Oviposition Sequence Research Articles

Host acceptance and oviposition behaviour of solitary wasp, Anisopteromalus calandrae (Howard) (Hymenoptera : Pteromalidae), A parasitoid of stored grain pests

The host acceptance and oviposition behaviour of the ectoparasitoid, Anisopteromalus calandrae (Howard) (Hymenoptera : Pteromalidae) was observed on unexposed (hidden) and exposed host of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) under laboratory conditions. The egg-laying behaviour was accomplished in eight phases in hidden hosts of S. oryzae i.e., inside wheat kernels but it was much shorter having five steps in those of exposed hosts. Average total time taken by a mated A. calandrae in unexposed host (inside wheat kernels) during different oviposition sequences was 55 minutes. On the other hand, average total time taken by a mated A. calandrae in exposed host of S. oryzae during oviposition sequences was 91.1 minutes. A. calandrae preferred fully developed S.oryzae grubs rather than half- grown pre-pupae and early pupae in exposed condition. Generally, eggs were laid on or near S. oryzae host larvae or pupae inside wheat kernel because of ectoparasitic nature of A. calandrae. More eggs are deposited in case of S. oryzae hosts at the abdominal region dorsally, sometimes eggs were laid on the meta-thoracic segment dorsally but rarely eggs were laid on late S. oryzae pupae prior to adult transformation. Oviposition by a mated A. calandrae female parasitoid was influenced by the host’s size and shape on exposed as well as unexposed (within seed kernel) conditions. Generally, the 3rd and the 4th instar larvae and pre-pupae of S. oryzae were preferred for egglaying in exposed condition. The parasite did not lay eggs on naked R. dominica larvae or pupae.
 Bangladesh J. Zool. 46(2): 205-216, 2018

Reproductive ethology of the Fijian predator-inquiline wasp Pseudofoenus extraneus (Hymenoptera: Gasteruptiidae: Hyptiogastrinae)

ABSTRACTParasitoid wasps of the subfamily Hyptiogastrinae (Gasteruptiidae) are known to lay eggs in the nests of solitary bees and wasps. Their larvae are considered predator-inquilines, consuming the host’s eggs and larvae and then the nest provisions. Pseudofoenus extraneus is endemic to Fiji, and the only member of the subfamily Hyptiogastrinae known to have colonised the archipelago. The host relationships and oviposition sequence of this species have not been previously reported. We show that the primary host is the halictine bee Homalictus fijiensis and describe P. extraneus behaviour around Homalictus nest aggregations and the entering of host nests. Wasps were observed entering Homalictus nests on nine occasions, as well as perching near nests and antennating nest entrances. The high abundance of H. fijiensis in Fiji may help to explain how a parasitoid was able to successfully invade such a remote oceanic archipelago as Fiji.

Interspecific host discrimination and intrinsic competition between Aphelinus asychis and Aphidius gifuensis in Myzus persicae

AbstractAphelinus asychis Walker (Hymenoptera: Aphelinidae) and Aphidius gifuensis Ashmead (Hymenoptera: Braconidae: Aphidiinae) are solitary kionobiont endoparasitoids, which can parasitize the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). We determined the influence of oviposition sequence and various time intervals (0, 24, 48, and 72 h) between two ovipositions on self‐ and conspecific discrimination and interspecific intrinsic competition between A. asychis and A. gifuensis. When offered unparasitized M. persicae and those parasitized by the other parasitoid species, the two parasitoid species oviposited more often in unparasitized hosts. Aphelinus asychis and A. gifuensis could, however, not avoid to multiparasitize hosts parasitized by the other species. Both parasitoid species had a limited interspecific discrimination ability through ovipositor insertion to detect internal cues. Aphidius gifuensis most often out‐competed A. asychis. The outcome of this interspecific competition was not influenced by oviposition sequence or time intervals between two ovipositions. Aphidius gifuensis eliminated competitors by physical combat at the first instar and probably by physiological suppression in later stages; A. asychis possibly used physiological suppression in all larval stages.

