larvae (unspotted)tha tha dbee n "stored" inth elaborator yfo r9 week sbefor ethei r 30 feedingwa sstudied .Th efeedin gactivit ywa sstudie dwit hth eartificia ldie t usedi nth einsectary .Faece swer ecollecte dapproximatel yever y 12hour sfro m thestar to fth eexperimen tdurin gfiv econsecutiv edays .Larva ewhic hpupate do r dieddurin gthes eday swer ediscarded .Th eperio dbetwee nth eobservation sroughl y coincidedwit hth e12L/12 Dphotoperio dprevailin gi nth eexperimenta lroo m(an d alsooutside) .Larva ewer eweighe deac hmornin gafte rfaece sha dbee ncollected . However,larva ei nthi sexperimen twer e not disturbedi fa cocoo nwa sspun .I n thatcas eth eweigh twa sestimate db yinterpolation .Finall yth efeedin gactivit y wasexpresse da sm gdr yweigh to ffaeces/10 0m g (fresh)larva/hr . Allexperiment smentione dabov ewer ecarrie dou ti na constan ttemperatur e room.(25. 0+ 1.0°C )wit ha relativ ehumidit yo f70-80 1an da photoperio do f 12L/12D. 3.3. 3 Physiological studies Thephysiologica lstudie swer estarte dwit hnon-diapaus elarva eo f C. partellus. Growthrat ean decdysia lfrequenc ywer eobserve da t2 5C o nartificia l dietfro mth ehatchin go fth eeg gthroughou tth elarva lperio dtil lpupation . Larvaewer ekep tseparatel yi nglas stube s (2.5x 7. 5cm )t opreven tcannibalism . Observationsstarte dwit hfreshl ymoulte d5t hinsta rlarva e (about1 2day sold ) selectedfro mth einsectary-stoc kan dtransferre dt oth econstan ttemperatur e room (25C) .Observation so ngroup so f1 8larva ewer ecarrie dou tever y2- 3day s duringa 3-wee kperio dunti lpupatio nwa scompleted . Atth etim eo fthi swor kth ediapaus einducin gfactor swer eno tknown ,thu s thephysiolog yo faestivatin glarva ecoul donl yb estudie dwit hlarva ei nwhic h thediapaus ewa snaturall yinduced .Thes elarva ewer eobtaine dfro mth esam e experimentalfield suse dt oinvestigat eth erol eo fth eclimat ei nth ediapaus e syndrome (chapter 2).A ton eoccasio ndiapausin glarva ewer ecollecte dfro ma ne w maizefiel dsituate dnearb yKikambala ,calle d"Mtwapa" .Observation si nthi sfiel d startedlat ewhe nmaiz eha dreache dful lmaturity .Al lfiel dsample scontaine d larvaeo fbot h C. partellus and C. oriehaleociliella. Onlyfift hinsta ro rfurthe r developedlarva ewer eused .Earlie rinstar sar eno tcapabl eo fenterin gdiapause . Oxygenconsumptio nwa smeasure da t25° Cwit ha Scholande rMode lVR-30 0micro - volumetricrespiromete r (SCHOLANDER 1952).Measurement so f9-1 8 larvaewer etake n athal fhou rinterval sdurin gth eda y (=ligh ti nth eexperimenta lroom )fo ra periodo f2- 3hrs .Eac hlarv awa splace dint oa smal lwir ecag et opreven ti t fromenterin gth ecompensatin gchambe ro rth eKOH-tray .Vial swer eequilibrate d 31 for 5h rbefor erecordin gth e initialreading . Moisturecontent s anddr yweight swer eobtaine db yweighin g larvaebefor ean d after2 4hr si na 9 0C dryin goven . Fatswer eextracte d fromdr ymateria lwit hdiethy lethe ri na Soxhlet t apparatus forapproximatel y8 hrs .Th epercentag e fatwa s subsequentlydetermine db y comparingth eweigh to ffat-extracte d larvaewit hth eweigh tbefor eextraction . No individualobservation swer edone .Group so f9-1 8 larvaewer eextracte da s awhole . Heartrate swer edetermine db yobservin g individual larvaeunde ra dissectin g microscopea t2 5+ 1. 0C . Thedevelopmen to fth eteste swa s investigatedb ymeasurin gth etesticula r volume of8-1 2individuals .Teste swer edissecte di nsalin ean dth emajo r axis (a) and minoraxi s (b)wer emeasure dwit ha calibrate docula rmicrometer .Volum e 00wa s calculated accordingt oth eformul aV = TT/ 6a b assumingtha tth e testisha sa n ellipsoidshape . 3.4 RESULTS 3.4.1 Ccmstruoticm of vesting site and spinning behaviour Prepupaean dpupa edissecte d fromgree nmaiz edurin gth erain yseaso nwer e frequently found lyingentirel y freeamon g frassproduce ddurin gthei rpreceedin g larvalstage .Occasionall y thefoo dremnant swer ekep t togetherb ya thi nlaye r ofsil kfilaments .Suc ha structur ehoweve rwa s invariablyencountere d around aestivating larvaei ndr yan ddea dstems .Compare dt oth epupa lchambe ro fnon - diapausing larvaeth elaye ro ffoo dparticle swhic hfor mth eoutsid ewal lo fth e "diapausechamber "wa s thick (athicknes so f3m mwa squit ecommon )an dth einne r wallo fthi s layerwa s linedwit ha smoot hver y closelywove ncove ro fsilk .Thes e differencesi nbuildin gbehaviou rwer e confirmedi nth elaboratory .Tabl e4 show s thataestivatin g larvaeconstruc ta thicke rcocoo ninsid ea close dmeta lcag etha n non-aestivating individuals.I nsuc ha nunnatura lsituatio n(n ofood! )cocoon s werenearl yalway smade ,eve nb ynon-diapaus elarvae . 32 Table4 .Cocoo nformatio no fnon-diapausin gan ddiapausin g larvae4 day safte r transfert oa meta lcage . type of larva n number of larvaewhic h had spun: no cocoon a thin cocoon a thick cocoon non-diapausing 21 4 17 0 diapausing 23 1 6 16 3.4.2 Feeding behaviour Fieldobservation sreveale dtha ttunnelin ginsid edryin gmaiz estem scoul d continuefo rsevera lweek safte rcessatio no fth erains .I twa sno texceptiona l duringth edr ydeaso nt ofin dstem si nwhic hth epit hwa sa tsevera lplace s completelyreplace db yfras s (whichinclude sfaeces )fo rlength so f10-2 0cm .Suc h extensivetunnelin gwa sneve rfoun di nyounge rfres hstems .Larva epresen ti n suchstem swer eal lfull ygrow nan dman ywer eunspotted .A fe wweek slate rpupa e weren olonge rfoun dan dalmos tal lth elarva eha dconstructe da diapaus echamber . Thusi ti sapparen ttha tpre-diapaus elarva ewer eobserved .Thei rfeedin gperio d isconsiderabl yprolonge dan dthu sals othei rtota lfoo dintak emus tb eincrease d duringth epreparation sfo raestivation-diapause .Judgin gfro mth econstructio n ofth ediapause-chamber ,i ti sver ylikel ytha tfeedin gcease sa ssoo na sthi s Table5 . Accumulated amountso ffras sproduce db ydiapausin g larvaeo npiece so f drymaiz estem safte rdifferen tperiod sdurin gwhic hlarva ewer elef tundisturbe d orwer edisturbe d 2xweek . treatment period after mg dry weight of no. which frass accumulated frass of was collected per 100m g larva larvae (mean + S.E.) undisturbed 3 days 21.5 + 0.9 20 3 months 34.3 + 3.7 20 8 months 30.0 + 4.9 15 disturbed 2xweek ; 1 week 53.4 + 1.3 22 frass 1J week 75.1 + 1.4 22 was removed 2 weeks 100.8+ 1.8 22 at each 2{week s 118.7 + 1.8 22 disturbance 3 weeks 133.2+ 2.3 22 33 chamber isformed .Thi s conclusion isals o supportedb y the fact that empty diapause-chamberswer eneve r found inth e field. Further investigations on feedingbehaviou rwer e carried out inth e laboratory: table 5show s the accumulation of frass fromdiapausin g larvaeo n pieceso fdr ymaiz e stems. Larvae leftundisturbe d ina dr ymaiz este mfo r4 daysha dproduce d anaverag e of 21.5m g frass (drywt.)/10 0m g larva (fresh wt.). This quantitywa sno t significantly higher (p= 0.05 ) after 3month s (34.3m g frass)o r even 8month s (30.0m g frass)o fundisturbe d presence.However , disturbance ofth e larvae inthei r resting sites (obtainedb y opening the stems) largely increased the frassproduction :withi n 1wee k frassha d already accumulated toa significantl y higher amount (p= 0.05 ) thanamount srecorde d for any ofth eundisturbe d larvae inthi sexperiment . Whendiapausin g larvaewer eprovide dwit hmois t food (artificial diet)the y started feeding almost immediately and as aresul t also started defecating.Th e qo — o> . 80 fc 70 h- oE T o 40- O III 30- 5 e 20- J : < 10 > CO • I'M ir LU n- _ L Fig.10. Day and night feeding activity (expressed infres hwt .o f faeces)o f 3 groups of 8-9 aestivating larvaeo n artificial diet inrelatio n to their weight.Vertica lbar s represent I IDA Y INIGH T standard errors of themeans . 34 Fig.11. Day and night feeding activity (expressed in fresh wt. of faeces) of agrou p of 17 non-diapause larvae (L6)o n artificial diet in relation to theirweight.Vertica l bars represent standard errors of I IDA Y NI6HT themeans . possible effecto fdisturbanc eo fth elarva e could inthi s caseno tb e demonstrated separately sinceal llarva e remained active throughoutth e observationperio d once theywer e offered diet.Fig .1 0show s thatth efaece l productionwa sfairl yhig hfo ral ldiapausin g larvae.Thi s iseve nmor e striking whenthe yar ecompare dt onon-diapausin g larvae (fig.11)whic har epresume dt o havea highe r feeding activity. Larvalweight so fdiapausin g larvae remained rather constant duringth efiv eday so ffoo d intake (fig.10),bu tnon-diapausin g larvae gainedweigh t (fig.11). Inth esam e figureon eca nse etha tth efeedin g activityo fal ldiapausin g and- t oa les s extent- non-diapausin g larvaei s positively correlatedwit hth elight-dar k rhythm. Larvaear eclearl y day-active. 3.4.3 Physiology of non-diapause larvae Non-diapause female larvaerequir ea naverag eo f36. 3+ 1.4day san dmal e larvae30. 6+ 1. 5day s tillpupatio na ta temperatur eo f2 5C .Fig .1 2show sho w the larvalpopulatio ni ssubdivide d inth edifferen t instarsa tan ygive n time aftereg ghatch .On eca nals ose etha tth elarva l developmento fmale san d females isequa ltil lth emoul t intoth e6t hlarva l instar.Afte r this therei s differentiation:th e6t hlarva l instari sshorte r forfemale s thanfo rmales ,bu t femalesnormall y require 7larva l instarsan dmale s only6 .A nadditiona l instar may occasionally occur:3 ou to fth e2 6femal e larvaean d3 ou to fth e1 9mal e larvaeha da 6t han d7t hmoul t respectively.Th ewidth so fth ehea d capsulesfo r each instarar eshow ni ntabl e6 . Thegrowt ho fth elarva ea t25° Co nartificia l dietwa sinvestigate d ina 35 100' L ^^- •ji^ 7 90 - // •/ 80 70 60 f 50 - L1 L2 L3 I L4 J L5 ./ L6 ./ PUPA 40 30 _ / ""V 20 10 : 0 / //./. rf» 1 1 1- | ' i 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 DAYS AFTER HATCHING OF EGG Fig.12.Larva ldevelopmen to fnon-diapaus emal ean dfemal e larvaeo f Chilo partellus onartificia ldie t (25 C). Table6 :Widt ho fhea dcapsule so fdifferen t larvalinstar so f Chilo partellus (25°C). ins tar males femal es mean width of increase no. mean width of increase no. head capsule of head capsule of (mm) + S.E. larvae (mm) + S.E. larvae 1 0.254 + 0.003 19 0.255 + 0.001 26 2 0.383 + 0.005 x 1.51 19 0.383 + 0.005 X .50 26 3 0.557 + 0.014 x 1.45 19 0.542 + 0.010 X .42 26 4 0.800 + 0.025 x 1.43 19 0.784 + 0.018 X .45 26 5 1.108 + 0.036 x 1.38 19 1.107 + 0.026 X .41 26 6 1.371 + 0.050 x 1.24 16 1.445 + 0.041 X .31 26 7 1.359 + 0.043 x 0.99 3 1.666 + 0.028 X .15 16 8 1.820 + 0.022 X .09 3 36 UO-i ,- n—i—i—i—i—i—i—i—i—i—r 8 101 21 41 61 82 02 22 42 62 83 03 23 43 63 84 0 LARVALAG E (DAY S) Fig.13.Larva l growth of non-diapause male and female larvae of Ch.Ho partellus on artificial diet (25 C)Vertica l bars represent standard errors of themeans . separate experiment and is shown infig . 13. Females andmale s had the same growth rate till theyweighe d about 50m g onda y 20.A t the end of the larval development females had increased till an average of about 120mg ,whil emale s only reached half thisweight . The standard deviations of the average larvalweight s tended to increase at theen d ofth e observation period due to the fact thatmos t of the larvaeha dpupated : the last figures shown represent only 4ou t ofth e initially 22 females and 2ou t of the initially 26males . Anothe r growth rate curve ofnon-diapaus e larvae isshow n infig . 14.I n this curve,male s and femaleswer e combined. Each dot represents 18differen t larvae (unlike thepreviou s figure inwhic hw ewer e always dealingwit h the same larvae). Records startedwit h the 4thmoul t to 5th instar larvae.Thi s curve is similar to thepreviou s one (fig. 13)an d isprovide d as areferenc e for the further graphs on respiration,wate r content and fatconten t of the non-diapausing larvae.Th e rate ofoxyge n consumptionwhic h isnearl y 10u l0~/m gdr y weight/hr just after ecdysis,decrease d rapidly during the further development until a level of slightly more than 3.5 ul 0_wa s reached after 30day swhe nmos t larvae had pupated. Not shown inthi s figure is the respiration ofprepupa ewhic h further went down to an average of 2.2 pi 0~.Th ewate r content of the non-diapausing 37 1—'—I—'—I—'—I—'—T" "T" Fig.14. Growthan dphysiologica l 12 16 20 24 28 32 conditiono fnon-diapaus e larvae t LARVAL AGE (days) of Chilo partellus onartificia l moult toL5 diet (25°C). larvaedi dno tchang edramaticall y although therewa sa gradua ldecreas e from 82°*t o78° so fwater .Prepupa lwate r contents averaged 741.Th efa tconten twa s quitevariabl e during larval development. Lowestvalue so fabou t 121o fth e larvaldr yweigh twer e foundi nlarva e 11day s afterth efourt h larvalmoul t whenth eextraction s startedbu twithi n9 day sfa tconten t increasedt onearl y30$ . 3.4.4 Physiology of larvae entering aestivation-diapause Itwa sno tfel ta susefu lt odevot ea specia l experimentt oth emoultin g frequencyo flarva e entering diapause.Th emos t important observationi si nfac t that supernumerarymoult s during diapaused ooccur .The yhav eofte nbee nme tan d inal lphase so fth ediapause .Som eevidenc ewa sobtaine d thata larva lmoul tma y be inducedb ydisturbanc e duringth ediapause :seldo mwa smor e thanon ehea d capsulefoun dnea rt oa "diapaus e chamber"i nth efield . 38 h* 20- i 10- 0 II iL LLi. Fig.15. The physiological condition of Chilo sp. larvae in amaiz e field during thewe t season of 1974a s related to rainfall and the incidence of aestivation-diapause. Vertical 1/12 197/. bars represent standard errors of themeans . Theobserve dchange si nth ephysiologica lconditio no flarva edurin gpre - diapausear eshow ni nfig .1 5 (wetseaso n 1974),fig .1 6(we tseaso n1975 )an d fig. 17(dr yseaso n 1975).T ofacilitat eth esurve ypercentage so funspotte d anddrough tresistan tlarva ei nth epopulatio na swel la sth erainfal l- al l alreadygive ni nth ecorrespondin g figures6 ,7 an d8 - ar erepeate dhere . Thefirs tobservation swer edon ei na nexperimenta lfiel ddurin gth ewe t seasono f197 4(fig .15) .The ywer estarte da ssoo na sth efirs tunspotte dlarva e appeared (10Sept.) .A ttha ttim eth elarva eha da naverag eoxyge nconsumptio no f 2.6u l0 2/mgdr ywt./h ran da wate rconten to f68.21 .Th eQC Ugraduall ydecrease d toles stha n1 y lC Li nth ecours eo fth eseason .Wate rconten tals ostarte d decreasingt oa minimu mo f65 %followin gdr yweather .Durin ga perio do frai n howeverth ewate rconten tincrease dagain .Th efa tconten to fth elarva ei nth e 39 Fig.16. The physiological condition of ChiZo sp. larvae ina maiz e field during the wet season of 1975 as related to rainfall and the incidence 0 of aestivation-diapause. 