Idiobiont Parasitoids Research Articles

New approaches to the control of Neodiprion sertifer (Geoffroy, 1785) (Hymenoptera: Diprionidae)

Neodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae) is a major pest on Pinus spp. in Europe. In this study, new control methods were tried to control N. sertifer. The effectiveness of Bauveria bassiana (Nostalgist, Bb %1.5 1 x 10 8 kob /ml min, 250 ml/100L), azadirachtin (Nimbecidine, 0.3g azadirachtin/l, 500 ml/da-100L; Nimiks4.5, 40g azadirachtin /l, 200 ml/100L; Neem Azal ®-T/S, 10 g azadirachtin /l, 300ml/100L) and spinosad (Oread, 480 g spinosad/l, 10ml/100L) was tested on N. sertifer larvae. In addition, the effect of the idiobiont parasitoid Bracon hebetor (Say) (Hymenoptera: Braconidae) venom was evaluated. Bauveria bassiana, spinosad and azadirachtin were applied to the larvae by spraying method. Different numbers of B. hebetor females (1-5 females) were also tested on N. sertifer larvae. All experiments were carried out at 25 ± 1°C, 60-70% relative humidity and 16L:8D h photoperiod. After B. bassiana application, the survival rates were 71.66% and 61.66% at the 6th day and 7th day. The maximum efficacy was obtained with azadirachtin in Nimiks 4.5 (40 g azadirachtin/l). The highest mortality (100.0%) was found at 24 h after the application of spinosad (10ml/100l). The most effective combination of B. hebetor female venom on N. sertifer larvae is 5 females and 7 days duration. The study shows that spinosad, azadirachtin and B. hebetor female venom can achieve effective control of N. sertifer larvae.

Parasitism Features of a Fig Wasp of Genus Apocrypta (Pteromalidae: Pteromalinae) Associated with a Host Belonging to Ficus Subgenus Ficus

Non-pollinating fig wasps (NPFWs), particularly long-ovipositored Sycoryctina wasps, exhibit a high species specificity and exert complex ecological effects on the obligate mutualism between the plant genus Ficus and pollinating fig wasps. Apocrypta is a genus of NPFWs that mostly interacts with the Ficus species under the subgenus Sycomorus, and the symbiosis case between Apocrypta and F. pedunculosa var. mearnsii, a Ficus species under subgenus Ficus, is unique. As fig's internal environments and the wasp communities are distinct between the two subgenera, we addressed the following two questions: (1) Are the parasitism features of the Apocrypta wasp associated with F. pedunculosa var. mearnsii different from those of other congeneric species? (2) Is this Apocrypta species an efficient wasp that lives in its unique host? Our observation revealed that this wasp is an endoparasitic idiobiont parasitoid, as most congeneric species are, but developed a relatively long ovipositor. Furthermore, the relationships of the parasitism rate versus the pollinator number, the fig wall, and the sex ratio of the pollinator, respectively, showed that it possessed a higher parasitism ability than that of other congeners. However, its parasitism rate was low, and thus it was not an efficient wasp in its habitat. This difference between parasitism ability and parasitism rate might be a consequence of its oviposition strategy and the severe habitat conditions. These findings may also provide insights into the mechanism to maintain the interaction between the fig tree and the fig wasp community.

Strong effects of food quality on host life history do not scale to impact parasitoid efficacy or life history

Parasitoids are small insects, (e.g., small wasps or flies) that reproduce by laying eggs on or within host arthropods. Parasitoids make up a large proportion of the world’s biodiversity and are popular agents of biological control. Idiobiont parasitoids paralyze their hosts upon attack and thus are expected to only target hosts large enough to support offspring development. Host resources generally impact host attributes and life histories including size, development, and life span. Some argue slow host development in response to resource quality increases parasitoid efficacy (i.e., a parasitoid’s ability to successfully reproduce on or within a host) due to longer host exposure to parasitoids. However, this hypothesis is not always supported and does not consider variation in other host traits in response to resources that may be important for parasitoids (e.g., variation in host size is known to impact parasitoid efficacy). In this study we test whether trait variation within host developmental stages in response to host resources is more important for parasitoid efficacy and life histories than trait variation across host developmental stages. We exposed seed beetle hosts raised on a food quality gradient to mated female parasitoids and measured the number of hosts parasitized and parasitoid life history traits at the scale of host stage- and age-structure. Our results suggest host food quality does not cascade to impact idiobiont parasitoid life histories despite large food quality effects on host life history. Instead, variation in host life histories across host developmental stages better predicts parasitoid efficacy and life histories, suggesting finding a host in a specific instar is more important for idiobiont parasitoids than finding hosts on or within higher quality resources.