Nisbah kelamin dan pola peletakan telur parasitoid Trichogramma chilotraeae Nagaraja & Nagarkatti (Hymenoptera: Trichogrammatidae) pada berbagai jumlah inang

The objective of the research was to study sex ratio and oviposition sequence of egg parasitoid Trichogramma chilotraeae in relation with host density under laboratory condition. Parasitoid response with respect to oviposition sequence was examined by exposing five different host (egg) densities: 3, 6, 12, 24 and 48 on female parasitoids T. chilotraeae. Results showed that in general, female parasitoid laid its female progeny at the beginning of oviposition sequence. Host density was found to have a strong effect on sex ratio. Sex ratio increase with increasing of host number.

Intrinsic competition between primary hyperparasitoids of the solitary endoparasitoidCotesia rubecula

1. In nature, competitive interactions occur when different species exploit similar niches. Parasitic wasps (parasitoids) often have narrow host ranges and need to cope with competitors that use the same host species for development of their offspring. When larvae of different parasitoid species develop in the same host, this leads to intrinsic and often contest com.petition. Thus far, m.ost studies on intrinsic competition have focused on primary parasitoids. However, competition among primary.hyperparasitoids, parasitic wasps that use primary parasitoids as a host, has been little studied. 2. This study investigated intrinsic competition between two primary hyperparasitoids, the gregarious Baryscapus galactopus and the solitary Mesochoru,s gemellu,s, which lay their eggs in primary parasitoid larvae of tesla rubecula, while those in turn are developing inside their herbivore host, Pieris rapae. The aims were to identify: (i) which hyperparasitoid is the superior competitor; and (ii) whether oviposition sequence affects the outcome of intrinsic competition. 3. The results show that B. galactopus won 70% of contests when the two hyperparasitoids parasitised the host at the same time, and 90% when 13. galactopus oviposited first. When M. gemellus had a 48 h head start, the two hyperparasitoids had an equal chance to win the competition. This suggests that M. galactopus is an intrinsically superior competitor to M. gemellu,s, Moreover, the outcome of competition is affected by time lags in oviposition events. 4. In contrast to what has been reported for primary parasitoids, we found that a. gregarious hyperparasitoid species had a competitive advantage over a solitary species.

Influence of body size on fecundity and sperm management in the parasitoid wasp Anisopteromalus calandrae

AbstractA large body size is considered to be advantageous to the reproductive success of females as a result of several factors, such as the allocation of more resources to reproduction and the efficient management of sperm transferred by males. In the present study, the effects of female body size, female mating status and additional food availability on fecundity and the offspring sex ratio are investigated in the parasitoid wasp Anisopteromalus calandrae Howard (Hymenoptera: Pteromalidae). Because of haplodiploid sex determination, females must fertilize eggs to produce female offspring but not to produce male offspring. As predicted, female fecundity and the number of female offspring are positively correlated with body size. However, although the volume of the spermatheca increases with female body size, the amount of sperm stored in the spermatheca is relatively constant, irrespective of body size. Consequently, larger females produce a greater proportion of male offspring, especially at the end of the oviposition sequence, suggesting that larger females that possess more resources for reproduction and produce a larger number of offspring are more likely to suffer sperm depletion. The results of the present study also show that mated females have an increased fecundity compared with virgin females, although the opportunity to feed on honey along with host feeding has no impact upon fecundity or the sex ratio.

