M. Loosjes

Institute of Phytopathological Research, Wageningen

Ecology and genetic control of theonio nfly, Delia antiqua (Meigen)

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Centre for Agricultural Publishing and Documentation

Wageningen - 1976

Z0((?^ Abstract

Loosjes,M . (1976)Ecolog y and genetic control of the onion fly,Deli a antiqua (Meigen). Agric. Res.Rep . (Versl. landbouwk. Onderz.) 857. Pudoc Wageningen. ISBN 90 220 0611 5. (vii)+ 179 p., 95 figs, 39 tables, 331 refs, Eng. and Dutch summaries. Also: Doctoral thesis Leiden and Meded. Inst, plziektenk. Onderz. 743

Literature data on the onion fly's biology are given. The field work on its ecology, relevant for genetic control, is reported, with an emphasis on dispersal. The methods used are discussed, especially marking the flies at emergence, releasing sterilized pupae dug in the soil, recapturing flies by flight interception traps,an d sampling of pupae. Some data are given on the prediction of emergence, the incidence of diapause and Entomophthora infection of the flies.Th e distribution of damage and pupae can be descri­ bed by the negative binomial, and problems are encountered in estimating confidence intervals for the mean density. Densities of pupae normally are some 100 0 -20 000 per ha. From estimates of the life-span distribution of female flies and the frequency of oviposition phases the fecundity is estimated. Reproduction factors are found tob e about 7 and 3 for the two flights,respectively . Dispersal is shown to be in general independent of the wind direction. Several methods of estimating a diffusion coefficient to describe the fly dis­ persal are applied. The best results are obtained by computer simulation with heterogeneity in time and space,yeildin g 2 000m /day in onion fields and 14 000m^/da y outside these. Dispersal is age dependent, occurring less in reproductive phases.Th e logarithm of the total number recaptured of the released group is about linearity related to the distance from the release site.Fiel d trials on control by sterile males are described, and data on competitiveness and reproduction are given. In an onion growing area Ih a treatment gave successful control.A release schedule for the practical application of genetic control to the onion fly is given with estimates for release site density, barrier zone depth, over- flooding ration, and optimal distribution of available steriles over the two flights and the subsequent years.Fo r the Netherlands, an estimated mass-rearing output of 1.5 x 10^ competitive fly equivalents is needed.

Free descriptors:Anthomyiidae , competitiveness, damage distribution, diapause, diffusion, Diptera, dispersal, flight interception trap,releas e strategies,reproduction , sampling methods, simulation, sterile insect technique.

ISBN 90 220 0611 5

The author graduated as Doctor of Science at the State University of Leiden, theNether ­ lands, on a thesis with the same title and contents,o n 15Decembe r 1976.

© Centre for Agricultural Publishing and Documentation,Wageningen , 1976.

No part of this book may be reproduced and/or published in any form, by print,photoprint , microfilm or any other means without written permission from the publishers. Contents

1 INTRODUCTION '

2 INTRODUCTORY DATA ONTHE ONION FLY ANDITS CONTROL 3 2.1.GENERA LBIOLOG Y 3 2.1.1 Taxonomy 3 2.1.2 Morphology 3 2.1. S Geographical distribution 7 2.2 ECOLOGY 8 2.2.1 Life cycle 8 2.2.2 Population dynamics 10 2.2.3 Niche 11 2.3 ONIONGROWIN GAN DPES TCONTRO L 13 2.3.1 Onions in the Netherlands 13 2.3.2 Damage 14 2.3.3 Pest control 17 2.4 SUMMARY 19

3 ENVIRONMENT ANDDISCUSSION OFMATERIALS AND METHODS 21 3.1 ENVIRONMENT 21 3.1.1 Experimental area 21 3.1.2 Weather 24 3.2 FLIESUSE DFO RTH EEXPERIMENT S 26 3.2.1 Mass rearing 26 3.2.2 Sterilization 27 3.3 DISCUSSIONO FMETHOD S 28 3.3.1 Marking 28 3.3.1.1 Markinglarva e 28 3.3.1.2 Markingemergin gflie s 29 3.3.1.3 Markingb ysterilizatio n 30 3.3.1.4 Wingvei naberration s 31 3.3.1.5 Size 31 3.3.2 Releasing 32 3.3.2.1 Releasingpupa e 32 3.3.2.2 Releasingflie s \ 35 3.3.3 Trapping flies 36 3.3.3.1 Flightinterceptio ntrap s 36 3.3.3.2 Attraction 39 3. S.4 Obtaining eggs 41 3.3.5 Sampling flies, larvae and damage 42 3.3.6 Sampling pupae 43 3.3.7 Fly inspection 46 3.3.8 Field observation of fly behaviour 47 3.4 SUMMARY 48

50 ONION FLÏ ECOLOGY 4.1 LIFECYCL E 50 4.1.1 Prediction of emergence •)" 4.1.2 Flight curves •" 4.1.3 Incidence of diapause •'•' 4.1.4 Number of flights 58 4.2 NICHE 59 4.2.1 Oviposition site 59 4.2.2 Larval and adult food 62 4.2.3 Parasitoids 63 4.2.4 Entomophthora "^ 66 4.2.5 Predators 4.3 ESTIMATIONO FDAMAG EINTENSIT YAN DPOPULATIO NDENSIT Y 67 67 4.3.1 Damage intensity 4.3.1.1 Damagepatter n 67 4.3.1.2 Distributiono fdamag e 4.3.1.3 Precisionestimatio n 70 4.3.1.4 Plotsiz e 73 4.3.1.5 Damage frequency in time 74 4.3.2 Pupal population density ^ 4.3.3 Fly population density 78 4.3.4 Relation between density and damage 83 4.4 MORTALITY 83 4.5 REPRODUCTION 87 4.5.1 Mating 87 4.5.2 Oviposition 89 4.5.3 Reproduction factor 92 4.6 SUMMARY 93

DISPERSAL 95 5.1 PRELIMINARYDISPERSA LEXPERIMENT S 95 5.2 FACTORSAFFECTIN GDISPERSA L 96 5.2.1 Weather and onions 96 5.2.2 Barriers 99 5.2.3 Passive dispersal 100 5.2.4 Fly properties 101 5.3 DIFFUSION 102 5.3.1 Introduction 102 5.3.2 Calculation of diffusion coefficient from field observations of fly behaviour 103 5.3.S Calculation of diffusion coefficient from release-recapture experiments 105 5.4 DISPERSALSIMULATIO N 107 5.4.1 Simulation model 107 5.4.2 Analysis of a release-recapture experiment 109 5.5 NUMBERSVERSU SDISTANC E 113 5.6 AGE-DEPENDENTDISPERSA L 119 5.6.1 Trapping place versus age 119 5.6.2 Age distribution of immigrating flies 122 5.6.3 Dispersal with regard to genetic control 123 5.6.4 Migrated fractions of reproducing populations, in relation to distance 126 5.7 SUMMARY 126

6 GENETIC CONTROL 129 6.1 FIELDTRIAL SA TTH ESCHUILENBUR G 129 6.1.1 Introduction 129 6.1.2 Reproduction 131 6.1.3 Competitiveness 132 6.2 GENETICCONTRO LFIEL DEXPERIMEN TO NOVERFLAKKE E 134 6.2.1 Introduction 134 6.2.2 Fly sterility 136 6.2.3 Competitiveness 139 6.2.4 Egg sterility 141 6.2.5 Damage 143 6.2.6 Sampling of pupae 143 6.2.7 Reproduction 144 6.3 ANORMALIZE DFIEL DEXPERIMEN T 146 6.4 RELEASESTRATEGIE S 147 6.5 SUMMARY 153

7 CONCLUDING REMARKS 154 7.1 DISPERSAL 154 7.2 PESTSITUATIO N 154 7.3 GENETICCONTRO L 155

SUMMARY 158 SAMENVATTING 160 ACKNOWLEDGMENTS 163 REFERENCES 164 APPENDIX 177 1 Introduction

Themai n insectpes to fonion si ntemperat e regionso fth enorther nhemispher ei sth e onion fly,Deli aantiqu a (Meigen) (e.g.Hennig ,1953 ;Balachowsk i& Mesnil ,1935 ;Essig , 1926; Miller,1956 ;Metcal f& Flint ,1962) . Itma ydestro yu pt o50-100 4o fth ecrop . Effective chemical controlmeasure s havebee ndevelope dan dapplie dmainl y during thepas t fewdecade s (Dustan,1938 ;Wright ,1938 ;McLeod , 1946;Maan , 1947). Researcho nth eonio nfl yha sbee ndon eo nit sgenera lbiolog y (e.g.Eyer ,1922 ; Kästner,1929b ;Isaev ,1932 ;Maan ,1945 ;Miles ,1956 ,1958a ;Rygg ,1960 ;Perro nan dco ­ workers,1951-1972 ;Ellington , 1963)an do nspecia laspect s like laboratory rearing (Friend& Pattern ,1956 ;Frien de tal. , 1957,1959 ;Alle n& Askew , 1970), attractants (Peterson,1924 ;Matsumot o& Thorsteinson , 1968a,1968b ;Matsumoto ,1970 )an d reproduction (Missoimier& Stengel ,1966) .A bibliograph y hasbee ngive nb yScot t (1969),mor e selected references arefoun di nHenni g (1974). Literature compilationso nit s lifehistor y have beenmad eb yBeirn e (1971)an dSchnitzle r (1967). Developmento fresistanc eagains tpesticide suse d (Howitt,1958 ;Anonymous ,1967 ; Brown,1974 )an dth ehazard s thatpesticide s constitutefo r theenvironmen t causedre ­ searcht ob estarte d aiminga tth edevelopmen to fgeneti c controlo fth eonio nfl yi n theNetherland s (Noordirik,1966 )an dals oi nCanad a (McClanahan& Simmons ,1966 ;McEwe n et al., 1973).Th emetho do fgeneti c controlwa s first appliedb yKniplin g (1955), Baumhovere tal . (1955)an dLindquis t (1955). Thedevelopmen to fth egeneti c control methodha sbee nreviewe db yProverb s (1969), Smith& vo nBorste l (1972)an dWhitte n& Foster (1975). Theordinar y typeo fgeneti c controli sth esteril e insect techniqueo rsteril emal e technique.B yreleas eo fsterilize dmale so fth esam especie si nhig hnumbers ,th epossi ­ bilityo fa wil d femalet omat ewit ha wil dmal ei slowere dt oth eexten ttha t the average numbero freproducin g offspringpe rfemal ei sles stha ntwo ,resultin g ina populatio n decline.Othe rpossibilitie so fgeneti c control arebase do nmor e subtlegeneti cmanipu ­ lations,lik e induced chromosomerearrangements . Thisrepor t contains theecologica lpar to fth eresearc hfo r thedevelopmen to fge ­ neticcontro lo fth eonio nfl yi nth eNetherlands ,carrie d outb ya researc htea ma t Wageningen.Othe r aspectsexamine db ythi sresearc h teamare : -mas srearin g (Ticheler& Noordirik ,1968 ;Ticheler ,1971 ;Noorlander ,i nprep.) , -sterilizatio n (Ticheler& Noordink , 1968;Noordink , 1971), -us eo fradioisotope s (Noordink, 1971), -histopatholog y (Theunissen, 1971,1973a ,1973b , 1976), -sterile-mal e fieldtrial s (Tichelere tal. ,1974a ;Theunisse ne tal. , 1974,1975) , -chromosom e rearrangements (Wijnands-Stäb& va nHeemert ,1974 ;Robinso n& va nHeemert , 1975; vanHeemert ,1973a ,1973b ,1975 ;Vosselman ,i nprep.) ,

1 -simulatio no fcontro lstrateg y (Wijnands-Stäb& Frissel ,1973) . Theteam' sresearc ho nth esteril einsec ttechniqu ean dgenera laspect s isreporte d in:Jaarversla g Instituutvoo rPlantenziektenkundi gOnderzoe k 1964(1965 )an dfollowing , andmor econdense d inAnnua lRepor t Institutefo rPhytopathologica lResearc h197 2(1973 ) andfollowing .Th egeneti cresearc hpar ti scovere dby :Applicatio no fatomi cenerg yi n agriculture,Annua lrepor t196 9associatio nEuratom-ITA L (1970)an dfollowing .Togethe r thesedat aca nb efoun din :Commissio no fth eEuropea nCommunit yEuratom ,Annua lrepor t 1971,programm ebiolog y- healt hprotection ,Luxembour g (1972)an dsubsequen tissues .

Theai mo fth estud ywa st oprovid edat ao nth eecolog yo fth eonio nfly ,necessar y forapplicatio no fgeneti ccontrol ,an dt oinvestigat eth efeasibilit yo fgeneti ccontro l undernorma lfiel dconditions .A tleas tpartl ybecaus eo fthi sprogramme ,an dbecaus eo f thelimite dmanpowe rmad eavailable ,th edat apresente dar ea somewha tunbalance daccoun t ofth eonio nfly' sbiology .Especiall yth edat ao nth elif ecycl ean dnich ear elimite d tomer eincidenta lobservations .Mor edetail sar epresente do ndensitie san dreproduction , asthes easpect sar eclosel ylinke dt oth edispersa lwhic hi sth emai nobjec tstudied . Reproductionan dmortalit ywer eno tchose na sth emai nobjec tbecaus einvestigation s inchang eo fpopulatio nsiz ehav et ostar tb ydelimitin gpopulation san dmeasurin gth e degreeo fexchang eamon gthem .Also ,th eexperimenta lanalysi so fpopulatio ndynamic si s ratherlaborious ,wherea sth edat arelevan ti na steril emal econtro lprogra mca nb eob ­ tainedfro monl yexecutin gan danalysin gpilo tproject swit hsteril ereleases ,a spointe d outb yfo rexampl eLindquis t (1969)an dWeidhaa s (1973). Thedat acollected ,especiall ythos efro ma pilo texperiment ,ar euse dt oprovid ea n outlooko nth epractica lapplicatio no fsteril emale s inDutc honio ngrowing . Asth eresearc ho nchromosoma lrearrangement s isno tye ti na fiel dtestin gstage , thefiel dwor kwil lb econsidere donl yi nrelatio nt oth esteril einsec ttechnique . Theexperiment swer ecarrie dou tfro m197 0t o1974 .Th efiel dwor kwa sdon emainl y onth eforme rislan do fOverflakke ei nth eS Wo fth eNetherlands ,wit ha bas ea tth e FoundationDutc hOnio nFederatio n (SNUiF)a tMiddelharnis .Th elaborator yexperiment s weredon ea tth eInstitut efo rPhytopathologica lResearc h (IPO)a tWageningen . Alsosom eo fth edat aobtaine dfro ma serie so ffiel dtrial so ncontro lb ysteril e malesa tth eexperimenta l farm 'theSchuilenburg 'nea rWageninge n (Tichelere tal. ,1974a ; Theunissene tal. ,1974 ,1975 )ar einclude di nthi sreport . 2 Introductory data on the onion fly and its control

2.1 GENERALBIOLOG Y

2.1.1 Taxonomy

Theonio nfl yi sa dipteron ,belongin gt oth efamil yAnthomyiidae .Th e synonymscur ­ rentlyi nus ear eChortophil aantiqu a (Meig.),Deli aantiqu a (Meig.)» Phorbiaantiqu a (Meig.),Hylemy aantiqu a (Meig.)an dHylemyi aantiqu a (Meig.).Th elas ti sa late rcor ­ rectiono fth eorthographica lmistak ei nHylemya . Followingth erecen trevisio no fth eAnthomyiida e (Hennig,1974) ,Deli ai suse dhere . Inearlie rpublication so fth eonio nfl yresearc htea mHylemy aha sbee nuse dbecaus eo f itspredominanc ei ninternationa luse . Inearlie rapplie dentomologica l literatureals oth efollowin g synonymsoccur : Anthomyiaantiqu aMeig. ,A .ceparu mMeig. ,Hylemyi acepetoru m (Meade),H .ceparu m (Meig.),Pegomyi acepetoru m (Meade),P .ceparu m (Meig.),Phorbi acepetoru mMeade , P. ceparum (Meig.)an dLeptohylemyi aantiqu a (Meig.).

2.1.2 Morphology

Adult Thespecie sDeli aantiqu aca nmostl yb eidentifie dfro mit sgenera lappearanc e (Fig.1) :it ssize ,it soliv egre y (males)o rslightl yyellowis hgre y (females)dorsa l parto fth ethora xwhic hi spracticall yunstriated ,an dth egenera lshap eo fth emal e genitaliai nsid eview .I ncas eo fdoub tth efollowin g characteristicsca nb eused .Male s havea typica l irregularro wo frelativel yshor thair so nth etibi ao fthei r3r dleg ,a t themedial-cauda l side (Fig.2). Femaleshav etw o hairsa tth elateral-rostra lsid eo fth e 2ndtibia ,wherea smos tresemblin gspecie shav eonl yon ehai rthere .Resemblin g species withtw ohair sther ehav eth epre-ala rhai ro nth ethora xa slon ga sth eothe r thoracical hairs,i ncontras tt oth eonio nfl yan dsevera lo fit srelative swher ei ti sonl yhal fa s long (Fig.3) . Themai nse xdifference sare ,apar tfro mth ethora xcolou ran dth eothe rcharacteris ­ ticsmentioned ,th eabdome n (males:slender ,wit ha blac k longitudinalline ,externa lge ­ nitalia;females :rounded ,ligh tgrey )an dth esiz eo fth eeye s (males:eye snearl ytou ­ chingeac hother ;females :eye sclearl yseparated) . Fora mor edetaile ddescriptio no fth eadul tmal emorphology ,an dfigure so fth emal e genitalia,se eHenni g (1974).Fo rth emorpholog yo fth erelate dbea nsee dflies , D.platur aan dD . florilega,se eHenni g (1974) (males)an dAgeev a (1968)(male san dfe ­ males). Thedeterminatio ncharacteristic smentione dar erathe rvariable .Onc ea mal eonion fl y Fig. 1.Onio nfl yadult .Righ tmale ,lef tfemale ;o nto pdorsa lview ,belo wsid eview;x6| .

wasfoun dwithou tit slef tprealar ehair .Th enumbe ro fhair so nth efemal etibia- 2ran ­ gedfro m1 t o4 .Rarel yth euppe ron eo fth etw o 'normal'hair swa sabsent .A teithe r sideo fthi spai ro fhair sa nadditiona lsmalle rhai rcoul doccur . Severalaberration si nwin gvein swer efound .Thes ewer emostl yappendage san dthick ­ eningso fth ecros sveins .The yoccurre di ndifferen tpopulation swit hfrequencie so f 5-251.Simila raberration shav ebee ndescribe dfo rth eonio nfl yb ySaage r (1959)an dfo r severalrelate dspecie sb ySic k (1967)i nfrequencie so f0.01-4.351 .

4 Fig. 2.Mal e onion fly, ventral view of right 3rd leg, x20.

Fig. 3. Onion fly, sidevie w of thorax with pre-alar hair indicated, *20.

The laboratoryrearin go fth eonio nfl yusuall yproduce da fe wpercen to faberran t males.Thes eha dcharacteristic s intermediatebetwee nth emale san dth efemales :th eeye s wereseparate dbu tno ta smuc ha si nth efemales ,an dth eshap eo fth eabdome nwa sinter ­ mediate.Reduce dmal eexterna lgenitali awer epresent .The ycontaine d testesan dn oOva ­ ria.I nwild population s3 suc hmale swer e foundamon g 7057individuals .A simila ronio n flywa smentione db yTiensu u (1935),als oreare di na laboratory .Suc haberration s inth e sexexpressio nhav ebee nmentione dfo rrelate d speciesb ySic k (1967),Henni g (1974, D.platura) ,an dSmit h (1971,1972 ,D .brassicae) . Sometimesa considerabl e fraction,u pt o 20%,o fth elaborator yreare dfemale sha da misformedovipositor :i tcoul dhardl yb eextruded .Th eovarie so fthes efemale sonl yde ­ velopedunti lth estar to fyol k formation (Theunissen,1973a :stag e S5).Als othe ydi d notmate .

Egg Theeg gi s1.1-1. 3m mlong ,whitish ,an dit schorio nha sa characteristi cri mstruc ­ ture (Fig.4) .I ti sopene db yth eemergin g larvaalon gon eo fth eside so fth esutur e runningalon gth erostra lhalf .Egg so fD .platur aar emaximall y0.9 6mm ,significantl y shortertha nD .antiqu aegg s (Miles,1953 ;Dusek ,1969 ; Buth, 1976). Fig. 4.Onio nfl yeggs ,*60 .

Larva Themorpholog yo fth elarv aha sbee ndescribe di ndetai lb y Kästner (1929b), Balachowski& Mesni l (1936),Maa n (1945)an dDu& k (1969). Itdevelop s through threein ­ stars.Th e1s tinsta ri seas yt orecognis eb yth eshap eo fth ecephalopharyngea lskele ­ ton (Fig.5) ,th edifferenc ebetwee nth e2n dan dth e3r dinsta ri smos teasil y seenfro m thenumbe ro fstigmat ape r abdominal stigmatophore,2 an d3 ,respectively . The larvae caneasil yb econfuse dwit h thoseo fD .platur awhic h areals o frequently foundi nonions .Th edifferenc ei sth enumbe ro ffinger-lik eprocesse so fth eprotho - racale stigmatai nth e3r dinstar : 10-13i nD . antiquaversu s7- 9i nD .platur a (Dusek, 1969; 5-8accordin gt oMiles ,1953) .I nth e2n dinsta r larvaethes enumber sar etw oles s (Dusek, 1969). First instar larvae canb edistinguishe db yth emandibula r parto fth e cephalopharyngeal skeleton,havin g two teetho fequa l sizei nD . antiquaan do funequa l sizei nD .platur a (Dusek, 1969).Also ,ther ear esligh tdifference si nth ecauda lknobs .

r ,v wn .--— f V\ " f ,* 1\ i, •i \ "§%£**"

Fig. 5.Cephalopharyngea l skeletono flarva :lef t 1stinstar ,righ t2n d instar,x40 .

6 Fig. 6.Onio nfl ypupa :lef tlatera lvie wo fcauda lend ,x45 ;righ tdorsa lview ,xlO . FromDu¥ek ,1969 .

Pupa Thepupa ear e5.5- 7m mlong ,occasionall yreduce dt oeve n4. 5mm .Thes e smaller onesma yb econfuse dwit hD .platur apupae ,whic har e3- 5m mlon gor ,accordin gt oDuse k (1969),4-5. 2 mm.Ther ear esligh tdifference si ngenera lappearanc ean di nth e larval caudalknob stha tar e stillvisibl eo nth epupae .Th ethir dpai ro fknobs ,counte dfro m dorsalt oventral ,i si nth eonio nfl ylarva elarge rtha nth e 1st,2n dan d4t hpairs , whereasi nD .platur athe yar eo fabou tequa lsiz e (Duïek,1969 ) (Fig.6) .Anothe rdif ­ ferencei sth enumbe ro ffinger-lik eprocesse so fth eprothoracal estigmata ,i fthes ear e still intact.Schnitzle r (1969)di dno tgiv eclea rdifference sbetwee nantiqu aan dplatur a pupae.

2.1.3 Geographical distribution

Thegeographica ldistributio no fth eonio nfl yi sgive ni nFig .7 .Earlie rreference s havebee nmappe db yMaa n (1945)an dth eCommonwealt h Instituteo fEntomolog y (Anonymous, 1957).Additiona ldat awer eobtaine d fromHenni g (1974),Revie wo fApplie dEntomolog yA upt ovol .62(1974 )an dCooperativ eeconomica l insectrepor tvol .9(1959)-12(1962) .Othe r informationo nth edistributio nha sbee ngive nb yJone s& Man n (1965) (Egyptmentioned) , Kuwayamae tal . (1960)(Japan)an dVappul a (1965)(Finland). Originallyth eonio nfl ywa sa palaearcti c species.Th efl ywa s introduced into Americaan dsprea dther et oth ewes tdurin gth e19t hCentury .I nJapa ndamag ewa s first reported fromHokkaid oi n1938 ,an dha ssprea dove ral lmajo r islands (Kuwayamae tal. , 1960).Th efl yha sbee nincidentall y interceptedo nth eHawaiia nisland s (Whitney,1927 ; possiblyals oEhrhorn , 1915). Theonio nfly' soccurrenc ei nGeorgia ,Alabama ,Nort han dSout hCarolin aan dMissis ­ sippi (Anonymous,1957 )wa sno tmentione db ySton ee tal . (1965); accordingt oChittende n (1916)suc haccount srefe rt oD .platura .No tindicate di nFig .7 ar eth ereference so n onionflie sfro mBrasi l (inHennig ,1974 )an dColumbi a (Anonymous,1917) ,a sthes esee m questionable.Th e'onio nfly 'o r'onio nmaggot 'i nAustralia npublication srefer st o D.platura . Fig. 7.Geographica l distributiono f theonio nfly . generaloccurrence ,+ : loca l observation.Source sse etext .

Datafro mth eMediterranea ncountries ,wher eth eonio nfl yi sno tusuall ya seriou s croppest ,ar escarce .Also ,th einformatio nfro mSiberi aan dChin ai scertainl yincom ­ plete.

2.2 ECOLOGY

2.2.1 Life oyole

Theonio nfl yhibernate sa sa diapausin gpupa .I nsprin gth eflie semerge ,wit ha se x ratioo f1:1 .Protandr yoccurs ,th emale semergin go nth eaverag ea fe wday searlie r (Maan,1945 ;Rygg ,1960) .Emergenc ei ssai dt ocoincid ewit hth eflowerin go fdandelio n (Baker,1925) ,o rwit hth epin kbu dstag eo fappl etree s (Lafrance& Perron ,1959) . Becauseonion sar egenerall yno tgrow ntw oyear si nsequenc eo nth esam efield ,th e flieshav et omigrat eafte remergence .The ymat ea ta nag eo fnearl y1- 2week s(Miller , 1956; Balachowski& Mesnil ,1936 ;Ticheler ,1970 ;Bol ,1972) ,an dno tshortl yafte remer ­ gencea sreporte db yLamp a (1905),Eye r (1922),Maa n (1945)an dRyg g (1960). Copulationi sonl yrarel yobserved ,eve ni nmas srearings .Th eonio nfl ywa sclaime d tob emonogamou s (Broersma& Luckmann ,1968) ,bu tpolygam yha sbee nprove nclearl yt o occur (Noordink,1967) .Male sma ymat ea tleas t5 time si n4 hour san dcopulatio nlast s 2-4minute s (Bol,1972) . Thefemale sar eanautogeneous :the yhav et ofee do nprotein sbefor eeg glayin g (Missonnier& Stengel ,1966 ;Missonnier ,1967) .Th eegg sar elai do ndifferen tAlliu mspe ­ cies,afte ra pre-ovipositio nperio do fabou t1- 2weeks .Th eduratio no fth epre-oviposi - tionperio di spresumabl ydependen to ntemperatur ean do navailabilit yo ffoo d(Tyndale - Biscoe& Kitching , 1974). Thelarva eemerg eafte ra fe wdays ,an dente rth ebas eo fth eonions .Durin gsom e weeksth elarva efee dther eo nth eonion tissue .Especiall ywhe nth eonion sar esmal lth e larvaema ymigrat et oothe ronions ,throug ho rove rth esoil ,t oge tenoug hfood .Full - grownlarva epas sdow nthroug hth esoi lan dpupat ethere .Pupa ear efoun ddow nt o 15c m anda ta naverag edept ho f4- 5 cm (Rygg,1960 )o r 7-8 cm (Maan,1945 ;Isaev , 1932). Mostly 2o r3 flight spe ryea roccur .I nnorther nNorwa ythi s isreduce dt oon efligh t (Rygg. 1960),wherea s inwarme rregion ssometime smor e than3 flight s arereporte d (Alma ata4 (Bundzhe,1965) ,Turke y4 (Keyder& Atak , 1972),S WFranc e4- 5 (Bonnemaison,1962 ; but3 accordin gt oBalachowsk i& Mesnil ,1936) ,Austri a3- 4 flights (Schreier,1953 )bu t basedo ninsufficien t evidence).Th elate rflight sar egenerall yincomplete ,th eothe r pupaeo fthes egeneration shavin g goneint ohibernatio ndiapause . Diapause isinduce db y lowtemperature s (Miles,1958b ;Missonnie r& Brunei ,1972) ,an d alsob yshor tdays .Th erelatio nbetwee nth epercentag ediapaus ean dth erearin gcondi ­ tionso fdaylengt han dtemperatur eha sbee nestablishe db yMcLeo d (1965)an di nmor ede ­ tailb yRamaker s (1973) (Fig.34) .Diapaus eterminatio ni stemperatur edependen t (Kelderman,1972) . Foodqualit ymigh tals oaffec tth epercentag ediapause ,a sfoun dfo r Pegomyiabeta e (Malekghassemi, 1969). Someauthor sreporte ddiapaus efrequencies ,base do npupa etha twer ehel dunde r non-representativecircumstance so rdi dno tconstitut ea representativ esampl e (Rygg, 1960; van 'tSant ,1967 ,1970 ;Miles ,1953) . Perron& Lafranc e (1961)foun d ina stud y infiel dcage si nQuébe cdiapaus epercentage s forth ethre esuccessiv egeneration sof : 0-19,43.5-9 1 and99-100 .Suc hdat aar ehighl ydependen to nclimate .I nwarme rregion s aestivationoccurs ,reducin gth enumbe ro fgeneration s inIsrae lt otw oan dshiftin gth e lifecycl eb yhal fa yea rcompare dt onorther nEurop e (Rivnay,1958 ;Yathom , 1963). On Kyushu (southernJapan )bot haestivatio nan ddiapaus eoccur ,wit htw ogeneration sbefor e andon eafte rsumme r (Kato,1958) .Not etha tth e2n dan d3r dfligh tflie sar eo fth e1s t and 2ndgeneration ,respectively . Extensive laboratorydat aar eavailabl eo nth eduratio no fth edevelopmenta lstage s inrelatio nt otemperature .Thes edat aofte ndisagree .Factor sfoun dt oaffec tth erat e ofdevelopmen tar e larvalfoo d (Friende t al., 1959),humidit y (Ellington,1963 )an dse x (a.o. McClanahan& Simmons ,1966) . Otherfactor scausin gdifference sbetwee nth edat aca n be temperaturemeasuremen ta tunrepresentativ esites ,difference s indefinitio no fstar t anden do fth estages ,an dus eo fgeneticall ydifferen tonion fl ypopulations .Averag e durationso fth edevelopmenta lstage sar esummarize d inTabl e 1.Afte rcompletio no fdia ­ pauseth edevelopmen to fth epupa eproceed s similart otha to f3-day-ol dnon-diapausin g pupae (Theunissen, 1976). Theflie sar esuppose dt o livei nth efiel d for2- 3week s (Balachowski& Mesnil ,1936 ) or3- 4week s (Kästner,1929b ;Maan , 1945). Dispersal issai dt ooccu rwit hth eprevailin gwin d (Eyer,1922) ,bu tthi sstatemen t wasbase do nobservation so fdamag ewhic hcoul deasil yhav ebee nexplaine db yothe rfac ­ tors.Accordin gt oEye r (1922),th efl yi scapabl eflyin gove r 3k mo fwater ,provide d thatth ewin d isfavourable . Table1 .Averag eduratio n inday so fdevelopmenta l stageso f theonio nfly ,i nrelatio n totemperature .Estimated,fro mlaborator ydata .Fro mTichele r andNoorlande r(pers . commun.)\ an dj literature i• _ .>ab

Temperature in° C

10 15 20 25 30 egg 12 5 3 2 larva 1stinsta r 10 5 3 2 2nd instar 10 5 3 2 14 3rd instar 35 20 13 9 pupa 50 25 16 12 11 pre-ovipositionperio d 22 10 7 5 a.Eyer ,1929 ;Maan ,1945 ;Miles ,1958b ;Frien d etal. , 1959;Rygg ,1960 ;Ellington ,1963 ; Yathom,1963 ;McClanahan ,1966 ;McClanaha n& Simmons ,1966 ;Tichele r &Noordink ,1968 ; Brunei& Missonnier ,1969 ;Alle ne nAskew ,1970 ;Ticheler ,1971 ;Kelderman ,1972 ; Missonnier &Brunei ,1972 ;Houwing ,1973 ;Eckenrod ee tal. ,1975b . b.I nth eTable s0 = observe d zero,- = essentiall y zeroan d •= n oobservation .

2.2.2 Population dynamics

Quantitativedat ai nth eliteratur eo nonio nfl ypopulatio ndynamic s inth efiel dar e veryscarce .Densitie s inth efiel dhav ebee ngive nfo rchemicall ytreate donio nfield s 2 byMcEwe ne tal .(1973) ,averagin g3. 4hibernatin gpupa epe rm ,o fwhic h83 %emerges . 7 Perron (1972)gav efo runtreate dfield so nth eaverag e2 0pupa epe rm ,o fwhic h 70%emer ­ ges.Th edistributio no fdensitie sove rth efield ssample di sa ver yske wone . Thesurviva lo fimmatur estages ,a sgive nb yMcEwe ne tal .(1973) ,40-60% ,seem sto o high,probabl ydu et oth eexperimenta lan dcalculatio nmethod suse dwhic har eno tclearl y described.Perro n& Lafranc e (1961)gav elif etabl edat abase do na cag epopulation .The y foundne treproductio nfactor sfo rth ethre egeneration so f17.5 ,2 5an d10.5 ,an da fecundityo f58 ,3 6an d2 4egg spe rfly ,respectively .Suc hdat acanno tb eextrapolate d safelyt oth efiel dsituation . Perron (1972)reporte dsom edat ao nhi sextensiv esampling so fdifferen tstage so fth e onionfly .Unfortunatel yther ei sn oindicatio ngive no nho wh eobtaine dth egive nper ­ centagesfo rsurviva lo feggs ,larva ean dpupa efro mhi ssamplings ,an dth esamplin gpro ­ cedureapplie dma yhav emisse da considerabl efractio no fth eeggs .Fo rth efirs tfligh t hegav emortalitie so fabou t45-78 %i nth eeggs ,74-96 %i nth elarva ean d 56-84%i nth e pupae,an dabou t30 %mortalit yamon ghibernatin gpupae .Th edifference sobserve dwer eat ­ tributedt oth esoi ltyp ean dAlliu mspecies ,bu ti ti sno tclea rwhethe ran yo fthes e differencesi ssignificant .Moreove rhi sstatement ssometime sconflic twit hth edat apre ­ sented. Forth erelate dDeli abrassicae ,pupa lparasitis mha sbee nfoun dt ob eth efacto r stabilizingpopulatio nsiz e (Mukerji,1971) .Fo rth eonio nfl ya simila rsituatio nma yb e expected.

10 2.2.3 Niche

Host plant preference in oviposition Theonio nfl y isclosel yassociate dwit hdifferen t Alliumspecie sb yth echoic eo fovipositio nsite .Specie sattacke dar eAlliu mcep aL . (onion,shallot) ,A . ampeloprasumL . (leek,pear l onions), A. fistulosumL . (Welsh onion), A. sativumL . (garlic)an dA . schoenoprasumL . (chives).Shallo t isgenerall yreferre d toa sA .ascalonicu mL. ,bu t according toJone s& Man n (1963,p.34-35 )i tshoul db ein ­ cluded inA . cepa.Similarl y leek isofte ncalle dA .porru mL .Onion san dA . cepax fistulosum arepreferre d toA .fistulosu m (Perrone t al., 1958,1960 ;Perro n& Jasmin , 1963),onion sar epreferre d toA .cep ax fistulosum (dePonti ,1976) ,an donion sar epre ­ ferredt oshallot san dbot ht olee k (Maan,1945) .Accordin g toLabeyri e (1957)thes epre ­ ferencesar ehighl ydependen to nth eseason .Garli ci sno tseriousl yattacke d (e.g.Jone s & Mann,1963) .Differen tcultivar so fonio nhav ea slightl ydifferen tpreferenc e (Matthewmane tal. , 1953), sometimesmentione da ssignifican t (Sleesman,1934 ;Hube r& Sleesman,1935) ,sometime sno ts o (Perrone t al., 1958),bu t inth e lastcas eprobabl y duet oth e limitedset-u po fth eexperiment .Ther e isa stron gpreferenc efo rinjure d anddisease d (rotting)onion s (Labeyrie,1957 ;Workman ,1958 ;Armstrong ,192 4an d others), andfo ronion s infestedwit h theonio nste meelworm ,Ditylenchu sdipsac i (Kühn)(Anonymous , 1973).Undamage d fullydevelope donion sar eno tattacke d (Perron& leRoux ,1962 ;Perron , 1972). Denseronio ngrowin g results inhighe reg gpopulatio ndensities ,withou ta signif ­ icantdifferenc e innumber so fegg spe ronio n (Perron,1972) .Also ,onion so fheav yflac ­ cidgrowth ,suc ha s2n dyea ronion s thathav ebee nplante dto odeep ,ar ever y attractive (Gray,1924) ,an dma yb euse d asa tra pcro pt ocontro lonio nmaggo t infestation (see Section 2.3.3). Thesepreference sare ,wher eknown ,du et oovipositio ndifference s (Perrone t al., 1960),an dar esuppose dt ooriginat efro mchemica ldifference so fAlliu modours .Ovipo ­ sitioni sdirecte db ychemica lstimul ifro mcomponent so fonio nflavou r (Matsumoto& Thorsteinson,1968a ;Matsumoto , 1970),Mülle r (1969)suppose dplan t shapean d lightt ob e effectivea tshor tdistances .I nth efield ,th etactil estimul irequire dfo rovipositio n areprovide d forb yth eonio nan dth esoil .Egg sar elai do nonio nplant so rver ynea r tothes ei neart hcrevices ,an dsometime so nleaves .

Larval food The larvaefee do nth esubterranea npar to fth eonio nste mor ,afte rbul b formation,th eonio nbul btissue .I nsumme ronion sma y surviveonio nfl yinfestation .At ­ tackedonion sro tb ybacteria l infection,generall ysof tro t (Erwiniacarotovor a (Jones)), introducedb yth elarv ao rhavin ggo tacces sb yth einsect sattac k (Johnson,1930 ; Gorlenkoe t al., 1956). Otherbacteria l andfungu s infectionsma yb eassociate dwit h ita s well (Zeceva& Becvarov ,1973 ;Jone s &Mann , 1963). Thisbacteria lpredigestio n isno tobli ­ gatory,a s iti sno talway spresen t inth efield ,an dasepti crearin go fonio nfl y larvaei n thelaborator y isquit epossibl e (Friend& Patton ,1956 ;Frien de tal. , 1957;Alle n& Askew , 1970; Ticheler,1971) .However ,presenc e ofmicro-organism sha sa stron gpositiv eeffec to n therat eo flarva ldevelopmen t (Friende t al., 1959;Gorlenk oe tal. , 1956).Th esof tro t canb ereare dfro mth econtent so fth epupa e (Johnson,1930 )an dals ofro mth einsid eo f larvae,flie san deve negg s (Gorlenkoe tal. , 1956).Th epresenc eo fbacteri a insideth e

11 eggsseem st oconflic twit hasepti crearin gafte rsterilizin gth eoutsid eo fth eegg s (Friende tal. ,1957 )wher eth ebacteri aar epresen tto o (Gorlerikoe tal. , 1956). Thelarva eaccep tothe rfoo da swell :the yar eoccasionall yfoun di nothe rplant s likecabbag e (Maan,1945 ;Lundblad ,1933 ;Kalandadz e& Savkacisvili ,1958) ,radis han d spinach (Miller& McClanahan ,1959) ,radis h (Severin& Severin ,1915 )an dtulip san d lettuce (Smith,1922 )ofte nbecaus eo fchange si nth efoo davailabl eafte reg gdepositio n ononion s (e.g.Mille r& McClanahan ,1959) .Also ,th elarva eca nb ereare di nth elabora ­ toryo na nartificia ldie tbase do ncarro tpowde r (Ticheler,1971) .Severi n& Severi n (1915)mentione dhorse-dun ga slarva lfood ,bu tsubsequen texperiment sfaile dt oconfir m this (Kästner,1929b ;Maan ,1945) . Inmas srearing ,cannibalis mma yoccur :larva econsum e pupaetha thav ebee nforme di nth elarva lrearin gmediu m (Noorlander,per scommun.) .

Adult food and attraatants Theflie sar ereporte dt ofee do ndifferen tflowers ,mainl y Umbelliferae,Taraxacu man dAlliu m (Baker,1928 ;Kästner ,1929b ;Maan ,1945 ;Rygg ,1960) . Noordink (1973)di dexperiment so nradioactiv elabe ltransfe ri nfiel dcages ,an dgo t positiveresult swit hsom eflowerin ggrasses .Bake r (1928)observe dflie so nmanure ,an d supposedit sattractio nwa swarmt h (oncoo ldays )o rit smoistur econten t (fordrinkin g onho tdays) . Theflie sca nb eattracte db ysevera lsubstance s (Howard,1918 ;Peterson ,1924 ; Kästner,1929a ;Yathom ,1963 ;Niemczyk ,1965 ;Anonymous ,1965a ;Noordink ,1966 ;Eckenrod e etal. ,1975b) .Th emos tpowerfu lattractan tfoun di nth elaborator yan di nfiel dtest s outsideonio nfields ,i sn-propy ldisulfid e (Matsumoto& Thorsteinson ,1968a ;Matsumoto , 1970; Noordink,1967) ,on eo fth eonions 'constituent s (Carson& Wong ,1961 ;Brodnit ze t al.,1969 ;Boelen se tal. , 1971). Iti sals oon eo fth eattractant sfo rth elarva e (Matsumoto& Thorsteinson , 1968b). Colourshav ebee nfoun dt oattrac tsevera lrelate dspecies ,yello wgenerall ybein g themos tattractiv e (Sick,1967 ;Kring ,1968 ;Brune i& Langouet ,1970 ;Finc h& Skinner , 1972). Inth eonio nfl yMulle r (1969)foun da preferenc efo rbrightnes sbu tno tfo r colour.

Parasitoids, parasites and predators Manyspecie shav ebee nreporte dt oparasitiz eo n theonio nfly .Afte reliminatio no fsynonyms ,incorrec tquotation san dpropabl yincorrec t records,onl ya limite dnumbe ri slef t (Loosjes,i nprep.) .Th ecommo nspecie samon gthes e areth eparasitoid sTrybliograph arapa e (Westw.)(Hymenoptera ,Cynipidae )whic hattack s mainlyyounge rlarva e (Wishart& Monteith ,1954) ,Aphaeret aminut a (Nées)(Hymenoptera , Braconidae)whic hattack slarva e (Salkeld,1959 )an dAleochar abilineat a(Gyll. ) (Coleoptera,Staphylinidae )whic hattack spupa e (Read,1962) .Heterotylenchu saberran s Bovien (Nematoda)attack sth elarva ean dleave sth eadul tfemale sthroug hth egenita l system,causin gsterilit y (Bovien,1937) . Entomophthorainfectio namon gth eflie si scommo ni nsummer .I tha sbee nexamine di n detailb yPerro n& Crêt e (1960).Th einfectio nspread sespeciall ywit hhig hfl ydensitie s andwit hhumi dweather .Infecte dflie ssho wa typica ldyin gposition ,attache dt ohig h pointsi nth evegetatio n (van' tSant ,1970 :Fig .5 ,Mille r& McClanahan ,1959 :Fig .1) . Theavailabl edat ao npredator sar ever yincomplete ,an dwil lb esummarize delsewher e

12 (Loosjes,i nprep.) - Therear en oindication stha tther eexist sa predato rtha tlimit s itsactivitie st oth eonio nfly .Importan tpredator so fth eimmatur estage sar e Staphilinids (a.o.Aleochar abilineat a (Gyll))an dCarabids ,an do fth eflie spredatory - fliesan dinsectivorou sbirds .

Onion aoinhabitants Especiallyi nsummer ,rottin gonion sma ycontai na numbe ro fdiffer ­ entspecie so ffl ylarvae ,a swel la ssom eothe ranimal s (Merrill& Hutson ,1953 ;Hudo n& Perron,1954 ;Schreier ,195 3an dothers) .Th e specieswil lb eliste delsewher e(Loosjes , inprep.) .Mos tspecie sma yb echaracteristi co fdecayin gorgani cmatter .Ther ear ever y fewdat ao nthei rrelationships . Thepolyphagou sbea nsee dflies ,Deli aplatur aan dD .florilega ,o fwhic hth elatte r ismor eprominen ti nScandinavi a (Rygg, 1960),ar esometime sfoun dt ob eprimar yattacker s ofonions ,especiall yseedling s (Merrill,1951 ;Miles ,1956) .The yhav ebee nsai dt ob e attractedfo rovipositio nt odisturbe dsoi lsurfaces ,e.g .du e toweedin g (Miles,1953 , 1956; Barlow,1965 ;Hassan ,1974 ;Mille r& McClanahan ,1960) .However ,Eckenrod ee tal . (1975a)prove dtha tth eattractio no fbea nsee dflie st osee dan dseedling swa sdu et o thedevelopmen to fsom especie so fmicro-organism spresen tthere .Th ecurren tus eo f disinfected seedwil lthu slimi to reliminat eth eimportanc eo fthes eflie sa sprimar y attackers. Onecas eo fprimar yattac ko fEumeru stuberculatu sRond ,ha sbee nreporte d (Merrill & Hutson,1953) .Fo rlarva ldevelopmen tthi sspecie s is,however ,obligatoril ydependen t onmicro-organism s (Creager& Spruijt ,1935) .

2.3 ONIONGROWIN GAN DPES TCONTRO L

2.2.1 Onions in the Netherlands

Oniongrowin gmethod swidel ydiffe ri ndifferen tcountries .Becaus ethi sstud yi s aboutth eonio nfl yi nth eNetherlands ,som edat ao ngrowin gonion sther ear egiven . Themethod suse dare : 1. Spring-sownonions .Sowin gi si nMarc ha t7 k gseed/ha ,i nrow s 25-40c mapart . Harvesti si nAugust/September .The yma yb estore dunti lth enex tspring . 2. Onionsets .Sowin gi nMarc ha tabou t10 0k gseed/ha ,i nrow s2 5c mapart .Harves t inJuly .Th ebul bsiz ei s8-2 2m mdiameter .Thes eonion sar eplante dth enex tyear . 3. Onionsgrow nfro msets .Plantin gi nMarch ,i nrow s30-4 0c mapart ,usin gabou t 1200kg/ha .Harves ti nJuly ,n ostorage . 4. Silverskinonions .Sowin gi nMarch/Apri la t10 0k gseed/ha ,disperse dove rth efield . Harvesti nJuly/August .Use di npicklin g industry. 5. Autumn-sownonions .Sowin ga sspring-sow nonion sbu ti nAugust .Harves ti nJul yo f thenex tyear . 6. Onionseed .Plantin g inMarch ,abou t2 0b y5 0c mapart ,usin gfull-grow nspring-sow n onions.Harves ti nSeptember . The areascommerciall ygrow ni nth eNetherland sar egive ni nTabl e 2.Onion growin g hasbee nknown i nth eNetherland sa tleas tfro mth e13t hCentury ,an di sa tth emomen t

13 Table2 .Commercia lonio ngrowin g inth eNetherlands ,dat afro m1970-1974 .

Species Crop Surface inh a %Wit hchemica l onionfl ycontro l

Alliumcep aL . springsow nonion s 7500 - 10000 100 onionset s 600 - 800 100 onionsgrow nfro mset s 500 - 1000 25 silverskinonion s 700 - 900 100 autumn-sownonion s 0 - 15 partly onionsee d 10 - 30 0 shallots 150 - 200 few Alliumampeloprasu mL . leek 900 - 1400 5 it pearlonion s 2 100 Allium schoenoprasumL . chives 1 - 2 100 Alliumspp . ornamentals 10 - 20 few totalcommerciall ygrow n 11000- 1400 0

concentratedmainl yo nsand ycla yo nth eforme risland si nth esouthwes tan di nth ene w poldersi nth ecentre . Theothe rAlliu mspecie sar eo fmino rimportance .Shallot sar egrow nlocally ,espe ­ ciallyo nsand ysoil sbehin dth edunes .Plantin g isi nFebruary/April ,an dharves ti n June/August.Lee ki sgrow ni nsom ehorticultur eareas .I ti splante d inMarch/Jul yan d harvestedAugust/May .Pear lonion san dchive sar erar ei nhorticulture ;Wels honio nan d garlicar eno tgrow ncommercially .Privat egrowing ,mostl ylee kan dfurthe ronion san d chives,cover sa negligibl eare acompare dwit hcommercia lculture . OtherAlliu mspecie si nth eNetherland sar esom ewil dspecies :A .vineal eL .(wil d onion),A .ursinu mL . (ramson),A .scorodoprasu mL . (rocambole)an dA .oleraceu mL. ,an d anincreasin gnumbe ro fspecie sa sornamenta lplant si ngardens .Excep tA .vineal eal l ofthes eca nb econsidere da srathe rrar ean do fn opossibl equantitativ eimportanc et o theonio nfl ypopulations .Richen s (1947)i nhi sextende dwor ko nA .vineale ,ha dno t foundrecord so finsec tpests .

2.3.2 Damage

Intemperat eregion sth edamag et oth eonio ncro pb yth eonio nflie si softe nconsid ­ erable,unles ssom econtro lmeasure sar etaken .Damag elevel so fu pt o50-95 %ar ereporte d byHammon d (1924),Flin t& Compto n (1925),Metcal f& Flin t (1939),Smit h (1948),JjSrgense n (1955),Mille r (1956),Bundzh e (1965)an dothers .Damag ei sespeciall ysever eafte rwe t springs (Metcalf& Flint ,1939 ;Doane ,1953 ;Peterso n& Noetzel ,1954 ;Workman ,1958 ; Beirne,1971) ,an di nles swel ldraine dlow-lyin gfield s (Lovett,1923 )becaus eo fth e higherlarva lsurviva li nmois tsoil s (Sleesmani nAnonymous ,1937) .Damag ei sheavie ri n shelteredplace s (e.g.Peterso ne tal. ,1963 )an do ncorner s (Wilson& Whitcomb ,1929) . Moreextensiv eonio ngrowin gi ssai dt ohav ecause dth eonio nfl yt obecom ea seriou spes t (Wilson& Whitcomb ,1929) .Som eloca lonio ngrowin garea si nEnglan dar efre efro monio n fliesaccordin gt oMile s (1958b). Thedamag edepend so nsoi lstructure ,bein gmor esever eo nlighte rsoil s (e.g.Dustan ,

14 1932). The causei ssuppose d tob eth epreferenc e ofeg gdepositin g females (Dustan,1932 ; Maan, 1945),lowe rtemperature s andhighe rmoistur e content inth eto playe ro fth elight ­ ersoil s (Dustan, 1932), easier larvalmigratio n inlighte rsoil s (Maan,1945 )an d earlier 1stfligh t duet ofaste rwarmin gu po fsand y soils (Schnitzler, 1967). Perron (1972),i n hispopulatio n studies,foun da highe rpupa lmortalit y inheavie r soils.H ementione d as important,difference sbetwee norgani c (light)an d clay (heavy)soils ,highe r parasitism andhighe rnumbe r ofegg spe r femaleo norgani c soils,bu t theseassumption s areno tsup ­ portedb y thedat apresented . Whendat afro mdifferen t authors arecompare d itha s tob etake n intoaccoun t that in Canadaan dth eUnite d States themai nonio ngrowin g areas areo nmuc k soil,wherea s in Europe sandy clay isnorma l foronio ngrowing . Damageb yth efirs tgeneratio n larvae ischaracterize d by tinybrownis hremnant s of thesubterranea npart so fonio nseedlings ,an dstil lgreenis h leaves thathav e fallen over.Desiccatio n anddecompositio nquickl ymak e these leavesdisappear .Thi sdamag e can bedestructiv e toth ecro pespeciall ywhe nth eonion swer e sown latecompare dwit h the ovipositionperio d ofth efirs t flight flies.Whe n anattacke d seedlingha sbee n consumed, thelarva emigrate ,seemingl ya trando m (Workman,1958) ,generall y toth enex t seedling. Maan (1945)estimate d inlee kdurin g the firstgeneratio na rati oo f 1:15 to 1:20 ofseed ­ lingso nwhic heg gbatche sha dbee n laidt oseedling s damaged.Kästne r (1929b)foun d this ratio tob e 1:11 inonions .On e single larva issai d tob e ablet odestro yu p to 4 (Kendall,1932 )o r8 (Beirne,1971 )seedlings .I nth e laboratoryWorkma n (1958)foun d that one larvacoul dea t 28 'seedlings'o f4 m m long.Whe nth enumbe ro fadjacen t seedlings thatar edamage d islimited ,th eremainin g onionsma y compensate forthi sdamage . Typical fordamag e later inth eyea r istha t thecentra l leafofte nwilt s first,fol ­ lowedb y theothers .Agai n the leaves startdyin g atthei rbases .Attac k causes theonion s torot .I fth eonio ni sno tdea dbefor e the larvaepupated ,i tma ybecom edisformed .Th e secondgeneratio n larvaema y causemor edamag e thanth emer e losso fyield, becaus e onions thatar erottin g atth etim eo fharves tca npreven teconomi c storage:thes ehav e tob e picked outo r theywil l infect theothe ronions . ' Damagedat afro muntreate d plots inth eNetherland sdurin g the lastdecades ,fro mex ­ periments ofth eSNUiF ,ar egive ni nFig .8a .Th eeffec to fsoi ltyp eo nthes edat ai s shown inFig .8b . Ininterpretin g damagedat ao funtreate d plots oneshoul db e awaretha tth euntreate d plot isonl yrepresentativ e for itsow nsituatio n andno t foruntreate d fields ofdiffer ­ entsiz ean do fdifferen t situation. Iti sno tjus tth e individual onionflie spresen t at thatsit etha tar etreated ,bu t apar to fa population .Also ,th epopulatio n sizepresen t inth eare a iso f influence,an d isdependen t onth e localdamag e incidence inth epre ­ cedingyear . Thedat ao fth eSNUi Far efro mchec kplots ,generall y 3plot so f 2x 5m ,i ntest sfo r chemical controltreatments .I nthes eexperiments ,th esecon d flight flies,emergin gmain ­ lyfro m theuntreate dplots ,wil lhav e laidegg s onal lplot s ando nan yonio nfield s in thesurroundings .S othes edat aunderestimat e thesecon d flightdamag e tob e expected in untreated areas.O nth eothe rhand ,thes econtro lexperiment s haveofte nbee ndon e at placeswher e infestation couldb e expected (damage inth eprecedin gyea ro rare awit h

15 damage in% 00- • v • «t0:*. •—•-•— • 80- o • • 0 • t 60- • • a o • • • o 0 • 0 0 • • • • 40- o o • o o • 0 o • °.ol 8 • • 30- o ° • • o • • § • *o o • • 0- -i 1 1 >—9— -1—f- —i 1 r 1 w 1 * 1 1— -r •34 '36 '38 '40 '42 '44 "46 '48 '50 '52 '54 '56 '58 '60 '62 '64 '66 '68 70 72 74 76 y«ar

100-1 •- —œ—-• —-• - • 8 • o • • • 80- • 0 • • 0 o b 60- • 00« • oo 8 • • 40- ° • • •». • • 0 20- O O •• 0 • • • 1 • f • • Q 1 1 T 1 () S 10 15 20 25 30 35 40 45 clay fraction in %

Fig.8 .Percentag edamag eo nuntreate d plots inth eyear s 1939-1976(a:o = estimated, •= observed) ,an d comparedwit hth ecla yfractio no fth esoi l (b:o = estimated clay fraction,• = knowncla yfraction) .Dat afro mSNUiF .

veryligh tsoil) ,resultin g ina noverestimation .A sthes efactor sma ycance leac hothe r out,fo rth etim ebein gth eobserve ddamag elevel so nth echec kplot sconcerne dma yb e takena srepresentativ efo rthos et ob eexpecte dwhe non esingl efarme rdoe sno ttak e effectivecontro lmeasures . Carden (1960)an dRawlin se tal . (1960)bot hfoun dtha tever y 10%damag eresult si n a 10$yiel d loss.Accordin gt oth edamag eleve ltha tcause sth efarmer st ocomplai no r

contactth eSNUiF ,significan tyiel dreductio nwil loccu ra tove rabou t 10«odamage ,ex ­ presseda spercentag eo fth enumbe ro fseedling semerged .Th esam eleve lwa sreporte db y Rawlinse tal . (1960).Th eeconomi cthreshol dwil lb eabou tth esame ,wit hth elo wcost s ofth estandar dpesticid eapplication .Th eshif tt oprecisio nsowin grestrict scompen ­ sationfo rdamag eb yth eonions ,s oi twil llowe rth eeconomi cthreshold .

16 2.3.2 Pest control

Control methode Formerlyth e onionfl ywa sno tcontrolled .I nth eNetherland s thenonion s couldhardl yb egrow no nsand ysoils ,an delsewher e fluctuatingdamag e levelsoccurre dan d wereaccepted .Rotte nonion sa tharves tdi dno tthreate nstorag es omuc hbecaus ethe ywer e pickedou tb yhand .O fman yonio nfl ycontro lmethod spropose dan dteste di nEurop ean d America (e.g.Femal d& Bourne ,1914 ;Kästner ,1929a ,1929c ;Balachowsk i& Mesnil , 1936) onlya fe wsee mt ohav egive nreasonabl eresult ssometimes ,lik ecul lonion sa sa tra p crop (a.o.Lovett ,1923 ;Dudley , 1925),poisone d sweetenedbai tonion s (Kästner, 1930), ornaphthalen e (Thompson, 1930). Thefirs tver y effectivemetho dwa scalome lsee ddressing ,foun db yGlasgo w (1929) anddevelope db yDusta n (1937,1938 )an dWrigh t (1938). Thismetho dwa sto o expensivefo r generalapplication .Chemica ltreatmen to ffields ,furrow so rseed sbecam ea genera lprac ­ ticeafte r 1946,du et oth emoderat epric eo fth enewl ydiscovere dorganochlorin ecom ­ poundsan dt omor eeffectiv eformulation san dapplicatio nmethod sdevelope d (e.g.McLeod , 1946; Maan, 1947).

Resistance Resistanceo fth eonio nfl yt oorganochlorin ecompound sstarte di nth eUnite d Statesi n195 3 (Howitt,1958 )an di sno wwidespread :Unite dStates ,Canada ,Japan ,Franc e andth eNetherland s (Anonymous,1967) ,Unite d States (Finlaysone tal. , 1959;Peterso ne t al., 1963),Canad a (McClahahane tal. ,1958 ;Harri se tal. , 1962),Polan d (Narkiewicz- Jodko, 1974),Englan d (Gosticke tal. ,1971 )an dFinlan d (Anonymous,1969b) . Therewer e stillsusceptibl estrain si nsom earea si nEnglan d (Gosticke tal. , 1971)an dFranc e (Missonnier& Brunei ,1972) .Wher eorganochlorin eresistanc eha sdeveloped ,organophos ­ phorouscompound sar euse dfo rcontrol .However ,resistanc et odichlofenthio nha soccur ­ redalread y (Perron,1965 ;va nKampen ,1969 ;Anonymous ,1969a , 1970). Organochlorineresistanc ei sbase do na singl egen e (Togwood& Brown ,1962) .Th eef ­ fecto fthi sresistanc ewa s investigatedb yMissonnie r& Brune i (1972):th elarva ldevel ­ opmentwa sslightl yfaste ran dth eadul tfemal esurviva lwa s slightly longeri nth ere ­ sistantstrain ,bu tth efecundit ywa sconsiderabl y reduced. Afterdevelopmen to fresistanc eth epopulatio nsiz ean dit sfluctuation sbecam elar ­ gertha nbefor eth eintroductio no fchemica lcontrol .Thi sincreas ei sattribute dt oth e moreextensiv ecroppin gtha twa smad epossibl eb ythi scontrol ,an dt oth eeliminatio n ofpredator s andparasite s (Missonnier& Brunei ,1972 ;compar eth esimila rcas eo fth e cabbageroo tfly :Morris ,1960; Read ,1964 ;Coaker ,1966 ;Mukerji ,1971) . Generallyver y highdamag e levels (upt o100% )hav ebee nreporte d afterth edevelopmen to fresistanc e (Finlaysone tal. , 1959;Anonymous ,1964 ;Beirne , 1971).