Transcriptional regulation of host insulin signaling pathway genes controlling larval development by Microplitis manilae parasitization.

Idiobiont parasitoids using other insects as hosts sabotage the host growth and development to ensure their offspring survival. Numerous studies have discovered that insect development is subtly regulated by the conserved insulin signaling pathway. However, little is known about how wasp parasitization disrupts host development controlled by the insulin signaling pathway. Here we address this study to determine the effect of wasp parasitism on host Spodoptera frugiperda development using the idiobiont parasitoid Microplitis manilae as a model. Upon M. manilae parasitization, the body weight, body length, and food consumption of host insect were dramatically reduced compared to the unparasitized S. frugiperda. We next identified the core genes involved in host insulin signaling pathway and further analyzed the domain organizations of these genes. Phylogenetic reconstruction based on the insulin receptors clustered S. frugiperda together with other noctuidae insects. In the latter study, we profiled the expression patterns of host insulin signaling pathway genes in response to M. manilae parasitization at 2, 24,and 48 h, significant decreases in mRNA levels were recorded in S. frugiperda larvae upon 24and 48 h parasitization. These current findings substantially add to our understanding of the physiological interaction between parasitoid and host insects, thus contributing to revealing the molecular mechanism of parasitic wasps regulating host development.

Effects of male age, body size and mating status on female mate preference and offspring sex ratio in Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae)

Mate choice is one of the main components of sexual selection, with females usually considered to be the selective sex. Male status is an important factor that affects female choice and to a large extent female mating preference. Pachycrepoideus vindemmiae (Rondani) (Hymenoptera: Pteromalidae) is an important solitary ectoparasitic idiobiont parasitoid that attacks several fly species and thus can be used as a biological control agent. We explored the influence of male status on mate selection, fecundity and offspring sex ratio. The results show that (1) P. vindemmiae females prefer to mate with young and large males and tended to choose males with only one mating experience; (2) the age, body size and mating status of males did not significantly affect female fecundity; and (3) the proportion of male offspring was larger when females mated with older, small and more often mated males. These results show that P. vindemmiae females prefer to mate with young and large males that had mated few times, and that mating with these males results in a higher proportion of female offspring. In addition, this study also indicates the way of rearing P. vindemmiae that produce more female offspring for use as biological control agents.

Anti-oxidative, genotoxic and mutagenic effects of idiobiont, endoparasitoid, Pimpla turionellae L. (Hymenoptera: Ichneumonidae) venom on its host Galleria mellonella L. (Lepidoptera: Pyralidae)

Parasitoid species regulate the nutritional and physiological states of their hosts to ensure their eggs and larvae successfully develop inside the host. Due to the insecticidal and paralyzing properties of venoms from idiobiont parasitoids, parasitic wasps are important natural enemies of several insect pests. For this purpose, in this report, we investigated the oxidative, genotoxic, and mutagenic potential of venom from Pimpla turionellae L. (Hymenoptera: Ichneumonidae) on the laboratory host Galleria mellonella L. (Lepidoptera: Pyralidae). The insecticidal assay showed the LC50 and LC99 values of endoparasitoid venom for G. mellonella pupal stage to be 0.44 µg and 1.17 µg in 2 µl insect saline buffer, respectively. According to the mechanical stimulus–response (MSR) assay, pupal paralysis increased significantly within four hours post-injection at LC50 and higher venom concentrations. Envenomation by LC10, LC30, and LC50 concentrations of endoparasitoid venom and parasitism reduced the activities of superoxide dismutase, catalase, and glutathione-S-transferase enzymes and the level of malondialdehyde in the hemolymph of host pupae 1, 2 and 4 h post-treatment. On the other hand, comet and micronucleus assays displayed that, envenomation by the effective concentrations of P. turionellae venom-induced concentration and time-dependent DNA and chromosomal damages in host hemocytes. Therefore, these data indicated that envenomation by P. turionellae induces anti-oxidative stress, genotoxicity, and mutagenicity which alter the hosts’ physiological state to create a suitable host environment for the successful development of their progeny. In conclusion, we suggest that this study could provide useful information for bioinsecticidal potential of idiobiont wasp venom for sustainable integrated pest management programs.