Risk assessment of non-target effects of Closterocerus chamaeleon (Girault) parasitoid of the eucalypt gall maker Ophelimus maskelli (Ashmead) (Hymenoptera, Eulophidae)

The pre-release risk assessment, a recommended practice in biological control programmes, was carried out before introducing Closterocerus chamaeleon (Girault), a eulophid parasitoid of the eucalypt gall maker Ophelimus maskelli (Ashmead) (Hymenoptera, Eulophidae), in Sicily, Italy. We evaluated its host specificity in laboratory small arena no-choice tests on six non-target hosts, using O. maskelli as a control species. The non-target species fit with at least one of the following criteria: a) common geographical origin; b) ecological or behavioural affinities with the target host; c) concealed habit of the preimaginal stages; d) taxonomic affinity; e) taxonomic affinity with hosts of congeneric parasitoids of the candidate agent; and f) presence in Italy/Sicily. Closterocerus chamaeleon performed an oviposition sequence of 10 recognisable behaviours, always leading to parasitization when exposed to O. maskelli. The same behaviour sequence was carried out on the gall maker Leptocybe invasa Fisher et La Salle, the only non-target species living on Eucalyptus, but just until Step 6, i.e. until ovipositor extraction and insertion, and never until egg-laying. All of the other non-target hosts were ignored. Furthermore, the adult parasitoid longevity was assessed in three rearing conditions: 1) no food/no parasitisation permitted; 2) food/no parasitisation permitted; and 3) food provided after parasitisation. Adult wasp longevity was significantly higher in treatment 2 (21.1 days ± 4.1 SE) than in treatment 1 (3.6 days ± 0.5 SE) or 3 (3.8 days ± 0.6 SE). Laboratory tests carried out in this study on C. chamaeleon indicated high host selection ability, later confirmed by our post-release field data.

Modelling the egg components and laying patterns of broiler breeder hens

There is scant information about the reproductive process in broiler breeders, with which to develop a feeding strategy that will be economically optimal for these birds. This study aimed to model the egg production of a flock of broiler breeder hens, using non-isometric equations. The number of eggs produced by 60 broiler breeder hens aged 24–60 weeks was monitored, as was the weight of these eggs and the weights of the components, yolk, albumen and shell. Oviposition sequences and the number and length of pauses between sequences were analysed. Non-isometric functions were applied to predict the weight of the egg; yolk weight was predicted from the age of the hen, while albumen and shell weights were predicted from yolk weight; and egg weight was obtained by summing the component weights. The incidence of soft-shelled and double-yolk eggs was also determined. Yolk weight (YW, g) can be described as YW = 18.03 × (1 – e–0.015 × (t – 103.4)) × e(0.001 × t), where t is the age of the bird (days). The weights of albumen (AW) and shell (SW) were based on YW predictions as follows: AW = 14.38 × YW0.375 and SW = 0.358 × (YW + AW)0.687. The rate of double-yolk egg (DY) production is described by DY = 2.28 × e(0.209 × TFE), and the rate of soft-shelled egg (SS) production by SS = 1.126 + 0.148/(1 – 0.024 × TFE) – 0.056 × TFE, as a function of time from first egg (TFE). On the basis of the results obtained, the model developed here is an accurate reflection of the changes that occur in the number of eggs produced by broiler breeders, as well as in the egg itself and in its components over the entire laying period. This model can thus be used in predicting the nutrient requirements of individual broiler breeder hens, which, when combined with simulated data from a large number of individuals, will accurately describe the laying performance of a flock of broiler breeders.

Oviposition Behavior of the Pollen Beetle (Meligethes aeneus): A Functional Study

The recognition by female phytophagous insects of a plant as a ‘good’ or ‘bad’ host for egg laying is based on a variety of cues (either visual, physical or chemical). Specific cues are often looked for during stereotypic oviposition behaviors, composed of several phases having their own function(s). In this study the oviposition behavior of the pollen beetle Meligethes aeneus, a pest which lays eggs in flower buds of only some brassicaceous plants, was described in detail on five oilseed rape (Brassica napus) genotypes. In parallel, setae borne by the ovipositor were characterized by scanning electron microscopy. Observations showed that the stereotypic oviposition sequence is functionally divided into three independent phases: external inspection, internal inspection and egg laying. The ovipositor plays a role in all phases by gaining information about external and internal bud parts. This role appears to be only physical since all the setae it bears are mechanoreceptors. Despite the fact that the pollen beetle is a specialist for oviposition, important variations in secondary metabolites that are typical of its host plant family (i.e., glucosinolates) on the bud did not influence clutch size. The crucial phase in the oviposition sequence seems to be the external inspection, during which poor and high-quality host plants are probably discriminated. Chemical information on bud surface is likely to be determinant in this process.

