Brood size and sex ratio in response the gregarious parasitoid … · Visser, 1990; Godfray, 1994;...

Submitted 3 August 2016Accepted 17 December 2016Published 24 January 2017

Corresponding authorBaoping Li lbpnjaueducn

Academic editorLeon Higley

Additional Information andDeclarations can be found onpage 9

DOI 107717peerj2919

Copyright2017 Li et al

Distributed underCreative Commons CC-BY 40

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Brood size and sex ratio in responseto host quality and wasp traits inthe gregarious parasitoid Oomyzussokolowskii (Hymenoptera Eulophidae)Xianwei Li Liangting Zhu Ling Meng and Baoping LiSchool of Plant Protection Nanjing Agricultural University Nanjing Jiangsu China

ABSTRACTThis laboratory study investigated whether the larval-pupal parasitoid Oomyzussokolowskii females adjust their brood size and sex ratio in response to body size andstage of Plutella xylostella larval hosts as well as to their own body size and the order ofoviposition These factors were analyzed using multiple regression with simultaneousentry of them and their two-way interactions Parasitoids brood size tended to increasewith host body size at parasitism when the 4th instar larval host was attacked but didnot change when the 2nd and 3rd instar larvae were attacked Parasitoids did not vary inbrood size according to their body size but decreased with their bouts of oviposition ona linear trend from 10 offspring adults emerged per host in the first bout of ovipositiondown to eight in the third Parasitoid offspring sex ratio did not change with host instarhost body weight wasp body size and oviposition bout Proportions of male offspringper brood were from 11 to 13 from attacking the 2nd to 4th instar larvae andfrom 13 to 16 across three successive bouts of oviposition with a large variationfor smaller host larvae and wasps When fewer than 12 offspring were emerged froma host one male was most frequently produced when more than 12 offspring wereemerged two or more males were produced Our study suggests that O sokolowskiifemales may optimize their clutch size in response to body size of mature P xylostellalarvae and their sex allocation in response to clutch size

Subjects Animal Behavior EntomologyKeywords Sex allocation Plutella xylostella Sex ratio Clutch size Oviposition behavior

INTRODUCTIONParasitoids make oviposition decisions depending on a variety of factors including thequality of hosts and characteristics of ovipositing wasps (Charnov et al 1981Van Alphen ampVisser 1990 Godfray 1994 Ellers amp Jervis 2003) Host quality for parasitoid developmentis often assumed to scale with host size and this pattern is true for idiobiont parasitoidswhich arrest host growth at the time of oviposition (Askew amp Shaw 1986 King 1990 Ottoamp Mackauer 1998) This pattern however may not be universally applicable to koinobiontparasitoids which allow the host to continue to develop after it has been parasitized (Werren1984 Waage 1986 Mackauer Sequeira amp Otto 1997 Harvey Sano amp Tanaka 2010) andthus the future resources for developing koinobiont larvae can vary depending on the host

How to cite this article Li et al (2017) Brood size and sex ratio in response to host quality and wasp traits in the gregarious parasitoidOomyzus sokolowskii (Hymenoptera Eulophidae) PeerJ 5e2919 DOI 107717peerj2919

age or development stage at the time of oviposition (Harvey amp Strand 2002Harvey 2005)though there are some koinobiont parasitoids still preferring larger body hosts (King1989 Elzinga Harvey amp Biere 2003 Kant Minor amp Trewick 2012) In addition to hostquality parasitoid oviposition decisions may also depend on characteristics of ovipositingwasps including their body size and states such as egg load age and nutrition statesThe wasp size is frequently considered to be the main target for selection (Godfray 1994Ode amp Strand 1995 Bezemer Harvey amp Mills 2005) It can affect fitness by influencingsearching efficiency longevity or egg supplies (Mayhew amp Heitmans 2000 Milonas 2005Jervis Ellers amp Harvey 2008 Kasamatsu amp Abe 2015) In addition it may also influencethe quality of host attacked in that a small female wasp may not be able to use a largegood quality host that is more effective in defense against attacks (Godfray 1994 HenryMa amp Roitberg 2009) Parasitoid state can affect many parasitoid behaviors (Van Alphen ampVisser 1990 Roitberg amp Bernhard 2008 Harvey Poelman amp Tanaka 2013) For exampleoviposition experience and physiological constraints such as egg load can influenceparasitoid oviposition decisions (Cloutier et al 1991 Henneman et al 1995 Sirot Ployeamp Bernstein 1997 Ueno 1999 Rosenheim et al 2008 Dieckhoff et al 2014) Thereforeparasitoids may integrate the information provided by a variety of cues about hosts andthemselves to make oviposition decisions