Exotic generalist arthropod biological control agents: need to improve environmental risk assessment to ensure safe use

Exotic generalist arthropod biological control agents (GABCAs) have been historically marginalized in classical and augmentative biological control due to their broad diet breadth, but an increasing demand for a more sustainable pest control is encouraging their reconsideration. This special issue compiles a collection of papers revealing that risks of several exotic GABCAs were overestimated, not all generalists are riskier than specialists and their environmental risk assessment (ERA) solely based on exposure analysis is inadequate. Three papers demonstrated that generalists were not involved in predicted non-target interactions: generalist idiobiont parasitoids probably do not exhibit interference competition with each other, an oligophagous exotic egg-larval koinobiont parasitoid does not compete with a native larval koinobiont, and an invasive generalist predator does not escape from its enemies. Two innovative methods for selecting non-target species are proposed, one based on existing food web data to predict indirect non-target effects, and the other on functional traits to predict competition with native natural enemies. Also a comprehensive GABCA-ERA method is proposed that integrates adverse effect analysis to the ‘conventional’ exposure analysis. The method was scrutinized by two studies: one suggesting that it could have resulted in faster and less costly decisions on two exotic generalists in New Zealand, and the other suggesting that eight exotic GABCAs released in Argentina might potentially reduce native natural enemies. We hope this special issue will stimulate the continued advance in the biosafety research of GABCAs so their safe use does not stagnate.

Reprograming of epigenetic mechanisms controlling host insect immunity and development in response to egg-laying by a parasitoid wasp.

Parasitoids are insects that use other insects as hosts. They sabotage host cellular and humoral defences to promote the survival of their offspring by injecting viruses and venoms along with their eggs. Many pathogens and parasites disrupt host epigenetic mechanisms to overcome immune system defences, and we hypothesized that parasitoids may use the same strategy. We used the ichneumon wasp Pimpla turionellae as a model idiobiont parasitoid to test this hypothesis, with pupae of the greater wax moth Galleria mellonella as the host. We found that parasitoid infestation involves the suppression of host immunity-related effector genes and the modulation of host genes involved in developmental hormone signalling. The transcriptional reprogramming of host genes following the injection of parasitoid eggs was associated with changes in host epigenetic mechanisms. The introduction of parasitoids resulted in a transient decrease in host global DNA methylation and the modulation of acetylation ratios for specific histones. Genes encoding regulators of histone acetylation and deacetylation were mostly downregulated in the parasitized pupae, suggesting that parasitoids can suppress host transcription. We also detected a strong parasitoid-specific effect on host microRNAs regulating gene expression at the post-transcriptional level. Our data therefore support the hypothesis that parasitoids may favour the survival of their offspring by interfering with host epigenetic mechanisms to suppress the immune system and disrupt development.

Venomics of the ectoparasitoid wasp Bracon nigricans

BackgroundVenom is one of the most important sources of regulation factors used by parasitic Hymenoptera to redirect host physiology in favour of the developing offspring. This has stimulated a number of studies, both at functional and “omics” level, which, however, are still quite limited for ectophagous parasitoids that permanently paralyze and suppress their victims (i.e., idiobiont parasitoids).ResultsHere we present a combined transcriptomic and proteomic study of the venom of the generalist idiobiont wasp Bracon nigricans, an ectophagous larval parasitoid of different lepidopteran species, for which we recently described the host regulation strategy and the functional role of the venom in the induction of physiological changes in parasitized hosts. The experimental approach used led to the identification of the main components of B. nigricans venom involved in host regulation. Enzymes degrading lipids, proteins and carbohydrates are likely involved in the mobilization of storage nutrients from the fat body and may concurrently be responsible for the release of neurotoxic fatty acids inducing paralysis, and for the modulation of host immune responses.ConclusionThe present work contributes to fill the gap of knowledge on venom composition in ectoparasitoid wasps, and, along with our previous physiological study on this species, provides the foundation on which to develop a functional model of host regulation, based both on physiological and molecular data. This paves the way towards a better understanding of parasitism evolution in the basal lineages of Hymenoptera and to the possible exploitation of venom as source of bioinsecticidal molecules.

Impact of a shared sugar food source on biological control of Tuta absoluta by the parasitoid Necremnus tutae

