Separating the Effects of Experience, Size, Egg Load, and Genotype on Host Response in Trichogramma (Hymenoptera: Trichogrammatidae)

The effects of experience, egg load, and wasp size on the response of four strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae) to three economically important hosts, Heliothis punctigera (Noctuidae), Phthorimaea opercullela (Gelechiidae), and Sitotroga cereallela (Gelechiidae) were investigated. Experience effects due to rearing host and oviposition were considered in all combinations of host species. Both these effects altered response levels to low-ranked hosts but not to highly preferred hosts. Size was correlated with host response in some strains; larger females took more encounters with a host before accepting it, while egg load was not correlated with number of host encounters. However, egg load, rearing host, and size all affected acceptance of the low-ranked host S. cereallela. Females were more likely to accept this host if they were reared on S. cereallela, had a small size, and had a high egg load. Effects were consistent across strains, although overall acceptance levels differed among strains.     

Plant cues influence searching behaviour and parasitism in the egg parasitoid Trichogramma nr. brassicae

Abstract. 1. The effect of experience of plant cues at emergence on searching behaviour and parasitism was investigated in two strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae).
2. Wasps reared on Sitotroga cereallela were allowed to emerge on a tomato plant or in a vial, with or without food. For one of the strains, females emerging on tomato searched significantly longer on a tomato seedling than females emerging in a vial.
3. The experience effect lasted between 1 and 2 days. It involves associating plant stimuli with the remains of the host, because females emerging from their host on a tomato plant had an increased searching response to tomato, but females transferred to the plant immediately after emergence did not.
4. The effect of emergence environment on parasitism of the host Helicoverpa punctigera on tomato and lettuce seedlings was tested. Wasps were allowed to emerge on seedlings of tomato or lettuce, or in an empty vial. For one strain, females experienced with tomato at emergence parasitized significantly more hosts on tomato than did females emerging on lettuce or in a vial. Parasitism on lettuce was not influenced by the treatments.     

Oviposition Behaviour and Reproductive Performance of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) Reared in Artificial Diet

Biotypes of Trichogramma australicum were reared on artificial diet "A", Helicoverpa armigera (Hübner) (natural host) eggs and Sitotroga cerealella (Olivier) (factitious host) eggs. We evaluated the quality of these biotypes by comparing their oviposition behaviour and reproductive performance on H. armigera eggs. Female T. australicum reared in vitro accepted H. armigera eggs for oviposition and displayed similar behavioural components of oviposition to females reared on natural hosts. However, handling time during oviposition in H. armigera eggs by females from in vitro rearing was significantly longer than handling time of females reared on the natural host because the females needed a significantly longer time for host feeding. In vitro reared females produced significantly more progeny and parasitised more H. armigera eggs than the females reared on S. cerealella. Improvements to the artificial diet for T. australicum may reduce handling time of the in vitro reared females and increase the female population. These improvements may include changes in nutrient content and size of the artificial eggs.     

Learning pays off: influence of experience on host finding and parasitism in Lariophagus distinguendus

Abstract. 1. The influence of experience on egg maturation, parasitism rate, and behaviour during host searching was investigated for Lariophagus distinguendus (Först.) (Hymenoptera: Pteromalidae) parasitizing larvae of the granary weevil Sitophilus granarius (L.) in grains of wheat Triticum aestivum L.
2. Dissection of female parasitoids and parasitism bioassays at high host density revealed that experience with hosts (e.g. by oviposition or by host feeding) is not required either for triggering oogenesis or for oviposition.
3. In parasitism experiments at low host density, when single host-infested grains were offered within a bulk of healthy grains, host finding and parasitism rate were increased by experience.
4. Behavioural observations revealed that searching time required for finding an infested grain was shorter for experienced parasitoids than for naive parasitoids, because travel time from grain to grain is shorter for experienced parasitoids, and because experienced parasitoids spend less time than naive parasitoids on non-infested grains.
5. In conclusion, experience due to host exposure increases parasitism and thereby the fitness of the parasitoids. It is discussed that this increase is more likely due to learning than to different egg load dynamics of experienced parasitoids.     