Alternative oviposition tactics inZygonyx torridus(Kirby) (Odonata: Libellulidae): modes and sequential flexibility

Zygonyx torridus inhabits waterfalls, rapids and riffle sections. Males patrol over these sites. After copulation the partners perform an extensive search while flying in tandem over a wide range. Behavioural studies in Mauritius 1997 and 2014 showed that there is considerable plasticity in oviposition behaviour. Three main modes could be distinguished: (A) egg-laying in tandem during flight; (B) the female placing the eggs while dipping in flight without physical contact with the male; and (C) the female placing the eggs when settled without physical contact with the male. On several occasions two modes, and in a single case all three types, were observed within one oviposition sequence. In odonates, such a high degree of plasticity in reproductive behaviour was not reported previously.

Potential sources of intra-population variation in the overwintering strategy of painted turtle (Chrysemys picta) hatchlings.

Many temperate animals spend half their lives in a non-active, overwintering state, and multiple adaptations have evolved to enable winter survival. One notable vertebrate model is Chrysemys picta, whose hatchlings display dichotomous overwintering strategies: some hatchlings spend their first winter aquatically after nest emergence in the autumn, whereas others overwinter terrestrially within their natal nest with subsequent emergence in the spring. The occurrence of these strategies varies among populations and temporally within populations; however, factors that determine the strategy employed by a nest in nature are unknown. We examined potential factors that influence intra-population variation in the overwintering strategy of C. picta hatchlings over two winters in Algonquin Park, Ontario. We found that environmental factors may be a trigger for the hatchling overwintering strategy: autumn-emerging nests were sloped towards the water and were surrounded by a relatively higher percentage of bare ground compared with spring-emerging nests. Autumn-emerging hatchlings were also relatively smaller. Overwintering strategy was not associated with clutch oviposition sequence, or mammalian or avian predation attempts. Instead, autumn emergence from the nest was associated with the direct mortality threat of predation by sarcophagid fly larvae. Body condition and righting response, measured as proxies of hatchling fitness, did not differ between overwintering strategies. Costs and benefits of overwintering aquatically versus terrestrially in hatchling C. picta are largely unknown, and have the potential to affect population dynamics. Understanding winter survival has great implications for turtle ecology, thus we emphasize areas for future research on dichotomous overwintering strategies in temperate hatchling turtles.

Trajectories of Reproductive Effort inColeomegilla maculataandHippodamia convergens(Coleoptera: Coccinellidae) Respond to Variation in Both Income and Capital

Lady beetles such as Coleomegilla maculata DeGeer and Hippodamia convergens Guerin-Meneville have been categorized as income breeders because egg maturation depends on resources available during reproduction. However, capital resources acquired during larval feeding influence reproductive success via effects on adult body size and other traits. We produced three sizes of beetles by varying larval access to food and subjected mated females to alternating periods of food surplus and deficit. Both species exhibited temporal variation in clutch size that reflected changes in income, the amplitude of fluctuations being greater in H. convergens. Egg mass in C. maculata appeared to increase as a fixed function of oviposition sequence but also was affected by maternal body size, whereas H. convergens egg mass fluctuated more in response to food supply. Fertility was largely unaffected by income fluctuation but appeared constrained by capital, especially in H. convergens. Dynamic changes in reproductive effort (daily mass of eggs/female mass at emergence) mirrored changes in clutch size, the amplitude of fluctuations being greater in H. convergens, the species with higher reproductive effort. Generally, large females compensated for income fluctuations better than small females, likely because of their greater capital and possibly an ability to consume larger meals when food was available. The greater sensitivity to income observed in H. convergens likely reflects a higher degree of aphid-specificity compared with the more generalist C. maculata because effective exploitation of ephemeral aphid outbreaks would favor rapid reproductive responses to changes in food supply.