Honeydew is a sugar-rich food source produced by sap-feeding insects, notably by major pests such as aphids and whiteflies. It is an important alternative food source for the adult stage of various key natural enemies (e.g., parasitoids), but it may be used also as food by agricultural pests. Necremnus tutae is an idiobiont parasitoid, and it is the most abundant larval parasitoid associated with the South American tomato pinworm, Tuta absoluta, in recently invaded European areas. The impact of N. tutae on T. absoluta populations was evaluated under greenhouse conditions with and without the presence of a honeydew producer, the aphid Macrosiphum euphorbiae. In addition, laboratory experiments were performed to evaluate the longevity of N. tutae and T. absoluta adults when fed with water, honey or honeydew produced by the aphid. In the greenhouse, N. tutae effectively reduced T. absoluta population by the end of the experiment, and this independently of the presence of the aphid; still the presence of M. euphorbiae led to delayed and reduced T. absoluta population peak when controlled by the parasitoid (there was a fourfold increase in parasitoid density in presence of aphid). The longevity of both N. tutae and T. absoluta females increased in the presence of honeydew (when compared to water only) under laboratory conditions; it hinted that honeydew could be used by an herbivore as T. absoluta. The interactions between the two phytophagous species showed contrasting effects, and this mostly independently of parasitoid presence. Tuta absoluta had no impact on aphid population dynamics. By contrast, the production of T. absoluta larvae was higher in the first part of the experiment as the adults lived longer (feeding on aphid honeydew) and produced more larvae. In the second part of the experiment, there were fewer T. absoluta larvae in the presence of the aphid, likely owing to resource competition and/or negative plant-mediated indirect interactions. We demonstrated that honeydew producers could impact parasitoid-host population dynamics both through direct and indirect interactions and that potential positive effects of a sugar food source toward a pest can be nullified in the long term by other negative effects occurring simultaneously.

Predators and parasitoids of the harlequin ladybird, Harmonia axyridis, in its native range and invaded areas

The harlequin ladybird Harmonia axyridis (Coleoptera: Coccinellidae) has rapidly spread in several continents over the past 30 years and is considered an invasive alien species. The success of H. axyridis as an invader is often attributed to weak control by natural enemies. In this paper, we provide an overview of current knowledge on predators and parasitoids of H. axyridis. The common feature of predators and parasitoids is that they directly kill exploited organisms. Currently available data show that H. axyridis, displaying a variety of chemical, mechanical, and microbiological anti-predator defenses, is usually avoided by predators. However, some birds and invertebrates can eat this ladybird without harmful consequences. The primary defenses of H. axyridis against parasitoids include immune response and physiological and nutritional unsuitability for parasitoid development. These defenses are probably relatively efficient against most ladybird parasitoids, but not against flies of the genus Phalacrotophora. The latter are idiobiont parasitoids and hence can evade the host’s immune response. Indeed, rates of parasitism of H. axyridis by Phalacrotophora in the Palaearctic region (both in the native range in Asia and in Europe) are relatively high. While strong evidence for enemy release on the invasive populations of H. axyridis is lacking, several cases of parasitoid acquisition have been recorded in Europe, North America, and South America. We conclude that enemy release cannot be excluded as a possible mechanism contributing to the spread and increase of H. axyridis in the early stages of invasion, but adaptation of parasitoids may lead to novel associations which might offset previous effects of enemy release. However, further work is required to elucidate the population-level effects of such interactions.

Development of a solitary koinobiont hyperparasitoid in different instars of its primary and secondary hosts

Parasitoid wasps are excellent organisms for studying the allocation of host resources to different fitness functions such as adult body mass and development time. Koinobiont parasitoids attack hosts that continue feeding and growing during parasitism, whereas idiobiont parasitoids attack non-growing host stages or paralyzed hosts. Many adult female koinobionts attack a broad range of host stages and are therefore faced with a different set of dynamic challenges compared with idiobionts, where host resources are largely static. Thus far studies on solitary koinobionts have been almost exclusively based on primary parasitoids, yet it is known that many of these are in turn attacked by both koinobiont and idiobiont hyperparasitoids. Here we compare parasitism and development of a primary koinobiont hyperparasitoid, Mesochorus gemellus (Hymenoptera: Ichneumonidae) in larvae of the gregarious primary koinobiont parasitoid, Cotesia glomerata (Hymenoptera: Braconidae) developing in the secondary herbivore host, Pieris brassicae (Lepidoptera: Pieridae). As far as we know this is the first study to examine development of a solitary primary hyperparasitoid in different stages of its secondary herbivore host. Pieris brassicae caterpillars were parasitized as L1 by C. glomerata and then these parasitized caterpillars were presented in separate cohorts to M. gemellus as L3, L4 or L5 instar P. brassicae. Different instars of the secondary hosts were used as proxies for different developmental stages of the primary host, C. glomerata. Larvae of C. glomerata in L5 P. brassicae were significantly longer than those in L3 and L4 caterpillars. Irrespective of secondary host instar, every parasitoid cluster was hyperparasitized by M. gemellus but all only produced male progeny. Male development time decreased with host stage attacked, whereas adult male body mass did not, which shows that M. gemellus is able to optimally exploit older host larvae in terms of adult size despite their decreasing mass during the pupal stage. Across a range of cocoon masses, hyperparasitoid adult male body mass was approximately 84% as large as primary parasitoids, revealing that M. gemellus is almost as efficient at exploiting host resources as secondary (pupal) hyperparasitoids.