Learning of host searching cues by the larval parasitoid Microplitis croceipes

We conducted laboratory experiments using a wind tunnel to determine the effects of prior experience on the learning and retention of learned responses in the larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Although most females that had either antennated host frass or oviposited in a host in the presence of vanilla odor, made oriented flight to the odor from downwind in the wind tunnel at 30 min after experience, only those that had oviposited in a host with the odor responded to the odor at 24 h after experience. Females that had oviposited in the non‐natural host beet armyworm (BAW) larva with or without the odor did not respond to the odor at 30 min after experience. These results indicate that an oviposition in the host in the presence of odors strongly affects associative learning and the persistence of learned response to the odors. When females were allowed to antennate host frass in the presence of vanilla and to subsequently oviposit in a host within an interval of 5 min or less, their learned response to vanilla also persisted for 24 h. Similarly, when females were conditioned to link vanilla with host frass and then allowed to make an ovipositor contact with host hemolymph, their learned response persisted for 24 h. However, antennal contact with hemolymph after such conditioning of vanilla with host frass did not improve the persistence of learned response to the odor. These results indicate that ovipositor contact with host hemolymph during oviposition is partially responsible for an increased retention of learned response. Females responded to vanilla 48% of the time at 30 min after antennating host frass without the odor, but their response to the odor significantly decreased after oviposition in a BAW larva subsequent to the antennation of host frass. This result indicates that oviposition in a BAW larva decreases subsequent response to general odors. Based on the results, we discuss the foraging behavior of M. croceipes dependent on learning and subsequent experiences.     

Trade-off in oviposition strategy: choosing poor quality host plants reduces mortality from natural enemies for a salt marsh planthopper

Abstract.  1. Both host plant nutrition and mortality from natural enemies have been predicted to significantly impact host plant selection and oviposition behaviour of phytophagous insects. It is unclear, however, if oviposition decisions maximise fitness.
2. This study examined whether the salt marsh planthopper Pissonotus quadripustulatus prefers higher quality host plants for oviposition, and if oviposition decisions are made so as to minimise mortality at the egg stage.
3. A controlled laboratory experiment and 4 years of field data were used to assess the rates of planthopper oviposition on higher quality 'green' and lower quality 'woody' stems of the host plant Borrichia frutescens . The numbers and percentages of healthy eggs and eggs that were killed by parasitoids or the host plant were recorded.
4. In all years, including the laboratory experiment, Pissonotus planthoppers laid more eggs on lower quality woody stems than on higher quality green stems. While host plant related egg mortality was higher in woody stems, the percentage of eggs parasitised was much greater in green stems. This resulted in a lower total mortality of eggs on woody stems.
5. The results of this study demonstrate that, although Pissonotus prefers lower quality host plants for oviposition, this actually increases fitness. These data seem to support the enemy free space hypothesis, and suggest that for phytophagous insects that experience the majority of mortality in the egg stage, oviposition choices may be made such that mortality is minimised.     

Preimaginal conditioning does not affect oviposition preference in the diamondback moth

Abstract.  1. In holometabolous insects, learning has been demonstrated in both larval and adult stages. Whether learning can be retained through metamorphosis from larva via pupa to adult has long been a subject of debate. The present study is designed to distinguish between preimaginal and imaginal conditioning in the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) using oviposition preference tests on females exposed to various types of learning experiences during immature and adult stages.
2. Cohorts of test insects were reared from egg to pupa on an artificial diet, or on one of two host plants, Chinese cabbage, Brassica campestris L. ssp. pekinensis , and common cabbage, Brassica oleracea L. var. capitata . The ensuing females reared on the three kinds of food showed similar oviposition preference between the two plants. A brief experience of the less preferred host, common cabbage, by adults slightly increased their preference for this plant.
3. Cohorts of test insects were reared from egg to pupa on an artificial diet with or without the addition of a neem-based oviposition deterrent (Neemix^® 4.5). Larval feeding experience did not alter oviposition response to the deterrent. However, emergence conditioning and early adult learning, achieved through experience of a residue of the deterrent carried over from the larval food on pupal cuticle and cocoons, altered oviposition preference significantly.
4. The combined results revealed no evidence of preimaginal conditioning in this insect but a strong effect of emergence conditioning and early adult learning on oviposition preference.     