1/11197 5 Vertical bars represent standard errors of themeans . firstsampl ewa salread y46.41 .On ewee klate rmuc hmor efa tha daccumulate d (averageo f54.11 )an dthi sleve lwa sconstan tdurin gon emor emonth .Thereafte r thefa tconten tdecrease dt oreac hlevel sbetwee n3 8an d431 .Th emos timportan t resultfro mthi sfiel dexperimen ti stha teve na tth estar to fth eobservation s whenn ounspotte dan da nintermediat epercentag e (35%)o fdrough tresistan tlarva e wasfound ,th ephysiologica lconditio no fth elarva eappeare dt ohav ealread y changedsomewhat ;oxyge nconsumptio nan dwate rconten twer efairl ylo wan dfa t contentwa shig hb ycompariso nt olarva etha twer enon-aestivatin g (fig.14) . Not showni nfig .1 5i stha ti nthi sfiel dals oth epupatio nlevel swer ever ylo w throughoutth eobservatio nperio d (seeals ofig . 6). Inorde rt oinclud epossibl echange s before theonse to fimmaculatio n 40 5-1 oz _ 4- oz*$ 3- '"t H 3* 2- UJ — Fig.17. The physiological condition of Chilo sp. larvae ina maiz e field during the dry season of 1975a s related to the incidence of aestivation-diapause. Maize was irrigated till the end of February. Vertical bars represent standard 1/2 errors of themeans . DATE observations were startedmuc h earlier during thewe t seasono fth e following year (fig. 16).Moreove r morephysiologica l aspectswer e taken into account. Resultswer ea sfollows :respiratio n decreased froma ninitia l consumptiono f 5.4 pi0 2/mgdr ywt./h rt o1. 3u lwhe n the lastobservatio nwa smade .Hear t rate went down from7 3beats/mi nt o44 .Wate r content decreased from 801t oa minimu m of 67%an dther ewa sa subsequen t increaset o74 1durin g the last observations when also theweathe rwa s slightlymor ehumid .Th efa tconten t gradually increased from 37%i nlarva eo fth e first samplet omaximu m levelso faroun d 541 lateron ; from the lasttw osample s however "only" 50% fatwa s extracted. Larvalweight s initially increased.Th efollowin g decrease corresponded witha growt ho fth e pupalpopulation ,whic h reacheda pea ka tth een do fJune .Th eincreas ei nlarva l weight thereafter should therefore mainlyb eattribute dt oth enex t generation. After this increaseweight s remained rather constantwit ha naverag eo f85-9 5m g whichi snorma lfo rfull y developed larvae (fig. 14).Thus ,th e dramatic 41 Fig.18.Th ephysiologica l condition of Chilo sp.larva e ina maiz e field during theshor t rains of 1975a s related torainfal l andth eincidenc e of aestivation-diapause. Vertical bars represent standard errorso f DATE themeans . physiological changes tookplac ebefor ean yunspotte d larvaecoul db efoun dan d sometimes evenwhe nth epercentag e drought resistant larvaewa sstil lbelo w 20$. Fig. 17present s thephysiologica l conditiono flarva ei nirrigate d maize stems duringth edr yseason . Larvae inthi s field initially consumed 3.7y l0,,/m g drywt./hr ;wate r contentwa s 77.3%,fa tconten t 25.2%.Althoug h agraduall y decreasing rateo frespiratio n andwate r content anda nincreasin g fatconten t was observed inth ecours eo ftime ,level s comparable toaestivatin g larvaeo f thepreviou s figureswer eneve r reached. Fig. 18show sth edat ao fa ne wmaiz e field ("Mtwapa")whic hha djus t reached maturity atth etim eo fth efirs t observation.A ttha t time alsoth efirs twhit e larvae couldb efound .O fspecia l interest areth ehig h larvalweight swhic hwer e recorded inthi s field:u pt oa naverag eo f11 0m g inth ebeginnin go fDecember . 42 \ 0.20- /t- t 1 0.15- E -J / o LU 0.10- / z "5 / z> o i E / g 0.05- ^% ^^^—•— Oxygen consumption ofth elarva ewa slo wthroughou tan dfluctuate dbetwee n1. 5 and 2p i0 2/mgdr ywt./hr .Wate r contentwa sequall y normal fordiapausin g larvae: 66-68%. Thefa tconten twa shig h (54.3%)i nth efirs t sample,an ddecrease d gradually thereafter. The testicular volumeo fnon-diapausin g male larvae (fig.19 )increase d 3 3 only slowly from lesstha n0.0 1mm " toabou t0.0 6m m duringa perio do f9 day s afterth e4t hmoult .Durin g thefollowin g days therei showeve ra sudde n increase •z tilla naverag eo f0.2 0mm" . Pupation follows shortly thereafter (seeals o fig. 12).Measurement s ofth etesticula r volumeo fdiapausin g larvaewer e done withmateria l fromth e197 5we tseaso nmaiz e field (seeals ofig .3 an d 16). Unfortunatelyn odat awer e obtained fromth efirs t samples.Whe nth eobservation s startedth elarva ema yalread yhave nbee n inth epre-diapaus e phase.Anyway ,fro m fig. 19i ti sclea r thatth eteste sneve r reacha highe rvolum e than0.05-0.0 6m m, which is- a sshow n- th evolum eprevailin g innon-diapausin g larvaejus t before their accelerated developmentwhic h startso nda y22 . 3.4.5 Morphological changes in larvae entering aestivation-diapause Table 7show sth eaverag ewidt ho fth ehea d capsuleso flarva esample d from five experimental fields duringth ewe tseason so f1973 ,197 4an d1975 .Onl yhea d capsuleso flarva e completely lacking cuticular spots i.e.pre-diapaus eo r diapause larvaewer emeasured . The general trendwa stha t during thegrowin g seasoni nalmos tal lfield s (except 43 W cu T3 C/l CN CM CN CN CN J2 CU CU + o o o o o 0,0,0,0,0, 3 J= + + + + + LO LO en u~) u~t J3 •u SOS'-' -0 •H 3 CD CU cu .G 4J ccj U > o o o o O U CN O CN CO O -a p. CO M -^VOCO O CO rH co co co a> o> 01 •H - CO to M N — — CN CN H T) C/3 ro CN co CN CN CN co CO CO 44 Table8 .Widt ho fhea d capsuleso fth elas tlarva linstar so fnon-diapausin g larvaegrow no nartificia ldie tan dyoun gmaiz erespectively . typeo ffoo d meano fhea dcapsul e+ S.E .(mm ) 00 oo av.g oan do o artificialdie t 1.67+ 0.0 3 1.41 +0.0 3 1.56+ 0.0 3 (n= 26 ) (n= 19) (n= 45 ) youngmaiz e 1.66+ 0.0 3 1.41 +0.0 2 1.53+ 0.0 3 (n= 15 ) (n= 15 ) (n= 30 ) onesow n25/4/75 )a maxima laverag esiz eo fth ehea dcapsul ewa sreache dtha t waslarge rtha nth eaverag eo fnon-diapausin g larvaegrow no ndie to ryoun g maize (table 8). Thesemaxim awer erecorde dwhe nalmos t100 1o fth elarva eha d lostthei rcuticula rpigmentatio nan dusuall yals oa ta tim etha t (some)pupa e werestil lpresen ti nth efield .Th eobservatio ntha tn oincreas ei nhea d capsulediamete rwa sfoun di nth emaiz efiel dsow no n25/4/7 5ma yindicat etha t sucha nincreas edoe sno talway stak eplace .Anothe rexplanatio nhoweve rma yb e thata nincreas edi doccu rbu tbetwee n2/ 9an d27/9 .Als oi nothe rfield smea n widtho fth elarva lhea dcapsul esometime stende dt odecreas ewhe ndiapaus e becamemor eintens e (table7) . Table9 represent sth esummarize dresult so fth ephysiologica lconditio n ofunspotte dlarva ecompare dt ospotte dan dtransitiona lindividual sfro mth e samesamples .Larva ewer eobtaine dfro m1 1differen tsamples . Onlyrespiratio ncoul db erelate dt oth epolymorphism ;unspotte d larvaeconsume d lessoxygen .Althoug hth edifferenc ei ssignificant ,i ti sb yn omean sa sbi ga s Table9 . Therat eo f0 „consumptio nan d thewate r contento flarva ewit h differentcuticula rpigmentation . larvalpigmentatio n spotted and transitional (n= 110) unspotted (n= 88 ) meanoxyge n waterconten t meanoxyge n waterconten t consumption+ S.E . (%) consumption_ +S.E . (%) (ul02/m gdr ywt./hr ) (yl02/m gdr ywt./hr ) 1.81+0.08* 67.36+0.75 1.50+0.06* 67.91+0.55 significantdifferenc ea t 1%leve l (t-test) 45 thatbetwee ndiapausin gan dnon-diapausin glarvae .N orelatio ncoul db efoun d betweenth ecuticula rpigmentatio nan dth efa tcontent . 3.5 DISCUSSION Inth efiel daestivatin glarva ewer ealway sfoun di na chambe rconsistin g ofroughl ywove npiece so ffras swit ha ver ysmoot hinne rcoatin go fsilk .Suc h achambe ri sonl yslightl ylarge rtha nth elarv awhic hi tencloses .Whe ni nth e laboratoryaestivatin glarva ewer eremove dfro mthei rrestin gsite ,the ytende d -i nth eabsenc eo fplan tmateria l- t oconstruc ta thicke rcocoo ntha nnon - diapauselarva ewh omad en ococoo no ronl ya thi none .Als oth efeedin gactivit y ofnon-aestivatin gan daestivatin glarva ewa s observed.I nth eearl ystage so f thediapaus elarva econtinu efeedin gfro mthei rmaiz eplan teve nthoug hthi si s visiblydeteriorating .Thi sbehaviou rha sbee ndemonstrate dfo rman ymor epre - diapauselarva ean dma yb eassociate dwit hth eaccumulatio no freserve sfo rth e oncomingunfavourabl eseason . Iflef tundisturbe di nthei rstem ,aestivatin glarva edissecte dfro mthei r diapause-chambersi ndr ymaiz eproduce da nequa lamoun to ffras safte r3 day so r 8months .Howeve rwhe ndisturbe dthi sproductio nincrease dconsiderably .Fro m thisw eca nconclud etha taestivatin glarva ed ono tactivel yfee do ndr ymaize ; theyonl yutiliz ethi sfoo dwhe nthe ynee dt oconstructio no rrepai rthei r diapause-chamber.Ofte nreporte dfeedin gactivitie so fothe rdiapausin glarva e (3.2)ma yals owel lb edu et odisturbanc ealone . Whendiapausin glarva ewer eprovide dwit hartificia ldiet ,the yinvariabl y exhibita hig hfoo dintak e (ofteneve nhighe rtha nnon-diapaus eindividuals ) priort othei reventua lpupation .Althoug hth edat aar eno tshow nth esam eresult s wereobtaine dwhe ndiapausin glarva ewer egive nfres hmaiz estems .Thes edat a combinedwit hth eearlie robserve dextende dfeedin gperio do fpre-diapaus elarva e doi nfac tsho wtha tdiapausin glarva ear ever ywel lcapabl eo fconsumin gfood . Butwhethe ro rno tthe yd os oi sprimaril ydependen to nth etyp eo ffoo dwhic hi s available.Fres hfoo d (maizeo rdiet )stimulate singestion ,dr ymaiz eblock sit . Iti stherefor eno tcorrec tt osa ytha tdiapausin glarva ei nth efiel dhav ea reducedfoo dconsumptio ncompare dt onon-diapausin glarvae .Th edifferenc ei sno t theresul to fth estat eo fdiapaus ebu tcertainl yals oreflect sth efoo d situation. Theartificia ldie tingeste db yth edifferen tdiapausin glarva ei sno tconverte d intogrowt ho flarva ea si sth ecas efo rnon-diapaus elarvae .A simila rresul t, wasobtaine dwit hhibernatin glarva eo f C. suppressalzs whichstar tt ofee do n 46 oldric estem sshortl ybefor ediapaus ei sterminated .Thi sfoo dintak ei sno t expressedi na nincreas ei nbod yweigh tan dwa sthough tt oserv efo rth e productiono fmetaboli cwate r (KOIDSUMIan dMAKIN O 1958).A secon dexplanatio n mayb etha tdiapaus elarva eonl yhav elimite dmean st outiliz eth ediet .E.g . iti sknow ntha tth eproteas eactivit yi nth emidgu to foverwinterin g larvaeo f C. pavtellus isalmos tni lcompare dt otha to factivel yfeedin glarva e (PANTe t al.1959) .Als oKDIDSUM Ian dMAKIN O (1958)state dtha t"th edigestio nan dabsorptio n offoo ddurin gth ehibernatio nperio d (onlylittle )ar eno ts oremarkabl ea st o inducefurthe rdevelopmen to fth elarvae" .The ydi dhoweve rno tmentio nwhethe r thisi sdu et oth ereduce dconsumptio no rt ometaboli cchange si nth elarva . Thephysiologica lconditio no fste mbore rlarva ei nth efiel dchange d considerablyupo nenterin gint odiapause .A decrease drat eo foxyge nconsumption , rateo fheartbeat ,wate rcontent ,a nincrease dfa tconten tan da narreste d developmento fth eteste swer ealway sfound .Bu tth ephysiologica lconditio no f non-diapauselarva ewhic hdevelo pnormall ychange sals odurin gth elife-cycle . Generallyi tseem stha tth etrend swhic htak eplac edurin gth enorma llarva l developmenttil lth eprepupa lstag ei sreached ,ar efurthe rcontinue dwhe na larvaenter sdiapause .Fo rexample ,th eQC Lgraduall ydecrease dt o3. 5y lCL/m g drywt./h rprio rt opupation .A simila rtren dwa sals orecorde dfo rlarva eo fth e Europeancor nbore r 0. nubilalis (BECKan dHANE C 1960,LEWI Se ta L1971 ,LYNC H etal .1972) ,th ecor nea rwor m Heliothis zea (EDWARDS1970 )an dth eEgyptia n cottonleafwor m Spodopteva littoralis (ABOUL-NASRe tal .1976) .Othe rrecorde d changesi nnon-diapaus elarva einclud ea decreas eo fwate rconten t (from82 %i n early5t hinsta rlarva et o78 1i nfull ygrow nlarvae )an da nincreas eo ffa t content(fro m1 2t o301) . Intabl e1 0figure sar eshow no nth ephysiologica l conditiono fnon-diapaus ean ddiapaus e (mid-diapause)larva eo fsom eHeterocer a ascompare dt o C. partellus. Figuresar ei nclos eagreement . Inchapte r2 w ehav ealread ydemonstrate dth eclos erelationshi pbetwee nth e incidenceo fdiapaus ean dth erainfall .Supplementar yevidenc ewa sno wobtaine d fromth epresen tstudie so fth ephysiologica lconditio no fth este mbore rlarvae : in197 4(fig .15 )observation sonl ystarte dwhe nth efirs tunspotte dlarva ewer e noticed.A ttha ttim eth elarva econsume da naverag eo f2. 6y l0 2/mgdr ywt./hr , hada wate rconten to f68.2 1an da fa tconten to f46.4°s .Al lthes efigure swer e infac tdifferen tfro mth echaracteristic so fnon-d^apausin glarva ean dwer emor e similart othos eo faestivatin glarvae .W econclude dtherefor etha tth elarva ei n thisfiel dha dalread yentere dth eprediapaus ephas ewhe nth eobservation s started.Th efirs tsampl ei n197 4wa stake nafte ra lon gperio d (11weeks )o f almostcomplet edrought .Thi scause da standstil li nth egrowt han ddevelopmen t 47 ~2 3 — to • U M i/"i p*i at a: o» r- u — C/3 a\ z — O H ?