Oomyzus sokolowskii (Kurdjumov) is a gregarious larval-pupal koinobiont endopara-sitoid of the diamondback moth Plutella xylostella (L) (Talekar amp Shelton 1993 Talekar ampHu 1996 Silva-Torres et al 2009) which is one of major herbivorous pests on cruciferouscrops (Furlong amp Zalucki 2007 Zalucki et al 2012 Li et al 2016) Because P xylostellapopulations have developed resistance to numerous pesticides (Liu Tzeng amp Sun 1981Ferreacute et al 1991 Li et al 2006) biological control with natural enemies offers greaterpotential (Talekar amp Shelton 1993 Delvare 2004 Sarfraz Keddie amp Dosdall 2005) Theparasitoid O sokolowskii has been found parasitizing P xylostella worldwide (Wang et al1999 Nakamura amp Noda 2001 Silva-Torres et al 2009 Li Niu amp Liu 2014) showing thepotential for biological control of P xylostella (Talekar amp Hu 1996 Furlong Wright ampDosdall 2013) For O sokolowskii developmental performances in attacking P xylostellalarvae of different instars two non-choice studies are not consistent in their conclusionsthough the female wasp prefers mature larvae under choice circumstances (Talekar amp Hu1996) While Wang et al (1999) showed similar performances in the development timenumber and sex ratio of offspring in attacking host larvae of different instars Nakamuraamp Noda (2002) showed that O sokolowskii brood size increased with host body size whenhosts for parasitism were confined to the prepupal stage It would be interesting to examinewhether or not parasitoid brood size varies as a function of host body size depending on hostlarval stage at parasitism In addition states of ovipositing wasps may influence ovipositiondecisions It has been shown that older O sokolowskii females declined in the progenyproduced per female and the number of parasitoids emerged per host (Silva-Torres Barrosamp Torres 2009 Sow et al 2013) However scant attention has been paid to the effect ofO sokolowskii female body size on its oviposition behavior Therefore to fully understandO sokolowskii oviposition strategy we need studies involving both host quality and wasptraits

Li et al (2017) PeerJ DOI 107717peerj2919 214

This laboratory study aimed to answer the question how doO sokolowskii females makeoviposition decisions on brood size and sex ratio in response to both host quality and theirown traits We examined combined effects of body size and age of P xylostella larvae aswell as body size and ovipositing order of the female wasp by using mutiple regressionmodels with simultaneous entry of these factors and their two-way interactions Our studyprovides new data to the understanding of oviposition behavior in gregarious parasitoids

MATERIALS amp METHODSInsectsPlutella xylostellawas collected in the early spring 2014 fromapakchoi (Brassica chinensisL)field on eastern suburb of Nanjing Jiangsu and thereafter maintained on potted pakchoiseedlings in insectary at 25 plusmn 1 C 60 plusmn 5 RH and a photoperiod of 168 h (LD)

Oomyzus sokolowskii was obtained from the Key Laboratory of Northwest Loess PlateauCrop Pest Management of Ministry of Agriculture of China Northwest AampF UniversityYangling Shaanxi It wasmaintained with P xylostella 4th instar larvae as hosts in the insec-tary A group of four host larvae was introduced into a 4 ml centrifuge tube which was cov-ered by 100mesh plastic screen for ventilation and suppliedwith a piece of fresh pakchoi leafas food Then a female O sokolowskii was released into the tube After 24 h the larvae wereremoved from the tube and transferred individually to 10-cm-diameter Petri dishes con-taining excised fresh pakchoi leaves which were replaced daily The host pupae parasitized(different from normal ones by dark body color) were collected in groups in vials whereemerged parasitoid adults were maintained for one day to ensure fully mating Naivefemales emerged within one day were used in the experiments