Effects of pre-adult and adult experience on host acceptance in choice and non-choice tests in two strains ofTrichogramma

The effect of adult learning through an oviposition experience, and pre-adult learning through development inside a host was investigated in two strains of an Australian egg parasitoid,Trichogramma nrivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae),Papilio aegeus (Papilionidae), andHypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre-adult experience affected host preference in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host species. An oviposition experience had a stronger effect on host preference than pre-adult experience. In choice tests, pairwise combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of the first host. The implications of learning inTrichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and inundative release.     

Comparative Analysis of the Reproductive Attributes of Three Commercially-Produced Trichogramma Species (Hymenoptera: Trichogrammatidae)

The reproductive attributes of commercially-produced Trichogramma platneri, T. minutum and T. pretiosum reared from eggs of both Ephestia kuehniella and Sitotroga cerealella were monitored at 25 C. The age-specific fecundity, longevity and progeny sex ratio and adult size were determined for individual females from all six combinations of Trichogramma and rearing host, using E. kuehniella as the experimental host. Rearing host had a significant influence on the lifetime fecundity, 3-day fecundity and longevity of all three Trichogramma species. In general, the performance of T. minutum and T. pretiosum was better when reared from S. cerealella, but that of T. platneri was superior when reared from E. kuehniella. The lifetime fecundity of the Trichogramma species was linearly related to longevity and the ranking between species was T. pretiosum > T. minutum > T. platneri. The age-specific pattern of oviposition for T. platneri was distinctly precocious, with 40% of its lifetime fecundity oviposited on the first day, in contrast to 17-24% for the other two species. Progeny sex ratio over the lifetime of the Trichogramma females was slightly male biased and differed significantly from 0.5 for T. minutum and T. platneri. Daily sex ratio for parasitoids reared from the most productive rearing host was female biased only for the first day of oviposition for T. platneri in contrast to the first 5-6 days of oviposition for the other two species. There was little evidence that any of the reproductive attributes of these Trichogramma species, reared from small host eggs, was dependent on the size of the adult females.     

斑痣悬茧蜂产卵器刺扎寄主经历对刺探行为的影响

【目的】本文旨在评价斑痣悬茧蜂Metrorus pulchricornis(Wesmael)刺扎寄主的行为机理。【方法】采用非选择性试验于室内观察了刺扎次序对其产卵决策的影响;并采用双选试验观察了具有刺扎不同寄主(健康的、自身刺扎过的、他蜂刺扎过的寄主)的经历如何影响寄生蜂对自身刺扎与他蜂刺扎过的寄主的选择。【结果】非选择性试验结果表明:当面对健康寄主时,寄生蜂刺扎次序对刺扎耗时在5%概率水平上没有显著影响,但在10%概率水平具有显著影响;刺扎次序对寄生率没有显著影响,第1至5次刺扎的寄生率依次为63.3%、46.7%、76.7%、70.0%和66.7%。双选试验结果发现,刺扎不同寄主的经历处理对刺扎寄主选择性没有显著影响(P>0.05),具有刺扎健康的、自身刺扎过的和他蜂刺扎过的寄主的经历使寄生蜂选择被他蜂刺扎过的寄主的比例分别为65.5%、44.8%和50.0%。但刺扎经历显著影响刺扎耗时(P<0.05),具有1次刺扎健康寄主经历的蜂的刺扎耗时显著短(2倍)于具有刺扎自身刺扎过的寄主经历的蜂,但与具有刺扎他蜂刺扎过的寄主经历的蜂没有显著差异(P>0.05)。【结论】学习在斑痣悬茧蜂刺扎探测寄主行为的作用很小。     