Control in the Netherlands Knownan destimate dpercentage so fspring-sow nonion si nth e Netherlands treatedwit hdifferen tpesticide sfo ronio nfl ycontro lar egive ni nFig .9 . Becauseth eare aunde rspring-sow nonion si slarges tan dbecaus ethes eonion sar eth e most importantfo ronio nfl yreproduction ,th edat eca nb etake na sth epart so fth e onionfl ypopulation s controlled.Th eeffec to fchemica ltreatment si sgive nfo rth e mostimportan tchemical suse di nFig . 10.

17 85 y»'

Fig. 9. Chemical control of the onion fly on spring-sown onions in the Netherlands, expressed as percentage of the area. Based on data from SNUiF. 1947-1950 actual data; 1951-1976 estimations; 1977-1986 extrapolation according to a possible programme. x = loss of market share due to development of resistance; a = DDT; b = dieldrin; c= aldrin and heptachlor; d = ethion; e = diazinon; f = chlorfenvinphos; g = dichlofenthion; h = trichloronate; i= trichloronate, in case of resistance probably carbofuran; j = sterile insect technique.

-i—i—i—i—i—i—i—i—i—i—i—i—rT-'n—r 72 '74'7 6 '36'3 8'4 0 '42'4 4 '46 '48'5 0'5 2'5 4'5 6 '58'6 0'6 2'6 4'6 6'6 8'7 0 year

Fig. 10.Effectivit y of chemical control of the onion fly in the Netherlands. Data from SNUiF.+ = calomel;• = DDT; o = dieldrin, aldrin and heptachlor; x= dichlofenthion ; A= trichloronate.

Resistance to organochlorine compounds was noted first in 1962 inthre e areas (van Kampen, 1963) andha d spread to all onion growing areas by 1965 (Anonymous, 1964, 1965b, 1966). Most growers changed todichlofenthion .Durin g theyear s 1967-1968 resistance against dichlofenthion developed andwa s complete in 1969 (vanKampen , 1969;Anonymous , 1969a, 1970). Since then control has been effected with trichloronate.Thi s reached 100% of themarke t due to its limiting effect on thepopulatio n increase of the onion stem

18 eelworm (Kaai& Koert ,1971) . In197 6ther ewa s stilln o signo fresistanc e totrichlo - ronate. Thepossibilit y ofshiftin g toth esteril e insect technique isindicate d also in Fig.9 .

Residues Pesticide residueshav ebee nanalyse d only ina fe wcases .A normal application ofdieldri n resulted atharves t in0.01-0.01 5mg/k g inth eonion s (Ehlers& Liedtke , 1958),o r in0.1 1 mg/kg inth eoute rscales ,residue s inpeele d onionsbein g undetectable (Byrdy, 1963). InCanad a 0.02 mg/kgdieldri nwa s found inonions ,bu tn oDD To r aldrin although thesewer eals opresen t inth esoi l (Harris,-1969) . Inth eUnite d States,wher e onions areofte ngrow nfo ryear s insuccessio n onth esam e fields,residue so fman y pes­ ticideswer efoun d inth esoi lbu tnon eo fthe m inth eonion s (Wiersmae tal. , 1972). Suett (1974)foun dresidue s ofpirimipho so f0.0 4 mg/kg inonion s atharvest .Chlorven - finphos alsogav erelativel y lowresidu e levels inpeele d onions (including breakdown products lesstha n0.0 9 mg/kg,Beyno ne t al., 1968).Wher e theseauthor sgav edat a on othervegetable s aswell ,i tca nb esee ntha t theresidu e levels inonion sar e relatively low.

2.4 SUMMARY

According toth erecen trevisio no f theAnthomyiida eth eonio n flyshoul db e called Deliaantiqu a (Meigen). The femaledeterminatio n characteristic of twohair s lateral-rostral onth etibia- 2 wasno talway svalid .Win gvei n aberrationswer e frequent,an despeciall y in laboratory rearing aberrantmale s andfemale soccurred . Immature stages of theonio nfl yma yb econ ­ fusedwit hthos eo fDeli aplatur awhic h areals ocommo n inonions ,bu t differentiating characteristics areavailabl e foral lstages . Theonio nfl y isa holarcti c species. Ithibernate s asa diapausin gpupa .Ther e are generally onecomplet ean don eo r two incomplete flightspe ryear .Th e females arepoly ­ gamous andanautogeneous ,an dhav ea pre-ovipositio n period of 1-2weeks .Egg s are laid onAlliu m species.Th e larvae feedo nthese ,an dpupat e inth esoil .Diapaus e is induced by lowtemperatur e andshor t days. Onlyfe wdat ao npopulatio ndynamic s areavailable ,an dmos to f themma yb eno tre ­ presentative ofth eactua lsituatio n inth e field. Differentonio nvarietie s andrelate d species are attacked todifferen textents , attributed toodou rpreference s ofovipositin g females.Onio nfl yattac k is accompanied by anon-obligator y bacterial infection.Th e larvaeaccep t foodothe r thanonion . Theadult s feedo nflower s and flowering grasses.Th ebes t attractant for adults known isn-propy ldisulfide .Commo nparasitoid s areth estaphylini dAleochar abilineata , andth ebraconi dAphaeret aminuta .Severa l other,possibl y alsono t host-specific, parasitoids areknown .Th e flies areattacke d commonlyb y afungu sdisease .Al l thepre ­ dators alsosee mt ob eno t species specific. Rotting onionsma ycontai n a largevariet y ofdifferen t species,mainl y flylarvae . Theyar eal lsecondar ypests ,excep t sometimes thebea nsee d flieso nseedlings .

19 Spring-sownonion sar eth emos tcommo nAlliu mcro pi nth eNetherlands .O fth ewil dre ­ lativesonl yAlliu mvineal ei scommon ,bu tseem sno tt ob eattacke db yth eonio nfly . Lossesdu et oonio nfl ydamag ema yamoun tt o50-100% ,an dar epartl ydependen to nsoi l type.Th eappearanc eo fdamag eha stypica lfeature stha tdepen do nth edevelopmenta l stageo fth eonio nattacked .Th eeconomi cthreshol d isa ta damag eleve lo fabou t 10%. Chemicalpes tcontro lha sbecom ewidesprea dafte rth eintroductio no forganochlorin e insecticidesi n1946 .Resistanc et othes ecompound sdevelope dfro m195 3onwards ,i nth e Netherlandsi n1962-1965 .Sinc ethe ncontro lha sbee npractise dwit hdifferen torgano ­ phosphorouscompounds .O fthese ,dichlofenthio nha salread yme twit hresistance .Currentl y usedi nth eNetherland si strichloronate ,becaus eo fit seffec to nonio nste meelwor m reproduction. Insecticideresidu elevel si nonion sar egenerall ylo wo rundetectable .

20 3 Environment and discussion of materials andmethod s

Informationi sprovide do nth eenvironmen t inwhic hth eexperiment swer edon ean do n theprevailin gweathe r conditions.A sman y experimentswer ewit h sterilized fliesfro ma laboratorymas s rearing,som edat ao nthi srearin gan dsterilizatio nar egiven . Themethod s thatwer edevelope d anduse di nth efiel dwor kar edescribe dan devalu ­ ated,especiall yfl ymarking ,releasin gan dtrapping ,an dsamplin go fpupae ,a sthes e methodsar eimportan ti nsteril emal eexperiments .

3.1 ENVIRONMENT

3.1.1 Experimental area

Thefiel d trialswer e carriedou to nth eforme r islando fOverflakkee .Thi s areaha s beenon eo fth emai nonio ngrowin g areasfo ra lon gtime .Th eislan di snearl y completely flat,an dpartitione db ydike saroun dpolder stha thav ebee nreclaime d sinceth e15t h Century.Apar t fromth eroads ,water ,isolate d farmsan da doze nvillages ,almos tal lth e landi suse dfo r agriculture.Tree san dshrub sar escarc e except alongth edikes ,aroun d thefarm san di nth evillages .Meadow sar epresen to nmos t slopeso fth edike san do n someslightl y lowerparts ,forme rcree kbeds .Typica lscener yi sshow ni nFig . 11. Thecrop sgrow nar emainl ywheat ,potatoe san dsugar-beet ,wit h smalleramount so f tulips,gladioli ,onions ,beans ,barley ,carrots ,chicory ,an ddifferen t agricultural

Fig. II. Typical scenery ofOverflakkee , theforme r island onwhic hmos t experiments were carriedout .

21 ROTTERDAM

Fig. 12. Map of the former island of Overflakkee and surroundings, showing the location of the main release-recapture experiments, a = Vroegindewei 1972-2 (Fig. 13), b = Mij s 1973 and 1974 (Figs 14 and 15).

0 500m Fig. 13.Ma po fth erelease-recaptur e experimentVroegindewe i 1972-2.Fo r locationse eFig . 12.* = releasesite ; •= trap; =ditch ; •= buildings ;« = onionfield ;&3Qd= water.

22 o releasesit e '///M/, onionfiel d197 2 üiü onionfiel d197 3

Fig. 14. Map of the release-recapture experiment Hijs 1973-2. For locat ionse eFig.12 .

onionfiel d197 3 onionfiel d197 4 x Fig. 15.Ma po fth erelease-recaptur e experimentMij s 1974..Fo rlocatio nse eFig .12 .Symbol s seeSectio n4.3.3 ; 'exp'i sth esteril einsec ttechniqu etria lfield ;lef tpar to f'con ' isth euntreate d controlfield .

23 Table3 .Genera ldat ao nrelease-recaptur eexperiments .

Experiment»year,flieht Numbero f St erile/ Marks Pupaei n Number flies fertile3 diapause re :aptured released van Loon 197C -2 11 450 S a 32P,65Zn,89Sr no 147 Pollemans 1971 23 490 S b dailydyes , Zn no 394 Buijs 1972-1 16 990 F c 1dye/sit e yes 71 Vroegindewei 1972-2 26 800 F d 1dy e no 409 Mij s,van Es & de Wit1973 - 24 800 F e 1dye/sit e yes 191 Mi. s 1973-1 61 270 F f dailydyes/sit e no 1 030 Mi- s 1973-2 96 400 F g dailydye s no 2 416 Mi_ s 1973-2 135 900 F h 1dye/sit e no 3 263 Mi_ s 1974-1 73 950 F i 1dye/sit e yes 642 Mi" s 1974 141 1 680 S j 1-2dyes/grou p no 10 373 Mi" s 1974-1 171 610 S k 1dye/sit e no 688 Mijs 1974-2 57 600 F 1 1dy e no 682

Schuilenburg 1971-1 5 830 F m "Zn no 80 Schuilenburg 1971 48 100 S n 2P or 1dye/grou p no 791 Schuilenburg 1972 614 600 S 0 1dye/grou p no 4 655 Schuilenburg 1973 158 0 100 S P 1dye/grou p no 14 205 Schuilenburg 1974 111 8 500 S q 1dye/grou p no 4 614 a.Letter s indicate locationo freleas esites :a :centr eo fonio nfield ,b :forme ronio n fieldan ddik enea ronio nfield ,c :5 frome ronio nfields ,d :onio nfield,nea redge ,e : 3untreate d experimental plots,f : 100m fromexperimenta l plot in4 directions ,g :onio n field,nea redge ,h :differen tdistance s fromtw oonio n fields,i :3 forme ronio nfields , j: onionfiel dedge ,1 7weekl yreleases ,k :2 forme ronio nfields ,5 weekl yreleases .1 : edgeo fcontro lfield . m:nea ronio nfield ,n :near(2n d flight:in)onio ntield ,1 0releases ,o :i nonio nfield , 19weekl yreleases ,p :generall y inonio nfield , 19weekl yreleases ,q :i nonio nfield , 18weekl yreleases .

andomamenta lplant sgrow nfo rseed ,lik egrass ,carrot san dviolets .Th esoi li smainl y sandyclay . Duringth epas tdecade sth efar man dfiel dsize shav eincrease dconsiderably .Th e averageonio nfiel dsiz eo nOverflakke edurin gth eexperiment swa s2-2. 5ha .O nth e average2/ 3o fth eonio nfiel dborder sconsiste do fditches ,generall ycontainin gwater . Thepercentag eo flan doccupie db yonio ngrowin g inthos epolder so fOverflakke e whereth eexperiment swer edon erange dfro m5 t o 15.I n182 0thi swa sonl yabou t H (Boers,1843) ,bu tbefor e 1880th eonio ncro pdensit yha dprobabl yreache d5 1o fth e area (estimatedfro mdat afro mth eSNUiF) . InFig .1 2th eforme rislan do fOverflakke ei sshow nwit hth elocatio no fth earea s inwhic hth emai nrelease-recaptur eexperiment swer edone .Detaile dmap so fthes earea s aregive ni nFig .13-15 . Generaldat ao nal lrelease-recaptur eexperiment sar egive ni nTabl e3 .

3.1.2 Weather

Themaximu mdail ytemperatur ean dth edail yrainfal lar egive ni nFig ,1 6an d Table4 .Observation sar efro mdifferen tsite so no rnea rOverflakkee ,dependin go n theiravailability .Th enumbe ro fmonthl yvalues ,outsid eth erelevan t8 0o r90 1confi -

24 l-^ljL jty |. Jl , , n.pfljh l jf f J)n ^Pflj 1974

-20

-10 . i4.M Jr nL P,flAL lil AJ\ift » M O»

25 Table 4. Monthly weather data, Overflakkee 1970-1974. Data from the Royal Netherlands Meteorological Institute (KNMI) (Anonymous 1972; pers. commun.).

b b 1970 1971' 1972 1973 1974 Average Average Confidence interval 1970-1974 1931-1960c 805T 90% Maximum temperature per day in C

April 9.0** 12.9 11. 5 10.2* 13.1 11 3 12.7 10.5-14.9 9.9-15.5 May 17.8 19.0* 15.8 16.3 14.9* 16 8 16.8 15.0-18.6 14.5-19.1 June 22.8** 17.9 17.2** 20.5 18.2 19 3 19.5 17.8-21.2 17.3-21.7 July 19.8 22.5 20.8 21. 0 18.2** 20 5 21. 2 19.5-22.9 19.0-23.4 August 22.6 21. 5 19.9 22.6 20.7 21 5 21.3 19.3-23.3 18.7-23.9 September 19.5 19.2 16.7* 19.0 16.5* 18 2 18.8 16.8-20.8 16.3-21.3 October 14.2 12.7-15.7 12.3-16.1 Rainfall per month in mrr

April 73 21 51 50 16* 42 41 20- 7 5 May 20* 71 68 70 22 50 45 (21 -80 ) June 17* 90 92 33 72 61 55 23- 9 3 July 99 41 135* 73 109 91 70 (26 -120) August 30 60 43 31 74 48 73 28-13 5 September 85 25* 62 68 136 75 76 (29-138 ) October 72 23-13 2

Testing forsignificance : temperature:30 %outsid e confidence interval (n.s.), 13%outsid e 90%confidenc e inter- val (n.s.); rainfall: 17%outsid e confidence interval (n.s.).

a. Nieuwe Tonge (Overflakkee). b. Temperature data from Hellevoetsluis (Voorne), rainfall data from Dirksland (Overflakkee). c.Middelharni s (Overflakkee). d. Temperature: calculated with standard deviation from Vlissingen (Walcheren),1931-1960; rainfall: interval from Middelharnis (Overflakkee), 1931-1960. Interpolated values between brackets.

dence intervals,di dno tsignificantl y differ from that expected. Soth eweathe r ofth e summers of1970-1974 ,durin g which theexperiment s were done,ca nb etake na sreasonabl y representative. Fromth efive-yea r averages itca nb esee n that only Aprilwa scolde r than average.

3.2 MATERIALS:FLIE S USED FORTH EEXPERIMENT S

3.2.1 Mass rearing

The flies used inth ereleas e experiments were obtained fromth emas s rearing atth e IPOi nWageningen .Fo rdetail s onth erearin g methods seeTichele r (1971)an dNoorlande r (1974). The larvaewer e reared ona nasepti c artificial medium,base d oncarro t powder,a ta constant temperature of2 2C o r1 7C ,unde r daylength conditions of1 6hour s or1 0hour s lightpe r2 4hours ,fo robtainin g non-diapausing ordiapausin g pupae,respectively .Non - diapausing pupae canb estore d fora tleas ta yea r at3°C ,bu tth equalit y ofth eresult ­ ing flies decreases.The y shouldb ea t15-20' »o fthei r agewhe n transferred tocol d storage.

26 Theflie semerg e 12-13day safte r transfero fstore dpupa et o21°C .Th eflie swer e kepti ncages ,generall y6 0x 4 0x 4 0c mperspex ,wit h 2500flie seach ,a t2 1C .The y were givenwater ,dr yfoo dan donio nodour .Egg swer edeposite do ndevice swhic hprovide d thenecessar y chemotropican dtactil estimuli .Th ene treproductio n factorpe r generation wasdurin g theyear s concerned about 10x .Th eto pproductio n amountedt o2.1 0 pupaepe r month. Asmentione d (Section2.1.2 )th erearin gproduce d aberrantmale si nfrequencie so f about 2-10%.

3.2.2 Stern.lizati.on

Pupaewer e sterilizeda to nth eaverag e 85%o fthei rage ,bein g oneda ybefor eth e starto femergence .Th esterilizin g agentwa s3 k Rgamma-radiatio n froma Co-source, orX-ray s froma nelectro ngenerator .Thi sdos ecause s complete infecundityi nth efe ­ males.Abou t0.6 %o fth eegg so fno n irradiated femalesmate dt oirradiate dmale shatc h (Noordink,pers . commun.).Fo rmor edetail so nsterilizatio n seeTichele r& Noordin k (1968) andNoordin k (1971). Formor edetail so nsterilizatio n seeTichele r& Noordin k (1968)an dNoordin k (1971). Accordingt ocommo nusage ,th eter msterilit yan drelate d termsar euse d throughout thisreport .Ofte nhoweve r the termsterilit yi suse dt oindicat e absenceo fsperm , whereasi nsterilize d onion flies,competitiv e spermi spresen tbu t contains dominant lethalfactor ss otha tegg s 'fertilized'wit hthi ssper md ono tdevelop .Th econtrovers y aboutth eeffec to fmultipl emating so nth e feasibilityo fth esteril emal emetho dfo r insectpes t control,arisin g fromth eus eo fth eter msteril ei nthi scontext ,ha sbee n elaboratedb yvo nBorste l (1960).Th eeffec to ngeneti c controlo fdifferen t assumptions aboutth eeffec to fsterilizatio no nth epresenc ean dth ecompetitivenes so fsperm ,als o inrespec tt oth enumbe ro fmatings ,ha sbee nformulate db yBerryma n (1967). Thepercentage s sterility giveni nthi srepor talway srefe rt opopulations ,no tt oth e degreeo fsterilit yo findividuals . Fertile females,whe nmate dt omale s irradiatedwit ha tleas t 1.5-2 kR,live d1. 3time s longer andha d theirfecundit y increasedb ya facto r 1.6-1.8 (Noordink, 1974),provide d that irradiationha dtake nplac ea tth erigh tmomen t (seeTichele r& Noordink , 1968).A similareffec t canb efoun di nth edat ao fMcClanaha n& Simmon s (1966).I ti sinterestin g thata simila r increasei nfecundit y resulted frommatin gwit h 65Zn-labelledmale s (Noordink, 1974).A possibl e causei sa radiatio neffec to nth emal e accessory glandsub ­ stance,whic hha sa neffec to novipositio n (e.g.Leahy ,1967 ;Rieman n& Thorson ,1969 ; Swailes, 1971). Competitivenessi sa measur eo fth edifferenc ebetwee ncertai n individualso rpopu ­ lationsan dth ewil d typeo fth esam especies .I ti sexpresse da sth enumbe ro findivi ­ duals thatar eequivalen tt oon ewil d individual. Tocalculat e thecompetitivenes so fsteril emale sfro meg gsterilit ydat aobtaine d incompetitio nexperiments ,thes edat ahav et ob ecorrecte dfo r thenatura lsterilit yo f about5 %o nth eaverage ,fo r the0.6 %hatc ho f'sterile 'eggs ,an dfo rth esurplu so f eggs laidmentione d above.Thus ,a par to fth esteril eeggs ,t ob ecalculate d froma

27 fertile controlgroup ,ha s tob e considered asoriginall y fertile,an dth enumbe ro f sterileegg sha s tob e correctedb y a factor 1/1.7 (thefacto r 1/0.994ca nb e neglected). When thedat ao fth ecompetitio nexperiments ,give nb yNoordin k (1971)an dTichele r (1969) arecorrecte d inthi sway ,matin g competitivenessvalue so f0.79-1.0 4ar e found,wit h on theaverag e 0.87.Becaus eo fth ehig hdependenc yo f thefecundit y increaseo nth eag ea t irradiation (Ticheler &Noordink , 1968), thiscompetitivenes s canb e considered tob eno t significantlydifferen tfro m 1. Wheneg g sterilitydat ahav ebee ncorrected , ifneeded ,lik e indicated above,th e competitiveness c ofa typ epresen t inth epopulatio n ina fractionp ,an dwit h effect ina fractio ne ,ca nb efoun dfro me = ap/{ap + (1-p)).Thi s equationca nb ewritte na s

a =(e-ep)/(p-ep ) (1)

The sameresult sca nb e obtainedwit hth eformula e thatar egive nan d amplyexplaine d by Fried (1971).

3.3 DISCUSSIONO FMETHOD S

3.3.1 Marking

Fliesca nb emarke d inman ydifferen tway s (seee.g . Southwood, 1966). Becausehig h numberso fmarke d flieswer eneeded ,an dbecaus e inmos t experiments iti s inadvisable tohandl e them,method so fapplyin g recognisablematerial s toth e flieswer eno tattrac ­ tive.Th eremainin gpossibilitie s aremarkin g the fliesexternall ya t emergence,inter ­ nallyb y larval ingestion,o rchangin g thegenotyp e (markers,sterility )o r thephenotyp e (bymean s of therearin g circumstances).Geneti cmarker swer eno tavailable .Th eflie s wereusuall ymarke dwit hdayligh t fluorescentdye s atemergence .

3.3.1.1Markin g larvae

Theunissen (1969)mixe d rhodamineB andacridin eorang e throughth e larvaldiet . Both substanceswer eshow nt ob e toxict oth e larvae,an ddi dno tmar k theadults .I di d similarexperiment swit hHeleco n 2266,fluorescein ,DayGl ored ,neutra l red andCalc ooi l R-1700.Fluorescei nan dneutra lre dcoul db erecognise d inth eadults ,bu t theywer etoxic . Theothe rsubstances ,o fwhic h theCalc ooi lwa s toxic,di dno tmar k theadults . Noordink (1973)mixe d several rareeart helement s through the larvaldiet ,i norde rt o recognise theadult safte rneutro nactivation .Th e incorporatedelements ,however ,dis ­ appearedfro mth e larvaea tpupation .Moreover ,thi smetho dproduce smuc hradioactiv e waste,s o itsapplicatio nshoul db e restricted. Radioactive labellingwa smad eeffectiv eb yNoordin k (1971).Th emos tusefu l labels foundwer e 32P forshort-ter m experiments and 65Zn for long-term experiments.Th e G5Zn is transferredver ywel l toth enex tgeneratio n (Noordink,1973),sotha t it isespeciall y suitable for experiments onreproduction . The half-lifeo f 32P is 14.3days .Noordin k (1970)foun d9-1 0day sa seffectiv e

28 (biologicalan dphysical )half-lif ei nonio nflie si nth e laboratory.Th eeffectiv ehalf - lifeo f32 Pi nonio nflie si nth efiel dwa scalculate dfro mdat ao ftw orelease-recaptur e experiments,unde ralmos tidentica ltemperatur econditions .Effectiv ehalf-live so f 6.3an d5. 8day swer efound .Th edifferenc eca nb eattribute dt ochance ,s oth eeffectiv e half-lifeo f32 Pi nonio nflie si nth efiel dca nb etake na s6 days . Thephysica lhalf-lif eo f65 Zni s24 5days ,it sbiologica lhalf-lif ema yb eeve nlon ­ gerapar tfro m lossi noviposition .

3.3.1.2Markin gemergin gflie s•

Application Inmos to fth eexperiment st ob edescribe dhere ,th emarkin gmetho ddevelope d byNorri s (1957)wa sapplied :th eflie sar eforce dt opas sa dy e layerwhe nthe yar emo ­ vingt oth esoi lsurfac eafte remergence .The ybecom ecoloure dal lover .Afte rreachin g thesurfac ethe yretrac tthei rptilinum ,o nwhic hth edy ei sretained .Thi smetho dcom ­ binessevera ladvantages : (a)th eflie sar eno thandled , (b)n osubstance snee dt ob e incorporatedi nth elarva etha tmigh tb eharmful ,(c )i tca neasil yb eapplie dt olarg e numberso findividuals ,(d )i tca neasil yb echecke d immediatelyafte rrecapture ,(e ) severaldifferen tdye sar eavailable ,an d(f )th edy ecanno tb elost . A disadvantagei stha tth eflie sgenerall yhav et ob ekille dbefor eth emar kca nb e checked.Furthermor eth ehea dshoul db epresent ,an dth efl yshoul dpreferabl yno thav e beeni na fluid .

Fig. 17.Constructio no fdy ean dreleas euni tfo remergen ­ ceo fflies ,cross-section . Thepupae ,mixe dwit hearth ,wer epu ti na containe r ofPV Ctubing ,o.d .8 cm ,whic hi sstandar drai npipe .Th e bottomwa sclose db ypolyethylen e foil,tightene dwit ha PVCring .O nth econtaine ra dy euni twa splaced ,whic h wasoriginall y togetherwit hth erin ga rai npip econnec ­ tingpiece .T oit sbotto mplasti cgauze ,mes h2 mm ,wa s glued.I twa sfille dpartl ywit hearth ,th eundermos tpar t ofwhic hwa sgarde nmoul dbecaus e thelittl eroot san d clodsi ni tpreven t theeart hfallin gdow nthroug hth e gauze.Thi seart hwa sslightl ycompresse d andcovere dwit h fineeart hgranule swit ha smal lsiev et oge ta smoot h surface.Ove rthi sa thi nlaye ro fdy epowde rwa sapplied , whichwa scovere dagai nwit ha fe wmillimeter so fsieve d earth.Eac hdy euni tneede d about 10g o fdy epowder .Thi s amountcovere d the5 0 cvp-o feart hcompletely ,an dresult ­ edi na 100^markin go fa tleas tth efirs t500 0flies . Somegras so ra stic kwa slai do nth edy euni ts otha tth e youngflie scoul dclim bou teasily . Theeart h inth epupae-containe r shouldb ecompresse d andreac ht ojus tunde rth euppe rrim ,s otha tafte rfit ­ tingth edy euni tther ei sn oempt y spacelef tbetween . Also,th eeart hshoul db esomewha tclayis hs otha ti twil l notsettl edow nwhe nflie shav eemerged .Eve nthoug hman y fliesuse d thesam ehole sfo rreachin gth esurfac eth e qualityo fth edy emar k theyobtaine dwa sno timpaired . Tochec kemergence ,trap swer eplace d oncertai nunits . Thesewer eo fextrude dPMM A(plexigum )tubing .Plasti cgau ­ ze, mesh2 mm ,wa sglue d toth ebase .Fo remptying ,th eto p sidewa sprovide dwit ha funne lo fplankto ngauze ,tha t couldb eclose dwit ha wa do fpape rtissue .

29 Thedye sI use dwer esevera lRadGl opigments ,a typ eo fdayligh tfluorescen tpowder , witha particl esiz eo f5 ym .Th edy ewa susuall yapplie daccordin gt oth eprincipl e described inFig .17 .Thi smodificatio nallow sth edy ecolou rt ob echange ddurin gth e emergenceperiod ,als opermittin greusag eo fth edy elayer . Amodificatio no fth emarkin go femergin gflies ,ofte nuse di nsteril emal eprogrammes , consistso fmixin gth epupa ewit hth edy epowder ,an dlettin gthe memerge .Becaus eth e confinemento fyoun gflie sma ychang ethei rnorma lbehaviour ,thi smetho dwa sonl yuse d incidentally.However ,n oeffec to nth edispersa lo fth eflie swa sfoun d (Section5.2.4) . Thereleas ecages ,use dwit hthi smethod ,ar edescribe d inSectio n3.3.2.2 .

Recognisable dyes Fourteendifferen tRadGl ocolour swit hparticl esiz eo f5 ,2- 4an d 1-2y mwer eteste dfo rdistinguishability .Al lresulte d inwel lmarke dflies .Clearl y recognizablewer eth ese tconsistin go fblu e (B),gree n (G),yello w (Y),orang e (0)an d carmine (magenta)(C )wit hal lthei rcombination s inpair sexcep t0C .Moreove rsom ecom ­ binationso fthre edifferen tcolour swer eals oclearl yrecognizable :BYO ,BYC ,GY Oan d GYC.I nthes ecombination sO Ccanno tb eused ,an dB Gi sdifficul tt odistinguis hfro mB Y inth epresenc eo f0 o rC .Thes edifficultie saris ebecaus eth edy epowders ,whe nmixed , partlysho weve nwit h8 0x magnificatio nthei rcombine dcolour ,lik egree nfo rBY .There ­ foreth emixin gshoul dno tb edon eto owell .Y prove dt ob ea weake rcolour ,s omor etha n 1:1shoul db euse do fi ti nmixtures ,wherea so fB an dC les sma yb eused .

Fitness of dyed flies Apossibl eeffec to fth edy eo nth efitnes so fth eflie sunde r fieldcircumstance swa slooke dfo ri non eo fth erelease-recaptur eexperiment s(exp . Pollemans 1971).Pupa elabelle dwit h Znwer edu g inth efiel dunde rdy eunit stha t werechange ddaily .On eda ya dy euni twithou tdy elaye rwa sprovided .Th erecapture s given oreaso nt oassum ean ydiminishe d fitnesso fdye dflies .Th eobserve ddecreas ei n numbero frecapture swit htim eo femergenc ewil lhav ebee ndu et oprédatio n(se eSectio n 3.3.2.1)an doccurre da swel li na simultaneou sreleas eo fdye dflies ,emergin ga ta distanceo fabou t10 0m fro mth elabelle dgroup . Theflie sclea nthemselve sth efirs tfe wday safte remergence .S oan yeffec to fa changedcolou ro fth eflie so nthei rlife-spa no rcompetitiveness ,a sobserve dfo rre d dyedmedflie sb yHolbroo ke tal . (1970),i sno tt ob eexpected .

3.3.1.3Markin gb ysterilizatio n

Obviouslysterilizatio ni sa markin gmetho d insteril emal eprogrammes .I nth este ­ rilemal eexperimen tMij s 1974 (Section6.2 )sterilit yo fth efemale swa sassessed ,apar t fromth edy emark sused ,b ythei rovar ydevelopment .I nfemale ssterilizatio nstop sovar y development (Theunissen,1971) .I twa sshown ,b yinspectin gfertil efemale s (wildan d released)tha t95.3 %o fth efertil efemale scaugh tha da yol kformatio nvisibl eb ychec ­ kingwit h8 0x magnificatio nunde ra microscope ,an dcoul dthu sb erecognise da sbein g fertile.Thi syol kformatio ncorrespond swit hth estage sS 5an dhighe ri nth eclassifi ­ cationo fTheunisse n (1973a).Th ehig hpercentag eo ffertil efemale sidentifiabl ea s such,i sdu et oth erelativ elo wprobabilit yo fcapturin gyoun gone s (Table25) .

30 Theunissen (1972)foun dtha tsaf e identification ofmale s asbein gsterilize dwa s onlypossibl ehistologically .Thi smetho d isto otime-consumin g forpractica l application infiel dwork .Thu ssterilit y isonl ya usefu lta g for females,especiall ywhe n theste ­ riles are inth emajority .

3.3.1.4Win gvei n aberrations

Wingvei naberration s (Section2.1.2 )coul db euse d fora markin gmethod .Differen t populations screened forthi scharacte rha ddifferen twin gvei naberratio npattern s and frequencies.A preliminary laboratory experiment failed tosho wan yheredity .Accordin g toSic k (1967)thickening s ofth evei nr 2+,ma yb e theresul t ofenvironmenta l conditions during thepupa lstage .However ,th ewid evariabilit y offers thepossibilit y forselection , orb y inbreedingheritabl ewin gvei naberration sma yb e found. Wheni nlaborator yrearin g certainaberration s canb e selected for,o rwhe nthes e can be induced inth ephenotypes ,the yca nb euse d asa natura lmarke r infiel dstudies . Because ofapparen t lacko ffunctio nan d theirhig hnatura l frequency,thes e aberrations probablyhav en odeleteriou s side-effects.Th e identification isver ysimpl ean dca ni n clearcase sb edon ewit hth enake deye .

3.3.1.5Siz e

Inprincipl e flysiz eca nb euse da s a feature forrecognition .A s ameasur e ofth e fly's size,th e lengtho fth ewin gvei nr, +3wa s chosenfo rpractica lreason s (relatively longan dseldo m damaged).Th e innerangle s thatth evei nmake swit h theothe rvein s are considered as itsbeginnin g andend . Its length iswel lcorrelate dwit h thepupa lweigh t (correlationcoefficien t forfemales :r = 0.929).Th ewin gvei nlengt hfitte dth enorma l distribution forth emales ,bu tno t forth e femalesdu et orelativel yhig hnumber s of shorterwin gvei nlengths . Fliesca nb e reared thatar eo nth eaverag edifferen t insiz efro mth ewil dpopula ­ tions,generall y smaller.Becaus epartl y overlappingnorma ldistribution s canb esepara ­ tedstatistically ,siz eca nb euse d asa mar k formales ,o rfo rfemale s iflarge r than normal,whe nth enumber srecapture d are largean don e isno t interested inth e individual recaptures.Thi sma yb eso ,fo r instance,i ndeterminin g thepercentag e sterility among flies. Thedange r inusin g flieso fa deviatin g size lies inth epossibl eeffec to n their competitiveness,an do nth efac ttha tthei rbehaviour ,fo rexampl e indispersal ,i sno t representative forth ewil d flies.Th e latter aspect isconsidere d inSectio n5.2.4 . Reduced competitiveness due tosiz eha sbee nreporte d forsmalle rmale sb yRiede l (1967) withth ecabbag eroo tfly ,Deli abrassica e (Bouché),an db yAlle y &Hightowe r (1966)wit h thescre wworm ,Cochliomyi ahominivora x (Cqrl.).

31 S.3.2 Releasing

3.3.2.1Releasin gpupa e

Themetho duse di nreleasin gpupa eha sbee ndescribe dmainl y inSectio n3.3.1.2 . Ploughingcause swil dpupa et obecom edisperse dthroughou tth euppe r25-c mlaye ro fth e soil.Thus ,t oge ta nemergenc ecurv eo fdiapausin glaboratory-reare d flies thati s identicalt otha to fth ewil dones ,container so f2 5c mlengt hwer eburie di nth esoil . Theemergenc eo fth eflie si nth esprin gi sdependen to nth esoi ltemperature ,s oth e

emergence in% 100

Fig. 18.Emergenc eo fdiapausin g pupaefro mdifferen tdepth sunde rbar e soil,Schuilenbur g 1972. 5,1 0o r 15c mdepth, -- - pupa emixe d over0-1 5 cmdepth .

emergence in% 100

Fig. 19. Emergence of diapausing pupae under different vegetations. Pupae mixed over 0-25 cm depth. Experiment Buijs 1972. under silverskin onions; - - - under sugar-beet; under winter wheat, rather low crop; — •• under winter wheat, rather high crop.

32 pupaetha tar eles sdee pi nth esoi lwil lemerg eearlier .Experimenta ldat ao nth eeffec t ofdept har egive ni nFig .1 8an dals ob yRyg g (1960). Iti sclea rtha tth evegetatio n willhav ea ninfluenc eto ob ykeepin gth esoi ltemperatur elower .Thi seffect ,i.e .o f thecro pfollowin gth eonions ,i sshow n inFig . 19.Som esimila rdat ahav ebee ngive nb y Tichelere tal . (1974b). Forexperiment s inwhic hth eemergenc e curveshoul db epreferabl yshort ,pupa ewer e generallypu t incontainer so f 12c m length,an ddu g inonl ypartl y topreven tfallin g over.Th ereleas eunit swer eplace d inth ecro po r inth evegetatio n inth editch . To limitprédatio no fth enewl yemerge d fliesb ybirds ,th ereleas eunit swer ecover - 2 edwit ha fe wm ofiro ngauze ,mes h 3cm .Piece so fpolyethylen efoi lwer eattache dt o thisa sa protectio nagains train .Prédatio nb ymic eo nth epupa ewa sprevente db yth e plasticgauz ebotto mo fth edy eunit . Theemergenc ewa sno t influencedb yth epresenc eo fa dy elayer ,bu ta cove rfro m rainprove dt ob eessential .Th ebotto mo fth epupa e containershoul db eclose dwit h foilan dno twit hgauze .A gauzebotto mcause d 5-10%o fth eflie st omov edownward san d dieo r (ifmes ho f1 m mo rmor e isused )escap ean demerg ewithou tdye .Wit hrain yweath ­ eran dwithou tcove rfro mrai nthi spercentag ereache d40 . Therecaptur erate so fdail ycohort srelease dwithou tprotectio nagains tbird s (see Section3.3.1.2 )sho wa decline ,especiall yeviden t inth egrou prelease d inth emor e exposedsit e (sugar-beetfiel dversu sgrass yslop eo fdike) .Thi swil lb eth eresul to f a learningproces so finsectivorou sbirds .Th eprevailin gcol dweathe rwil lhav eaffecte d theactivit y levelso fbird san dflie sdifferently ,probabl yresultin g ina hig hprédatio n level. Therecaptur erate so fsuccessiv eweekl yrelease so fflie s (Fig.20 )als oindicat e theeffec to fprédation .Th efirs ttw ogroup semerge d inrathe rcol dweather ,resultin g ina widel ysprea demergenc ean dprobabl y lowerfl ysurvival .Th eobviou sdeclin e in recapturerate sa tth een do fMa ywil lb e theresul to fa learningproces so finsecti ­ vorousbird stha twer eregularl yobserve dnea rth ereleas esites .Th e laterrecaptur e rateswer emor eo r lessstable .Th ereaso nfo rth ehig hrat eo fth egrou pemerge d 21Jul y isno tknown . Duringthi sserie so frelease stw oexperiment swer ecarrie dou tt ofin dway st odimi ­ nishprédation .I nth efirs texperimen tth eeffec to fdifferen tnumber so fflie semergin g perreleas esit ewa sanalysed .O ntw ooccasion sth eflie swer erelease d intw ogroups , oneemergin g inhig hnumber sa ton esite ,th eothe r inlo wnumber sa tsevera lsite s (Table 32). Theflie sfro mcrowde dreleas esite sha d a35-45 1highe rrecaptur erat e (Fig. 20,uppe rpoint so n1 3an d2 9July) .Thi sdifference ,i fsignificant ,ma yb edu et oth e birds havingalread ylearne dt ofin dth ereleas esite sb yeye .Thu sa tth emor ecrowde d sitesth eflie sha dth eadvantag eo fcrowdin gunde ra constan tprédatio npressure .A nef ­ fecto fdensit yo nth einitia ldispersa lactivit yma yhav eplaye da rol ea swell . Theothe rexperimen tconsiste do fth estandar dreleas eo flarg enumber so non esit e combined,wit hth esimultaneou sreleas eo fflie sfro mcage sa sdescribe d inth enex t section,1- 2day safte rthei remergence ,als oo non esite .Th ereleas eo fflie sfro mcage s resulted ina nimmediat esprea do fth eflie su pt oabou t 10m distance ,wherea sth eflie s thatemerge d inth efiel dafte rhavin g leftth ewir egauz ecove rmostl ystaye da tfirs t

33 recapturerati o 1.2-

1.0--

0.8-

0.6

I I —r— I I ~I— 04 OS 08 month 06 07 10 30 10 20 30 10 30 10 20 30 30 day Fig.20 .Competitivenes so fsuccessiv erelease so fsteril eonio nflies ,expresse d asth e ratioo fobserve drecaptur erat et oth erecaptur erat eo fth ediffusel y emergingwil d flies,versu s thedat eo f 50%emergence .Fo r theflie srelease d outsideth eexperimenta l field thepercentag eo f therecaptur erat eo ffertil eflies ,release d fromdiapausin g laboratory-reared pupae,ha sbee nuse d asth ebes tpossibl eapproximation .Experimen t Mijs 1974.Dat ase eTabl e32 . o,X =dat afro mexperimenta lfield(l l Juneles sreliabl eobservation) ;X = flies released fromcages ;• = datafro mcommercia lonio nfields .

withina fe wmetres .Ther ewa sa rathe rconsisten tdifference ,th erecaptur erat ebein g 60-701highe rfo rthos erelease da sflies . Inth eSchuilenbur g experiments,especiall yi n197 3an d1974 ,prédatio no fbird so n thenewl yemerge dflie swa sobvious .Satisfactor yresult sar eclaime dfro mth eus eo fa webo fartificia lfibre s (Starex)ove rth ereleas eunit s (Tichelere tal. ,1975] ,Th eon ­ lysaf emethod ,however ,wil lb et opreven tth eoccurrenc eo fhig hinitia lconcentration s ofrelease dflies . Depotso fpupa et ochec kth eemergenc ewer econstructe da sdescribe d inSectio n 3.3.1.2.O ntw ooccasion sth eemergenc edurin gth eda ywa schecked .Th eresult sar egive n inFig .21 .Th edepot sthu sshoul db evisite dpreferabl y inth elat eafternoon .Fo rprac ­ ticalreason sthi sha sgenerall ybee ndon ebetwee n1 6h 0 0an d1 8h 00 .

cumulative %

Fig. 21.Onio n fly emergence from depots, and catches in flight interception traps, during aday . • = emergence, 25Ma y 1972; 12 15 18 21 24 O = emergence, 27 June 1972; time ofda y inh + = trap catches, 27 June 1972.

34 3.3.2.2Releasin gflie s

Flieswer erelease d accordingt otw omethods .Th efirst ,use di nth eexperimen tMij s 1973-2,wa sdesigne dt opermi tth eflie st ob ekep tcage di fnecessar yfo rsevera ldays . The fliesemerged ,marke db yth emetho ddescribe di nSectio n3.3.1.2 ,i nth eperspe x rearingcage so f6 0x 4 0x 4 0cm ,a ta densit yo f624 0flies/cage .Foo d andwate rwer e provided.I ndu e timeth ecage swer etransporte d intoth efiel db ynight ,an dcovere d withblac kpolyethylen e foilexcep tfo ron esid ewhic hwa s leftopen. B yth enex tafter ­ noonal lhealth y fliesha dlef tan dth ecage swer eremoved .Applicatio no fthi smetho d mayhav eha da ninfluenc eo nth edispersa lspee d (seeSectio n 5.2.4). A lessvoluminou smetho dwa suse da tth een do fth e experimentMij s 1974,a smentio ­ nedi nth eprecedin gsection .Th eflie semerge do nsmal ltray splace di n'cages 'o f 3 2 60x 4 0x 1. 2cm ,a ta densit yo fabou t3 flies/c m, o rnearl y2 flies/c m ofrestin g surface.Thes e 'cages'wer e6 0x 4 0c mwoode nframes ,o nth eundersid eo fwhic h irongauze , mesh1 mm ,ha dbee nstapled ,thu sformin ga kin do ftray .Th euppe rsid eo fth efram e wasprovide dwit ha ban do fplasti c foam (draught-stopper).Thes etray swer epile dup , theon ecoverin gth e other.Thi spil eo f'cages 'wa skep ti ncomplet edarknes st opre ­ vent localaggregatio no fth eflies ,an doccasionall y somewate rwa sdrippe dthroug hth e cages.Th eflie sha dt ob erelease da ta naverag eag eo f1- 2day st opreven t excessive mortality.Th epercentag emortality ,includin g fliesno tye temerge da tth emomen to f release,wa sdependen to nth efl yconcentration :densitie so f1.6 ,3.2 ,4. 8an d6. 5 flies/cm resultedi nmortalitie so f19 ,18 ,2 4an d34$ ,respectively .Thes evalue sar e notexac tbecaus e thegauz euse dwa sto ocoars efo rth eflie so fth egrou pconcerne d averagepupa lweigh t 14.4nig) :som ehundred so fflie scam ethroug hth egauz ean dhundred s diedi ntryin gthis .Thi sdi dno toccu ri nanothe rgrou pwit h 16.2m gaverag epupa lweight , soth epercentag eo fflie sno trelease dfro mthi sgroup ,13$ ,wil lb einevitabl ewit hth e currentsprea di nemergence .Th emaximu mconcentratio nt ob euse dma yb eestimate da t about5 flies/c m. Theflie swer e releasedb yputtin g thepil eo fcage suncovere di nth efiel da s showni nFig .2 2fo rabou thal fa nhour .

Fig. 22."Releas eo fflie sfro mcages .

35 3.3.3 Trapping flies

Fliesca nb etrappe di nman ydifferen tway s (e.g.Southwood ,1966) .Fo rtrappin gonio n fliesgenerall ybai ttrap shav ebee nuse di nwhic hth eflie sdrow n (Noordink,196 7an d others),o ri nwhic hbai twa suse dt oge tth eflie si na funne lplace dove ri t(Peterson , 1924;Matsumoto ,1970 ;Eckenrod ee tal. ,1975 ban dothers )o rint osom eothe rdevic e (Lafrance,1951) .Stick ytrap shav ebee nuse db yRoesle r (1953),Shirc k (1957)an d Ellington (1963). Toinspec tth eptilinu mfo rth edy emark ,an dth eovarie sfo rsterility ,th eflie s hadt ob efres han ddry .Fo rassessin geg gsterility ,femal eflie swer eneede dalive . Thereforegenerall yfligh tinterceptio ntrap swer eused ,i nwhic hman yo fth eflie s stayedaliv eunles sther ewer esom epredator spresent .Th efligh tinterceptio ntra p wasdevelope daccordin gt oth especifi cneed sencountered ,an dwa sgenerall yuse dwithou t attractants otha tth enumbe ro fvariable sinfluencin gth ecatc hsiz ewa slimited .Late r someexperiment swer edon eo nattraction ,especiall yt oincreas eth ecatc ho fth efligh t interceptiontraps .

3.3.3.1Fligh tinterceptio ntrap s

Construction Thebehaviou ro fth eflie snea rdifferen tgauz escreen spu ti nth efiel d hasbee nobserved .Th eflie sseldo mfl yabov eth eloca lvegetation .I na nonio nfiel d thisi su pt o5 0cm ,an do nditc hbank sgenerall y 10-30cm ,dependin go nth emowin gin ­ tensity. Trappingequipmen thighe rtha n5 0cm ,place di nonio nfields ,i seasil ydamage db y thesprayin gbooms ,necessar yfo rherbicide san dfungicides . Afterexperienc ewit ha preliminar ytra pmodel ,develope dfro mth eprincipl eo f Malaise (1937)(Loosjes ,1971) ,a simpl efligh tinterceptio ntra pwa smad e (Fig. 23), comparablet othos edescribe db ye.g .Gressi t& Gressi t (1962),Butle r (1965)an dAuber t etal . (1969).Th etra pconsiste do fa plasti cgauz escreen ,stretche db ythre enylo n ropesove rtw oaluminiu mpoles .Collector so fplexigu mtubin gfitte dint oplexigu mring s gluedo nth egauz eroo fi nbot huppe rcorners .Th escree nheigh twa s5 0cm ,i nsom ecase s 75o r10 0cm ,th eentranc eheigh twa s1 0c m less.Whe ntrap so fdifferen theigh twer e placedsid eb ysid ether ewa sn osystemati cdifferenc eamon gthei rcatches ,provide dtha t thevegetatio nwa sclearl ybelo w4 0cm .

Location Thelocatio no ftrap sha sa considerabl einfluenc eo nth enumber so fflie s caught.Onio nfl ypopulation saggregat enea ronio nfields .S oth enumbe ro fflie strappe d isa functio no fth edistanc efro ma nonio nfiel dand ,durin gth e1s tflight ,als ofro m thedistanc efro ma ninfeste donio nfiel dth eyea rbefore .Th eeffec to fth etra ppositio n isshow ni nTabl e5 ,comparin gcatche si ntrap splace dwithi na radiu so fabou t10 0m o f eachother .Clearl yth eoptimu mpositio ni salon gth esid eo fa nonio nfield ,borderin ga ditcho ra cro p (cereals)whic hprovide sshelter ,an dwit hth etra pentranc eturne dawa y fromth eonio nfield . Thevariatio namon gth ecatche si ntrap stha thav eseemingl ysimila rposition sca n

36 Fig.23 .Fligh t interception trapa suse di n mostrelease-recaptur eexperiments . Ontop :tra pi noptima lpositio ni nth efield ; below:collector .

Table5 .Effec t oftra ppositio no ncatc hsize .Dat aexpresse d asrelativ ecatche spe r trap,fo rstandar dpositio n- 100.Betwee nbracket sdat afro mon etra ponly .Othe rdat a based on2-1 2traps .

Trappositio ncod e 1 10 Pollemans1971- 1 100 15 Pollemans1971- 2 100 62 36 43 18 30 Vroegindewei 1972-210 0 (20) (32) (138) 61 27 21 Schuilenburg 1972 100 45 75 45 36 vanE s1973- 1 100 80 Mijs1973- 1 100 93 Mijs 1973-2 a 100 26 20 Mijs 1973-2b 100 72 (5) 9 a.Positio ncode :1 = edg eo fonio nfield ,ditc hbank ,ope nsid eawa yfro monions ;2 - edgeo fonio nfield ,cereals ;3 = edg eo fonio nfield ,other s (potatoes,sugar-beet) ; 4» edg eo fonio nfield ,ditc hbank ,ope nsid etoward sonions ;5 - a s4 ,bu thalfway ' downditc hbank ;6 = a s 1,bu ta 3 m wid epat hbetwee ntra pan donions ;7 » a s2 ,bu t placed atrigh tangle st oedg eo ffield ;8 = i nonio nfield ;9 = outsid eonio nfield , ditchbank ; 10= outsid eonio nfield ,i nothe rfield .

37 stillb econsiderable .Fo rte ntrap si na nonio nfiel dth emea nan dconfidenc einterva l foron eyear' scatc hwer e44 4an d299-589 ,respectively . Onewoul dexpec ttha tth enumbe ro fflie scaugh ti nth etrap sdepend so nthei rfligh t direction.N oeffec to ftra ppositio no ncatc hsiz ewit hrespec tt oth edirectio no fdis ­ persalwa sfound .Th efligh tdirection stherefor ehav ea lo wcorrelatio nwit hdirectio n ofdispersal ,whic hca nb edu et opredominantl yrando mmovement .

Daily rhythm Inorde rt okno wth eperio dfo rwhic hth eweathe rcoul db ecorrelate dt o thecatc hsize ,th emomen to fcheckin gth etrap si nrelatio nt oth edail yrhyth mo ftrap ­ pingshoul db eknown .Therefor eth eactivit yo fth eflie san dth eoccurrenc eo fcapture s werechecked . Theresult so fth emos textensiv edat ase tobtaine dar egive ni nFig .21 .Man yinci ­ dentalobservation sindicate dtha tth edail yrhyth ma sfoun dhere ,wit ha maximu mcatc h towardsth een do fth eday ,wa srepresentativ eo fth enorma lsituation .A simila rrhyth m hasbee nfound ,lik ei nman yothe rinsects ,fo rth eactivit yrhyth mo fth eonio nfl yi n thelaborator y (Brunei& Rahn ,1971) . Thusth ebes ttim efo rchangin gth ecollector si seithe rafte rsunse to rearl yi n themorning .Fo rpractica lreason sth ecollector swer echange dgenerall ybetwee n8 h 0 0 and1 0h 00 ,an dal lflie swer econsidere dt ohav ebee ntrappe dth eda ybefore .

Influenae of weather Thedail ycatc hsiz ei sproportiona lt oth eloca lpopulatio nden ­ sityan dt oth eactivit yo fth eflies .Th eforme rfacto rcause slong-ter mchanges ,th e latterdepend so nth eag edistributio no fth eflie scausin gals olong-ter mchanges ,a s wella so nth eweathe rwhic hcause sshort-ter mfluctuations .Th echang ei nnumber so fth e fliescaugh tfro mon eda yt oanothe rwil lmainl yreflec tth einfluenc eo fth eweathe ro n theactivit yo fth eflies . Toestimat ethi sweathe reffec tfro mth etrappin gdata ,catche so nconsecutiv eday s wereanalyse di nrelatio nt oth ecorrespondin gmaximu mtemperature spe rday ,measure da t thestandar dheigh to f1. 5m abov eth esoi lsurface .Thi sweathe rparamete rwa schose n becausei ti seasil yavailable ,an di sindependen to fnigh ttemperature swhic har eno t relevanthere .Th emetho duse di ssimila rt otha to fWilliam s (e.g. C.B.Williams ,1961 ; seeals oJohnson ,1969 ,p .249) .Th eaverag efacto rwit hwhic hcatche schange dwa scal ­ culatedpe r0. 5C chang ei nmaximu mtemperature sfro mon eda yt oth enext .Fig .2 4give s thepercentag echang ei ncatc hsize ,wit h100 1pu ta ta maximu mtemperatur eo f2 0C ,a s calculatedfro mth edat ao f24 9pair so fconsecutiv eday si n1970-1973 . Therelatio nshow ni nFig .2 4wa suse dt ocorrec ttra pcatches ,an dothe rdat a dependento no rcorrelate dwit hfl yactivity ,t oyiel dthos eexpecte da t 'standarddays' , i.e.day swit ha maximu mtemperatur eo f20°C .Thu sth epresumabl ylarge rpar to fth e influenceo fth eweathe ri seliminated . Rainan dstron gwind sdiminis hcaptures ,bu tbecaus ethe yar ecorrelate dwit hlowe r temperatures,littl ewoul dhav ebee ngaine db yincludin gthes efactor sa swell .Moreove r themomen to foccurrenc ei sver yimportant ,an dthi scoul dno tb etrace dfro mth eavail ­ ableweathe rdata . Onewoul dexpec ttha tcatche so ffligh tinterceptio ntrap sar edependen to nthei r

38 ratativ* catch si»

200-

100-

1 1 1 1 1 1 1 1 1 I i r~ 10 12 14 16 18 20 22 24 26 28 30 32 34 °C Fig. 24.Relatio n between catches in flight interception traps and maximum temperature per day in C. Catches expressed as percentage of catch on standard days (20 Cmaximu m temper­ ature). Data from Overflakkeean d the Schuilenburg, 1970-1973.

positionrelativ et oth ewin ddirection .Dat afro mth eSchuilenbur gexperimen ti n197 1 (Section6.1 )wer eanalyse dfo ra win ddirectio neffect .Fiv epair so ftrap swer eplace d ina nonio nfield ,thre etrap sfacin gN Wan dthre eSE ,an dtw ofacin gN Ean dtw oSW .Fo r allday swit hth ewin dblowin gi na certai ndirection ,th edifferenc ei ncatc hi neac h pairo ftrap sfacin gupwin dan ddownwin dha sbee ntake nint oconsideration .Th edistri ­ butiono fthi sdifferenc ewa sabou tnormal ,wit hmea nan d95 % confidenceinterva lo f 1.31±9.48 , inwhic hpositiv evalue sdenot emor e fliesi ntrap s facingdownwind .Thi s issignificantl ydifferen t fromth eexpecte dmea no fzer o(* 168=3.53) . Thusmor eonio n flieswer e trappedi ntrap s facingdownwin dprobabl ybecaus e flightswer epredominantl y upwind.Als otrap s facingdownwin dma yoffe rmor eshelte ragains tth ewind .Th eaverag e numberscaugh tpe rtra ppe rda ywer efo rtrap sfacin gdownwind ,upwin dan dt oth etw o sides:5.65 ,4.34 ,4.8 9an d4.89 ,respectively . Fortrap splace dalon gth eedge so fonio nfield sth ewin deffec tseeme deve n less, but thisimpressio ncoul dno tb echecke dbecaus ea situatio ni nwhic hthi scoul db etes ­ tedi sno tusuall yencountered .Moreove r localdifference si nth evegetatio no rothe r factors causeth edifference sbetwee ntrap sa tonio nfiel dedge st ob ehighe rtha n betweentrap si nonio nfields ,thu sobscurin ga possibl ewin ddirectio neffect .

3.3.3.2Attractio n

Someknow nattractant s (Section2.2.3 )wer eteste dfo rus ei nwate rtraps .Thes etrap s 3 wereyellowis hsquar eplasti ctrays ,1 6x 16cm ,containin g50 0c m waterwit hattractan t anda fe wdrop so fdetergent .A preliminar ytes twa sdon et ochec kth eattractivenes so f onionjuice ,obtaine dwit ha juic ecentrifuge .Th eonio njuic eputrified ,an dunde rth e

39 Table 6. Attractivity of different concentrations of some attractants. Experiment Mijs 1973.

Number of Attractant Average number of flies traps per trap per day 6 beer 4%, 20% and 100% 0.2 6 onion juice 2%, 10% and 50% 0.2 8 onion juice 10%, renewed every 2-3 days 0.1 4 beer 20% + onion juice 10% 0.3 2 n-propyl disulfide 1% 8.8 2 n-propyl disulfide 0.2% 13.2 2 n-propyl disulfide 0.04% 10.4

2 control (wateronly ) 0.0 12 flight interception traps 2.7 prevailingweathe rwa soptimall yattractiv edurin gth esecon dweek . A 12-daytes twit honio njuice ,bee ran dn-propy ldisulfid ewa sdon esubsequently .Th e n-propyldisulfid ewa sdissolve d in2 5c m paraffinoil ,floatin go nwate ri nth etray . Thetrap swer eplace d3 m fromeac hothe ri na ro walon gth eedg eo fa nonio nfield .Th e resultsar egive ni nTabl e6 .Obviousl yn-propy ldisulfid ewa smos tattractiv et oonio n flies.Th eeffec to fth econcentration suse dwa sneve rsignificant .Th erati omale st o femalesi nth en-propy ldisulfid ebaite dtrap swa s4:1 ,wherea si nth eothe rtrap si twa s 1:1. Preliminaryobservations ,Augus t1973 ,indicate dtha ta n-propy ldisulfid esourc e placedunde rth eroo fo fa fligh tinterceptio ntra pha da positiv eeffec to nth ecatc h size.Thi swa sstudie di nmor edetai li nth eexperimen tMij s1974 .Fligh tinterceptio n traps,bot hwit han dwithou tattractant ,wer eplace dalon gth eedge so fth eexperimenta l field,an di ntw oplace sa tove r30 0m distanc efro mth eneares tonio nfield .Th eattrac ­ tant,12. 5m lo f0.4 %solutio no fn-propy ldisulfid ei nparaffi noil ,wa spu ti na tra y asbefore ,the ncovere dwit hplasti cgauze ,mes h 1mm .Severa ltime sne wattractan twa s added.Onetra pwa sprovide dwit hrottin gonio njuice . Fig.2 5show sth erati oo fth ecatche s intrap swit hattractan tt othos ewithout ,a s afunctio no ftim esinc eadditio no fattractant .Fa rfro monio nfield sattractant swer e muchmor eeffective :th efirs tapplicatio naugmente dth ecatche sb ya facto ro fove r1 0 becausether ewer en ocompetin gonio nodours .Th eeffect so fsubsequen tapplication so f attractantappeare dt odiminis hwit htime .Th emos tprobabl eexplanatio ni sthat ,b yno t cleaningth etra ywhe naddin gne wattractant ,certai ndecompositio nreaction soccurre d thatcounteracte dth eeffec to fth en-propy ldisulfide . Overal lth eperiod sdurin gwhic hth eattractan tdi dsho wa neffect ,th ecatche si n trapswit han dwithou tattractan thav ebee ntotalle dfo rth esexe sseparatel yan dcombi ­ ned.Th eresult sar egive ni nTabl e7 .Bot hattractant shav ea large reffec to nth ecat ­ cheso fth emale stha no nth ecatche so ffemales . Matsumoto (1970)foun dtha t90 %o fth eonio nflie si nn-propy ldisulfid ebaite dtrap s werefemale swit heggs .A sh edi dhi sexperiment so nfallo wlan dth ebai twil lhav eat ­ tractedth efemale sfo roviposition .Th epresen texperiment swer emainl yi nonio nfields . Thelimite ddat acollecte doutsid eonio nfield sd ono tpermi tan yconclusio no nth ese x ratiothere .