~< H-l C/3 ti •a a " c 4J o in o aj u e >N I • 4J u 3 c •i a> y-i x B J 4J o w CO u B ai <1) 0 0 fr* U B 3 y ^^ -- >, 14 oi 91 a) u s W J= 0) (n w to c *J 00 0) CO 00 3 H w a •r4 o « B S •^ >* l-l o o CO CO o o 01 U X U) S 01 U )-l O CO l-i CO os 01 0) 3 l-l 3 4J i-i CH CO r»i 01 3 Q> 4J a +i s < U 00U 00U •H U CO -O ID >b j COO -ft O >i-l 'i-l too a TJ ! j4 r^ r-l o fH t_l B vO Og &Q, i i-H 0) ' QJ CM m •—' es CM *^ s^ CM £4, •H o B u o t-l V •M •a s *n •H b <—i 4J j; 4J J3 -I r-l— W£ U H r-IAJ §•••3 01 4«J lff\ 01 0) 0) 3 .s >B £ XI I I -FI vO -H N -H CO O 111 3 o I -* "O — TJ — M-l OS >4-l o o B 0) 4) CO t>0 > 5?!5 O -1 a v 01 <-. t-<3i r-A Q £S 48 ofth emaiz eplants ;the yneve r developed beyond thetasselin g stage. Apparently also the stemborer s inhabiting theseplant swer e affected. They had changedphysiologicall y although thiswa sno tye t reflected inth e pigmentation and only little inth edrough t resistance ofth e larvae. The experimental fieldo f 1975 (fig. 16)differe d from 1974i ntw oaspects : 1.ther ewa smor e rainfalldurin g thegrowt h ofth emaiz ewhic h resulted in a completematurit y ofth eplants ,2 .th eobservation s were started amply before any signo fcuticula r colour change ordrough t resistance inth e larvae could be found.Th ephysiologica l condition oflarva e inth e first samplewa s asfollows : respiratory ratewa s 5.4 yl0~/m gdr ywt./hr ,wate r content 801an d fat content 361,allo fwhic h suggestnon-diapaus e larvae.Afte r the first observation most physiological qualitieswer e fairlyconstan t during therain yperiod . Only fat content showed acontinuou s increase.A s soona sth erain s ceased on8 Jul ymajo r changes tookplace :respirator y ratedroppe d from 3.5 ylt o 1.6 ylO./m gdr y wt./hr,wate r content from 72t o 681,heartbea t ratedecrease d from 75t o 54 beats/minan d the fat content increased from 45t o 521.Obviousl y once again, drought appeared tob e amajo r factor inth e inductiono fdiapause .Th e fact that (little)pupa ewer e found evendurin g the 2wee kperio d after cessation of therai n (fig. 7)indicate s thata t leasta smal lproportio n of the larval population,mos t likely theoldes t larvae,wa sno t effected by theweathe r change.A s in 1974,th echang e incuticula r pigmentation onlybecam e visible afterth emajo rphysiologica l changesha d occurred. Convincing evidence ofth erai ndependenc e ofaestivatio n came fromth e experiment inwhic hmaiz ewa s irrigated during thedr y season (fig. 17).Larva l oxygen consumption andwate r content remainedhig h and fatconten t lowthroughou t the irrigation period. Although both therespirator y ratean dth ewate r content gradually decrease when larvae diapause and alsodurin g thediapaus e itself,thes eprocesse s dono t always followa smoot h curve.Agai nrai nseem s tob e the influential factor. Some caution shouldb e exercisedwit hthi s interpretation, since thequantit y ofrai n isno t theonl y factorwhic h determines themoistur e condition ofth e field. The durationo fth erainfal l andth erat eo fevaporatio n (dependent onth e sun/clouds ratio)ar e equally important. Larval fat content increases during thefirs tphas e ofdiapaus e and this is possibly theresul t ofth econtinue d feeding ofth e larvae during the pre-diapause period forwhic h some field evidencewa spresente d in3.4.2 .Fa t contents always started decreasing aftersom etim epresumabl y due to aslo wutilizatio n ofthi s food reserve.N o convincing evidencewa s obtained that thebod yweigh t of 49 diapauselarva eexceed stha to fnon-diapaus elarvae ,bu twidt ho fth ehead - capsulesofte nappeare dt ob elarge rfo raestivatin glarvae . Wefinall yretur nt oth equestio nwhic hw easke dourselve si nth e introduction:"whe nd olarva eperceiv eth etoke nstimul iwhic hlead 't oth e entranceo faestivation-diapause?" .Fro mth eresult smentione di nth epreviou s chapteri twa salread yclea rtha tth ediapaus einducin gfactor smos tlikel yhav e tob elooke dfo ri nth econditio no fth eplant .Th epresen tresult ssugges ttha t wemigh tsuccee di nfindin gth efactor(s )i fw einvestigat eth eplan tbefor eth e larvaear eturnin gunspotte dand/o rar ebecomin gdrough tresistan ti.e .whe nth e firstchange si nth ephysiologica lconditio no fth elarva eappear .Th e asynchronousmanifestatio no fchange si nth ephysiologica lconditio no fth e larvaean dth elos so fthei rbod ypigment swa sdemonstrate di n3.4.5 . Iti stru e thatunspotte dlarva ewer efoun dt ohav ea lowe rrat eo frespiratio ntha n spottedindividual so fth esam esample .Bu tthes eresult shav et ob eregarde d withcautio nsinc eals ounspotte dlarva eo fth esam esample sha da highl y reducedrat eo frespiratio na scompare dt onon-diapaus elarva eindicatin gtha t thespotte dlarva eha dalread yentere dth epre-diapaus estage .N orelatio na t allcoul db efoun dbetwee nth epolymorphis man dth ewate ro rfa tcontent .Fro m theseresult si ti sno tclea rwha tcause sth elos so farticula rpigmentation . Itma yb ea direc tresul to fth echange dconditio no fth elarva lfoo da si s suggestedfo r D. saoeharalis byKATIYA R (1960)an dfo r B. fusaa byUSU A(1970) . Buti tma yals ob etha tth efactor(s )primaril yinducin gaestivation-diapaus e (i.e.th ehos tplant )onl ypla ya nindirec trole .Thi si sfo rexampl eth ecas e withlarva eo f D. grandiosella whichente rdiapaus e (andtur n"immaculate" )whe n thetemperatur edecrease san dth edaylengt hshortens .Diapaus ecoul dhoweve rb e induceddirectl ywit hjuvenil ehormon e (YINan dCHIPPENDAL E 1974).I nthi scas e juvenilehormon eseeme dt oregulat eno tonl yth epolymorphis mbu tals oth e physiologicalprocesse sinvolve di nth ediapause .Simila rmechanism shav ebee n foundfo rman yothe rdiapausin ginsect s (LEES1956 ,BEC K1968 ,CHIPPENDAL E1977 ) andma ywel lb evali dfo r C. partellus aswell . 50 4 The incidence of aestivation-diapause asrelate d to the condition of the host plant (maize) 4.1 INTRODUCTION Inth epreviou schapter si twa sshow ntha tth eonl yclimati cfacto r affectingaestivation-diapaus e ofth elarva eo fth espotte dstal kbore r Chilo pavtellus (Swinhoe)an dth ecoasta lstal kbore r Chilo orichalcociliella (Strand) israin .Afte ra perio do fdr yweathe rphysiologica lan dsubsequen tmorphologica l changescoul db eobserved . Itwa sthough ttha tth emos tlikel ymediu mthroug h whicha ste mbore rdetect sdrough ti sth econditio no fit shos tplant .Th epresen t researchwa scarrie dou tt oinvestigat ewhethe rther ear eground sfo rthi s reasoning.Water ,protei nan dsuga rconten to fth efoo dplan twer econsidere da s possiblesignal sleadin gt oth einitiatio no faestivation-diapaus ei nth eabov e mentionedstal kborers . 4.2 LITERATURE Althoughdiapaus ei nth etemperat ean dsubtropica lregion si sprimaril y controlledb yphotoperio dan dtemperature ,foo dha softe nbee nfoun dt ob ea factorwhic hinfluence sth epercentag eo fdiapause .Wel lknow ni sth erelatio n betweenth ecompositio no fth ecotto nbol lan dth ediapaus ei nth epin kbollwor m Pectinophora gossypiella. SQUIRE (1940)firs tsuggeste dtha tdiapaus ei spromote d bya nincreas ei nfa tconten tan da decreas ei nwate rconten to fth ecotto nboll , butthi srelationshi pwa sonl yconvincingl yprove dmuc hlate r (ADKISSON1961 , BULLan dADKISSO N196 0an d1962 ,RAIN Aan dBEL L 1974).CROWDE Re tal . (1975) observedtha tearl ycro pmaturit y (inducedb yirrigatio ncut-off )increase dth e incidenceo fdiapause .Th ematurit yo fth efoo dplan tals oenhance dth eincidenc e ofdiapaus ei nlarva eo fth eric este mbore r Chilo suppressalis (PATHAK1968 ) ando fth ecodlin gmot h Laspeyresia pomonella (PHILLIPSan dBARNE S1975) . 51 Inal lthes ecase showeve r (short)photoperio dan d (low)temperatur eha deffect s overridingthos eo ffood .Als oth etyp eo ffoo dma yb eimportant :larva ema y enterdiapaus ewhe nfeedin go non ehos tplant ,bu tma y- unde rth esam e environmentalcondition s- no td os oo nanother .Example so fthi sar eth eIndia n mealmot h Plodia interpunotella (WILLIAMS1964 )an dth eplu mfrui tmot h Grapholita funebrana (SARINGERan dDESE O 1968). Inth etropic sth econditio no fth efoo di softe nreferre dt oa sth e primarydiapaus einducin gfactor .Th edat ao nth eexac timpac to fth ehos tplan t ondiapaus ear ehoweve rfragmentar yan dincomplete .VA NDE RGOO T (1925)reporte d thatth edormanc yo fth ewhit eric ebore r Soirpophaga innotata (= Tryporyza innotata) onJav ai sinitiate db yth eripenin go fth eric este mafte rth eear s startdevelopin gan dtha tthi sdormanc yi sindependan to fth erainfal lan dth e moistureo fth eplant .Observation so fROTHSCHIL D (1971)i nMalaysia nBorne o withth esam ebore ra swel la swit h T. inaertulas seemedt osuppor tthi sidea . Noresearc hwa sdon et ofin dth eactua lplan tfactor(s )responsibl efo rth e arresteddevelopmen to fth e Tryporyza larvae.HYNE S (1942)describe dth erestin g stageo fth elarv ao f Diatraea lineolata onTrinida dan dsuggeste dtha tth e quiescence,whic hcoincide dwit hth edr yperio do fth eyear ,wa sdu et oth edr y conditiono fth emaiz estem .Evidenc efo rthi side awa sprovide db yth e observationtha trestin glarva epupate dwhe nthe ywer etransferre dfro mdr yol d maizestem st ofres hgree nstalk s (aquic kresponse )o rt odea dwette dstem s (aslowe rresponse) .Whe nth elarva ewer ekep ti nth edr ypit hthe ystaye di n therestin gstage .KEVA N (1944)workin gwit hth esam einsec tbelieve dtha t"i t isth elac ko fsuitabl efoo drathe rtha nth efoo ditsel fwhic hi sth ecaus eo f thediapause" .A sevidenc eh ementione dtha tspotte dlarva ewhe ntransferre d fromgree nstem st omoistene d"dry "stalk so rt ogree nstalk swhic hha dbee n allowedt obecom erotte nusuall ylos tthei rspot san dbecam eyellow .KEVA N suggestedtha tchemica lchange si nth este mwer eth emos timportan tfactors . Howeverals o"larva etha twande rawa yfro mth efoo dprovide dente ra prolonge d restingstage "an dthu stota llac ko ffoo dma yals oresul ti ndiapause . Similarly,th ediapaus eo fth emaiz este mbore r Busseola fusaa isthough tt o beinduce db yth ehos tplant .Th edryin gou to fth emaiz eplan twa smentione d asa facto rinitiatin gth ediapaus eb ySWAIN E(1957 )i nTanzani aan db ySMITHER S (1959)i nsouther nRhodesia .Thi swa sderive dfro mth efiel dobservatio ntha t diapauseincrease da sth efoo dstarte ddryin gou tan dtha tn odiapausin glarva e werefoun di nirrigate dmaiz eo ri ntiller so fwil dgrasse san dsorghu m (which containhig hwate rcontents) .USU A (1973)workin gi nNigeri awit hth esam este m 52 borermentione dtha tothe rfactor si nth eripenin gmaiz estem ,apar tfro mwater , areinvolve di.e .th eincreasin gcarbohydrat econten tan dth edecreasin gprotei n content.Bu th edi dno tgiv econclusiv eevidenc etha tthes efactor sar ecritical . Itwa sonl ydemonstrate dtha tmor elarva eente rdiapaus ea sth emaiz eplan t matures.Equall ylittl ei sknow no nth espotte dstal kbore r Chilo partellus. Restinglarva ear epresen ti nol ddr ystalk so rstubbl eremainin gi nth efiel d atth een do fth egrowin gseason .Thi sma yb ei nwinte ra trelativel ylo w temperaturese.g .Indi a (PANTan dKALOD E1964 ,KHA Nan dKHA N 1968),Pakista n (MOIZan dQURESH I1967 )o ri n"summer "a tth een do fth ewe tseaso ni nEas t Africa:NY E (1960)i nTanzania ,SCHMUTTERE R (1969)i nSudan ,MATHE Z (1972)i n Kenyaan dDELOBE L (1975b)i nMadagascar .Th ebreedin go f C. partellus seemedt o becontinuou si nUganda ,bu tdurin gth edr yseaso nwhe nlarva e (andpupae )ar e foundi nsorghu mtras han dstubbl e"th edevelopmen ti sprobabl yslowe ddown " (INGRAM1958) .Late rNY E (1960)di dcom eacros saestivatin glarva edurin gth e dryseaso ni nUganda .Th elarva ewer efoun di ndr ymaiz estem san di nth ehighe r partso fsorghu mplants .A tth esam etim eactiv elarva ewer eobserve di nth e lowerparts .Th eautho rconclude dtha t C. partellus "onlyundergoe sa restin g stagewhe nit shos tplan tdrie sou tcompletely "an d"tha tth elowe rpart so f sorghumremai nsufficientl ymois tfo rth elarva et ocontinu ebreedin gdurin gth e dryseason" .GONCALVE S(1970 )workin gi nMadagasca rcoul dfin dth espotte dstal k borerthroughou tth eyear ,bu tobserve d" alo wactivity "durin gth efou rmonth s ofth edr yseason .Onl yDELOBE L (1975b)mad ea neffor tt oexplai nth eincidenc e ofdiapaus ei nthi sborer .H esuggeste dtha tth eextremel ylon gdevelopmen to f lastinsta rlarva ewa spartiall ycause db yth edeterioratio no fth enutritiv e environment (sorghum).Again ,n oconclusiv eexperiment swer eperformed . 4.3 MATERIALSAN DMETHOD S 4. 3.1 Handling of samples Sampleso fmaiz estem s (CoastComposite )wer ecollecte ddurin gth emornin g hoursi nexperimenta lfield si nKikambala .Field san dsamplin gmethod swer e previouslydescribe di n2.3.3 .O nth eda yo fsamplin gth eaverag egrowin gstag e ofth eplant swa sdetermine db yusin gcriteri aoutline da tth ebotto mo ffig .20 . Alllarva edissecte dfro mth efiel dcollecte dstein swer ethe ndispatche dt o Nairobiinsid este mpieces ,whic hha dbee nrandoml ytake nfro mth esample .Onl y bottoman dcentra lpart so fth este mwer einclude dsinc eto ppart shardl ycontai n larvae.I fpossibl eth edryin gprocedur efo rth edeterminatio no fth ewate r 53 contenti nthi sste mmateria lwa sstarte dimmediatel yafte rth earriva lo fa samplewhic hwa susuall y 24hr safte rth estem swer ecut .Otherwis esample swer e sealedi na plasti cba gan dstore di nth edee pfreeze r (-20°C).Fo ral lsample s waterconten twa sdetermine dan dmos tsample swer eanalyse dfurthe rt odetermin e totalsugars ,reducin gsugar san dcrud eproteins .Fo rthis ,drie dmateria lwa s groundi na Wile ymil lt o40-mes hsiz eand ,i fno tuse ddirectly ,store di na smallair-tigh tcontaine ri na coo ldar kplace .Sinc eal lstem si non esampl e weremixed ,onl yth emea nchemica lcompositio no fth estem so fthi ssampl ewa s obtained. Larvalmateria lwa shandle da sdescribe di nchapte r2 .Fo rreason so f conveniencepercentage so fdiapausin glarva ei.e .drough tresistan tan d unspottedlarva e- als oshow ni nchapte r2 - wer erepeate di nth edifferen t figures. Inorde rt oobtai na nimpressio no fth ecompositiona lchange soccurrin gi n maizegrow nunde rnorma lcondition s (i.e.wit hsufficien twate ravailabl e throughoutth egrowth )stem sobtaine dfro ma privat efiel dclos et oNairob iwer e analysed fromth eearl yvegetativ estag et obeyon dmaturity . 4. 3. 2 Analysis of stem material Determination of water contents Afterrecordin gth ewe tweight ,th este mpiece s wereheate dfo r3 0mi na t10 0 Ct oinactivat eenzyme san dkil lth eplan tcell s (thisprocedur ewa sneglecte di fstem sha dbee nfrozen) .Th edryin gcontinue da t 70 Ci na nove nwit hmovin gai rtil la constan tweigh twa sreached .Th e percentagemoistur ewa scalculate dfro mth elos so fweigh tafte rdryin gan d expresseda spercentage so fth efres hweight . Determination of soluble sugars Sugarswer eextracte d (induplicate )wit h80 % ethanola sdescribe db ySMIT Han dGROTELUESCHE N (1966).Deproteinizatio no fth e extract (withneutra llea dacetate )wa sno tdon esinc epreliminar yexperiment s hadshow ntha tthi sste pcoul db eomitted .Aliquot so fth eextrac twer echecke d forthei rreducin gpowe rbefor ehydrolysi swit h1USO . (givingth econten to f reducingsugars )an dthereafte r (totalsolubl esugars) .Non-reducin gsugar ssuc h assucros ecoul dthe nb eobtaine db ysubtractin gth ereducin gsugar sfro mth e totalsugars .Th ereducin gpowe ro fa solutio nwa sdetermine db yth eShaffer - Somogyicopper-iodometri cmetho da sdescribe db yHEINZ Ean dMURNEE K (1940). Sugarcontent swer eexpresse da sglucose ,whic hwa suse da sa standard . 54 Determination of crude -protein Totalnitroge nwa sdetermine db yth emicro - Kjeldahlprocedure .Th edeterminatio n (induplicate )wa sdirectl ycarrie dou t withgroun dste mmateria lan dwa sno tpreceede db yan yfractionation . Multiplicationo ftota lnitroge nb y6.2 5 gaveth eamoun to fcrud eprotein . 4.3.3 Consumption and utilization of maize stems Thefeedin gbehaviou ro fnon-diapaus elarva eo nth epit ho fstem so fmaiz e plants (Hybrid512 )o fdifferen tgrowin gstag ewa sstudied .Th efollowin gindice s wereused :consumptio ninde x (C.I.),relativ egrowt hrat e (G.R.),efficienc yo f conversiono fingeste dfoo dt obod ysubstanc e (E.C.I.), conversiono fdigeste d foodt obod ysubstanc e (E.C.D.)an dapproximat edigestibilit y (A.D.).Th eindice s areexplaine di nmor edetai lb yWALDBAUE R (1968). C.I.'swer ecalculate da sfres h weighto ffoo deaten/day /mea nlarva lfres hwt .durin gfeedin gperio d (Cl.