Cryptic maternal effects in Hippodamia convergens vary with maternal age and body size

AbstractMaternal effects can mold progeny phenotypes in various ways and may constitute ecological adaptations. By examining the effect of oviposition sequence on progeny produced by different size classes of female ladybird beetles (produced by controlling larval access to food), we show that maternal signals can change through adult life and alter the developmental programs of progeny, ostensibly to synchronize their life histories with predictable resource dynamics, thus maximizing maternal fitness. We also show that female body size, as determined by larval food supply, interacts with female age to influence progeny fitness. When fed ad libitum as adults, small females reared with limited food access laid fewer, smaller eggs than large females reared with ad libitum food access. Maternal body size interacted with oviposition sequence to influence progeny development, but the latter had greater impact. Eggs laid later by medium and large females hatched faster than those laid earlier, larvae fed longer in the fourth instar, their pupation period was shorter, total developmental time was reduced, and adults emerged with greater mass, most notably daughters. Oviposition sequence effects on progeny from small mothers were non‐significant for total developmental time and progeny mass. Only large mothers increased egg size over time and egg mass was not consistently correlated with developmental parameters, indicating that progeny phenotype was impacted by other, more cryptic, maternal signals. Such signals appear costly, as food limitation during development constrained not only fecundity and egg size but also maternal ability to manipulate progeny phenotype. The production of faster‐developing offspring that mature to larger sizes late in the oviposition cycle may be adaptive for exploitation of ephemeral aphid outbreaks with predictable dynamics of prey abundance and competition.

Pollinating fig wasp Ceratosolen solmsi adjusts the offspring sex ratio to other foundresses

Local mate competition theory predicts that offspring sex ratio in pollinating fig wasps is female-biased when there is only one foundress, and increased foundress density results in increased offspring sex ratio. Information of other foundresses and clutch size have been suggested to be the main proximate explanations for sex ratio adjustment under local mate competition. Our focus was to show the mechanism of sex ratio adjustment in a pollinating fig wasp, Ceratosolen solmsi Mayr, an obligate pollinator of the functionally dioecious fig, Ficus hispida Linn., with controlled experiments in the field. First, we obtained offspring from one pollinator and offspring at different oviposition sequences, and found that offspring sex ratio decreased with clutch size, and pollinators produced most of their male offspring at the start of bouts, followed by mostly females. Second, we found that offspring sex ratio increased with foundress density, and pollinators did adjust their offspring sex ratio to other females in the oviposition patches. We suggest that when oviposition sites are not limited, pollinators will mainly adjust their offspring sex ratio to other foundresses independent of clutch size changes, whereas adjusting clutch size may be used to adjust sex ratio when oviposition sites are limited.

A preliminary histological investigation of gall induction in an unconventional galling system

In an unusual case involving a candidate biological control agent, the histologically complex stem galls of the weevil, Rhinusa pilosa (Coleoptera: Curculionidae) on yellow toadflax (Linaria vulgaris), are rapidly induced during oviposition and reach full size by larval hatch. To investigate gall induction, the oviposition behavior of R. pilosa was described. We experimentally disrupted ovipositing weevils at three key points in the oviposition sequence and compared host-plant tissue responses post disruption, to what occurs during normal gall induction using histological methods. De novo xylem production, intercellular spaces in the cortex, and hyperplasia and hypertrophy of the procambium and pith parenchyma surrounding the egg were some of the tissue- and cellular-level modifications observed only 3–5 days after normal oviposition. Normal gall development was not observed after any of the oviposition disruption treatments, although some of the cellular and tissue responses resembled those found after undisrupted oviposition. Feeding by the female during oviposition canal formation induced wound meristem and callus tissue formation, but no other modifications consistent with gall formation. When females were disrupted about 20 s into oviposition, a homogenously dense substance was observed, which was suspected to be ovipositional fluid. There was minor stem swelling 10 days later and histologically, periclinal cell divisions, de novo xylem, and pith cells with numerous stained plastids were observed as in normal gall development, thus suggesting that ovipositional fluid plays a role in gall induction.