Proteinase inhibitors from Nicotiana alata enhance plant resistance to insect pests

The ornamental tobacco (Nicotiana alata) produces one 6-kDa chymotrypsin inhibitor and four 6-kDa trypsin inhibitors from a single 40.3-kDa precursor protein. Three different approaches have been used to assess the potential of these proteinase inhibitors (PIs) in insect control. The first was an in-vitro approach in which all five inhibitors, the single chymotrypsin inhibitor or three of the four trypsin inhibitors were tested for their ability to inhibit gut protease activity in insects from four orders. The second approach was to incorporate the N. alata PIs in the artificial diet of the native budworm (Helicoverpa punctigera) and the black field cricket (Teleogryllus commodus). H. punctigera larvae and T. commodus nymphs had a significant (P<0.01) reduction in growth after ingestion of the PI and were more lethargic than insects on the control diet. Several of the H. punctigera larvae also failed to complete moulting at the third or fourth instar. The third approach was to express the N. alata PIs in transgenic tobacco under the control of the 35S CaMV promoter. When H. punctigera larvae were fed tobacco leaves expressing the N. alata PIs at 0.2% soluble protein, significant (P<0.01) differences in mortality and/or growth rate were observed.     

Effects of recent experience on foraging in tephritid fruit flies

In field-cage studies, we investigated how the foraging behavior of tephritid fruit flies is modified by experience immediately prior to release on host plants. We observed females of a relatively monophagous species,Rhagoletis mendax (blueberry maggot fly), an oligophagous species,Rhagoletis pomomella (apple maggot fly), and a polyphagous species,Ceratitis capitata (Mediterranean fruit fly). Just prior to release on a host plant, the following kinds of stimuli were supplied: (1) single oviposition in a host fruit, (2) contact with 20% sucrose, (3) contact with a mixture of protein food (bird feces and sucrose), (4) contact with water, and (5) a walk over a host-plant leaf. When flies foraged on host plants without resources, search was most intensive (as measured by number of leaves visited) following a single oviposition in fruit, but residence time generally was the same following exposure to sugar, protein, and fruit stimuli.Rhagoletis mendax andC. capitata females visited the fewest leaves following exposure to water or host leaves, whereasR. pomonella foraged equally intensively following exposure to food stimuli, water, or leaves. On host plants containing resources (fruit and protein food), a single oviposition dramatically increased the number of females of all three species that found fruit compared to females that received experience with food, water or foliar stimuli. We found no significant effect of recent brief experience with any of the stimuli on subsequent attraction to protein food. Overall,C. capitata exhibited a higher propensity to abandon host plants than eitherR. mendax orR. pomonella. We suggest that this may reflect adaptations to differences in distribution of host plants in nature, strategies of dispersal, and host range.     

Oviposition on host plants by a tropical forest grasshopper (Microtylopteryx hebardi: Acrididae)

Abstract. 1. The tropical forest grasshopper Microtylopteryx hebardi Rehn (Orthoptera, Acrididae, Ommatolampinae) oviposits inside leaves or stems of its host plants. This is the first known instance of oviposition inside living plant tissue (rather than in the ground, on top of leaves, or in detritus) for a tropical forest acridid.
2. In understorey secondary forest at La Selva, Costa Rica, M.hebardi females fed on fifteen species of host plants, but oviposited in only four of these.
3. In laboratory choice tests, females showed selectivity for oviposition host plants similar to that inferred from field observations.
4. Plant volume was a better predictor of the number of eggs laid per stem than variables that indicated leaf or stem characteristics of individual plants.
5. Unlike the ovipositor of acridids laying eggs in the ground, that of M.hebardi is equipped with toothed, sclerotized edges, probably used to bore into plant tissue.
6. Endophytic oviposition in M.hebardi may be related to finding host plants in a habitat that is complex, heterogeneous, and rich in plant species.     