^g^) anda sdr yweigh to ffoo deaten/day/mea n larvalfres hwt .durin gfeedin gperio d (C.I.dry) - F°r theres tal lindice swer ecalculate do nth ebasi so fdr yweights . Dryweight sa tth een do fa feedin gperio dwer edetermine ddirectly .Dr yweight s attn estar to fa nexperimen tha dt ob ecalculated ;thi swa sdon eb ydeterminin g thewate rconten to fequivalen tcontro lmaterial . Topreclud emoultin gdurin gth eobservation sonl y6t hinsta rlarva ewhic hha d recentlymoulte d (headcapsule sno tye ttanned )wer eused .Fo reac hexperimen t 10-15larva ewer eobserve dseperatel yove ra feedin gperio do f2 4hrs . 4.4 RESULTS 4.4.1 Diapause and stage of maize Figures20-2 3represen tth eincidenc eo fdiapaus ei nrelatio nt oth egrowin g stageso fmaiz eplant si nth ecours eo ftime .Th egrowin gcondition sfo rth emaiz e fieldswer equit edifferent :whe nenoug hwate rfo rgrowt ho fth eplant swa s available (i.e.whe nmaiz ewa ssow nearl yi nth egrowin gseaso na tth een do f April)a norma ldevelopmen toccurre dresultin gi nfull ymatur eplant so fstag e6 (fig. 20an d 23).Whe nmaiz ewa ssow nlate ri nth egrowin gseaso nful lmaturit y wasseldo mreached .Fo rexample :plant si nth efiel drepresente di nfig .2 2(sow n atth een do fJune )cease dt odevelo psoo nafte rtasselin g (stage4) .Whe n maizewa sgrow ndurin gth edr yseason ,plant sha da ver yslo wgrowt hrat ean d could- whethe rth eirrigatio nperio dwa sshor t (fig.21 atil lth een do f January)o rlonge r (fig.21 btil lth een do fFebruary )- no tdevelo pbeyon dth e 55 : loo-, not irrigated irrigated 100-j 2 ,2* Z S 1,80- o 60- 5 | GO o » 40- 'S 5? £0- \2» i/> 20- w 20- h- 0 i i 100-1 80- 60- 40- 20- 0 -1 1— 1/10 1974 1/3 1/4 1974 1/2 1/3 1975 DATE DATE Fig. 20.Th e seasonal incidence of diapause in larvae of Chilo sp.a s related todevelopmen t stage and water Fig. 21.Th e season incidence of content of themaiz e plant during the diapause in larvae of Chilo sp.a s wet season. Maizewa s sown 23Apri l related to developmental stage and 1974. Numbers refer to the developmental water content of themaiz e plant during stages of themaize : the dry season, a.maiz e sown 4 December stage 1: all stages before appearance 1973 and not irrigated beyond 28 January of 4th leaf 1974,b .maiz e sown 19Novembe r 1974an d 2: collar of 8th leaf visible; irrigated till 20Februar y 1975.Number s early leaves may be dead; refer todevelopmenta l stages of the leaf growth maize and are explained in fig.20 . 3: tips of tassels visible 4: pollen shedding; silksvisible ; ears start developing 5: ears fully grown,grain s maturing 6: grains mature and drying Asterisks indicate the appearance of themaiz e plant no asterisk: leaves and stem succulent and green (wilting may occur) one asterisk: leaves dry, stem green two asterisks: leaves and stem dry, plant dying. 56 vegetativestag e2 .N odoub tdu et oth eextremel yhig hevaporatio nrat edurin g thatseason .I nca nb esee ntha tlarva ewer eabl et oente raestivation-diapaus e inal lthes edifferen tstage so fth emaiz eplant .Thi sindicate stha tth e inductiono fdiapaus ei sno tdependen to nth eactua lstag eo fth emaiz eplant . Inothe rwords :th eplan tfactor swhic htrigge rth ediapaus ema yappea ri nan y developmentalstag eo fth ehos tplant .Larva efro mth efiel dshow ni nfig .21 b didno tente rdiapaus e duet ocontinue dirrigatio n (seeals o2.6) . 4. 4. 2 Diapause and chemical composition maize stem Aestivation-diapause ofste mborer si nth etropic sha softe nbee nrelate dt o themoistur econten to fth efoo dplant .Th epresen tresult ssho wtha tattentio n shouldb epai dt oth este mwhe nthi si sstil lgree n (leavesma yb ewilted )an d containsa fai ramoun to fwater .Th efigure s (20-23)sho wtha tsom eaestivatin g larvaear efoun da tan ytime ,bu ttha tth efirs tsignifican tincrease si n percentageunspotte dan ddrough tresistan tlarva etak eplac ei nstem swhic h contain70-8( Ho fwater ,wel lbefor eth ewate rconten tdecrease ssteeply .A studyo fth ephysiologica lconditio no fthes elarva e (insetsfig .2 2an d23 ) confirmedthi sb ydemonstratin gtha tth efirs tpreparation sfo rdiapaus ear emad e beforeth eappearanc eo funspotte do rdrough tresistan tlarvae .Th elarva lwate r content,th erespirator yrat ean dth erat eo fhear tbea tha ddroppe dnotably , andth efa tconten tha dincrease dwhe nth emoistur econten to fth estem sha d onlyslightl ydecreased ,i.e .fro m8 0t o7 5 %i n197 4 (fig.22 )an dfro m8 0t o 70I i n197 5 (fig.23) .I nbot hcase splant swer ewate rstresse dbecaus eo fth e lacko frainfall . Samplesfro mtw oexperimenta lfield swer eanalyse dfo rreducin gsugars , totalsugar san dcrud eprotein s (fig.2 2an d 23).Th esuga rcontent so fth e maizestem sfro mth etw ofield swer ever ydifferent .Tota lsuga rconten tdurin g theperio do fdiapaus einductio nwa sabou t6 % ofth este mfres hweigh t (29 % of thedr yweight )i n197 4 (fig.22 ) whereasi n197 5 (fig.23 )neve rmor etha n2. 5 % (freshwt. )o r9 %(dr ywt. )wa sfound . In otherexperimenta l fieldssimila r levelshav ebee nrecorded .Th elarg edifference sma yb edu et osoi lan d cultivation;th etw ofield swer esow na ta differen tlocatio no fth eCoas t AgriculturalResearc hStation ,a ta differen ttim eo fth eyea ran di ndifferen t years. Inbot hfield sth equantit yo freducin ga swel la snon-reducin gsugar s washighes ti nth epre-diapaus ephas eo fth elarvae . 57 o-o REDUCING SUGAR TOTALSUGA R CRUDE PROTEIN pffl. o * Q- % O * J <-> o < JZ100 Fig. 22.Th e seasonal incidence of diapause in larvae of Chilo sp.a s related to developmental stage and chemical composition of themaiz e plant during thewe t season.Maiz e was sown 20Jun e 1974.Number s refer todevelopmenta l stages of the maize and are explained in fig. 20.Th e inset 1/9 1/10 1/11 1/12 197A shows thephysiologica l condition of DATE the larvae during the same period. During thatperio d protein levels variedbetwee n 0.5 - 0.9V of the fresh wt. of the stemo r 2- 3%o f the drywt . Inanothe r experimental field larvae preparing fordiapaus ewer e found in stems containing 1.31protei n (freshwt. ) or4.2° 6 (drywt.) . As aresul t of the rapidly decreasingwate r content of the stemwhe n theplan t dies,protei n contents of the "fresh"stem s ultimately increase.Bu t at that time larvae have already entered diapause. 58 >REDUCIN G SUGAR > TOTAL SUGAR £_ 3- • CRUDE PROTEIN o o fe 'i 60- l- a> 2 S ; 40 • ;2o- g 2 u> o Fig.23 .Th eseasona l incidenceo f diapausei nlarva eo fChilo sp.a s relatedt odevelopmenta l stagean d chemical compositiono fth emaiz e plant during thewe tseason .Maiz ewa s sown 25Apri l 1975.Number s refert o developmental stageso fth emaiz ean d are explainedi nfig .20 .Th einse t shows thephysiologica l conditiono f the larvae during thesam eperiod . 4.4.3 Composition of the maize stem during its normal development The chemical compositiono famaiz e stem changes considerably duringit s growth. Table 11show s thati nth eearl y (vegetative) stages steinsha da hig h water content,a hig hprotei n contentan da lo wsuga r content. Duringth e furthervegetativ e growthth ewate r content remainedhigh ,wherea s theprotei n content gradually decreased andth esuga r content increased. Themajo r changes howeveroccurre dwhe nth eplan t started itsgenerativ e developmentwit hth e formationo fth emal e inflorescence,th etassel :th eplan t reduced thewate r contento fit sste m from9 0t o8 0%, an dth esuga r content increased from15. 1 to35. 8 %o fth este mdr yweigh to r1. 5t o7. 1 %o fth efres hweight .Whe n expressed aspercentage so fdr ywt . alsoth eprotei n content changeda ttha t timebu tbecaus eo fth esimultaneou s decrease inwate r content,th epercentag e 59 inth efres h stems remained constant. Iti sremarkabl e thatonl y minor differenceswer e foundbetwee nstem s from almostmatur eplant s andstem s4- 5 weeks beyond maturity. Table 11. Compositiono fmaiz e stems (Hybrid 512)a tdifferen t stages ofgrowth . z stage of growth length of n mean mean sugar and protein content stem till water point of content reducing total crude growth (cm) (%) sugars sugars proteins 6-8 leaves 5 5 91. 5 2.8 (0.24) 6.7 (0.57) 21. 4 (1.82) 8-9 leaves 25 5 90.8 6.8 (0.66) 15.1 (1.39) 16.0 (1.47) 9-10 leaves 60- 80 3 90.3 7.1 (0.69) 15.1 (1.46) 13.4 (1.30) tassel well 110- 130 5 80.2 13.6 (2.69) 35.8 (7.09) 6.9 (1.37) developed; pollen shed; ears developing plants 4-5 160- 200 5 79.7 11.3 (2.29) 39.7 (8.06) 6.4 (1.03) weeks beyond maturity; leaves dry, stem green expressed aspercentag e ofdr yweigh t andi nparenthese s aspercentag eo f freshweigh to fstem . 4.4.4 Consumption and utilization of maize The consumptiono fth epit ho fmaiz e stem obtained fromplant s indifferen t growing stagesi sshow ni ntabl e 12.Althoug h larvae consumed less andles s fresh stemmateria la sth eplan t aged,a significan t difference couldonl yb e demonstrated betweenth econsumptio no ffres h agedmaiz e (stageV )an dth eothe r maize stages.Becaus e ofth esimultaneousl ydecreasin gwate r content, significantly more dryweigh to fth eolde rstem swa singested ,whic hi ntur n resulted inhighe r growth rates.Mos t remarkable isth edifferenc e infoo d intake by larvae feedingo nstem so falmos tmatur e maize (stage IV)an dlarva e feeding on aged stems (stage V). Although thechemica l compositiono fthes e stemswa s almostequal ,larva e consumed significantly lesso fth efres ho rdr yage dmaiz e stemsan di nconsequenc eha da lowe r growthrate . Figureso nth edigestibilit y andutilizatio no fth evariou smaiz e stemsar e giveni ntabl e 12an dar egraphicall y showni nfig .24 .Th eA.D. ,E.C.D .an d 60 n IE IE Fig. 24 Digestibility and utilization of thepit h ofmaiz e stems in different stages of growth by 6th instar larvae of Chilo partellus. Numbers refer to the stages of the plant and are explained in table 12. I Iproportio n of undigested food (faeces) proportion of digested food metabolized for energy proportion of digested food used forbod y substance E.C.I,o fth ethre e vegetatively growingmaiz e stages I,I Ian dII Iwer e very much alike. Compared tothes e stages ahighe rproportio no fstem so ffurthe r developed plants (stage IVan dV )wa sdigested .Bu tsinc e this digested material was lessefficientl y converted intobod yweigh t thanth edigeste d materialo fth e younger stems,th eefficienc y ofconversio no fingeste d foodwa sapproximatel yth e same foral lstems .Th esignificantl y different A.D's,E.C.D.' san dE.C.I.' so f maturing (stage IV)an dage d (stageV )maiz e material indicate thata larv a perceives thesematerial s indifferen t ways. 4.5 DISCUSSION As longa sth eweathe r remaineddr yaestivatin g larvae couldb efoun d inth e field inplant s ofalmos tan ystag eo fgrowth : during thevegetativ e stage (fig. 21a),whe n sheddingpolle n (fig.22 )an dwhe n fullymatur e (fig.2 0an d23) . Inchapte r 2i twa sdemonstrate d that climatic factors other than rainca nb e excludeda sdiapaus e inducing factors.Th epresen t findings that larvaear e capable ofenterin g aestivation-diapause independent ofth egrowin g stageo fth e maize plant theyar einhabiting , suggest thatth eeffect so fdrough to nth eplan t mayb esimila r foral ldevelopmenta l stages. Someevidenc e supporting this hypothesiswa sgive nb yLEVIT T (1972)an dHSIA O (1973)bot h reviewing thegenera l responses ofplant s- irrespectiv e ofth edevelopmenta l stage -t owate rstress . Any following informationo nthi s subject isderive d from thesepapers . Themos t commonly affectedproces s ina wate r stressed plant isth egrowt h rate.Du et oa lac ko fturgor ,cell sd ono texpan d andals oth enumbe ro fcel l 61 4-1 in a to o CU cu • u CU CO CN m 00 i II UH *—co * — •u a, CN o H M 1 CN1 ?l + O 5 CO d CN CN CN co rl W - a M X X M rH cu cu VO vr> vO „ „ r* cu o + + 1 + 1 + 1 + N CO OS m r-l u ~~ id w CO CO co CN CN 4-1 a CO § CJ > •rl J3 H"i H ••-i CU UH 62 divisionsma y seriously be reduced.A maizeplan tbein g astenohydri cplan t which canonl y growwithi n anarro w range ofwate rstresse sma y particularly suffer. The flowering stage ofth eplan t ismos t sensitive. Inth e experimental fieldmentione d inthi spape r the growth retardation after thestar to f thedr y weatherwa sobvious . Itwa s found that thewate r contento f theplant s usually decreased somewhat after cessationo fth e rains,bu t ingenera lwate r turned out tob e remarkably well heldwithi n theplant ,probabl y due tostomata lclosur e and consequent reduced transpiration. Soon after the complete desiccation of all leaftissue s thestem s started drying out ata muc h fasterrat e thanwhe n green leaveswer e stillpresent .Th e size of the aestivating larvalpopulatio nwa s clearly inverselyproportiona l tothi s rapidly decreasingwate r content.Bu t iti s questionablewhethe r thisdramati cwate r losso fth eplan t induces the larvae in theplan t toente r diapause.Th e first rises innumbe r ofdrough t resistant andunspotte d larvaewer e foundbefor e thisrapi d fallo f thewate r content of themaiz e stem.Thi smean s that larvae entered apre-diapaus e phasewhe n stems contained 70-80% ofwater .Earlie r studies on thephysiologica l conditiono f the larvae confirmed this.Majo r changes inth ephysiolog y of the larvaewer e found totak eplac e soon after thedrough tstart s (fig.2 2an d 23,se e also chapter 3). Thus, ifth ewate r condition ofth ehos tplan tprovide s thetoken - stimulus fora larv at oente r aestivation-diapause,i ti scertai n that this is while thewate r stressedplan t still contains a largeamoun to fwater . Sugar contents ofmaiz e stems normally risegraduall y during the development of theplant .Thi swa s demonstratedb y JONES andHUSTO N (1914)an d confirmedb y thepresen t analyses (table 11).Du e tostomata l closurephotosynthesi s declines inwate rstresse dplants .Sinc e growth (forwhic h sugars arerequired )i s affectedb ywate r stressmor equickl y thanphotosynthesi s (producing sugar) is, sugar contents of theplan tma y even increase inth eearl y stages ofth estress . Inth eexperimenta l fields represented in fig. 22an d 23i t isshow n thatth e sugar content remained fairly constant (buta tver y different levels) formor e thanon emont h after thestar t of thedr yperiod .Thi sma yb e advantageous for theaccumulatio n of fatreserve sb y larvaepreparin g fordiapause .HIRAN O (1964) found that larvae of C. suppressalis growno n carbohydrate rich foodbecam e very fatty andhighl y tolerant toenvironmenta l resistances. Thevariabilit y ofth esuga r content instem s containingpre-diapaus e larvae in the field suggests that thequantit y ofsuga r ina ste m isno tessentia l to prevent diapause totak eplac e and thusdoe sno t seemt opla y arol e inth e 63 inductiono fdiapause . Proteincontent so fmaiz estem sar ealway shighes ti nth eearlies tstage s ofthei rgrowth .Unde rnorma lgrowin gcondition sther ei sa gradua ldecreas e duringth evegetativ estag ean da ver ymarke dreductio nsoo nafte rth estar to f thegenerativ estag edu et oa rapi dtranslocatio no fnitroge nt oth eyoun gear . Thereafterprotei nlevel sgraduall yfal lagai ntil llo wlevel sa tharvest . Thesetrend sshow nb yJONE San dHUSTO N (1914)wer eals ofoun di nKenya .I ti s notcertai nwhethe rdrough taccelerate sth eprocesse so fprotei nreductio ni n themaiz este m ornot .HSIA Omentione dtha tgenerall ydehydratio no fa plan t tendst oretar dsyntheti creaction san dt ofavou rhydrolyti creactions .H egav e someevidenc etha tthi sstatemen tals ohold sfo rth eprotei nmetabolis mi nmaize . Inconnectio nt oth epresen tresearc hmor einformatio nwoul dcertainl yb e interesting. Proteincontent so fth estem si nth etw oexperimenta lfield si nKikambal a wereinvariabl ylo wdurin gth eperio do fdiapaus einduction :0. 