Oviposition behaviorPlutella xylostella 2nd 3rd and 4th instar larvae were used as hosts Each larva wasindividually exposed to parasitism after weighed (AL204-IC with the measurementaccuracy of 001 mg Mettler Toledo Columbus OH USA) After introduced into a4 ml centrifuge tube containing a host larva a female wasp was continuously observeduntil a bout of oviposition was completed The wasp then was removed and immediatelyintroduced into another tube containing a same-aged host larva for the second bout ofoviposition and then for the third Three successive bouts of oviposition took ca 5ndash6 h tobe accomplished by a wasp which was considered as a replicate The number of replicatesfor the 2nd 3rd and 4th instar host larvae was 32 43 and 34 respectively After the threebouts of oviposition the wasp was collected and measured in the right hind tibia length(HTL) under the microscope as a measure of body size The parasitized host larvae wereindividually reared on excised pakchoi leaves in tubes until parasitoid offspring adultsemerged Emerged wasps from each host were counted as a measure of brood size andtheir sexes determined by their antennae with long hairs on each segments in males andwithout the hairs in females When the parasitized hosts were dead before wasps emergedthe hosts were dissected to count immature parasitoids as a measure of brood size buttheir sexes were not identifiable


Data analysesGeneral linear mixed-effects models (LMMs) were used to analyze brood size (numberof wasps emerged) which was transformed by logarithm before the analysis to satisfy theunderlying assumptions Generalized linear mixed-effects models (GLMMs) were used toanalyze sex ratio (binary variable) with a binomial error The subject wasp was included inthe model as a random effects variable to control for the correlation between three oviposi-tion bouts of each wasp Host body weight host instar (nominal) wasp size the temporalorder of oviposition (ordinal) and their second-way interactions were firstly included asfixed effects variables in the full model then excluded from it when they did not havesignificant effects using Type III Wald Chi-Square test to evaluate the significance of theterms by comparing the fit of full model to the fit of the reduced model without eachof them Orthogonal polynomial contrasts were used to detect trends (either linear orquadratic) in parasitoid performance with increasing bouts of oviposition When there wasa significant interaction between host instar and body weight general linear models wereseparately used to detect the relationship between brood size and host body weight for eachof host instars examined To analyze the relationship between the number of males in abrood and brood size the tree model was used to determine the threshold for splitting thebrood size of which the number of males in a brood changed as a step function The mixedeffects models were fitted by the laplace approximation using lsquolme4rsquo version 11ndash10 (Bateset al 2015) Data analyses were performed with R (R Development Core Team 2014)

RESULTSParasitoid brood size was affected by host body weight and instar interaction (WaldChi-Square test χ2

= 630 P = 004) and the order of oviposition (χ2= 1801 P lt 0001)

but not by wasp HTL (χ2= 001 P = 094) The regression analysis of brood size in

relation to host body weight for different host instars showed no significant relations forthe 2nd (χ2

= 209 P = 014) and 3rd (χ2= 090 P = 034) instars Brood size ranged

from 4 to 21 wasps with an average of 90 plusmn 03 (plusmnSE) in the 2nd instar hosts that variedin body weight from 001 to 003 mg and 2 to 19 with an average of 91plusmn 02 (plusmnSE) in the3rd instar hosts that varied in body weight from 003 to 014mg (Figs 1A and 1B) Howeverthe analysis showed a marginally significant relation between brood size and body weightof the 4th instar hosts (χ2

= 365 P = 0048) with a gradual increase by ca 20 in broodsize with each increase of 01 mg in host body weight brood size ranged from 4 to 14 waspswith an average of 93plusmn 03 (plusmnSE) across host body weight from 018 to 069 mg (Fig 1C)Brood size did not change with ovipositing wasp HTL (Fig 1D) but varied with thetemporal sequence of oviposition decreasing on a linear trend over increasing bouts ofoviposition (slope =minus011 SE = 003 t = 424) from 10 offspring adults emerged perhost in the first oviposition bout down to 8 in the third (Fig 1E)

Offspring sex ratio was not affected by host instar (Wald Chi-Square test χ2= 089

P = 064) host body weight (χ2= 016 P = 069) wasp HTL (χ2

= 001 P = 093) andthe temporal sequence of oviposition (χ2

= 369 P = 016) Average proportions of maleoffspring from attacking host larvae of different instars were 014 (SD = 010) for the