Variation in flight response of the specialist parasitoidMacrocentrus grandii goidanich to odours from food plants of its European corn borer host

The specialist parasitoidMacrocentrus grandii Goidanich (Hymenoptera: Braconidae) appears to parasitize its polyphagous host, European corn borer (Ostrinia nubilalis (Hübner)) (Lepidoptera: Pyralidae), in only certain habitats. To determine whether it differed in its olfactory response to host-habitat odours, volatiles from four plants were isolated using Tenax. Wind tunnel bioassays of the extracts revealed that, besides corn which was tested in an earlier study, olfactory stimuli for attraction ofM. grandii females were present in potato and snap bean but not in pepper or soybean. To further characterize the response to pepper and soybean, these extracts were bioassayed in combination with an attractive extract. The results indicated that pepper volatiles evoked a neutral response inM. grandii while response to soybean volatiles appeared to be neutral or slightly negative. The innate response to soybean volatiles was altered to one of attraction after oviposition experience on soybean. Seven days after oviposition, experienced females continued to respond positively to soybean volatiles. Components of soybean volatiles responsible for the change in flight behaviour resulting from oviposition experience were eluted by nonpolar and slightly polar solvents. These results support the idea that plant odour may be a factor determining the range of plants on whichM. grandii parasitizes its host. The study indicates the occurrence of associative learning of plant-related volatiles during oviposition inM. grandii, and suggests the involvement of diverse plant compounds in the learning process.     

The influence of ants and water availability on oviposition behaviour and survivorship of a facultatively ant-tended herbivore

1. The lycaenid butterfly Hemiargus isola associates facultatively with the ant species Formica perpilosa in arid areas of south-western North America. Ants solicit liquid food rewards from butterfly larvae as larvae feed on the host plant, Acacia constricta . Previous studies have shown that tending by F. perpilosa enhances larval growth and pupal survivorship.
2. The effects of ants and plant water content on oviposition behaviour and survivorship to the last larval instar were tested by excluding ants and supplementing water to host plants in a two-way factorial experiment.
3. Butterflies, which lay eggs singly on host plant inflorescences, laid significantly higher egg numbers and densities (eggs/inflorescence) on plants with ants than on plants without ants. This is the first report of a facultative, generalized ant-associate using ants as oviposition cues. Water supplements increased the number, but not the density, of eggs laid on plants. Therefore, it appears that egg-laying butterflies responded to number of inflorescences, rather than plant tissue water per se .
4. Plants with ants had significantly greater numbers of inflorescences during the experiment than plants without ants. Water supplements increased number of inflorescences slightly, but not significantly.
5. Ants increased larval survivorship. Twice as many fourth-instar larvae survived per egg laid on plants with ants than on plants without ants. Ants did not reduce the number of predators present on acacias, but may have reduced predator effectiveness. Ants also did not reduce the numbers of potential H. isola competitors present.
6. Water supplementation affected neither the survivorship of H. isola larvae, nor the intensity of ant tending. Water supplementation did not affect the abundance of predators on plants, but did increase the abundance of several herbivorous insect taxa.     

Toxicity of Bacillus thuringiensis insecticidal proteins for Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae), major pests of cotton

The susceptibilities of the major pests of cotton in Australia, Helicoverpa armigera and Helicoverpa punctigera, to some insecticidal proteins from Bacillus thuringiensis were tested by bioassay. A commercial formulation, DiPel, and individual purified insecticidal proteins were tested. H. armigera was consistently more tolerant to B. thuringiensis insecticidal proteins than was H. punctigera, although both were susceptible to only a limited range of these proteins. Only Cry1Ab, Cry1Ac, Cry2Aa, Cry2Ab, and Vip3A killed H. armigera at dosages that could be considered acceptable. There was no significant difference in the toxicities of Cry1Fa and Cry1Ac for H. punctigera but Cry1Fa had little toxicity for H. armigera. The five instars of H. armigera did not differ significantly in their susceptibility to DiPel on the basis of LC(50). However, there were significant differences in the susceptibility to Cry1Ac and Cry2Aa of three strains of H. armigera. Bioassays conducted with Cry1Ac and Cry2Aa showed that there was a small but significant negative interaction between these delta-endotoxins.     