40 Fig. 25.Increas e incatches ,du et o placing a tray with n-propyl disulfide under flight interception trap, expressed as ratio tocatche s inunbaite d traps. Traps ononio n field edges, experiment 6 « » 12 14 w days altar addition of n-propyl disulfide Mijs1974 .

Table 7.Effec t ofattractan t oncatche sb yfligh t interception trapso nedge s ofa n onion field, corrected fortemperature .Aberran t males included intota l only. Experiment Mijs 1974.

Attractant Total number offlie s captured Ratio with/without attractant with attractant without attractant males females total males females total males females total n-propyl disulfide 397.3 238.8 668.6 169.5 132.6 314.0 2.34 1.80 2.13 rotting onion juice 431.0 239.0 698.0 148.7 123.9 284.3 2.90 1.93 2.46

3.3.4 Obtaining egge

Ina steril emal eprogramme ,th esterilit yo fth eegg si sth eearlies tan dsafes t indicationwhethe rth esteril eflie shav ebehave da sthe ywer eexpecte dt odo .Therefor e methodso fobtainin gthi s informationar erequired .I nth eSchuilenbur gexperiment snea r Wageningen,becaus e laboratoryroo man dmanpowe rwer eavailable ,th efemal eonio nflie s caughtaliv ewer ekep ti nth elaborator yt ola ythei reggs .O nOverflakke ea nattemp t wasmad et oconcentrat eth eovipositio ni nth efiel do nartificia leg gdepositio ndevi ­ ces,i nshort ,eg gtraps .Th elatte rwor kwa sdon emainl yb yth estudent sJ.J.L .Huber , J.Roes tan dG.J .Buth . Whenegg swer ewante d fromwil d females,thes ewer epicke dou to fth ecatche sunde r CO2anaesthetization ,an dpu tint oseparat ecage sfo rdifferen ttrappin gsite san ddays .

41 Theywer ekep tther efo ron eweek .Afte rtha tthe ywer ekilled ,an di fneede dchecke d fordy emark ,ovar ydevelopmen tan dpresenc eo fsperm .Th ecage swer e8 o r1 5c m 0 plexigumtubing ,standin g ina Petr idish ,wit ha plasti cgauz eroof ,mes h 1mm .Water , dryfoo dan dNoorlander' sovipositio ndevic e (Ticheler,1971 )wer eprovided . Theeg gwer ecollecte dtwic ea week ,an dkep ta t2 2C an d100° srelativ ehumidit yfo r atleas tthre edays .Afte rtha tth esterilit yo fth eegg swa schecked .Th eresult swer e ratherlimited .Th emajorit yo fth efemale strappe dwer esterile ,an dthes ed ono tla y anyeggs .Th efertil eflie sdi dno tla ythei regg sa sreadil ya sexpected :88 1o fth e femalescontaine dmatur eegg sa tth een do fth eweek ,compare dwit h 55-60%i nth efiel d (Section4.5.2) .Thi sdrawbac kma yb ecircumvene db yusin ga differen tcag eo roviposi ­ tiondevice .A genera lan dinevitabl eproble mwit hthi smetho d istha ta tth elo wdensi ­ ties,a twhic hth einformatio ni sneeded ,ver yfe wfertil eflie sar ecaugh t (cf.th e datai nTheunisse ne tal. , 1975). Severaldifferen teg gtrap swer etested .A sattractant srottin gonio njuice ,freshl y cutonio npiece san dn-propy ldisulfid ewer eused .Al lexperiment swer edon ei nan da - roundonio nfields .Notche dearthenware ,notche dplastic ,sand ,filte rpape ran dsevera l combinationso fthes eprovide dtactil estimuli . Thenumber so fegg sobtaine db yth eeg gtrap suse dhav eremaine dto olo wt ob eusefu la t lowdensitie s (Huber,1973 ;Buth ,1976 ;Roest ,pers .commun.) .Incidentally ,whe nther ewer e highdensitie so fmatur efemales ,ther ewa sa substantia laccumulatio no fegg si nth eeg g traps,u pt ohundred so fegg spe rtrap .Socia lfacilitatio no fovipositio n iswel lknow n formmas srearing .I ti spossibl etha tth efemale swer emor econspicuou swhe ndepositin g eSgs inth eeg gtrap stha no nonions . Searchingfo ro rsamplin go fegg si sonl yfeasibl ea trathe rhig hdensitie so fonio n flies.Searchin gma ygiv ea nide ao fth echang ei nnumber swit htime ,bu tu pt o50 %ma y beoverlooke deasily .Sample sshoul dcontai nth eonio nbul ban dth elowe rpar to fal lth e leaves,an dth eeart hu pt oabou t2 c maroun dth eonio nplan tan da tleas t2 c mdeep .I t dependso nth esoi lstructur ean dth esamplin gmetho dwhethe rdeepe rsample sar eneces ­ sarybecaus eth eegg sca nslid edown .Th esoi lsample swer etake nwit ha spoo no rwit h a littlegraspe rlik etha to fa cran e (Webley,1957) .Th egraspe rtoo khal fo fa spher e of8 c m0 . Eggswer eextracte dfro mth esoi lsample sb ysimpl eflotation .Thi smetho dgive s clearlysomewha tles stha n100 1recovery .Th eonio nplan tpart swer esearched ,especiall y thelea fsheaths .

3.3.5 Sampling flies, larvae and damage

Flies Especiallywhe nonio nplant sar esmall ,th enumbe ro fflie si nth efiel dca nb e countedt oestimat eabsolut edensity .Th emajo rdrawbac ko fthi smetho d istha t itcanno t beuse d inth egrass yverge so fth efield swher emos tonio nflie soccur . Forfl ysample stha tar epresumabl yindependen to fth evegetation ,th emetho do f MacLeod& Donnell y (1957)wa sused .Tent so fclot hwer estretche dove ra niro nwir eframe . Theyha da to ptra pmad eo f8 c m0 plexigu mtube ,covere dwit h1 m mmes hplasti cgauz e anda sa nentranc ea plankto ngauz efunnel .Th etent' sbotto msurfac ewa s0. 5x 0. 5m .

42 Thesetent swer eplace di nth efiel dafte rsunset ,an dcovere dwit hblac kpolyethylen e foil.Wit h fairweathe rth etrap swer e inspectedth enex tafternoon .Th e sametyp eo f tentwa suse dt osampl eemergin g flies.Use da sa depo ttra pfo rpupa edu gint oth e soil,i tyielde dth esam epercentag eemergenc ea sth enorma ltyp edepo ttrap ,indicatin g thatn oyoun g flieswer e lost.Olde rflie sar eles spositivel yphototropic ,s oflie sma y bemisse di nsampling .

Larvae Larvaesometime swer e sampledb ysamplin gattacke donion san ddissectin gthem . First instar larvaear ever ydifficul tt ofin di nth eonio ntissu ewithou tth eus eo fa microscope.Whe n samplingth eonion son emus ttak ecar et oinclud ei nth esampl elarva e thatar ejus tunde rth eonion si nth esoil .

Damage Damagewa s sampledi n197 3o nregularl ydistribute dplot so f0. 5m onio nrow , andi n197 4o nrando mplot so f0.2 5m row .Attacke donion swer e indicatedwit ha smal l stickexactl ybesid ethe ms otha tafte rthe yha ddisappeare d theirorigina lposition s remainedclear . Theaverag eduratio no fth evisibilit yo fdamag ewa sestimate db ynotin ga teac h inspectionth evisibilit yo fonion sfoun ddamage dearlier .Thi saverag eduratio nincrea ­ sed linearily fromabou t2 0day sfo rdamag e thatbecam evisibl ei nearl yJun et o4 5day s fordamag etha tbecam evisibl ehal fJuly .Al ldamag ewa sstil lclearl yrecognisabl edurin g thefirs t2/ 3par to fthes eperiods .Youn g seedlings shouldb echecke dtwic ea wee kwhe n damagei st ob eexpected .A sa rul eo fthum bth enex t checkshoul dpreferabl yb ewithi n anumbe ro fday stha ti sequa lt oth eaverag eonio nheigh ti ncm . Theeffec to fplo t lengtho nth edat aobtaine di sdiscusse di nSectio n4.3.1.4 .

3.3.6 Sampling pupae

Pupaear epresen tonl ynea rattacke donions .The ywer egenerall ysample da tharvest . Fullpupa e thenar ediapausing ,empt ypupa erepresen tth esecon dflight .Bot hca nbelon g toa thir dfligh ti fpresent ,dependen to nth etim eo fsamplin gan do fthi sflight .An ­ otherstrateg yfollowe dwa st osampl epupa eon eo rtw oweek safte rattac kha dbee nnoted , inorde rt oobtai na representativ e sampleo f1s tgeneratio npupae .Th eonion si nth e sampletha tstil lmigh t containlarva ewer epu tback .Thi smetho dca nonl yb eapplie d with smallsoi lsamples ,i.e .o f5 c m0 ,becaus eotherwis eman yhealth yonion shav et o bedestroyed .The na nonio ni nth eneighbourin gro wwa s takena trando ma sa replacement .

Distribution of pupae in the soil Intw oplaces ,on eo nsan dan danothe ro nsand yclay , thesoi laroun dattacke donion swa scarefull ydu gou tan dth epositio no feac hpup afro m thecentr eo fth eonion' sro wwa smeasured .Th esidewar ddistributio nwa s identicali n bothsoi ltypes ,an dconforme dt oa norma ldistributio n (Fig.26) .Th edept hwa sdependen t onth esoi ltyp e (Fig.27) . Thebotto mo fonio nbulb si snormall ya ta dept ho f1- 3cm .

Sample size Sampleswer etake nwit hdiameter so f5 o r2 0cm ,centere do nattacke donions . Thefractio no fpupa etha ti ssample dwit ha certai nsamplin gcor ediamete ri sdependen t

43 number of pupae 1 18-

16H

14- i i

12- , l 10- i l , 8- r " 1

- —i 4- > 1 . 1 . 2- r^-i" 1 T-T- _ .^-j--- i i -1 -2 0 3 9 10 11 12 2 -11 -10 -9 -8 -7 -6 -5 -4 -3 -1 \ 2 4 5 6 7 8 distance from onion row in cm

Fig. 26.Sidewar ddistributio no fpupa ei nth esoil ,a smeasure d from theonio nrow .Dat a combined fromsan d (m= 0.1 ,s = 4.0 )an d sandycla y (m= -0.1 ,s = 4.1) .Teste dagains t normaldistribution :xfi+ = 17.2,n.s .Dat afro mGoere ean dOverflakkee ,1970 . observeddistribution ;- - - norma ldistributio nwit h m =0 ,s = 4.0 .

number of pupae

20 10 1

depth inc m Fig.27 .Dept hdistributio no fpupa ei nth esoil ,fo rdifferen t soiltypes . Left:cla yfractio n 10%,averag edept h9. 1 cm;Goere e1970 ; middle:cla yfractio n 15%,averag edept h6. 2 cm;Overflakke e1970 ; right:cla yfractio n20% ;Overflakke e1970 .

44 onth eaggregatio no fth e samples.A tfirs tconside ra ro wo fonion swhic hi s100 %infes ­ ted,an do fwhic ha part ,th epredetermine d sampling site,i sbein gsampled .Th efractio n of thepupa esample dca nthe ndirectl yb erea dof ffro mth esidewar d distributiono f pupaea sgive ni nFig .26 .Displacemen to flarva eparalle lt oth eonio nro wbefor epupa ­ tiondoe sno tinfluenc ethi sdistribution .Th epar tt ob esample di si nfac ta rectangula r surfacewit hth ewidt ho fth esampl ecor ediameter ,an dth e lengtho fth esamplin gsite . Nowconside rth ecas eo fa singl eattacke donion .I tha sbee nprove ntha tth ehorizon ­ talcomponen to fth e larvalmovemen tprio rt opupatio ni sindependen to fth edirectio no f theonio nrow .Thu sth edispersio no fpupae ,originatin g fromon eonion ,wil lb eth e cir­ cularnorma ldistributio ncorrespondin gt oth enorma lon egive ni nFig .26 .Percentag e pointsfo rth ecircula rnorma ldistributio nhav ebee ntabulate d (Owen,1962) . Thuswit ha 5 c m0 sampl eth efraction s sampled,fo rth etw oextrem ecase smentione d above,were :fro mth enorma ldistributio n 46.71an dfro mth ecircula rnorma ldistributio n 17.81.Fo r2 0c m0 sample sthes evalue swer e 98.7%an d95.6% ,respectively . Inth e fielddamag ei shighl yaggregate d (Section4.3.1.2) .Moreove rth emajorit yo f damagecanno tb esubdivide d intoattacke donion swhic h larvae lefti norde rt opupat eo r which larvaelef tt oattac ka neighbourin gonion .Therefor esample smostl ycontai nonl y slightly lesstha nth e% o fpupa eestimate d fromth enorma ldistribution .Ever ysampl e froma nonio no fth e lattertyp ewil l causeth epercentag e sampledt ocom eclose rt oth e oneestimate d fromth enorma ldistribution ,tha ti sfo rth ecas eo f100 % infested. Datao nth epupa esample dwit h5 an d2 0c m0 ar egive ni nFig .28 .Th efac ttha tno t 100%i scontaine di n2 0c m0 sample sca nb eneglecte dher ebecaus eit seffec to nth e percentage sampledwit h5 c m0 i sles stha n 1%.Ther ear etw oset so fdat adeviatin g from the theoreticalmode lgive nabove .Thes edeviation s correspondwit hdeviatin g soil structure,a sindicate di nth efigure .Whe nsoi lstructur ei sth ecause ,th eagreemen t ofdat afro mdifferen t soilsi nFig .2 6i sdu et ochance ,an dth evariance swil l actually bedifferent .Th e95 %confidenc e limitso fth estandar ddeviation so fth esidewar ddis -

parcantaga ofpupa a

60-

50

t 40- / // / Fig. 28.Percentag eo fpupa esample dwit ha 5c m0 samplin gcore ,a sa functio no finfes ­ 30 tationintensity .Expresse d aspercentag eo f thenumbe ro fpupa eobtaine dwit ha 2 0c m0 sampling core.Infestatio ni nnumbe r ofonion s / 20- / attackedpe rplo to f0. 5m row ,s o2 0onion s correspond withabou t 100%damage . Relationestimate d fromth evalue scalcu ­ latedfo rth eextrem ecase s (seetext) . 10 O= Dat afro msand ycla y (clayfractio n 15%); J}• dat afro msan d (clayfractio n 10%;the o at2 0onion sdamage d correspondswit hth e -r T TT- data of Fig. 26); infaatad onkma/m 8 = data from clay (clay fraction about 30%).

45 tributionso fpupa ei nsan dan dsand ycla yar e3.5-4. 5an d3.5-5.0 ,respectively ,wid e enought omak edeviation sa sfoun di nFig .2 8probabl e (e.g.a circula rnorma ldistribu ­ tionwit h 30%i n5 c m0 ha sa standar ddeviatio no f3.1) . Thelin edraw ni nFig .2 8i sa 'safe'suppose drelatio nfo rsand yclay .Dat at ob e collectedfo r2- 5attacke donion spe r0. 5m onio nro wma yyiel da steepe rinitia lincreas e inth epercentag esampled ,du et oaggregatio no finfestation . Sampleswer etake na sth etota lsoi lcore ,generall yals owhe nth ecentr ewa sles s thanth ecor ediamete rfro mth een do fa samplin gsite .Thi sprocedur ewil lresul ti na n overestimationo fpupa ewhe nattac koccur su pt oth een do fth esamplin gsit ean dno t beyondit .I ti scompensate d forb yth eunderestimatio no fpupa ei nth eopposit ecas e whichwil loccu ra sfrequently .Wit hdamag eo nbot hside so fth esamplin gsite' send , thenumbe ro fpupa ethu ssample dwil lb eto ohigh .However ,whe nther ewa sdamag eacros s theend ,visibl ea tharvest ,th esample swer etake nexactl yu pt oth esamplin gsite' s end.S oth enumbe ro fpupa ewil lhav eonl ybee noverestimate dwit hdamag en olonge rvi ­ siblea tharvest ,whic hcorrespond swit h lownumber so fpupa epe rattacke donio n (Fig. 47), andwil lthu shav ebee nnegligible .

Extraction Thepupa ewer eextracte dfro mth esample sb yflotation .Th esample swer e crumbledint obucket swit hwater ,stirred ,an dthe nth ewate rwa spoure dthroug ha 1 m m meshplasti cgauze .Thi sprocedur ewa srepeate donc eo rtwice .B ywashin gth emu dthroug h thegauz ean ypupa eo nth egauz ebecam econspicuous .Al lpupa efloa tafte rhavin greache d ? anag eo fabou t1 6hour s (22°C),tha ti s5 0o fth epupa lstag eduration .Th epupa eno t yetfloatin gan dan ylarva epresen twil lbecom esuspende db yth estirrin gan dsettl edow n onth emud' ssurface ,wher ethe yar eals orecovered .Empt ypupa ema yno tb es oeasil yre ­ covered.Subsequen tstirring san dwashing syielde dth enumber so fpupa egive ni nTabl e8 . Fromthes edat ath enumbe rrecoverabl ewit ha ninfinit enumbe ro fstirring sma yb eesti ­ mated.Recover yo fpupa efro mdepot sindicate dtha tth efractio no funrecoverabl epupae , ifany ,wil lb enegligible .

3.3.7 Fly inspection

Generallyth eflie st ob einspecte dcam efro mfligh tinterceptio ntraps ,s othe yha d tob ekille dfirst .Th etota lcatc hwa sanaesthetize dwit hCC Li nth etra pcollectors . Thenth eplankto ngauz efunne lo fth ecollecto rwa sturne doutward san dth econtent swer e shakenint oa Petr idish .A piec eo fpape rtissu ewit ha littl ebi to facetaldehyd ewa s

Table8 .Pupa erecovere d bysubsequen t extractions.Extrapolate dvalue sbetwee nbrackets . In 1974th eextractio nwa smor ecareful .

Numb ero f pupae extracted %Recovere d 1st 2nd 3rd 4th 5th in1 s t inlst+2n d

Mijs 197 3 fullpupa e 79 5 2 0 (0) 91.8 97.7 emptypupa e 400 159 26 3 0 68.0 95.1 Mijs 197 4 fullpupa e 143 5 (0 2) (0) (0) (96.5) (99.9) emptypupa e 241 39 (6.3) (1) (0.2) (83.8) (97.4)

46 added forkilling .I fth efemal eonio nflie swer ewante d aliveth ecollectors ' contents were shaken intoa siev ewit ha plankto ngauz ebottom ,u pthroug hwhic ha slo w current ofCO ,wa spassed .Th efemal eonio nflie s couldb eidentifie dan dselecte d there. Onionflie sca nb eidentifie dan dsexe db ythei rgenera l appearance.We t fliesar e muchmor edifficul tt oidentify . Tose ewhethe rth eonio nfl yfemale shav emated ,pul lou tth eoviposito rwit hth e spermatheca,pu tthi si na dro po fwate ro na slid ean di fneede dpul lth espermatheca e free fromothe r tissue,an dsqueez e themwit ha cover-glas sunde r themicroscope .The n with all females thathav ecopulate da lo to fsper mwil lburs tout ,a sca nb esee na t about 100x magnificatio nan dth ediaphrag mnearl y closed (Theunissen, 1974).T ochec k ovariandevelopmen t squeeze theovarie sou to fth eabdome nafte rremova lo fth eoviposi ­ tor,an dinspec tthe munde r about8 0x magnification .Th e stageso fovar y development aredescribe db yTheunisse n (1973a).Checkin gfo rth epresenc eo fsper man dovaria n development takes 2-3minute spe rfly . The largerwin gvei naberration s canb esee nwit hth enake deye .Fo rfindin g small aberrationsan dfo rmeasurin g thewin gvei n length,tak eth ewin goff ,pu ti tbetwee n twoslide san dinspec twit ha microscope ,magnificatio nu pt o2 0x . Thedy emar kwa sgenerall y checkedwit ha microscop ea t40-8 0x magnification .Tak eth e flies' abdomen,leg san dmout hpart sbetwee n leftthum ban dforefinger ,an dsqueez eth e fly slightly.The nth eptilinum ,an dno tth eproboscis ,wil l comeou twithou tth efl y gettingdamaged .Kee po rmak eth efly' shea ddry ,fo rwhe n theptilinu mbecome swe tth e coloursbecom ever ydifficul tt odistinguish .T oloo ka tth eptilinu m from dessiccated flieskee pth efly' shea dbetwee n leftthum ban dforefinger ,introduc ebot hpoint so f very sharp-pointed tweezers together througha neye ,an dallo wth epoint s thent osepa ­ rate slowly. Sortingo fflie san dcheckin g themfo rdy emark take s1 hou rfo r20 0fres hdea d flieso rfo r10 0dessiccate d flies.

3.3.8 Field observation of fly behaviour

The flightbehaviou ro fth e flieswa sobserve di nth e field,t oge ta nindicatio no f itsdispersal . Whena fl ywa s foundi nth efield ,it sbehaviou rwa srecorde do na portabl e tape recorder,wit h theai do fa stopwatch .A recor dende d aftera predetermine d period, but actually oftenearlie rbecaus eth efl ywa s lostsigh tof . Thebehavioura l datanote dwere :typ eo fsittin gplace ,orientation ,directio nan d distanceo fwal ko rflight ,cause sfo r alightingi fidentified ,an dremark so nfeeding , preening andpresenc eo fothe ronio nflie so rothe ranimal swithi nth eestimate d sight rangeo fth e individualrecorded .Othe rdat acollecte dwer eth eflies 'sex ,dy emark s ifan yvisible ,directio n anddistanc eo fth eobserve rt oth efl yrecorded ,an dth e presenceo fsunshin ean drai no nth efly .Moreove r regularly temperature andhumidit y weremeasure da tsoi lleve lwit ha nAssman nthermohygrometer ,an daverage ,maximu man d minimumwin d speeda t2 0c mheigh twer eestimate d froma cu panemomete rwit hwin d speed indicator.

47 observer

'numbe ro fflight s

Fig.29 .Directio no fonio nfl yfligh ti n onionfield ,wit hrespec t toth edirectio n inwhic h theobserve rwa s situated.Observa ­ tionsfro m 1971-1973, n =147 . Tested towards/away fromobserver :Xi =0.6,n.s.

Nearlyal ldat aha dt ob ecollecte di nonio nfields ,becaus eo fth ever y lowchanc e offindin gonio nflie soutsid eonio nfields .Thu sth eresult sar eonl yrepresentativ e forth esituatio ninsid ethes efields . Thefligh tdirectio nwa sindependen to fth edirectio nwher eth eobserve rwas ,althoug h hewa sgenerall y0.5- 2m fromth efl y (Fig. 29).

3.4 SUMMARY

Thefiel dexperiment swer edon ei na typica lDutc honio ngrowin garea ,wit h5-15 1 occupiedb yonions .Th eprevailin gweathe rwa sno tabnormal . Fliesuse dfo rrelease swer eobtaine dfro ma laborator ymass-rearing .Whe nneede d theflie swer esterilize dwit h3 k Rirradiatio ntreatment ,causin g 99.4%sterilit yi negg s fromuntreate dfemale smate dt otreate dmales .Th ematin gcompetitivenes so fth esteril e males,a smeasure di ncompetitio nexperiment si nth elaboratory ,wa sno tsignificantl y differentfro m1 . Flieswer emarke dsometime sb yincorporatin ga radioactiv elabe li nth elarvae ,bu t generallyb yforcin gth eemergin gflie st opas sthroug ha dy elaye rwhic hcoul db e changeddurin gth eemergenc eperiod .Radiatio ninduce dsterilit yi sa goo dta gfo r females,especiall ywhe nsterile sar ei nth emajority .Fl ysize ,a smeasure dfro mwin g veinlength ,ca nb euse da sa mar kespeciall yfo rmales ,provide dtha trecapture sar e large. Generallyflie swer erelease dfro mcontainer swit hpupa eburie d inth esoil .Dept h andvegetatio naffec tth etemperatur ean dthereb yth espee do femergence .Prédatio nb y birdso nth econcentration so fnewl yemerge dflies ,whic hi sinevitabl ewit hthi s method,i ssuppose dt ohav ebee nth ecaus eo fu pt o90 1loss .Flie scoul dals ob ere ­ leasedfro mcage swit hu pt o5 flie spe rc m. Flightinterceptio ntrap swer eused .Th ecatche scoul db emor etha ndouble dwhe n combinedwit hth eus eo fattractant s (rottingonio njuic eo rn-propy ldisulfide) .Th e optimumtra ppositio ni sa tonio nfiel dedge swhic hprovid eshelter ,an dfacin gout ­ ward.Mos tflie swer etrappe di nth eafternoon .Th edail ycatc hwa sstrongl yrelate dt o

48 themaximu m temperature,bu t only slightlydependen t onth ewin d direction. Eggs fromcapture dwil d femaleswer eobtaine db ykeepin gthe mfo rsom etim e alive inth e laboratory.Thi s laboriousmetho d oftengive s only little information.N oeffi ­ cienteg gtra pha sbee ndevelope dyet . Datao nsamplin gmethod suse d forflies ,eggs ,larva ean ddamag ear ementioned . For thesamplin g ofpupae ,th edistributio no fpupa e inth esoi lunde r attacked anionswa s examined.Th ehorizonta l distributionconforme d toa norma ldistribution ,th eaverag e depth was clearlydependen to nth e soil type.Th e fractions ofth enumber s ofpupae ,obtaine d with sampling coreso f5 o r 20c m 0; areestimate d asa functio no fth edamag e level.Ex ­ tractionwa sdon eb y flotationan dsubsequen t sieving,wit ha nestimate drecover y ofove r 954.. Themethod s forkillin g andsexin g theflies ,an do f inspection fordy emark ,mate d status offemale s andovar ydevelopment ,ar e described. Flybehaviou r inonio nfield swa s recorded.Th eobserve d flightdirection swer ein ­ dependent ofth epositio no fth eobserver .

49 4 Onion fly ecology

Inthi schapte ra tfirs tth edat aar ereporte do nth eonio nfly' slif ecycl ean d niche.Onl ysom easpect slik eth epredictio no femergenc ean dth eimpac to fEntomophthor a infectionar ediscusse di nsom edetail .Th eothe raspect stha twer econsidere donl ysuper ­ ficiallyar ereporte dnevertheless ,a sthe yma yhel pt oprovid ea bette runderstandin go f theexperiments . Inpes tcontro lb ysteril emales ,th epes tdensitie san dreproductio nfactor snee dt o beestimated .A swil lb eshown ,th elo wdensitie so fdamag ean dpupa ean dthei rhig hde ­ greeo faggregatio ncaus eproblem si nth edeterminatio no fth econfidenc einterval so fpo ­ pulationdensit yestimates . Thefecundit yo fth eflie si sestimate dfro mthei rsurviva lan dth efrequenc yo fdepo ­ sitiono feg gbatches .Reproductio ndata ,obtaine d fromsteril emal efiel dexperiments , arecompared .

4.1 LIFECYCL E

4.1.1 Prediction of emergence

Prediction from temperature records Thepossibilitie sfo rpredictin gth eemergenc eo f wildpopulation sfro msoi ltemperatures ,fo rus ei nsteril emal eprogrammes ,wer eanalysed . Thepupa ewer edistribute devenl ythroughou tth eto p2 5c mo fth esoi l (Section3.3.2.1) . Temperatureswer erecorde dfro mth estandar ddept ho f1 0c monly ,measure dbetwee nth ede ­ pots.Becaus ea temperatur esu m (accumulateddaydegree sabov ea certai nthreshold )neede d byth epupa ei sreache dlate ra tgreate rdepth ,th e1 0c mrecord sshoul dpredic toptimall y thepoin to fabou t40 1emergence . Laboratoryexperiment sb yTichele r (1975)indicate dtha tth etemperatur ethreshol dt o beassume dfo rpupa ldevelopmen tcoul dbes tb eplace da t6 C .Houwin g (1973)ha destimate d thisthreshol dt ob e9°C ,bu thi sdat adi dno texclud eth epossibilit yo flowe rvalues . Eckenrodee tal .(1975b )foun d4.5° Ca sdevelopmenta lthreshold ,Missonnie r& Boull e (1964) mentioned5 C . Fig.3 0give sth eemergenc ecurve sversu sth etemperatur esum .A sa referenc elabora ­ torydat aar eals ogiven .Thes ediffe rfro mth efiel ddat abecaus eal lpupa ewer ekep ta t thesam econstan ttemperatur ewhic hwa srathe rhigh ,compare dwit hth efiel dsituation . Therei sconsiderabl edifferenc ebetwee nth evariou sset so ffiel ddata .Thes edifference s canoriginat efro mvariatio ni non eo rmor eo fth efollowin gfactors :distributio no f viablepupa ethroughou tth esoil ,especiall y inth eto player ;soi lstructur ean dsurfac e reflection;amoun to fdirec tsunshin ean do fhumidity ;and ,a sth etemperature sha dt ob e measuredoutsid eth edepots ,th eduratio no fth epresenc eo fth edepo ttrap sbefor eemer -

50 >in%

500 550 température«u m Fig. 30.Onio nfl yemergenc efro mdiapausin gpupae ,plotte dagains t thetemperatur e sum, forfiel ddat aa smeasure d at 10c mdepth . -- - Fiel ddata ,Overflakke ean d theSchuilenburg , 1973an d 1974; laboratorydat aa t 20C (Noorlander,pers .commun.) . gence started.Moreove ri nth eSchuilenbur g experiments thepupa ewer emixe d throughth e upper1 5c monly . Forgeneti c controlmeasure s onewoul d liket oadjus tth ereleas e schedulea smuc ha s possiblet oth eemergenc eo fth ewil d flies.Th e firstpoin tt ob econsidere di swhe nt o startwit hreleases .Fo r thisth edat eo f5 1emergenc e frombar e soilwa staken .No wle t us assume thatb yrecordin g temperatures insidedepot san dtakin gothe rprecautions , the temperature sumneede d for S%emergenc ei sfixe dwit h reasonable accuracya t15 0dayde - grees.I tca nno wb edetermine dwhethe ra predictio nbase do nthi swoul db euseful .A pre ­ dictionneed st ob emad ea tleas t1 0day si nadvance ,becaus eo fth e timeneede d between taking thepupa e fromth estorag ean dth eemergenc eo fth e flies.Th e 5%emergenc ewil l occur somewherebetwee n2 0Apri lan d2 0May ,an dpredictio n should resulti na narrowe r range. Eckenrodee tal . (1975b)use dai rtemperatur e sumst opredic tth estar tan dmedia no f thefirs tflight ,bu tthei rdat ad ono tprovid e convincing evidence thatthi s prediction ismor e accurate thanwhe naverag e datei sused . Inth efollowin g calculations temperature records from1 0c mdept hwer eused .Tempe ­ rature datafro m lesserdepth swoul dhav eyielde da bette r 5%emergenc e estimate,bu to n theothe rhan d theaccurac yo fsuc hmeasurement s diminishesdu et oth esteepe r temperature gradients. Fig.3 1give s thedat aan ddaydegree s 10day sbefor e 150daydegree swa s reached. The lower 95%probabilit y limiti sgive nb yassumin gtha tth edeviation s fromth ecalcu ­ latedregressio n linear e independento fth edate .Fro mth e temperature recordsi tca nb e found thatth e cumulating temperaturesu mcrosse sthi s line 13+3day sbefor ei treache s 150daydegrees .Actually ,als oafte ryear so fdat acollection ,th einaccurac yo fth etem ­ peraturesu mrequire dwil l remainnoticeable .Th eassumptio ntha tth etemperatur esu mi s knownt ob ewithi na rang eo f ndaydegrees ,cause s thepossibl edeviatio no fth epredic ­ tedfro mth eactua l 5%dat et oincreas eb yn/ 3days ,a sca nb eestimate d fromth eaccumu -

51 45 50 days after 31 March Fig.31 .Dat ean d temperaturesu m 10day sbefor eth e temperaturesu mo f 150daydegree si s reached.Calculate d fromdat afro m 10c mdepth ,Nieuw eTong e (Overflakkee),fro mKNMI . Regressionline : y =-0.75 x+ 111.8;- - - 95 %one-side d lowerconfidenc elimit .

lationo fdaydegree si nth erelevan tperiod . Otherpoint so fth eemergenc ecurv eca nb epredicte di nth esam eway .However ,becaus e ofth eincreasin ginfluenc eo fth evegetatio nsuc hestimate swil lb eles srepresentativ e forth eactua lsituation . Tichelere tal .(1975) ,considerin gth epupa ldevelopmen tafte rdiapaus eversu stem ­ peraturei ndetail ,fo rinstance ,usin ga sligh ttemperatur eshock ,foun da complicate d reactionpattern .Thu sa simpl epredictio nmetho dwit htemperatur esum sma yb eimpossible .

Prediction from phenological parallels Anotherpredictio npossibilit yi sth eus eo f phenologicalparallel s (Section 2.2).Amon gth edat aavailabl e (Fisscher,1964 )th elea f buddingo fth eoak ,Quercu srobu rL. ,seeme dt ob eth emos tappropriat ebecaus eo fit s timeo foccurrenc ean dth ecommonnes so fth especies .I tbud so nth eaverag eo n2 May , with95 1confidenc elimit so f1 7Apri lan d 17Ma y (calculated fromFisscher ,1964) .Th e 5'oemergenc edat afo rth eonio nfl yoccurre do nth eaverag esom e1 2day slate r (Table 9).

Table9 .Experimenta ldat ao nth etim eo f5 %emergenc eo fonio nflie s inspring . Independent evidencei savailabl etha tth eemergenc efro m thedepo twa slate r (Mijs1.974 ) and earlier (Schuilenburg 1974)tha ntha to f thewil dpopulation .

5%Emergenc e Daysafte roa k TemperaturTem esu mwhe n5 % fromdepo t leafbuddin g had emerged fromdepo t deWi t197 3 24Ma y 12 154 Mijs197 4 6Ma y 21 199 Schuilenburg 1973 11Ma y 13 98 Schuilenburg 1974 17Apri l 2 148

52 The choiceo fmor erepresentativ e reference oaksan damor erepresentativ e depot location mayconfin eth econfidenc e intervalo fth enumbe ro fday sbetwee n leafbuddin gan dfl y emergencet oa usefu l length.Als o careshoul db etake ntha tth eoa klea fbuddin gi sob ­ serveda sa certai npercentage-point ,becaus e firstobservation so fa neven ti na popula ­ tiono funknow nsiz ear eno tver yuseful . Becauseo fth e limitednumbe ro ftrees ,thei rmicroclimat ewhic hi sdifferen t from thato farabl e land,an dth e agedependenc yo fthei rphenologica l events (Nienstaedt, 1974),i twoul db eusefu lt oloo kfo r common annualswit ha simila r averagedat efo r phenological parallels.Suc hplant s shouldenabl ea neve nbette rprediction . Fliesrelease d 'tooearly ' areno tuseles sbecaus eth eemergenc eo fth ewil d flies willhav e already started.Th e 2%emergenc e date lies1- 4day sbefor eth e5% date . Thenee do fth e firstrelease st ocoincid ewit h thefirs temergenc e ofwil d flies shouldno tb eoverstressed .I ti sno ta questio no f'startin g thesteril emal eprogramm e at lowdensities' ,whic hi ssensibl e onlyi fthes edensitie s refer towhol epopulations . Thepoin ther ei swhic hpar to fth epopulatio nma yb emisse dwithou tharmin gth e effect ofth ereleases .Becaus edu et oth elowe rtemperature s anearlie r starto fth e emergence willb efollowe db ya les sfas temergenc ecurv ean dbecaus e theearl yemerge d flieswil l developmor e slowly,a wee k delaywil lhardl y everhav ea discernabl e effect.

4.1.2 Flight curves

Flight curvesfo rth evariou syear san dlocation s aregive ni nFig . 32. The 1970-1972dat arefe rt owil d flies capturedo nnormall y treated onionfield so n sandy clay,excep tfo rth eserie so fGoere e 1972tha ti sfro ma nuntreate d experimental ploto nsand ysoi lan dsom eadjacen tuntreate d shallot fields,an dfo rth elas tpar to f the 1971 graph,whic hi sfro mth eonl y commercially grownonio nfiel do nth e island that receivedn ochemica l treatment against theonio n fly.Th edat ao f197 3originat e from threeuntreate d plots.Th eplo tMij swa s somewhat isolated from 1972onio nfields , whereas theothe rtw oplot sla yadjacen tt osuc honio nfl ysources .Als o indicatedar e thefertil e fliesrelease do nth eplo tMi js durin g the firstflight ,becaus e theycon ­ tributedt oth esecon d flightpopulation .Th e197 4dat a aregive nseparately ,fo rdif ­ ferentonio nfield swhic hha ddifferen t onionfl ycontro lan ddifferen tdegree so f isolation.Al lthes e fieldswer ei nth esam eare a (Fig. 15). Fordetail sabou tthi s experiment seeSectio n6.2 .Th ecatches ,expecte dwhe nparathio nwa sno tspraye do nsom e ofthes efields ,ar eindicated . Differencesbetwee nth ecurve sar epartl y attributablet ocontro lmeasure s anddegre e of isolation fromonio nfl ysources .Lac ko fcontro lo nlighte r soils (Fig.32 ,d ,g ) causeda considerabl epopulatio ni nsummer ,wherea so nheavie r soils (Fig.32 ,c ,e ,f ) thereha sbee n littleeffect .A highe rdegre eo fisolatio nresulte di na slowe rbuildu p of thepopulatio ni nsprin g (Fig.32 ,g ,j) .Th e remaining differenceshav et ob eascribe d toth eweathe r circumstances (especially theshort-ter m changesi nth e catches)an dt o thepopulatio n level.Th elatte rma yb ehighe ri narea swit hmor eextensiv e oniongrowing , i.e. Fig.32 ,a ,b (1st flight). Thepopulatio n decrease thatresulte d fromth esuccessiv e sterilemal etreatment s done

53 flies

î ¥

20n flies 1 % O+O+ 15- iA^ 10- b 5- ^^v eggs

emergence

05 06 07 08 09 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 20 30 10 20 30 10 20 30 10 20 30 10 20 30 10

flies flies

? ¥

flies ? ? .^^WV^i^yyAv^, flies eggs ^A. -k.

emergence flies

-\HAA\VV~

04 05 06 07 OB 00 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 10 20 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 10 month day Fig.32 .Fligh tcurv edat a indifferen t sitesan dyears . flies:Fligh tcurve s inflie spe rtra ppe rday ;%oo :percentag efemale spe r 100flie s captured;emergence :emergenc e insumme ro fa representativ e sampleo fpupae ;eggs : eggspe rm onio nrow . a. 1970,Overflakke e(va nLoon) ; b. 1971,Overflakke e(Pollemans) ; c. 1972,Overflakke e (Buijs, Vroegindewei); d. 1972,Goeree ; e.1973 ,Overflakke e (de Wit); f. 1973,Overflakke e (vanEs) ; g. 1973,Overflakke e (Mijs;- - - 1s tfligh trelease d fertiles); h. 1974,Overflakke e (Mijs,contro l field); i.1974 ,Overflakke e(Mijs ,tria lfield) ; j. 1974,Overflakke e (Mijs,fiel d 5,chemicall y controlled andrelativel y isolated); k. 1974,Overflakke e (Mijs,field s 1,2an d3 ,chemicall ycontrolled) ; flies

s$> I ty f. f At /ï l" ft »f * Î'wi j • / »V» i&5_^ * ¥**» V

flies

y^A^^^vAeL 1.1971 ,Schuilenbur g (onlyfemales) ; i—i—i—i—i—i—i—i—i—i—i—i—i—«—«—i—i m. 1972,Schuilenbur g (x= onl yfemales) ; 04 05 0» 07 00 09 102030103030 » 20 30 » 20 30 10 30 30 W30 n.1973 ,Schuilenburg ; month o. 1974,Schuilenburg . day atth eSchuilenburg ,i sals oclea rfro mth etrappin gdat a (Fig.32 ,1 ,m ,n , o). Therelatio nwit hth eweathe r (Fig.16 )i sclear .Th eeffec to fth edail ymaximu m temperaturean do fattractio nwer eeliminate d fromth edat ao fMij s 1974.Th eincidentall y negativevalue swer edu et ocorrection s thatha dt ob eapplie d (Section6.2.2) .

4.1.S Incidence of diapause

Theinductio no fdiapaus eha sbee nstudie db yKelderma n (1972)an dRamaker s (1973). Itwa sfoun dt ob estrongl yag e dependent:shor tdaylengt hinduce ddiapaus ei nth ethir d larval instar,an dlo wtemperature s induceddiapaus ei nth efirs tday so fpupa ldevelop ­ ment (Fig. 33). Thecombine deffec to ftemperatur ean ddaylengt ho ndiapaus e inductioni sshow ni n Fig.34 ;th edat ao fMcLeo d (1965)ar ei nreasonabl ygoo dagreemen twit h this.Th ecurve s areo fth enorma l typefo rlong-da yspecie s (Danilevskii,1965) .Th eestimate d courses ofth epercentag ediapaus einduce da tdifferen ttemperature sversu sdaylengt hsugges ta strongselectio npressur ei nfavou ro fa lo wpercentag ediapaus ea tlonge rdaylengths, providedth etemperatur ei sa tleas t 18°C,an da hig hpercentag ediapaus ewit h shorter daylengthseve nwit hhig htemperatures .Th eadaptiv evalu eo fthi si sclear .Th efirs t generationwil lb esusceptibl et odiapaus e inductionver ymuc hdependen to nsoi ltempe ­ rature,yieldin ga nincomplet esecon dfligh twhe nsoi ltemperature sar e relativelylow . This susceptibilitywil lb epartl ybalance db ya late rfirs tfligh twit hlo wsoi ltempera ­ turesi nspring .Th esecon dgeneratio nwil lg oint odiapaus emainl ydependen to ndaylength ,

55 diaoause in % 00ï —7^1 >---___ ,,-'-"">'- * «

80- /'' t 60- 1 \ 1 i i a 40- 1 i !> f 1 20- LI l- L3 --"'p L2 | \ _ 0- 1 i

?""•"-!— - /•'" A 0 '1 1 ! f 1 1 1 /b 1 1 1 1 1 | 1 ƒ ,** LI 1 L. ! L3 .,--/' p *-—-""x 1 1 i i 1 v i i % age in days

Fig. 33.Developmenta l stages sensitive todiapaus e induction. Age inday s at 18 C. L1,L2,L3: larval instars,P:pupa l stage;— — transition between larval instars; — - - — pupation. a. Effect of photoperiod on diapause, expressed as the percentage diapause induced when the photoperiod is changed atdifferen t moments in the larval and pupal development (Ramakers, 1973). x = Short day (10 h light per 24 h) changed to long day (continuous light); 0= long day changed to short day. b. Effect of temperature on diapause, expressed as the percentage diapause induced when the temperature is changed at different moments in the larval and pupal development (Kelderman, 1972).x = Cold (12°C) changed to warm (18°C); 0= warm changed to cold.

diapause in% 100-

80

0 4 8 12 16 20 24 hours photoperiod Fig. 34.Diapaus e induction as a function of temperature and photoperiod, photoperiod expressed as hours light per 24 hours (Ramakers, 1973).

56 soa war mautum nwil lno tcaus eman yflie st oemerg ewhe nth echanc eo freproductio ni s small. Tochec kwhethe rthes elaborator ydat aca nb eextrapolate dt oth efield ,on eha st o knowa twha ttim eth estage ssensitiv efo rinductio nar epresent ,an dt owha tdaylengt h andtemperatur e theyar eexposed . InFig .3 7i ti sindicate dtha tpupatio nmainl yoccur si nth eperiod s 10Jun e- 30July ,1 0Aug .- 1 0Oct. ,fo rth etw ogeneration srespectively .Th elarva epas sdow n throughth esoi lt o5- 8c mdee p (insand yclay )an dpupat ethere .Thu sus eo fth esoi l temperaturedat afo r6. 5c mdept hwoul db eoptima lfo rcorrelatio nwit hth elaborator y data.Temperatur emeasurement sar eavailabl e fordepth so f5 an d1 0cm .B yinterpolatio n inFig .3 4th eexpecte dpercentage so fdiapausin gpupa ewer eestimate dfo r theaverag e soiltemperature spe rdecade .Fig .3 5give sthes eexpecte dpercentage sdiapaus eversu s time,fo rdifferen tdaylengths . Iti sno t knownwha tdaylengt hi seffective .Instea dth elengt ho fth edar kperio d may inducediapause ,a sal llaborator yexperiment swer edon ewit ha 2 4hou rcycle . The photoperiodi seffectiv eo naverag eabou ta wee kearlie rtha nth etemperature ,an do n larvaetha tar egenerall yfoun d insideonions .Th ephotoperio d cannotb eeffectiv ethroug h changesi nth eonion sbecaus ei ti sals oeffectiv eo nlarva elivin gi na nartificia lmediu m inth elaboratory .Th elarva ema yperceiv eth eligh tdirectl ythroug hth eonion ,durin g visitst oth eoutsid eo fth ebulb ,an ddurin gmigratio nt oothe ronions .Th elatte roccur s too infrequentlyt oprovid esufficien t information,especiall yi nth esecon dgeneratio n larvaewhe ndaylengt hi sth ecrucia lfactor . Infrequentpresenc eo fth elarva enea rth ebulb' soutsid ewil lten dt oresul ti n

diapause in% 100-1 f»""0-

80

60

40-

20-

~t~ -r -r—i 1 r -T" 05 06 07 08 09 10 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 data of pupation

Fig.35 .Expecte d percentagediapaus efro m soiltemperatur ea t5 c mdept han dfo r different photoperiods,Overflakke e1962-1972 . • =astronomica ldaylength ,averag evalues ; X» astronomical'daylengt hminu s 1hour , averagevalues ; O• astronomica ldaylengt hminu s2 hours ,averag evalue san drang e (shaded). Expected averagean drang eo fpercentag ediapaus epe rflight :1s tfligh t 2ndfligh t astronomicaldaylengt h 10( 1-32 ) 75(61-93 ) astronomicaldaylengt hminu s 1hou r 16( 3-42 ) 86(78-95 ) astronomicaldaylengt hminu s 2hour s 27 (10-55) 94(90-99 )

57 Table 10.Percentage so fpupa ediapausin g inth efield .

1st g eneration 2nd generation

Schuilenburg 1973 8 83 Schuilenburg 1974 18 87 de Wit 1973 19 van Es 1973 23 . Mijs 1973 29 85 Mijs 1974 (control) 25 78 Mijs 1974 (experiment) 0 weighted average 21. 9 84.6

shorterligh tperiod stha nth egenerall ybiologicall yeffectiv edaylength ,whic hi sth e astronomicaldaylengt h (sunrise-sunset)plu shal fa nhou ri nmornin gan devenin g (Danilevskii,1965) . Diapausepercentage si nrepresentativ esample sar eavailabl efo rsom eyears ,a sgive n inTabl e 10.A sshow ni nth enex tsection ,a 3r dfligh tma yoccu ri nSeptembe ri fth e 2ndfligh twa sno tto olate .Pupatio nafte rAugus tgive s100 1diapause .Thes edat asug ­ gesttha tth esoi ltemperature sa t5 c mdepth ,togethe rwit ha photoperio dwit hth eligh t period1- 2hour sshorte rtha nth eastronomica ldaylengt har eprobabl yth emos trelevan t factorsfo rth einductio no fdiapaus eunde rfiel dconditions .Thi sha st ob eteste di n futureexperiments ,includin gmor edetaile d laboratorytest so ndiapaus einductio ni nth e relevanttemperature-photoperio dspace .

4.1.4 Number of flights

Forestimatio no fth enumbe ro fflights ,firs tth eduratio no fa generatio nneed st o beestimated .Th ese to fdat amos tappropriat efo rthi sar eth e Znlabelle drecapture s inth esteril emal eexperimen to nth eSchuilenbur g in1971 .I nwinte rlabelle dpupa eha d beendu gint oth esoil .The yemerge di nth esam eperio da sth e 1stfligh twil dflies .Th e offspringo f Znlabelle dfemale si sslightl y labelledan dca nb eidentifie db yautora ­ diography.B yscreenin gth erecapture sfo rlabellin gth erecaptur ecurve sfo rth eflight s werefoun dt ob eabou t5 0day sapart .Becaus eMa y 1971wa srelativel ywarm ,th eperio d betweenth e1s tan dth e2n dfligh twil lgenerall yb esomewha tlonger .Temperature si n Julyan dAugus tar ehigher ,s obetwee nth e2n dan d3r dfligh tther ema yb eles stim ei f the2n dfligh toccur sbefor eAugust .Th elate ri nth eyea ra fligh toccurs ,th emor ei t willb eth eoffsprin go fonl yth efirs tpar to fth eprecedin gflight ,becaus eth epercent ­ ageo fdiapausin gpupa eincrease swit htime .Consequently ,th e3r dfligh tcome searlie r thanexpecte dfro mth etota lo fth e2n dflight . Additionalinformatio no nth eoccurrenc eo fa 2n do r3r dfligh ti sgive nb yth eemer ­ gencedat a (Fig.32 ,d ,g )an dth eeg gdepositio ndat a (Fig.32 ,d).Bot hi n197 3an d197 4 thesamplin go fpupa ea tharves tindicate dtha tther ewa sa smal l3r dflight . Anotherindicatio no nth edelimitatio no fth eflight s isgive nb yth epercentag eo f females (Fig.32) .Fig .3 6show stha tthi spercentag e inth erecapture schange swit hag e becauseth efemal eflie sliv elonger .Roughl yi tca nb esai dtha tth epercentag eo ffe -

58 percentage of females 100

uu- b „<" o )/

50- o o s o • .v°*<"

1 1 1 1

c /° <*£ 50- , /> o '#, o

1 1 1 1 I <) 10 20 30 40 20 30 40 > inday s Fig. 36. Percentage females in recaptures versus age, for different release-recapture experiments. 0= 100 flies, • = 25 flies. Experiments: a. van Loon 1970-2; b. Pollemans 1971; c. Vroegindewei 1972-2; d. Mijs 1973-1; e. Mijs 1974-1 ( 0 = 5 or more flies per trap per km sheltered edge of onion field); f. Mijs 1974-2 ( O as in e.). malesi slinearil ycorrelate dwit hage .Extrapolatin g this correlationt owil dpopulations , thespee do fchang eo fth ese xrati oi sa measur eo fth edifferenc ebetwee n thebirt h anddeat hrate .A decreas eo fth epercentag eo ffemale s indicatesa highe rbirt hrate , anincreas e occursa thighe rdeat hrates . Withthes edat aan dthos egive ni nth eprecedin g sectionsth eflight sca nb eassume d tohav ebee na sindicate di nFig . 37.

4.2 NICHE

4.2.1 Oviposition site

Asmentione di nSectio n 2.3.1,ther ear esevera lwil dhos tplant stha tar epossibl e oviposition siteso fth eonio n fly.Alliu mvineal ei sb yfa rth emos t commonspecie si n theNetherlands ,s oit sprobabl e rolefo r supportingwil dpopulation swa s investigated, asthi smigh tresul ti na lac ko fisolatio nbetwee nonio n flypopulations . Someattentio nt oth erol eo fA .vineal e couldb epai d during theexperimen tMij s 1973.Thi sexperimen twa sdon emainl yo nan daroun da smal l0. 1h aonio nfield ,wit ha

59 relative fly density I- 1970

n- A A A A A M

~l 1 1—ST—ST 1 ' ! 1 1 1 1 1 1 1 1 _ 1971

—i— „u/MMlAVM»*.— t972 I- AAAAAA eee E- m-

e 1973

* A A A A nr- __«„.

n 1 1 1 1 1 1 1 1 1 1 1 r-

main damage

e e e e I- A A A A e e e e e

X- AAA A A m- A 1st aen. pupation ~ ^ 2nd gen. pupation i i i i i i i r i 1 111 i i 30 10 20 30 10 20 30 10 20 30 10 20 30 10 20 30 day

Fig. 37.Estimate d occurrence of flights, 1970-1974 and average. I,II and III:flights ; e: oviposition;A : emergence; - - - supposed flight occurrence. highconcentratio no ffertil eflie spresen t (Fig.32 ,g) .Abou t 100m fromthi sfield , andabou t1 0m fro ma releas esit eo ffertil eflies ,ther ewer eroa dverge swit ha vege ­ tationlocall ydominated ,eve ni nsummer ,b yA .vineale .Tra pcatche sther efaile dt o showan yaccumulatio no fth eflies .Moreove rn oinfestatio ncoul db efound . Wolff (1973)di dsom eexperiment so nth erol eo fA .vineale .I nth elaborator y femaleonio nflie swoul dla ythei regg so nthi sspecies ,bu tth elarva efaile dt ope ­ netrateint oth ebulb sunles sthes ewer ecut .Obviousl yth ehar dski no fth ebulb s preventsattac kb yonio nfl ylarvae .I nth efiel di nth esurrounding so fWageninge nh e couldno tfin dinfestatio no fA .vineale ,no rpupa ei nth esoi laroun dbulbs . Theexac tplace so fovipositio nca nb einferre dfro meg gsearchin gdata ,althoug h suchresult sar eaffecte db yth einfluenc eo fth esit eo nth eprobabilit yo fth eegg s

60 being foundb yresearc hworker san dothe rpredators .Egg swer e foundgenerall yi nth e leaf-axilsó fth elowe r leafs,an dwit hyoun gseedling smainl yo no ri nth egroun d close toth eplant . Ovipositing flies stronglyprefe r rotteno rdamage d onionst onorma lone s (Section 2.2.3).I na fiel dwit habou t 7%rottin gonion s 98.4%o fth eegg swer e laido nthes e (Roest,pers .commun.) ,th edifferenc ei neg gdensit ybetwee nrottin gan dnorma l onions beinga facto r 800.I tseem sver yprobabl e thatth eincreas ei nonio nfl ydamag e among onions injured,fo rinstance ,b yweedin go rtracto rwheel si sa tleas tt osom e extent duet oeg gdepositio npreference .Th eothe rprobabl e causei sincrease d survival among newly emerged larvae Itwa sinvestigate dt owha texten tresidu eonion s tippedo nwast egroun dwer e onion flysources .Especiall yo nth esmalle ro rles sofficia l rubbishdumps , irregularly sprayedwit hdifferen tpesticide so rno ta lall ,heap so frottin gonion smigh t contain highpopulatio n densities.Th ecatche so ftw o trapsplace da tsuc hsite swer e compared withdat afro mtrap s aroundonio nfield sadjacen tt oonio nfield sth eyea rbefor e (Fig. 38).Th edensitie swer e similar,bu tth ewast earea swer ever y small comparedwit h onion fields.Th elowe rpercentag eo ffemale snea rth ewast eonion s indicates thatthes ear e notpreferre dfo roviposition .Thu s oniontippin g sitesar eunimportan ti nth epopulatio n dynamicso fth eonio nfly .I nth eUnite d States tippedonion sar eoccasionall y saidt ob e themos t importantonio nfl ysource si nsprin g (Anonymous, 1933),bu tMerril l& Hutso n (1953)state d thatonio nflie sdi dno tbree di nolde rcul lpiles .Som eothe r Diptera relatedt orottin gonion s showeda highe rconcentratio no nthes esite s (Fig. 38).

fli« « partra p per day 10- Dalia antiqua

8-

6

4'

2

0

4 Eumarus »trigatua

2-

,-. «. ..-L,. 0 k. •cVmA

4- Lonchaaa chorea 2- M^A^ . . 0

4 Ortalia urticaa

2 A A A .", 0 ;/VAA ^ ,—/\/\ -^T- -i r- s a s 05 r H—06 i V f 07 i•' T f 0i8 ' V 'i 09 10 20 30 10 20 30 10 20 30 1002 0 30 10 20 30da y

Fig. 38.Catche s at onion tipping sites compared with catches on onion fields, in fli per trap per day for different species.Experiment s van Es and deWi t 1973. onion fields (18 traps); tipping sites (2 traps).

61 4.2.2 Larval and adult food

Theonio nfl ylarva ema yea tfro mfres honio nbul btissue ,bu tgenerall yth eattacke d onionsputrify .Als olarva ear eregularl yfoun d inonion stha thav ebee nattacke db yonio n stemeelworm . Duringth efirs tfligh tespecially ,onion swit honl ylarva eo fDeli aplatur awer e foundsevera ltimes .O fcours ei ti sno tcertai nwhethe ran yonio nfl ylarv aha dbee n presentbefor eo rnot .T odetermin ewhethe rD .platur ashoul db etreate da sa primar y ora secondar ypest ,th epopulatio ndensitie so fbot hDeli aspecie swer ecompare do n thefield ssampled .I fD .platur ai sa neffectiv eprimar ypes tit snumber swil lb ere ­ lativelyhig hwhe nD .antiqu ai sselectivel yeliminate db ygeneti ccontrol .Suc ha phe ­ nomenonwa sobserve dwit htortricid si nth egeneti ccontro lo fth esumme rfrui ttortrix , Adoxophyesoran aF.R . (Ankersmit,1975) .Fig .3 9show stha tth enumber so fD .platur a diminishedeve nmore .Not etha tth ehighes tpoin ti nth egrap hi sfro mth esam elocatio n theyea rbefore ,wherea sth enex thighes tpoin ti sfro mth esam eyea rbu tfro mth econ ­ trolfiel da tnearl y2 k mdistance .Thi sreductio ni nnumber sdoe sno timpl ytha t D.platur acanno tb ea primar yattacke ro fonions ,bu ti tshow stha tit spopulatio n buildupi sdependen to nsom efactor(s )associate dwit hD .antiqua .Effectivel yD .platur a isa secondar ypes to fonions .Becaus eo fth eovipositio npreference so fD .platur a (Section2.2.3 )an dth efac ttha tal lonio nsee di streate dwit ha fungicide ,th eobser ­ vedsituatio nma yno thol dfo runtreate dseed . Possibleprimar yattackers ,althoug ho nuntreate dfield sstil lquantitativel yunim ­ portant,ar ecutwor mlarva e (Lepidoptera:Noctuidae )an dwireworm s(Coleoptera : Elateridae).Damag edu et othes especie si srare . Rottenonions ,especiall yi nsumme rwhe nthe yhav ea reasonabl esize ,ofte ncontai n severalothe rinsec tspecie s (Table 11).