Moving your sons to safety: galls containing male fig wasps expand into the centre of figs, away from enemies.

Figs are the inflorescences of fig trees (Ficus spp., Moraceae). They are shaped like a hollow ball, lined on their inner surface by numerous tiny female flowers. Pollination is carried out by host-specific fig wasps (Agaonidae). Female pollinators enter the figs through a narrow entrance gate and once inside can walk around on a platform generated by the stigmas of the flowers. They lay their eggs into the ovules, via the stigmas and styles, and also gall the flowers, causing the ovules to expand and their pedicels to elongate. A single pollinator larva develops in each galled ovule. Numerous species of non-pollinating fig wasps (NPFW, belonging to other families of Chalcidoidea) also make use of galled ovules in the figs. Some initiate galls, others make use of pollinator-generated galls, killing pollinator larvae. Most NPFW oviposit from the outside of figs, making peripherally-located pollinator larvae more prone to attack. Style length variation is high among monoecious Ficus spp. and pollinators mainly oviposit into more centrally-located ovules, with shorter styles. Style length variation is lower in male (wasp-producing) figs of dioecious Ficus spp., making ovules equally vulnerable to attack by NPFW at the time that pollinators oviposit.We recorded the spatial distributions of galled ovules in mature male figs of the dioecious Ficus hirta in Southern China. The galls contained pollinators and three NPFW that kill them. Pollinators were concentrated in galls located towards the centre of the figs, NPFW towards the periphery. Due to greater pedicel elongation by male galls, male pollinators became located in more central galls than their females, and so were less likely to be attacked. This helps ensure that sufficient males survive, despite strongly female-biased sex ratios, and may be a consequence of the pollinator females laying mostly male eggs at the start of oviposition sequences.

Larval Competition BetweenAphidius erviandPraon volucre(Hymenoptera: Braconidae: Aphidiinae) inMacrosiphum euphorbiae(Hemiptera: Aphididae)

Interspecific competition between parasitoid larvae may influence the size, structure, and stability of the population, leading to a reduction in total parasitism and thus restricting the pest control. Aphidius ervi (Haliday) and Praon volucre (Haliday) are endoparasitoids that possess a wide host range and present considerable potential for the biological control of the aphid Macrosiphum euphorbiae (Thomas). The larval competition between A. ervi and P. volucre, and the possible intrinsic competitive superiority of one of the parasitoids in M. euphorbiae, have been studied. In single parasitism experiments, mated parasitoid females (n=10) were maintained individually in contact with M. euphorbiae hosts (n=30) inside petri dishes containing lettuce leaf discs and maintained in environmental chamber at 22 ± 1°C, 70 ± 10% RH, and 12-h photophase. The multiple parasitism experiments consisted of exposing single parasitized aphids (n=120) to the second parasitoid species. Two oviposition events were performed with a 4-h interval between them, namely the following: sequence A (oviposition by A. ervi, followed by P. volucre) and sequence B (oviposition by P. volucre, followed by A. ervi). Oviposition sequence A generated 24 A. ervi and 55 P. volucre adults, whereas oviposition sequence B generated 23 and 49 adults. P. volucre is an intrinsically superior competitor compared with A. ervi, and the use of the two species simultaneously may result in competitive exclusion and influence the stability of the parasitoid population.

The mechanism of sex ratio adjustment in a pollinating fig wasp.