Figure 1 Number of wasps emerged per host (brood size) in relation to host quality and wasp traitsNumbers of offspring parasitoids per host (brood size) in relation to host body weight of the 2nd (A) 3rd(B) and 4th (C) instar larvae at oviposition wasp body length (D) and the order of oviposition (E) Thesolid line in (C) represents a linear relationship between brood size and host body weight with intercept809 and slope 333 with a 95 confidence region (grey shade) The line in (E) represents a linear trendand the bars are mean and SE


2nd and 014 (SD = 011) the 3rd instar larvae with two extremely high sex ratios (maleproportion gt 05) for each of the two instars the mean proportion of males was 013 (SD= 005) for the 4th instar hosts (Fig 2A) Male proportion of offspring did not change withhost body weight (Fig 2B) and ovipositing wasp HTL (Fig 2C) with a few extremely highsex ratios produced from very small hosts (body weight lt 01 mg) or wasps (body lengthlt 045 mm) Proportions of males for successive bouts of oviposition were 013 (SD =009) for the 1st 013 (SD = 006) the 2nd and 016 (SD = 011) the 3rd with two muchhigher sex ratios produced from the 1st and 3rd bouts of oviposition respectively (Fig2D) The number of males per brood changed as a step function of brood size which splitat 12 with a significant difference between the two split groups (F1232= 6817 P lt 0001)A brood fewer than 12 contained one male (mean= 12 SD= 049) while a brood of morethan 12 had two males (mean = 168 SD = 224) with a few broods containing extremelynumerous males (Fig 2E)

DISCUSSIONIn this study we showed that O sokolowskii offspring brood size tended to increase withbody size of P xylostella 4th instar larvae but did not change with that of the 2nd and 3rdinstar larvae The pattern exhibited in the 4th instar larval hosts is similar to that shownin prepupal hosts documented by Nakamura amp Noda (2002) We therefore assume thatO sokolowskii females may take the cues associated with body size of only older larvalhosts when evaluating host quality to make the oviposition decision on clutch size Hostlarvae close to pupation can provide more accurate information about host quality interms of body size than younger ones do because body size changes much less with growthin mature than younger larvae Such evaluation of host quality can be advantageous forkoinobiont parasitoids to attack older larval hosts such as larval-pupal parasitoids FemaleO sokolowskii prefers to parasitize older than younger P xylostella larvae (includingprepupae) (Talekar amp Hu 1996) Though differential mortality rates during offspring de-velopment among different host instars may somehow potentially contribute to the patternwe observed in O sokolowskii such effect might be negligible because brood sizes werequite close to each other between host instars observed in our study while the number ofeggs (primary clutch size) are not different among these instars (Nakamura amp Noda 2002)

Body size is one of important attributes for female wasps because it is correlated withseveral components of the fitness (King 1987 Blackburn 1991 King 1993 Ellers amp Jervis2003 Henry Ma amp Roitberg 2009) In the case of gregarious parasitoids the fitness of a fe-male parasitoid can be strongly correlated with not only the number of eggs laid per host butalso the number of hosts attacked Our study showed thatO sokolowskii brood size did notchange with body size of ovipositing wasps We therefore assume that larger O sokolowskiifemales may realize their greater potential in reproduction by attacking more hosts insteadof laying more eggs per host Such strategy of clutch size allocation can be adaptive toexploiting clumped distribution of hosts As the only host of O sokolowskii P xylostellalarvae tend to clump together in the early stage disperse locally as they grow and thenaggregate again during pupation (Chua amp Lim 1979 Furlong Wright amp Dosdall 2013)


Figure 2 Brood sex ratio in response to host quality and wasp traits Sex ratios in relation to host in-star (A) host body weight (B) wasp body length (C) and bout of oviposition (D) and the relationship (E)between the number of males and offspring emerged (brood size) per host with a curve fitted by locallyweighted polynomial method with a 95 confidence region (grey shade) Bars in (A) and (D) are meanplusmn SE


For the performance of a slight linear decrease in brood size across successive boutsof oviposition shown in our study the most likely explanation is that egg expenditureon successive bouts of oviposition leads to a steady decline in number of eggs availableto oviposit when a group of hosts are encountered in quick succession Daily decrease inoffspring production occurs in O sokolowskii (Wang et al 1999 Li Niu amp Liu 2014) aswell as in other gregarious parasitoids such as in Cotesia glomeratus L attacking the whitebutterfly Pieris rapae (L) (Ikawa amp Suzuki 1982)