D. platura 600-

500-

400-

300-

200-

100 Fig. 39.Population s of Delia antiqua and D. platura, in thousands of pupae formed per ha per year. 0 100 200 300 400 500 600 • " untreated field; O= onion fly under D. antiqua genetic control.

62 Table 11.Dipter aan dColeopter a found inonio nbulb sattacke db yonio nlarvae .

Stage frequency Stage3 frequency*

DIPTERA: COLEOPTERA: Syrphidae Curculionidae Eumerus strigatus Fall. Ceuthorrhynchus Lonchaeidae suturalisF . 1 + Lonchaeachore a (Fabr.) Nitidulidae Muscidae Glischrochilus Fanniacaniculari sL . quadripustulatus a ++ Muscinaassimili sFall . Staphylinidae Cordiluridae Dinaraeaangustul aGyll . i, a +++ Cnemopogonapicali sWied . Athetafung iGrav . a + Otiididae Oxytelusrugosu sF . 1, a +++ Ortalisurtica e Aleocharabilineat aGyl l .a ++ Chloropidae Trogophloeuscorticinu s Elachipteracornut aFall . Grav. a + Sarcophagidae Catopidae Sarcophagacarnari aL . Ptomophagusmédiu sRe y a + Anthomyiidae Lathridiidae Deliaplatur a(Meig. ) Lathridiuslardariu sDe g .a + Deliapullul a (Zett.) Elateridae Fegomyiasp . Corymbitessp .o r Athoussp . 1 ++ a.1 = larva ,p = pupa ,a = adult . b.+++• common ,+ += regular ,+ = incidental .

Observationso nfeedin go fadult sar ever y incidental.The ywer e seenfeedin go n flowerso fTaraxacu mvulgare ,Alliu mcepa ,Euphorbi apeplu san dE .helioscopis .O n severaloccasion sn ofeedin g onionflie s couldb efoun do nan yo fth eflower si nth e neighbourhoodo fa nonio nfiel d althoughman y flieswer e seeni nth efield . Grasses wereno tchecked ,bu tthes ema yb eimportan t foodsource s (Section 2.2.3).Ther ear ese ­ veralobservation so fmainl y females,als oa tlo wonio nfl ydensities ,eatin go rdrinkin g frombir dexcrement s andsometime sals ofro mrotte nonions .Once ,insid ea trap ,a nonio n fly femalewa sSee nt ofee do nth epolle ncarrie db ya bumbl ebee .

4.2.3 Parasitoids

Someparasitoid swer ereare d frompupae .Th especie sobserve d areAleochar a bilineata (Gyll.) (Coleoptera:Staphilinidae) ,Aphaeret aminut a (Nées) (Hymenoptera: Braconidae)an dPhygadeuo nsp . (Hymenoptera: Ichneumonidae).Aphaeret aminut aan dth e CynipidTrybliograph adiaphan a (Hartig)wer ereare d fromD .platura . Parasitoids emerged only frompupa e fromth e lastpupa l samplingsi na year , August-September.Thei r frequenciesar egive ni nTabl e 12.Aphaeret aminut aemerge dwit h 5-12wasp spe rpupa ,o naverag e 8.Th efrequenc yo fAleochar aan dPhygadeuo nma yhav e beenunderestimate d becausethe yparasitiz eo npupae ,an dthes ewer esample dbefor e this stageended . The lowerdegre eo fparasitis mi nth eonio ngrowin g area (datafro mOverflakke ea s comparedwit h thoseo fth eSchuilenburg )ma yb edu et oth emor e intensivechemica l control

63 Table12 .Frequencie so fparasitoids .

Percentageo fful lpupa ea tharves twith : Totalnumbe ro f parasitized pupae Aleochara Phygadeuon Aphaereta total bilineata sp. minuta

Schuilenburg 1970 10 11 0 21 19 Schuilenburg 1971 S3 <19 0 22 7 Schuilenburg 1972 0 20 0 20 13 NieuweTong e 1971 0 0 16 16 13 vanE s197 3 0 1 1 2 2 deWi t197 3 0 0 2 2 2 Mijs197 3 0.6 1.2 1.4 3.2 16 Mijs197 4 >0 3 >A 7 6

there.I nth ecabbag eroo tfl ysuc hcontro li sknow nt odiminis hparasitizatio nconsider ­ ably (e.g.Coaker ,1966 )an dthi scoul dappl yt oth eonio nfl ytoo .

4.2.4 Entomophthora

Animportan tparasit eo fth esecon dfligh tflie sespeciall yi sth efungu sEntomophthor a sp.Som edat ao nth eincreas eo fth einfectio ndurin gth eseaso nar egive ni nFig .40 .In ­ fectedflie swit halread yexternall yvisibl esign smov eto oslowl yt oge ttrapped .Visibl y infectedflie swer efoun di nth etraps 'collector sbecaus eth eflie sgenerall ystaye dther e forhal ft oon eday .Afte rhavin gkep tflie sfo ron ewee ki ncage sa tth elaboratory ,th e funguswa sclearl yvisibl eo nman ymor eflie s (Fig.40a) .I nth ecage sn one winfectio n occurstha tresult si nexternall yvisibl esign swithi nthi sweek :th epercentag evisibl y infectedflie sdi dno tris ewit hth enumbe ro fflie spe rcag eincreasin gfro m1 t oove r2 0 (r= -0.31 6wit h n =15 ,dat afro ma perio dwit ha reasonabl econstan tpercentag einfected) . Fliesdie dabou ton eda yafte rth einfectio nha dbecom evisible .Bot hsexes ,includin g

% infected % infected ioon

•V* * V

05 08 07 08 09 11 21 31 10 20 30 10 20 30 19 29 8 18 28 10 20 30 ' 10 20 30 10 20 30 10 20 30 10 20 30 month day Fig.40 .Developmen t ofEntomophthor a infectiondurin g theseason ,expresse d asth e percentageo fflie swhic hha svisibl einfection . a.Schuilenbur g 1972.Female schecke d after onewee k inth elaboratory ,versu sda yo f trapping.Eac hpoin trepresent sa tleas t5 0females . b.Mij s 1974.Flie schecke d oneda yafte rhavin gbee ntrapped ,versu saverag eda yo f emergence.Eac hpoin trepresent s therecapture so fa release d cohorto fsterile s (• ) o r apar to fth ewil d population (x) .

64 Fig. 41.Percentag e fliesvisibl y infected by Entomophthora one day after having been trapped,versu s agewhe n trapped. Experiment Mijs 1974.Averag e of both sexes, second flight steriles. —— Average emergence;-g— 2 experimental data onfungu s infection and estimated average percentage infected; -expecte d fungus infectionwit h a constant infection rate of 6% per day; actual rate of infection, occurring 6day s earlier than indicated on the abscissa.

aberrantmales ,wer eequall y attacked (experimentMij s 1974:16 1infecte d flies,x^ 7= 19.76, n.s.). Thepercentag e fliesvisibl y infectedon eda yafte rhavin gbee n trapped,versu s their age,i sshow ni nFig .41 .Thi spercentage ,whe nth esprea d inemergenc e istake nint oac ­ count,rise s steeply from zeroa ta nag eo f6 day st oabou t 6%a t7 day so fage ,an dde ­ creases afterwards slowly.Th einfectio nwil lhav e started fromemergenc eonwards ,th e fungus taking6 day st odevelo p (Perron& Crête ,196 0:on eweek) .Th einfectio nrat ever ­ susag ewa sthu sabou t6 4durin gth efirs tda yo fadul t life,an ddecrease d thereafter identicallywit hth edecreas ea sshow nb yth egrap hfo rth evisibl y infected percentage offlies ,bu t6 day searlier .A muc hhighe r susceptibility ofver yyoun g fliesdu et osof t chitin,a ssuggeste db yTichele re tal . (1974a)di dno toccur .Th ehighe r infectionrat e ofyounge r fliesma yver ywel lb eascribe dt oth efl ydensity .Accordin gt othes edata , thenumbe ro fflie svisibl y infectedwil lb e18 $o fth etota lnumbe ro finfecte d flies alive. Inth efirs tsteril emal e fieldexperiment ,Schuilenbur g 1971,th esterilit y amongth e eggsdroppe d considerably comparedwit hfl ysterility .Becaus e thisdro pcoincide dwit h the increaseo ffungu s infection,an dbecaus eth eflie sha dbee nrelease dweekl yo nth e samespots ,Tichele r (1973)an dTichele re tal . (1974a)suppose d thatthes erepeate dcon ­ centrationso fsterile swer epreferentiall y attackedb yth efungus ,decreasin g competiti­ veness.Thes e authorssuggeste d thatsuc ha preferenc eha dbee nfound .Th ever yfe w -unpublished- datao nthi ssubjec tdi dno tsuppor t thishypothesi s (June 1971:7 5sterile s checked,expecte d fromtota lcatch :6 infected ,observed : 5infected) .Moreover ,i ti sno t clearho wth efungu s infectioncoul dexplai nth eobserve dphenomenon .Th esterilit ywa s assessed fromth eovar ydevelopmen t inth efemale s thatha dbee nkep ti nth elaborator y foron eweek .Th efemale swit hvisibl e fungus attack couldn olonge rb echecke dfo rste ­ rility,becaus eth eovariole sha dalread ycompletel y disintegrated. Ifth efungu swa s thecaus eo fa lowe rcompetitivenes s ofth emales ,i tha st ob eassume d thatth efractio n

65 ofsteril emale stha twer emad eineffectiv ewa smuchjiighe rtha nth efractio no fsteril e femaleswhic hha dvisibl efungu sinfectio n8 day safte renterin gth etrap .Fro mth ein ­ fectionrat eversu sag ean dth elac ko fse xdifference ,thi sassumptio nseem st ob eun ­ reasonable.

4.2.5 Predators

Preliminaryexperiment swer edon et oevaluat eth esuitabilit yo fusin gradioactiv e labelst oanalys eth erol eo fpredator so negg san dlarvae ,an dt ofin dth especie sin ­ volved.Feedin gexperiments ,b yconfinemen to findividua lpotentia lpredator swit hsom e Znlabelle degg sfo ron eo rmor eday si nlittl ecages ,hav ebee ndon emainl yb yBut h (1976).Th eresult sar egive ni nTabl e13 . Fromrotte nonion so nwhic hw eha ddeposite d labelledeggs ,severa lpotentia lpre ­ datorswer ecollected .The yma yhav eeate negg so rlarvae ,o rthe yma yb escavengers , havingingeste dth elabe lindirectly .Th eresult so fcheckin gthes epotentia lpredator s forth epresenc eo flabe lb yautoradiograph yar egive ni nTabl e14 . Inth eexperimenta lfield ssom e17 5potentia lpredators ,belongin gt oove r2 0species , werecollected .N olabe lcoul db efoun di nthese ,probabl ybecaus eo fth elimite dnumbe r

Table 13.Result so ffeedin g experimentswit hsingl epotentia lpredator sconfine dwit h Zn-labelledonio nfl y eggs.Mos tdat afro mBut h (1976).

Number of indi­ Number in which viduals used label demonstrated

COLEOPTERA: Staphylinidae:Paederina e 1 1 Carabidae:Trechu squadristriatu s 3 3 Bembidionustulatu m 1 0 Agonumdorsal e 3 2 Asaphidionflavipe s Carabusgranulatu s 1 0 Harpaluspubescen s 7 1 Calathusmelanocephalu s 1 1

ARANEIDA: Micryphanti da e 7 3 Opilionidae 1 0 ACARI: Trombidiidae

Table 14.Presenc eo f 65Zn inpotentia lpredator s (Coleoptera),collecte d fromrotte n onionso nwhic hlabelle d eggsha dbee ndeposited .Experimen tMij s1974 .

Number ofindividual s collected labelled

Staphylinidae:Dinarae aangustul a (larvae) 8 Dinaraeaangustul a (adults) 16 Oxytelus rugosus 14 Elateridae:Corymbite s sp.o rAthou ss p (larvae) 13 Carabidae:Trechu squadristriatu s 1

66 of labelled eggsuse d (7000egg s intw oonio n fields),i nrelatio nt oth epopulatio nden ­ sityan dmobilit y ofth epotentia lpredators .Los so f labelb ypredator swil lhav ebee n negligible,a s indicatedb yth eexperiment so fBreymeye r& Odu m (1969)wh o founda biolo - 65 gicalhalf-lif e for Zni npredator y spiderso f 12-120days ,dependen t onspecie s and oviposition frequency. Fromthes eresult s onema y conclude that,fo ranalysin gprédatio no nonio nfl y eggs, labels canb eusefu lwit hexperiment s inconfine d environments. Insom eexperiment s concentrations ofpupae ,burie d inth e soilfo rreleas e andno t yetcovere dwit h gauze,wer ever yeffectivel y preyedupo nb ymice ,pheasant s andpatrid - ges,a scoul db e seenfro mthei rtracks . Generally nearreleas e sites,th efollowin gbird swer e observedpreyin g onadul t onion flies,i norde ro ffrequenc y ofoccurrenc e inth eOverflakke e experimental areas: meadowpipi t (Anthuspratensi s (L.)),sk y lark (Alaudaarvensi s L.),blue-heade d wagtail (Motacilla flavaflav a L.), starling (Sturnusvulgari s L.),whit ewagtai l (Motacilla alba L.).an dree dbuntin g (Emberizaschoeniclu s (L.)).Mos tprobabl y also the less common winchat (Saxicola rubetra (L.))preye do nonio nflies .Becaus e onionflie s seldom flyhig ­ hertha nth evegetation ,prédatio no nthe mb y thedifferen t swallowspecie spresent ,a s supposedb yKästne r (1929b),wil lno thav e occurred. Thedrago n fly Ischnuraelegan s (Vanderl.)wa sobserve d capturing onion flies inth e field.Suppose dpredator s are thecommo ntoa d (Bufobuf oL. ) andth epredator y fly Scatophaga stercoraria (L.). The latterwa s oftenobserve dkillin g onionflie s inth e traps'collectors .

4.3 ESTIMATION OFDAMAG E INTENSITY ANDPOPULATIO N DENSITY

4.3.1 Damage intensity

Thepatter no fdamag eove ronio nfield swil lb e considered to indicateho wdifferen ­ ces indamag e levelma yb e tested for,an dwha tamount so fsample snee dt ob e taken to obtaincertai n levels ofprecisio n inestimatin g damage intensity.The nth epreferabl e plotsiz ewil lb e indicated,an dfinall y thedistributio n ofth epercentag edamage dpe r onionfiel d isgiven .

4.3.1.1 Damagepatter n

Onionfl ydamag e isno tequall y distributed over onionfields .I twa s investigated whether somestratificatio n ofth efield s isadvisable .Th edamag e atth ehead so f the fields,a sdelimite db yth edirectio n ofth eonio nrows ,wa s found tob eu p tote ntime s thedamag e levelo fth eres t ofth e fields.Th edifferenc ewa s onth eaverag e a factor ofabou t 4,s otha tstratificatio n isadvisable . Inth epresen t analysis thisha sno t yetbee ndone .Th e increaseddamag e levels onth ehead sma yb e attributed toth e fre­ quentoccurrenc e ofonion sbein gdamage db y tractorwheels ,a ssuc honion sar eprefer ­ red foreg gdeposition .Borde r effects incro pdamag e arequit e commonan dhav ebee n mentioned forth eonio nfl y (Kästner, 1930),althoug hunifor mdistributio no fdamag e

67 hasbee nreporte dals o (Perron& leRoux ,1962) .A smal lexperimenta lplo ti n197 2gav e someindicatio no fsuc ha neffec t (Huber,1973) ,bu tdat afro ma muc hlarge rfiel dfaile d tosho wan yborde reffect .

4.3.1.2 Distributiono fdamag e

Damageoccur si na highl yaggregate dwa y(Tabl e 15).Thi soriginate sfrom : 1. clusteredeg gdeposition ,an dlarva lmigratio nove ronl yshor tdistances , 2. somepreferenc eo feg gdepositin gfemale sfo rcertai ntype so fhealth yonion saccor ­ dingt oth eonions 'developmenta lstage ,siz eo rplan tdensity ,an dfo rartificiall yda ­ magedonion s (mainlyb yweeding ) (Section 2.2.3), 3. astron gpreferenc eo feg gdepositin gfemale sfo ronion salread yattacke db yonio n larvaeo rfunga ldisease s (Section4.2.1 ;Workman ,1958) ,

Table 15.Frequenc y distributions of damage and parameters of thedistributions .

NUIT ber of onions Experimen tn o darr aged 1 2 3 4 5 6 7 8 9 10 1 12 0 5 22 0 48 190 28 32 30 449 132 225 50 1 5 16 1 33 54 21 26 7 26 31 23 27 2 4 7 1 10 11 16 8 2 12 27 2 17 3 3 2 1 6 2 10 5 9 5 19 1 8 4 2 1 0 3 0 6 4 2 4 8 0 1 5 2 1 2 0 0 7 1 1 1 9 0 0 6 1 1 1 0 0 6 4 1 2 7 0 0 7 0 0 1 0 0 6 7 3 0 9 0 0 8 1 0 1 0 0 2 1 1 0 2 0 0 9 1 0 1 0 0 4 1 3 0 1 0 0 10 1 0 0 0 0 4 0 1 0 4 0 0

11 - 15 5 0 2 0 0 11 2 1 0 6 0 0 16-20 3 0 0 0 0 4 0 0 0 0 0 0 21-25 1 0 1 0 0 1 0 0 0 0 0 0 26- 30 0 0 0 0 0 1 1 0 0 0 0 0

2 2 Exp Location &Y e ar Plot Plot ,n m S m* k XY d P no. length pattern d inm 1 Lombok 1972 1/2 regular 34 6.235 40 79 11.78 0 .903 1 77 3 0 62 2 Schuilenburg 1970 3 random 50 1.0 2 1 775 1.76 1.60 6 0 42 1 0 52 3 1! 1971 5 regular 12 7.83 33 42 11.10 2 .731 4 " 1972 5 " 100 0.830 1 072 1.12 2 809 1 44 1 0 23 5 II 1973 5 II 257 0.319 0 351 0.42 3 .144 0 05 1 0 83 6 Mijs 197 3 1/2 II 127 4.528 28 89 9.91 0 .774 4 09 9 0 90 7 van Es 1973 1/2 II 92 2.391 14 42 7.42 0 .609 10 78 5 0 06 8 de Wit 1973 1/2 It 101 1.653 7 129 4.97 0 .466 5 97 4 0 20 9 Mijs 1974(exp ) 1/4 random 499 0.196 0 524 1.87 0 .0944 0 57 2 0 75 10 Mijs 1974(con ) 1/4 II 255 1.804 7 804 5.13 0 .404 8 49 7 0 29 11 Schuilenburg 1974 (exp) 5 regular 251 0.120 0 146 0.34 0 .562 12 H 1974 (con) 5 II 103 0.864 1 040 1.07 3 .382 1 71 1 0 19 tested simultaneously 35 29 34 0 41

n number of samples k parameter of th 2negativ e binomial distrib ution m mean frequency ofc amage d degr aeso f freedom s2 variance p probabili tyo f the obse rved x value. m* mean crowding

68 4. possibledifference si nsurviva lo flarva ea tdifferen tlevel so flarva ldensity . Fromthi scombinatio no ffactor stha tcaus eaggregation ,n ospecifie ddistributio n forth edamag eca nb ededuced .Thu sth enegativ ebinomia ldistribution ,whic hca nb e derivedfro ma wid evariet yo fmodel s (e.g.Anscombe ,1950 ;Southwood ,1966) ,seem sth e mostappropriate . Thefi to fth edamag edat at oth enegativ ebinomia ldistributio nwa steste daccordin g toth emetho dgive nb yBlis s (1971).Becaus eo fth elo wefficiencie so fapproximat eesti ­ mateso fth eparamete r kfo rth epresen tdistribution s (Anscombe,1950) ,th emaximu m likelihoodestimato ro f kwa sdetermine db yiterativel ysolvin g

MI .si.yf*«yq*— (2) ? » -l k +x .

(Bliss,1953 ;Fisher ,1953) ,i nwhic hf(x )i sth eobserve dfrequenc yo fx, andN i sth e numbero fsamples .Th eexpecte dfrequencie s$(« )wer ecalculate dfro m

Hó)= N/( 1+ $k (3)

and

•M •* (^r1) <*> 2

(Bliss,1953 ,1971) .Teste dwit hX _ 3agoo dfi twa sobtaine dfo ral l1 2distribution s (Table 15). 2 Gurland& Hin z (1971)giv ea metho do fX analysiscomparabl ewit hanalysi so fva ­ riance,applicabl et ountransfrome ddat ao ffou rgeneralize dPoisso ndistributions ,suc h asth enegativ ebinomial .Thi smetho dma ythu sb euse dwhe ndifference sbetwee ndamag e distributionshav et ob etested .Th egenerall yadvocate dprocedur eo ftransformin gth e datat oconfor mt oa norma ldistributio nan dapplyin ganalysi so fvarianc e (e.g.Taylor , 1961, 1965;Southwood ,1966 ;Harcourt ,1967 ;Iwa o& Kuno ,1968 )ma yno tb eexac t (Gurland & Hinz, 1971).Especiall ywit hth epresen ttyp eo fdistributions ,wit hlo wmea nan dhig h aggregation,th edistribution swil lremai nmonotonousl ydecreasin gan dno tbecom elik ea normaldistribution ,whateve rtransformatio ni sapplie d (cf.Taylor ,1961) .A sth e k valuesobtaine dwer ecorrelate dt oth emea nfo rth edat ao fOverflakkee ,calculatio n ofa commo n k (Bliss,1953 )wa sno tuseful .Th eSchuilenbur gdat agav ea wid escatte r of kvalues .Blis s (1971)foun dtha ti nsevera lcase swher en ocommo n kwa spresent ,a linearrelatio nexiste dbetwee nl g M andlg(m) ,wit ha slop eo f-0.5 .Thi srelatio n fitsfo rth eOverflakke edata ,assumin ga dependenc yo nplo tlengt h (Fig.42) .Th e Schuilenburgdat ama yconfir mthis ,whe naccoun ti stake no fsom eunderestimatio ni nth e aggregationi n197 0 (damageonl ychecke da tharvest )an di n197 3 (headso ffield sno t sampled). Becauseo fth ehig hnumbe ro fzer ocount sth etruncate dnegativ ebinomia ldistribu ­ tionwa sconsidere d (Bliss,1971) ,bu tthi sdi dno tgiv ea clearl ybette rfit .Therefor e therei sn oreaso nt oassum etha tpart so fth eonio nfield swer eno tliabl et ob eat ­ tacked. 69 4.3.1.3 Precisionestimatio n

Theprecision , D, isa measur eo fth ereliabilit yo fm a sa nestimat efo r v, tha tis , ameasur eo fth ewidt ho fth econfidenc einterval .Fo rcontagiou sdistribution sgenerall y themeasur e D = s/m isuse d (e.g.Kuno ,1969) . Itca nb euseful ,fo rinstance ,i nmakin g populationestimate sa tdifferen tdensitie swit ha nequa lprecision ,thu soptimalizin gth e samplingeffor tallocation . Forcontagiou sdistribution sther ear esom emethod so festimatin gth enumbe ro fsam ­ plesneede dfo ra certai ndegre eo fprecision ,base do non eo fth efollowin grelation s betweenth evarianc ean dth emean :

1. fromth enegativ ebinomia ldistributio n (Rojas,196 4 (in:Southwood ,1966) ;Kun oe t al.,196 3 (in:Iwa o& Kuno ,1968) ;Gérar d& Berthet ,1971) :

s2 = m + m2/k (5) whichi sa specia lcas eo f 2.fro mth eregressio no fmea ncrowdin g {m*= m +s /m -1;Lloyd ,1967 )an dth emean : m*= a + s m(Iwa o& Kuno ,1968 ,1971 ;Kuno ,1969 ,1972) :

s2 = (a+1) m+ (B-1> 2 (6)

and 3. Taylor'spowe rla w (Green,1970) :

s2 = am (7)

Kuno (1972)criticize dTaylor' spowe rla w (Taylor,1961 ,1965 ,1971 ;Southwood ,1966 ; Bliss,1971 )a sbein gpurel yempirical ,an dno tdescribin gth ebiologica lrealit ybecaus e itassume srando mdistributio nwhe n mapproache s zero.O nth eothe rhand ,th erelatio n betweenth emea ncrowdin gan dth emea ni sempirica la swell .Thi srelatio nha sbee ncri ­ ticizedb yTaylo r (1971)a si twoul dno tb eexactl ylinear :i tshoul dcontai na facto r 2 2 with m . Incorporatingsuc ha facto rresult si na relatio nbetwee ns andm whic hcanno t bedistinguishe dfro mth epowe rla weve nwit hth emos textensiv edat ase tavailabl e (Taylor,1971) .I nfac tgenerall yth enegativ ebinomia ldistributio ni sals oa nempirica l 2 descriptiono fth eobserve ddistributions ,an dthu so fth erelatio nbetwee ns and m. WithEquation s (6)an d (7)th evarianc ei scalculate dfro ms = I (a;.-a;)/(n-1),an d 2 % i- used,eithe rdirectl yo rvi a m* - m+ s /m -1, inestimatin gth erelatio nbetwee nth e variancean dth emean . Onth eothe rhand ,wit hEq n (5)th eparamete r k iscalculate d from (2)usin gal l x., andth evarianc ei scalculate dfro m(5) . Sabelis& d eReed e (1975)applie dal lthre erelation sfo restimatin gprecisio ni n orchardmit edistributions ,an dshowe dtha tclea rdifference sma yoccur .The yassume d Eqn (5)t ob eth emos treliable ,becaus ethe nth eestimate dvarianc ei sno tsubjec tt o thesever einstabilit ycause db yincidenta lhig hvalue so f x.. However,i nwit hEq n(5 ) 70 1-

xs XS

01 i i1 1 u—r -|—i i11 1ii— r T—I I II IT I ai 1 10

Fig. 42.Damag e distributions: relation between \Ik from the negative binomial distribution and themea n m, with plot size indicated inm . Regression line for 0.5 m plots: k = 0.37/m. 0 :0verflakkee; X: Schuilenburg; •:cas ewher e k has been underestimated.

Fig. 44.Damag e distributions: Taylor's power law. 0: Overflakkee, s2 = 4.079m1-273: X: Schuilenburg, s2 - 1.709m1,31ê.

Fig. 43.Damag e distributions: relation of themea n crowding m* to themea n m. Regression linem * = 1.60m + 1.04.

thevarianc ei sno tindependen to fth emean ,s oth e advantage claimedi sno tobvious . Thusther ei sn oreaso nt oprefe ron eo fthes erelation sbeforehand .Fo rth e onionfl y damage,al lthre emodel sma ydescrib eth esituatio nobserve d (Figs.42 ,4 3an d44) , althoughi tseem stha t m*i scurvilinearil yrelate dt om (Fig.43) . Nowth enumbe ro fsample srequire dfo ra give nprecisio nca nb ecalculate d fromth e meanan dth evarianc e (e.g.Southwood ,1966) .I npractic ei tma yb eeasie rt ous ea

71 'stopline 'i na grap ho f T ,th enumbe ro findividual si nn samples ,versu sn (Kuno , 1969).Th esto plin ei sa lin econnectin gpoint so fequa lprecision .Whe ni nsequentia l samplingth esubsequentl yobtaine dresult sar eplotte d inth egrap ho f ?nversu s n, the requiredprecisio ni sreache dwhe nth ecorrespondin gsto plin ei scrossed .Th eus eo f sucha grap hca nhav ea nadvantag eove rjus tcalculatin gth eprecisio no fth esampl eta ­ ken. Thisi ss owhe nth egrap hi sbase do na mode ltha tha sbee nshow nt ofi tman yex ­ tensivedat asets ,an di suse dfo restimatin gth eprecisio ni nrelativel ysmal lsample s fromwhic hth evariance ,an dthu sth eprecision ,ca nb eestimate dmuc hles sreliabl ydu e toth eskewnes so fth edistribution sa sindicate dabove . 2 2 2

Withs =f(m )= f{Tn/n), thesto plin eca nb efoun db yputtin g D = (n/Tn) £{Tn/n) inth efor m Tn= f (n) .Fo rth erelatio n (6)thi sresult si n (Kuno,1969) :

n 0 - (ß-1)n reducingfo rth enegativ ebinomia ldistributio nt o (Kuno,1969) :

Tn =-Z— ' (9)

Forth eOverflakke edat a k =c/m(fromFig .42 ,c bein ga facto rdependen to nplo t size), andincorporatin gthi sgives :

Y+1+/2Y+ T Tn=^z^__D2y m 2 2 in which Y= 2c nD . Using Taylor's power law one finds (cf. Green, 1970):

r - AbA n1"V2 (11)

2 Introductiono fa limi tN fo rth epopulatio nsample di sdon eb ymultiplyin gs by 1- rc/N (Kuno ,1969) .Fo ra 1 h aonio nfield ,sample dwit h0. 5m plots ,N i s6 0000 ,s o thiscorrectio nca nb eneglecte dhere . Thesto pline scalculate dar egive ni nFig .45 .Th eproble mi ninterpretin gthes e linesi stha tthi sprecisio ncanno tb erelate dt osom eexac tprobabilit ybecaus eth e probabilitydistributio no fth emea ni scalculate dwit hStudent' s t, requiringa stabl e 2 variancean dstochastica l independenceo f8 and m. Eitheron eo rth eothe rrequiremen t isno tmet ,a smentione dbefore .Th ebia ss ointroduce d isunknown ,s oth eprecision s inFig .4 5mus tb econsidere da ssom eapproximat emeasure .Thi sma ybecom eseriou ses ­ peciallya tth esmalle rsampl esize stha thav et ob euse d inpractice . Whenth emea ni scalculate dfro mdat aobtaine d insequentia lsampling ,thi si sbiased . Itha st ob ediminishe db ya facto rf(m)/(n(w-fc) )(Kuno ,1972 )i nwhic h mi sth epopula ­ tionmean ,an d n and b areth ecorrespondin gvalue so fth enumbe ro fsample sneede dan d ofth eslop eo fth esto plin efo rth eprecisio nconsidered .Th ecorrespondin gbia si n thevarianc e is,accordin gt oKun o (1972)negligible .

72 m.0. 1

Fig. 45.Damag edistributions :sto pline sfo rcertai nlevel so fprecisio n (D= s^/ m ),i n sequentialsampling . Underlying model: negative binomial distribution,?: = 0.37/m; Taylor'spowe r law,s 2 -4.079m 1-273; ••••mea ncrowdin g m*= I.60m,+1.04 .

4.3.1.4 Plotsiz e

Differentplo tsize swere used .I na nonio nfiel da certai nnumbe ro fdamage donion s T arepresen to nth eare ainspected .Whe n T iskep tconstant ,mor esmalle rplot sin ­ creaseth eprecisio n (Fig.45) .A tlowe rdensitie s this increasei sless ,a sca nb eima ­ ginedfro mth ehig h zerofrequencie sexpecte d then.Takin gmore smalle rplot sha so nth e otherhan dthre edisadvantages : 1. Theamoun to ftim e losti ngoin gfro mon eplo tt oanother .Wit hver y lownumber so f plotsthi s factorwil lbecom e important,bu tquantitativ e informationo nthi si sno tye t available. 2. Thevarianc ei nplo t length,a sstake dou ti nth efield ,wil lb erathe rconstant , andthu so fincreasin g importancei nsmalle rplots .Thi sfacto ri sfel tt obecom e serious inplot so funde r2 5c mlength . 3. Amore seriou sobjectio nt osmalle rplot si sth elimite dnumbe ro fonion stha ti s presenti nthem .Th eaggregatio nwil lb eunderestimate di fth enumbe ro fdamage donion s ina plo tfall si nth erang eo fth etota lnumbe ro fonion spe rplot .O nth eaverag ether e areabou t3 5onio nseedling spe rmetr eplo t length.Thus ,a sca nb esee nfro mTabl e 15, theaggregatio nwil lhave bee nslightl yunderestimate di nsom eexperiment so nOverflakkee . Thedistributio no fdamag ea tharves ti ncommerciall ygrow nonio nfields ,wit hche ­ mical'contro lo fth eonio nfly ,i sgive ni nTabl e 16.Fro mdat ao fth eSNUi Fi tcoul db e

73 Table 16.Frequenc y distribution ofdamag e level inspring-sow n onions atharvest . Data from4 9fields ,84. 5ha .Overflakke e1971 .

estimated %damag e % surface checked estimated %damag e surface checked

0 21, 2.0 0.6 0.1 24, 3.0 4.2 0.2 7, 3.5 4.1 0.5 4, 5.0 7.1 1. 0 10.0 10.0 4.7 1. 5 9.5 15.0 0.6

Weighted average percentage damage1.5 %

estimated thatth etota ldamage ,excep ta thig h damage levels (over 60%), isles s than twice thedamag eobservabl e atharvest .Thu snorma l levelso ftota ldamag ei npractic e areunder 5%o r2 onion s damagedpe rmetr e row,an don emetr eplot s shouldb esufficien t (cf.Tabl e 15:exp .7 & 10) .Fo rlowe r damage levels0. 5metr eplot s couldb eused .Fo r higher levels,plot s shouldb elarge rand ,a sca nb esee nfro m Fig.42 ,th edistributio n willbecom e approximately random,i.e .a Poisso ndistribution .

4.3.1.5 Damage frequency intim e

The cumulativepercentag e damaged versus time isshow ni nFig .46 .Mos t damagewa s duet o1s tgeneratio n larvae,feedin go nth eonio nseedlings .O fth edamag edu et o2n d generation larvae,onl ya par tbecam evisibl e during theregula r checking.Th eremainin g damagewa sfoun da tharves twhe nth eonion swer e pulledu pan dinspected .Therefor e inth e graphsth edat abefor eth elas t checkar esomewha tto olow .

damage in%

Fig.46 . Cumulative damage in% durin g theseason . a. 1973.0:Mijs ; X:vanEs; «:deWit. b. 1974, Mijs. O :trial field; X:control field (with a reduced 2nd flight, see Sect 6.2.7); »:field receiving normal chemical treatment.

74 number of pupae 6-

Fig. 47.Numbe ro fpupa epe ronio n attacked,versu sdat ao ffindin g damage.Experimen tMij s 1973.

4.3.S Pupal population density

Pupae distribution Thenumbe ro fpupa epe r Infestedonio ndepend so nth e developmental stateo fth eonio na tth etim eo fattac k (Fig- 47)an dgive sa nindicatio no fth erela ­ tiveamoun to ffoo d availablepe ronio ndurin g theyear .Clearly ,neglectin g damagei n Mayan dth efirs thal fo fJun ewil lhardl yaffec t thepopulatio nestimates . Thehead so fth efield sha dpupa ldensitie s thatdeviate d lesstha ndensitie so f damage.Th edensit yo fpupa ewa si nth eexperimen tMij s 19742. 1an d1. 6time shighe r onth ehead so fth eexperimenta lan dcontro l field,respectively ,tha no nth eres to f these fields,wherea s thedamag ewa s4 time shigher . Thedistribution so fpupa epe rsampl e arever y skew (Table 17). Thedat awer e tested forfi tt oth enegativ ebinomia ldistributio n (seeSectio n 4.3.1.2).Th efi twa s good exceptfo r twodistribution swit h some irregularitiesi nth e tails.Bot hthes edistri ­ butions couldb efitte dwel lt oth enegativ ebinomia lwhe nspli tu pove rtw oseparat e parts.I nth e firstcas e (experiment Lombok 1972)th edamage ,an dthu sth eoccurrenc e ofpupae ,wa sconcentrate d nearth eside so fth e field,an dth edistributio nwa sesta ­ blished separately forth epar to fth e fieldmor e than8 m fro mth efield sborde ran d thepar t lessso .Th eothe rcas e (Mijs 1974,contro l field)wa sspatiall yhomogenous . Divisiono fth edat abetwee nthos e fromth e firstan dthos efro mth esecon d generation pupae gavedistribution swit h different kvalues . The kvalue swer ecorrelate dt oth emean ,bu ti na differen twa y fromthos efo rth e damage.A rathe r linearrelatio nwa s foundo na lg/l gplo to fk versusm (Fig.48) . When ki sestimate db ymaximu m likelihood,th etes tquantitie s calculatedt otes t 7 thefi tar eno t asymptotically x distributed.Gurlan d& Hin z (1971)gav eanothe rmetho d ofestimatio no fk, whichtest sfo rfi twit htes tquantitie s thatare ,accordin gt othes e 2 authors,asymptoticall yx distributed. Thismetho dwil lno tnecessaril y givebette rre ­ sultsbu tha sth eadvantag e thatn olumpin go ffrequencie si srequired .Thu sth einforma ­ tionfro mth etai lo fth edistributio ni suse dbetter .Som edistribution so fpupa ewer e testedaccordin gt othi smetho d (Table 17).Th e k values obtained aresimilar ,bu tth e

75 probabilitiesdiffe rgreatly ,an di ngenera lth efi to fth epupa edistribution st oth e negativebinomia li sno tver yconvincing .

Table 17.Frequenc y distributions of pupae and parameters of thedistributions . Explana­ tion of symbols inTabl e 15.

Number of pupae Exp eriment no

1 2 3 4 5 6 7 8 9 10 11 12 la lb 10a 10b

0 22 0 48 190 28 32 50 449 132 225 50 0 0 135 135 °b 2 7 3 14 35 36 32 24 19 47 19 23 0 2 68 53 ob 10 14 8 8 16 21 3 7 0 2 13 21

3 1 3 2 4 3 2 4 3 5 6 1 3 0 1 9 10 4 1 2 0 3 2 4 0 2 2 5 0 5 0 1 2 6 5 1 2 1 1 2 2 1 3 1 10 0 2 0 1 6 4 6 0 1 0 2 2 4 1 0 0 5 0 0 0 0 0 2 7 0 1 0 1 1 4 3 0 0 2 0 1 0 0 3 2 8 0 0 0 4 0 1 3 1 0 1 0 3 0 0 4 1 9 1 0 1 1 0 0 1 2 0 2 0 1 0 1 1 4 10 1122150002000121

11-15 210227220 10 010233 16-20 6003120205012400 21-25 7110150001003400 26-30 4000010000003100 31-40 6000111001004210 41-50 1000100000001000 51-110 7000000000007000 (Gurland & Hinz, 1971) Exp. Sample s2 m* Jl A p no. 0 inc m 4 k P(xf)

1 20 46 26.02 543.89 45.92 1.023 16.44 5 0.006 1.22 3 0.43 2 20 50 1.84 15.08 9.03 0.255 1.89 1 0.17 3 20 12 5.50 45.00 12.68 0.677 4 20 100 2.08 16.24 8.89 0.205 1.38 3 0.71 5 20 257 1.05 17.01 16.29 0.040 1.27 3 0.74 6 5 127 3.89 49.56 15.63 0.247 5.92 6 0.43 0.277 0.09 7 5 92 1.66 18.34 11.69 0.145 4.33 3 0.23 0.149 0.51 8 5 101 1.35 12.1 5 9.37 0.129 0.68 2 0.71 0.145 0.26 9 20 499 0.1 2 0.28 1.53 0.060 0.86 1 0.35 0.079 0.08 10 5 255 1.89 19.69 11.33 0.13 2 19.68 7 0.006 0.148 0.007 11 20 251 0.05 0.09 1.01 0.029 12 20 103 1.21 7.21 6.15 0.16 8 2.03 2 0.37

la 20 21 41.14 628.43 55.42 2.737 0.43 1 0.51 lb 20 25 13.32 127.98 21.93 0.970 3.10 2 0.21

10a 5 255 0.97 8.90 9.19 0.096 3.91 5 0.56 0.095 0.25 10b 5 255 0.92 5.05 5.40 0.153 2.89 5 0.72 0.177 0.03 tested simultaneously 28.69 34 0.73 0.05 a. Plots without damage. b. Plots with damage. c. Division of experiments 1an d 10 into la/lb and 10a/10b see text. d. Experiments 1an d 10:undivide d data sets not included where divided sets available.

76 Fig. 48.Pupa ,distributions :relatio n Fig. 49.Pup adistributions :Taylor' s between kfro m thenegativ ebinomia l power law.s 2• 7.006m 1-373. distributionan d themea nm .Regressio n X: Dat ao fexperiment s 1an d 10(Tabl e line k= 0.14m°- 66. 17)afte rhavin gbee nspli tu pint otw o O:Overflakkee ; X:Schuilenburg. parts;no tuse d inth eregressio n calculation.

Fig. 50.Pupa ,distributions :relatio n ofth emea ncrowdin gm *t oth emea nm . Regressionlin e m* 1.53m +6.50 . X: A si nFig .49 .

Population estimation Precisionwa scalculate di nth esam ewa ya swa sdon ebefor efo r thedamage .Agai nth elinearit yo fth erelatio nbetwee nm *an dm wa sno tver ygoo d (Fig.50) .Th epowe rla wfitte dt oth edata ,eve nwithou ta neffec to fplo tsiz eo r samplingcor ediamete r (Fig.49) .Sto pline swer ecalculate da sfo rdamag e (Fig.51) , in thecas eo fth enegativ ebinomia ldistributio nwith k= 0.14m 0,66.Again ,th ecorrespond ­ ingprobabilitie scoul dno tb eindicate d exactly.

77 -0.1

^ D.0.1

D-0.15

D-0.2

1 IIMil l 10000

Fig.51 .Pup adistributions :sto p linesfo rcertai nlevel so fprecisio n (D= sm/m), in sequentialsampling . Underlyingmodel : negativebinomia ldistribution , k =0.14m 0-66; -Taylor'spowe r law,s 2 7.006m 1.373. 1•••mea ncrowdin g m =1.53 m +6.50 .

Nowwit hpractica lapplicatio no fth esteril einsec ttechnique ,th esampl esiz ewil l havet ob elo wbecaus eo fth elarg enumbe ro ffield st ob esampled ,an dconfidenc eli ­ mits,especiall yth euppe rone ,ar erequire dfo rth epopulatio nsize .A smentione dbefor e (Section4.3.1.3) ,usag eo fStudent' s t forcalculatin gthes ei sno tver yreliable .Dat a obtained inthi swa yar egive ni nFig .52 ,base do nth eEqn s (5),(6 )an d (7).Fo rlo w valueso f n theyca nfo rth emomen tbes tb econsidere da sindication so fth eorde ro f theconfidenc einterval . Itwa sinvestigate dwhethe rth eamoun to fwor ki nsamplin gpupa ecoul db ereduce db y observingmor eplot sfo rdamag etha nthos euse dals ofo rsampling .Fo rsevera lrepresen ­ tativedat aset sused ,th ecalculation sshowe dtha tthi sprocedur ewoul dno tb euseful .

4.3.3 Fly population density

Direct estimation of fly densities Onionflie sca nb ecounte di nfield swher eth eonio n plantsar estil lsmall .I na nonio nfiel dwhere ,fro mtrapping ,populatio ndensit ywa s knownt ob ehigh ,0.2 5 fly/m2wa sfound .Simultaneousl yth edensit yo nth editc hbank s 2 wasestimate dfro msample swit htent s (Section3.3.5 )t ob eabou t5 flies/ m .Bot hmethod s mayyiel dseriou sunderestimations . Samplingwit hthes etent swa sdon esevera ltime si nan daroun dth e197 4experimenta l 2 field.I nonion snearl y2 (range0.5-4 )flies/ m werefound ,an dnearl y3 (range0.5-8 ) onth editc hbanks .Thes enumber scorrespon dt o2 000 0- 2 500 0flie s (sterilean dwild )

78 tDm

0.01

Fig. 52.Pup adistributions :hal fwidt ho fth e95 %confidenc einterva l (tDm) fordifferen t valueso fth emean ,a sa functio no f thenumbe ro fsample sn .Underlyin gmodel sa si n Fig. 51. onthi sfield .Or ,200 0- 250 0wil d fliespresen ta tth een do fMa y andbeginnin go f July,o na fiel dwher e2 100 0wil dflie sha demerge d (compareFig .32i) .

Release recapture experiments Topermi testimatio no fwil dpopulation s accordingt oth e principleo frelease-recaptur ean dapplicatio no fth eLincoln-index ,fertil ediapausin g laboratory-reared pupaewer edu gint oth esoi li nearl yspring ,i nfield stha twer e onion-flysource sbecaus eo fth epresenc eo fonio nfield swit h somedamag eth eyea rbe ­ fore.Thes eflie swer eexpecte dt osho wabou tnorma lemergenc ecurves ,an dmi xwit hth e localpopulations .A temergenc eth eflie swer emarked .Trap swer eplace daroun dth e emergence fieldst otra pth eflie swhe nmigratin gt oonio nfields .Indee dthes e flies weretrappe d therea scoul db esee nfro mth elo wpercentag emate dan dth elimite dovar y developmenta scompare dwit hcatche sa tothe rsites .Th eresult so fth esimultaneou sex ­ perimentsi n197 2ar egive ni nTabl e 18.Thes efl ydensitie srelat et oth efe wfield s foundt ohav esom edamag ea tharves ti n1971 .

79 Table 18. Estimation of populations from release-recapture experiments, 1st flight 1972.

Situation Number of flies Wild population ha Onions Average ". i " j in 1971 number of flies released trapped . -> emerging per m' wild marked Vroegindewei 5960 325 29 6680 0 1.85 3.6 vanRossu m 1590 172 6 4560 0 1.9 2.4 Buijs 1000 198 8 2500 0 1.5 1.7

Large scale release-recapture experiment Populationswer eestimate dfro mrelease-recap ­ turedata ,obtaine ddurin gth efirs tan dsecon dfligh ti nth eexperimen tMij s 1974.Fo r thefirs tfligh testimation ,fertile -diapausin glaboratory-reare dpupa ewer epu ti nth e fieldi nearl ysprin go nthre esite sindicate db yG ,Y an dC o nFig .1 5accordin gt oth e dyemark sused . Fromth erecapture si tappeare dtha tth eemergenc eo fth ewil dflie stoo kplac eo n theaverag esom ethre eweek searlie rtha nthes e 'mixinggroups' ,an dals omor econcen ­ tratedi ntime .Th ereaso nfo rthi sdifferenc ewil lhav ebee nth ehabita tdifference s (cf.Fig .19) .Thes ecoul dno thav ebee navoide dbecaus eth ewil dpopulation semerge d fromfield splante dwit hcrop swhos emechanica ltreatmen tdi dno tallo wth edy emar k unitst ob eplace dthere . Asa comparabl e 'mixinggroup 'fo rth efiel do nwhic ha steril emal etreatmen twa s done (Section6.2) ,th esterile srelease ddurin gth efirs tfligh twer etake n (i.e.th e groupswit hdy emark sYO-BYO) .Thi sgrou pi sindicate do nFig .1 5b y S. Therecaptur edat ashowe dtha tth emigratio npatter no fgroup sG an dY wa ssimila r totha to fsteril eflie stha twer eals orelease do nthes esites .Fo rth esubsequen tcal ­ culationstherefor ethes esterile swer eincorporate d inth erespectiv emixin ggroups . Asi nth eothe rcalculation swit hrecaptur edat afro mth eexperimen tMi js 1974 ,thes e datahav ebee ncorrecte dfo rincomplet edye-markin go fsom erelease dcohort s (Section 6.2.1),fo rlocall yan dtemporar yincrease dcatche sdu et oth eus eo fa nattractan t (Section3.3.3.2) ,an dfo rth eeffec to ftemperatur eo ncatc hsiz ea sgive nb yFig .24 . Thenumber so ffirst-fligh twil dflie san do fth efou rmixin ggroup scaugh tar egive n inTabl e1 9fo rth edifferen tonio nfield sseparately .A sindicate dthes edat aca nb e treateda sa se to fequation swit hfou runknowns :th efactor sconvertin gth enumber so f competitiveflie spe rmixin ggrou pint oth enumber so fwil dflie semerge di nth esam e field (includingth eimmigrant stha tha darrive dther efro moutsid eth eare ai nwhic h trappingwa sdone .O fcours ethes eimmigrant scoun ther eonl yfo rtha tpar to fthei r lifetimetha ttoo kplac eafte rimmigratio nint oth efiel dconcerned .A sshow ni nSec ­ tion5.6.3 ,th enumber so fthes eimmigrant swil lhav ebee ninsignificant .Th eequation s havebee nsolved ,usin gthos epertainin g toth efield sneares tt owher eth emixin g groupsoriginated .Th eresultin gconversio nfactors ,fille di ni nth eequations ,giv e relativeaverag edensitie so fth ecatchabl efraction so fpopulation so nth eonio nfield s considered,spli tu paccordin gt othei rfield so forigin . Anunderlyin gassumptio ni nthi scalculatio ni stha tequa ldensitie si ndifferen t onionfield sresul ti nth esam enumbe ro fflie spe rtrap .Becaus etra ppositio nseverel y

80 Table 19.Calculatio no fconversio n factorso fmixin g groupst owil d flies,fro m numbers of flies trapped inon etrap/onio n field.Experimen tMi js 1974,1s tflight .Explanatio n seetext .

Trappingsit e Wildflie s Mixinggroup s S G ï C exp 59.04- 577.35s + 11.29g + 4.34y + 0.22c 5 26.06- 37.92s + 4.35g + 5.05y + 3.93c con 169.59- 6.31 s+ 0.94g + 1.47y + 45.5 1c 1 15.84- 10.57s + 63.34g + 4.24y + 0.45c 2 74.00- 22.72s + 71.02g + 34.23y + 0.52c 3 115.86- 42.04s + 55.85g + 147.94y + 0.50c 4 178.28- 4.21 s+ 0i00g + 1.80y + 1.32c conversionfactors : s- 0.092 5 g- 0.16 3 y- 0.68 3 c- 3.68 8

affects thecatc hsiz e (Section 3.3.3.1),deviation sma yb eexpecte d especiallyi nfield s witha lo wnumbe ro ftraps .Thi s factorma yb eresponsibl e forth ehig hnumber so fflie s foundo nonio nfield s3 an d4 ,eac hwit h onlyon eo rtw otrap swhic hwer ei na ver y shel­ teredposition . Thewil dpopulation s cannotb ecalculate ddirectl y fromth enumber srelease dan dth e corresponding conversion factors,a sth ecompetitivenes so fth erelease d fliesan dth e prédationo nthe mar eunknown .Thu sa mor ecomplicate d approachwa sneeded . Nowth efl ydensities ,a sindicate db yth etrapping ,di dno toccu rove rth ewhol e onionfields ,bu t onlya tth eedge swher e theseoffere d shelter.I nth epresen texperi ­ mental lth etrap swer e situatedo nsuc hedges .S oth erelativ epopulatio n densities applyt othese ,an dmultiplicatio no fth edensitie sb yth e lengtho fsheltere dedg eo f theonio nfiel dconcerne dyield svalue s thatar eapproximatel y proportionalt oth e catchablepopulation s (Table20) . Inthes ecalculation si ti sassume d thatth edispersa lo fth ewil d fliesi sth esam e astha to fth erelease d flies.I fth ewil d fliesha ddisperse d faster,man ymor e flies from 'elsewhere'woul dhav e appearedfo rfield s2 an d5 .A sth enumber s found therear e readily explaineda shavin g originated fromth e 1973-onionfiel dnea r 2,ther ei sn o reasont oassum e thatth erelease d fliesdisperse ddifferentl y fromth ewil d ones. Becauseno tal lth eflie s areconcentrate d alongth eonio nfiel dedge stha tprovid e shelter,th epopulation so nth efield swit ha large rsurface/sheltere dedg erati ocoul d havebee nunderrated .When ,t opreven t suchunderrating ,th erelativ edensitie s arecon ­ vertedt orelativ epopulation so nth ebasi so fth eonio nfiel dsurfaces ,th epopulation s emerging fromG ,Y an dC increas ewit h factors 1.S,1. 2an d2.1 ,respectively .I nSec ­ tion6.2. 2 theeffec to fthi schang eo nth ecalculate d competitiveness valuesi sgiven : somecompetitivenes s values riset oove r 1,especiall yo nfiel d 1.Thi s arehighl yim ­ probablevalues ,s oth e incorporationo fonio nfiel dsurface si nth ecalculation swil l ben oimprovement . Fromth edat agive nhere ,th eamoun to femigratio n fromth eare awher e flieswer e trappedwa sestimate d (Section 5.5).Whe nth eemigrate d fractionsar eincluded ,th esu m ofcolumn srepresen tth etota lcatc hfo r1 trap/k mo fal l sheltered onionfiel d edges, foreac horigin .Now fo r theexperimenta l fieldther ei sa reasonabl e estimationo fth e

81 Table20 .Estimate d relativecatchabl epopulations ,expresse d asnumber so fwil dflie s pertra ppe rk msheltere d edgeo fonio nfield ,distribute d byorigi nan d trappingsite . Calculated fromTabl e 19,extrapolation st ofield s6-1 0 calculated inSectio n5.5 . ExperimentMij s 1974,1s tflight .

„ • • b Trapping Edge Origin, site in km exp K+2) 3(+2) con elsewhere total

exp 0.38 20.30 0.70 1.1 3 0.31 0C 22.44 5 0.67 2.35 0.47 2.31 9.71 2.61a 17.46 con 0.55 0.32 0.08 0.55 91.4 8 0C 92.43 1 0.88 0.86 9.07 2.55 1.4 6 0C 13.94 2 0.28 0.59 3.24 6.55 0.54 9.81a 20.72 3 0.54 2.11 4.91 54.55 0.99 0C 62.56 4 0.85 0.33 0.00 1.0 4 4.14 146.02 151.54 6-8 0.08 0.10 0.93 7.79 9 0.16 0.27 1.5 7 1.65 10 0.22 0.21 0.29 0.04 total 27.32 19.04 71.47 118.08

Absolutepopulatio nestimates ,calculate d from 2100 0o nonio nfiel dexp : population 2100 0 7900 0 9080 0 haonion s (1973) 0.1 9.1 5.9 emerged flies/ha 21000 0 870 0 1540 0

a.Flie ssuppose d tohav eoriginate d fromnea ronio nfiel d2 . b.Th e 1974-onionfield sneares t toth eemergenc e sitesar eindicate d asorigin . c.Thes evalue sar ezer obecaus eo f thecalculatio nmethod .

numbero fpupae :2 356 0 (Section6.2.1) ,o fwhic habou t90° sca nb eassume dt ohav e emerged.Tha ti sabou t2 100 0emergin gflies .Fro mthi sth eothe remergin gpopulation s wereestimate d (Table 20),an dthei rdensitie sar eexpresse da snumber semergin gpe rh a onionfiel do fth eprecedin gyear .Not etha tth eexperimenta lfiel dwa sno ttreate dwit h insecticides,an dtha to nbot hth eexperimenta lan dcontro lfield sfertil eflie swer e releaseddurin gth eprecedin gyear . Thesam ecalculation swer emad efo rth esecon dflight .Durin gthi sfligh ta majo r disturbanceoccurre ddu et oth eparathio nsprayin go n3 1July .Fo rpopulatio ncalcula ­ tionsfro mrelease-recaptur edata ,onl ycatche safte rthi sdat ecoul db eused .A tfirs t thesam eprocedur ewa sfollowe da sfo rth efirs tfligh tdata .Thi sgav epopulation so f 2400an d7 640 0o nth eexperimenta lan dcontro lfield ,respectively .Obviously ,ther e hadbee nonio nfl ysource sdurin gth esecon dfligh ti nth etrappe dare atha tha dno t beenprovide dwit ha mixin ggroup .T oge ta mor ecomplet epictur ea differen tcalcula ­ tionwa smad esubsequently .Th emigratio npatter ndurin gthi spar to fth esecon dfligh t didno tdiffe ressentiall yfro mtha tdurin gth efirs tfligh t (Fig.81) .Therefor efro m thisgrap hth epercentage smigrate dwer erea dfo rsuppose dpopulation soriginatin gfro m thefield s1 t o5 inclusive .Th epercentage sno tmigrate dwer eobtaine db ysubtractio n ofal lcalculate dmigrate dpercentage sfro m100 .Togethe rwit hth eobserve dpercentage s ofth emixin ggroup so nth eexperimenta lfiel d (exp)an dth econtro lfiel d (con),thes e dataca nb euse da sa ne wse to fseve nequation swit hseve nunknowns ,a sshow ni nTabl e 21.A tth elef to feac hequatio nth erelativ epopulatio nsiz ea ttha ttrappin gsit ei s mentioned,tha ti sth erelativ edensit ymultiplie db yth enumbe ro fk mo fsheltere d onionfiel dborder .

82 Table21 .Estimatio no fpopulation si nexperimen tMij s 1974,2n dfligh tafte r3 1July .

Percentagedistribution so f2n dfligh tpopulation sove rthei rtrappin gsites .

Trapping Relative Origin site population exp. 5 con 1 2 3 4 exp 2.92 76.1 3.4 0.5 4.1 5.0 3.4 0.7 10.62 7.4 79.0 8.0 1.5 3.4 5.0 2.3 con 79.62 0.7 3.4 80.2 0.7 1.5 3.4 7.5 1 2.26 7.7 1.5 1.3 76.1 9.0 5.0 1.0 2 1.39 2.6 y.4 0.2 9.0 68.6 9.0 1.5 3 6.25 3.8 5.0 0.0 5.0 9.0 66.7 4.1 4 1.90 0.0 2.3 2.0 1.0 1.5 4.1 71.6 elsewhere 1.7 2.0 7.8 2.6 2.0 3.4 11.3

Solvingthes eequation sa si nTabl e 19give sth erelativ epopulatio nsize spe rorigin : 2.64 2.63 98.82 0.35 0.31 8.92 -0.72 With theunrealisti cnegativ evalu eeliminated ,th eabsolut epopulatio nestimates ,calcu ­ latedfro m2 100 0flie scorrespondin gwit ha nestimate d relativepopulatio no f27.3 2 (Table20 )are : 200 0 200 0 7540 0 300 200 690 0 0 Absolutepopulatio nestimate so ftota l2n d flight,fro mth eempt ypupa esample d (Tables36 ,37 ,38) : 930 0 10950 0 Percentageso fcatche so f2n dfligh tafte r3 1Jul y (Fig.3 2h ,i) : 21% 38% Estimated populationso f2n d flightafte r3 1July ,fro mth eempt ypupa esampled : 200 0 4200 0

Withth esam erati oo femergenc et onumbe rcaugh tpe rtra ppe rk mo fsheltere d onion fieldborde ra swa s foundfo rth efirs t flight(2 1000/27.32) ,th eabsolut epopulation s inth esecon d flightafte r3 1Jul ywere estimate d (Table 21).Th edifferenc ewit hth e firstcalculatio ni ssmall .Th eaccurac yo fth epopulatio nestimate so fth econtro l fieldma yb elo wa sca nb esee nfro mcompariso nwit hth e estimateobtaine d fromsample d emptypupa ean dth edistributio no fcatche sbefor ean dafte r3 1Jul y (Table21) .

