Entomopathogenicfung i against whiteflies Tritrophic Interactions betweenAschersonia species, Trialeurodes vaporariorum and Bemisia argentifolii, and glasshouse crops EllisT.M .Meeke s Promoter: Prof.Dr . J.C.va n Lenteren Hoogleraar in deEntomologi e Wageningen Universiteit Copromotor: Dr.Ir .J.J .Franse n Senior onderzoeker Entomologie Proefstation voorBloemisteri j enGlasgroente s Aalsmeer Samenstellingpromotiecommissie : Dr.J.K .Pel l (IACRRothamsted , UK) Dr. W.Gam s (Centraal Bureau Schimmelcultures, NL) Prof.Dr .J.M . Vlak (Wageningen Universiteit) Prof.Dr .Jr .A.H.C . vanBrugge n (Wageningen Universiteit) . 1 I / E.T.M. Meekes Entomopathogenic fungi against whiteflies Tritrophic interactions betweenAschersonia species, Trialeurodes vaporariorum andBemisia argentifolii, and glasshouse crops Proefschrift terverkrijgin g van degraa dva n doctor opgeza gva nd erecto r magnificus van deWageninge n Universiteit Prof.Dr .Ir .L . Speelman inhe t openbaar te verdedigen opwoensda g 27jun i 2001 desnamiddag st e 13.30i n de Aula 0 D'-? / On _'•v J r\j Meekes,E.T.M E.T.M.(2001) (2001). Entomopathogenicfung i againstwhitefly : tritrophicinteraction sbetwee nAschersonia species , Trialeurodes vaporariorum andBemisia argentifolii, an d glasshouse crops ISBN: 90-5808-443-4 Contents Chapter 1 General Introduction 1 Chapter2 Virulence ofAschersonia spp .agains t whiteflies 19 Bemisia argentifoliian d Trialeurodes vaporariorum Chapter 3 Dosean dtim edependen t mortality of thewhiteflie s 35 Bemisiaargentifolii an d Trialeurodes vaporariorum byAschersonia spp. Chapter4 Germination andinfectio n behaviour ofAschersonia spp .o n 49 Bemisiaargentifolii an d Trialeurodes vaporariorum on poinsettia Chapter 5 Persistence of thefunga l whitefly pathogenAschersonia aleyrodis, 69 onthre edifferen t plant species Chapter 6 Roleo fphyllospher e climate ondifferen t hostplant s inth e 81 interaction between entomopathogenic fungi andth e two pest species Trialeurodes vaporariorum andAphis gossypii Chapter 7 Relative humidity andhost-plan t speciesinfluenc e 99 mycosiso f whitefly, Trialeurodesvaporariorum, byAschersonia aleyrodis,A. placenta and Verticillium lecanii Chapter 8 Effect of gerbera cultivar onth e efficacy of entomopathogenic 113 fungi against Trialeurodes vaporariorum Chapter 9 General Discussion 125 References 145 Summary 163 Samenvatting 167 Nawoord 177 Listo f publications 179 CurriculumVitae 181 1 General introduction The research discussed in this thesis aimed at evaluating entomopathogenic fungi for biological control of whiteflies. In this chapter I first summarize whitefly pests, damage, biology and its control. Secondly, the background concerning entomopathogenic fungi and whitefly will be described. Finally, the aim of the project and the outline of the thesis is presented. Whitefly pestsan d damage About 1200 whitefly species have been described, but only few of them are considered as pests.Amon gth elatte rar eth egreenhous ewhitefly , Trialeurodes vaporariorum (Westwood) and, more recently, the silverleaf whitefly, Bemisiaargentifolii (Bellows & Perring) (syn. B. tabaci biotype B).B. argentifoliii spar t of theBemisia tabaci specie s complex, of which manybiotype s are described. The discussion whether B. argentifoliii s a separate species or not is still ongoing (e.g. De Barro& Hart , 2000;Gerling , 2000;Marti n etal., 2000) .I n this thesisth enam e B. argentifoliii s used. Thegreenhous ewhitefl y isa ke ypes to fman ygreenhous evegetable san dornamentals , whereasth e silverleaf whitefly hasbee n aseriou spes ti nfiel d cropsworldwid e since the mid seventies (Byrne etal., 1990a).Bot h species are highlypolyphagous , occur world wide and lead to serious economic losses (Gerling, 1990). The damage to crops is manifold: 1) Direct damage to plant foliage is caused by feeding ofwhiteflies . Adultan dimmatur ewhiteflie s arephloe mfeeders , usingthei rpiercing - sucking mouthparts to introduce digestive juices and to remove chlorophyll and starch. Infested plants may drop leaves prematurely and have reduced plant growth and vigour (Oetting &Buntin , 1996).2 )A by-produc to f feeding isth e excretion ofexces ssugar s in the form of honeydew. It accumulates on the upper surfaces of plant parts where it serves as a substrate for sooty moulds (e.g.Capnodium spp.) , thus reducing leaf photosynthesis. More important isth eeconomi cdamag edu et oresidue s of stickyhoneyde w on fruits, ornamentals andcotto nlin t(Byrn e& Bellows , 1991;Schuste ret al, 1996).Sometime s themer e presence of only a few whitefly nymphs and adults can cause problems. 