Sex ratio strategies in species subject to local mate competition (LMC), and in particular their fit to quantitative theoretical predictions, provide insight into constraints upon adaptation. Pollinating fig wasps are widely used in such studies because their ecology resembles theory assumptions, but the cues used by foundresses to assess potential LMC have not previously been determined. We show that Liporrhopalum tentacularis females (foundresses) use their clutch size as a cue. First, we make use of species ecology (foundresses lay multiple clutches, with second clutches smaller than first) to show that increases in sex ratio in multi-foundress figs occur only when foundresses are oviposition site limited, i.e. that there is no direct response to foundress density. Second, we introduce a novel technique to quantify foundress oviposition sequences and show, consistent with the theoretical predictions concerning clutch size-only strategies, that they produce mainly male offspring at the start of bouts, followed by mostly females interspersed by a few males. We then discuss the implications of our findings for our understanding of the limits of the ability of natural selection to produce 'perfect' organisms, and for our understanding of when different cue use patterns evolve.

Host discrimination and interspecific competition of Trissolcus nigripedius and Telenomus gifuensis (Hymenoptera: Scelionidae), sympatric parasitoids of Dolycoris baccarum (Heteroptera: Pentatomidae)

Trissolcus nigripedius Nakagawa and Telenomus gifuensis Ashmead (Hymenoptera: Scelionidae) are solitary egg parasitoids of Dolycoris baccarum L. (Heteroptera: Pentatomidae), a polyphagous seed-sucking bug of agricultural crops. Field examinations revealed that the two parasitoids are the most common species, but only a single species emerge from a host egg mass. To explain this observation we tested two hypotheses of interspecific host discrimination and asymmetry in competitive interaction between Tr. nigripedius and Te. gifuensis. Trissolcus nigripedius and Te. gifuensis could discriminate host egg pre-parasitized by either self or conspecific like other scelionid parasitoids that use external mark on host eggs. When provided with host eggs pre-parasitized by each other, both Tr. nigripedius and Te. gifuensis multiparasitized 94% and 100% of the host eggs without interspecific host discrimination, respectively. Interestingly, from the multiparasitized eggs irrespective of oviposition sequence, progeny of Te. gifuensis always survive better than Tr. nigripedius. Telenomus gifuensis is superior in immature competition probably due to shorter egg incubation period after oviposition, hence progeny of Te. gifuensis become first instar faster than that of Tr. nigripedius. However, adult Tr. nigripedius is always superior competitor in possessing and guarding the host eggs even after oviposition against Te. gifuensis. Therefore, the asymmetry in competitive interaction between Tr. nigripedius and Te. gifuensis may explain the emergence of a single species from a host egg mass in the field in spite of no interspecific host discrimination.

Does Host Value Influence Female Aggressiveness, Contest Outcome and Fitness Gain in Parasitoids?

AbstractIntraspecific competition for resources is common in animals and may lead to physical contests. Contest outcomes and aggressiveness can be influenced by the resource holding potential of contestants but also by their perception of the resource value (RV). Competitors may assess resource quality directly (real RV) but may also estimate it according to their physiological status and their experience of the habitat quality (subjective RV). In this article, we studied contests between females of the solitary parasitoidPachycrepoideus vindemmiaeRondani (Hymenoptera: Pteromalidae) when exploiting simultaneously a host, aDelia radicumL. (Diptera: Anthomyiidae) pupa. We tested the effect of factors modifying host value on the occurrence of agonistic behaviours, contest outcomes and host exploitation. The factors tested were: the quality of the previous habitat experienced by females, female egg load, host parasitism status and the stage reached by the owner female in her behavioural oviposition sequence. Females successfully protected their host against intruders during its exploitation, but not after oviposition, and their aggressiveness did not seem to be influenced by their perception of the RV. The fact that the host is subsequently parasitized by the opponent females appears to mainly depend on the host selectiveness of females.