4.3.4 Relation between pest density anddamage

Theavailabl e informationo nth erelatio nbetwee nth eonio nfl ypupa ldensit yan dth e damage leveli ssummarize di nFig .53 .Usefu li na steril emale contro lprogramm ei s knowledgeo fa relatio nbetwee nth edamag e levela tharves tan dth epopulatio no fdia - pausingpupae .Thi scanno tye tb eestimate dwit hreasonabl eaccuracy . As theweighte daverag edamag e level,a sfoun di nspring-sow nonion sa tharvest ,wa s about 1.5% (Table 16),th eaverag epopulatio npe rhectar ewil lb eo fth eorde ro f 10000 .

4.4 MORTALITY

Eggs and larvae Apreliminar yexperimen twa sdon et oasses sth emortalit yo fmarke degg s and larvae.A numbe ro f65 Zn-labelledegg swer epu to nonion si nth efield ,an dthes e

83 number of pupae

o o

105- o o -< H H o

104- -<

103

—I 1—I 1 I I I III 1—I I I 11 III 1—I I I 11 III ai 1 10 too damage in%

Fig.53 .Pes tdensit y expressed asnumbe ro fdiapausin gpupa epe rha ,versu sdamag e in% . O =Damag ea tharves tonly;-^ = totaldamage ; •= steril einsec ttechnique ;X = chemical control;othe rdat an ocontrol .

onionswer esample da tdifferen tintervals .Th eexperimen twa sdon ebot ho nundamage d ando ninfeste donion so na fiel dwit ha hig hpopulation ,an donl yo nundamage donion s ona fiel dwit ha lo wpopulation .Th eegg swer elai di nth elea faxil so rbetwee nth e onionan dth esoil ,i nbatche so f2-6 4egg spe ronion ,o ndifferen tdays ,wit hi ntota l 36replicates . Theemergenc eo fth eeggs ,a schecke dwit hdepo tgroups ,wa slo wdu et omanipulatio n andtransport .Correcte d foremergence ,an domittin gth e8 replicate stha twer ei nth e eggstag ei nth efiel ddurin ga nunexpecte dparathio nspraying ,287 6egg swer eused . Thelabe lwa sfoun di n2 53r dinsta r larvaetha twer esample da s1s tinsta rlarva e andreare d inth elaboratory ,al lsurvivor sbein gfoun di nalread yinfeste donion s(9.6 1 survival;Buth ,1976) .Th elabe lwa sfoun dals oi n1 63r dinsta rlarva esample da ssuch , againonl yfro megg slai do ninfeste donion s (2.51survival) .Labelle dpupa ewer eno t found,no ran ylarva eo nundamage donions .

84 Pupae Parasitizationi sdiscusse d inSectio n4.2.3 .Fo rOverflakke ea naverag eo f5 1 parasitized seemsa reasonabl eestimation . Prédationo nartificia lconcentration so fpupa e isknow nfro mbirds ,mic ean d ants, the latteractuall yo nth eemergin g flies.A s foundb yva n 'tSan t (1970)suc hconcen ­ trationsma yals ob edestroye db y fungi.Fo rwil dpopulation sthes emortalit yfactor s areunimportan tunles spopulatio ndensitie sar ever yhigh .Onl yth epupa etha tar ebrough t toth esurfac eb yploughin gar eprobabl yreduce dconsiderabl yb yprédation . Ifal lpupa e inth euppe r 1c mo fsoi lar eeaten ,mortalit ywoul db eabou t 41. Theweathe rdoe sno tsee mt ob edetrimenta lt opupae .Pupa ebrough t intoth efiel di n Decemberha da percentag eemergenc ei nsprin gsimila rt otha ti nth e laboratory,wher e theaverag eemergenc ewa s 85-951.Ellingto n (1963)foun d infiel dcage sa winte rmorta ­ lityo f0-41 . Thetota lmortalit y inth epupa l stagethu sma yb eestimate droughl ya tabou t 10-201.

Adults Datao nEntomophthor ainfectio na sa mortalit yfacto ro fsecon dfligh tflie shav e beengive ni nSectio n4.2.4 .Th eeffec to fothe rmortalit yfactor ssuc ha sbird san d predatoryflie si nunknown .Prédatio no nartificia lconcentration so fnewl yemerge dflies , asmentione d inSectio n3.3.2.1 ,wil loccu rwit hwil d fliesonl ya tver yhig hpopulatio n densities.Suc ha cas eha sbee nobserve db yPeterso ne t al. (1963). These xrati ochange swit hag e (Fig. 36).Th erelease dsterile swer egenerall y caught witha se xrati osimila rt otha to fwil d flies.Therefor e itseem sjustifiabl e toassum e thatth esurviva lcurv efo rwil d fliesi ssimila rt otha to fsteriles ,excep tfo rmorta ­ lityo nreleas esites . Thesurviva lcurve so frelease dflie sca nb erea dfro mrecaptur ecurve swhe nmigratio n hasbee ntake n intoaccount .Thi sapproac h isdisturbe db y theyoun g fliesbein gseriousl y underrepresented inth ecatche s (seee.g .Tabl e 25). Comparisono ftra pcatche swit hten t samplestake nsimultaneousl y showedtha tth ecatchin gprobabilit y canb e assumedt ob e constant fromabou ta nag eo fles stha non ewee konward ,s odecreas e incatche s thereafter willreflec tmortality . Themos textensiv ese to fdat aavailabl ear eth erelativ ecatchabl epopulatio nesti ­ mateso fsteril eflie si nexperimen tMi js 1974 (Table 25).A sca nb e seenfro mTabl e2 0 underexp, -th efac ttha tn odat afro mth eonio nfield s6-1 0wer eavailabl eca nb eneglec ­ tedfo rthes eflies .Flight san dsexe swer eexamine dseparately .Th epopulatio nsize sa t age zero,withou tth eflie stha twer e lostb yprédatio no nconcentration sa tth ereleas e site,wer eestimate db yextrapolatio no ngraph so flg(population )versu s age,afte rwhic h thesegraph swer eshifte dalon gth ey axist oge tcoincidenc eo fth erelativ epopulatio n sizesa tag e zeroa t 1000flie s (Fig.54) .Th eresultin g survivalcurve s lookreasonabl y likethos eo flaborator ydat afro monio nflie s (Noorlander,pers .commun. )an drelate d flies (e.g.Rockstei n& Miquel ,1973) . Thesurviva lo fth eflie si nth etw oflight s iscompare d inFig .55 ,afte rsynchro ­ nizationo fth ephysiologica lage sb ygettin gth eage sa tth efirs tmatin gt ocoincid e (determined fromFig .5 7an daverag etemperature so f 12.8an d 16.5°C,respectively) .Fo r bothsexe san dflight sth ecurve sar e inaccordanc ewit ha norma ldistributio no fage s reached.Obviousl ymortalit ydurin gth esecon d flight ishigher .Th edifferenc eca nonl y

85 partiallyb eexplaine db ymortalit yfro minfectio nwit hEntomophthor adurin gth esecon d flight,accordin gt oth einfectio nmode lgive ni nFig .41 .

age in days 15 25 30 35 40 45 10 15 20 25 30 _| _l 1_ I I I I _l relative population size

3- ooo .*>•** 1>V X x J°»^ ^ °o o X *°> ?R - X V « "o^v 2.5- 8 *V X^ X o 2 - >\ o\ o 2- X \\ b \ a \ \ 1.5 - \ \ 1.5- xx\ X O \0 \oo°o° # °\ 1 - \ ooo \ 1- X \ o \ \ xi \ \. 9 *° 0.5 - 0.5- V\ \ \ \ \ 0- 0- \ \ \ -0.5- XX \X o 0.5- **)r * oo

Fig.54 .Relativ epopulatio nsiz eo frelease d sterilesversu sag ei ndays .Experimen tMij s 1974.Correcte d toa nestimate d number of 1000a tag ezero . O:Females ; X:males ;a : 1stflight ;b :2n dflight .Curve sdraw ni nb yeye .

1st matingco.) X H M percentage of files I I I I 90

75

50

25

i I l I i i i i i i i i I i i i I i i i i i i i i i i i I i i i i i i i i i i i i 0 5 10 15 20 25 30 35 40 1st flight —r "I- -1 age inday s 10 15 20 25 30 2nd flight Fig.55 .Surviva lo fadul tonio nflies ,release d steriles.Experimen tMij s 1974.Dat a obtained from thecurve si nFig .54 .1s tan d 2ndfligh tag escale sadjuste d tosynchroniz e ageso ffemale sa t 1stmating . I,IIan d III:ovipositio nperiods ;O:females ;X:males ; 1stflight ;- - - 2n dflight .

86 percentage of females mated loo-r

e s 10 12 M age in days average age in days Fig. 56. Mating of fertile released females versus age. Experiment Mijs 1973-2. a. Flies released and recaptured in a large onion field. Each point represents 30-35 females checked. b. Flies released and recaptured at over 150 m from any onion field, as compared with the percentage expected from Fig. 56a. X : 6-12 females outside onion fields; O : 30-35 females in onion fields (different from Fig.56a because the data have been adjusted to the age distribution at release of the flies outside onion fields).

A.5 REPRODUCTION

4.5.1 Mating

All femalesmat ewithi na relativel y shortperiod ,startin ga ta nag eo fabou ta wee k (Fig.56) .Thi sperio dwa ssignificantl y prolongedfo rfemale s thatwer erelease dan d recaptureda tdistance so fove r 150m upwin d froma nonio n fieldan dwithou t onionfield s within4. 5k mupwin d (Section5.2. 1 ,se eFigs .1 2an d14) .Absenc eo fonio nodou rwa s foundt oretar d ovarydevelopmen t andmatin g (Ticheler 1970). Conformingt oth edat ao f Table1 ,a linea rrelatio nbetwee nrat eo fmatin gan dtemperatur ewa sassume d (Fig. 57). Inth eexperimen t Schuilenburg 1971,th eag eo fmos t recaptured flieswa sno t known. The averagematin gag ecoul db eestimate d thenfro mth epercentag eo ffemale s thatha d mated:becaus eal lfemale smate ,th e34 %unmate drecapture d femaleswer eth eyounge r ones. Inth eaverag e cumulative recapture curveo fmarke d femalesversu sag ei nthi s experiment 341wa sreache di n8. 2days ,thi sbein ga nestimat eo fth eaverag eag ea tfirs tmating . The onionfl yfemal ei spolygamous .Experiment so fNoordin k (pers.commun. ; 1967) indicate thatrematin gi sgenerall ywithi na wee kafte rth efirs tmating .Whe nno tgive n thepossibilit yt oremate ,a matin gma ypermi ta femal et ola yfertil eegg sdurin g some 20day s thereafter (TableI Vi nNoordink , 1971). The frequencyo fmultipl emating sca nb eestimate d fromth epercentage s sterilityi n eggdeposition so ffemale s caughti nth eSchuilenbur g experiments.B ynatura l sterility ofsom e 101th einformatio no nth emale s involvedi sobscure di nth edat aobtained .I f therewa sn onatura l sterility,th enumbe ro feg gbatche swit ha sterilit yo f1 t o49 % inclusivewoul d equaltha to fbatche swit ha sterilit yo f5 1t o99 1 inclusive,becaus e theprobabilit yo fa femal ematin gwit ha steril ean da fertil emal ei sindependen to f thesequenc eo fthes emating s (fullcompetitivenes so fsper mfro msterilize dmale s assumed, andprovide d thatth esterilit y amongth emale si sno tchangin g fast).I fon etake sth e

87 age of females days- days -6

0.15-

0.10- '0

0.05- -20

13 14 15 16 17 18 19 20 °C Fig. 57.Ag eo ffemale sa tmatin gan d eggripenin gversu s averagedail y temperaturea t 150c mheight .Experiment sMi js 1973-1(left) ,Vroegindewe i 1972-2(middle)an dMij s 1973-2 (right). o:10 %(uppe rpoint )an d90%(lowe rpoint )mated ; ©: 50%mated ;• : 10%wit heggs ; ®: 50%wit heggs .

natural sterility into account,th enumbe r ofbatche s with eggs that are'fertilized ' part­ lyb ysper m from sterilized males andpartl yb ysper m from normal males canb eestimate d as twice thenumbe r ofbatche s with anobserve d sterility of5 6t o99 1 inclusive. The second mating has adominatin g effect,an di tca neliminat eth eeffec t ofth e first mating after awee k (Noordink,pers. commun.). Forth emomen t letu sassum e thatal l multiple matings result ina detectabl e percentageo foffsprin g fromal l males concerned. The datao nth esterilit y ofeg gdepositions , corrected asindicate d above, are:

sterile fertile mixed 1st flight 21 % 29* 50% 2nd flight 23?o 53°6 24%

A reasonable mating model istha t females will remate acertai n numbero fdays , d, afterth epreviou s mating,matin g occurring atage s t,, t,» •••Fro m Fig. 55th efraction s alive a. have been taken,fo rdifferen t values of d. Letth eprobabilit y ofmatin g witha fertile maleb eƒ an dwit h a sterile male \-f. Thefractio n fertile eggdeposition s is the sumo fth efraction s mating n times multipliedb yth eprobabilit y ofmatin g only with fer­ tile males,an dthi s sumcorrecte d forth enon-mate d fraction.Or :

88 fractionfertil e= (1/a .) J (a. -a. )ƒ" ,an dsimilarl y c1 n rn n+1 fractionsteril e= (1/a .) l (a. - a. ) (1-/)n 'l n n *n+1 fractionmixe d =(1/a t) I K -a ^ ) (l-^d-/)")). 1 n n n+1

Asa .i sa functio no f d, dan dƒ ca nb eestimate dwit h theseformula eb yiteration : 1stfligh t ƒ= 0.5 5 d= 5. 7 2ndfligh t ƒ= 0.6 6 d= 5. 1 Therat eo fmatin gi nth esecon dfligh ti sthu s5.7/5. 1=1. 1time shighe r thani nth e first flight,wherea sth espee do fphysiologica l ageing,a smeasure d fromth eag ea tth e firstmating ,i s1.3 5time shighe ri nth esecon d flight (Fig.55) .Th ecaus ema ybe ,apar t fromchanc ean da bia si nd t ob ementioned ,th efac ttha tdat a fromdifferen tyear swer e mixed:th esterilit ydat awer efro m197 1an d1972 ,an dth esurviva lcurve suse dwer e from 1974.T oobtai nth e dvalue stha tfi t thesesurviva lcurve sbest ,th edifferenc ebetwee n the dvalue swa s increasedt oa facto r 1.35,b ychangin gbot hvalue swit ha facto r "V*l•1/ 1-3 5i nopposit edirections ,resultin gi nd value so f6. 3(1s tflight )an d4. 6 (2ndflight) .Th eaverag enumber so fmating spe rfemal eemerged ,calculate d fromFig . 55, are:1. 7(1s tflight )an d1. 0(2n d flight). Becauseth e effecto fprio rmating si seliminate dt osom eextent ,th eactua lrat eo f matingwil lb esomewha thigher .O nth e otherhan dth e rateo fmatin gwil lhav ebee nactu ­ ally lower,becaus e theprobabilit yo fmatin gwit ha fertil eo rsteril emal echange dcon ­ siderablydurin gth eexperiment s concerned.Th eeffec to fsuc ha chang eo nth e1s tfligh t calculationswa s investigated.I fw eassume ,fo rexample ,instea do fa constan tƒ valu e of0.55 ,tw oequa l fractionswit hvalue so f0.8 5an d0.25 ,thi schang eha st ob ecompen ­ satedfo rb yincreasin g dfro m0.5 7t o0.85 . Theprobabilitie s (1-f)o fmatin gwit ha steril emale ,0.4 5an d0.34 ,correspon d rea­ sonablywel lt oth e observed effective sterilities amongth eflie strappe di nth ecorres ­ pondingperiods :0.5 7an d0.43 .Th edifferenc ecan b eexplaine d assuminga competitivenes s ofsterile so f0.65 ,bu tchanc ema yb eresponsibl ea swell .

4.S.2 Oviposi tion

Itwa s investigatedwhethe rth e ovipositionfrequenc y couldb ederive dfro mth efre ­ quencieso fovar ydevelopmenta l stages.A tfirs tth eovar ydevelopmen t classificationo f Theunissen (1973a,1976 )wa sused ,stage sS 5t oS10 ,base do nth eamoun to fyol kexpres ­ seda sa percentag eo fth e ovariole lengthoccupied .T oeliminat ebiase destimations , the yolkan dovariol e lengthswer emeasure d (onerepresentativ eovariol epe rfemale) .Th e frequencydistributio no fthes epercentage s (Fig.58 )suggest s 33%an d66 %a smor ereal ­ istictransition sbetwee nstage stha nth e 25%,50 4an d75 %use db yTheunissen . Theegg sar egenerall yno t laidi non ebatch .Frequenc ydistribution so fth enumbe r ofovariole san dth enumbe ro frip eegg spresen tar egive ni nFig .59 .Fro mthi sth efe ­ maleswit hegg scoul db edivide d intothre estages :no tye tovipositin g (over3 6eggs) , ovipositionstarte d (19-36eggs )an dovipositio nendin g (1-18eggs) .Fo rpractica lrea -

89 number of females 50

Fig.58 .Frequenc ydistribu ­ tiono flengt ho fyol ka sper ­ centageo fovariol elength . ExperimentsMi js 1973- 1an d 1973-2,flie so fal lage s combined. r —— Oldesteg gchamber ; 90 -- nextoldes teg gchamber . length of yolk in % number of females

20-

number of ovarioles

Fig. 59. Frequency distributions of numbers of ovarioles and eggs. number of eggs Experiments Mijs 1973-1 and 1973-2.

sonsth estage swit h34-66° syol kan d67-99 %yol kwer etake ntogether ,a swel la sth e stageswit h 1-18an d19-3 6eggs . Therelativ eaverag eduratio no feac hstage ,assumin gequa lcatchin gprobabilitie s forth edifferen tstages ,wa sderive dfro mth efrequencie so ffemale si nthes estage s afterth efirs tovipositio nha dstarted . Thepercentag edistributio no fth efemale sove rthes estages ,versu sthei rag ea s found inexperiment sMij s1973- 1 andMij s 1973-2,i sgive ni nFig .60 .Th eage sindicate d wereadjuste dt oth escal eo fth e197 42n dfligh tmortalit ydat a (Fig.55) ,wit hth eli ­ nearityo fth erelatio no frat eo fovar ydevelopmen tt otemperatur e (Theunissen,1974 )t o eliminatedifference sbetwee ndays ,yieldin grelativ eages ,an dwit hth eag ea tth eaver ­ agetim eo ffirs tmatin gt ocalculat eth eabsolut eages .Theunissens 'dat acoul dno tb e usedt ocalculat eabsolut eage sbecaus ehi sexperimen twa sdon eunde rclearl ysuboptima l circumstances thatretarde ddevelopment . Thedistanc ebetwee nth egraph so feac hpai ro fstage swa smad et ocorrelat ewit hth e averagerelativ eduratio no fthes estage sa sestimate dabove .Du et oth edecreasin gnum ­ berscaught ,th egrap hbecome sles sreliabl etoward sth eright . InFig .60 ,th eaverag edevelopmen t isrepresente db ya straigh tlin ewhic hha st o passa smuc ha spossibl ethroug hth erelativ emaxima lfrequencie s inth egraphs .Th e

90 percentage of females 40-1

~T~ -1 1- 10 15 20 25 agei nday s Fig. 60.Distributio no ffemale sove rdifferen t stageso fovar ydevelopmen tversu sage , fromwhic hth eduratio no fgonadotrophi ccycle si sestimated .Ag eexpresse d inday sa ta n averagetemperatur eo f 16.5C(situatio n in2n dfligh t 1974).Experiment sMij s 1973-1an d 1973-2. - -- Fastes tfemale ; estimated averagefemale ; [_~j ovariapartl ywit hno tye tfull y developed eggs(dat aincomplet eu pt oag eo f 14days) . Stageo fovar ydevelopment :1 =1—33 %yolk ,11 =34-99 %yolk ,111 =ove r3 6eggs ,IV = 1-36eggs . fastestdevelopin g femalesoviposi tever y4 days .Th eaverag e femalei sconsiderabl y slower,a sca nb einferre dfro mth ediminishin g rateo finitia l increasei nfrequencie s offurthe rdevelope dstages .A reasonabl e estimateo faverag eovipositlo nrat eseem st o beonc eever y7 days ,wit h firstovipositio na ta nag eo fabou t 12days .Or ,a cycl edu ­ rationo f11 5daydegree san da pre-ovipositio nperio do f20 0daydegrees .Th efastes tde ­ veloping femalewil lstar tth esecon dcycl ebefor eth eslowes t femalestart swit hth e first.Thu sth erelativ emaxim ai nth efrequencie scorrespondin gt oth e secondan dhighe r gonadotrophic cyclesar eles sconspicuous . Therei ssom eadditiona l supportfo rthi sestimation .Th eeg gtrap spresen tdurin g experimentMij s 1973-2 (buto nanothe r field)caugh tver yhig hnumber so fegg sa tabou t 130an d260-31 0daydegree s afterreleas eo flarg enumber so fflie so f20-4 0daydegree sold . Inman y speciesgonadotrophi c cyclesca nb eidentifie d fromth epresenc ean dsiz eo f follicularrelic s (e.g.Detinova, 1968 ;Vog te tal. , 1974). Follicular relicsar epresen t inmultiparou sonio nflies ,bu twit hth eavailabl e informationthe ycanno tb euse drelia ­ blyt odistinguis hnulliparou s fromparou s females,a si sals oth ecas ei nsom erelate d species (Anderson,1964) . Itma ybecom epossibl et oidentif yth egonadotrophi c cyclesb y developingmor e elaboratean dtime-consumin g observationmethods .I nth elaboratory ,pa ­ rous femaleswithou tegg scoul db edistinguishe da ssuc hb yth epresenc eo fn olonge r functionalovariole s (smalleran do fa differen t appearance),o rb yvarianc eo fth eper ­ centageo fyol kpresent ,whic hi ssignificantl yhighe rafte rdepositio no fth efirs t eggs.Bot haspect showever ,stil ld ono tenabl ea soun ddiscriminatio nbetwee nnulliparou s andparou sonio nfl yfemales .

91 4.5.3 Reproduction factor

Thenumber so fegg slai dpe rfemal eca nno wb eestimate d fromth emortalit yan dth e rateo foviposition .Th epercentag eo ffemale stakin gpar ti nth esubsequen toviposition s isestimate d inTabl e22 . Thedifferenc ebetwee nth etw oflight s isa facto r2.1 .Thi sca nb eattribute dt o differences infl ysurvival ,partl ybecaus eo fth efungu sdisease .Becaus efemale swil l stopeg glayin gbefor ethe ydi efro mfungu sinfectio n (Theunissen,pers .commun.) ,th e 2ndfligh tfecunditie swil lb eactuall ylowe rtha nth ecalculate d 18.5egg spe rfemale . Thereproductio nfactor s inth esteril emal eexperiments ,th eeffec to fth esterile s beingeliminated ,ar esummarize di nTabl e23 .Th ethir dflight' sreproductio nwa sesti ­ mateda tzer oo rnegligible . Reproductionwa sclearl yhighe ro nth elighte rsoil so fOverflakke etha no nth e Schuilenburg,b ya facto r2 pe rgeneratio no r2. 5fo ra year .Th edifferenc ebetwee nth e twoflight swa sa rathe rconstan tfactor ,2. 3o nth eOverflakke econtro lplot .Th edif ­ ferencei nfecundit ywa sestimate da t2. 1 (Section4.5.3) ,o rles swhe na sterilizin gef ­ fecto fEntomophthor awa stake nint oaccount .Fro mth efecunditie san dreproductio nfac ­ torsa sestimate dabove ,th etota lmortalit y inth eegg ,larva lan dpupa lstage scoul d beestimate da t65 1an dles stha n68*. .i nth etw oflight so nth eOverflakke econtro lplot , and82 1an dles stha n85 %i nth eSchuilenbur g fieldtrials . Iti sno tye tknow nwha teffec tth edensit yha so nreproduction .Thi seffec tma yin ­ creasereproductio nwhe ngeneti ccontro lreduce spopulatio nlevel st olowe rvalue stha n previouslyoccurre d (Geier,1969 ;Berryma ne tal. ,1973 ;Lawson ,1967 ;Pa l& LaChance , 1974).Suc ha nincreas eoccurre d ina geneti ccontro lfiel dtes twit hCule x (Weidhaase t al.,1971) . Inth eonio nfly ,chemica lcontro lkeep sth epopulatio nfa rbelo wth eleve la twhic h

Table22 .Calculatio no ffecundit ype rflight ,dat afro mFig s5 5an d6 0

Gonadotrophic cycleno . Averagemomen to fovipositio n 1stfl i ght 2nd flight age (d) %aliv e age (d) %aliv e

1 16 58 12 31 2 26 17 19 5.5 3 35 1.7 26 0.3 4 45 0.1 33 0.0 numbero fgonadotrophi c cyclespe rfligh t 0. 77 0.37 fecundity 39 18.5

Table23 .Reproductio n factorsi nfiel d trialso nsteril e insect technique,effec to fth e sterilemale sexcluded .Detail s seeTable s27 ,3 7an d38 .

1stfligh t 2ndfligh t fora yea r

Mijs 1974(exp ) 6.01 2.49 11.97 Mijs 1974 (con) 6.97 2.98 12.78 Schuilenburg (1971-1974average)3.5 5 1.44 4.99

92 mortalityfro mcompetitio n canb eexpected .Also ,parasite s andpredator s thatcoul dcaus e densitydependen tmortalit y areprobabl y quantitatively unimportant asthe y areno t spe­ ciesspecifi c andbecaus eonio nflie s area minorit y among theAnthomyiid spresen t inth e agricultural areasconcerned .Thu spopulatio n levels lowertha na tpresen twil lmos tpro ­ bablyno tsho wa n increasedreproduction .On emigh teve nexpec treproductio n to decrease at lowerdensitie s duet oscarcit yo frotte nonion s onwhic h survival ishigher .A tver y lowdensitie s reproductionwil lb e limited alsowhe n thechanc eo fa femalet omee ta mal e becomes lesstha n 1.Whe nw e consider thereproductio n factorsobserve d inth esteril e insecttechniqu eexperimen tMij s 1974,factor so f6- 8 inth e 1stfligh tan d2- 4 inth e 2ndfligh tsee mreasonabl eassumptions .

4.6 SUMMARY

Thepossibilitie s ofpredictin g emergence fromsoi l temperature recordso rfro moa k leafbuddin g areevaluated . Bothmethod s seempromising . Flight curves fordifferen tyear s andcircumstance s aregiven .Diapaus e isinduce db y daylengthan dtemperature .Extrapolatio no fthes e laboratorydat at ofiel d circumstances givesa goo dagreemen twhe nth eeffectiv edaylengt hi sassume d tob e 1-2hour s shorter thanth eastronomica l daylength.Percentage s diapausing areo nth eaverag e 204fo r first generationpupa e and &S% forsecon d generationpupae .S oth esecon d flight isusuall y a partialone ,an da thirdfligh ti ssmal lo rabsent .Th ese xrati o inth ecapture s changes about linearilywit hth eaverag e age,becaus e females livelonger . Alliumvineal e doesno t support awil dpopulatio no fonio nflies ,s owil dhos t plants canb econsidere d tob eabsent .Th epreferenc eo fovipositin g females forrottin g onions isquantified .Onio nwast edisposa l siteswer e found tob eunimportan t forth epopulatio n dynamics ofth eonio nfly . Underth eprevailin g circumstances,th ebea nsee d flyprove d tob e asecondar y pesto f onionseedlings ,a sit spopulatio nwa snearl y eliminatedb ya neffectiv e genetic control ofth eonio nfly . The species ofdipter e larvaean dbeetles ,observe d inonions ,ar elisted . Incidental observations offeedin gonio nflie sar ementioned .Th eparasitoid sAleochar abilineata , Aphaeretaminut aan dPhygadeuo nsp .wer e observed. Infectiono fflie swit hEntomophthor a iscommo n insummer .Th e infectionrat ewa s found tob e 6%pe rday ,wit h increasing ageo f theflie sdecreasin g toabou t 3%. This fungusin ­ fectioncoul dno texplai nth ereduce d competitiveness observed inth efirs t field trial on sterile insecttechniqu e atth e Schuilenburg. Preliminary experimentswit h radioactive labeltransfe r revealed someactua lan dpo ­ tentialpredator s ofegg s andyoun g larvae.Som epredator s ofpupa e andadult sar emen ­ tioned. Onion flydamag e inuntreate d fields occursmainl y inJune ,du e toth efirs t generation of larvae.Damag ewa smor e severe atth ehead so fth efields ;a nedg eeffec twa sno t found. Theoccurrenc e ofdamag e fittedth enegativ ebinomia l distribution,wit h k dependent onth e mean.Th enumbe ro fsample s asa functiono fth emean ,neede d fora certai n levelo fpre ­ cision,wa scalculate dwit hth evarianc eestimate d fromth enegativ ebinomia l distribution,

93 fromTaylor' spowe rlaw ,o rfro mth erelatio no fmea ncrowdin gt oth emean .Thes epreci ­ sionlevel sar eapproximat evalue sbecaus eo fsom ebia si nthes ecalculations .Plo tsiz e fordamag eestimatio nshoul db ei npractic e0.5- 1 m. Theoccurrenc eo fpupa eals oconforme dt oth enegativ ebinomia ldistribution ,wit h k dependento nth emean .However ,teste dwit hanothe rmethod ,th efi twa squestionable .Th e numberso fsample sneede dfo rcertai nlevel so fprecisio nwer ecalculate da sfo rdamage . Confidencelimit sestimate dfro mthes edat awil lb erathe runreliabl efo rth esmal lsam ­ plesize san dlo wmean st ob eexpecte d inpractice . Mostfl ypopulatio nestimate swer eobtaine dfro mrelease-recaptur eexperiments .Wit h markedflies ,emerge dfro mreare ddiapausin gpupa ean dmixe dwit hth efirs tfligh tflie s 2 inth efield ,population so f1.7-3. 6flie semergin gpe rm werecalculate dfo rsom efield s withrelativel yhig hdamag elevels .Fro mrecaptur edat ao fa releas eexperimen twit hre ­ leaseso ndifferen tfields ,wit hon epopulatio nknow nfro mpup asamplings ,othe rpopula ­ tionscoul db eestimated . Datao nth erelatio no fth enumber so fdiapausin gpupa et odamag ea tharves tar egi ­ ven.Th evariatio ni sconsiderable .Densitie so nchemicall ytreate dfield swer eabou t 1000-2000 0pupae/ha . Froma nexperimen to nsurviva lo flabelle degg san dlarvae ,a hig hmortalit y inthes e stageswa scalculated .Th emortalit yo fdiapausin gpupa ewa sestimate da tabou t10-20°s . Survivalcurve so fflie swer eestimate dfro mrecaptures ,takin gint oaccoun tmigration , andunderrepresentatio no fver yyoun gflie si nth ecatches .Th elife-span sconforme dt o anorma ldistribution ,wit hmea nvalue sfo rfemale stha twer eabou t1. 4time slarge rtha n formales . Therelatio no fth eag edistributio na tth etim eo fth efirs tmatin gversu stempera ­ turei sgiven .Fro msterilit ydat ao fth eegg slai db yfertil efemale si na fiel dtria l onsteril einsec ttechnique ,th efrequenc yo fmating scoul db eestimate da tabou tonc e every5- 6days . Fromth efrequencie so fdifferen tphase si nth egonadotrophi ccycl eversu stime ,th e frequencyo fovipositio nperiod swa sestimate da tabou tonc ea week .Combinatio no fthes e datawit hth emortalit ycurve sgav eaverag efecunditie so f3 9an dles stha n18. 5egg spe r femalefo rth e1s tan d2n dflight ,respectively . Reproductionfactor swer ecalculate dfro mth esteril e insecttechniqu eexperiments . The2n dfligh treproductio nwa snearl ya facto r2. 5 lowertha nth e1s tfligh treproduc ­ tion.Reproductio nfactor sunde rnorma lonio ngrowin gcircumstances ,onio nfl ycontro l excepted,wer e 7(1s tflight) ,3 (2ndflight )an d1 3(fo ra year) . Inth eSchuilenbur g experimentsthes evalue swer ehal fa shigh .Fro mth ecalculate dfecunditie san drepro ­ ductionfactors ,mortalit y inth epre-adul tstage scoul db eestimate da tabou t65 1(ligh t soil)an dabou t 85%(heav ysoil) .

94 5 Dispersal

Dispersal isa critica l factor ingeneti ccontrol :i tcondition s thedelimitatio no f populations andthereb yth eminima lare at ob e treated,an d itdetermine s thereleas e sitedistances .Also ,whe nth ereproductio no fpopulation s ismeasured ,exchang ewit h otherpopulation sneed st ob e taken intoaccount . Most informationo ndispersa lha sbee ncollecte d fromrelease-recaptur eexperiments . Thegenera ldat ao nthes eexperiments ,includin g thesteril emal erelease so nth eSchui - lenburg,ar esunmarize d inSectio n3.1. 1 (Table3 ,Fig s 13-15). InSectio n 4.3.3 support isgive nfo rth eassumptio ntha tth edispersal ,a sobserve d inthes eexperiment swit hla ­ boratory-reared flies,ca nb etake n asrepresentativ e forth ewil d flydispersal . Firstth eeffec to fsom efactor s likeweathe r andonion so ndispersa l isexamined , thenth erat eo fdispersa l isestimate d indifferen tways ,assumin g thatth edispersa l canb e considered asa diffusio nprocess .Als o anexampl eo fanothe rapproac h indis ­ persalanalysi s isgiven .T oovercom e theproblem s inestimatin g therat eo fdispersa l fromth efiel ddata ,tha taros e fromheterogeneit y intim ean dspace ,a simulatio nmode l wasuse d toestimat e flydiffusio nparameters . The impacto fwil dpopulations ,emergin gnea ra field treatedwit h sterilemales ,o n theoutcom eo fthi scontrol ,i sestimate d fromth eaverag ematin g age,th eag edistribu ­ tiono f immigrating flies,th edistributio n offlie sove rdifferen t sitesversu s age,an d therelatio no fth enumber s caughtversu sdistance .Thes edat awer e obtained froma nex ­ tensiverelease-recaptur e experimentdon emainl ya sa fieldtes to nsteril e insecttech ­ nique.Als o it iscalculate d fromthes edat aho wpre-reproductiv e dispersal changed the numbersemerge dan d released intothos eactuall yreproducin g onth eonio nfield scon ­ cerned.

5.1 PRELIMINARY DISPERSAL EXPERIMENTS

A fewpreliminar y experimentswer edon eo ncolonizatio nb yplacin guntreate donions , thatha dbee nslightl ydamage dartificially ,a sa tra pcro p inth efield . InMa y1970 , trayswit hgreenhouse-grow n onionseedling swer eplace d atdifferen tsite s inOostelij k Flevoland,a nare areclaime d inth esixties ,o nwhic h cultivationwa s stillspreadin gb y onth eaverag eabou t 1km/yea rwestwards .Thre etray swer eplace dnea r thewesternmos t onionfields ,an d twoalon g thewester ndik e separatingth epolde r froma mor e recently reclaimed stilluncultivate d area (Fig.61) .B yth een do fAugus t 1970onio nfl y larvae orpupa ewer e found intw oo fth etray snea ronio nfields .Thu sth eflie scoul dkee ppac e with thesprea d ofonio ngrowing . Another experimentwa sdon eo nth edike s connecting the former islandso fOverflakke e toothe rforme r islands.Thes ear esurrounde db ywate ro rtida lmudflats ,an dar eabou t

95 g.61 .Occurrenc eo fonio nflie si na icentlyreclaime d area. =Unde r cultivation,wit habou t3 %onions ; =mainl ylarge-scal ecultivation ,n oonions ; c= no tye tcultivated ; 0= westernmostonio nfield s (1970); A.= tra ponion splaced ,n olarva efound ; • =tra ponion splaced ,som elarva efound .

50m wid ean dabou t6 k mlong .Som eyoun gonion swer eplante d inlittl egroup sa tdistan ­ ceso f0-210 0m fromth eisland ,ever y 100o r20 0m ,i nth egrass yverges ,i nMa y1972 . Subsequentcheckin greveale donl ya tth efirs tcontro ldate ,3 week safte rplanting ,on e onionfl ylarv aa t20 0m fro mth eisland ,o non eo fth etw odike sconsidered .Clearl ythe ­ sedike sar efo rth eflie sno tth ecrowde dmigratio nfunnel sthe yconstitut efo rbird s andcars .

5.2 FACTORSAFFECTIN GDISPERSA L

5.2.1 Weather and onions

Therat ean ddirectio no ffl ydispersa lma yb edependen to nsevera lfactors .Befor e amor egenera lapproac ht odispersa lanalysi si smade ,th eeffec to fthes efactor swil l beconsidered . Toanalys esuc heffects ,th erat eo fdispersa lwa smeasure dunde rdifferen tcircum ­ stances.Thi srat eca nb emeasure dfro mth etim ei ttake sfro memergenc et oth efirs tre ­ capturea ta certai ndistance .Suc ha measuremen tstrongl ydepend so nth esiz eo fth ere ­ leasedpopulatio nan do nth etrappin gintensity .T oobtai na measuremen t independento f thesefactors ,th edispersa lrat ewa smeasure dfro mth etim ei ttake sfro memergenc et o themomen ttha ta certai npercentag e (i.e.5 o r10 )o fth etota lnumbe ro fflie srecap ­ tureda ta certai ndistanc ei sreached .Thi smeasuremen t isproportiona lt oth eaverag e netdisplacement . Theweathe raffect sfl ydisplacemen tmeasure db yfligh tinterceptio ntrapping ,a s analysedfo ra temperatur eparamete r inSectio n3.3.3.1 .Th erat eo fdispersa la sdefine d aboveshoul dthu sconfor mt oth esam erelatio na si sindee dfoun d (Fig.62) . Therela ­ tionestimate di nSectio n3.3.3. 1i sbase do nmore ,an dmor eaccurate ,dat acompare d withth erelatio no fFig .62 .Therefor ethi srelation ,a sgive ni nFig .24 ,wa suse dt o

96 rat« of migration in m/day 250-1

200-

O ° / ° ••'"' /

150- / .••

O.-' o 100 .••''/O o o Fig. 62.Relativ e rate ofmigratio n versus temperature, ascalculate d from theday s 50- o / between average emergencet o10 %recapture d / ona nonio n field at70 0m distance . Experiment Schuilenburg 1973. Regression line y - 7.91a;- 57.2 ; 5 10 15 S S 3ö c" trapping probability (Fig.24) .

eliminate theprobabl y largerpar to fweathe r influenceo ndispersa l rate,b ytransfor ­ ming thedat at othos e expectedo nstandar d days (max. 20°C). Another important effecto fweathe rma yb eexpecte d fromwin d direction.Thi sma yaf ­ fectthe preferre d flightdirectio nan d thereby thedispersa l ratea sobserve di na cer ­ taindirection .The effecto fwin d directionha st ob eanalyse di nconnectio nwit hth e presenceo rabsenc eo fonio n odour.I na nare a likeOverflakke enearl y allupwin dmove ­ menti ssomeho w towardsa nonio n field.Durin g oneexperimen tdat a couldb ecollecte d onupwin ddispersa li na directio nwher e theneares t onionfield swer ea ta distanc eo f at least4. 5k m(o nth enex t island),an dther ei na ver y lowdensity .I twa s found that

-15- upwind

-2

500 750 atanca in m

Fig. 63.Effec t ofwin d directiono nonio nfl ydispersal ,i nabsenc eo fonio n odour, shown from thelg( %recapture d pertrap ) versus distance from thereleas e site. Experiment Mijs 1973-2. Regression line: upwind y - -0.00360x -0.992; downwind y - -0.00356a:-0.989 .

97 inthi scase ,wit hth ewin dpresumabl ycarryin gn odetectabl equantit yo fonio nodour , dispersalwa sindependen to fwin ddirectio n (Fig. 63). Datao nth eeffec to fwin ddirectio no nrat eo fdispersal ,i nth epresenc eo fonio n odour,ar esummarize di nFig .64 ,separatel yfo rdispersa lthroug honio nfield san d othervegetations .Ther edoe sno tsee mt ob ea neffec to fwin ddirection . Fig.6 4show stha toutsid eonio nfield sth erat eo fdispersa li sabou ta facto r2. 5 fastertha ntha tthroug hth eonio ncrop ,possibl ybecaus eth eonio nodou rha dsurpasse d anuppe rlimi tfo rinductio no factivity .Th epresenc eo fsuc ha limi twa sdemonstrate d byWolf f (1973).Onio nfield sconstitut eunnaturall y largean dconcentrate dsource so f onionodour ,s oth econcentratio nma yver ywel lb eto ohigh .Anothe rexplanatio ni sth e probablydifferen tcompositio no fth eodou rnea ronions ,du et oth einstabilit yo fsevera l ofit scomponent s (Carson& Wong ,1961 ;Saghi re tal. ,1964 ;Brodnit ze tal. ,1969 ; Boelense tal. , 1971).Th elatte rmechanis mma ywor kver ywel lunde rnatura lcircumstan ­ cest okee pth eflie snea ronions . Thefl ybehaviou robservation si nonio nfield sgav esom eindicatio no fa nupwin dpre ­ ference (Fig.65) .Also ,th etrappin gprobabilitie s ina nonio nfiel dwer edependen to n winddirection ,whic hma yb eattribute dt oa preferentia ldispersa ldirectio n (Section 3.3.3.1).

rate of migration in m/day 1000-1

t * <8 O

100-

"9 O

O £

45° 90° 135° 180° average per 90° 135° experiment "5= Fig.64 .Effec to fonio ncro pan dwin ddirectio no nrelativ erat eo fmigration ,calculate d from theday sbetwee naverag eemergenc et o5 %recapture d ona site ,tim ecorrecte d to standard days.Abscissa :averag eangl ebetwee ndispersa ldirectio nan dupwin ddirection . Left:throug honio ncrop ,right :outsid eonio ncrop . Weighted difference2.46 . Experiments: X Mijs 1974,flie srelease d ontria lfield ;O Mij s 1974,pupa erelease do n trialfield ;AVroegindewe i 1972-2;VMij s 1974,pupa erelease d oncontro lfield .

98 wind

10. 20 'nurnbtr of flight«

Fig. 65.Fligh tdirectio nwit hrespec tt o winddirection .Observation sfro m1971-1973 , n=183.Teste d against/withwin ddirection : X^=4.36 ,P = 0.04 ,jus tsignificant .

Recaptures throughout theyea ro na distan t field,expresse da spercentag eo frecap ­ tureso nth e fieldo forigi no nth esam eday s (to eliminate effectso fpopulatio ndensi ­ tyan dweather-dependen tdifference s intrappin gprobability )wer ecompare dwit hth ewin d direction.Ther ewa sn ocorrelatio ns otha tmigratio n towards another onionfiel di sin ­ dependento fwin ddirection .

5.2.2 Barriers

Dispersalca nb edisturbe db ybarriers .Thes e canb eeithe rabsorbin g (killingth e flies)o rreflectin g (halting the flies).A wate ro fabou t2 0m wid ewa sn obarrie rfo r thedispersin g flies: therecapture s across thewate r conformedt oth eexpectatio n from the linear relationo flg(recaptures )versu sdistanc ewhic hi sgenerall y found (seeSec ­ tion 5.5;Fig .80c) . Severalexperiment swer edon enea ra wate ro f3- 4k mwide .I twa s investigatedwhet ­ herit seffec t couldb ebes t considereda sabsorbin go rreflecting .I fflie sfl yeasil y over thewater ,som ema ycros si tan dother sma yreturn ,givin g intermediateresults ,a s when someo fth eflie s arewashe d ashore alive.A reflectin gbarrie r increases thepo ­ pulationdensitie swit ha facto r approaching2 nea r thebarrie ran dals owit ha facto r approaching2 ove rth ewhol e areawhe nth ereleas epoin ti snea rt oth ebarrier. A nab ­ sorbingbarrie rwil l severely reduce thepopulatio ndensitie snea r it,approachin gpopu ­ lationeliminatio nwhe nth ereleas epoin ti sclos et oth ebarrier . Consider theoblon g trial fieldi n1974 ,lyin gperpendicula rt oth ewate r (Fig.15) . Flieswer e releaseda fe wtime snea ron eo rbot hend so fthi sfield .Fig .6 6compare s theaverag e recapture siteso fsuc hgroup s against timeo nthi s fieldwit hthos eo fwil d fliesan dflie stha t emerged allalon g theedge so fth efield .Th e dispersalo fth e groupsrelease dneare rt oth ewate r seemed slower,a scoul db eexplaine db ya steepe r populationdensit y gradient causedb yth ewate ra sa reflectin gbarrier. A nabsorbin g barrierwoul dhav e causeda seemingl y fasterdispersal .Als o therecaptur e rateswer e

99 relativ« position 4*

time in Standard days Fig.66 .Averag erecaptur e sitesalon g anoblon gonio nfield ,o fflie srelease d aton e endo fth efield .Experimen tMij s1974 . Wildflie san dflie srelease d evenlydistribute d along thelon gsid eo f thefield ; x,A,+ : flie srelease d nearth eS Wen do f thefiel d atdifferen ttimes ; 0,V: fliesrelease d near theN Een do f thefiel d atdifferen ttimes . Dayzer o is1 3July .

notdependen to nth ereleas esit eposition s (seeTabl e3 2an dFig .2 0 :release dnea r thewater :GC 2,BYC 2,GY 2;a tth eothe rend :B0 2,BY 2> B2,BG 2,C 2).Thu sth ewid ewate r canbes tb econsidere da sa reflectin gbarrier . Theassumptio nwa schecke db yreleasin gsom ehundre dflie s0. 1 mfro mth ewater ,du ­ ringfin eweathe rwit ha S Wwin dblowin goffshore ,an di nabsenc eo fonio nodour .Flight s startedi nal ldirections ,bu tth eflie stha tfle wove rth ewate rreturne dwithi n0. 2m ofth eshore ,wit honl yon eexception ,a fl ytha tlande do nth ewate rsom emetre soff ­ shore.Onl ya fe wflie slande do nth ewate rwhe nflyin gbac kt oth eshore .Mos to fthes e werewashe dashor eundamage dprobabl ybecaus eth ewate rwa sver ycalm .Th eother sfloate d awayquickl ydu et oth ewind .The yma yhav ereache dth eothe rsid eo fth ewate r(cf . Norlin,1964) .

5.2.3 Passive dispersal

Anytraffi cma yserv efo rtranspor to fonio nflies .Severa ltime sonio nflie swer e transportedo nth eoutsid eo fth eauthor' scar ,ove ra tleas t1 km .Onio nflie sar efoun d oncar sregularly ,probabl yfeedin go ndea d insectso r 'sunning'.Especiall yonio ntrans ­ portma yprovid elon gdistanc etranspor tfo rth eflies .Becaus eth enumbe ro fflie strans ­ portedwil lb ever ysmal lcompare dwit hth epopulation spresent ,thi sdispersa li sunim -

100 portantexcep tfo rcausin greinfestatio nafte reradication ,o rfo rspreadin gresistance . Anothermor eo r lesspassiv etranspor tma yoccu rb yaeria lcurrents .I ndat ao faeria l catchesAnthomyiida ear ementione d inrathe rsmal lnumber s (e.g.Hard y& Milne ,1938 ; Glick,1939 ,1960 ;Glid e& Noble ,1961) . Iti simpossibl et oasses sfro mthes edat ath e quantitative importancefo rth eonio nfly ,on eo fth elarge rAnthomyiids .Fro mfiel dob ­ servations itdoe sno tsee mprobabl etha tonio nflie sente rth eaeria lplankton :flight s weregenerall y atth eleve lo fth eto po fth evegetatio nan dneve rmuc hhigher .Wit h strongwind sth eflie sremaine d lower;wit ha win do f 15m/se cth eflie swer eobviousl y verywel labl et ochoos ethei row nfligh tdirection . Any losso frelease dflie st oth eaeria lplankto nwoul dappea r inth edat aa sa mor ­ tality factorfo rthes eflies ,an dcanno tb edistinguishe d from it.Th eshap eo fth e mortalitycurv e (Fig.55 )ca nhardl yb e interpreteda sbein gcause dmainl yb y sucha typ e ofemigration .However ,i tma yb etha tonl yver yyoun gflie ssho wthi smigration ,whic h isa commo nan d logicalphenomeno n (Johnson,1960) .Whethe ryoun gonio nflie sexhibi t suchbehaviou rcanno tb eascertaine d fromth erecaptur edat ao fth erelease d flies.No w a quantitatively importantaeria lmigratio nwil lremov ea considerabl efractio no fth e populations,an dad da considerabl eamoun to fwil d fliespe rarea .Suc ha namoun ti sim ­ portanti n 'isolated'onio nfield swit h lowpopulations ,causin gth eapparen treproduc ­ tionfactor sther et oris ewhe nth epopulation so femergin g fliesar ereduce de.g .b y sterile insecttechnique .A sca nb esee ni nTabl e 27,th ereproductio nfactor so nsuc h an 'isolated'fiel dd ono t showa clea rdensit ydependence .Thu sa longdistanc edis ­ persal wouldno tb equantitativel yimportant . Anotherargumen tagains tsuc hlon gdistanc edispersa l isth erathe rgradua lsprea d ofresistanc e (Section 2.3.3): ittoo ka t leastthre eyear so rabou tsi xgeneration sfo r resistance tobecom eestablishe d inal lDutc honio ngrowin gareas ,startin g froma tleas t threesources .Also ,mor etha nte nyear safte rth estar to fresistanc e inth eNetherlands , susceptiblestrain swer e stillpresen t inEnglan d (Gosticke tal. , 1971),Franc e (Missonnier& Brunei ,1972 )an dPolan d (Narkiewicz-Jodko,1974) .Gostic ke tal . (1971) evenfoun dstrain so fwhic h 3%an d0 $survive da discriminatin gdos eo fdieldrin ,a t distanceso f0. 8 and 1.6 km,respectively ,fro mth esit ewher ea strai nwa s foundwhic h had 551surviva li nthi stest .I tseem stha tth esprea do fresistanc ei smor eth eresul t ofth econtro lhistor ytha no fdispersa lo fresistan tflies.

S.Z.4 Fly properties

Flysiz ewa s foundt ohav ea neffec to nrecaptur eprobabilit y (Fig.67) .I tca nb e seenfro mth eexperimen tPolleman s 1971 thatthi s isno ta neffec to fa highe rmortalit y rate.Ther eth ever ysmal lflie s (average9. 2m gpupae )showe dver y limiteddispersa l (Fig. 80b),bu tthei rmortalit yseeme dfairl ynorma la sthe ywer ecaugh tu p toa nag eo f about4 0day s (correctedt ostandar ddays ;tha ti scomparabl et oth e2n dfligh tdat ai n Fig. 55).Thu sth eobserve ddecreas eo fth efractio nrecapture dwit hdistanc ewil lhav e beendu et oa slowe rdispersal . Differencesbetwee nth esexe swil lb econsidere d inSectio n5.3. 2 and,togethe rwit h theeffec to fage ,i nSectio n5.6 .

101 recaptured flies in % 4-

•o o Fig.67 .Percentag eflie srecapture dversu s 0J ,2 averagepupa lweight . pupal weight in mg Experiment Schuilenburg 1971.

Thereleas emetho dca ninfluenc eth erat eo fdispersa lbecaus eo finteractio nbetwee n theflie sa tver yhig hinitia ldensities .Densit yha sbee nfoun dt oincreas emigratio n activityi na wid evariet yo fspecie s (e.g.Wolfenbarge re tal. , 1974),includin gonio n flylarva e (Robinson,pers .commun.) .Th eeffec to fdifferen tconcentration sa tth eemer ­ gencesit edi dno taffec tth epercentag eo fflie stha temigrate dfro mth eexperimenta l field (Table 32),no rth erat eo fdispersal .Recaptur edat afro mflie srelease dfro mcrow ­ dedcage sresulte di na dispersa lrat ewhic hwa sa tleas tinitiall y increased.However , withanothe rtyp eo fcag e (Section3.3.2.2 )a neve nmor eintens ecrowdin gcause dn osig ­ nificantdeviation .Th ehig hrat eo fdispersa li nth eforme rrelease sca nb eexplaine db y theabsenc eo fonio nodour .

5.3 DIFFUSION

5.3.1 Introduction

Especiallywhe npes teradicatio ni saime dat ,th emaximu mdistance stha tca nb e reachedb ydispersin gflie sar eo finteres tbecaus ethes eaffec tth eprobabilit yo fre - infestationan dth edept ho fth ebarrie rzon etha tha st ob eretaine daroun da nemptie d area.O fcours eth eoldes tfl yan dth efastes tfligh tobserve dar erathe rmeaningless , andan y 'dispersalmaximum 'shoul db econnecte dt osom eprobabilit yo fth eoccurrenc eo f thatvalu eo ra highe rone . Themos tusefu ldispersa lparamete rfo rcalculatin gthi si sth ediffusio nspee da s developedi nphysic sfo rparticles .Th eadvantag eo fa diffusio nmode lfo rdispersa li s itssimplicity ,it sdisadvantag ebein gth eofte nrigorou ssimplificatio no fth ebiologi ­ calreality .I tha sbee nuse dt odescrib eman ybiologica ldispersa lphenomen aofte nwit h sufficientaccurac y (e.g.Mclntyr ee tal. ,1946 ;Skellam ,1951 ;Broadben t& Kendall ,1953 ; Beverton& Holt ,1957 ;Jones ,1959 ;Richardson ,1970 ;Scotte re tal. , 1971).Althoug h somecomplication s canb ecope dwit h (e.g.Holt ,1955 ;E.J .Williams ,1961 ;Holgate ,1971 ; Skellam, 1973),a mor edetaile dadjustmen to fth ediffusio nmode l i biologicalheteroge ­ neitiesquickl ycomplicate sth eformulae . Thediffusio nspee di smeasure db yth ediffusio nconstant ,diffusio ncoefficien to r 2 diffusivityD ,or ,afte rSkella m (1951),b yth emea nsquar edisplacemen ta =4D .Beverto n

102 & Holt (1957)us ea dispersio n coefficientD tha tequal sa . Th e dimensions arespee dx 2 distance,her e inm /day .

5.3.2 Calculation of diffusion coefficient from field observations of fly behaviour

Thediffusio ncoefficien t canb ecalculate d fromth enumbe ro fflight s npe runi t 2 time,wit h independent directions,an dth eaverag e flight distance d, byD = nd/ 4 (Beverton& Holt ,1957 ,p.138 ;Pielou ,1969 ,p.130) .Thes edat acoul db eestimate dfo r dispersali nonio nflie s fromth eobservation so ffl ybehaviour .I nth edeterminatio no f both flight directionan ddistanc e flown,an ydeviation s fromth estraigh tpat hconnec ­ tingth ebeginnin gan den dpoin thav ebee n ignored.Th esubsequen t flightdirection swer e independento feac hothe r (Fig.68) ,a sobserve d alsofo rth ecabbag e rootfl y(Hawkes , 1972).However ,Skella m (1973)showe d thatthi si sn oprerequisit efo rth ediffusio nfor ­ mulat ob eapplicable . Theaverag edistanc e flowncoul dno tb edetermine d directly,becaus e several times a flywa s lostsigh to fan dcoul db esai d onlyt ohav e flown,fo r example,a tleas t5 o r at least1 0metres .Generall y thisoccurre dwit h the longer flights.No wi twa s found thatth efligh tdistance s conformedt oth elog-norma l distribution overth e observable range,an dwer eno t contradictorywit h thisdistributio n over longerdistance sa swa s determined fromth eextrem epossibl evalue so fpartl y knownfligh tdistances .Thes eex ­ tremepossibl evalue swere :eithe ral l flights ceaseda tth emomen tth eflie swer e lost sighto f(uppe rpoint si nFig .69 )o ral l flights continued indefinitely (lowerpoint s inFig .69) .B ylinea rextrapolation ,th efrequencie so fth e longerdistance swer ees ­ timateda sa preliminar ymodel .Th emea nan dvarianc eo fth etransforme d distribution canb erea dof fth egraph :m(lg(œ) )= lg1.4 8= 0.1 7 ande 2(lg(a;))= (lg5. 1- lg1.48) 2=

precedingfligh t

number offlight s

Fig. 68.Fligh tdirection swit hrespec t toth e directiono fth eprecedin gflight .Observation s from 1971-1973rc=114., Teste d same/opposite direction:x ?= 0.74 ,n.s .

103 percentage of flies

99.9

99-

95 90-

50

10- 5-

0.1-

1 1—I' I I I I I I 1 1—I 1 I I I I 1 1—I I I I I I I 1 1—I I 0.01 0.1 1 10 100 distance inm Fig. 69.Distributio no ffligh tdistance sfro mobservation s inonio nfields :cumulativ e frequencyversu sdistanc eflown . O :Females ,11 2flights ;X : males ,9 7flights . Twosymbol sa ton edistanc e indicateth epossibl erang eo fth epercentage ,becaus eo f individuals thatwer elos tsigh tof .

0.29.Transformin gbac kt oth elog-norma ldistributio nth eorigina lmea nca nb eobtaine d from i 2 ml» =10 m(lSW) + 2s (18^ (12) or, m(x) =2.0 6m . Themale sprovide ,moreover ,anothe rproblem .The ysho wtw otype so fflights : flightssimila rt othos eo fth efemales ,thu scontributin gt odispersal ,an dshor t flightsconsistin go fcrossin ga tth evegetatio nto plevel ,th efl yofte nreturnin gt o exactlyth esam esite .Thi sbehaviou r isinterprete d asbein gflight si nsearc ho fa mate (compareth esimila rbehaviou ro frelate dspecies :Downes ,1969 ;Gruhl ,1924 ,1959 ; Vogel,1957 ;Mille r& McClanahan ,1960 ;Hawkes ,1972) .N oelicitin gstimul iwer eidenti ­ fied,apar tfro mth efac ttha tmale ssittin gnea reac hothe rusuall yfle wu pa tnearl y thesam emoment .Thes eflight swer eexclude dfro mth edat ab yassumin gfo rmale sa n equalpercentag eo fdispersa lflight swit h zerodisplacemen ta swa sobserve dfo rth efe ­ males.Th eresultin gfligh tdistanc edistributio no fth emale si ssimila rt otha to fth e females. Thefrequenc yo fflight swa scalculate dals ofo rth esexe sseparately .I nth e15. 3 hourso fobservatio no ffemales ,12 2flight swer erecorde d (flightsa tth ebeginnin go r endo fa nobservatio nperio dar ecounte dfo rhalf) .Thu sa femal efl yflie sever y7. 5mi ­ nutes,o r8 time sa nhour .Th edaylengt hma yb epu ta tabou t1 4hour s (Fig.21) ,yieldin g about11 0flight sa day .Wit ha measure dflyin gspee do f2- 3m/sec ,ove rsuc hshor tdis -

104 tancesa sobserve dth eduratio no fth e flightsi snegligible .Fligh tdistanc ean dduratio n ofth eprecedin g restingperio dar eno tcorrelated . 2 Thediffusio ncoefficien ti nonio nfield sca nno wb eestimate da tD = 11 0x 2.0 6/4 , 2 orabou t 120m /da yfo r females. Formales ,afte reliminatin g thesam efractio no fflight s (17.7%)a sdon ei nth ecal ­ culationo ffligh tdistances ,th edat aare :i n9. 8hour so fobservatio n 117flights ,tha t 2 ison eever y5 minute so rabou t16 7flight spe rday ,an dD = 17 5m /day .Th edispersa li n anonio nfiel di sthu sfo rth emale s1. 5time shighe r thanfo rth efemales ,du et oa hig ­ her frequencyo fflights .