3) The marketability of ornamental plants depends on aesthetic features. The presence of whitefly adults and honeydew will not escape the notice of consumers. For export of plants orplan t products a zero-tolerancei svalid ,especiall ywhe nth einsec ti sa quarantin epes ti nth eimportin gcountry . Infested plants destined for the international market risk rejection. Interception can lead to destruction orre-expor t of anentir e shipment (Fransen, 1993;Schuste r etal., 1996).4) Both Chapter 1 whitefly species servea svector so f severaleconomicall y important viral plant pathogens (for overview seee.g. Brown etal., 1996 ;Duffus , 1996).Hence ,onl ya fe w adults carryinga viru s can cause serious damage to acrop . Whitefly biology Adultwhiteflie s arewinged , free-flying insects.Th efemale s laythei r eggspreferabl y onth e abaxialsid eo fyoun ghost-plan tleave s(va nLentere n& Noldus , 1990).Thei regg sar einserte d intoth elea f tissueb ymean s of apedice l (Paulson &Beardsley , 1985).Throug h thispedice l watero f theplan tca nb eabsorbe d toovercom e desiccation of theegg s (Byrneet al., 1990b). Thehatchin gcrawler s (first-instar nymphs)usuall y settlei n theproximit yo f the oviposition site following a search for a suitable location and start feeding. Sometimes the crawler can coverlarg edistances , whichha sbee n attributed tohost-plan t suitability (van de Merendonk &va nLenteren , 1978). Onrar eoccasion scrawler scoul deve nmov ebetwee nplant s(Summer s etal, 1996).A ssoo n asa suitabl elocatio n isfoun d theybecom e sessileb yfixin g themselves to the leaf with their mouthparts. All four nymphal instars, following the settling of the crawler, will spend their life at the same location, reinserting their mouthparts into the leaf tissuefollowin g eachmolt .Th enympha lstage sca nb edistinguishe db ysevera l morphological characters andeasies tb ysiz e(Weber , 1931;Lopez-Avila , 1986).Th efourt h instar transforms into a so-called pupal stage during which the scale-like nymph transforms into the winged adult that emerges through a sliti n thedorsu m of its shed exoskeleton. Theduratio n of this life-cycle isdependen to nwhitefl y species,temperatur ean dhost-plan tsuitability .Fo rinstance , thedevelopmenta l time ofT. vaporariorum onpoinsetti a isfaste r than that of B. argentifolii at20°C ,bu ta t2 5° Ci ti sth eothe rwa yroun d (Fransen, 1994).Fo rmor edetaile d information about whitefly morphology, life-history parameters, behaviour or host-plant preference see, for example,va nLentere n &Noldu s (1990),Byrn e &Bellow s (1991),va n Roermund &va n Lenteren (1992)o rGerlin g(2000) . Whitefly management strategies In natural ecosystems and agro-ecosystems where nopesticide s areused , an arrayo f natural enemies can keep whitefly at low numbers by a combination of predators, parasitoids and pathogens.Severa lexample sar eknow no fperfec t naturalcontro lo fwhitefly , e.g.i ntomatoe s inth e 1960'si nCalifornia , incotto n duringth eperio d 1925- 1992i n Sudan (van Lenterenet al., 1996), in citrus beginning 1900's in Florida (McCoy, 1985) or in pimento on Jamaica (Borner,1956) .Whe ninsecticide san dfungicide s areapplie dnatura lenemie sar eexterminate d and whitefly pests are theresul t (van Lenteren etal., 1996) . General introduction In protected crops, especially in ornamentals, the low tolerance of pest insects is reflected bywidesprea d and frequent useo f insecticides.Biologica l control infloricultur e is moredifficul t compared withbiologica lcontro l infrui t vegetablesfo r severalreasons .Firstly , more chemicals are available for ornamentals than for fruit vegetables, because of safety regulations for consumption of vegetables. Secondly, in fruit vegetables only the fruits are harvested, which allows ahighe r population level of thepes t onth eleaves . Incontrast , most ornamentals arebein g soldwit hflower s andleaves ,an dtherefor e shouldb efre e of injury and presenceo finsects .Thirdly , the criterion of zerotoleranc e for both pest and natural enemies hasbee nuse d asa standar d for allproduct s until now,thoug h iti s onlyneede d asa nexpor t requirement for a few countries (Fransen, 1993). Nowadays, increasing knowledge and concern about the effects of chemical pesticides on the environment and the problem of resistence development against pesticides by insects (Dittrich & Ernst, 1990; Horowitz & Ishaaya, 1996)ma ycaus echemical st ob en olonge ravailabl ei nth efuture . Therefore research has shifted towards other means of control, such as integrated pest management (IPM), includingbiologica l control andguide d control, andbreedin g for host-plant resistance, using chemical control only as an ultimate resort. Biological control using predators, parasitoids and/or pathogens, can offer areliabl e method tocontro l whitefly. Predators and parasitoids About 75 species of whitefly predators havebee n described. However, many more species preyupo nwhiteflies ,