Our study did not show the influence of host size host life stage wasp body size andoviposition sequence on parasitoid offspring sex ratio Invariable sex ratios in response tohost age and size were previously observed in O sokolowskii (Wang et al 1999 Nakamuraamp Noda 2002 Silva-Torres et al 2009) The lack of sex allocation response to changes inhost size in O sokolowskii may exclude widely held Charnovrsquos host quality hypothesis asan explanation Charnovrsquos hypothesis (Charnov et al 1981) was developed specifically forsolitary parasitoids in which offspring body size is strongly correlated with host body sizeHost size for many idiobiontic solitary parasitoids is thought to more strongly influencefemale thanmale fitness (Werren 1984Charnov amp Skinner 1985King 1993) In the case ofgregarious parasitoids however the fitness of the adult wasp is determined primarily by theclutch size and possibly the sex composition (Griffiths amp Godfray 1988 Hardy Griffiths ampGodfray 1992Godfray 1994Ode amp Heinz 2002) Maintaining constant female-biased sexratios in response to variation in host quality and wasp traits in O sokolowskii suggests thatthis parasitoid may be able to adjust offspring sex ratios Female-biased sex ratios are mostfrequently exhibited in gregarious parasitoids where there is a high probability the matingoccurs between siblings and that brothers compete together for mates (Godfray 1994 Odeamp Hunter 2002 Ode amp Hardy 2008) Such observations can be explained by Hamiltonrsquos(1967) theory of local mate competition (LMC) which predicts that a single female shouldlay only enough males to fertilize all her daughters In the case of O sokolowskii wheresib-mating is common among offspring from a host foundresses are expected underLMC to adjust the number of males in response to brood size Our study showed thatO sokolowskii produced one male in most of broods under 12 wasps and two males inbroods over 12 except a few largest broods with extremely numerous males from attackingvery small host larvae We suspect that these few broods were consequences of constraintsunder non-choice circumstances in the experiments When these extreme data points areexcluded our study is the same as Nakamura amp Noda (2002) in finding that only one malewas produced when the brood contained fewer than nine offspring and 2ndash4 males when itcontained more than nine offspring

ACKNOWLEDGEMENTSWe thank Yuanxing Sun for providing O sokoloskii and Lintao Li for the help in theexperiments and the two reviewers for providing helpful comments on improving themanuscript


ADDITIONAL INFORMATION AND DECLARATIONS

FundingThis research was supported by the Natural Science Foundation of China (NSFC-31570389) The funders had no role in study design data collection and analysis decisionto publish or preparation of the manuscript

Grant DisclosuresThe following grant information was disclosed by the authorsNatural Science Foundation of China NSFC-31570389

Competing InterestsThe authors declare there are no competing interests

Author Contributionsbull Xianwei Li conceived and designed the experiments performed the experimentsanalyzed the data contributed reagentsmaterialsanalysis tools wrote the paperprepared figures andor tablesbull Liangting Zhu performed the experiments contributed reagentsmaterialsanalysis toolsbull Ling Meng conceived and designed the experiments analyzed the data contributedreagentsmaterialsanalysis tools reviewed drafts of the paperbull Baoping Li conceived and designed the experiments analyzed the data contributedreagentsmaterialsanalysis tools wrote the paper reviewed drafts of the paper

Data AvailabilityThe following information was supplied regarding data availability

The raw data has been supplied as Data S1

Supplemental InformationSupplemental information for this article can be found online at httpdxdoiorg107717peerj2919supplemental-information

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Harvey JA Sano T Tanaka T 2010 Differential host growth regulation by the solitaryendoparasitoidMeteorus pulchriconis in two hosts of greatly differing mass Journalof Insect Physiology 561178ndash1183 DOI 101016jjinsphys201003018

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Nakamura A Noda T 2002 Effects of host age and size on clutch size and sex ratioof Oomyzus sokolowskii (Hymenoptera Eulophidae) a larval-pupal parasitoid ofPlutella xylostella (Lepidoptera Yponomeutidae) Applied Entomology and Zoology37319ndash322 DOI 101303aez2002319