5.3.3 Calculation of diffusion coefficient from release-recapture experiments

Thediffusio ncoefficien tca nals ob ecalculate d fromrecaptur edata .Whe nth epat - 2 terno fth epopulatio nversu stim eca nb eestimated ,th erelatio n pt =exp(-r t/4Dt ) can beuse dt oestimat eD (Scottere tal. , 1971;Pielou ,1969) ,wher e pt isth efractio no f thepopulatio noutsid ea circl ewit hradiu s r+ aroundth e origina ttim e t. Thus,wit h 2 2 themedia ndistanc e rt =4Dt.ln2 ,an dD ca nb efoun dfro mth eregressio no fr on t. Thisapproac hcoul db edirectl y appliedi nth eexperimen t Pollemans 1971,wher edu e toth ecol dan dwe tweathe rth eflie smove donl y littlean dthu scoul db ecounte daroun d 2 thereleas esite .Th e resultwa sD = 1.7 5m /day . Thepopulatio ndistributio naroun dth eorigi nca nb ecalculate d fromth erecaptur e datawhe na correctio ni smad et oobtai na nequa ltrappin g intensityove rth ewhol eare a concerned.Th edat ao fsom eexperiment swer ecorrecte d accordingly.Becaus eo fth eloca l accumulationsi nonio nfield san dth econsiderabl e areas forwhic hth elo wnumber srecap ­ tureda tlarge rdistance swer etake nt ob erepresentative ,th ecorrecte ddat aobtaine d arerathe runreliable .Dat aca nb euse donl yu pt oth emomen twhe nconsiderabl enumber s offlie shav esupposedl y leftth eare awher eflie swer etrapped .

150.000-

100.000

50.000-

Fig. 70.Estimatio no fdiffusio ncoefficien tfro mth eregressio no f thesquare dmedia n distanceo fth erelease dpopulatio no nth etim ei nstandar ddays . X :Experimen tMi js 1973-2,release s fromfl ycage sove r 150m fro man yonio nfield , onionodou rabsent ;r |- 6 5000 4, D = 2 340 0m 2/d. O :Experimen tVroegindewe i 1972-2,release sfro mpupae ,dispersa l throughan dbetwee n onionfields ; rî » 10000 * ,D - 3 60 0m 2/d.

105 Asshow ni nFig .70 ,i na nare awit ha usua lonio nfiel ddensity ,D i sfoun dt ob e 2 3600m /day ,an da muc hhighe rvalu e isfoun dfo rdispersa loutsid eonio nfield safte r ? releasefro mcages :abou t2 340 0m /day . Anothermetho dwa sa sfollows .Th edensit ya ta give npoin ta tdistanc e r isgive n by (e.g.Pielou ,1969 )

1 -,2 Ur't) =4DTTf exP4D * (13)

Acertai nthreshol ddensit ywil lresul ti na nexpecte dnumbe ro fon efl ype rtra ppe rday . Thisthreshol dwil lb ereache do ndifferen tplace sa tdistance s r andtime s t . Thus,b y puttingf(r..,*.. )= f(r 2,*2)fo rth efirs trecapture spe rdistance ,i tfollow stha t

2 2 L D= -!— ! —L (14) 41n(t2/tpi liketh esimila rformula efo ron ean dthre edimensiona lcase sgive nb yBosser t& Wilso n (1963).Whe napplie di nexperimen tVroegindewe i1972 ,widel ydifferin gvalue swer efound , includingnegativ eones .Applicatio no fEq n (14)t oth eoutpu to fa dispersa lsimulatio n model (Section5.4 )reveale dtha tthi sinstabilit ywa scause db yth edistributio no f emergenceove rth emorning so fsevera lconsecutiv edays ,an db yth econcentratio no fth e flieso nonio nfields .Th emetho d isthu sver ysensitiv et oheterogeneities ,s oi twil l begenerall yinapplicabl et obiologica ldata . Witha regula rspacin go fth etrap sove rth eare aove rwhic hth eflie sdisperse ,th e diffusioncoefficien tca nb efoun dfro mth eincreas eo fth evarianc e (2Dt)wit htim e (Richardson,1971) .Thi sca ngiv eindication sabou tth eeffec to fag eo rtim edependen t factorso ndispersa l (e.g.weather ,Dobzhansk y& Wright ,1943) .Du et oth efas tdisper ­ sal,th elimite dnumbe ro ftrap savailabl ean dth eheterogeneit yo fth eexperimenta l areasthi sapproac hcoul dno tb efollowe di nth eonio nfl yexperiments . Theconsiderabl edifference sbetwee nth ediffusio ncoefficient sobtaine dabov ere ­ quiresom ecomment .Th evalue scalculate dfro mth eobservation so ffl ybehaviou rar e ratherunreliable ,a sth equantitativel ymor eimportan tflights ,thos eove rlonge rdis ­ tances,wer eestimate db yextrapolation ,withou thavin gan yindicatio no nth ereliabilit y ofsuc ha nextrapolation .Th eactua lvalu ema yb esomewha tlowe ro rver ymuc hhigher ,a s canb esee nfro mth epossibl enon-linea rextrapolation s inFig .69 .Th efigur eo f1.7 5 2 m/da yobtaine dabov erefer st oslowl ydispersin gflie s (Section5.2.4 ;Fig .80b) , duringcol dweather ,s oi twil lno tb erepresentativ ea tall .Also ,th emetho do fdirec t observationo fth efl ydistribution s caneasil y leadt ounderestimation ,a sth ever ylo w densitiesa thighe rdistance sar edifficul tt oobserve . 2 Asmentioned ,th efigure so f3 60 0an d2 340 0m /da yar eno tver yreliabl eeither , butthe yca na tleas tb esuppose dt oindicat eth erea lmagnitude ,a sther ei sn oimportan t biasi nth eobservatio no ri nth ecalculatio ntoward shighe ro rlowe rvalues .

106 5.4 DISPERSALSIMULATIO N

S. 4.1 Simulation model

Anattemp twa smad et oge tmor e reliable estimatesfo rth ediffusio ncoefficien to f onionflies ,b ycompute r simulationo fthei rdispersal . Inco-operatio nwit h Dr.M.J . Frissel (ITAL,Wageningen) ,a simulatio nmode lwa sde ­ veloped,fo r analysing thedispersa lo fth e onion fly.Th ecompute r languageuse dwa s CSMP-3.Wit hth ecompute rprogram ,give ni nth eAppendix ,fl ydensitie si ncell so fa two - dimensional grid-cell systemwer e calculateda sa functio no ftime ,unde rdifferen tas ­ sumptions aboutth edispersa lo fth eflies .Th emode li sdeterministic .Fo rlo wnumber s ofdispersin g fliesa stochasti cmode li spreferabl e (Wehrhahn, 1973).

Included features Thelengt ho fth etim e steps,th egri dcel lsiz ean dth egri d sizeca n be chosen,th elatte rwithi nth e limits setb yth ecomputer' s capacities.Emergenc eo r releaseso fflie sca nb esimulate di nan yamoun ti nan ycel la tan ytime .I nth eversio n presentedhere ,mortalit yi sa functio no ftim eo rplace ,s oage-dependen tmortalit yca n onlyb esimulate dwit h instantaneous emergence. Dispersal,a sfa ra strivia lmovemen ti sconcerned ,i ssimulate db ycalculatin gth e diffusiono fflie sbetwee ncells .Th ecompute rprogra mwa s checkedb ymakin g runsassu ­ minga spatiall yan dtemporall yhomogeneou s environment.Th eresult s closely fittedth e datacalculate dwit ha conventiona l analytical approach. Sitestha tar epreferre db yth e fliesar erepresente db ypreferre d gridcells , the accuracyo fthi srepresentatio n dependingo nth ecoarsenes so fth egrid .Preferenc ei s expressedi non eo rbot ho ftw opossibl eways : arresting,tha ti sa reductio no fth edif ­ fusioncoefficien to fth e fliespresen ti nth epreferre d cells,o rattracting ,causin g theflie st oexhibi ta nadditiona lmigratio ni nth edirectio no fattractiv e cells.Attrac ­ tionwa s introducedb ytransferrin g fliesi nupwin ddirectio nt oth e adjacent grid cell(s). Parameterswer eth efractio ntransferre d peruni t time,an dth egri dcell s inwhic h anemo- taxiswa sassume dt ooccur ,th elatte rdependin go nth ewin ddirection .Fo rsimplicit yth e attractionwa skep tconstan tove r thesecells ,thu si nthi srespec t therewa s onlya ye s orn osituation . The influenceo fweathe rwa s introducedi nth emode li ntw oways .Win ddirectio nwa s used forth eanemotaxis ,an dtemperatur e formodifyin g thediffusio n coefficient.A rela ­ tionbetwee ntemperatur ean ddiffusio n coefficientca nb efoun d fromth erelatio nbetwee n temperaturean drelativ enumbe ro fflie scaugh ti nth e flightinterceptio ntrap s (Fig.24) . Thenumbe ro fflie scaugh twil lb elinearil y relatedt oth eaverag edisplacemen t dx. A 2 diffusioncoefficien t canb edefine db yD=(dx) lit, where t istime ,i nanalog ywit hth e diffusionfro mparticle s (e.g.Kruyt , 1952).Thu sth ediffusio ncoefficien ti sproportio ­ nalt oth e squareo fth ecatc hsize .I nth e simulationrun smad es ofar ,generall yth e diffusion coefficientwa skep t independento fth etemperature . Barriers,reflectin go rkillin g eitheral lo ra par to fth eflies ,ca nb eprovide d fora ever ygrid-cel lboundary .I nth erun smade ,onl ya completel y reflectingo rkillin g barrierwa suse dalon gon eo fth egri dborders . 107 Becauseth edensitie soutsid eth egri dcel lsyste mar epe rdefinitio nunknown ,som e extrapolationwa sneede dt ocalculat eth enumber scrossin gth esystem' sborder .T oesti ­ mateth ebia scause db ythi sextrapolation ,som erun swer edon ebot hwit hsmalle ran dlar ­ gergri dsizes .Th eresult sindicate dthat ,wit hth eparameter susuall yuse dhere ,th e underestimationo fth enumbe ro fflie spresen ti nth eborde rcell si su pt o 5%,an dmuc h lessfurthe rfro mth eborder .Th erun swit ha smal lgri dsiz ewer enearl yal ldon ewit ha suboptimalextrapolatio nequatio nfo rcalculatin gth ediffusio nove rth esystem sborder . Thismetho dcause doverestimation su pt o15 1i nth eborde rcells .

Diffusion equation Theequatio nuse di nth emode lt ocalculat eth eamoun to fflie sdif ­ fusingwil lb eexplaine dhere ,additiona lremark sbein gmad e inth emode l itself(Appen ­ dix 1). Fick'sdiffusio nequatio nca nb ewritte na s

da dm= D ~~r~ a dt (15) ax ^ inwhic h dmi sth eamoun tdiffusing ,D i sth ediffusio ncoefficient , do isth econcentra ­ tiondifference , dx thedistanc ebetwee nthes econcentrations , q thesurfac ethroug hwhic h thediffusio ntake splace ,an d dt theinfinitel yshor tperio dove rwhic hmeasurement sar e made.Th eamoun tdiffusin gi srepresente di nth ecompute rprogra mb yIN .Th enumber so f fliespe rgri dcel lar eQC ,grid-cel llengt hi sDX ,thu sth edifferenc ei nconcentration s 2 2

QC/DX is (QC1-QC2)/DX .Th edistanc ean dth esurface ,o fwhic hth evertica ldimensio ni s only1 unit ,throug hwhic hdiffusio ntake splac ear ebot hDX .Thu sth eequatio ni nth e modelfo rdiffusio nfro mcel lH-1 ,V t ocel lH ,V (seeFig .71 ;H an dV ar egrid-cel lin ­ dices) is: IN(H,V,2 )= D«(QC(H-1,V)-QC(H,V))/DX** 2 (16) whereth ewes tt oeas tdisplacements ,fro mH,V- 1 toH,V ,ar egive ni nIN(H,V,1) ,an dth e southt onort hdisplacements ,fro mH-1. Vt oH,V ,ar egive ni nIN(H,V,2) .Th ediscret etime - stepsove rwhic hdiffusio nwa scalculate dwer e 1/16o r1/3 2day . Thearrestin gpreferenc ewa sintroduce db ymultiplyin gth econcentration sb yth efrac ­ tionso fth epopulation sassume dt otak epar ti nth ediffusio n (QPREF). Nowconside rth enorther nborde ro fth egrid ,fo rhorizonta l IN,wit ha gri dsiz eo f 11x V a sa nexample .Th enorma lequatio nshoul dhav econtaine dH = 12 .However ,Q C(12,V ) ispe rdefinitio nunknown ,an dQPRE F (12,V)i stherefor eobsolete .Th edifferenc ebetwee n thedensitie s in(11,V )an d (12,V)i sthu sunknown ,an di sno wtake nproportiona lt oth e differenceo fth edensitie sbetwee n (10,V)an d (11,V).

H*1,V H-1.V ln(H+1,V,2)

'inCH.Vfl,!) Fig. 71.Simulatio n model grid-cell with codes of cells H,V*1 and flymoves .

108 A reflectingbarrie ri sintroduce di nth eexampl eo fth enorther nborde ruse dabove , byputtin g IN(12,V,2)= 0 .; a killin gbarrie ri sprovide db yIN(12,V,2 )= (D»OC(11,V)* QPREF(11,V))/DX**2,a sher eQC(12,V )remain szero .

5.4.2 Analysis of a release-recapture experiment

Fordifferen tparamete rvalues ,th emodel' s outputwa scompare dwit hth eexperimenta l datab ycomparin gth edistribution so fth erecapture dnumbe ro fflie sove r relevant groups oftrap so rgri d cellsfo r eachtrappin gperio d (day) (Table 24;cf .Fig .76) .Thi sproce ­ durereduce sth einfluenc eo fth elocatio no findividua l traps,an deliminate sth eeffec t ofth eunknow n survivalan do fth eweathe ro nth enumber s recapturedpe rday .Th emodel' s degreeo fdissimilarit ywit hth eexperimen twa sexpresse da sth esu mo fsquare ddeviati - 2 onsdivide db ythei rexpectations ,x • Becaus e therewer eman y smallexpecte d (simulated) ? values,considerabl e lumpingo fdat awa sneede dt oappl yth ex test.Bu tth egoa lher e 2 wasoptimalization ,i.e .minimalizatio no fx » an dfo rthi s lumpingo fdat aca nb eomitted . Theresult sca nb euse dt oevaluat ewhic hse to fdiffusio nparameter sdescribe sth e actual situationmos t successfully. Simulationo fsevera lexperiment si sneede dt oconfir m whetherth eparamete rvalue s obtainedar erealistic . Thesimulatio no fth eexperimen tVroegindewe i 1972-2i sreporte dhere .Th egri di s showni nFig .7 2(compar eFig . 13),wit hpositiv e anemotaxisove r 150m a tN Ewind . Therelativ edissimilarit yo fth emode lwit hth eexperimenta l datai sgive ni nFig s 73an d74 ,fo rdifferen tparamete rvalues .Diffusio nalon eobviousl yi sno ta goo d des­ criptoro fth edispersa lbehaviou ro fth eonio nfly .Th e expected recaptureswer econcen ­ tratedo nonio nfield sby .a reduce ddiffusio ni npreferre d gridcell s (Fig.73) .A goo d 2 fitwa sobtained ,optimu ma ta diffusio n coefficiento fabou t7 00 0m /day ,reduce dt o about2 50 0m 2/day insideonio n fields.Thes evalue sca neasil yb efoun d fromth eestima ­ ted linesalon gwhic hth edeviation so fth emode l fromth eobservatio nt oth epositiv e andth enegativ e side,a smeasure db yth eX values,ar ei nbalanc efo ra certai ntra p group. An indicationo fth eresult so fth emode la tthes evalues ,usin gth esmalle r grid

Table 24. Hypothetical example of how the model's output was compared with experimental data. Grid cells (sites) abed total fly density at time t, from simulation 100 10 0.1 number of traps per grid cell 2 5 1 expected relative catch 20020 0 50 50 1 0.1 0.251.1 1 actual catch intrappin g period concerned 29 20 1 0 50 expected catch 39.8 10.0 0.2 0.0 50

X2 2.9 10.0 3.2 0.0 16.1 X2 from other trapping periods,calculate d similarly 23.4 totaldeviatio n 39.5

109 Fig.72 .Ma puse d insimulatio no fexperi ­ mentVroegindewe i 1972-2,smal lgri dsize . Grid cell length5 0m . :0nionfields ;A :releasesite ; 0= trap(s) ;—»- :extr amov edu et opositiv e anemotaxis,show nfo rN Ewind .

o nions 6-

- IjB

V 4- \

171 _--x * ï \j*-~ — R

239 86 =s*,70 2- IfcZ? ? ~^0

^-in-~ 112 112 123 157

0- 8 10 D in 103 m2/day

Fig.73 .Simulatio no fexperimen tVroeg ­ Fig.74 .Simulatio no fexperimen tVroeg ­ indewei 1972-2,x 2value sfo rdifferen t indewei 1972-2,x 2value sfo rdifferen t combinationso fdiffusio ncoefficient s combinationso fdiffusio ncoefficient s insidean doutsid eonio nfields ,smal l outsideonio nfield san d extranumbe ro f grid size. Linesalon gwhic hposi ­ flies transferred dailyb ypositiv eanemo ­ tivean dnegativ edeviation sfo ra grou p taxis.Diffusio ncoefficien t insideonio n oftrap sar ei nbalance ;R = releas e fieldskep tconstan t at200 0m 2/day. field,0 = othe ronio nfield ,X = out ­ Explanation seeFig .73 . sideonio nfields .

110 Fig.75 .Simulatio no fexperimen tVroegindewe i 1972-2.Isodensit ylines ,fo ra diffusio n coefficiento f700 0m 2/day,insid eonio nfield s250 0m 2/day.Line sa tmultiple so f5 0 fliespe rgri d cell.

size,i sgive ni nFig .75 .Th econcentri ccircles ,isodensit yline so fflies ,ar eno t disturbedoutsid eth eonio nfields .Thu saccumulatio no fflie so na fiel ddoe sno tde ­ creaseth efl ydensit yi nth eare afurthe rawa yi nth esam edirection . Thepercentag erecapture dwithi nth ereleas eonio nfiel ddrop srathe rsteadil yac ­ cordingt oth emode l (Fig.76) . Thesligh tirregularit yi nth eobserve ddat ai si ncon ­ formitywit hFig .84 :a concentratio no fflie so nonio nfield sa tth eag eo fmating .Th e irregularitiesar eno tthos etha tar eobtaine dwhe nattractio ni sintroduced . Theresul to fintroducin gattractio ni sshow ni nFig .74 .Th eattractio ndistanc e usedwa s15 0m .Smalle rvalue swoul dhav elittl einfluenc eo nth eoutput .O fth elarge r valuesonl y40 0m wa stried ,bu tthi sgav eobviousl yunrealisti cresults . Optimumfi twa sfoun da tn oattraction ,bu tth epossibilit yo foccurrenc eo fsom e attractioncanno tb eexcluded . Whenaccoun twa stake no fth eincrease dprobabilit yo fflie sbein gcaugh toutsid e onionfield sdu et oth ehighe rfligh tactivit yther e (Section5.2.1) ,th eresult schan - 2 gedconsiderably .Fig .7 7give sth ex valuesobtaine di nthi scase .Th eoptimu mfi tca n 2 2 beestimate da tdiffusio ncoefficient so f1 380 0m /da yan d1 90 0m /da youtsid ean din ­ sideonio nfields ,respectively .Th epreferenc efo ronio nfield si sthu sa facto r7-7.5 . Asmentione dbefore ,a chang ei ntra pcatche si sproportiona lt oa chang ei ndisplacement , andth ecorrespondin gchang ei ndiffusio ncoefficien ti sth esquar eo fth echang ei ncat ­ ches.Thu sa preferenc efacto ro f6.2 5wa sexpected .Fro mFig .7 7i tca nb esee ntha tth e observedvalu edoe sno tconflic twit hth eexpecte done . Fromth eaverag edail ymaximu mtemperatur edurin gthi sexperimen t (18.7°C)i tca nb e 111 percentage of flies recaptured age inday s 5 7 9 11 13 15 13 15 17 19 21 100-1 1—__L—l__J_ L. J I I I L_

D =700 0 Du = 2500

L J^ 1 I 1 I I I I II

90-

80- ~"^ -. -^ ^--- .- ~- -v. ~-^_

70- ^^v-^ ^~^~~— - ~-v^_ D = 4000 ^~~ D = 4000 "— 60- Du«2000 Du= 2000 50 J TR 400 = 1 J TR150= 1 Fig. 76.Simulatio no f experimentVroegindewe i 1972-2.Percentag edistributio no frecap ­ turesove rfou rgroup so f trapsversu sda yafte raverag eemergence . I:releas efield ;II :outsid eonio nfield s (uncorrected data,se etext) ,III :onio nfiel d toth ewes t (seeFig .72) ,IV :onio nfield s toth enort han d east (seeFig .72) .

°o 3 2J5 1J3 8J> V « »-''

x s y ^-"

2g9 121 M 8^2 6#7 2- V ^ ^—-*-R Fig. 77.Simulatio no fexperimen tVroeg ­ O indewei 1972-2,x 2value sfo rdifferen t /-""'^ y,' combinationso fdiffusio ncoefficient s 1- 70 •} "

estimatedtha tth etra pcatche swer e82 %o fthos efo rstandar dday s (max.2 0C ;Fig .24) . 2 Thediffusio ncoefficient sfo rstandar dday swoul d thenb eabou t2 000 0m /day ,an di n ? onionfield sabou t3 00 0m /day . Thesevalue sca nb econsidere dth ebes testimate savailabl ea tth emoment ,a sb ysuc h 13 simulational lrecaptur edat aar euse dan dheterogeneit y intim ean dspac ei saccounte d for.

112 5.5 NUMBERSVERSU SDISTANC E

Theoretical model Whenth e logarithmo fth etota lnumbe ro fonio nflie srecapture dpe r trapwa splotte d againstth e distance fromth e origin,generall ya linea rrelatio nwa s observed.I twa s investigatedwhethe r thiswoul d followfro mth eassumption so nsurviva l anddispersa lmad eabove . Letth edispersa lb esufficientl y approximatedb ya simpl ediffusio nprocess .Th e den­ sitya ta give npoin ta tdistanc er fro mth eorigi ni sthe ngive nb y i{r,t) (Eqn 13).Le t the flieshav enormall ydistribute d life-spans (Section 4.4),th efractio naliv ea ttim e t beinggive nb yg(i) .Th edensit ya ttim e t anddistanc e r isthu s f(r,*)g(t).Assumin g a certainfractio no fth eflie spresen to na uni tare at ob etrapped ,independen to f t and r, thenth etota lo frecapture spe rdistanc ei sproportiona lt o £fO,*)g(t). This was calculatedfo rsom eparamete rvalues ,an dgav ever y slightlyconcav ecurve s (Fig.78) . Asfo rth emomen tonl yth edegre eo flinearit yan dth eslop enee dt ob econsidered ,th e recaptureswer ecorrecte di nthi sfigur et oge t10 0flie sa t10 0m distance .Th eslop ei s dependento nth elife-spa ndistributio nan do nth ediffusio ncoefficient .Give nth efor ­ mer,th elatte rca nb eestimate d fromth eslop e (Fig.79) .

Experimental data The experimentsdiffe r considerablyi nth eslop eo fth eregressio no f totalrecapture sversu sdistanc eo na semi-lo ggrap h (Fig.80) .I nth e experiment Pollemans197 1 thever y slowdispersa lwil lhav ebee ndu et ocol dweathe ran dsmal lflie s (Section5.2. 4) .

Ig numbar of flias recaptured

2

«-

1-

0.5-

—i 1 1 i r (W 1 1.5 „dittanc2 a ink m

Fig.78 .Logarith mo frelativ erecapture sversu sdistance ,accordin g toa theoretica l model (seetext) ,fo rtw ovalue so f thediffusio ncoefficient . X« males ;O « females ; D» 2 500 0m 2/day; D= 5 00 0m 2/day.

113 slope

• X / / / /

• / / / / / / / / / ' ;

-3 o / / / / / / / /

T—' I ' I ' I I I I I I ' 1—' I 'I'll I I I I 2 S 10 20 50 - ,. 100 Din10Jmyd«y Fig.79 .Estimate d slopeo f theapproximatel y linear relationo f thel g(relativ erecap ­ tures)versu sdistanc e (Fig.78) ,i nrelatio nt oth ediffusio ncoefficien tassume d inth e underlyingmodel .X =males ;0 = females.

Thedat ao fexperimen tMi js 197 4wer eanalyse dfo rth eflight san dsexe sseparatel y (Fig.8 0e ,f ) . Theslope swer eequa lfo rth esexes ,bu tsteepe ri nth e2n dflight .Du ­ ringth e2n dfligh tth eaverag emaximu mtemperatur ewa shighe rtha ndurin gth e1s tflight , about1 9versu s 17C .Highe rtemperature scaus efaste rdispersa l (Section5.2.1) ,bu tth e 2ndfligh tflie sliv eshorter ,als owhe na correctio nfo rtemperatur edifference swa sap ­ pliedt oth esurviva lcurve s (Fig.55) .S oles sdispersa li sexpected ,an dexplanatio n ofth eavailabl edat adoe sno trequir eth eassumptio no fdiffusio ncoefficien tdifferen ­ cesbetwee nth eflights . AsFig .7 9i sbase do nth elife-span so fth e1s tfligh tsterile si nth eexperimen t Mijs1974 ,th eslope so fth eregressio nline so fthes eflie s (Fig.8 0e )ca nb euse d

Fig.80 .Linearit yo f therelatio no fth el g( %recaptured )versu sdistance . Experiments Regressionline s a.va nLoo n 1970-2 y =-0.93a ;-1.0 9 b.Polleman s 1971 y =-8.17a ;-0.8 6 c.Buij s 1972-1 y =-2.91a :-0.4 2 d. Vroegindewei 1972-2 y = -1.82a; -1.11 e. Mijs 1974-1, steriles on exp y = -1.15a; -0.95 males (+ ) y = -1 .13a: -1 .01 females ( • ) f.Mij s 1974-2,sterile so nex p y =-1.50a :-1.2 8male s (+) y =-1.54 x-1.3 8female s (• ) ean df : Encircle d pointsbase d onove r 10traps ,regressio n lineweighte d accordingt o numbero ftraps .

114 Ig percentage of flies recaptured

"• 1 r

-i r- i i 2 distance in km

115 2 2 tofin ddiffusio ncoefficients :2 500 0m /da yfo rmale san d1 800 0m /da yfo rfemales . Thesevalue sar esomewha thighe rtha nthos eobtaine db ysimulatio no fexperimen t Vroegindewei 1972-2,especiall ya sdispersa lthroug honio nfield si sincluded .

Migrated fractions of catchable populations, in relation to distance Forth eexperimen t Mijs 197 4th epercentag edistributio no fth erelease dflie sove rth edifferen ttrappin g sitesca nb ederive dfro mth edat agive ni nTabl e19 .A scapture soutsid eth eonio nfield s areneglected ,th eflie swhic har eoutsid eonio nfield sca nbes tb ethough to fa sbein g onth eneares tonio nfield .Thes epercentage sar ecompare dwit hth edistanc emigrate d (Fig.81) .I nconformit ywit hFig .80 ,a linea rrelatio nca nb eassume dbetwee nth edis ­ tancemigrate d O) and lg{y), thelogarith mo fth epercentag emigrated : lg(y)= -1.14 5 x +1.59 . Obviouslythi srelatio ndoe sno tgiv erealisti cfigure sfo rth epercentage smigrate d toth eonio nfield sneares tt oth ereleas esite s (4point s inth elef tto pcorner) ,pre ­ sumablybecaus eonio nflie sconcentrat eo nonio nfields :th eflie saccumulatin go nth e fieldneares tt oth ereleas esit ebecom eles savailabl efo rmigratio nt oothe rfields .

percentage of flies migrated

1 1 1 1 1 1 0 OS 10 IS 20 25 3D distance in km Fig. 81.Percentag eo fflie smigrate dversu sdistance ,catchabl epopulations .Experimen t Mijs 1974.Regressio n lineso f 1stfligh tdata : lg(j/)= -1.145 X+ 1.59 (based onal lpoints) ; - -- lg(# )• -0.851a :+ 1.23 (recaptureso nfiel d atorigi nexcluded) ; lg(y)= -0.851 X+ 1.2 9 (asbefor ebu tcorrecte d toth eaverag epercentag eo na linear scale). O = 1stflight ;X = 2ndflight .

116 Soonio nfield stha tar efarthe rawa yli e'i nth eshadow 'o fneare r fields.A swa ssee n fromdispersa lsimulatio n (Fig.75 )th edirectio ni nwhic hthes efield sli ei sno tver y important.Thu s irregularityo fth eonio nfiel ddistributio nove rth erecaptur edistance s willdistur bth elinearit yo fth erelatio nbetwee n lg(j/)an d x. A shadoweffec to ffield s thatar efarthe rawa ycanno tb esee nclearl yfro mth edata ,becaus edat afro mdifferen t release sitesar ecombine dhere ,smalle rnumber so fflie sar eaccumulatin go nthes e fieldsan dchanc efluctuation sbecom edominant .A sa reasonabl eapproximatio no flg(i/ ) versusdistanc eth elinea rrelatio nwa scalculate dwithou tth edat ao fth eneares tonio n fields: lgQ/)= -0.85 1 x +1.23 . Becauseno tth emea nvalue so flg(# )versu sdistanc ebu tth emea npercentage sthem ­ selvesar eo finterest ,th elin eha st ob eraise dslightly .Fro mth evertica ldistributio n ofth edat aaroun dth eregressio n line,th euntransforme dmea ni sfoun dfro mEq n(12 )t o be1.1 5time shighe rtha nth etransforme dmean .Th eregressio nlin et ob euse dfo rextra ­ polationsthu sbecomes :lgG/ )= -0.85 1 x +1.29 . Inthes ecalculation sth eabsenc eo fflie sfro mG o nfiel d4 woul dhav egive ndiffi ­ culties.Becaus eo nfiel d4 on efl yfro mth ecomparabl egrou pY resultedi n1.5t ,an do n thecontro lfiel dth epercentag eo fY wa stwic ea shig ha stha to fG ,i twa sassume d that fromG 0.75 1cam eo nfiel d4 . FromFig .8 1th epercentage smigrate dt oonio nfield soutsid eth eare awher ewa strap ­ pedwer erea doff .Fo reac hrelease d groupth etota lo fpercentage sha dt ob emad eequa l againt o1001 .Th efigure sdi dno tchang es omuc htha tth eregressio nha dt ob erecalcu ­ latedwit hthes ecorrecte dvalues .Th eresultin gmigratio npatter ni sgive ni nrelativ e numbers inTabl e2 0an di nabsolut enumber s inFig .82 .

Fig. 82.Migratio n pattern of catchable populations.Experimen t Mijs 1974, 1st flight. Symbols see Section 4.3.3. 1m m width = 2000flies , = 1000-2000 flies; lightly shaded - emergence site, heavily shaded » onion field.

117 Notetha tth econsiderabl edispersa lo fflie sfro mth esource sG an dY t oonio nfiel d 2,an dth elo wfractio nremainin gnea rth eorigi no fespeciall yG ,wil la tleas tt osom e extentb ecause db yflie soriginatin gfro ma possibl esourc enea rfiel d 2,becaus ethi s sourceha dn omixin ggrou po fit sown . Theflie soriginatin gfro msourc eC wil lhav ebecom emixe dincompletel ywit hth e C-dyedmixin ggroup ,becaus ethi sgrou pfo rpractica lreason sha dt ob erelease dnea rth e controlfiel d (Fig.15) .Therefor eth emixin ggrou pC i sunderrepresente damon gth eflie s caughto nfiel d4 tha temerge dfro msourc eC .Th ewil dflie sthere ,no t 'explained'b y themixin ggroup swil lthu shav eoriginate dpartl yfro msourc eC . Thecorrespondin gdat ao fth e2n dfligh tafte r3 1Jul yd ono tdiffe ri nmigratio nes ­ sentially fromth e1s tfligh tdata ,a sshow ni nFig .81 . Itshoul db ekep ti nmin dtha tth emigratio npattern ,a sderive dhere ,describe sth e averagedistributio no fth epopulation sinsofa rthe yar ecatchable .A smentione di n Section4.4 ,ver yyoun gflie sar eunderrepresente d insuc hfigures .Th emigratio npatter n ofal lflie saliv eca nb eobtaine db yadequat ecorrection :th epercentage so fmigrate d flieswoul db eabou thalve dan do nth efield sadjacen tt oth eemergenc esite sthe ywoul d riseb yove r 10%.A mor eusefu lmeasur eo fmigratio n isgive nb yth edistributio no fth e populationsdurin gth eperio dtha tthe yar ereproducin g (seeSectio n5.6.4) .

Deviations from linearity Upt ono wdispersa lha sbee nconsidere di nexperiment stha tha d asomewha thomogeneou sdistributio no fonio nfield sversu sdistance ,excep taroun dth e origin.Whe nflie sar emigratin g ina nare awher eonio nfield sar ever yscarce ,on emigh t supposetha tth eaccumulatio no fth eflie so nthes eonio nfield swoul dresul ti na highe r percentagerecapture da tlarge rdistance stha nexpecte d froma linea rrelation .Thi ssi ­ tuationwa spresen ti nexperimen tMij s 1973-2 (Fig.14) .Th epercentag erecapture da t about1.7 5k mdistanc ewa sindee drelativel yhig h (Fig.83) ,causin gth erelatio nlg(° 6re ­ captured)versu sdistanc et obecom ehollow ,especiall yfo rflie stha tha dbee nrelease d outsideonio nfield s (aan db i nFig .83) . Inth esmal lonio nfiel d (Fig.14 ,left )thi saccumulatio nwa smor epronounced :th e recapturespe rtra po fth egroup srelease d5 0an d10 0m fro mth esmal lonio nfiel dwer e about3. 5 timeshighe rtha nwhe nrelease d inth esam ewa ynea rth elarg eonio nfiel d (Fig. 14,right) .Whe nth edat aar ecorrecte d forth eextr aaccumulatio no nth esmal l field,th epoint sa an dc com e0. 5 loweri nth egraph .Als oth epoin td wil lcom esome ­ whatlower .Th efac ttha tth epoint sa an db ar estil lrelativel yhig hthen ,ca nb edu e toa ninitia lhig hdispersa lspee d (Fig.70a) . Onepai ro ftrap s (crossesi nFig .83 )ha dconsistentl yhighe rrecapture stha nth e others.Th egenera lleve lca nb ehighe rbecaus eo fa favourabl epositio no fth etraps , whichresult si na large rfractio no fth epopulatio npresen tbein gcaptured ,o rbecaus e offavourabl efeature so fth esite ,causin ga large rfractio no fth epopulatio nbein g present.Th elatte rwa sher eth ecase ,a sth esit ewa sver ysheltere d (adee pditch ,an d treesi nth edirection so fth emai nwinds) .Not etha tdat ao fdifferen treleas esite s arecombine d inthi sfigure . Ingenera li tca nb estate dtha ta highe rfractio ntha nca nb ededuce dfro mFig .7 8 willb erecapture d

118 Ig percentage recaptured par trap 0-1

No" •Co \ o„ x * \ \ Nx \ *\x o \ \ \ \ \ xx s \ \ \ x o \ \ \ \ x\ •

-3-1

I 1 1 1 p 1 1 i r i 0 0.5 1 1.5 2 distança in km Fig. 83.Logarith mo fth epercentag erecapture d pertra pversu sdistance .Experimen t Mijs 1973-2.Explanatio nse etext . X =On epai ro ftraps ,0 = othertraps ;a,b, c andd = deviatin gdat areferre d toi ntext .

1. ina nisolate donio nfiel d(Jes scompetitio nfo rflie swit hothe ronio n fields), 2. ina smalle ronio nfiel d (theconcentratio no fflie so nth esmalle rfiel di smor e importanttha nth elowe rattractivenes so rchanc eo fencounterin gth efiel ddu et oit s smaller size), 3. atver y favourable sitesa smor eflie sar epresent , 4. whenth etra plocatio ni smor efavourable . Lowerfraction stha nexpecte dfro mth elinea rrelatio nwil lb efoun di nth eopposit e situations.A smentione di nSectio n5.2.2 ,locatio no freleas eo rrecaptur esite sa t differentdistance sfro ma reflectin gbarrie rca nals odistur bth e expected linearity.

5.6 AGE-DEPENDENTDISPERSA L

5.6.1 Trapping place versus age

Theag ea twhic hdispersa ltake splac ei srelevan twhe nth e impacto fdispersa lo n reproductioni sconsidered .A tfirs ti ti sestablishe dwher eth esteriles ,release ddu ­ ringexperimen tMij s 1974,wer etrappe di nrelatio nt othei raverag eage .Fo rthi spur ­ poseth esterile shav ebee ndivide d intotw o groups,i.e .wit hdy emark sYO-BY Oan dwit h dyemark sOB - (viz.th e releasedata ,Sectio n 6.2.1).Thi sdivisio nwa smad ebecaus e thesegroup semerge d andwer epresen tdurin gperiod swit hdifferen taverag etemperatures , whereasth etemperature swithi nthes eperiod swer erelativel y constant (Fig.16 :period s

119 6Ma y- 1 3Jun ean d1 4Jun e- 3 1August ,1974) .Als oth emale san dfemale swer etreate d separately,becaus eth edetail so fthei rmigratio npattern smigh tdiffer . Atfirs tth epercentag erecapture dversu sag ewa scalculated .Fo reac hrelease dgrou p thedat eo f50 %emergenc ewa sestimate dgraphically .Th edail yrecapture so fth eflie s pertra pwer eliste dwit hthei rdate so f50 %emergenc esynchronized .The nth edat ao fth e differentrelease dgroup swer etake ntogether ,fo reac hsit eseparately ,an dconverte dt o cumulativepercentage srecaptured .Als othei raverag ecumulativ epercentag eemergenc ecur ­ vewa scalculated ,weighte daccordin gt oth enumber sreleased .Wit hthi semergenc ecurv e therecaptur ecurve swer ecorrected ,thu seliminatin gth eeffec to fth esprea di nemergen ­ ce,givin gth ecumulativ epercentag erecaptur ecurve sagains tage .Fro mthes eth efracti ­ onsrecapture dpe rda ywer eread .Thes efraction swer econverte dt orelativ edensitie sb y multiplyingthe mb yth etota lnumbe ro fflie so fth ecorrespondin gse xan ddy emark strap ­ pedo nth esit econcerned .Thes edat awer econverte d torelativ epopulatio nsize sb ymul ­ tiplicationb yth elengt ho fsheltere donio nfiel dborder ,a swa sdon ei nSectio n4.3.3 . Theresult sar egive ni nTabl e25 . Hereth ecatche soutsid eonio nfields ,mad eo nsheltere dedge so fnon-onio nfields , areincorporate d inth ecalculations .Th edensitie swer econverte dt orelativ epopulatio n sizesb ymultiplicatio nb yth elengt ho fsheltere dedge so fnon-onio nfield si nth eare a forwhic hth ecatche scoul db esuppose dt ob erepresentative ,an ddivide db y2. 5t ocor ­ rectfo rth ehighe rtrappin gprobabilit y (Section5.2.1) .Thes efigure sar eles saccurat e thanth efigure sfro monio nfields ,becaus ethe yar ederive dfro monl ysi xtrap swit h very lowcatches ,whic htrap sar etake na srepresentativ efo rabou t1 0k mo fsheltere d fieldedge . Fig. 84summarize sth edat aobtained ,expresse da sth epercentag edistributio no f fliesove rth eexperimenta lfield ,outsid eonio nfield san do nothe ronio nfields ,agains t age.A s inFig .55 ,th eag escale shav ebee nadjuste dt oge tcoincidenc eo fth efemales ' agesa tfirs tmating .Fo r2n dfligh tfemale sth eage sa tfirs tmatin gan da tfirs tan d secondovipositio nar eindicate da si nFig .55 .The yfi tver ywel lt oth eperiod si nwhic h thefemale sar econcentrate do nth eonio nfields .Exactl yth esam eirregula rpatter no f dispersal issee ni nth eindependentl yderive ddat ao nth e1s tfligh tfemales .Therefor e itha st ob eassume dtha tth ephysiologica lagein gi nth e1s tfligh ti sslowe rtha ntha t ofth e2n dfligh tb ya facto r1. 5 insteado f1.35 .Th efacto r 1.5 isno tseriousl ycon ­ flictingwit hth edat ai nFig .57 ,fro mwhic hth efacto r 1.35wa sestimated . Usingth efemales 'age sa tmatin gan doviposition ,thu scalculate dan dgive ni nFig .84 , tocalculat eth efecundit y (Section4.5.3) ,yield s30. 5egg spe rfemal efo rth e1s tflight . Thegraph sfo rth emale shav ea simila r irregularity,i.e .a concentratio no nonio n fields,occurrin g inth etw oflight swit ha nag edifferenc eo fabou t1.5 .Th emos tobviou s explanationi stha tthi sconcentratio no nonio nfield sindicate sth eaverag eag eo fma ­ tingo fth emales .Thu smale sprobabl ymat ea ta nag eo fabou t1. 4time sth eag eo fth e femalesa tthei rfirs tmating .I ti sa commo nphenomenon ,especiall yi nMuscidae ,t o finddispersa lbetwee nphase so fovipositio n (Chapter8 i nJohnson ,1969) .

120 Table 25.Relativ e catchable populations against age,pe rtrappin g site. Experiment Mijs 1974,sterile s released onexperimenta l field.

Age in Trapping sitea days males fern a les exp 5 con 1 2 3 4 no total exp 5 con 1 2 3 no total 1st flight 4 22 0 0 0 0 0 0 0 22 0 0 0 0 0 0 0 0 5 1031 0 0 0 0 0 0 0 1031 0 0 0 0 0 0 0 0 6 856 0 0 0 0 0 0 0 856 496 0 0 0 0 0 48 544 7 1580 0 0 0 0 0 0 0 1580 530 0 0 0 0 0 569 1099 8 878 0 3 0 0 0 0 194 1075 547 0 0 0 0 0 70 617 9 1009 Ü 40 0 19 0 0 1196 2264 496 0 0 0 32 0 63 591 to 812 15 31 0 64 151 0 1810 2883 496 183 0 0 1 184 588 1452 11 439 12 7 0 96 133 54 388 1129 428 49 0 0 11 8 88 584 12 417 103 11 10 38 0 0 210 789 308 12 0 103 8 33 25 489 13 329 173 0 0 0 0 57 501 1060 291 49 13 15 17 13 6 404 14 307 164 1 0 0 42 42 517 1073 274 43 5 0 11 18 0 351 15 285 127 3 0 0 11 0 356 782 291 6 14 28 34 72 626 1071 16 329 157 12 0 4 0 0 16 518 308 12 17 0 4 0 50 391 17 198 254 0 0 0 67 161 146 826 291 41 7 0 0 0 13 352 18 110 82 0 0 0 97 0 97 386 308 224 13 3 0 72 0 620 19 110 61 0 60 0 2 0 194 427 291 16 33 18 34 223 0 615 20 13 33 0 0 0 9 0 566 621 274 28 0 9 40 251 0 602 21 9 6 0 0 0 0 0 275 290 154 4 1 0 7 26 0 192 22 9 6 7 20 0 5 0 0 47 171 6 2 13 6 5 57 260 23 9 9 6 19 0 6 0 0 49 137 59 0 32 3 3 158 392 24 9 9 0 0 0 0 0 0 18 120 4 3 18 2 10 215 372 25 9 0 0 0 0 0 0 0 9 120 0 7 15 3 5 0 150 26 9 0 0 46 0 0 0 0 55 137 0 7 32 1 0 0 177 27 0 0 0 0 0 0 0 0 0 137 0 1 28 6 102 0 274 28 et seq.0 0 0 0 0 104 0 0 104 240 77 9 274 34 0 0 634 2nd flight

0 0 0 0 0 0 0 0 271 271 0 0 0 0 0 0 0 0 1 0 0 0 0 0 16 0 348 364 0 0 0 0 0 0 0 0 2 883 0 0 0 0 13 0 620 1516 516 0 0 0 0 0 0 516 3 817 65 0 54 8 1 0 1123 2068 994 0 0 30 8 0 0 1032 4 1368 85 1 310 8 34 0 503 2309 810 7 0 31 4 32 592 1476 5 1236 60 2 194 37 14 0 1084 2627 700 29 0 50 17 60 294 1150 6 1346 47 1 419 30 36 0 1975 3854 645 54 0 111 4 7 298 1119 7 1148 67 0 178 41 19 0 639 2092 608 103 5 85 5 17 130 953 8 795 169 5 163 63 22 0 329 1546 700 100 4 67 15 47 10 943 9 530 172 4 62 57 23 0 310 1158 442 44 2 7 15 44 91 645 10 309 70 2 0 14 12 0 348 755 424 17 1 30 13 12 77 574 11 177 37 3 11 48 0 0 0 276 295 13 2 30 19 0 0 359 12 132 40 0 43 5 0 0 0 220 239 9 0 20 15 0 0 283 13 22 27 2 78 4 0 0 194 327 203 20 0 24 7 0 0 254 14 22 32 3 39 5 0 0 0 101 166 20 0 96 13 0 0 195 15 9 45 3 0 0 0 0 0 57 129 10 3 44 9 0 38 233 16 9 55 3 0 0 0 0 0 67 129 2 6 33 4 15 212 401 17 9 20 3 0 0 0 0 0 32 129 0 0 59 21 30 183 422 18 9 5 0 0 0 0 0 0 14 74 7 0 22 3 14 0 120 19 9 0 1 0 0 0 0 0 10 74 13 0 0 0 11 0 98 20 et seq.0 0 4 0 15 0 0 0 19 91 41 5 0 20 27 0 184 a. Onion fie Ids see Fig. 15; no = outside onion fields. On field 4 no females were reoap- tu red.

121 percentage of flies 100

â 1

50

OH r- -1 1 1-

, 1 '\ 1

18 20 22 age in days

Fig.84 .Percentag edistributio no fcatchabl epopulation sove ronio nfiel dwher e emerged,othe ronio nfield san delsewhere ,versu sage .Se xan dfligh tindicated . ExperimentMi js 1974 . Underthi slin ei nonio nfiel dwher eemerged ; betweenthes eline soutsid eonio nfields ; - -- abov ethi slin ei nothe ronio nfields . ;=Suppose d ageo fmating ; |= suppose d ageo foviposition .

5.6.2 Age distribution of immigrating flies

Anotheraspec to fage-dependen tdispersa li sth eag edistributio no fimmigrant sa t thetim eo fimmigration .I nthi scontex tmigratio ni suse dt oindicat edispersa lfro m oneonio nfiel dt oanother .T oestimat ethi sag edistribution ,th epercentag edistribu ­ tionso fcatche sagains taverag eag eo nth edifferen tonio nfields ,a sderive dabove , wereused .Thes edistribution sca nb ethough to fa sth esu mo frecaptur edistribution so f cohortso fimmigrant simmigratin ga tdifferen tages .A cohor to fsiz e x., arrivinga tag e n, willyiel do nth efiel dwher ei timmigrate da recaptur ecurv etha ti ssimila ri nshap e toth erecaptur ecurv eo nth efiel do forigi nfo rflie so fag e n andonwards ,whe non e

122 p*rcmtage of immigrants recaptured

20 25 •g*i nday « Fig.85 .Cumulativ epercentag eo frecapture so fimmigrant sversu sage ,an d imitatedcurv e derivedfro mestimate d recapturecurve so f immigratedcohorts .Experimen tMi js 1974 .A s examples:a :female s2n dflight ,sterile simmigratin g tofiel d5 ; b:female s2n dflight ,sterile s immigratingt ocontro lfield ; • =recaptures ; o =imitate d curvefro msu mo festimate drecapture so fimmigratin g cohorts;•••• =immigratin gcohort sseparately ;arrow sar erelativ ecohor tsize swit hag e whenimmigrate d indicated. assumestha tth ecatchin gprobabilit yo fflie si sindependen to fthei rmigration .Whe n thenumbe ro fflies ,presen to nth efiel do forigi na tag e n, is x, therecapture so f theimmigratin gcohor tar e x./x timesth erecapture so nth efiel do forigin .No wth ecu ­ mulativedistribution so fcatche sagains taverag eag eo nfield swher eth eflie simmigrated , have,b ytria lan derror ,bee noptimall yapproximate db yth esu mo fcumulativ edistribu ­ tionso fimmigratin gcohorts ;a nexampl ei sgive ni nFig .85 . Asth efirs timmigrant sarriv ea tage swhe nth elo winitia lcatchin gprobabilitie so f youngflie shav epassed ,th esiz eo fth eimmigratin gcohort swil lb eproportiona lt oth e relativenumbe rcaugh to nth efirs tda yo fthei rpresence ,a sindicate di nFig .85 .Th e actualnumbe ro fflie srecapture do nth efiel dconcerne di sdistribute dove rth edifferen t immigrationday saccordin gt othes erelativ ecapture so nth efirs tda yo fpresence . Thenumber so fflie sar etotalle dpe rimmigratio nag ean dpe rdistanc emigrated .Th e resultingcumulativ epercentag edistribution sar egive ni nFig .8 6fo rth emigratio ntra - jectsencountered .Th edat afo rmigratio nove ra distanc eo fabou t170 0m wer emuc hles s accuratedu et oth elowe rnumbers ,an ddi dno tdiffe ressentiall yfro mth edat ao nmigra ­ tionove ra distanc eo fabou t80 0m .T osom eexten tindependen to fpreviou sfinding s (Fig.84) ,ther ear eindication so freduce dfemal emigratio ndurin gth ereproductiv epha ­ ses.

5.6.S Dispersal with regard to genetic control

Themos tinterestin gaspect so fdispersa lfo rapplicatio no fsteril einsec ttechni ­ queare : 1. Whati sth epercentag eemigratio no fsteril emale sfro mth etreate dare abefor ema ­ ting?

123 percentage of immigrants arrived 100

1700n 50-

20 2nd flight age in days Fig.86 .Cumulativ epercentag eo fmigrant sarrive dversu sage .Experimen tMij s 1974.Se x anddistanc e indicated. 1stflight ,recapture d over80 0m : 156males,10 9females ;ove r 1700m :3 0an d26 ; 2ndflight ,recapture d over80 0m : 176males ,8 9females ;ove r 1700m : 10an d13 .

2. Whati sth enumbe ro fimmigratin gfertil emale si nth etreate dare abefor emating , asa functio no fdistanc ean dsiz eo fth epopulatio nthe yoriginat efrom ? 3. Whati sth enumbe ro fimmigratin gfertil efemale si nth etreate dare abetwee nmatin g andoviposition ,a sa functio no fdistanc ean dsiz eo fth epopulatio nthe yoriginat e from? Theseaspect swil lb econsidere dfo ron etreate donio nfield . Asca nb esee nfro mFig .84 ,th epercentag eo fsteril emale stha temigrate dbefor e matingi sabou t50 .Th esurviva la tth eaverag ematin gag ei ssom e25 % (Fig.55) . The fractiono fa populatio nemergin ga ta give ndistanc etha tmigrate sint oth efiel dcon ­ sideredcanno tb efoun ddirectl yfro mFig .8 1o rTabl e20 ,a sthes efigure srefe rt ocat - chablepopulations ,summe dove rthei rwhol e lifetime.A tth emomen to fmatin gabou t40%

124 ofmale saliv ehav emigrate dt oothe rfield s (Fig.84) .Th epercentage stha thav emigra ­ tedt oothe rfields ,a sgive ni nTabl e 20,ar e15-25% .No who wfa rthe yhav emigrate d isno tver y importantwit hrespec tt oth eag edistributio na tarriva l (Fig.86) .Thus , thedistributio no fth e40 1emigrate d flieswil lb esimila rt otha to fth eabou t 20% emigratedflie s (Table 20). Withth esurviva la t25 %thes efigure sca nroughl yb ehalve d tofin dth epercentag eo fth eemerge dpopulatio ntha tha smigrate dt oothe r fieldsa tth e timeo fmating ,versu sdistance .Or ,wit ha regressio nlin ea si nFig .81 ,lg(% )= -0.85(distancei nkm )+1.0 .Wha tthi smean sfo rpopulation so fdifferen tsize sa tdif ­ ferentdistance si svisualize di nFig .87 ,assumin ga highe rpercentag eimmigrate dfo r shortdistance s (under0. 5km ;Fig .81) . Asa rul eo fthumb ,th emagnitud eo fth enumbe ro fmale smigrate dbefor ematin gi s foundb ydividin g1/ 4o fth eorigina lpopulatio nb ya facto r1 0fo reac h0. 8k mdistance . Ofth e immigratingfemales ,10-15 % immigratebetwee nmatin gan doviposition ,a sca n beestimate d fromFig .86 .I ntota l 30-40%o fth efemale saliv eemigrat efro mthei remer ­ gencesit e (Fig.84) .S o10-15 %o fthese ,o rabou t4 %o fth efemale saliv eimmigrat et o otherfield sbetwee nmatin gan doviposition .Suc h 'disturbing'female sar eabou t2 %o f thefemale so femergin gpopulations ,a sabou thal fo fth efemale sdi ebefor eth efirs t oviposition (Fig. 55).Th esam elin eo fargumen ta sfo rth emale sabov elead st oa si ­ milarrul eo fthumb ,onl ya facto r5 lower .A sthes efemale swil lhav eencountere dalrea -

km /l ^••30. 100 ^(10) •y\h

2.5 - .,1000 /(8-3;

2- .,3000

1.5 -

.,10000 / (33) 1-

.,30000 0.5- / M

^7oT 1 1 ' 1 1 TMI 1 1 H 00 "loooo ~\ ' 1 l'un "Jooooo" ' MM population Fig. 87.Immigratio no ffertil emale sa sa functio no fdistanc ean dpopulatio nsiz ea t theorigi no fth eimmigrants .Figure s indicateth enumbe ro fimmigratin gfertil emales ; betweenbracket s thesterile:fertil erati oresultin gfro mimmigratio n ina fiel dwher e 1000 0fertil emale semerg ean d 10000 0steril emale sar ereleased ,thei remigratio n takenint oaccount .

125 dysevera lsteril emale so nth efiel dwher ethe ymated ,thei rpotentia lharmfu leffec t willb ereduced .I nSectio n6.2. 4 theeffec to fthes efemale so neg gfertilit ywa scal ­ culatedfo rexperimen tMi js 197 4o ncontro lb ysteril emales .

5.6.4 Migrated fractions of reproducing populations, in relation to distance

Inreproducin gpopulations ,th enumbe ro freproducin gfemale s isimportan tand ,fo r sterilemal econtrol ,th esterile/fertil erati oi nth emales .Th enumber so fmale sar e nots oimportan ther ebecaus ethe yar ever ypolygamous .Th erati oi nth emale sca nb e foundfro mth edat agive ni nth eprecedin gsection ,th enumber so freproducin gfemale s willb econsidere dhere . Forexperimen tMi js 1974 ,th emigrate dfraction so fcatchabl epopulations ,a sgive n inSectio n5.5 ,ca nb econverte dt oestimate dmigrate dfraction so freproducin gpopula ­ tions.Th ecalculation sar egive ni nTabl e26 .Th etota lpopulation so femergin gfemale s arefoun dfro mTable s2 0an d21 ,divide db y2 becaus ea temergenc eth ese xrati oi s1:1 . Theaverag efraction saliv ewhe nreproducin g (ovipositing)ar efoun di nTabl e2 2 for subsequentovipositions ,an dth ecorrectio ngive ni nSectio n5.6. 1 hast ob eapplie dt o 1stfligh tdata .Thes edat awer esimplifie dt oassume dpercentage so f60 %o fth e1s t flightfemale san d 37%o fth e2n dfligh tfemale sovipositin gonce .Thu sth enumber so f femaleflie sreproducin gwer ecalculate d (Table 26).Ho wthes enumber swer edistribute d betweenth efiel do femergenc ean dothe ronio nfield sca nb efoun dfro mTabl e25 ,b yad ­ dingu pal ldat afro mday sdurin gwhic hth efemale sar esuppose dt ooviposit ,tha ti s whenfemale sar econcentrate do nth eonio nfields .Th eresul ti sfo rth e1s tfligh t (days17-21 ,2 5e tseq.) : 46%emigrated ,an dfo rth e2n dfligh t (days11-14 ,1 8seq.) : 28°semigrated .A sn osuc hdat aar eavailabl efo rth eothe ronio nfields ,thes epercen ­ tagesfro mth eexperimenta lfiel dar eapplie dthere . Forestimatin gth edistributio no fthes eemigrate dfemale sove rth edifferen tonio n fields,th edat ao fTable s2 0an d2 1wer eused .Th eresult sar egive ni nTabl e26 ,a s estimatednumber so ffemale sreproducing ,divide db yorigi nan dreproductio nsite .Th e pre-reproductivedispersal ,tha tca nb esee nfro mcompariso no fth ebotto mro w (totals emerged)wit hth erigh than dcolum n (totalsreproducing) ,i slevellin gth epopulation s tosom eextent .