5- 0.9 1(fres h wt.)o r2 - 3° s(dr ywt.) . Slightlyhighe rcontent so f1.3 1(fres hwt. )o r4.2 1 (drywt. )als oallowe ddiapause .I non eo fth eexperimenta lfield sgrow ndurin g thedr yseason ,diapaus edevelope di nth eyoun gmaiz eplant ssoo nafte rth e irrigationwa scease d (fig.21a) .Stem so fplant si nthi sstag enormall yhav ea highprotei nconten tan di twoul dhav ebee ninterestin gt okno wwhethe rsuc ha contentwa smaintaine ddurin gth esubsequen tperio do fdrought .Th equantit yo f proteinha softe nbee nprove dt ob eo fgrea timportanc efo rth egrowt han d developmento fa larg enumbe ro finsect s (HOUSE1961) .Normall yprotei n requirementso fste mborer sar ehigh :e.g . C. suppressalis (HIRANO 1964), D. gvandiosella (REDDYan dCHIPPENDAL E 1972). 0. nvibilalis larvaenee dmuc h proteini nth eearl yinstar san donl ylittl ewhe nfurthe rdevelope d (BECK1956) . Butsuc hrequirement swer eseldo mrelate dt odiapause .A nexceptio nt othi sma y beth ediapaus eo fth emaiz estal kbore r B. fusoa (USUA 1973).Th epresen t experimentsonl ysho wth esimultaneou spresenc eo fpre-diapaus elarva ean dlo w proteincontent so fth este mi nwhic hthe yfee da ttha ttime . Influenceso fhos tplant so nth ephysiologica lconditio no finsect sar eofte n relatedt odifference si nchemica lcompositio no fth eplant .Th ecomponent sar e frequentlyexpresse da spercentag eo fplan t dry weight (HIRANO1964 ,USU A1973 , McCAFFERY 1975).Conclusion sfro msuc hobservation sar eonl yvali di fi tca nb e assumedtha t1 .th ecompare dfoo di ssimila rexcep tfo rth ecomponen tunde r investigationan d2 .th einvestigate dcomponen ti sno tinfluencin gth equantit y offoo dconsumed .Suc hcondition sar eseldo mfulfille dfo rplan tmaterial .Thus , 64 whenphysiologica lresponse so finsect st oplant sar einvestigated ,th efeedin g behaviouro fth einsec to nwhol efres hplant sha st ob eincorporate di nth e researchan di fspecifie dcomponent sar estudie dthe yma ybette rb eexpresse d inpercentag eo f fresh weighto fth eplant .Severa lexample sar eknow no finsect s makingthei rfoo dintak econditiona lt ophysica lo rchemica lqualitie so fth e food (seereview so fWALDBAUE R 1964,GELPERI N 1971an dBARTON-BROWN E 1975). Oneexampl ei sth elarv ao f Celerio euphorbiae which,whe nreare do nartificia l dietswit hdifferen tconcentration so fnutrients ,progressivel yconsume dmor e freshfoo da sth ewate rconten to fth edie tincrease d (andth enutrien t concentrationdecreased) .Th egrowt hrat eo fth e Celerio larvaeappeare dt ono t beaffecte d (HOUSE 1965).HOEKSTR Aan dBEENAKKER S (1976)foun dlarg edifference s indr yweigh tconsumptio no ffiv edifferen tgrasse sb y Loausta migratoria. After conversiono fth edr yweigh tfigure sint ofres hweights ,a highl ypositiv e correlationcoul db edemonstrate dbetwee nth eamoun to ffres hgras sconsume dan d thewate rconten to fth egrass .Apar tfro mwater ,i ti spossibl etha tothe r componentswhic hwer edifferen tbetwee nth efiv egrasse shav eregulate dth e feeding.Growt hwa sagai nno taffecte db yth edifferen tfoo dintake . Similarresult sa sabov ewer eobserve dfo rth econsumptio no ffres hmaiz e ofdifferen tdevelopmenta lstage sb y Chilo partellus larvae.Progressivel yles s pithmateria lo fa ste mwa seate na sth emaiz eplan tdevelope d furtheran d containedles swater .I twa sver yinterestin gt ofin dtha tsignificantl yles s freshste mmateria lwa sconsume dfro ma maturin gplan ttha nfro ma nage dplant , inspit eo fth ever ysimila rchemica lcompositio no fth estems . Eventh ewate rconten to fth estem si sequal ,s oth elarv adoe sno tnee dt o compensatefo rdecrease dnutrien tconcentration s aswa sshow nfo r Celerio larvae (HOUSE 1965).I ti smor elikel ytha ta structura lcomponen to fth este mha s resistedfeeding . Theobservatio ngive sris et oa hypothesi ss ofa roverlooked .I twa sfoun d thati nnatur e Chilo larvaegraduall yceas efeedin gwhe nenterin gaestivation - diapause (chapter 3).However ,th ecausa lrelationshi pbetwee nfeedin gan d diapausei sno tknown .I tma yb etru etha tth ereduce dfeedin gi sa resul to fth e diapause,bu tth erevers ema yb eequall ypossible .I ti sknow ntha tman yplant s reactt owate rstres sb yearl ymaturatio no ftissues ,show ni nth eformatio no fa morecompac tstructur ean dthicke rcel lwall san dcuticle s (KRAMER 1959). Inth e presentresearch ,a nindicatio nwa sobtaine dtha ta structura ldifferentiatio n ofa maiz eplan tma ylea dt oreduce dfeedin go flarva ei nsuc ha plant .Wit h consistentquantitie so fnutrient si nth efoo dplant ,reduce dfeedin gresult s 65 Table 14.Developmen to f4th ,5t han d6t hinsta rlarva eo f Chilo partellus after differentperiod so fresidenc ei nage dmaiz estem so rartificia ldie t(control) . sampling period 0 - 14 days 15 - 28 days 29 - 42 days /—* s~\ 73 6*8 T3 T3 food larval oo S-5 CU 60 B~8 CU &o 6-S O 13 S«' O 3 •H + cu 3 •eH ^ + CU 3 •aH + CU stage •V CD CO T3 > CD CO •V CU CO O •>H CO 41 H -H O •H CO CU rH -H O •H> CO CU r-1 -H u CO CO > U > > CO co > V4 CO CO > • u • fc > P. P. 3 • 4J • U U P. P. 3 • u . B u> P. P. 3 0 c O 3 >-•ct) 3 3 X o a O 3 CO 3 3 X 2 C O 3 CO 3 3 !«! C -H 13 10 rH P. P. CU a -H (3 CO i-< p. P. CU C -H 13 CO i-( P. p. CU aged L4 94 52 100 0 44 19 84.2 15.8 30 5 100 0 maize L5 87 59 98.3 1.7 43 19 73.7 26.3 30 19 78.9 21 .1 L5/L6 20 12 100 0 40 22 50.0 50.0 30 16 12.5 87.5 diet L4 50 40 100 0 50 40 52.5 47.5 50 40 15.0 85.0 L5 50 48 97.9 2.1 50 48 35.4 64.6 50 48 2.1 97.9 L5/L6 50 41 78.1 21 .9 50 41 29.3 70.7 50 41 4.9 95.1 3-7sample sfro mstem so rdie twer etake na tdifferen ttime sdurin gth eindicate d periods.Opene dstem scoul dno tb ereused ,s odifferen tstem swer euse dfo reac h observation.Ag elarva eL4 :8 an d9 days ,L5 :1 2an d 13days ,L5/L6 : 18days . Table 15.Pigmentatio no f4th ,5t han d6t hinsta rlarva eo f Chilo partellus afterdifferen tperiod so fresidenc ei nage dmaiz estems . larval sampling period stage 2) 0 - 14 days 15 - 28 days 29 - 42 days 1 1 nD % TR ) % us ) n % TF % US n % TR % US L4 52 17.3 9.6 16 0 56.2 5 0 100 L5 58 20.7 24.1 14 7.1 92.9 15 6.7 93.3 L5/L6 12 33.3 58.1 11 0 100 2 0 100 1)n -numbe ro frecovere d andsurvivin glarva e TR- transitiona llarva e US- unspotte d larvae I) L4:8 an d9 day sold ,L5 : 12an d 13day sold ,L5/L6 : 18day sold . 76 5. 4.3 Larval growth and •pupation on diets i i i i i i 0 102 0 304 0 0 10 20 30 40 0 10 20 304 0 0 10 20 304 0 0 102 0 30 40 AGE, days after moult to fifth larval instar Fig. 28.Growt hcurve sfo rlarva eo f Chilo partellus onartificia ldiet so f differentchemica lcomposition .Se efo rcompositio ntabl e13 . Theeffec to fvariou s dietso nlarva lbod yweigh tar eshow ni nfig . 28. Proteins turnedou tt opla ya dominan t rolei nth eweigh tgain .Growt hrat ewa s extremelyslo wwhe ndiet s contained less than0.45? .protei n (dietsA ,F an dK) ; aftera nexperimenta lperio do f4 0day snon eo fth e larvaeo nthes ediet sweighe d more than40-6 0mg .O nth eaverag enorma lgrowt hwa s obtainedwhe nth ecasei n contentswer e 1.7-1.81o rmor eo fth edie t freshweight .Wate ran dsuga rseeme d tob erathe rineffective .Larva lgrowt ho ndiet swit h aboutth esam esuga ran d protein contentsbu twit hdifferen tquantitie so fwate r (e.g.1- Han d2- Bo r1- 1 and 2-C)prove dt ob eth esame .Likewise, diet swit hdifferen tsuga rcontent s andotherwis e identicalquantitie so fwate ran dprotein ,di dno taffec tth elarva l weightincrease .Eve na suga rconten to f1.4 1wa s sufficientfo ranorma lgrowth . Theeffect so fth e artificial dietso npupatio nwer ei nlin ewit h theabov e mentionedeffect so nbod yweigh t (fig.29) .Larva e growno ndiet swit h little proteindi dno tpupat ei nlarg enumber swherea spupatio nrate swer enorma lwhe n moreprotei nwa s ingested.Th epupatio nrat eo flarva e feedingo nlo wprotei n dietsremaine dver yslo wbeyon d theperio do f4 0day sshow ni nth efigure ; two weeks lateronl ya fe wmor epupa ewer e formed.A nimportan tobservatio nwa s that 77 100n 80 60 ? 20H rr i i *-f»r § 100] F £ 80 2 60 LU tu40. 2D | 100 3 8°: 60 40- j 20 : yy2 : 0 102 03 04 0 0 102 03 0 40 0 102 03 04 0 0 10 203 0 40 0 102 03 0 40 AGE,day s after moult to fifth larvalinsta r Fig.29 .Pupatio no flarva eo f Ckilo partellus onartificia ldiet so fdifferen t chemicalcomposition .Se efo rcompositio n table13 . moultingcontinue dt otak eplace .Again ,n osignifican tinfluenc ewa sobserve d ofwate ro rsuga ro nth elarva ldevelopment . 5.4.4 Pigmentation and physiology of larvae on diets Duringth epreviou sexperiment sI notice do nsom ediet ssubstantia lnumber s ofunspotte dlarvae .Sinc elos so fcuticula rpigmentatio nwa sconsidere da sa n elemento fth eaestivation-diapaus esyndrom e (chapter2 )i twa sthough t appropriatet ohav ea close rloo kint othi sphenomenon .Thi swa sdon ei na ne w experimenti nwhic hth ebehaviou ro flarva ewa sobserve do na numbe ro ffreshl y prepareddiet so fth esam ecompositio na sth ediet smentione di n5.3.3 .Pupatio n rateswer ei nagreemen twit hthos ei nfig .29 .Th echange si nth ecuticula r pigmentationo fth eremainin glarva ear egive ni ntabl e16 .N osign so fchang e wereobserve ddurin gth efirs t1 5day so flarva lfeedin go nan yo fth ediets . Larvaereare do ndiet scontainin g0.45 1protei nhardl yturne dunspotted .Whe n 78 Table 16.Change s in cuticular pigmentation of 30 spotted 5th instar larvae after afeedin g period of 10,2 0 and 30 days on artificial diets of different chemical composition. chemical composition of the diet (% of freshwt . ) larvalpigmentatio n (numbers ) P u eun •H 4J 0 4-1 l-l after 10 days after 20 days after 30 days CO •a 6-S 6*5 n SP TR US n SP TR US n SP TR US 1-F 86 2.8 0.3 30 30 0 0 21 21 0 0 13 13 0 0 1-G 86 2.8 0.6 27 27 0 0 24 24 0 0 22 13 6 3 1-H 86 2.8 1.1 28 28 0 0 20 12 5 3 14 6 1 7 1-1 86 2.8 1.7 27 27 0 0 14 8 2 4 6 2 1 3 1-K 86 4.2 0.3 27 27 0 0 24 24 0 0 20 20 0 0 1-L 86 4.2 0.6 27 27 0 0 21 18 3 0 10 4 5 1 1-M 86 4.2 1.1 26 26 0 0 21 11 5 5 16 3 2 11 1-N 86 4.2 1.7 27 27 0 0 14 9 5 0 9 1 2 6 2-F 70 6.0 0.45 30 30 0 0 24 24 0 0 17 15 2 0 2-G 70 6.0 0.9 26 26 0 0 23 12 3 8 21 5 3 13 2-H 70 6.0 1.8 26 24 2 0 12 4 3 5 5 0 0 5 2-1 70 6.0 2.7 29 29 0 0 13 8 1 4 1 0 0 1 2-K 70 9.0 0.45 29 29 0 0 29 22 7 0 26 19 5 2 2-L 70 9.0 0.9 29 29 0 0 27 14 3 10 23 2 6 15 2-M 70 9.0 1.8 27 27 0 0 22 14 4 4 14 0 1 13 2-N 70 9.0 2.7 28 28 0 0 7 4 0 3 2 0 0 2 *SP - spotted TB - transitional US - unspo tted moreprotei nwa spresented ,increasingl ymor eunspotte dlarva ewer eformed .Th e highestyiel do funspotte dlarva ewa sobtaine dwit hdiet scontainin gintermediat e levelso fprotei n (0.9- 1.11).I ti sremarkabl etha tals olarva ewhic hha d consumeddiet swit hhighe rprotei ncontent sregularl yturne dunspotted .Sinc e pupationrate so fthes elarva ewer ehigh ,onl yfe wlarva ewer eunspotte dafte r 30days .N orelatio nwit hwate ran dsuga rcontent scoul db efound . Aftera feedin gperio do f33-3 9day swate rcontent san drespirator yrate s weredetermine do fthos elarva ewhic hha dretaine dthei rlarva lstag ei n sufficientnumbers .Diet s 1-Fan d2- Fwer eno ttake nint oconsideratio nbecaus e ofth epoo rconditio no fman ylarva ereare do nit .Result sar eshow ni ntabl e17 . 79 Table 17, Water content and respiratory rate of larvae of Chilo partellus after a feeding period of 33-39 days on artificial diets of different chemical composition. Diet Chemi cal days after mean water content mean oxygen composition mou It to + S.E. (%) consumption + S.E. of the diet 5t h larval (yl0 0/mgdr y wt./hr) (% of freshwt. ) insta r G •H u u O M 3 M S P. s-s 6-S &« 1-G 86 2.8 0.6 36 72.3 + 1.2 (19) 2.33 + 0.15 (11) 1-K 86 4.2 0.3 33 72.3 + 1.0 (18) 2.68 + 0.38 ( 8) 1-L 86 4.2 0.6 33 67.2 + 1.3 (18) 2.46 + 0.11 (12) 1-M 86 4.2 1.1 39 69.6 + 1.7 (10) 2.31 + 0.13 (10) 2-G 70 6.0 0.9 36 66.0 + 1.4 (15) 1.93 + 0.10 (12) 2-K 70 9.0 0.45 33 63.7 + 0.9 (20) 1.41 + 0.14 (12) 2-L 70 9.0 0.9 33 63.6 + 1.0 (20) 1.83 + 0.11 (12) 2-M 70 9.0 1.8 39 62.3 + 1.8 (12) 1.76 + 0.15 (12) Differencesbetwee ndiet s 1an d2 significan twit ht-tes ta tp 0.05. Numbersbetwee nbracket srefe rt onumbe ro fobservations . 5.4.5 Sensitivity of larvae to diet Allpreviou sexperiment swer emad ewit h fifth instar larvae.Th eeffect so n larvaeo fothe rage swer e studiedi nth epresen texperiment .Fo rthi sw eselecte d diet2- Go nwhic h larvaeha dbee nproduce dwit hqualitie sneares tt othos eo f aestivating larvae fromth e field.Thi s diet contained 70%water ,0.9 1protei n and6.0 1sugar .Fift h instar larvaereare do nthi sdie t retarded theirgrowt h anddevelopmen t (fig.2 8an d29) , lostthei r articularpigment s (table 16) and showeda reduce drespiratio n (table17) . Growth curvesar egive ni nfig .30 .Maximu mlarva lweight swer e aboutth e same foral l larvaean dsimila rt oweight so flarva ereare do nth ebasi cdie t (fig.13) .Growt ho f1 5an d2 0day sol dlarva ewa s completed withinth e observationperio do f3 4days .Younge r larvaecontinue dt ogai nweigh t throughout thisperiod . Therate so fpupatio n (fig.31 )wer ei nlin ewit h this;th edevelopmen to f 4thinsta ran dearl y5t hinsta r larvaehardl yshowe d anyprogress .Onl yfe w pupaewer e formedwherea smortalit ywa shig ha scompare dt omor e aged'larvae . 