Biological studies on Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae), egg parasitoid of Tuta absoluta Meyrick (Lepidoptera: Gelechiidae)

The tomato moth, Tuta absoluta Meyrick, is one of the most important tomato pests in South America. In Argentina, management strategies include only chemical control. In this work, the parasitoid wasp Trichogrammatoidea bactrae Nagaraja was evaluated as a potential natural enemy against this pest. Biological and population parameters were estimated by developing a life table under laboratory conditions at 25 ± 1oC, 14:10 photoperiod and 60 ± 10% RH. Three cohorts of 26-30 T. bactrae females each were placed with one of the three following treatments: 1 - Sitotroga cerealella (Olivier) eggs on a piece of cardboard; 2 - S. cerealella eggs on a piece of tomato leaf, and 3- T. absoluta eggs on a piece on tomato leaf. The following parameters were estimated for each cohort: survival (egg to adult), longevity, fecundity and oviposition period of females, sex proportion of the F1, net rate of reproduction (Ro), mean generation time (T) and intrinsic rate of population increase (r m). Survival of the T. bactrae immatures was higher than 90% on both, S. cerealella and T. absoluta eggs. The female survival curves corresponded to type III and showed no significant differences among treatments. The three cohorts did not show significant differences between sex ratio, female longevity, oviposition period, fecundity and the population parameters studied. These results indicate that T. bactrae would be a potential biological control agent of T. absoluta.     

Oviposition by screwworm flies (Diptera: Calliphoridae) on contact with host fluids

Factor affecting oviposition by screwworm flies, Cochliomyia hominivorax (Coquerel), contacting different host fluids were examined in a laboratory bioassay. Fresh bovine blood, which does not release the attractive odors involved in host finding, nevertheless stimulated as many or more females to oviposit than did the other fluids tested. These other fluids included attractive fluid from screwworm-infected wounds (a favored oviposition site in nature) and cultures of Providencia rettgeri (a bacterium implicated in attractant production). Oviposition did not vary with batch of fresh blood or frozen storage, making blood a useful standard for comparing oviposition rates among studies. Oviposition did vary with the substrate to which the blood was applied, suggesting that an interaction between tactile and chemical stimuli is important for host recognition. Both insemination and darkness during bioassay increased oviposition rates, but the magnitude of these effects was small compared with that due to substrate. Age had no effect for at least 1 wk after females became gravid.     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.     

Effects of size and fluctuating asymmetry on field fitness of the parasitoid Trichogramma carverae (Hymenoptera: Trichogrammatidae)

1. The effects of body size and asymmetry in morphological traits on field fitness were studied in the parasitoid Trichogramma carverae .
2. Significant fluctuating asymmetry was detected in four bristle counts and two wing measurements made on forewings. There was no evidence for directional asymmetry in any of the traits. An estimate of field fitness was obtained in grapevines by collecting released wasps arriving at oviposition sites consisting of egg rafts of the tortricid Epiphyas postvittana .
3. Comparisons of ovipositing and emergence samples indicated that wasps at oviposition sites were relatively larger and more variable in their size distribution. A non-parametric analysis of the relationship between fitness and size indicated that extremely large wasps had the highest fitness and suggested that small as well as large wasps may have had a fitness advantage.
4. For asymmetry, the only trait showing an association with field fitness was wing length. Wasps with a low length asymmetry were more likely to be collected at oviposition sites, although fitness curves indicated that wasps had a similar fitness once an intermediate length asymmetry was exceeded.
5. Mother–daughter comparisons for wasps from a genetically heterogeneous stock provided no evidence that size measures or asymmetries were heritable when wasps were reared on a factitious host.
6. These findings have implications for improving parasitism rates in inundative releases.