5.7 SUMMARY

Onionflie scoul dkee ppac ewit hth e1 km/yea rsprea do fonio ncultivatio ni na newl y reclaimedarea .Dike sconnectin gth eforme risland si nth eS Wo fth eNetherland sdi dno t constitutemigratio nroute sfo rth eflies . Therat eo fdispersa li sdependen to ntemperature ,bu twa sfoun dt ob ei ngenera lin ­ dependento fwin ddirection .Mor edetaile ddat ao ndispersa linsid eonio nflie sreveale d somepreferenc efo rupwin dflights .Ne tdisplacemen toutsid ea nonio ncro pi s2. 5time s fastertha nthroug honio nfields . Thewid ewater saroun dOverflakke eca nb econsidere da sreflectin gbarrier st oth e flies,a sindicate db yrecaptur edat aan ddirec tobservation .Incidentally ,lon grang e

126 Table 26.Distributio no ffemale s atth eaverag eag eo fovipositio n over theonio n fields, different sources seperately. Experiment Mijs1974 . a. 1stfligh t

Onion field where emerged exp K+2) 3(+2) total Dumber of flies emerging population 2100 0 9080 0 1460 0 5490 0 9 500 females alive(60% ) 630 0 2724 0 438 0 1647 0 285 0 females emigrated(46% ) 289 8 1253 0 201 5 757 6 131 1 Numberof ovipositing females x 10 onion field where ovipositing: exp 3.4 0.1 0.1 0.5 4.2 5 1.0 4.6 0.1 1.0 1.3 8.0 con 0.1 14.7 0.0 0.2 15.1 1 0.4 0.7 2.4 1.1 4.5 2 0.2 .3 0.7 2.9 1.5 5.6 3 0.9 .5 1.0 8.9 11.2 4 0.1 1.9 0.0 0.5 - 6-8 0.0 3.7 0.0 0.4 - 9 0.1 .8 0.1 0.7 - 10 0.1 .0 0.0 0.1 - total 6.3 27.2 4.4 16.5 2.9 b. 2ndfligh t

Onionfiel dwher eemerge d exp 5 con 2 3 total Humber of flies emergingpopulatio n 200 0 2 000 75 400 300 200 6 900 femalesaliv e(37% ) 370 370 13 949 55 37 1 277 femalesemigrate d (28%) 104 104 3 906 15 10 358 Numberof ovipositing females x 103 onionfiel dwher eovipos i ting: exp 0.2 0.0 0.1 0.0 0.0 0.0 0.3 5 0.0 0.2 1.6 0.0 0.0 0.1 1.8 con 0.0 0.0 10.0 0.0 0.0 0.0 10.1 1 0.0 0.0 0.3 0.0 0.0 0.1 0.4 2 0.0 0.0 0.0 0.0 0.0 0.1 0.2 3 0.0 0.0 0.0 0.0 0.0 0.9 1.0 4 0.0 0.0 0.4 0.0 Ü.0 0.0 . 6-10 0.0 0.0 1.5 0.0 0.0 0.0 . total 0.4 0.4 13.9 0.1 0.0 1.3 •

dispersalma yresul t frombein g carriedb ytraffic .I ti sno tprobabl e that significant numberso fonio nflie sjoi nth eaeria lplankto nfo rlon gdistanc edispersal . Smallonio nflie ssho wa slowe rdispersal .Hig hconcentration sa tth ereleas e sites didno tsee mt oresul ti na faste rdispersal . Theonio nfl ydispersa lwa sdescribe db ya diffusio nprocess .Th ediffusio ncoeffi ­ cientwa scalculate d fromfiel dobservation so fth efrequencie san ddistance so fflights ,

127 2 2 andwa sfoun dt ob eabou t 120m /da yfo rfemale san d17 5m /da yfo rmale s insideonio n fields.Calculatio no fth ediffusio ncoefficien tfro mth eincreas eo fth emedia ndistanc e 2 ofth eflie sfro mth eorigi nversu stim egav e360 0m /da yi na nare awit ha naverag e onionfiel ddensity . Adispersa lexperimen twa ssimulated ,essentiall yb yassumin gdiffusio no fth eflies . Introductiono fpositiv eanemotaxi sdi dno timprov eth efi to fth emodel' soutpu tt oth e experimentaldata .Afte rcorrectin gth etrappin gprobabilit youtsid eonio nfield sfo rit s highervalu edu et oth eincrease dfligh tactivit yo fflie sthere ,th eoptima lfi to fth e model'soutpu tcoul db eestimate dt ob eobtaine dwit ha diffusio ncoefficien to fabou t 2 2 1400 0m /day ,reduce dt oabou t2 00 0m /da yinsid eonio nfields . Therelatio no fth elogarith mo frecapture sversu sdistanc ewa sfoun dt ob eabou tli ­ near.Whe ni ti sassume dtha tth eflie sdiffus ei na homogeneou senvironmen tan dhav e normallydistribute d life-spans,a nearl ylinea rrelatio ni sexpected .A linearrelation ­ shipwa suse dt oobtai nb yextrapolatio nsom emissin gdat ai na large-scal erelease-re ­ captureexperiment .Whe nther ear efe wonio nfields ,recaptur erate swer ehighe ra tgrea ­ terdistance scompare dwit hthos eestimate dfro mth elinea rmodel .Possibl ecause sfo r deviationsfro mth elinearit yar eindicated . Fromth edistributio no frecapture dflie so ndifferen tsite sversu sthei rage ,i twa s foundtha tmigratio ni nfemale swa sreduce ddurin gth eperiod so fmatin gan doviposition . Inth emale sther ewa sa simila rtemporar yconcentratio no nonio nfields ,supposedl yfo r mating.Th eag edistributio no fimmigrant sa tth emomen to fimmigratio ngav ea simila r picture.Abou t70° so fth eimmigrant sarriv ebefor eth eaverag eag eo fmating . Atth emomen to fmatin gabou t50° so fth emale saliv ehav elef tth eonio nfiel dwher e theyemerged .Fro mthi sth eimpac to fwil dpopulation so na singl efiel dtreate d with sterilemale si sshown ,dependen to nth edistanc ean dth erelativ esiz eo fsuc hpopula ­ tions.Th efractio no ffemale saliv etha tha smate dbu tno tye toviposite dafte rmigra ­ tingwa sestimate da t 2%o fth enumbe remerged .Fro mth edistributio no ffemale sove r thefield swher ethe yemerge dan dth efield swher ethe yoviposited ,th eeffec to fpre - reproductivemigratio nwa sderived .

128 6 Genetic control

Field trialso nth eus eo fsteril emale s foronio nfl ycontro lar edescribe d here. Theseexperiment swer eth efina lgoa lo fth eresearc h phaseo fth eproject ,an dwer edon e todemonstrat e ecological feasibilityo fth esteril e insect techniquefo rth eonio nfly . Atth esam e time,thes eexperiment sprovide dth eopportunit yt oestimat esom eparameter s ofpopulatio ndynamic s relevantt orelease so fsteril e onionflie si npractice . Firsta serie so fexperiment sar ereviewe dbriefly ; thesewer edon emainl yb yothe r memberso fth eonio nfl yresearc hteam ,i na nare aremot e from thecommercia l oniongro ­ wing areas.Then ,a nexperimen ti non eo fth emai nDutc honio ngrowin garea si sdescribe d indetail .Finall yestimation sar egiven ,insofa ra spossibl e fromth eavailabl e informa­ tion,o nho wth esteril e insecttechniqu eshoul db eapplie di npractice .

6.1 FIELDTRIAL SA TTH ESCHUILENBUR G

6.1.1 Introduction

A serieso ffiel d trialso nsteril e insecttechniqu ewer e carried outfro m197 1t o 1974b yth eonio nfl ytea mo nth eexperimenta l farmth e Schuilenburg,som e1 0k mS Wo f Wageningen.Som edat ahav ebee nreporte db yTichele re tal . (1974a)an dTheunisse ne tal . (1974, 1975). Theexperiment swer e donei nthi sare abecause ,a tth etim ethe ywer ese tup ,th edis ­ persalpropertie so fth eonio nfl ywer eno tye tknown ,an di twa sthough t thatth esit e chosenwoul db eisolate d fromothe ronio nfl ypopulations ,a sther ewa sn ocommercia l oniongrowin gi nthi sarea .Th eisolatio nma yno thav ebee nver y good,a sonion swer e growni nkitche ngarden swithi na fe wk mdistance .Th elocatio nwa sno trepresentativ e foronio ngrowin g areasa sth esoi lwa s ratherheav y (clay fraction 30-451),an dlo w damage levelsar etherefor eexpected .I nthi spreliminar y field trialsuc h levelswer e anadvantag ebecaus ethe y limitedth edemand so nth emass-rearin g output. Thereproductio n factorshav ebee ndiscusse di nSectio n 4.5.3,an ddamag edat ahav e beengive ni nTabl e 15. Thenumber so fsterile srelease dwer e correlatedwit h thesubsequen teg g sterility. Optimumcorrelatio nwa s foundfo reg gsterilit ywit h thesu mo fth enumber so fsterile s released onewee kan dtw oweek s earlier.Thu sth eaverag e ageo fmatin g canb eestimate d at1- 2weeks .Th eexistenc eo fa correlatio n indicated thatth esteril e insect technique workedi nth efield ,a sa desire deg gsterilit y couldb eobtaine db yreleasin gth ere ­ quirednumbe ro fsteriles . Bothsexe swer ereleased . Sterilized females impedeth econtro li nspecie swit ha lo w mating frequency (Ailam& Galun ,1967 ;Cuellar , 1973).I nth eonio nfl ymale ,th ematin g

129 Table 27.Populations , sterility and reproduction, Schuilenburg field trials on sterile insect technique, 1971-1974.Guesse d values are between brackets; the other values, given in italic,wer e calculated from these and observations.

Year Populations, sterility and diapause Reproduction factors ,,. b b . . b flies eggs migration

1970

1971 r = 5.87 5.69 10.54

r2= 0.30 0.21 0.29

r = 2.79 2.32 4.93 y

1972 r= 1.56 1.58 2.92

r2= 1.08 1.24 1.73

r = 1.35 1.88 4.63 y

1973 r= 6.78 1.64 3.03

r2= 1.52 1.16 1.61

3.41 1.58 3.97

1974 r = 0.92 1.71

r= 3.84 5.36

| 200 2.52 6.85 y

Average reproduction factors: 2.75 2.45 3.55 1.17 0.67 1.44 2_ 2.99 1.90 4.99 y a. s=effective sterility, c?=diapausing fraction, subscripts denote flights. b. i°.=ls t flight reproduction, r„=2nd flight reproduction,^ reproduction for a year (r =r d. + (\-d.)r.r~d~). First column calculated with the sterilities among the flies as given, second column calculated with the sterilities among the eggs, third column with corrections for emigration included and, where available,base d on sterility among eggs. c. From 9000 laboratory-reared pupae with a competitiveness of 0.31 as estimated from recapture data. These pupae were fertile and introduced to increase thewil d population.

130 frequencyi srathe rhig h (Section 2.2.1).Th e related cabbageroo t flymale sca nmat e effectively about5 0time s (J.L.Smith , 1973).

6.1.2 Reproduction

Datao nreproductio n aregive ni nTabl e 27.Th e populationso fdiapausin gpupa ean d thepercentage so fsterilit y differ slightly fromthos egive ni nth e literature mentioned inth eprecedin g section,becaus e thosedat aar ebase do npreliminar y calculations. The aimo fsteril erelease si st omat e fertile femaleswit h sterilemales .Thus ,th e relevant figurei sth esterilit y among themale sme tb yfertil e females;thi sfigur ei s calledher e theeffectiv e sterility.Estimatio no fth epercentag e sterility amongth e flies fromth etota lo frecapture spe rfligh to fsterile san dfertile swil l tendt oyiel d toohig hvalues ,a sth efligh t curveso fsterile san dfertile swil l oftenno tb econgru ­ ent.Becaus eo flac ko fknowledg eo npredictio no ffligh t curves,a constan treleas e rate was chosen,thu sdeliberatel y not tryingt oattai ncongruenc yo ffligh t curves.Th eef ­ fective sterility canb eestimate d fromth epercentag eo fdail y sterility among themale s duringa fligh tb ytakin g thenumbe ro ffertil e femalestha twer e caughto nth e sameda y asweightin g factor.I nsom eexperiment s considered hereth esterilit ywa s checkedi non ­ lyon esex ,an dthe nthi s sterilitywa s extrapolatedt oth eother . Inth e 1971an d197 2dat ath enumbe ro ffertile sha dt ob ecalculate d fromth eper ­ centageo fsterilit yi na sampl eo fth ecatch ,an dthi sresulte di nbiase dvalue so fth e effective sterility.Compariso no fweighte d andunweighte dpercentage s sterility (Table 28)show s thatth edifferenc ebetwee n thesea sfoun di n197 1i ssimila rt oth e differences foundi n197 3an d1974 .Th elarge rdeviatio ni n197 2ca neasil yb eexplaine db yth emor e important differencesdurin g that seasonbetwee nth esteril ean dfertil e flightcurves . Soth ebia si nth ecalculatio no fth eeffectiv e sterilityi n197 1an d197 2ca nb econsi ­ dereda sunimportant .Not e thatth edifference sbetwee nweighte d andunweighte d sterility are largeri nth e2n dflights ,whic h are thus lesswel lmimicke db yth ereleases . Thereproductio n factorscalculate dfo r197 1 areno tver yreliabl ebecaus eo fth elo w numbero fsample s (12)an dfo r197 4becaus eo fth e lownumbe ro fpupa epresent .I tseem s probable thatth e2n dfligh tpopulatio ni n197 1wa soverestimate dan dtha ti n197 4thi s populationwa s underestimated.

Table28 .Compariso n ofweighte d andunweighte d percentage sterilityamon g theflies . ExperimentsSchuilenbur g 1971-1974.

Year Flight Weighted Unweighted Difference

1971 1 73.8 67.5 6.3 2 51.5 41.3 10.2 1972 1 62.5 47.0 15.5 2 67.4 43.8 23.6 1973 1 94.0 85.7 8.3 2 94.8 82.8 12.0 1974 1 94.9 91.5 3.4 2 89.8 85.2 4.6

131 In197 1ther ewil lprobabl yhav ebee na thir dfligh t (Fig.37) .I fth ediapaus efre ­ quencyo fth e2n dgeneratio npupa eha dbee na tth elo wvalu eo f0.8 ,ther ewoul dhav ebee n a3r dgeneratio no f100 0flies .The nth ereproductio nfactor swoul dhav ebee n r. =5.58 , r? =0.4 3an d r =2.83.Th ethir dflight sar eassume dno tt ohav ereproduce dbecaus eo f thegenerall yunfavourabl eweathe ra ttha ttim ean dth escarcit yo fonion sa sthe yha d alreadybee nharvested . TheSchuilenbur gpopulation sar econsidere dabov et ob econfine dt oth eexperimenta l field.I nrealit ybot hsterile san dfertile swil lhav eemigrate d fromth eexperimenta l field,an dfertile sma yhav eimmigrated .Th eimmigratio nwil lno thav ebee nver yimpor ­ tantquantitatively ,a sestimate d inSectio n6.1.3 .Anothe rindicatio na st oth erelativ e importanceo fimmigratio nt ob eexpecte d inthi sare aca nb efoun dfro mth econtro lfiel d in1973 ,a ta distanc eo f0. 7k mfro mth eexperimenta lfield .Thi sfiel dwa sprovide dwit h 65 Znlabelle dflie sfro mdiapausin gpupa eburie d inearl yspring .I fon eexclude sthes e labelledflie sfro mth ecaptures ,th e1s tfligh tsterilit yo nth econtro lfiel di sstil l lowertha ntha tobserve di nth eexperimenta l field.Th edifferenc eca nb eexplaine db y assuminganothe rsourc eo fwil dflies ,an dth enumber simmigrate d fromther ear eestima ­ teda t700 .Simila rnumber sca nb eexpecte dt ohav emigrate dfro mther eint oth eexperi ­ mentalfield .Expresse da sa fractio no fth ewil dflie scaugh to nth eexperimenta lfield , theseca nb eestimate da s14$ . Thisnumbe ro fextr aimmigratin gwil dflie so nth econtro lfiel dca nals ob eexplain ­ edb yassumin gth edispersa lo fth ewil dflie st ob efaste rtha ntha to fth elaborator y rearedflie sb ya facto ro fabou t2.5 .But ,i fon econsider sth elo wnumber so fflie s concerned,an dth epresenc eo fnon-commercia lonio ngrowin g inth enea rsurroundings ,th e latterexplanatio ndoe sno tsee mver yprobably . Figureso npre-reproductiv eemigratio nca nb eobtaine da sfollows .Th erecapture so f sterilespe rtra pa t0. 7k mdistanc ei n197 3an da t2. 3k mdistanc e in197 4wer e3. 1 and 0.3$o fthos eo nth ecorrespondin gexperimenta l fields,whic hdat afi trathe rwel li n Fig.81 .S oth eemigratio nfro mth eexperimenta l fieldwil lhav ebee ncomparabl et oth e emigrationfro mth eexperimenta lfiel do fMi js 1974 ,whic hwa so fequa lsiz ean dals o ratherisolated .Thu sth epre-reproductiv eemigratio nca nb etake na s46° sdurin gth e 1stfligh tan d28 1durin gth e2n dfligh t (Section5.6.4) . Theeffec to fimmigratin gfertile si sinclude di nth eobserve dsterility .Th eeffec t ofemigrant sha st ob ecorrecte dfo rb yreducin gth ewil dpopulation sb yth epercentage s givenabove .Th eresultin greproductio nfactor sar egive ni nTabl e27 ,righ tcolumn .

6.1.3 Competitiveness

Duringth eSchuilenbur gexperiment sther ewer econsiderabl elosse so fsteril eflie s aswer ereporte dfo rth eOverflakke eexperiment so nsteril einsec ttechniqu e (Fig.20 , Table 32).Th elosse swer eattribute dt oprédatio nb yinsectivorou sbirds ,whic hwa s actuallyobserve dhere .Thes elosse sappea ri nth edat aa slowere dcompetitivenes svalue s (Table29) . Anotheraspec to fth ecompetitivenes s issee nfro mth edifferenc ebetwee nsterilit y amongth eflie san dsterilit yamon gth eeggs .Fo reac hfligh tth eeffectiv esterilit y

132 Table 29.Competitivenes s of sterile flies found from recapture rate. Experiments Schuilenburg 1971-1974.

Year Flight Number offlie s Ratio sterile/fertile Competitiveness emerged released expected observed3 calci fertile sterile

1971 1 14 400 318 000 22 2.82 0.14 2 20 600 157 000 7.6 1.06 0.13 1972 1 10 450 383 200 37 1.67 0.05 2 6 900 231 400 34 2.07 0.06 1973 1 5 900 1 013 900 172 15.67 0.09 2 5 500 566 200 103 18.23 0.18 1974 1 4 350 683 400 157 18.61 0.12 2 300 435 100 1450 8.80 0.01

Unweighted percentage sterility. Sterility assessed fromdy emarks ,an da sno tal lrelease d steriles were well dyed, the figures areto olow . Rather unreliable because afe wimmigratin g females will haveha da seriou s impact onth erelativ e sizeo fth efertil e population, andbecaus e theestimate d population is probably toolo w(Sectio n 6.1.2).

Table 30.Matin g competitiveness of sterile flies.Experiment s Schuilenburg 1971-1973.

Year Fl ight Effective Observed Competitiveness Number Estimated number steri Lity steril ity calculated of eggs of females that laid among flies among eggs these eggs3 1971 1 67.5 66.5 0.96 5210 155 2 41.3 16.9 0.29 6437 227

1972 1 02 47.0 47.6 '• K 6692 207 2 43.8 61.3 2.03b 5448 196 1973 1 85.7 40.7 0.12 938 23 2 82.8 77.4 0.71 1759 57 a.Estimate d separately foreac h cage inwhic h females were kept. b. Sterility assessed fromdy emarks ,an da sno tal lrelease d steriles werewel l dyed, the figuresar eto ohigh ,cf .Tabl e29 .

(Section6.1.2 )i scompare dwit hth esterilit y amongth eegg s laidb ycapture d fertile femalesi nth elaborator y (Theunissene tal. , 1974),an dth ecompetitivenes s iscalcu ­ latedfro mthes edat a (Table 30).Th e observedeg gsterilitie swer ecorrecte dfo ra natural sterilityo fa nestimate d 10%,bu tno tfo rth eincreas ei neg gdepositio no f females aftermatin gwit h sterilizedmale s (Section 3.2),becaus e thiseffec ti shighl y dependento nth epupa lag ea tirradiation ,whic hvarie d somewhatdurin gthes eexperiments . Thecompetitivenes s valueso fTabl e3 0wil l thusa tleas ti npar tb eto ohigh ,e.g . the 2ndfligh t 1972value .Especiall yi nth e197 12n dfligh tan dth e197 31s tflight , the calculated competitiveness valuesar eprobabl y significantlybelo w1 ,an dnee d some explanation. Asth emethod suse dfo r assessing sterilityi negg san dfemale swer eessentiall yth e samethroughou t theseyears ,the y cannotb ea sourc eo fincidenta ldeviations .Possibl e

133 Table31 .Possibl ecause so f lowvalue sfo rmatin g competitiveness:weighte d average durationo f storageo fpupa ean d averagepupa lweight .Experiment sSchuilenbur g1971-1974 .

Year Flight Duration of storage Weight in mg in days

1971 1 21 9.11 2 40 10.74 a 1972 1 49 12.73 - 2 13 13.04 1973 1 80 12.58 2 69 12.21 1974 1 193b 12.89 2 87c 14.14

a. 31% 113-212 days, 69% 0-15 days. b. 75% stored in diapause. c. 100% stored in diapause.

causesar eimmigratio no fwil dfemales ,o rreduce dcompetitivenes so fsteril emales . In1971 ,30 %o fal lfemale scaugh tdurin gth e2n dfligh twoul dhav eha dt ob eimmi ­ gratedmate dfemale st oaccoun tfo rth elo wcompetitiveness .Thi spercentag ei sclearl y unrealistic,a sthes efemale swoul db eonl ya mino rfractio no fal limmigratin gfemale s (seeFig .86 ;Sectio n5.6.3) . Areduce dcompetitivenes so fth emale scoul db edu et oa lowe rpupa lweight .Also , theduratio no fstorag eo fpupa ea t3 C wa schecked ,becaus eVosselma n(pers .commun. ) foundrecentl ytha tthi sstorage ,althoug hno taffectin gfl yemergence ,di dreduc eth e flyperformanc e insingl epai rmatings .Th epupa lweight san dstorag eperiod so fth e sterilesrelease dar eindicate d inTabl e 31.Th ereduce dcompetitivenes svalue sca nb e explainedb yassumin ga combine deffec to flo wpupa lweight san dlonge rstorag eperiods .

6.2 GENETICCONTRO LFIEL DEXPERIMEN TO NOVERFLAKKE E

6.2.1 Introduction

Experimental area Theexperimenta lare ai sshow ni nFig .15 .Th eexperimenta lan dcon ­ trolfiel dwer ecultivate db yth esam efarmer ,ensurin ga minimu mo fdifference si n treatmentbetwee nthes efield sexcep ti nonio nfl ycontrol . Theexperimenta lfiel dwa sabou t1 h a (30x 30 0m) .A nuntreate dcontro lplo to f about0. 5h a (42x 13 2m) , about1. 7k mfro mth eexperimenta l field,wa spar to fa lar ­ geronio nfield ,th eothe rpar treceivin gth enorma linsecticid etreatment . Thesmal l197 3onio nfield ,situate di nth ecentr eo fth e197 4experimenta lfield , wasno ttreate dagains tonio nfly .Th edamag ether ewa s 24%,wherea sth eothe r197 3 onionfield si nth esurrounding sha dn onoticeabl edamage .Th eexperimenta lfiel dwa s supposedt ob erelativel y isolatedbecaus eo fit sdistanc efro mothe r 1973an d197 4 onionfields .Th esoi laroun dth eare ai nwhic hth eexperimen twa sdon ei sheavier ,re ­ ducingth elikelihoo do fsignifican tpopulation swhic hmigh tcaus eimmigratio no nth e

134 Table32 .Release san drecapture so fsteriles .Experimen tMij s1974 .

Numbero f Average % Dateo f Release Dye b Numbero f Recaptured % pupae weight Emergenc e50 % method mark flies r Recaptures inm g emergence released actualcorr . onex p experimental field

7692 2 12.0 84.8 6 May a 6.5 YO 65 230 1123 47.42 71 10448 2 11.8 95.8 9 May a 9.9 GC 98 786 1914 83.60 70 9788 8 12.6 90.8 18 May 3J 4.5 YC 44 895 800 95.74 79 (b 3 - none 43 987 . . . 10754 6 13.2 52.4 21 May I ' 2.5 BYC 28 274 485 42.26 77

other onion fields Field

4944 4 12.6 90 18 May a 42.8 BY 42 800 261 67.16 1 5351 2 13.2 71.0 21 May a' 38.0 BC 37 962 194 60.45 3 4892 6 13.7 46.0 30 May a' 22.5 BO 22 495 124 26.88 1 4940 4 14.5 61.6 3 June a' 30.4 GY 30 428 71 12.74 3 4888 5 13.6 77.6 11 June a' 37.9 GO 37 929 38 3.60 3

a.Metho do freleas ean dnumbe remergin gpe rreleas esit ei nthousand so fflies .Metho da : standardmetho do freleasin gpupa ewit hdy emark ,se eSectio n3.3.2.1 ;a' :withou tcove r againstth erain .Metho db :scatterin gpupa eb yhan d inth egrass yverge so f thefield , evenlydisperse d overth elengt ho fth efield .Metho d c:pupa eburie d inth esoil ,2- 5c m deep,betwee nth eonion snea r theedg eo f thefield .Metho dd :a sc ,bu tcovere dwit h gauze,mes h3 cm .Metho d e:release d asflie sfro ma pil eo ffla tcages ,se eSectio n 3.3.2.2. b.Dy emark sse eSectio n3.3.1.2 . c.Recapture spe rtra ppe rk msheltere d edgeo fonio nfield ,correcte d forunmarke dsteri ­ les,fo rtemperatur ean dfo rattraction . d.Flie srelease d on6 , 14an d 19August,respectively .

135 experimentalfield . Apartfro mth eexperimenta lan dcontro lfield sal lonio nfield swer etreate dwit h trichloronate,eithe ra sa see ddressin go rapplie da sgranulates .Th eonion so nth e experimentalan dcontro lfield semerge dabou t1 5April ,wer eharveste do n2 September , andtake nfro mth efield si nOctober .Th echemica ltreatment swer erathe rnormal ,an d consistedo finsecticid e (parathion,3 1July ,preventiv eagains tth eonio nmot hAcrolepi a assectella (Zeiler)an dth eonio nthrip sThrip stabac iLind.) ,fungicid e (zineb/maneb, fourtime sdurin gJuly )an dherbicide s (propachloori nApri lan d2 7May ;ioxyni lo nth e controlplo tonly ,1 1June) .Th eherbicide sma yhav eaffecte dth eonio nfl ypopulation s (cf.Godan ,1969) .

Releases of steriles Inprincipl eth epes tcontro ltreatmen to nth eexperimenta lfiel d consistedo fweekl yrelease so f10 000 0sterilize dpupae .Th eactua lnumbe ro fpupa e receiveddeviate dgenerall ysomewha tfro mthis ,sometime so npurpose .Ther ewer echange s inth ereleas emethod ,becaus eo flac ko ftim eo rbecaus e improvementswer edeveloped . Thus,mortalit ybefor ean ddurin gemergenc ewa svariabl ea swer eth enumber so fsterile s releasedpe rweek .Th edat ao nth erelease sar esummarize d inTabl e32 .A sca nb esee n there,wit hprope rreleas emethod sa naverag eemergenc eo fabou t90 s»ca nb eexpected . Duringth e1s tflight ,sterile swer erelease dals oa tth etw oneares tsource so f wildflies ,i norde rt odiminis ha possibl edisturbin ginfluenc eo fimmigratin gwil d flieso nth eexperimenta lfield .

Fertile populations present Thewil dpopulatio no fhibernatin gpupa ei nth eexperimenta l fieldwa sestimate dfro mpupa esampling so n2.25 1 ofth eare aa t2 3560 ,wit ha parasitis m of3.2% .I ti ssuppose dtha tabou t90° swil lhav eyielde dflie si nspring .Th epopulation s nearth econtro lan dothe rfield swer eunknow nan dwer etherefor eestimate db ymixin gthe m withfertil eflie srelease dfro mdiapausin glaboratory-reare dpupae .Th epopulatio nsize s aregive ni nSectio n4.3.3 .Becaus ethe ywer ecalculate dfro mth epopulatio ni nth eexpe ­ rimentalfield ,an ybia si nth eestimatio no fthi spopulatio ni sth esam ei nth eothe r populations.

6.2.2 Fly sterility

Sterility data Sterilitywa s indicatedb yth edy emar kapplie da trelease ,an dfo rth e femalesals ob ythei rovar ydevelopmen t (Section3.3.1.3) .Sometime sbecaus eo fpractica l limitationsa par to fth esterile swer erelease dwithou ta dy emark .T oaccoun tfo rthes e acorrectio nha dt ob eapplie dt oth edat afo rth emales ,whic hwa sestimate dfro mth e ratiomarked:unmarke damon gth esteril efemales .Durin gth erecaptur eperio do fth egrou p dyedBY Cther ewer eles sunmarke dsteril efemale stha nwa sexpected ,durin gth erecaptur e periodo f0-dye dflie sther ewer emore .Thes enumber so funmarke dsteril efemale scapture d couldb eexplaine db ya nassume dprédatio no fabou t60 %o nth epupa etha tha dbee nrelea ­ sedsimultaneousl ywit hth eBYC-dye dones ,an da nassume ddye ,recognitio no fonl y 1/7par t ofth eO-dye dflies .Thi scorrection ,applie dt oth eunmarke dsteril emale swa sa nim ­ portantfacto ri nth eperio d2 3Ma y- 1 July ,an di tdi daffec tth eaccurac yo fth edata .

136 Table 33.Averag e percentage sterility among theflie s during the1s tan d2n dflight . Experiment Mijs 1974.Aberran t males excluded,

Site Flight % Sterili ty % Sterility(releasesothe rtha n sterileso ntria lfiel dexcluded ) malesan d males effective females malesan d males effective females

exp 1 91.65 89.92 88 54 91.84 90.13 88.83 2 92.10 90.36 88 44 92.27 90.43 88.09 5 1 57.5 52.4 55 2 60.7 55.7 57.5 2 42.9 43.3 44 4 47.8 48.7 44.1 con l(May) 4.3 4.5 5 4 3.9 4.4 5.4 1 3.5 3.9 3.2 3.9 2 0.4 0.3 0.4 0.3 1 1 71.6 71.6 41.5 40.8 2 63.3 49.2 67.9 52.9 2 1 51.5 41.1 24.9 16.9 2 51.3 44.8 49.3 43.5 3 1 56.9 55.9 27.5 20.8 2 32.4 32.7 31.8 32.7 4 1 2.8 4.2 2.3 3.5 2 0.0 0.0 0.0 0.0 exp/5 1 85.2 97.8 85.4 100.0 2 100.0 100.0 100.0 100.0 exp/1 1 58.5 60.4 43.5 70.4 2 99.2 99.0 99.2 99.0 5/con 1 4.8 12.1 1.2 0.0 2 0.0 0.0 0.0 0.0

Theaverag esterilit ype rfiel ddurin gth e1s tan d2n dfligh ti sgive ni nTabl e33 . Thevalue sar eals ogive na sobtaine dafte reliminatio no fal lrelease sexcep tthos eo f sterileso nth eexperimenta l field. Thesterilit ype r10 0flie scapture di sgive ni nFig .88 .Th efigure sfo rth efemale s are lessrelevan tfo rgeneti ccontrol ,bu tbecaus eo fthei rmuc hhighe rreliability ,a s nocorrection sha dt ob emade ,the yar eals ogiven .

Sex differences Datafo rbot hsexe sappea rt ob ei nmoderatel y goodagreemen twit heac h other,th esterilit yo fth emale so nth eexperimenta l fieldbein gconsistentl y somewhat lowertha ntha to fth efemales .Suc ha se xdifferenc ecoul dhav ebee ncause db ya highe r maleo rsteril emal edispersa lactivity ,bu tth edat adi dno tsuppor t thisview .Selec ­ tiveprédatio no nsteril emale sma yoccu ri fthes e remainfo ra longe rperio dnea rth e emergence site thanfemales .Whethe r theyd os oi sno tknown ,bu tth e effectwoul db e counteractedb yprotandry ,becaus e insectivorousbird s learnwher eth e release sites are.Th emos tprobabl eexplanatio ni sfoun di nth edifferenc ebetwee nth e sexesi npre ­ ferencefo ronio nfields ,a sshow ni nFig .84 .Betwee nth etw oflight sth emal e sterility droppedt obetwee n8 0an d85t ,wherea sth efemal esterilit yremaine dconstant .Th e rea­ sonsfo rthi sdifferenc ear eno tclear .I tma ya tleas tpartl yhav ebee ncause db yth e correctionstha twer eapplied .Mal esterilit ydecrease da tth een do fth eseaso nbecaus e

137 sterility in% 100

_ •—- 80

* a 40-

yX* *XX V

too •...;. ..-.•. * ••..•*.. • H

60

40-

* *xx. -*—x-x-x— -x^**x— x—|— 04 05 06 07 08 30 10 20 30 10 20 10 20 30 10 20 30

Fig. 88.Percentag e sterility versus time. Experiment Mijs 1974.Eac h point represents 100flie s caught. • = trial field;A = onion field 5 (between trial and control field); X = control field. a. Males, aberrant males excluded. During June corrections for unmarked sterile males are quantitatively important. b. Females.

100' w_^ o- S o o -*~~

40-

20

-1— -1— -1— 04 05 06 07 08 month 30 10 30 20 20 30 10 30 day

Fig. 89.Percentag e effective sterility versus time, average values per 10 fertile females caught. Experiment Mijs 1974,tria l field. During June corrections for unmarked sterile males arequantitativel y important. ofth eshorte r life-spano fmale san dbecaus erelease sende dearlie r thanemergenc eo f wildflies .

Effective sterility Theeffectiv e sterility (Section6.1.2 )wa smeasure db ycalculatin g thepercentag e sterility among themale sfo r eachda yan deac hpai ro ftrap s (thetrap s wereusuall yi npair sclos et oon eanother )separately ,an dth eaverag ewa sweighte d accordingt oth enumber so ffertil e femalesi nthes ecatches .Fertilit yo ffemale swa s assessed fromovar ydevelopment ,s oyoun g fertile femaleswer eno tinclude da ssuc hi n thiscalculation .Becaus e theyhav eno tye t reached theag eo fmating ,the yshoul db e leftou to fth ecalculation . Thecours eo fth epercentag eo feffectiv e sterilitydurin g theseaso ni sgive nfo r thetria l fieldi nFig .89 .Th efligh taverage sar egive ni nTabl e 33.Durin gth etw o flightso nth etria lfield ,th eeffectiv e sterilityi so nth eaverag e1. 2an d2.2 s»,res ­ pectively lower thanth eunweighte d sterility amongth emales .O nfiel d5 an do nth e control field,th eeffectiv e sterilitywa sno tconsistentl y lowertha nth e corresponding unweighted sterility.Thi sresul ti sdu et oth esensitivit yo fthi smetho do fcalculatio n torando mperturbation sa tlowe rabsolut enumber so fmale scaugh tpe rtra plocatio npe r day,combine dwit h thecorrection sfo rth eunmarke d sterilemales . Becauseth echeckin go fovar ydevelopmen tha dt ob estoppe di nJun eo nmos t fields asmanpowe rwa s lackingan dbecaus eunmarke d sterilefemale swer epresent ,ofte nth eef ­ fectivesterilit ycoul dno tb ecalculated . FromTabl e2 8i tca nb esee ntha tth ediffer ­ encebetwee nweighte dan dunweighte d sterilityi sno tver y large.Thu sth eunweighte d ste­ rilityha sbee nuse dwher e theweighte dwa sno t available.

6.2.2 Competitiveness

Whenth erelease d sterile fliesar efull ycompetitiv ewit hth ewil d flies,th este ­ rility amongth eflie sca nb ecalculate d fromth enumber s releasedan dth ewil dpopula ­ tionestimates ,afte rcorrectio n formigration .T overif ywhethe r thecompetitivenes swa s impeded,th enumbe ro ffull y competitive sterilefl yequivalent swa scalculate d fromth e correspondingwil dpopulatio nan dth epercentag e sterilityobserved .Divisio nb yth eac ­ tually releasednumbe rgive sth ecompetitivenes s (Table34) . Becausei nthi sexperimen t sterilitywa smeasure d onlyi nth eflie scaught ,an dno t inth eeggs ,th ecompetitivenes svalue s calculated applyt oth ecatchabl e fliesonly . Thematin g competitiveness (flysterilit yversu s eggsterility )wa ssuppose dt ob e1 (Sections3. 2an d6.1.3 ) Thecompetitivenes so fth efertil ean dsteril eflie srelease d elsewherewer ecalcula ­ tedi nth esam eway ,bu t thesedat aar e lessreliabl ebecaus eo fth eles sreliabl epopu ­ lationestimate s involved. Theaberran tmale s (Section 2.1.2),constitutin go nth eaverag e 4%o fth eflies , are includedi nth enumber s released. Formas srearin g theyar ea full y incompetitivefrac ­ tion,lowerin gth ecompetitivenes si nthi sexperimen tb y0.01-0.0 5 (Table34) . Severalcompetitivenes svalue sar ewel lbelo w 1,especiall yo nth etria lfield .Th e valuesove r1 indicat emos tprobabl y the inaccuracyo fth edat arathe r thana superio r

139 Table 34.Calculatio n of competitiveness. Experiment Mijs 1974. . . b Onion Wild Released Ratio Competitive fl ies released Competitiveness a field & flies type released present released (a) (c) flight present to wild (b) number %L calc. actual exp 1 17 249 YO-GYO S 11.255 194 137 74.3 261 288 551 718 0.47 0.49

9 125 GYC-C2 S 11.937 108 925 76.1 143 134 859 963 0.17 0.17 Î* 17 249 (YO-0)d S 6.098 105 184 74.3 141 567 249 065 0.57 con 1 71 048 C F 0.268 19 041 77.6 24 537 48 191 0.51 0.53 1.15 e 2 61 201 G2 F 0.390 23 868 80.2 29 761 57 600 0.52 0.54 1 1 10 715 BY,B O S 3.030 32 466 47.8 67 921 65 295 1.04 1.08 1.78 1 10 715 G F 0.545 5 840 47.8 12 218 11 797 1.04 1.08 1.7 7 3 1 48 088 BC-GO S 0.935 44 962 76.6 58 697 106 319 0.55 0.57 0.60 1 48 088 Y F 0.258 12 407 76.6 16 197 13 959 1.16 1.21 1.26 a. Dye marks (see Table 32 and Section 4.3.3), and sterile or fertile. b. (a) Calculated from preceding figures, (b) aberrant males not included in number released, (c)wil d populations calculated from onion field surfaces instead of from sheltered edges of onion fields, see text. c. From Tables 20 and 21. d. Steriles only insofar as their combined emergence curve was similar to that of the wild flies. e. Only after 31 July. qualityo fth ereare dflies .Seriou sunderestimatio no fth ewinte rmortalit ywoul dhav e increasedal lcompetitivenes svalues ,resultin gi nsom erathe rimprobabl yhig hvalues . Asmentione dbefor e (Section4.3.3) ,th eus eo fonio nfiel dsurface sinstea do fshelte ­ rededge si ncalculatin gpopulation sfro mdensitie sals oyield sunrealisticall yhig h competitivenessfigures . Thecompetitivenes scoul dhav ebee nlo wdu et odifferen tcauses :(a )th esuboptima l sterilereleas eschedule :a mor eo rles scontinuou sreleas eo fsterile scompare dwit h amor eo rles sconcentrate demergenc eo fwil dflies , [b) therearin ghistory ,affectin g theperformanc eo fth eflie san d (c)th efat eo fth eflie safte remergence ,affectin g theirsurvival . a Theeffec to fth esuboptima lreleas eschedul ewil lb elow ,i nvie wo fth esligh tdif ­ ferencebetwee neffectiv ean dunweighte dsterility .It simpac twa sanalyse db yusin gfo r thecalculatio no fth ecompetitivenes sonl yth esu mo ffraction so fdifferen trelease d cohortsinstea do fal lth efirs tfligh tsteriles .Thes efraction swer echose ni nsuc ha waytha tth ecombine demergenc eo fthi sgrou pwa sabou tequa lt oth eestimate demergenc e curveo fth ewil dflies .The nth ecompetitivenes s increasesfro m0.4 7 to0.57 .Thi sdif ­ ferencemigh tb edu et odifference s inrecaptur erat eo fth edifferen tsteril ecohorts , rathertha nrecapture so fflie srelease da tth ewron gmoment .Th erecaptur edat aar e summarizedi nTabl e32 .Th epercentag erecapture dpe rtra ppe rk msheltere dedg eo fonio n fieldi sfo ral l1s tfligh tsterile scombine d6.48 ,an dfo rthos eemergin gsynchronousl y withth ewil dflie s7.63 ,tha ti sa facto r1.1 8higher .Th edifferenc ei ncompetitive ­ nesswa sa facto r1.21 .Thu si ti sclea rtha tth easynchronou semergenc edi dno tserious ­ lyaffec tth ecompetitiveness . Anotherargumen tstem sfro mth efac ttha tth eemergenc ecurv efo rth e2n dfligh ti s

140 normallymor e spread thantha t forth e 1stflight .The nth ecompetitiveness ,i flowere d becauseo femergenc edifferences ,shoul db ehighe rdurin g thesecon d flight.Actuall y itwa smuc h lower. b Oftenmas s rearing affectsperformanc e ofth e fliesproduced .Th eonl ydat a available onth equalit y ofth ereare d fliesuse dar e thoseo fth epupa lweight .Th e laboratory- rearedpupa eofte nweighe d lesstha nth ewil d ones,an dth esmalle rflie semergin g from thesema yhav ea loweredcompetitivenes s (Section 3.3.1.5).Th erathe rconstan t average pupalweigh t and therecaptur e ratedi dno t showan ycorrelatio n inth epresen texperi ­ ment,s othi squalit y aspecto fth e fliescanno thav ebee nth eorigi no fth ediminishe d competitiveness. Iti spossibl e thatother ,no t size-related,qualit y aspects affecting thecompetitivenes s occur,althoug h itdoe sno tsee mprobable :on eha s toassum e that severe changes inth e laboratory conditions occurredwhic hdi dno taffec tpupa lweight . a Toanalys eth eeffec to fth ereleas emethod ,tw oexperiment swer ecarrie dou tdurin g thiscontro lexperiment :on eo nth eeffec to fth enumbe r offlie semergin gpe r release site,an danothe ro nth eeffec to freleasin g flies insteado fburyin gpupa e inth e field. Theseexperiment s aredescribe d earlier (Section 3.3.2.1).A smentione d there,th echan ­ gingrecaptur erat eamon g thesteril ecohort s canver ywel lb e interpreted asa neffec t ofchangin gprédatio npressure .Thi seffec tdepend so nth eseason ,o n learningb ypre ­ datorsan do nth e localfl ydensitie sproduce db yth ereleas emethod .Th e competitiveness values ofth esuccessiv ecohort so fsterile sar egive n inFig .20 . Thefertil e released groupsd ono thav e equal competitiveness values,probabl y also duet oprédation :the yha da prolonge demergenc ecurve ,an dth enumber srelease d at C were aboutfou rtime sa shig ha sa tG an dY .Moreover ,a tth ereleas epoin to fC insec­ tivorousbird swer eobserve d regularly.

6.2.4 Egg sterility

Thedat ao neg g sterility,obtaine dwhe ndevelopin g aneg gtrap ,ar eto oscarc et o permit anyconclusions .Th eeg g sterility canb e lower thanth efl ysterilit y because offemale s immigrating betweenmatin g anddepositio no fegg sfertilize db ysper m from thismating ,an dbecaus eo fdiminishe dmating competitivenes s ofth emales .Becaus e of lacko fdat ath e latter factorwa s assumed toequa l 1 (cf.Sectio n 6.2.7). Theeffec to fimmigratio no neg g sterility canb eestimated . FromFig .86 ,concer ­ ning thefemal e immigrants coming fromabou t 800m distance,on eca ndeduc etha t 10-15% ofth e immigrants immigratebetwee nth efirs tmatin g and thefirs toviposition . Iffo r the secondreproductiv e cycleth esam erati o isassume dbetwee n immigratingbefor e (70ou to f80-85 )o rafte r (10-15ou to f80-85 )matin gprecedin g egg laying,ther ewil l beanothe r 20à15 x10à1 5/ 80à85o rabou t2.5 1o fsuc h immigrants.A s thefirs tmatin g mayhav e aneffec to nth esecon doviposition ,whic heffec t isstil lunknown ,calcula ­ tionswer emad ewit hth eextrem evalue s ofzer oan d 1001influence ,independen t ofth e malebein g fertileo rsterile .Henc e atota l of 10à15+ 2.5 + (0o r 1)* (20à1 5- 2.5)= 12.5à 17.5%o r 30% ofth eeg gdeposition s canb e estimated tooriginat e frommating s

141 outsideth eexperimenta lfield .Th eabou t15 1migh treflec tth eactua lsituation ,bu t 30°si sa theoretica luppe rlimi ttha twil lno tb ereache dbecaus ei timplie scomplet e ineffectivenesso fsubsequen tmatings ,whic hi sno tso . Thirdan dhighe rreproductiv ecycle sca nb eneglecte d (Sections4.5. 2 and4.5.3) . Thefigure sderive dabov eca nb eapplie dt oal lmigratio ndistances ,becaus eth edat a fromdifferen tdistance sdi dno tdiffe rsignificantl y (Section5.6.2) .Th e2.5° so ffe ­ malesimmigratin gafte rhavin gmate dfo rth esecon dtim eoutsid eth eexperimenta lfiel d wereassume dt ohav emate do na nonio nfiel dhalfway .Th eeg gsterilit yno wca nb ecal ­ culatedfro mth eimmigrants 'origin san dth eactua lfl ysterilit yi nth edifferen tonio n fields,an di sgive ni nTabl e35 . Thedifference sbetwee nfl ysterilit yan dth ecalculate deg gsterilit yar ever ysmal l duringth e1s tflight .Th eeffec to fth esterile srelease delsewhere ,whic hwa spartl y nullifiedb yth efertile srelease dthere ,wa snegligible .Durin gth e2n dflight ,du et o thesmalle rloca lpopulatio nan dth erisin gpopulatio no nth econtro lplot ,th eeffec t ofimmigrant so nth eeg gsterilit ywa ssomewha thighe ran dmigh teve nhav ebecom eseriou s especiallyi fth e1s tmatin gha da stron geffec to nth e2n doviposition . Theseriousnes so fa reductio no fth esterilit yb ymigratio nfro m88.44 1i nth eflie s to84.97 %o rles si nth eegg sbecome sclea rwhe nth epercentag edistributio no fth efer ­ tileegg sove rth efield sfro mwhic hthei rmother semerge di slooke da t:withou timmi ­ grantsth eresultin geg gpopulatio nwoul dhav ebee nhalved ,an dove ra quarte ru pt oon e thirdo fth efertil eegg swoul dhav ebee nlai db yfemale stha tcam efro mth ebi gpopula ­ tiono nth econtro lfield :nearl y 10000 0flie semergin ga tnearl y2 k mdistance .Thu s withsmal lloca lpopulation s immigrationma ybecom eimportan ti ncounteractin gth epopu ­ lationreductio naime da tb ysteril emal erelease s (seeFig .87) .

Table35 .Eg g sterilityo ntria lfield ,calculate d from thefl ysterilit y inTabl e3 3 andassumin g that 15%o f theimmigrant so nth eexperimenta lfiel d arrived afterhavin g mated elsewhere.Assume dmatin gcompetitivenes so f I.Experimen tMij s 1974. c Field of % Of reproducing Contribution to the % Egg sterility under origin fema l es coming total Xo f egg different assumptions from t-h LSfiel d steril ity ferti l ity (a)a (b)a first flight exp 81.1 71.8 9.3 1 3.4 2.9 0.5 3 12.0 10.0 2.0 con 3.5 2.7 0.8 total 87.5 12.5 86.9 86.3 second flight exp 51.2 45.3 5.9 1 0.9 0.8 0.2 2 0.6 0.5 0.1 3 11. 4 9.1 2.3 5 5.3 4.3 1.0 con 30.6 23.3 7.3 total 83.3 16.7 82.5 77.6 a.(a )Release sothe rtha no fsterile so nth eexperimenta lfiel dexcluded , (b)Assumin gn oeffec to f 2ndan d furthermatings . b.Fro mTabl e26 .

142 6.2.5 Damage

Theresult so fregula rdamag eassessmen to nth eexperimenta lan dcontro l fieldan d ona normall y chemically treated field areshow ni nFig . 46b. Thedamag eo nth econtro l fieldwa sclearl y aboveth eeconomi c threshold.Th eonion s fromthi sfiel dcoul dstil lb eharvested ,bu tth erotte n infested onionsmad e storage inappropriate.Th echemica l treatmento fth eadjacen tonio nfiel dcause d the 1stfligh t offspringt ob elargel y eliminated,s oa rea l control fieldwoul dhav eha damuc h higher damage duringth e2n d flight. Thedamag eo nth eexperimenta l fieldremaine dwel lbelo wth eeconomi cthreshold ,s o froma practica lviewpoin t theexperimen twa s successful.

6.2.6 Sampling of pupae

Inth eautum no f197 4population swer e estimatedb ysamplin gpupa eo nth etria lan d control fields.O fth econtro l field,a nare ao f3 0m wid ewa s sampled, 72%o fth eun ­ treated field.Th e results aregive ni nTabl e 36.Especiall y thediapausin g population onth etria l fieldcoul dno tb eestimate dver y accurately duet oth ever y lowpopulation : 9 pupaewer e found,whic hmean t9 x 19 1pupa epresent . Thediapausin gpupa e canb eoffsprin g eitherfro mth e 1sto ffro mth e2n dflight . The diapausing fractiono fth e 1stgeneration ,a sdetermine di nplot swher eonl ydamag ewa s observedbefor e1 0July ,wa sestimate da t25 1o nth e control fieldan d0 1o nth etria l field.Th ediapausin g fractiono fth e2n dflight ,determine d fromplot swit honl y damage after 10July ,wa sestimate da t80 % (datao fbot h fieldscombined ;eac hdiapaus epercen ­ tage givenher ei sbase do nbu t about3 0pupae) .Th eremainin g 20%mus thav egive nris e toa 3r dflight .Thi s3r dfligh t cannotb esee nclearl yi nth efl ytrappin g data,bot h becauseo fth elarg eoverla pbetwee nth e2n dan dth e3r dflight ,an dals obecaus e this flightmus thav eoccurre dfro mth een do fAugus t onwards,s omainl y after trappingha dt o stopbecaus eo fth eharvest .Hal fSeptembe r theweathe r turnedcol d andwe tan dremaine d sofo rmonths .Thu sth e3r dfligh twil lhav e stoppedhal fSeptember ,withou t realrepro ­ ductionpossibilities .Th epupa e thatgav e riset oth e3r dfligh twer e founda sempt y pupaebecaus eth esamples ,take ni nth ebeginnin go fSeptember ,remaine di nth e field and thepupa e couldno tb erinse d outunti lth esecon dhal fo fSeptember . Thisexperimen twa sth efirs tcas eo fgeneti ccontro lo fonio nflie si na nonio n growing area,s oth efirs tcas ewher e thepossibilit yo fnich e replenishmentb yothe r species couldb echecke d adequately.A smentione d (Fig.39) ,th esever e selectivere -

Table36 .Population sfro mpup a samples, experimentMij s1974 .

Field Pupae Allocationt ogeneration s empty pupaea tharvest : exp 976 0- 1 x1s tgen .+ 0. 2x 2n dgen . con 12506 0= 0.7 5x 1stgen .+ 0. 2x 2n d gen. diapausing population exp 172 5= 0.8x 2n dgen . con 9882 0» 0.2 5x 1s tgen .+ 0. 8x 2n d gen.

143 ductiono fth eonio nfl ypopulatio nals oresulte di na reductio no fth ebea nsee dfl y population.N oothe rpes tfille dth eemptie dnich eo fth eonio nfly .

6.2.7 Reproduction

Reproduction on the control field Table3 7contain sth erelevan tdat aan dcomputatio no f thereproductio no fth eflie so nth econtro lfield .Th ecorrectio nfo rth eflie srepro ­ ducingo nth eadjacen tchemicall ycontrolle dfiel di smad eaccordin gt oth elength so f thesheltere dedge so fth efields .Thi scorrectio n isrigh twhe nfemale sd ono t laythei r eggsmor etha n4 2m (thecontro lfiel dwidth )awa yfro mthes eedges .I ffemale sd ola y theiregg sfurthe raway ,the nth ecorrectio napplie dshoul drathe rb ebase do nth efiel d surfaces.The nth eestimatio no fth epopulatio nreproducin go nth econtro lplo twoul db e reduced,thu senlargin gth ereproductio nfactor .O nth eadjacen tchemicall ycontrolle d fieldth e1s tgeneratio nyoun glarva ewer eal lkilled ,a sca nb esee nfro mth edamag e data (Fig.46b) . Duringth e2n dfligh tth ecorrectio nfo rth eeffec to fth echemicall ycontrolle dfiel d isles sevident .A tfirs ti tmigh tb equestione dwhethe rth eflie ssho wa preferenc efo r theuntreate dsid eo fth efield ,becaus eo fattractio nb yth erotte ninfeste donion sthere . Comparisono fth erecapture so ffemale so nbot hside so fth efiel dindicate dn opreference . Theattractivenes so frotte nonion sthu swil lonl yac ta tshor tdistances .Secondly ,th e

Table37 .Reproductio no nth econtro lfield .Experimen tMi js 1974 .Releas esite so f fertiledye d fliesse eFig.1 5an d Section4.3.3 . 1st flight populationsemergin g wild: 9080 0 C:4 8 200 corrected forcompetitivenes s 9080 0 24 540 afterpre-reproductiv edispersa l 4900 0 13 250 G&Y: 240 total:6 250 0 reproducingo ncontro lfiel d 2180 0 corrected formal esterilit y 2095 0 1stgeneratio npupa e 14600 0 1stfligh treproductio n factor x 6.97 2nd flight

populationsemergin g wild:10950 0 G2:5760 0 corrected forcompetitivenes s 10950 0 2975 0 afterpre-reproductiv e dispersal 7880 0 2145 0 total:10025 0 reproducingo ncontro lfiel d 3495 0 corrected formal esterilit y 3485 0 2ndgeneratio npupa e 7790 0 2ndfligh treproductio nfacto r x2.2 4 whenparathio nkille d 25%o fth e2n dfligh t x2.9 8 3rd flight populationemergin go ncontro lfiel d 1560 0 populationemergin go nchemicall y treatedpar t 240 0 assumed reproductionfacto r3r dfligh t x0

Totalreproductio n fora year ,assumin g90 %emergenc eo fpupa e insprin g x9.9 8 whenparathio nkille d 25%o fth e2n dfligh t X12.78

144 Chemicalcontro li sn olonge rcompletel yeffectiv ei nsummer :Heimequi n& Lacroi x (1966) founda 100 %effectivit yo ftrichloronat edurin gsom e 100days .Thu sa 3r dfligh tca nhav e emerged fromth echemicall ycontrolle d field.Bu ta sthi sfligh tca nsafel yb eassume d nott ohav ereproduced ,i tha sn oeffec to nth ecalculation so freproduction .S oth esam e correctionha sbee napplie da si nth e1s tfligh tcalculations ,agai nkeepin gi nmind tha t thismigh t slightlyunderestimat e thereproductio nfactor . Thedat aar epresente dwit han dwithou t taking intoaccoun tth eeffec to fth epara - thionspraying ,t oindicat ebot hth eactua lreproductio nan dth ereproductio ntha twoul d haveoccurre dwithou t thisdisturbanc eo fth eexperiment .

Reproduction on the trial field Table3 8contain sth e relevantdat aan dcomputatio no f thereproductio no fth eflie so nth etria lfield .Th ereproductio n factors,afte relimi ­ nationo fth eeffec to fth esteriles ,ar e onlyslightl y lesstha no nth econtro lfield . Forth e2n dfligh tthis ,ma y seem strangea sth e reproductiono nrotte nonion s ismuc h better thano nnorma l ones (Section4.4 )an drotte nonion swer ever yscarc eo nth etria l fieldbu tcommo no nth econtro l field.A smentione di nth eprecedin g section,female s dono treac tt orotte nonion sove rlarg edistances ,s othe ymigh thav eha ddifficultie s infindin gany .I tma yb etha tthi sadvers eeffec to flo wonio nfl ydensitie si sbalan ­ cedb ya positivel ydensit ydependen t factora sfo rexampl eprédatio ncoul dbe .Assump ­ tiono fa lowere dmatin gcompetitivenes so fth esterile swoul dresul ti nlowe rrepro -

Table 38.Reproductio n on the trial field. Experiment Mijs 1974.Releas e sites of fertile dyed flies see Fig. 15an d Section 4.3.3.

1st flight with steriles population emerging wild: 21 000 after pre-reproductive dispersal 11 340 G: 380 Y: 430 C: 260 total: 1240 0 corrected for egg sterility(Table 35) 1 550 1st generation pupae 9 330 1st flight reproduction factor x 6.01 x 0.75 2nd flight population emerging wild: 9 330 after pre-reproductive dispersal 6 720 G2: 210 total: 6 930 corrected for egg sterility(Table 35) 1 160 2nd generation pupae 2 160 2nd flight reproduction factor x 1.87 x 0.31 when parathion killed 25%o f the 2nd flight x 2.49 x 0.41 3rd flight population emerging wild: 430 assumed reproduction factor 3rd flight x 0 x 0 Total reproduction for a year, assuming 90%emergenc e of pupae in spring x 8.99 x 0.19 when parathion killed 25%o f the 2nd flight xll.97 x 0.25 reduction in experiment versus control: 1st flight 2nd flight year 0.108 0.139 0.020

145 ductionfactor scalculate dfo rth eexperimenta l field,s oi tca nb eassume dtha tth ema ­ tingcompetitivenes swa sno tseriousl yaffected . Thereproductio n factoro nth econtro lfiel dfo ra yea rwa sabou t 13,whic ho nth e trialfiel dcoul db ereduce dt o0.2 5 duet oa sterilit yo fabou t90 $fo rbot hgenerations .

6.3 ANORMALIZE DFIEL DEXPERIMEN T

Whenth egeneti ccontro lexperimen tMi js 197 4ha st ob euse dt opredic tho wsteril e maleswoul dperfor mi npractica lcircumstances ,i ti susefu lt oconver tth eresult sint o thosetha tca nb eexpecte d froma mor e idealexperiment ,don ea sa larg eare atreatment . Inlarg eare atreatments ,th esteril ean dfertil epopulation sca nb eassume dt ob e distributedmor eo rles shomogeneously ,s omigratio nha sonl ya neffec tnea rth eborde r ofth etreate darea .Tabl e3 9give sresult so fth eexperimen tMi js 1974 ,compare dwit h theresult swhe nal lmigratio nwa seliminated .Absenc eo fpre-reproductiv emigratio n causesth ereductio nt ob emuc hmor esevere . Ifa releas emetho dwer euse dtha tprevent sinitia lconcentration so fflies ,an dtha t hasn oadvers eeffec to nth eemergence ,emergenc ewoul db e90° 6an dcompetitivenes sabou t 1.The nth esam ereductio na si nth eactua lfiel dexperimen tcoul dhav ebee nattaine d with40 500 0pupa einstea do fth e1 86 300 0actuall yused .Wit hal lmigratio neliminated , thenumbe ro fpupa eneede dwoul dhav ebee n21 5000 . Obviouslyth econtinuou sreleas eo fa fixe dnumbe r,o fsterile spe rwee ki sno tth e mosteconomic .I twa srealize dbefore ,tha tt oobtai na noptima leffec tth erelease sdu ­ ringth e1s tfligh tshoul db ehighe rtha ni nth e2n dflight ,becaus eo fth edecreasin g population,th ediapausin gfractio nan dth elowe rreproductio no fth e2n dflight .Th e presentpartition ,62.4 % inth e1s tflight ,gav ea reproductio nfacto rfo ra yea rnear ­ lyidentica lt oth efacto rtha twoul dhav ebee nobtaine dwit hth eoptimu mpartition .

Table39 .Reproductio no nth etria l field,experimen tMij s 1974,compare dwit hresult s toexpecte d ifn omigratio noccurred .