80 Fig. 30.Growt hcurve sfo r Chilo partellus larvaeo fdifferen tag e 1 T ona nartificia ldie tcontainin g 10 15 70% water,6.0 %suga ran d0.9 % TIMEAFTE RSTAR TEXPERIMEN T(days ) protein. L.4,10 days old (n=70 ) L5,13 days old (n=130) L5,15day s old (n=50) taiHiiiii^- -\ r***"wi^j I—2 ^Ulllllllllllllilllllllil i In £w8£ - i - ^l|l H " 3LUC*D - ^miii J >N - W'S D .... 5* «- H -is? - """ 1 1 I I 1 1 i ' i 1 1 I I 1 1 I 1 10 20 30 10 20 30 10 20 30 10 20 30 TIMEAFTE RSTAR TEXPERIMEN T(days ) | |%LARVA EQU I% MORTALIT Yf |%PUPA E Fig. 31.Developmen to f Chilo partellus larvaeo fdifferen tag eo na n artificialdie tcontainin g70 %water ,6.0 %suga ran d0.9 %protein . Thechange si ncuticula rpigmentatio n areshow ni ntabl e 18.Al llarva e ultimately tendedt otur n fromth espotte d intoth eunspotte dmorph . A final observationwa s doneo nth e drought resistanceo flarvae .I ti s kwowntha t95 1o fnon-diapaus e larvaedi eo rpupat ewithi n1 6day swhe nplace d indr ypiece so fmaiz e stema t25 °C (chapte r 2).Whe n4t han d5t hinsta r larvae Table 18.Change s in cuticular pigmentation of spotted larvae of different instar and age after afeedin g period of 20 and 34day s on an artificial diet containing 70%water ,0.9 % protein and 6.0% sugar. * larva l stage and age larval pigmentation (numbers) % US of .nitial at start of experiment after 20 days after 34 days number o :larva e (n) n SP TR US n SP TR US L4, 10 days (70) 48 35 5 8 42 10 8 24 34 3 L5, 13 days (130) 93 53 15 25 73 9 12 52 40 .0 L5, 15 days (50) 26 14 2 10 22 1 1 20 40 .0 L5/L6, 20day s (50) 20 9 1 10 14 1 1 12 24 0 SP spotted TR- transitional US - unspotted \-i 10day s old (n 20) 1-5,13day s old n=30) 0 10 20 30 40 50 60 70 DAYSAFTE R TRANSFER FROM DIET G2T0 DRY CONDITIONS • %LARVA E HI %MORTALIT Y ^ % PUPAE Fig. 32. Drought resistance of Chilo partellus larvae after feeding on diet 2-G during preceding period of 34 days. 82 whichha dbee nfeedin go ndie t2- Gfo ra perio do f3 4day swer eplace di n similardr ycondition s (petridis hwit hdr yfilte rpaper )the ysurvive dthi s periodfo rth egreate rpar t (fig.32) .Fro mthi si tseem stha tth edrough t resistanceo flarva ewhic hha dbee nfeedin go nth eexperimenta ldie tha dindee d increased. 5.5 DISCUSSION A largenumbe ro fnon-diapaus efift hinsta rlarva eo f Chilo partellus entereddiapaus eafte rthe ywer eintroduce dint ostem so fage dmaiz eplant s (5.4.1.).Pupatio nwa sno tmuc haffecte ddurin gth efirs tfiv eweek so fpresenc e inth esteins ,thereafte rpupate dwa sretarde dan donl yfe wpupa ewer eformed .A certainrat eo fpupatio nnormall yoccur samon gaestivatin glarva ean dha sals o beenfoun dt otak eplac ei nth efiel d (chapter 2). Furtherevidenc etha tlarva e hadentere ddiapaus ecam efro mth edisappearanc eo fth ecuticula rpigmentatio n andfro mth elo wrespirator yrat ean dwate rconten twhic hwer eal lals o demonstratedi nfield-collecte daestivatin glarva e (chapter3) . Atth etim eo fintroduction ,stem scontaine dabou t75 %water ,8 1suga ran d 1.3%protein ;tissue swer erelativel yhard .Al lthes econdition so fth estem s werecomparabl et ostem si nwhic hlarva ewer efoun dt oente raestivation-diapaus e inth efiel d (chapter 4). Theabov ementione dresult sconfir mth efiel ddata ,bu t dono tgiv econclusiv eevidenc eo nth eimportanc eo fth echemica lo rstructura l natureo fth este mfo rth einductio no fdiapause .Th edifferen tresponse so f larvaet odifferen tsectio no fth eage dplant swit hrelativel yhig han dlo w moisturecontent s (5.4.1)see mt oindicat ea possibl einvolvemen to fwater ,bu t itma yals ob etha tthes edifference sar eth eresul to fa slightl ydifferen t chemicalcompositio no r- a swa sshow ni n4.4. 5 -a differenc ei nfeedin g behaviouro fth elarv aitself . Itwa sshow ntha tdifferen tlarva linstar shav ea differen tcapacit yt o respondt odiapaus einducin gcue s (5.4.2).Whe nfourt hinsta rlarva ewer e introducedint oage dmaize ,fe wlarva epupate dan dfe wentere d aestivation- diapause.Th emortalit yo fthi sstag ewa shigh .A hig hproportio no fearl y fifthinsta rlarva eentere daestivation-diapause ,bu tmos tlat efift han dsixt h instarlarva epupated .I ti sprobabl etha tthes eolde rlarva eha dproceede dto o farwit hth epreparation sfo rth epupa lmoul tan dwer eno tsensitiv et oth e diapauseinducin gfactor si nth eage dmaize .A losso fcuticula rpigmentatio nwa s observedi nal lthre elarva lstage sintroduced .Du et othei rhig hpupatio nrate , 83 onlyfe wunspotte dlarva eoriginatin gfro mol dlarva ecoul db efoun dafte rsi x weeks.Therefor eth etota lnumbe ro funspotte dlarva eobtaine dfro myounge r larvaewa sconsiderabl yhigher . Thechemica lcompositio no fmaiz estem swhic hha dbee nfoun dt oinduc eth e highestincidenc eo faestivation-diapaus e inth efiel d (4.4.2)an di nth e laboratory (5.4.1)wa ssimulate di n3 0artificia ldiet swit hvaryin gprotein , sugaran dwate rcontents . Proteinappeare dt ob eth ecrucia lfoo dfacto rregulatin gweigh tincreas ean d rateo fpupation .Casei ncontent sbelo w0.45 1o fth edie tfres hweigh twer e inadequatean dresulte di nver ypoo rgrowt han dextremel ylo wpupation .A n increaset o0.9-1.1 $provide dsom eimprovemen twherea snorma lgrowt han d developmentwa sobtaine da ta minima lprotei nconten to f1.7-1.81 .Thi si s preciselyth erequiremen tfo rth elarva eo fth eEuropea ncor nborer , 0. nubilalia (BECK 1956). Sugarswer eles scrucial :a suga rconten to f1 .4 $ (lowertha nan yo fth emaiz e stemsencountere di nth efiel ddurin gdiapaus einduction )permitte dnorma l developmenta slon ga sprotein swer esufficientl yavailable . 0. nubilalis larvae require1.8 $glucos ei nthei rdie t (BECK1956 )an dth egrowt ho f D. grartdiosella larvaewa sonl yslightl yretarde do ndie tsupplemente dwit h1.65 %glucos e (CHIPPENDALEan dREDD Y 1974). Ifa lo wwate rconten twoul dhav eplaye da dominatin grol ei nth einductio no f aestivation-diapause,a differenc eshoul db efoun dbetwee nlarva egrow no ndie t1 (86$o fwater )an ddie t2 (70 $o fwater) , independento fothe rcomponent so fth e diet.N odifferenc ewa sfoun do nlarva lgrowt ho rpupatio neve ni fth eproportio n ofth edifferen tcomponent swa sidentical .However ,respirator yrate san dwate r contentswer elowe ro flarva efro mth ediet scontainin greduce dwate rcontent s (table 17).Thi sresul tstrengthen sth eabov ementione dsimila rresult so flarva e from"moist "botto msection san d"dry "middl esection so fth eage dmaiz eplant s (5.4.1). Theprotei nconten to fth edie tno tonl yaffecte dgrowt han ddevelopmen t butals oappeare dt oinfluenc ecuticula rpigmentation .Larva egrow no ndiet s deficienti nprotei n (<0.45$ )alway sremaine dspotted .A salread ymentione d larvaeo nthes ediet shardl ygre wan dthe yseldo mmoulted .CHIPPENDAL Ean dREDD Y (1972)demonstrate dtha tmoultin gi snecessar yfo rlarva eo fth esouthwester ncor n borer D. grandiosella tochang efro ma spotte dnon-diapaus efor mint oa nunspotte d diapauseform .A simila rphenomeno nwa sobserve dfo r C. partellus (unpublished results). Whendiet swit ha protei nconten thighe rtha n0.45 $wer eingested'b y 84 larvae,moult scoul dtak eplac ean dman ylarva echange dt oth eunspotte dform .O n high-proteindiet s (>1.7-1.84 )pupatio nrat ewa shig hwit hfe wunspotte dlarva e remainingafte r3 0days ,bu to ndiet swit hintermediat elevel so fprotei n (0.9-1.14)les spupa ean dmor eunspotte dlarva ewer efound . Differentlarva linstar ssupplie dwit ha lo wwate r (704)/lowprotei n(0.94 ) diet (5.4.5)appeare dt oreac tt othi sdie ti na simila rwa ya st oage dmaiz e stems (5.4.2):Lat e5t han d6t hinsta rlarva ewer edevelope dto ofa rt ob e sensitivet oth ediapaus einducin gstimul io fth edie tan dpupated .Th e developmento fyounge rinstar swa sincreasingl yretarded ,bu tth emortalit yrose . Unspottedlarva ewer eobtaine dfro man yinstar ;larges tnumber sfro m5t hinstars . Itwa sshow ntha t4t han d5t hinsta rlarva ereare do nth eabov ementione ddie t hada nincrease dresistanc et odr yenvironmenta lconditions ,whic hi sa norma l qualityo faestivatin glarva e (chapter2) . Theresult so fth eexperiment swit hartificia ldiet sindicat etha t aestivation-diapause isinduce db yth econditio no fth efood .Mor edat aar e required,e.g .o nth ephysiologica lconditio no fth elarva ,t osubstantiat ean d furtherdefin ethes efindings . Onprotei ndeficient sfoo d (i.e.age dmaiz estems ,tabl e 15o rdiet ,tabl e 18)no tonl yyoun glarva ebu tals olat efift han dsixt hinsta rlarva elos tthei r cuticularpigmentatio neve nthoug hpupatin gsoo ntherafter .I npreviou schapter s itwa sdemonstrate dtha tspotte dlarva ecoul dexhibi tphysiologica lcondition s resemblingtha to fdiapaus elarva e (fig.15 ,16 ,18) .Thes eobservation sindicat e thatth elos so fcuticula rpigmentatio nitsel fma yno tb ea criterio nfo rdiapaus e asreliabl ea spreviousl yassumed .Diapausin glarva eo f D. grandiosella are normallyunspotted .Th ediapaus ei sinduce dan dmaintaine db ya nintermediat e titreo fjuvenil ehormon e (YINan dCHIPPENDAL E 1974,1976) .A sligh tincreas eo f theJ Htitr ei nunspotte ddiapausin glarva eresulte di necdysi sint oth espotte d formwithou tterminatio no fth ediapaus e (CHIPPENDALEan dYI N 1976).Th e observationso n C. partellus agreewit hth eresult so fCHIPPENDAL Ean dYI Ntha t diapausean dcuticula rpigmentatio nar erelate dbu tno tinseparabl ephysiologica l processes.Considerin gthis ,I conclud etha ton eshoul db ecarefu lwhe nusin gth e disappearanceo fpigment sa scriterio nfo rdiapaus ea slon ga sth eprecis efactor s regulatingth ecuticula rpigmentatio nar eno tknown .I twoul db emor epreferabl e tocombin eth epigmen tcharacteristi cwit hsevera lphysiologica lcriteri aa s demonstratedi nth epresen tstud y (chapter3) . 85 6 Hormonal involvement in aestivation-diapause 6.1 INTRODUCTION Thelarva eo fth espotte dstal kbore r Chilo partellus andth ecoasta lstal k borer Chilo oriohaloooiliella entera stag eo faestivation-diapaus ewhe noncomin g adversecondition sfo rfurthe rdevelopmen tar eannounce db yth ecessatio no f rains (chapter2) .Onl ywhe nrain sreappear ,diapaus ei sterminated . Theinduction ,maintenanc ean dterminatio no fdiapaus eha sbee ndemonstrate d tob edirectl ycontrolle db yendocrin emechanism si na wid erang eo finsect s (LEES1956 ,D EWILD E1970 ,CHIPPENDAL E 1977).Previou sobservation stha t diapausinglarva eo fth eabov ementione d Chilo sp.ar ecapabl eo fundergoin g stationarymoult swithou tterminatin gdiapaus esugges ttha tsuc hlarva ehav e 1)a tleas tperiodicall yactiv eprothoraci cgland san d2 )a juvenil ehormon e titrewhic hi ssufficientl yhig ht opreven tpupa lecdysis . Thepresen tresearc hwa scarrie dou tt oinvestigat ethi shypothesis . 6.2 LITERATURE Thehormona lregulatio no flarva ldiapaus eha srecentl ybee nreviewe db y CHIPPENDALE (1977).Evidenc ei saccumulatin gtha tth einductio nan dmaintenanc e oflarva ldiapaus ei nman yinsect si sregulate db yth ecorpor aallat a (CA)whic h continuet oactivil ysecret ejuvenil ehormon e (JH)durin gth ediapause .Example s ofthi sar eno wknow no fth eric este mborer , Chilo suppressalis (FUKAYAan d MITSUHASHI1961 ,YAG Ian dFUKAY A 1974),th esouthwester ncor nborer , Diatraea grandiosella (YINan dCHIPPENDAL E 1973,1974 ,1976) ,th eEuropea ncor nborer , Ostrinia nubilalis (YAGIan dAKAIK E 1976)an dth eslu gmoth , Monema flavescens (TAKEDA 1978).I nal lthes ecase sdiapaus ewa sterminate dwhe nth eactivit yo f theC Adecreased .Mos tevidenc efo rth einvolvemen to fJ Hwa sderive dfro m 86 surgicaloperation san dfro mapplicatio no fjuvenoid so rinjectio no fecdysones . Insom ecase sth eactivit yo fth eC Awa smeasure ddirectl yb ydeterminin gth e sizeo fth eC Aand/o rth eJ Htitr ei nth ehaemolymph .Detail swil lb egive ni n paragraph6. 5 ifconnecte dt oth epresen tresearch . CHIPPENDALEan dYI N (1976)postulate dtha tth elarva ldiapaus eo f D. grandiosella isi nfac tno tmerel ycontrolle db yJ Hbu trathe rb yth einter actionbetwee nth ecerebra lneurosecretor y (NS)syste man dth eCA .The ysuggeste d thatintermediat elevel so fJ Hfoun di ndiapausin glarva eo f D. grandiosella inhibitth eN Scell so fth ebrai ninvolve di nth eproduction ,transpor to r releaseo fecdysiotropin .A hig ho ra lo wtitr eo fJ Hma yactivat ethes eN S cellsan dthu sinduc epupa lecdysis .A simila rmechanis mi sthough tt ob e involvedi nth elarva ldiapaus eo f M. flaveseens (TAKEDA 1978).I nbot hcase s howevern oconclusiv eevidenc eexists .Th efeedbac ko fJ Ht oth eN Scell so f thebrai na swel la sth econtro lo fth eC Aitsel fb yth ebrai nrequir efurthe r studies. 6.3 MATERIALSAN DMETHOD S 6.3.1 Juvenile hormone titre Inlarva lmateria lobtaine dfro mth eexperimenta lmaiz efiel dsow no n2 5 April197 5J Htitr ewa sdetermine dt ofollo wth echange sdurin gth einductio n ofth ediapause .Dat ao npupatio ni nthi sfiel dwer egive ni nfig .7 an do nth e physiologicalconditio no fth elarva ei nfig .16 .Fro msample so f25-3 0larva e takena tregula rweekl yintervals ,heamolymp hwa sremove dwit ha micr ocapillar y tubean dpooled .Quantitie sobtaine damounte dt o0. 5- 1. 0ml . TheJ Htitr eo fdiapausin glarva eexpose dt odiapaus eterminatin gcondition s (moistfilter-paper )wa sdetermine dwit hlarva ei nwhic hdiapaus eha dbee n inducedb ygrowin gthe mo nage dmaiz estem s (chapter5) .Al llarva eha dbee ni n diapausefo rabou t1 mont han dwer etherefor ei na nearly-diapaus estage . Pooledhaemolymp hsample sfro m14-2 0larva e (300-600yl )wer eobtaine dfollowin g exposuret omois tfilter-paper . JHwa sextracte dfro mth ehaemolymp hwit hether/ethano lan dextract swer e quantitativelyassaye do nfres hpupa eo fa loca lstrai no f Galleria mellonella. Theprocedure sar edescribe di nmor edetai lb yD EWILD Ee tal . (1968).Dilution s ofextract swer ealway steste do na minimu mo f1 5pupae .On eGalleri aUni t (G.U.) 87 equalsth equantit yo fJ Hwhic hprovoke sa positiv ereactio ni na tleas t5 0 % ofth epupa et owhic hth eJ Hcontainin gdilutio nwa sapplied .I nou rexperiments , theG.U .wa sfoun dt ocorrespon dwit h6 x 10~"y gCecropi aJH . 6.2.2 Head ligatures and injections with fi-ecdysone unspottedlarva ewer eobtaine dfro mth efiel da tth ebeginnin go fth edr y season.The ywer esubsequentl ykep ti nth elaborator yunde rdr ycondition sfor threemor eweek st oassur ethei rdiapaus econdition .Th eeffec to fisolatio no f bodypart sfro mJ Hsuppl ywa sstudie db yligatio no fth ecervica lregio nwit h afin esil kthread .Non-ligate dlarva eserve da scontrols .Th eeffec to f B-ecdysoneo nligate dan dnon-ligate ddiapaus elarva ewa sinvestigate db y injectinga singl edos eo f1 an d4 y gecdyson ei n1 y lo fdistille dwate ron e andseve nday safte rth eligatur ewa smade .Contro linjection swer ecarrie dou t withpur ewater .Th eperformanc eo fecdysi swa sfollowe ddurin g5 day safte r eachtreatment .A necdysi swa sonl yconsidere da sprogressiv ewhe na visibl e differentiationo fwin gbud swa sdetecte dan dwhe nth eana lplate ,proleg san d crochetsha dtransforme dint oa n (irregular)cremaste ra swa sdescribe dfo r prothetelic Chilo suppresealis larvaeb yFUKAY Aan dHATTOR I (1957).Usuall y suchchange sar eaccompanie db ysclerotizatio nan dtannin go fth ecuticl eo f especiallyth eabdomina lparts . 