Ode PJ Hardy ICW 2008 Parasitoid sex ratios and biological control In WajnbergW Bernstein C Van Alphen J eds Behavioral ecology of insect parasitoids fromtheoretical approaches to field applications Oxford Blackwell Publishing 253ndash291

Ode PJ Heinz KM 2002Host-size-dependent sex ratio theory and improving mass-reared parasitoid sex ratios Biological Control 2431ndash41DOI 101016S1049-9644(02)00003-8

Ode PJ Hunter MS 2002 Sex ratios of parasitic Hymenoptera with unusual life-histories In Hardy ICW ed Sex ratios concepts and research methods CambridgeCambridge University Press 218ndash234


Ode PJ StrandMR 1995 Progeny and sex allocation decisions of the polyembryonicwasp Copidosoma floridanum Journal of Animal Ecology 64213ndash224DOI 1023075756

OttoMMackauer M 1998 The development strategy of an idiobiont ectoparasitoidDendrocerus carpenteri influence of variations in host quality on offspring growthand fitness Oecologia 117353ndash364 DOI 101007s004420050668

RDevelopment Core Team 2014 R a language and environment for statisticalcomputing Available at httpwwwR-projectorg

Roitberg BD Bernhard P 2008 State-dependent problems for parasitoids case studiesand solutions In Wajnberg E Bernstein C Van Alphen J eds Behavioral ecology ofinsect parasitoids from theoretical approaches to field applications Oxford BlackwellPublishing 337ndash356

Rosenheim JA Jepsen SJ Matthews CE Smith DS RosenheimMR 2008 Timelimitation egg limitation the cost of oviposition and lifetime reproduction by aninsect in nature American Naturalist 172486ndash496 DOI 101086591677

Sarfraz M Keddie AB Dosdall LM 2005 Biological control of the diamondbackmoth Plutella xylostella a review Biocontrol Science and Technology 15763ndash789DOI 10108009583150500136956

Silva-Torres CSA Barros R Torres JB 2009 Effect of age photoperiod and hostavailability on the parasitism behavior of Oomyzus sokolowskii (Kurdjumov)(Hymenoptera Eulophidae) Neotropical Entomology 38512ndash519DOI 101590S1519-566X2009000400013

Silva-Torres CSA Ramos Filho IT Torres JB Barros R 2009 Superparasitism and hostsize effects in Oomyzus sokolowskii a parasitoid of diamondback moth EntomologiaExperimentalis et Applicata 13365ndash73 DOI 101111j1570-7458200900903x

Sirot E Ploye H Bernstein C 1997 State dependent superparasitism in a solitary para-sitoid egg load and survival Behavioral Ecology 8226ndash232DOI 101093beheco82226

Sow G Arvanitakis L Niassy S Diarra K Bordat D 2013 Life history traits of Oomyzussokolowskii Kurdjumov (Hymenoptera Eulophidae) a parasitoid of the diamond-back moth African Entomology 21231ndash238 DOI 1040010030210202

Talekar NS HuWJ 1996 Characteristics of parasitism of Plutella xylostella (LepPlutellidae) by Oomyzus sokolowskii (Hym Eulophidae) BioControl 4145ndash52DOI 101007BF02893291

Talekar NS Shelton AM 1993 Biology ecology and management of the diamondbackmoth Annual Review of Entomology 38275ndash301DOI 101146annureven38010193001423

Ueno T 1999Host size dependent sex ratio in a parasitoid wasp Researches on Popula-tion Ecology 4147ndash57 DOI 101007PL00011982

Van Alphen JJM Visser ME 1990 Superparasitism as an adaptive strategy for insect par-asitoids Annual Review of Entomology 3557ndash79DOI 101146annureven35010190000423


Waage JK 1986 Family planning in parasitoids adaptive patterns of progeny and sexallocation In Waage JK Greathead D eds Insect parasitoids London AcademicPress 63ndash95

Wang XG Liu SS Guo SJ LiuWC 1999 Effects of host stages and temperature onpopulation parameters of Oomyzus sokolowskii a larval-pupal parasitoid of Plutellaxylostella BioControl 44391ndash402 DOI 101023A1009912420598