1stFligh t 2ndFligh t migrationmigratio n migrationmigratio n present absent present absent emergingwil dpopulatio n 2100 0 2100 0 933 0 945 0 reproducingwil dpopulatio n (Table38 ) 1240 0 2100 0 693 0 945 0 competitive sterilespresen t (Table34 ) 261 300 14310 0 reproduction factor,withou t steriles (Table38 )x 6.0 1 x6.0 1 *2.4 9 x2.4 9 reproductionwit hsteriles ,observe d (Table38 )x 0.7 5 x0.4 1 percentage flysterility ,observe d (Table33 ) 91.65 92.10 percentage flysterility ,calculate d 92.56 93.81 percentageeg gsterility ,calculate d (Table35 ) 87.48 83.32 percentageeg gsterility ,calculate d 92.56 93.81 reproductionwit hsteriles ,calculate d x0.4 5 x0.1 5 reproduction factor fora year ,migratio n present (Table38 ) x0.2 5 reproductionfacto r fora year ,migratio n absent x0.0 5

146 6.4 RELEASE STRATEGIES

Whenapplyin gth esteril e insecttechniqu efo rfl ycontrol ,som eessentia linforma ­ tioni sneede d aboutplace san dtime so freleas ean dth enumber stha tshoul db ereleased . Mosto fthi s information,wit hregar dt oth eonio nfl yi nth eNetherlands ,i sno tye t availablewit hsufficien taccurac yt oappl yth emetho dreasonably .Th erelevan tpara ­ metersan dthei rmagnitude ,however ,ca nb eestimate d fromth edat apresented . Onlyonio ngrowin gwil lb econsidered ,lee kgrowin gi sno tinclude dbecaus eth e onionfl yi sa les s importantpes to nit ,an dbecaus e leekgrowin gi sconcentrate di n otherpart so fth ecountry .

Release sites Releasesite s shouldb ediffuse ,t opreven tconcentration so fsterile s susceptiblet oprédation .Thu si ti sbes tt oreleas eth eflie sfro msom evehicl ealon g certainreleas e lines.Assumin gstraigh t lines,on e hast ofin dho wfa rthes eline sca n be aparts otha tth edensit yo fsterile sthroughou tth eare ai smor eo rles sconstan ta t themomen tthe ymate .A roug hestimat eca nb eobtaine d fromth edat ai nTabl e2 6an dth e distances fromFig .15 .Wit h 50%o fth eflie si nfield sneares tt oth eemergenc esite s (upt osa y10 0m distance) ,an dthereafte ra logarithmi cdecreas e (cf.Fig .81) , there ­ lativedensitie sove ra transec tsquar eo ntw o release linesar eshow ni nFig .9 0fo r differentreleas e linedistances .Releas e linesthu sshoul db ea tles stha n1 k mdistanc e ofeac hother .I tha st ob etake nint oaccoun tthat ,whe nrelease sar emad eb yca rin ­ steado fb yaeroplane ,i ti seve nmor edangerou st ohav esite stha td ono tge t themini ­ mumsaf eleve lo fsteriles ,becaus eth ereleas e lines (roads)wil lhav et ob eabou tth e sameeac hyear . Forestimatin gth edept ho fth ebarrie r zonet ob etreate daroun da nare awher econ ­ troli sb ysteril ereleases ,Fig .8 7i suseful .I na nare awit hpopulation so feaua lsize , anonio nfre ezon eo fles stha nabou t1 k mwil lcaus ea noticeabl edeclin ei nth e sterile: fertilerati oamon gth eflies .Durin g thenex tyea ro fcontro lth ebarrie rshoul db e

relative density 1.0

1 1 1- 0.8 1.0 release lin* distança in km Fig. 90.Relativ edensitie so fsterile sbetwee ntw oreleas e lines,fo rsom ereleas elin e distances.Assumption sse e text.

147 shiftedoutwards ,a sth edifferenc ebetwee nth esteril emal etreate dan dchemicall ytrea ­ tedpopulation swil lb eincrease dconsiderably .

Frequency Theminimu mfrequenc yo frelease sneede dt oge ta mor eo rles sconstan tste ­ rilepopulatio ndensit yshoul db eknown .Pupa etha twer eburie d inth efiel dweekl ygav e therathe rregula rpercentag esterilit yamon gth emale sa sobserve di nth eexperimen tMi js 1974(Fig s88 ,89) .I nth eSchuilenbur gexperiment sth epupa ewer eals oburie dweekl yan d nocycli cchange swer eobserve d ineg gsterility .Release so fflie scaus emuc hles s spreadi nemergenc ea sonl yflie so f1- 2day sol dca nb erelease d (Section3.3.2.2) . Weeklyrelease so fflie sma yb eno tenoug ha sth esurviva lo fth emale si srathe rshor t especiallydurin gth e2n dfligh t (Fig.55) . Itcanno tye tb edetermine dho wlo wth e releasefrequenc yca nb emad ebefor eth esaving si nth ereleas ecost soverrul eth eexpen ­ ditureo nrearin gth enumber sneede dextr at okee pth eminimu mdensit ya ta saf elevel .

Distribution over the flights Thepartia l2n dfligh tcreate sth eproble mho wt odistri ­ buteth erelease sove rth etw oflight st oobtai na noptimu mpopulatio nreduction .Th e3r d flighti sneglecte dhere .Th ereductio nha sbee ncalculate dfo rdifferen tvalue so fth e percentagediapaus ei nth e1s tgeneratio n (Fig.91 )an dfo rth ereproductio nfactor so f the1s tan d2n dfligh t (Fig.92) .Th ereproductio nfactor sar eo flittl einfluenc eo nth e

/•„(S)

Fig.91 .Grap hfo rchoosin g aconvenien tƒ inrelatio nt o d,. Actualreproductio nfo ra year , r (s),versu sfractio no favailabl esterile srelease di 1stfligh t (ƒ),fo rdifferen tpercentage so fdiapausin gpupa eo f 1stgeneratio n (d.), assumingavailabl esterile s20 xwil d population,an dreproductio nfactor s r. =5 , r9- 2.

148 f.(* )

Fig.92 .Grap hfo rchoosin g aconvenien tƒ inrelatio n toF jan dr, . Actualreproductio nfo ra year , Py(,s), versus 2ndfligh treproductio n (r,)an dfractio n ofavailabl esterile srelease d inth e 1stfligh t (ƒ),fo rtw olevel so fth e 1stfligh t reproduction (r,) , assuming 20%diapaus e inth e 1stgeneration . 4, r= 8 ;cross-sectio na tƒ = 0. 8 shaded. optimumdistributio ni nth erang ebetwee n6 0an d85 %o fth e available fliesrelease di n the1s tflight .A sth epercentag ediapaus ei snormall yi nth erang eo f0-30 $ (Table10) , about80 $seem sth ebes tvalue .

Number of flies needed Atfirs ti twil lb eestablishe dho wman y fliespe ryea r arenee ­ dedt oobtai na certai nreductio na tth een do fth eyear .Th enumbe ri sexpresse da sa ratiot oth ediapausin gpopulatio nt ob etreated .I tha sbee nassume dtha t80 $o fth e sterilesar e releaseddurin gth e1s tflight . Forsom eassumption sabou treproductio nfactor san dth efractio no fth e1s tgenera ­ tiontha tgoe s intodiapause ,th eeffec to fdifferen treleas eratio si sshow ni nFig . 93. Forth emomen t letu sassum e thata releas erati oo f2 0sterile spe rfertil ei ssaf e enoughan deconomicall y feasible.Th eeffec to freproductio n factorsan d1s tgeneratio n diapauseo nth ereductio nattaine dwit hthi srati oi sshow ni nmor edetai li nFig . 94, withth ereproductio n factorsobserve ds ofa ri nth efiel d indicated.Obviously ,plannin g forsteril emal erelease s requiresmor edetaile d informationo nth eactua lparamete rva ­ lues. Anotherproble mi nplannin grelease si sho wt odistribut eth e controleffor toptimal ­ lyove rsubsequen tyears .Th ebes ti st oai ma ta constan t outputfro mmas srearin gwhils t thesteril e insecttechniqu ei sintroduce di nth eare aunde rconsideration ,i.e .th e

149 0.6-

Fig. 93.Grap h for choosing aconvenien t a. Actual reproduction for ayear ,r>j,(s) ,versu s theoverfloodin g ratio a (available steriles versus initialwil d population), for differ­ 0.2 ent assumptions ofF, , r and the diapausing fraction of the 1stgeneratio n (d.), for /=0. a: r2-'i, d 0.2; a': dj=0.4; b: i-ï-5, r2=2, d 0.2;b' : d^O.4; b": ^=0.0; r 2 )k,d]=0.2.

21.432a'1-1*85 —I 1 1 1- ry(s) 10 20

r, rv(S)=o.02 5

Fig. 94.Grap hvisualizin g the effects tob e attained withƒ » 0.8 and a =20 . Actual reproduction for ayear , r-y(s), as function of thereproductio n factors Pj and v ,fo r three levels of the 1stgeneratio ndiapaus e (dj). d.= 0.4; dj= 0.2; - - - d±= 0.0 . Observed reproductionvalue s indicated.

150 Netherlands.Le t theAlliu mcro pt ob etreate dcove r Ahectares ,wit ha pes tdensit yo f p viablediapausin gpupa epe rhectare ,an da reproductio nfacto rpe ryea ro fr. Letth e reproductionfactor ,includin gth eeffec to fth esteriles ,b echose na sr' ,an dth enum ­ bero fyear sdurin gwhic hth emetho di sintroduce di npractic ea s n. Notetha ther ea constan tpopulatio nreductio nfacto ri schose ninstea do fth eofte n advocatedconstan treleas erate .Th elatte rmetho di sth ecaus eo fth estatemen ttha tth e sterileinsec ttechniqu ebecome smor e efficienta tlo wpes tdensities ,a sth epopulatio n isreduce da ta nincreasin grate .However ,thi sapplicatio ni sgenerall ya wast eo fste ­ riles,unles sther ear eurgen treason sreduc eth epes tquickl yt over ylo w levels. At firsti tha st ob eestablishe dwha tpar to fth etota lare ashoul dreceiv eit s firststeril emal etreatmen tpe ryear ,whe nth emass-rearin goutpu ti skep ta ta con ­ stantlevel .Th erelativ enumber sneede dpe rare aar e1 i nth e 1styear ,i» 1i nth e2n d 2 year, (r') inth e3r dyea ran ds oon .Assumin gth emetho dt ob eintroduce deac hyea r ina ne warea ,an do fcours et ob econtinue dwher ei tha sbee nintroduced ,on efind sth e fraction ao fth etota lare atha ti st ob etreate di nth efirs tyear :

S1 = 1/(n-(n-1)r') (17)

whichare ai sincrease dever yyea rb y

a± = O-r')*, (18)

Thetota lamoun to fflie sneede dpe ryea ri sthu s<4p/(w-(n-1)r') ,multiplie db yth e overflooding ratiorequired . Nowconside ra tfirs tth ecas eo fa pes twit ha singl egeneratio npe ryear ,wit h populationsiz e Fan dth enumbe ro fsterile srelease dS .Tha nr '= rP/(S+f) ,s oth eover - floodingrati o S/F= (r/r')-1 .Th enumbe rrequire dannually ,* , is: Ap(r-r') N= (n-(n-1)r')r' (19)

However,du et oth epresenc eo fa partia l2n dgeneratio nthi smode lha st ob eadjus ­ ted.Th eoverfloodin gratio ,o ,i sno wexpresse da sth erati oo fth etota lnumber so f sterilest ob erelease dversu sth ediapausin gpopulatio no ffertiles .T ohav ea saf eva ­ lue,th euppe r linei nFig .9 3wil lb eused .Thi s lineca nver ywel lb eapproximate db y therelatio nr '= 21.43 2a -1-1*85 (correlationcoefficien t 0.998),or ,a = r'-°- 67/0.127. Themass-rearin goutpu trequire dno wca nb efoun dfrom :

Apr'-0'67 N= 0.127(«-(n-1)r') (20)

Forth esituatio ni nth eNetherlands ,th eparameter sar eestimate da sfollows . The onioncro pcover sabou t1 200 0ha ,wit hfluctuation so fabou t 10%(Tabl e 2). Thepopula ­ tiondensit yo fdiapausin gpupa eha st ob efixe da ta rathe rsaf e level,sa y2 000 0pe r ha (Fig.53) .No wN ha sbee ncalculate daccordin gt oEq n(20 )fo r differentvalue so f r' andfo rdifferen toption sfo rth enumbe ro fyear sdurin gwhic hth emetho dwil lb eintro -

151 rearing output

2.103 - /I»4

1.10s -

1 1 1 I T l I 1 1 O80 067 0.50 0.33 0.25 0.20 .17 ry is) Cxo24 14 8 S 4 4 3 years until d<100 Fig. 95. Required mass-rearing output per year in competitive fly equivalents versus the reduction factor to be chosen, for some numbers of years (n) over which the method is introduced in the Dutch onion growing areas.

duced (Fig.95) .Fro mthi sgrap ha reasonabl eschem efo rintroductio no fth esteril e insecttechniqu eca nb ederived ,especiall ya s Ni sdirectl yproportiona lt oth eothe r variables, Aan dp . Achoic efo ra highe rnumbe ro fyear sreduce sth erequire dmass-rearin gcapacity .O n theothe rhan dth epreferabilit yo fth esteril einsec ttechniqu et oth ecurren tchemica l control,becaus eo fit sselectivit yan dlac ko fpollutio nan dresistanc edevelopment , willshif tth epreferenc et oa shortes tpossibl e introductionperiod .A balance dchoic e mayb eabou t4 years .Th eannua lreductio nfacto rshoul db esafel yabov e1 ,an dca nb e chosena t4 .Thi swoul dmea na mass-rearin goutpu to f1. 5x 1 0 fliesannuall yfo r4 years , decliningthereafter .Dependen to nth ecompetitivenes so fth eflies ,th ereleas emetho d andth epercentag eemergenc eo fth epupae ,th enumbe ro fpupa et ob ereare dha st ob e higherb ya facto rbetwee n1. 2an d20 .A sindicate da tth ebotto mo fFig .9 5i twil ltak e intota l4 year sunti la diapausin gpopulatio ni sreduce dt oa leve lo fles stha n10 0 fliespe rha .Afte rtha ttim eprobabl yth emos teconomi cprocedur ei st ocontinu eindefi ­ nitelywit hreleas eo fstandardize d lownumber sb ysimplifie dreleas eprocedures .Th eai m shouldno tb eeradication ,a sthi si sa nunstabl esituatio n (Kojima,1971) ,unles si ti s worldwide. A favourablecircumstanc ei stha tfo rth eonio nfl yth esteril einsec ttechniqu ei s notdisturbe db yth ecurren tchemica lcontro lbecaus ewit hth elatte rth enewl yemerge d larvaear ekilled ,wherea ssteril emale spreven tth eoccurrenc eo fman ysuc hlarvae .A s thesteril emale sresul ti na mor esever esuppressio no fth epopulations ,chemica lcon ­ trolwil lb euseles salread yi nth efirs tyea ro fmas srelease so fsterilize donio n flies.

152 As indicatedi nTable s 37an d38 ,th eparathica ispraying ,whic h isgenerall ydon e oncei nJul yo rAugust ,reduce sth e2n dfligh treproduction .Becaus ei twil lequall y killsteriles ,i tdoe sno t impedeth esteril e insecttechnique .

6.5 SUMMARY

Inth eserie so fexperiment so nsteril einsec ttechniqu edon e in1971-197 4o nth e Schuilenburg,th ewil dpopulatio nwa sseverel yreduced .Reproductio nfactor swer ecalcu ­ latedpe r flight.Whe npre-reproductiv edispersa lwa stake nint oaccount ,a naverag e factoro f5 fo ra yea rwa sfound .Th enumber so fsteril eflie scaugh twer eabou t 10%o f thenumber sexpected ,probabl ydu et oprédatio nb y insectivorousbirds .Th eeg gsteri ­ litywa sgenerall y lowertha nth efl ysterility .Thi sma yhav ebee nth eresul to flo w pupalweight san d longstorag eperiod so fnon-diàpausin gpupae . OnOverflakke eth eexperimen tMi js 1974demonstrate dth eecologica lfeasibilit yo f thesteril e insecttechniqu efo rth eonio nfl yi nnorma lpractice .Th eeffectiv esteri ­ lityo nth eexperimenta lfiel dwa s 88.5%.Th ecompetitivenes so fth esteriles ,a sjudge d fromth erecaptures ,wa swel lbelo w 1,an di sattribute dt oprédation .Eg gsterilit y dataar eno tknown ,bu twhe nequa lmatin gcompetitivenes so fth esterile si sassumed , thissterilit y isexpecte dt ohav ebee nabou t 88% inth e 1stan d 85% inth e2n dflight . Damageo nth etria lfiel d wasonl y 2.4%,o nth econtro lfiel di twa s 17.4%althoug h themajorit yo fth e 2ndfligh tdi dno treproduc eo nth econtro l field itselfbecaus eo f theset-u po fth eexperiment . Thereproductio nfacto rfo ra yea rwa s 13o nth econtro l fieldan d0.2 5 onth etria l field.I fth esteril eflie sha da ful lmatin gcompetitiveness ,th elatte rfacto rwoul d havebee n1 2wit hn osterile sapplied .A s thisfacto rca nb eexpecte dt ohav ebee nac ­ tuallylowe rtha nth ereproductio no nth econtro lfield ,th ematin gcompetitivenes so f thesterile swil lhav ebee ngood . Fromth eexperimen ti twa scalculate dtha twithou tth epre-reproductiv emigration , theannua lreproductio nfacto ro nth etria lfiel dwoul dhav ebee n0.0 5 insteado f0.25 . Whenth esteril e insecttechniqu e isapplie d inpractice ,releas eroute sar eneede d andthes eshoul db e lesstha n 1k mapart .Betwee ntreate dan duntreate dpopulation so f equalsiz ea barrie ro fabou t 1k mca nb econsidere dt ob esufficient .Th ereleas efre ­ quencyo fonc ea wee kworke dwel lwhe npupa ewer ereleased . Fora noptimu meffect ,abou t80 %o fth esterile savailabl ei na yea rshoul db ere ­ leaseddurin gth e 1stflight .A ratioo fsterile srelease dpe ryea rt owil dpopulation s insprin go f20: 1wil lb esufficien tt oachiev ereductio nb ya facto ro fa tleas t4 . Anefficien tprogramme ,wit ha constan tmass-rearin goutpu tan daimin ga ta constan t reductionfacto ro f4 ,require sa mass-rearin gcapacit yo f 1.5x 109 competitivefl y equivalentspe ryear .Thi s isbase do na saf eestimat efo rth ereproductio nfactor ,an d ona sprea do fth eintroductio no fgeneti ccontro love r4 years .

153 7 Concluding remarks

7.1 DISPERSAL

Thedispersa lpatter no fa specie sinhabitin ga discontinuou senvironmen twil lhav e evolvedt obalanc eth eadvantag eo freproducin go na no tye tinhabite dfavourabl esit e withth edisadvantag eo ffailur et ofin da sit efo rreproduction .Wit ha certai nrat eo f dispersal,scarcit yo fsite sfo rreproductio nwil lresul ti nmor emortalit yfro mmigra ­ tionan dthu slowe rpopulatio nlevel s (Huffaker,1965 ;Gadgil ,1971) . Itma yb etha tth e onionfl ydoe sno tbecom ea seriou spes tunti la certai nintensit yo fonio ngrowin gi s reached. Theonio nfl ydispersa l isrelativel yeas yt oanalys ea sth eenvironmen tca nb e clearlysubdivide d intotw olevel so faverag eattractiveness :onio nfield san dothe r places.I nfl yspecie ssuc ha divisio nofte ncanno tb emad es oeasily ,a swhe nanimal s orwil dplan tspecie sar eimportan thosts .Dispersa lo fthes especie sha softe nbee n described inrathe rgenera lterms ,lik e 'initialwanderin gflight ,resultin g inaccumu ­ lationo nattractiv esites' ,an d 'mostflie sremai nnea rth ereleas esit ewherea sfe w reachconsiderabl edistances '(e.g .Muse adomestica :Schoo f& Siverly ,1954 ;Simuliidae : Baldwine tal. ,1975 ;Deli abrassicae :Hawkes ,1972 ;Rhagoleti scerasi :Boiler ,1969 ; Luciliasericata :MacLeo d& Donnelly ,1963 ;Cochliomyi ahominivorax :Hightowe re tal. , 1965). Iti sprobabl etha tth edispersa lo fthes especie si si nprincipl esimila rt otha t ofth eonio nfly .Johnsto n& Hee d (1975)foun dfo rDrosophil anigrospiracul adispersa l ratet ob ehighl ydependen to nth edistance sbetwee nattractiv esites ,an dstat etha t dispersalshoul db edetermine d separatelywithi nan dbetwee nattractiv eareas .A sca n beexpected ,i nthos ecase swher eth e 'attractivesites 'ar emor eo rles sevenl ydis ­ tributedove rth eare aconsidered ,a pur ediffusio nmode lreasonabl ydescribe sth efl y dispersalobserve d (e.g.Lucili acuprina :Mclntyr ee tal. ,1946 ;Drosophil apseudoobscura : Dobzhansky& Wright ,1943) . Theobserve ddegre eo fdispersa lo fth eonio nfl yi sfavourabl et ogeneti ccontrol , asi trequire sa reasonabl ycoars ereleas esit epattern ,an dprovide so nth eothe rhan d areasonabl edegre eo fisolatio nb ydistance .

7.2 PESTSITUATIO N

Inth eNetherland sth eonio nfl yi sa seriou spes to fonions ,an di ti sth eonl yim ­ portant insectpes to fonion si nthi scountry ,s otha ti ti srelativel yeas yt ointroduc e integratedo rbiologica lcontro lmeasures . Apartfro mth esteril einsec ttechnique ,cultura lan dbiologica lcontro lmeasure s

154 haveno t shownmuc hpromis efo r futureapplication .Growin gwinte rwhea tafte ronion s (cf.Fig .19 ) isth eonl ymeasure ,tha tma yb efeasibl et oreduc edamag ean dth epes t density. Increasing thedistanc ebetwee nonio nfield so fsubsequen tyear si sno t pos­ siblefo rth etim ebeing ,a si trequire s lessextensiv e oniongrowin go rstringen t co-operationo rgovernmenta l regulation.Th eus eo fcul lonion s (Section2.3.3 )i sonl y applicableo na smal lscal eo ri nlabour-intensiv e croppingmethod swhic hare'fo rth e presentto oexpensiv e forgenera luse .Positiv e results frombreedin gonion sfo r resis­ tancet oonio nflie s (dePonti ,1976 )ar eno t expectedi nth enea r future.Th enon-spe ­ cificpredator s andparasite sma yno tb eo fmuc hhelp .O nth eothe rhand ,becaus eo fth e relativelyhig hdamag e leveltha t canb etolerated ,densit y dependent factors shouldi n principleb emanipulatabl et okee ppopulation sbelo w therequire d level.Probabl yth e mostpromisin gone ,th epredator-parasit eAleochar abilineata ,ha s beenteste d inmas s releasesi nth eUSS R againstth ecabbag eroo t flyan dth eonio nfly ,bu tfo r thelat ­ terwit h insufficient results (Sumakov,unpubl.) . But,whateve r controlmetho di sapplie di nfutur et oth eonio n fly,mos to fth ein ­ formationpresente dher ewil lb eusefu la sal l controlshoul db ebase do na nunderstan ­ dingo fth epest' sbiology .

7.3 GENETICCONTRO L

Thesteril e insecttechniqu ei ssometime s criticizedbecaus eo fsom efailure si n field testsencountere d afterit ssuccessfu l introduction forth escre wworm .However , therear ealread y someseve nspecie s inwhic h themetho di sapplie d successfully (Lindquiste tal. , 1974).A sindicate db yHell e (1972),th ereason sfo r the failures wereprobabl ydu et ohast ei ndevelopin g thismetho d forpractice :th econdition swhic h apes t shouldsatisf ywer eno tmet ,rearin gan dsterilizatio nmethod swer e inadequate, knowledgeo fth epest' sbiolog ywa s insufficiento rlogisti cproblem si nlarge-scal e applications arose.I nfac t fieldexperiment swer edon e inwhich ,wrongl yo rpremature ­ ly,contro lwa sexpecte d insteado finformatio no nth efeasibilit yo fth emetho dan d thewa yo fapplication .Also ,th ebreakdow no fth escre wwor mcontro li n197 2wa sno t a failureo fth emetho dbu to fit sapplication :ineffectivenes so fth ebiologicall y suboptimally reared fliesan da declin ei nintensit yo fcheckin gfo rinfestation , coincidingwit ha favourabl eenvironmen tfo r thepes t (muchwildlife ,mil dwinter ) aresuppose d causes (R.H.Smith ,1973 ;LaChance ,1974 ;Bus he tal. , 1976). Fortunately thesteril e insecttechniqu ea sapplie do nOverflakke ei n197 4wa ssuc ­ cessfula sa contro lmeasure .Fro mth e fieldwor k done alreadyan dfro mth eSchuilenbur g experimentswhic hha d indicated theeffectivenes so fth emethod ,i twa s cleartha tin ­ sight intoth enumber st ob erelease di npractic e couldb egaine d fromreleasin gsterile s ina nonio ngrowin g area.Bu tn oguarante e couldb egive ntha tth eplanne drelease swoul d indeedresul ti nth edegre eo fcontro lneeded . Iti softe nclaime d thatn oresistanc eca ndevelo pagains t genetic control.However , assoo na sdifference sbetwee nmass-reare d individuals andwil done soccur ,preferentia l matingma ydevelop .Th eestablishmen to fsuc h 'resistance'wil lb ever ydifficul ti nsi ­ tuationswher ewil d localpopulation s regularlybecom e extinct,an dwher esurvivor sar e

1SS constantlymixe dwit hlaboratory-reare d fliesb yth eresidua lfertilit yo fth esterilize d males (here0.6% ,Sectio n3.2) .I nth esteril einsec ttechniqu eprogramm efo rth eonio n fly,ne wstock sar eregularl yestablishe dfro mmateria lcollecte d inth efield ,t oreduc e inbreedingan dt olimi teffect so fselectio npressur e inth elaborator ytha tar ediffe ­ rentfro mth efiel dsituation . Nevertheless,shoul dsom epreferentia lmatin gdevelop ,the ni tca nb eeliminate db y replacingth ewil dpopulatio nwit ha laboratory-reare dstrain ,usin gth eprincipl eo f negativeheterosi swith ,fo rexample , chromosomalrearrangement s (Robinson& Curtis , 1973; Fitz-Earlee tal. , 1975).Becaus eo fth ewor ko nchromosoma lrearrangement s inth e onionfly ,thi smetho dca nb eexpecte d tob eoperationa l indu etime .I tca nb eapplie d withth etyp eo fresistanc econcerne dbecaus eonl ya limite doverfloodin grati oi sre ­ quiredove rloca lan dstil llimite dpopulations . Anotherpossibilit yo fresistanc ei stha tagains tth esterilizin gagent .Resistanc e tochemosterilant sha sbee nfoun dalread yi na nearl ystag e (Hazarde tal. ,196 4;se e alsoProverbs ,196 9fo rlate rcases) . Someresistanc et osterilizatio nb yirradiatio n couldb einduce di nAede saegypt i (Stahler,1971) ,bu ti nsimila rexperiment swit h Triboliumcastaneu mn oresistanc ecoul db einduce dwithi n2 5generation s (Brower,1974) . Moreover,an ysuc hresistanc ecanno tb eextrapolate dt ogeneti ccontro la sirradiatio n isapplie dther eonl yonc eo na certai npopulation . Amor egenera lproble mrelate dt oresistanc ei sth ecreatio no fempt yniches ,whic h areunstabl esituation si nevolution .Thi si sa ninevitabl ecircumstanc ean dwil lemplo y futuregeneration so fresearc hworkers . Geneticcontro l iscriticize da sno tbein gsaf efo rth eenvironment .Thi sapplie s especiallyt ochemosterilants ,whic hfo rtha treaso nar eno tuse di nth ecurren tonio n flyprogramm ealthoug hthe yar eeffectiv e (Luckmanne tal. ,1967) .Ther ei sa nimportan t quantitativedifferenc ebetwee nth eradiatio nuse dfo rsterilizatio nan dth epesticide s useddirectl y inth eenvironment .Fo rpractica lreason sth epossibilit yo fusag eo f otherles scontroversia lsterilizin gagent sfo rth eonio nfly ,a shea to ru.v .treatment s (Riordan,1964 ;Proverbs ,1969) ,hav eno tye tbee ninvestigated . Majorlimitation si nth eapplicatio no fth esteril einsec ttechniqu ear eit sinitia l costsan dit sspecie sspecifity .Also ,i trelie so na reasonabl edegre eo ftechnologica l development,bu twit hscientifi cai dan dusin gaeria lrelease si tca ni nprincipl eb e appliedeverywhere .Th ecost slimi tit sus et omajo rpest si neconomicall yimportan t cropso rt omedicall y importantdiseas evectors .Th ecost swil lexcee dth ereturns ,a s withinsecticides ,i nmos tfoo dcrop si ndevelopin gcountrie s (Ticheler,1975) .Th espe ­ ciesspecifit yi sa necologica ladvantage ,bu tmake sth eeconomica laspec teve nmor eim ­ portant.O nth eothe rhand ,Brade r (1975)indicate dtha tth edevelopmen to fintegrate d controlmethod si sno tespeciall yexpensiv eo rtim econsumin gwhe ncompare dt opesticid e development. InDutc honio ngrowing ,abou t1. 8 x10 °Dfl .i sspen tannuall yo ninsecticide san d theirapplicatio nagains tth eonio nfly ,i na cro pyielding ,du et ofluctuatin gprices , 30-120x 10 6Dfl .annuall y (priceleve l 1974). Itha sbee ncalculate d (deVries ,inter ­ nalrepor tLEI ,th eHague) ,base do na mass-rearin goutpu to f2. 5x 10 9pupa eannuall y duringth eyear so fintroductio no fth emethod ,tha tgeneti ccontro l iseconomicall ycom -

156 petitivewit h thecurren tchemica lcontrol .Sinc ethen ,mas s rearingha sbee n improved (Noorlander,i nprep.) , andth eintroductio nstrategie swer erefine d (Section 6.4). So theeconomi cprospect s aregood .However ,a si ti sth efirs tcontro lmetho d inth e Netherlands ofthi styp et ob eapplie dove r larger areas,i tstil lmeet sobjection s from fundproviders ,a sca nb e expected inan yne wdevelopmen t (Helle, 1972).

157 Summary

Theai mo fth estud ywa st oprovid edat ao nth eecolog yo fth eonio nfl ywhic hi sne ­ cessaryfo rapplicatio no fgeneti ccontrol ,wit ha nemphasi so ndispersal ,an dt oinves ­ tigateth efeasibilit yo fgeneti ccontro lunde rnorma lfiel dconditions . Literaturedat ao nth eonio nfly' sbiolog yar egiven ,alon gwit hsom egenera ldat ao n oniongrowin gan donio nfl ycontro li nth eNetherlands . Mostexperiment swer edon eo nOverflakkee,a nonio ngrowin gare ai nth eS Wo fth e Netherlands.Th eprevailin gweathe rcoul db econsidere da srepresentative .Th eflie suse d inrelease swer eobtaine dfro ma laborator ymass-rearin gan dgenerall ywer esterilized . Thisdi dno timped ethei rcompetitiveness . Theflie swer emarke da temergenc ewit hdaylight-fluorescen tdye-powders .Othe rmar ­ kingpossibilitie swer eals oconsidered .Generall ypupa ewer ereleased ,burie d inth e soil.Thi smetho d increasedprédatio no nnewl yemerge dflies .Recapture swer emad eb y flightinterceptio ntraps .Wher edamag ewa snoted ,soi lsample swer etake nfo restimatin g pupalpopulations .Th eeffec to fth esampl ecor ediamete rwa sanalysed .Othe rfiel dre ­ searchmethod sar etreate dbriefly . Limiteddat ao nth eonio nfly' snich ear egiven .Th epossibilitie s forth epredictio n ofpupa lemergenc ei nsprin gwer eanalysed .Dat aar epresente do nth eincidenc eo fdia ­ pausean do nth eoccurrenc eo fflights .Alliu mvineal edi dno tsustai na nonio nfl ypo ­ pulation.Deli aplatur awa sa secondar ypes ta scoul db esee nfro mit ssever ereductio n byth eselectiv eeliminatio no fth eonio nfly .Th einfectio nrat eo fadul tonio nflie sb y Entomophthorawa sestimated . Thedistributio no fdamag ean dpupa econforme dt oth enegativ ebinomial .Fro mthi s distribution,fro mTaylor' spowe rla wan dfro mth erelatio no fth emea ncrowdin gt oth e mean,precisio nwa scalculated .Th evalue sobtained ,an dth econfidenc e limitscalcula ­ tedfro mthese ,ar eno treliabl efo rth ecurren t lowpopulatio nlevel san dhig hdegree s ofaggregation ,an dfo rth elo wnumber so fsample sneede d inpractice .Mos tdensitie so f diapausingpupa ei nchemicall ytreate dfield sar ebetwee n1 00 0an d2 000 0pe rha . Thelife-span so fth eflie sconforme dt onorma ldistributions .Fro mthes edata ,com ­ binedwit hth efrequencie so fovipositio nperiods ,a sestimate dfro mth efrequencie so f differentphase si nth egonadotrophi ccycl eversu sag eo fth efemales ,fecunditie swer e calculateda t3 9an dles stha n18. 5egg spe rfemal efo rth etw oflights ,respectively . Thecorrespondin g reproductionfactors ,estimate dfro mfiel dtrial swit hsterilize din ­ sects,wer e7 an d3 . Dispersalwa sfoun dt ob edependen to ntemperature ,bu ti ngenera lindependen to f winddirection .Dispersa lwa sdescribe db ya diffusio nprocess .Th ediffusio ncoefficien t hasbee nestimate di ndifferen tways .Th ebes tresult swer eobtaine dfro msimulatio no f flydiffusio nwit hheterogeneit y intim ean dspace .Thi syielde ddiffusio ncoefficient s

158 2 2 ofabou t 200 0m /day inonio nfield san d 1400 0m /day outside onionfields . Therelatio no fth e logarithmo fth etota lnumber srecapture dversu sdistanc ewa s found tob e about linear,bot h from fieldobservation s and froma simpl emode l inwhic h diffusion andnormall y distributed life-spanswer e assumed.Migratio nwa sreduce d during periods ofmatin g andoviposition .A t theag eo fmatin gnearl yhal fo fth emale sha d emi­ gratedfro mth ereleas e field. Immigrationo ffemale sbetwee nmatin g andovipositio nwa s rare.Th e impacto fsurroundin gwil dpopulation s ona singl efiel d treatedb y sterilema ­ les isquantified . Fromfiel dtrial so nsteril e insect technique,don enea rWageningen, th e reproduction ofwil d flieswa s estimated atabou t 5fo r ayear .Ther ewer e indications ofsever epré ­ dationo nnewl y emerged sterile flies,an d ofa reduce dmatin g competitiveness. Thesteril e insectapplicatio nunde rnorma lpractic ecircumstance s onOverflakke ei s described indetail .Th ereproductio n factoro nth e checkplo twa s 13fo ra year ,an d was reduced onth etria l field to0.2 S bya neffectiv e sterility of 88.5$.Predatiq n on thenewl yemerged 'sterile swa ssevere ,bu t themating competitiveness ofth esteril e fliesseeme dgood .A sa control thesterile swer esuccessful . Forpractica l applicationo fsterilize donio n flies,releas eroute sshoul db e less than 1k mapart ,an dbarrier sbetwee n equalpopulation s shouldb e about 1k mwide .Pe r year,2 0time s thewil ddiapausin gpopulatio nshoul db ereleased , 80%durin g the 1st flight.A nefficien t introduction ofth e sterile insect technique forth eonio nfl y in q theNetherland swil l require 1.5 x 10 competitive flyequivalent s for fouryears ,an d lessthereafter . Somecriticis m against genetic control isconsidered ,an dpossibilitie s foronio n flycontro l inth eNetherland s are indicated.

159 Samenvatting

Doelva nhe tonderzoe kwa she tverzamele nva ngegeven sove rd eecologi eva nd euie - vlieg,Deli aantiqu a (Meig.).te nbehoev eva nd eontwikkelin gva nd ebestrijdin gme tge ­ steriliseerdemannetjes ,e nteven so mdez emethod eonde rpraktijkomstandighede nt etes ­ ten.D enadru kla go ponderzoe knaa rd emigrati eva nd evliegen . Deuievlie goverwinter tal spo pi ndiapauz ee nheef tmeesta léé nvolledig ee néé non ­ volledigevluch tpe rjaar .D eeiere nWorde ngeleg do puien .D ebo lword tgegete ndoo rd e larvene ngaa tda nrotte nwaardoo ree noogs tgehee lverlore nka ngaan .D egangbar ebe ­ strijding ischemisc he nd euievlie gheef ta ltege nverschillend emiddele nresistenti e ontwikkeld. Hetveldwer kwer dverrich ti nd ejare n1970-197 4o pOverflakkee ,waa ro p5-15° êva n hetlan duie ngeteel dworden .D eweersomstandighede nware nnormaal .D evliege ndi ege ­ bruiktwerde nvoo r 'loslaatproeven'werde nmassaa lgekweek to phe t laboratorium.Desge ­ wenstwerde nz egesteriliseer ddoo rbestraling .Hierdoo rwer d99.4 %sterie lva nd eeiere n gelegddoo ronbehandeld evrouwtje sn aparin gme tgesteriliseerd emannetjes . Devliege nwerde ngemerk tdoo rz ebi jhe tontpoppe nee nlaagj edaglicht-fluoresceren ­ dekleurpoede rt elate npasseren .Gesteriliseerd evrouwtje skunne nworde nherken daa nd e nietverde rontwikkeld eovarien .Meesta lwerde nd evliege ni nhe tvel dgebrach tdoo rd e poppeni nee nber mva nhe tuievel di nt egraven . Voorhe tvange nva nvliege nwerde ngaze nvangscherme ngebruikt .Me tee nloksto fko n devangs thieri nmee rda nverdubbel dworden .D ebest eplaat svoo rvangscherme ni saa nbe ­ schutterande nva nd euienvelden ,me td eopenin gva nhe tvel daf .D egroott ede rvangs t wasster kafhankelij kva nd etemperatuur ;d ewindrichtin gwa sva nweini ginvloed . Eengrondmonste rva n2 0c mdoorsnee ,rondo mee naangetast eui ,beva tvrijwe lall e poppendi eal slar fui tdi eu igekrope nzij no mzic ht everpoppen .Ee nmonste rva nS c m doorsneebeva td ehelf to fminde rva ndi epoppen ,afhankelij kva nd emat eva nschade . Bijhe twaarneme nva nuievliege ni nhe tvel dblee khu nvliegrichtin gonafhankelij k tezij nva nd erichtin gwaari nd ewaarneme rzic hbevond . Hetvoorspelle nva nhe tbegi nva nd eeerst evluch t leekmogelijk ,zowe lo pgron dva n bodemtemperaturenal so pgron dva nfenologisch eparalelle n (b.v.uitlope nva nd ezomer - eik).Laboratoriumgegeven sove rd einducti eva ndiapauz edoo rmidde lva nkort edaglengt e enlag etemperatuu rkome noveree nme tveldwaarneminge nwannee rword taangenome nda td eef ­ fectievedaglengt e1- 2uu rkorte ri sda nd etij dtusse nzonsopgan ge nzonsondergang .Va n deeerst evluch tgaa tgemiddel d 20% indiapauze ,va nd etweed evluch t 8S%. Debonevlieg ,Deli aplatura ,blee ki nuie nonde rd ehuidig epraktijkomstandighede n eensecundair eplaa gt ezijn .D eparasitoide nAleochar abilineata ,Aphaeret aminut ae n Phygadeuonsp .werde ni nklein epercentage sui tuievliegpoppe ngekweekt .s'Zomer sworde n vliegenaangetas tdoo rd eschimme lEntomophthor asp .I n197 4wer dpe rda g 6%va nd ejong e

160 vliegenhierdoo r geïnfecteerd,voo rouder evliege n liepdi tteru gto t 3%. Deschad eaa nuie nword tvoora lveroorzaak t doord e larvenva nd eeerst egenerati e in juni.D everdelinge nove rd eproefstroken ,zowe lva n schadeal sva npoppen ,konde nrede ­ lijkworde nbeschreve n alsnegatie fbinomial everdelinge nme td eparamete r k afhankelijk vanhe tgemiddelde .He t aantalmonster sda tnodi g iso mee nzeker egraa dva nnauwkeurig ­ heid tekrijge n isbereken d als functieva ndi tgemiddelde .Hierbi j isd evarianti ege ­ schato pverschillend emanieren :me td enegatie fbinomial everdeling ,me tTaylor' s 'po­ wer law'e nme the tverban d tussend e 'meancrowding 'e nhe tgemiddelde .Di t zijn allen benaderingendi evoo rd ebeperkt eaantalle nmonster s end e lagegemiddelde ndi e ind e praktijkverwach tkunne nworden ,vri jonbetrouwbar e betrouwbaarheidsintervallen opleveren. Metverschillend e terugvangproevenme t gemerktevliege nwerde npopulatie s geschat.Ge ­ ziend eschad eo ppraktijkvelde nkunne nd epopulatie s overwinterendepoppe ndaa r geschat wordeno p 1000à 2000 0pe rha .Rekenin ghoudend eme tmigrati ee nme td egering ekan so p hetvange nva njong evliege n zijnui td eterugvangste n overlevingscurvenbepaald .D e vrouwtjes leefdengemiddel dbijn aanderhal fmaa l zolangal sd emannetjes ,e nwe l gemid­ deld 18dage n ind eeerst evluch t (mei-juni)e n9 dage n ind etweed evluch t (juli-augustus) enmaximaa l éénà anderhalv emaand . Devrouwtje spare nvana fongevee ree nwee kn auitkomst .Ui td everdelin gva nhe tper ­ centage steriliteit vaneieren ,geleg ddoo rwild evrouwtje s inveldproeve nme tgesterili ­ seerdeuievliegen ,ko ngescha tworde nda t zeelk e 5à 6 dage nparen . Ind ecyclisch e ont­ wikkelingva nd eovarie nkunne nverschillend e fasenworde nonderscheiden .Ui the tver ­ loopva nd e frequentiesva ndez e fasen ind etij d isgevonde nda td eeilegperiode n één totanderhalv ewee kuitee n liggen.Gecombineer dme td e overlevingvolg thieruit ,da t in deeerst evluch t eenvrouwtj e gemiddeld 39eiere n legt,e nminde r danhal f zovee l ind e tweedevlucht . Uitd egegeven sva nd eveldproeve nme td esteriele-insektenmethod eko nd e reproduktie (vanpo p totpop )worde ngeschat .O pOverflakke ewerde nreproduktiefactore ngevonde nva n 7 (eerstevlucht )e n3 (tweedevlucht) .O p zwaregron dbi jWageninge n lagendez e faktoren half zohoog. Denett overplaatsingssnelhei d vand evliege nwa swe lafhankelij k vand etemperatuur , maar slechts ingering emat eva nd ewindrichting .Buite nuienvelde n lagdez e snelheid 2,5maa l zohoo gal sbinne nuienvelden .He twate rron dOverflakke e konworde nopgeva t als eenspiegelend ebarrièr evoo rd evliegen .He t rondvliegenva nd evliege nwer d beschouwd alsee ndiffusieproces .D ediffusiecoëfficiën t isonde rander egescha tui td e frequenties end eafstande nva n inhe tvel dwaargenome nvluchten ,e nui td e toenameva nd eafstan d vanhe t loslaatpuntwaarbinne nd ehelf tva nd epopulati e zichbevond .Nauwkeurige rschat ­ tingenware nmogelij kme tee nsimulatiemodel ,waari nrekenin gko nworde ngehoude nme ton ­ regelmatigheden ind eruimt e (uienvelden)e n ind e tijd (uitkomstcurve,weersomstandighe - 2 ? den). Erwerde ndiffusiecoëfficiënte n gevondenva n 1400 0m /dag,verminder d tot 200 0 mV dag inuienvelden . De logaritmeva nd e totale terugvangsten,uitgeze t tegend eafstan dvana fhe t loslaat­ punt,ga fbi jbenaderin g rechtlijnigeverbanden .Di twer d ookgevonde nuitgaand eva nee n normaleverdelin gva nd e levensdurene nee ndiffusi eva nd evliege n inee nhomogee nmi ­ lieu.Onde rander eee nonregelmatig everdelin gva nuievelde n geeftafwijkinge nva ndi t 161 verband. Uitd everdelin gva nd evliege nove rverschillend eplaatsen ,uitgeze ttege nhu nleef ­ tijd,wer dgevonde nda td evrouwtje s zichvoora lconcentrere no puienvelde ngedurend epe ­ riodenva npare no feiere nleggen .Ui td eleeftijdsverdelin gva nvliege no phe ttijdsti p datz eva nelder see nuievel dbinne nkwamen ,volgd eda tongevee r70 %va ndez eimmigrante n aankwamvoorda tz egepaar dhadden .Wannee rz epare nheef tinmiddel s50 %va nd eda nno g levendemannetje she tuienvel dwaari nz euitkwame no fwerde nlosgelate nverlaten .Ruwwe g kanhe taanta lvóó rparin ggeïmmigreerd emannetje so pee nuienvel dgevonde nworde ndoo r eenkwar tva nhe taanta lelder suitgekome nmannetje st edele ndoo ree nfacto r1 0vóó r elke0, 8k mafstan dva nwaa rz euitkwamen .He taanta lvrouwtje sda timmigreer ttusse n paringe neile gi s1/ 5va ndi taanta lmannetjes . Uitd eseri eveldproeve nbi jWageninge nme td esteriele-insektenmethod ete rbestrij ­ dingva nd euievlie gblee kda td emethod ei nhe tvel daa nd everwachtinge nvoldeed .D e veldproefo pOverflakke ei n197 4toond ed ebruikbaarhei d aanva ndez emethod eonde rprak ­ tijkomstandigheden.D eschad eo phe tproefvel dwa s2,4 %e no phe tonbehandeld econtrole - veld 17,41,ondank she tfei tda tdaa rd etweed evluch tte ngevolg eva nd eproefopze tgro ­ tendeelsuitgeschakel dwerd .D eeconomisch eschadedrempe llig tomtren t 10%.D ereproduk - tiefactoro phe tcontrolevel dwa s 13o pjaarbasis ,o phe tproefvel dbeperk tto t0,2 5te n gevolgeva nee neffectiev esterilitei tva n88,5'» . Afgezienva npredati edoo rvogel ste n gevolgeva nd etoegepast e loslaatmethode,ware nd ei nhe tvel dgebracht esteriel evlie ­ gencompetitie fme td ewilde . Bijpraktijktoepassin gva nd esteriele-insektenmethod ete rbestrijdin gva nd euie ­ vlieg zijnloslaatroute snodi go pminde rda n1 k mafstan dva nelkaar .Ee nbufferzon eva n ongeveer1 k mbreedt eo mhe tme tsteriel evliege nbehandeld egebie dza li nhe talgemee n voldoende zijn.Ee noptimaa leffec tword tverkrege nwannee r 80%va nd ei nee njaa rbe ­ schikbaresteriel evliege ni nd eeerst evluch tword tlosgelaten .Me tee nverhoudin gva n steriele (perjaar )tege nfertiel evliege n (ind eeerst evlucht )va n20: 1ka nd epopula ­ tiei néé njaa rto tee nkwar to fminde rworde nteruggebracht .Ee nefficiën tprogramm a waarbijd emethod everdeel dove r4 jaa ri nNederlan dword tgeïntroduceerd ,vereis tee n produktieva n1. 5x 1 0 vliegenpe rjaar . Devliege nvertone nee nverspreidingsgedra gda tgeschik ti svoo rhe ttoepasse nva nd e steriele-insektenmethode:he tmaak tee nredelij kgro floslaatpatroo ne nee neenvoudig e isolatiedoo rafstan dmogelijk .Ander eniet-chemisch ebestrijdingsmethode nvoo rd euie ­ vliegtone nno gnie tvee lperspectief .D esteriele-insektenmethod eheef the tvoordee lda t resistentiee nverstorin gva nhe tmilie uhierbi jgee nproblee mvormen .Beperkinge nzij n echterd eafhankelijkhei dva nee nbehoorlijk etechnologisch eontwikkeling ,d esoortspe - cificiteit,d ebeginkosten ,e no phe togenbli koo kno gd eprobleme nva nhe tintroducere n vanee nnieuw emethode .

162 Acknowledgments

Although the fieldwork wa s relatively isolatedb ydistance ,th epresen t studyha s beenpar tan dparce lo fth ewor ko fth eonio nfl ytea mo nth esteril e insecttechnique . I gratefully acknowledgeth eco-operativ e support of,an dth e invaluable discussions with,th etea mmembers ,especiall yWinol dNoordink ,Ja nNoorlander ,Ja nTheunisse nan d JanTicheler ,an dal l thosewh o sharedi nth eprogramme :Jimm y Kelderman,Elian eLemmers , AafkeTigges-Gootjes ,Soll yVoorhoeve ,th etranslocatio n sectiono fth eonio nfl ytea m and allth emor e temporary assistantsan d students. Inth efiel dwork th e inexhaustible enthusiasmo fThij sde nBreeje ,Jo bva nde r Burg andYvonn e Schwenckeha sbee na grea t support,an dI regre tth elimitednes so fth epe ­ riods they could co-operate.Als ovalue dwa s theassistanc eo fSerek eMeres ,Maria n Pol- hout andFre dSoerodimedjo .I appreciate d thecontact swit h Gert-JanButh ,Joha nHube r andJa nRoest ,wh oinvestigate d aspectso fth e fieldwork a sa par to fthei r study. Royva nde rVeer ,wh opatientl y guidedm ealon g thepitfall so fstatistics , and MartinFrissel ,wh otranslate dm yvagu e ideaso nfl ydiffusio n intoconcret eCSMP ,ha d an important sharei nth edigestio no fth e information collectedi nth e field,althoug h they areno t responsible forwha tI wrot edown . My sincere thanks aredu et oal l thepeopl ean dorganization s thatmad eth eprojec t possible.I ti swit hgratitud e thatI mentio nProf .D rD.J . Kuenen,wh ofirs t contacted me aboutth e job,an dlate raccepte d theburde no fth e scientific supervisiono fm ythe ­ sis.Th efund swer ekindl ymad e availableb yth eCentra lOrganisatio n forApplie d Scien­ tific Researchi nth eNetherland sTNO .Th elat eD rH.J .d eFluite ran dProf .Dr .J .d e Wilde actuallymad ei tpossibl e form et ostar tth ework i nth eDepartmen to fEntomolog y of IPO,unde rth esupervisio no fth eAgricultura l Universityo fWageningen .I a mgrate ­ fultha tth eentomologist s and,unde r IrG.S .Roosje ,th eothe r IPO-workers acceptedm e asa collègue ,althoug hI wa sonl ya nirregula rwinter-visitor .Th epersone lo fth e SNUiF,unde rM rJ.L . Koert,provide dman yhighl yvalue d facilitiesi nth e field. Determinations wereprovide db yD rC .va nAchterber g (Braconidae),M rW.C .Boelen s (Staphylinidae),D rW.J .Kabo s (Diptera)an dM rJ . Quinlan (Cynipidae). Earlierdraft so fth etex twer e readb yProf .D rD.J . Kuenen,Prof .D rJ .d eWilde , DrI rJ.H.G .Ticheler ,M rR .Aalpo l andMr sE.M . Brouns-Murray,an dpart so fi tb y IrR.F .va nde rVeer ,D rM.J .Frissel ,Mr sJ.M . Loosjes-Koolhaasan dD rR .Rabbinge . Their critical commentsha da grea t sharei nmakin gcleare rwha tI trie dt oreport . MrsE.J . Lansink-Zengerink kindly typed thefina ldraft ,M rC.A .Koeda mmad eth e photographs,an dM rC.F .Scheffe l andM rM .Janse ndre wth egraphs . FinallyI wis ht othan k thefarmer so nOverflakkee ,wh ower e always readyt ole tm e experimento nthei rfields ,especiall y thedirecto ran dth emanage ro fth e former 'N.V.d ePallandtpolder' ,M rA.H .Mij s andM rJ . vand eNieuwendijk .I hop etha t their hospitalitywil lultimatel y contributet ohealthie r farming.

163 References

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176 Appendix

TITLE MIGRATIONONIONFL Y * LOOSJES-FRISSELMA Y197 6VERSIO N5 GRI D 11* 2 6 INITIAL NOSORT PARAMETERD X=5 0 FUNCTIONEMERG T- 0.-1. .0.001-0. .30. .0 . *EMERGENC EA SF(TIME ) FIXEDN C STORAGENC(286 ) STORAGESOURCE(286 ) * NUMBERO FEMERGIN GFLIE SPE RGRI DCEL LPE RFLIGH T TABLES0URCE(l-286 )- 193*0. ,100000. .92*0 . STORAGEPREF(286 ) * PREFERENCEFO RCELL S FIXEDN DO2 N - 1.28 6 2 PREF(N)= 1 . *PREFERENC EFÛLLOUIN GFIELD SREDEFINE D PARAMP R= 0. 1 PREFU06)• = PR PREFU94)- P R PREF(205)- P R PARAMD D= ?000 . * DIFFUSIONCOEFFICIENT .M** 2PE RDA Y FUNCTIONDECAY T= 0. .0. .18. .0 . * DECAY= MORTALIT YFRACTIO NPE RDAY .A F(TIME ) STORAGETEMP(18 ) TABLETEMPU-18 )= 18*20 . FUNCTIONDISPF T- 0..1. ,18. .1 . *DISPERSIO NFACTO RACCOUNT SFO RVARIATIO N INSPEE DDU ET OTEMPARTUR EVARIATION S STORAGE0UTT(5 ) FIXEDJ J- 1 * OUTT*INDICATORFO ROUTPU TI NMA P TABLEOUTTU-5 )- 3.5 .4.5 .5.5 .6.5 .7 . C- INTGRLCa. .DC.286 ) TELLER -0 PARAMSKI P= -1. DYNAMIC NOSORT TELLER-TELLER+1. FIXEDJ J JJ= TIM E+ 1.0000 1 DISPF= AFGEN(DISPFT .TEMP(JJ) ) D- DD*DISP F * CALCULATIONO FEMERGENC E * EMERGENCEONL YONC EPE RDA Y EMERG- 1./DELT*AFGEN(EMERGT ,TIME ) STORAGEEMER(286 ) DECAY= AFGEN(DECAYT .TIME ) SEMERG- 0 . * DO 10N « 1.28 6 EMER(N)- EMERG*SOURCE(N ) 10 SEMERG =SEMERG+EMER(N ) _ „_ „„,.,. TEMERG- INTGRL(0..(SEMERG-DECAY*TEMERG) ) *TEMER G> POPULATIO NALIV E

177 CALCULATION OFDIFFUSIO N (SYMBOLIN ) PRRAM UATER =0 . FIXED H,V ,H V * HORIZONTAL IN (POSITIVE LEFT-TO-RIGHT) DO 9H = 1,1 2 DO 9V =1,2 7 DO 9 HV= 1.2 9 IN(H,V,HV) =0 . •'<- LEFT SIDE DO 11 V =1,2 6 IN(1,V,2 )=(D*(OC (1,V)*QPPEF(1 ,V)-QC(2,V)*QPREF(2,V:0.-'DX**2 ). . . *IUSU I(D C( 1 ,V) ,0. ,1. )* ( Q C( 1 .V )«QPRE F( 1 ,V ) ),'(Q C(2 ,V )*QPRE F (2.V)+0.00001) * INSU TOPREVEN T NEGATIVE QCVALUE S 11 IN(1,V,2) =FCHSLI(IN(1.V.2) , IN( 1 ,V ,2) ,O. .0 .) * FCNSLIT OPREVEN T ACCIDENTAL IMMIGRATION * CENTRAL DO 12H = 2,1 1 DO 12V =1,2 6 12 INCH.V,2) = (D*CQC((H-D.V)*QPREF((H-l).V)-OC(H,V)*aPREF ... (H,V )).-'DX**2 ) * RIGHT SIDE DO 13V =1,2 6 IN(12 ,V,2 )= (D*(QC (10 ,V)*QPREF (10 ,V)-QC (1 1,V)*QPREF C1 1,V ))•• ' DX**2)*INSUCQCC1 1 ,V ),0 ., 1 . )*(QC (1 1 ,V)*QPREF C1 1,V )),'(ÜC (10 ,V ) *QPREF(10,V)+0.00001) IFCUHTER .EQ. !.)IN(12,V,2 ) =0 . IF (IJATER .EQ. -1)IN(12,V,2 ) = (D*(QC(11 .V )*QPREF <11 .V ) -0.) .-•'.. , DX**2) 13 INC12,V,2) = FCNSt.J(IN(12,V,2),0.-0.,IN(12,V,2) ) * VERTICAL IN (POSITIVE TOP-TO-BOTTOM) * TOPSID E DO 14H = 1.11 INCH,1,1)=(D*(QC(H.1)*QPREF(H,1)-QC(H,2)*QPREF(H,2))/ DX**2)*INSU(QCCH,1 ),0. ,1.)*(QCCH ,1)*QPREF(H .1 ) >,-'CQ CCH.2 ) *QPREF(H,2)+0.00001) 14 _ IN(H,1,1) =FCNSLJ(IN(H,1 ,1) ,INCH ,1,1 ) ,Q..0.) >:CENTRA L DO 15V = 2.26 DO 15H = 1.11 15 IN(H,V,1 ) = (I)*(QC:H,CV-1))*QPREFCH .(V-D)-QC(H.V) * QPREF(H,V))/DX*t!2) * BOTTOM SIDE DO 16H = 1,11 INCH,27,l)=(D*(QC(H,25)«3PREFCH,25:'-QC(H,26):+QPREF(H,2b)) / DX**2)*IMSUCQCCH,26),0. .1 .) *(Q CCH,26)*QPRE F(H ,26 )) ,-'CÜ CCH ,25 ) *QPREF(H,25)+0.00001) 16 INCH,27,1) = FCNSI.J(IN(H,27.D.0.,0. .IN(H.27 ,1) ) •-• DEATH RATE DO 31 H = 1,11 DO 31V = 1.26 31 DRCH.V) = DECAY*QC(H,V) * CALCULATION TOTAL CHANGES * ======„======•D O3 2H = 1,11 DO 32V = 1,26 N =H + CV-1)*11 32 DCCN) = INCH.V.1)+INCH,V,2)-INCH+1,V,2)-INCH,V+l,1) -DRCH,V) + EMERCN) * PREPARE OUTPUT ;): ======IF(KEEIF (TIMP E.NE .GE. .1 )COLITTCJ)-0 GO TO 301 . 0001)) GO TO 300 GU Til.'T U 30» CONTINUE IFCCFL0ATCJ).'2.-J/2 ) .G T 8 ) URITE 6,306) URITEC6,302) LIRITEC6.303 )TIM E . TELLER TEMERG L.JRITEC6,302) DO 333 N = 1.2B6 333 NCCN) - CCN)+0.5 URITE(fa,305)NC 306 FORMATC1H1) 302 FORMATC1H ) 305 FDRMATCllC.18 ) ) 303 F0RMATC29H FLIES PERGRI D CELL ATTIM E F6.2,9X,6HTELLERF7.0, S 5X,1SHTOTAL POPULATION F7.0) URITE(fa,302) J = J+l 301 CONTINUE

178 METHOD RECT TIMER FINTI M =18.,OUTDE L = 1.,DEL T • 0.125 TERMINAL h'OSORT IFCSKIP .LT. 0.) GO TO 500 * MAPS OF INPUTCONDITION S IFUANTE D 500 CONTINUE END * OTHER PARAMETER VALUES IFUANTED . FOR SUBSEQUENT RUNS END STOP

179