6. 3.3 Experiments with JH-analogue Theeffect so fth ejuvenil ehormon eanalogu e (JHA)Z R61 9o ngrowth , developmentan dmoultin go fnon-diapaus elarva ewer estudied .Larva lmateria l wasobtaine dfro mth einsectar ywher elarva eo f Chilo partellus wereroutinel y bredo na nartificia ldie t (see2.3.1) .Thre egroup so f5 0lat efift hinsta r larvaewer etopicall ytreate dwit h2 y gJH A (in2 y lacetone )twic ea week ,2 y g JHAonc ea wee kan d2 y laceton etwic ea wee k (control).Th eapplication swer e continuedthroughou tth eobservatio nperio do f4 0days .Record swer etake no n larvalbod yweight s (asa group) ,pupatio nan dstationar yecdyses . Inon eexperimen tth eeffec to fJH Awa sfollowe do ntw oqualitie so f aestivatinglarva ewhic hearlie rha dbee nuse da scriteri at odetermin e aestivation-diapausei nth efield :los so fcuticula rpigmentatio nan ddrough t resistance.Fiv egroup so fabou t3 0larva eeac hwer etreate dtopicall ytwic ea weekwit h0.5 ,1.0 ,2. 0an d4. 0y gJH A (ZR619 )i non ey laceton edurin g3 Jweek s 88 ofgrowt ho ndiet .A napplicatio no f1 y laceton eserve da sa control . Pupation,deat han dlarva lpigmentatio nwa sdetermine d3 day safte rth elas t applicationwa scarrie dout .Th eremainin glarva eo feac hgrou pwer ethe n subdividedi ntw oequa lgroup so fwhic hon ewa stransferre dt opiece so fdr y maizeste man danothe rwa skep to ndiet .Surviva lan dpupatio nwa srecorde d onemont hlater . 6.4 RESULTS 6.4.1 Juvenile hormone titre during diapause induction, maintenance and termination •5 XXX)- E 800- 200- Fig.33.J Htitre si nth ehaemolymp ho f fieldcollecte d larvaeo f Chilo sp.befor e 1/6 1/7 1/8 1/9 1/10 1/11 1975 anddurin gth eincidenc eo faestivation - no early mid late diapause diapause diapause diapause diapause Fig-3 3show stha tth eJ Hconten ti nth ehaemolymp ho ffiel dcollecte d larvaewa srelativel ylo w (100-200G.U./ml )a slon ga sth emajorit yo fth e larvaewa si na non-diapaus econdition .Larva ewer econsidere da snon-diapaus e because 1.sample scontaine dpupa ean dver ylo wpercentage so fdrough tresistan t andunspotte dlarva e (fig.7 )an d2 .th erespirator yrat ean dwate rconten to f thelarva ewer eno tdepresse d (fig.16).Whe nenterin gdiapaus eJ Hlevel s increasedt oabou t 1000G.U./m lan dthi sleve lgraduall ydecrease dt oabou t 200G.U./m la sdiapaus econtinued .Thes efinding ssugges ttha trelativel yhig h levelso fJ Har eresponsibl efo rth einductio no fdiapaus ei n Chilo larvae whereasth ediapaus ei smaintaine db yintermediat elevel so fthi shormone . Theaestivation-diapaus eo f Chilo larvaei sterminate db yexposur eo fth elarva e tomois tconditions .Fig.3 4 showstha t-althoug h4 0I o fth elarva edie dafte r aperio do f2 0days -th eremainin g6 0 % hadpupate ddurin gtha tperiod .Hal fo f theselarva eha dalread ypupate dwithi n1 1days . Table1 9demonstrate stha t moistcondition sinduc ea rapi ddecreas ei nJ Hconten to fth ehaemolymp ho f diapausinglarvae ,allowin gth elarva et oterminat eth ediapaus ean dpupate . 89 'MOIST CONDITIONS =DR Y CONDITIONS Fig.34.Effec to fmoistur eo nth eterminatio n -i 1 1 1 5 10 15 20 ofdiapaus ei nlarva eo f Chilo sp.Bot h DAYSAFTE RTRANSFE R experimentswer estarte dwit h4 0larvae . Table 19. Effectso fmoistur eo nth eJ Hconten ti nth ehaemolymp ho f diapausing larvaeo f Chilo sp. experiments daysafte rtransfe r JH titre no. tomois tcondition s (G U./mlhaemolymph ) 1 0 750 3 80 2 0 1280 3 230 8 130 6. 4. 2 Effects of head ligatures and/or £,-eodysone on diapausing larvae Table2 0show stha tver yfe wstationar yan dn oprogressiv eecdyse s occurredi nnon-ligate dan dligate dlarvae ,whic hha dbee nuntreate do rinjecte d withdistille dwater .Mos tlarva eremaine dunaffected .Thi sresul tsuggest sa n inactivityo fth eprothoraci cgland so fth elarva euse dfo rthi sexperiment . Howeverwhe nth eleve lo fecdyson ewa sartificiall yincrease db yinjection , moultingdi doccur .I nnon-ligate d larvaestationar ymoult swer eabundan tan d progressivemoult srare . Iconclude dtha tth equantit yo fJ Hcirculatin gi n thehaemolymp ho fthes elarva ei ssufficientl ylarg et omaintai nth estat eo f diapause.Thi swa sals oth ecas ewhe necdyson ewa sinjecte don eda yafte rth e neckligatur ewa smade .Apparentl yJ Hi sstil leffective .I ncontrast ,whe n larvaeha dbee nligate d7 o rmor eday sbefor eth eecdyson einjectio ntoo kplace $ onlyprogressiv eecdyse swer eobserved ,indicatin gtha tJ Htitr eha ddroppe d toa leve lwhic hn olonge rprevent spupation . 90 Table 20. Effects of neck ligation and/or 8-ecdysone on ecdysis of diapausing larvae of Child sp. situation 5 days after treatment ligature treatment no. of no. of no. c f no. of larvae stati onary progressive larvae unaffee ted ecdyses ecdyses - untreated 42 37 2 0 - 1y lwate r 15 11 0 0 - 1 yg ecdysone 20 0 13 0 - 4 ug ecdysone 20 1 14 1 + untreated 29 22 4 0 + 1y lwate r (1) 14 13 0 0 + 1p iwate r (7) 15 14 0 0 + 1y g ecdysone (1) 17 0 11 3 + 4 yg ecdysone (1) 20 8 9 2 + 4 yg ecdysone (7) 15 2 0 13 + 4 yg ecdysone (9) 12 3 0 5 + 4 yg ecdysone (15) 14 5 0 7 number of days between ligation and treatment with ecdysone. 6. 4. 3 Effects of JHA on non-diapause larvae o 200 •^»--«r ^-S"av—ft Fig.35.Effec to fth eJH AZ R61 9o n bodyweigh to flat e5t hinsta r larvae of Chilo partellus duringa perio do f 36day so ftreatment . Code: > 9 2y laceton e twicea week , k A2 y gJH Aonc ea week ,O - O2 y g JHA twicea week .Number s refert o 20 30 numbers ofsurvivin g larvae. DAYS AFTER START APPLICATIONS Theeffec to fJH Ao nliv eweigh to f5t hinsta r larvaei sshow ni nFig . 35. Nosignifican tdifference si nlarva lweight swer e observeddurin gth efirs t weeko ftreatments .Thereafte rhoweve r larvae treatedwit hJH Acontinue dt ogai n weight,wherea s theweight so faceton e treated larvaeremaine d constantan dlate r 91 startedt odecline .Thi sdeclin e couldb eassociate dwit h the formationo fpupa e inthi s controlgrou p (Fig.36) .Twent yday s afterth estar to fth eJH A applications larvaewhich wer e treated oncea wee k ceased gainingweight , possiblybecaus eo freduce d feeding.Th emaxima lweight s obtainedwer e about 1.3x thos eo fth econtro l larvae.Th egrou po flarva e treated twicea wee kwit h JHAeve nbecam eheavier :afte r3 0day s larvaeweighe d over 200mg , i.e. about 1.7x th emaximu mweigh to fth econtrols . Fig.36 .Effec to fJH AZ R61 9o n developmento flat e5t hinsta r larvaeo f Chito partellus duringa perio do f 36 dayso ftreatment . Code:#——%2 piaceton e twicea week , k A2u gJH Aonc ea week.O-—o 2u gJH A twicea week . Numbers refert onumber s DAYS AFTER START APPLICATIONS surviving (larvae+ pupae) . Fig.36show s thatonl y one (abnormal)pup awa s formedi neithe ro fth ehormon e treated groupso flarvae .I ncontrast :2 6pupa ewer e formedi nth e controlgrou p while2 4larva edied .I nbot ho fth ehormon e treated groupseve nmor e larvaeha d died after3 6day so ftreatment :3 1larva e aftera napplicatio n twicea wee kan d 35larva e aftera napplicatio n oncea week . Fig.37 .Effec to fth eJH AZ R61 9o n stationary ecdyseso flat e5t hinsta r larvaeo f Chito partellus duringa perio d of3 6day so ftreatment . Code:*—#2 ylaceton e twicea week , A A2 u gJH Aonc ea week ,o O2 u g JHA twicea week .Th estationar y ecdysis was expressedb ytakin g thenumbe ro f head capsules found since thepreviou s 20 30 observationa s% o fth enumbe ro f DAYS AFTER START APPLICATIONS surviving larvae. 92 Fig.3 7show stha tstationar ymoult si nal lthre egroup so flarva einitiall y followedth esam epattern .A ver ylarg enumbe ro fhea dcapsule spe rlarv awa s foundbetwee nday s4 an d7 an dlittl emoultin gtoo kplac ethereafte rtil lda y 11. Intermediatelevel so fhea dcapsule swer efoun ddurin gth efollowin gperio dtil l day2 1whe nonl yfe wstationar ymoult swer eobserved .Difference sbetwee nth e groupsdevelope dthereafter :larva lecdysi scease di nth eaceton etreate dlarva e whereasi twa sobviou stha tth eprolonge ddevelopmen to fhormon etreate dlarva e isaccompanie db yextr amoults . Nosignifican tdifference si nth epigmentatio no fhormon etreate dan d controllarva ewer eobserve dafte r3 |week so fapplication s (table21) . Table 21.Effec t of JHA ondevelopmen t and larval pigmentation of early fifth instar larvae of Chilo partellus. 2) no. of JHA no. of larvae larval pigmentation larvae treatment after after treatment used treatment SP TR US 29 1y l acetone 24 17 3 4 31 0.5 yg JHA 28 5 20 3 29 1.0 yg JHA 27 10 17 0 30 2.0 yg JHA 29 7 22 0 29 4.0 yg JHA 29 16 8 5 1)JH A (ZR619 )wa s topically applied twice awee k during 3jweek s period 2) SP-spotted TR-transitional US-unspotted Thesefinding ssugges ttha tth ecuticula rpigmentatio ni sno tdirectl yrelate d tojuvenil ehormone . Table2 2show stha tlarva ewhic hha dreceive da JH-treatmen tdi dno tsurviv e anybette ro ndr ymaiz etha nsolven ttreate dcontrols .Deat hrate swer ehig h inal lgroups ,bu tsom elarva ewhic hha dreceive daceton eo ra lo wdosag eo f 0.5y gJH Apupated .I nothe rgroup sJ Htitre sprobabl yremaine dsufficientl y hight opreven tpupation . Whenlarva ewer etransferre dt odie tafte rth eJH Atreatment ,surviva lwa s generallybetter .Als omor elarva epupated :firs tonl yaceton ean d0. 5y gJH A treatedlarva ean dlate r- whe nJH Aha dlos tit seffectivit y- som elarva e treatedwit hhighe rdosages .I twa sconclude dtha tdrough tresistanc e- a qualitybelongin gt oth ediapaus esyndrom eo fnatura laestivatin glarva e- isno tgoverne db yJH . 93 Table 22.JH Atreatmen t onlarva eo f Chilo partellus subsequentlykep to n differentsubstrates . no. of JHA substrate effects after 16day s effects after 30 days larvae treatment post-JHA post--JHA treatment post-JHA treatment used treatment no. no. no. no. no. no. larvae pupae death larvae pupae death 12 1p i acetone dry maize 5 1 6 0 4 8 14 0.5 pg JHA 4 0 11 1 5 8 15 1. 0p g JHA 4 0 11 1 0 14 15 2.0 pg JHA 2 0 13 1 0 14 15 4.0 pg JHA 4 0 11 0 0 15 12 1p i acetone diet 4 5 3 0 8 4 14 0.5 yg JHA 4 4 6 1 4 9 12 1.0 pg JHA 7 0 5 0 2 10 14 2.0 pg JHA 14 0 0 2 3 9 14 4.0 pg JHA 12 0 2 5 3 6 Treatmentswer ecarrie dou tb ytopica lapplicatio no fth eJH AZ R61 9durin g aperio d of 3{ weeks,wher eupo nth elarva ewer etransferre d toth etw o substrates. 6.5 DISCUSSION Toelucidat eth erol eo fJ Hi nth eregulatio no faestivation-diapaus eo f C. partellus and C. orichaloociliella theJ Htitr ei nth ehaemolymp ho ffiel d collectedlarva ewa sdetermine dbefore ,durin gan da tth een do fdiapause . Non-diapauselarva econtaine da naverag eJ Hquantit yo f100-20 0G.U./m l haemolymph.Thi sconten tseem st ob elo wa scompare dt otitre sfoun di nrelate d stalkborers .Fo rexample ,non-diapaus elarva eo f D. grand-Cosellla contain 300-3000G.U./m l (YINan dCHIPPENDAL E 1976)an di nlas tinsta rnon-diapaus e larvaeo f C. suppressalis 2400G.U./m lwer efoun d (YAGIan dFUKAY A1974) . Inbot hinsect sJ Htitre srapidl ydroppe dt o6 0G.U./m lan d3 0G.U./m l respectivelyshortl ybefor eth epupa lmoult .I twa sknow ntha tth eearl ysample s oflarva lmateria lcollecte dfro mth eexperimenta lfiel dcontaine da fairl y largenumbe ro fpupae .Thi sprobabl yexplain sth elo woveral lJ Htitr ei nth e pooledhaemolymp ho fth enon-diapaus elarva ei nth eearl ysamples .Th elac ko f pupaei nth enex tsample sa swel la sth edepressio no fth elarva lmetabolis m andwate rconten t (fig.16 )indicate dth eonse to fdiapause .Durin gthi sperio d ofdiapaus einductio na relativel yhig hJ Hconten to fabou t100 0G.U./m lwa s 94 found,whic hha ddroppe dt oabou t40 0G.U./m lon emont hlate ran dultimatel y reacheda leve lo f20 0G.U./m li nth elat ediapaus elarvae .Thes eresult s clearlydemonstrat eth econtinuou sactivit yo fth eC Adurin gth ediapause .A n elevatedleve lo fJ Han da subsequen tdecreas edurin gth ecours eo fth ediapaus e wereals oreporte dfo r C. suppressalis (YAGIan dFUKAY A1974) , D. grandiosella (YINan dCHIPPENDAL E 1976)an d M. flavesaena (TAKEDA 1978).Th efindin gtha tth e JHtitr eo faestivatin g Chilo larvaedecrease drapidl y (i.e.withi n3 days )t o sub-diapauselevel safte rexposur eo fth elarva et omois tcondition si nadditio n toth efac ttha tpupatio ni sstarte dsoo nthereafter ,suppor tth eide atha t C. partellus and C. oriahalooailiella belongt oth egrou po finsect si nwhic h larvaldiapaus ei sregulate db yJH . Furtherevidenc efo rthi swa sobtaine dfro mth edifferen treaction so f non-ligatedan dligate ddiapausin glarva et og-ecdysone .Withi nth efiv eday s ofobservatio nver yfe wecdyse sa tal ltoo kplac ei nbot hth enon-ligate dan d ligateduntreate do rsolven ttreate dcontrols .Becaus eo fth eshor tobservatio n periodi ti sno tknow nwhethe rth eterminatio no fdiapaus ei nth eligate dlarva e wouldultimatel yhav ebee naccelerate da swa sfoun dfo r D. grandiosella aftera 30day sperio d (YINan dCHIPPENDAL E 1973). Injectiono fB-ecdyson eprovoke decdysi si nth emajorit yo fth ediapausin g larvae,whethe rthe ywer eligate do rnot : Innon-ligate dlarva estationar yecdyse swer epredominant .Thi sresul tma y reflectth eearl ydiapaus estag eo fth elarvae ,whic hha dbee ncollecte dshortl y afterrain si nth efiel dha dceased .I tha sbee nshow nfo r V. grandiosella (YIN andCHIPPENDAL E 1973),fo r C. suppressalis (YAGIan dFUKAY A1974 )an dfo r M. flaveseens (TAKEDA1978 )tha tmor elarva eten dt opupat eafte rtreatmen twit h ecdysonea sdiapaus eproceeds .Onc emor eth edecreasin gJ Hconten tdurin gth e periodo fdiapaus ewa shel dresponsibl efo rthi schangin grespons e toecdysone . Inligate ddiapausin glarva eth etyp eo fecdysi sappeare dt ob edependen to n thetim eelapse dbetwee nth eligatio nan dth einjectio no fecdysone .I fthi s periodwa sonl yon eday ,mos tlarva emoulte dint oa nex tlarva lstage .I twa s concludedtha tth eJ Hha dno tye tdissipated .I fhoweve rthi sperio dwa s7 day s ormore ,onl yprogressiv eecdyse scoul db eprovoked .Thi sresul tsuggest stha t attha ttim eth eJ Htitr ei nth ehaemolymp hha dsufficientl ydecrease dt oallo w pupationto .tak eplace . Severalexperiment swer econducte dt odetermin eth eeffec to fa J Hanalogu e (JHA)o nnon-diapaus elarva eo f Chilo partellus. Itwa sdemonstrate dtha tth e larvalstag eo fnon-diapaus elarva ema yconsiderabl yb eprolonge ddurin gth e 95 periodo fJH Aapplication s andtha textr amoult soccur .Th eJH Adi dno tappea r toactivat e theC Ao fth erecipien t larvae sincepupa ewer e formedwhe nth eJH A treatments ceased.Simila rresult sha dbee nobtaine d for D. grandiosella (YIN andCHIPPENDAL E 1973,1974 ,1976) , C. suppressalis (YAGIan dFUKAY A 1974)an d 0. nubilalis (YAGIan dAKAIK E 1976). Theresul to fth eJH Aexperiment s confirm thepreviou s resultsmentione d inthi sparagraph . No furtherevidenc ewa s obtained thatJH Aaffect s anyothe raspec to f.th e diapause syndrome.I twa s foundtha t larvae treatedwit hJH Aattaine dmor e than normalweights ,bu t- althoug hheav ydiapausin g larvaewer e frequently collected fromth efiel d- a nextr aweigh t couldneve rb e associatedwit h aestivation- diapause sinceals osmal ldiapausin g larvaewer e oftenobserved .JH Aha sno t been found toinfluenc e anyo fth easpect s ofdiapaus ewhic hhav ebee nuse d in thepresen t research ascriterio nfo rdiapaus enamel y thecuticula rpigmentatio n and thedrough tresistance .Som eevidenc ewa sobtaine d thatals oth e respiratory rate isno taffected .YI Nan dCHIPPENDAL E (1974)clearl ydemonstrate d thatlarva e of D. grandiosella withhormonall y (JHA)induce ddiapaus ewer e morphologically (pigmentation)an dphysiologicall y comparablet olarva ewit h environmentally induceddiapause .Thi ssituatio ndiffer s from larvaldiapaus e of Chilo partellus and Chilo oriahalaooiliella. Toobtai nth ecomplet e syndromebelongin g tothei r diapause (chapters 2an d 3)mor e isrequire d thanJ Honly .O nth eothe rhand , severalexperiment s inthi sparagrap hhav e demonstrated thatJ H isa tleas t involved inth eregulatio no fth elarva l diapause of Chilo sp.i nKenya . 