Werren JH 1984 A model for sex ratio selection in parasitic wasps local mate com-petition and host quality effects Netherlands Journal of Zoology 34123ndash143DOI 101163002829684X00056

Zalucki MP Shabbir A Silva R Adamson D Liu SS FurlongMJ 2012 Estimatingthe economic cost of one of the worldrsquos major insect pests Plutella xylostella(Lepidoptera Plutellidae) just how long is a piece of string Journal of EconomicEntomology 1051115ndash1129 DOI 101603EC12107


age or development stage at the time of oviposition (Harvey amp Strand 2002Harvey 2005)though there are some koinobiont parasitoids still preferring larger body hosts (King1989 Elzinga Harvey amp Biere 2003 Kant Minor amp Trewick 2012) In addition to hostquality parasitoid oviposition decisions may also depend on characteristics of ovipositingwasps including their body size and states such as egg load age and nutrition statesThe wasp size is frequently considered to be the main target for selection (Godfray 1994Ode amp Strand 1995 Bezemer Harvey amp Mills 2005) It can affect fitness by influencingsearching efficiency longevity or egg supplies (Mayhew amp Heitmans 2000 Milonas 2005Jervis Ellers amp Harvey 2008 Kasamatsu amp Abe 2015) In addition it may also influencethe quality of host attacked in that a small female wasp may not be able to use a largegood quality host that is more effective in defense against attacks (Godfray 1994 HenryMa amp Roitberg 2009) Parasitoid state can affect many parasitoid behaviors (Van Alphen ampVisser 1990 Roitberg amp Bernhard 2008 Harvey Poelman amp Tanaka 2013) For exampleoviposition experience and physiological constraints such as egg load can influenceparasitoid oviposition decisions (Cloutier et al 1991 Henneman et al 1995 Sirot Ployeamp Bernstein 1997 Ueno 1999 Rosenheim et al 2008 Dieckhoff et al 2014) Thereforeparasitoids may integrate the information provided by a variety of cues about hosts andthemselves to make oviposition decisions

Oomyzus sokolowskii (Kurdjumov) is a gregarious larval-pupal koinobiont endopara-sitoid of the diamondback moth Plutella xylostella (L) (Talekar amp Shelton 1993 Talekar ampHu 1996 Silva-Torres et al 2009) which is one of major herbivorous pests on cruciferouscrops (Furlong amp Zalucki 2007 Zalucki et al 2012 Li et al 2016) Because P xylostellapopulations have developed resistance to numerous pesticides (Liu Tzeng amp Sun 1981Ferreacute et al 1991 Li et al 2006) biological control with natural enemies offers greaterpotential (Talekar amp Shelton 1993 Delvare 2004 Sarfraz Keddie amp Dosdall 2005) Theparasitoid O sokolowskii has been found parasitizing P xylostella worldwide (Wang et al1999 Nakamura amp Noda 2001 Silva-Torres et al 2009 Li Niu amp Liu 2014) showing thepotential for biological control of P xylostella (Talekar amp Hu 1996 Furlong Wright ampDosdall 2013) For O sokolowskii developmental performances in attacking P xylostellalarvae of different instars two non-choice studies are not consistent in their conclusionsthough the female wasp prefers mature larvae under choice circumstances (Talekar amp Hu1996) While Wang et al (1999) showed similar performances in the development timenumber and sex ratio of offspring in attacking host larvae of different instars Nakamuraamp Noda (2002) showed that O sokolowskii brood size increased with host body size whenhosts for parasitism were confined to the prepupal stage It would be interesting to examinewhether or not parasitoid brood size varies as a function of host body size depending on hostlarval stage at parasitism In addition states of ovipositing wasps may influence ovipositiondecisions It has been shown that older O sokolowskii females declined in the progenyproduced per female and the number of parasitoids emerged per host (Silva-Torres Barrosamp Torres 2009 Sow et al 2013) However scant attention has been paid to the effect ofO sokolowskii female body size on its oviposition behavior Therefore to fully understandO sokolowskii oviposition strategy we need studies involving both host quality and wasptraits














































































































Brood size and sex ratio in response the gregarious parasitoid … · Visser, 1990; Godfray, 1994;...

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Transcript of Brood size and sex ratio in response the gregarious parasitoid … · Visser, 1990; Godfray, 1994;...