96 Summary Stalkborer sar ehighl ydestructiv et oa larg enumbe ro fimportan t graminaceouscrop sal love rth eworld .Som eexample so feconomicall yimportan t stalkborer sari da genera ldescriptio no fthei rlife-cycl ear ementione di n chapter1 .I nth esam echapte rdifficultie si ncontrollin gth einsect sar e described.Th ecrucia lrol eo faestivation-diapaus ei nth elif ehistor yo f tropicalstal kborer si selucidate dan dth eimportanc eo ffurthe rresearc ho n thissubjec ti sdemonstrated . Aestivation-diapause intw oPyrali dstal kborers , Ckilo partellus (Swinhoe) and Chilo oriehalcoeiliella (Strand)wa sinvestigate dunde rfiel dan dlaborator y conditions. Therelatio nbetwee ndiapaus ean dclimat edurin gthre econsecutiv eyear si s describedi nchapte r2 .Yearl yan dseasona lfluctuation si nth elarva lan dpupa l populationso fth etw ostal kborer si nmaiz eappeare dt ob econsiderable .A slon g asth ewate rcondition sfo rplan tgrowt hwer esuitable ,insect sha da continuou s development.Unde rthes econdition slarva eha dpigmente dspot san dcoul dno t survivedr yconditions .Soo nafte rcessatio no fth erain s (orirrigation )rate s ofpupatio ndecreased .A ttha ttim elarva elos tthei rcuticula rpigmentatio nan d becameresistan tt odrought .Compariso no fth eincidenc eo faestivatio ni nth e fieldwit hth eprevailin gclimati ccondition sshowe dtha tonl ylac ko frai ncoul d beassociate dwit hth earreste dlarva ldevelopment .N oeffect so ftemperature , relativehumidit yo rphotoperio dcoul db efound .Thes eresult sindicat etha tth e hostplan tma yb einvolve di nth einductio no fdiapause . Chapter3 i sconcerne dwit hcharacteristic so fpre-diapaus ean ddiapaus e larvae.Evidenc ewa sobtaine dtha tunde rnatura lcondition slarva ed ono tfee d duringdiapaus ea slon ga sthe yar eno tdisturbed .Th ephysiologica lconditio no f field-collectedste mbore rlarva echange dconsiderabl yupo nenterin gdiapause :a decreasedrat eo foxyge nconsumption ,rat eo fhear tbea tan dwate rcontent ,a n increasedfa tcontent ,an darreste ddevelopmen to fth eteste swer efound .Thes e 97 changesnormall y occurredbefor e larvaewer e turningunspotte d and/orwer e becoming resistant todrought . The conditiono fth ehos tplan t inrelatio n todiapaus e induction is described inchapte r 4.Diapaus e couldb e induced insidemaiz eplant s of different developmental stages.I twa s shown that the first (physiological)sign s of thediapaus e syndrome appear in larvae feeding instem s containing 70-801wate r andver y little (<1.3 $o fth e freshwt. )protein .Th e considerable variationi n thesuga r content ofstem s containingpre-diapaus e larvae suggests that sugari s not important inth e inductiono fdiapause . Marked differenceswer e found inth e consumption andutilizatio n ofstem s ofmaiz e plants indifferen t developmental stages. Itspossibl e relevance todiapaus e is discussed. Inchapte r 5experiment s are described on the induction ofaestivation - diapauseb y varying the food condition.Mos tearl y 5th instar larvae of C. pavtellus entereddiapaus e afterbein g introduced into agedmaiz estems , containing 75%water ,8 % sugar and 1.3%protei n (freshwt.) . Pupationrate , cuticularpigmentation ,QO 2 andwate r contento fthes e larvaewer e comparable to values obtained from fieId-collected aestivating larvae.Larva ewhic hha d developedbeyon d theearl y 5th instarwer e lesssensitiv e toth e diapause inducing factors ofth eage dmaiz e stems:mos to fthe mpupated . Testo f 30differen t dietswit h varyingprotein ,suga r andwate rcontents , indicated that diets containing0.9-1. 1% protei n and 701wate rwer ebes t in inducing diapause.Earl y 5th instar larvae ondiet swit h the above mentioned protein content grewslowl y (butreache dnorma lweights) ,moulte d intoth e unspotted form andha d aretarde d rate ofpupation .Larva eo ndiet swit h lower protein contentshardl y developed atall ,wherea s ondiet swit hhighe rprotei n contents larvaepupate dnormally .Larva e reared ondiet s inwhic h thewate r contentha dbee n reduced from thenorma l levelo f 86% to 70%,resulte d ina reduction ofth e larvalwate r content and respiratory rate,clos e tovalue s normal for field-collected diapause larvae.Evidenc ewa s obtained that larvae reared on diapause inducing diets attained acertai n degree ofdrough tresistance . Early 5th instaro ryounge r larvaewer e themos tsensitiv e stages todiapaus e inductionb ydiet . Many larvae onage dmaiz e steinsan d artificial diets turnedunspotte d eventhoug h pupating soon thereafter.Th e relevance of thecuticula rpigmentatio na s a criterion for aestivation-diapause isdiscussed . 98 The endocrine involvement inth e aestivation-diapause isdescribe d in chapter 6. From juvenile hormone titre determinations and ligation experiments evidencewa s obtained that the diapause isregulate d by an intermediate level of JH.Applicatio n ofJ H tonon-diapaus e larvae prevented pupation ofthes e larvae but didno t evoke other aspects of the diapause syndrome. 99 Samenvatting Stengelboorders zijn zeerschadelijk e insektenvoo ree ngroo t aantal belangrijke grasachtige gewasseni nd e gehelewereld .Enig evoorbeelde nva n ekonomischbelangrijk e stengelboorders enee nalgemen ebeschrijvin gva nhu n levenscyclus zijngenoem di nhoofdstu k 1.I nhetzelfd ehoofdstu k ismeldin g gemaaktva nmoeilijkhede nbi jd ebestrijdin gva ndez e insekten.Aestivatie - diapauzei sva nuitermat e grootbelan g ind elevensloo pva ntropisch estengel boorders.Ee nuitgebrei d onderzoek overdi tonderwer pwer d gewenstgeacht . Aestivatie-diapauze intwe estengelboorder sbehorend eto td ePyralidae ,nl . Chito partellus (Swinhoe)e n Chilo orichaloo oil-Leila (Strand),wer donderzoch t inhe tvel de ni nhe tlaboratorium . De relatie tussendiapauz ee nklimaa t gedurende drieopeenvolgend e jareni s beschreven inhoofdstu k 2.D ejaarlijks e-e nseizoen s schommelingen ind elarval e enpupal epopulatie sva nd ebeid e stengelboorders inmai sbleke ngroot .Zolan gd e plant voldoendewate rte rbeschikkin ghad ,konde nd einsekte n zichkontinu eont - wikkelen.Qnde rdi eomstandighede nhadde nd elarve n gepigmenteerdevlekke ne n waren zenie t instaat droogtet edoorstaan .Spoedi gn ahe tophoude nva nd eregen s (ofva nd eirrigatie )na mhe tverpoppings-percentag e onderd elarve n af,gin gd e kutikulairepigmentati e geleidelijk verlorene nwerde nd elarve n resistent tegen droogte.Ui tee nvergelijkin gtusse nhe toptrede nva naestivati e inhe tvel de n de daarbij heersende klimatologische omstandighedenblee kda tslecht sgebre kaa n regenme td evertraagd e larvale ontwikkelingi nverban d gebrachtko nworden . Temperatuur,relatiev e vochtigheide ndaglengt eware nnie tva ninvloed . Deze resultatenwijze no pee nmogelijk ero lva nd ewaardplan t ind eindukti eva nd e diapauze. Inhoofdstu k 3worde n enigekenmerke nbezie nva nlarve ni npre-diapauz ee n indiapauze .Onde rnatuurlijk e omstandighedenneme nd elarve ngedurend ed e diapauze geenvoedse lo ptenzi jz eworde n gestoord.D efysiologisch e gesteldheid van stengelboordersui the tvel dveranderd e sterkwannee rd ediapauz e intrad. 100 Waargenomenwerde nee nverlagin gva n zuurstofkonsumptie,hartsla ge nwatergehalte , eenverhogin gva nhe tvetgehalt e enee nstilstan d ind eontwikkelin gva nd e testes.A l deze veranderingen traden gewoonlijk op voordat de larven ongevlekt en/ofdroogt e resistentwerden . De relatie tussendiapauz e induktie end etoestan d vand ewaardplan t is beschreven inhoofdstu k 4.Diapauz e konworde n geinduceerd inmaisplante ni n verschillende stadiava nhu nontwikkeling .D e eerste (fysiologische) tekenen van het diapauze syndroombleke n zichvoo r te doen in larvendi e zichbevonde n in Stengelsme tee nwatergehalt e tussen 70e n 80$e nee n laageiwitgehalt e (< 1.3$ vanhe tver s gewicht). Het suikergehalte ind everschillend eStengel swa s zeer uiteenlopend. Suiker isdaaro mvermoedelij knie tbi j dediapauz e induktie betrokken. Groteverschille nwerde ngevonde n ind ekonsumpti ee nd ebenuttingsgraa d van Stengels vanmaisplante n inverschillend e ontwikkelingsstadia. Hetmogelijk e verbandme tdiapauz e isbesproken . Inhoofdstu k 5zij neksperimente nbeschreve n handelend over de induktie van diapauze doormidde lva nverschillend e soortenvoedsel .Larve n inhe tbegi nva n het 5estadium , geintroduceerd inoud emaisstengel sme t 75$water ,8 $suike r en 1.31eiwi t (vers gewicht) gingen grotendeels indiapauze .D emat e vanverpopping , pigmentatie van dekutikula ,zuurstofverbrui k enwatergehalt e vandez e larven warenvergelijkbaa rme t die,gevonde nvoo r aestiverende larvenui the t veld. Larvendi everde rontwikkel dware n danhe tbegi nva nhe t 5estadiu mware nminde r gevoelig voord ediapauz e inducerende faktorenva n de oudemai s Stengels:d e meestenverpopten . Uiteksperimente nme t 30verschillend e dietenwaari n eiwit,suike re nwate r gehalteswerde n gevarieerd,blee k datvoora l de dietenme t0.9-1.1 $ eiwit en 70$wate r diapauze konden induceren.Larve n inhe tbegi nva nhe t 5estadiu m groeiden langzaam opdiete nme tbovengenoem deiwitgehalt e maarbereikte nee n normaaleindgewicht .N avervellin gverlore n zehu npigmentati e end everpoppin g was sterk geremd.Larve n opdiete nme t een lagereiwitgehalt e ontwikkelden zich vrijwel geheelniet ,terwij l opdiete nme tee nhoge r eiwitgehalte de verpopping normaalwas .Larve n gevoedme t dieetwaari n dehoeveelhei dwate rwa sverminder d vanhe tnormal e gehalte van 86$to t 70$,bleke nee nwatergehalt e enademhalings - quotient tebezitten ,dichtbi j die vandiapauz e larvenui the tveld .Aanwijzinge n werdengevonde nda t larvenopgekweek t opdiapauz e inducerendedieten ,teven s een zekeremat eva n droogte resistentie verkregen. Larvenjonge rda nbegi n 5e stadium warenhe t gevoeligst voordiapauz e induktie doordieet . 101 Gedurended eeksperimente nme t oudemaisstengel se nme tkunstmatig e dieten werdendikwijl s larvenaangetroffe ndi enu npigmentati e verlorenhadde nterwij l zekor t daama tochverpopten .D ewaard e vand ekutikulair epigmentati e als kriteriumvoo r aestivatie-diapauze isbesproken . Dero lva nhormone nbi j de aestivatie-diapauze ishe t onderwerpva nhoofd - stuk 6. Uit titerbepalinge n vanjuvenie lhormoo ne nui t snoeringseksperimenten konworde nafgelei d datdiapauz eword t gereguleerd door intermediairehoeveel - hedenJH .Ee nJ H applikatie bijniet-diapauz e larvenvoorkwa mverpoppin gmaa r leiddenie t tothe t ontstaanva nander e aspektenva nhe t diapauze syndroom. 102 Acknowledgements Theresearc hpresente di nthi sthesi swa scarrie dou ta tth eInternationa l Centreo fInsec tPhysiolog yan dEcolog yi nNairobi ,Kenya .I a mgratefu lt oal l friends- i nKeny aan di nth eNetherland s- whohav econtribute dt oth e completiono fthi sthesis . Firsto fal lI lik et othan kProf .J .d eWild efo rgivin gm eth eopportunit y towor ka tth eICIP Ean dfo rbein ga nattentiv edirecto ro fresearc hdurin gm y staythere .Hi scontinuou sencouragement ,an dhi ssuggestio nan dcriticis mdurin g thepreparation so fth emanuscrip tar ehighl yappreciated . Thanksar eals odu et oProf .T.R .Odhiambo ,directo ro fth eICIP Efo r providingm eth efacilitie st owor ki nth e"dudu "laboratory .Man yscientist san d techniciansa tth eICIP Ehav econtribute dt oth ever ypleasan tworkin gatmospher e thatI hav eexperience da ta persona la swel la sa scientifi clevel .I a m especiallygratefu lt otw oo fm ycolleagues ,Dr .Davi dDenlinge ran dDr .Joh n Clearwaterfo rthei rhel pan dinteres tdurin gm ywor ki nKeny aan dthei rvaluabl e suggestionsconcernin gpart so fth emanuscript .I than kMr .Stephe nOthien ofo r hisaccurat ean ddedicate dassistanc ei nth eexperiments ,Mr .Jame sQngudh afo r breedingth einsect san dMr .Lamber tMorek afo rcarryin gou tth eGalleria-test . Acknowledgementsar eextende dt oMr .J.R .Goldson ,Mr .B.R .Adam san d Mr.C.N .Gathungu ,successiv esenio ragricultura lresearc hofficer so fth e NationalAgricultura lResearc hStatio ni nKikambala ,fo rallowin gm et od ofiel d experimentso nth eground so fthei rStatio nan dt oMr .Mali oEnoc kan dhi sstaf f forcarryin gou tthes eexperiments . Theroug hmanuscrip twa sconverte dint oth epresen tshap eb yth ehar dwor k ofRi aCuperu san dRit aSchenkhuize n (typing),Frederi kvo nPlant a (drawings)an d Mr.J.W .Branger t (photographicwork) . Duringth ewritin go fthi sthesi si nWyche nI woul dlik et othan km yfamil y andfriend sfo rthei rpatienc eb yallowin gm et oisolat emysel fa tsom etime san d todeman dattentio na tothers .Withou tthei runderstandin gan dsuppor tthi swor k wouldno thav ebee ncompleted . 103 References Aboul-Nasr A.E., Esaac E.G. and El-Gogary S. (1976) Oxygen consumption by larvae and pupae of Spodoptera littoralis (Boisd.)reare d ondifferen thos t plants. 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