Comparing Immature Development and Life History Traits in Two Coexisting Host-Feeding Parasitoids, Diglyphus isaea and Neochrysocharis formosa (Hymenoptera: Eulophidae)

Coexisting natural enemies that share a common host resource in the same guild usually exhibit variation in their life history traits, due to their need to share a similar ecological niche. In this study, we compared the immature development times and adult life history traits of two coexisting, host-feeding parasitoids, Diglyphus isaea Walker and Neochrysocharis formosa Westwood (Hymenoptera: Eulophidae), of which both attack larvae of the same agromyzid leafminers. These two species are both synovigenic, idiobiont parasitoids, whose adults consume host fluids (“host feeding”) and lay anhydropic eggs. Of the two, D. isaea has a larger body but little or no initial egg load, and engages in similar lifetime host-feeding events. However, it achieves higher fecundity, longer adult longevity, and higher host suppression ability than N. formosa, which has a smaller body and higher initial egg load. Although D. isaea engages in similar lifetime host-feeding events with N. formosa, all of its gains in life history traits per host-feeding event of D. isaea were larger than those of N. formosa. The age-specific fecundity and host mortality curves of N. formosa were more skewed in early life than those of D. isaea. In addition, the ovigeny index of N. formosa was negatively correlated to body size. Our results confirmed that two coexisting parasitoids, which share the same host resource, show different immature development patterns and life history traits, suggesting that different resource allocation mode could be a general rule of coexisting species sharing the same habitat or host.

Adult diet affects the life history and host-killing behavior of a host-feeding parasitoid

Neochrysocharis formosa (Westwood), an important biocontrol agent of agromyzid leafminers worldwide, is a host-feeding, idiobiont parasitoid. Female wasps have three types of host-killing behaviors: reproductive (parasitism), non-reproductive host feeding (host feeding), and host stinging without oviposition or feeding (host stinging). In this study, we compared the life history and host-killing behaviors of female parasitoids under four adult diets: starvation, hosts only, hosts plus honey (10%w/v honey solution), and honey only. Furthermore, we analyzed the host-feeding and oviposition preferences of adult females in the hosts-only and hosts-plus-honey treatments. Female parasitoids feeding on hosts had significantly increased longevity, higher fecundity, more host-stinging events, and caused a higher total host mortality than parasitoids in the starvation treatment. The honey supplement significantly increased longevity, fecundity, host-stinging events, and total host mortality, as well as average daily fecundity, but did not alter host-feeding events, host-stinging events, or daily total host mortality. However, the honey supplement did reduce the number of daily host-feeding events and induced a shift toward oviposition. Finally, we found that the non-reproductive host killing caused by host feeding and host stinging enhanced the control potential of N. formosa. These results should contribute to a better understanding of the biocontrol efficiency of destructive host feeders.

Vertical stratification of ichneumonid wasp communities: the effects of forest structure and life-history traits.

Parasitoid wasp communities of the canopy of temperate forests are still largely unexplored. Very little is known about the community composition of parasitoids between canopy and understory and how much of this difference is related to forest structure or parasitoid biological strategies. In this study we investigated upon the difference in the community composition of the parasitic wasps Ichneumonidae between canopy and understory in a lowland temperate forest in northern Italy. We used general linear models to test whether parasitic strategy modifies species vertical stratification and the effect of forest structure. We also tested differences in β-diversity between canopy and understory traps and over time within single forest layers. We found that stand basal area was positively related to species richness, suggesting that the presence of mature trees can influence local wasp diversity, providing a higher number of microhabitats and hosts. The ichneumonid community of the canopy was different from that of the understory, and the β-diversity analysis showed higher values for the canopy, due to a higher degree of species turnover between traps. In our analyses, the vertical stratification was different between groups of ichneumonids sharing different parasitic strategies. Idiobiont parasitoids of weakly or deeply concealed hosts were more diverse in the understory than in the canopy while parasitoids of spiders were equally distributed between the two layers. Even though the ichneumonid community was not particularly species-rich in the canopy of the temperate forests, the extension of sampling to that habitat significantly increased the number of species recorded.

Contrasting patterns of ovarian development and oogenesis in two sympatric host-feeding parasitoids, Diglyphus isaea and Neochrysocharis formosa (Hymenoptera: Eulophidae)

Diglyphus isaea (Walker) and Neochrysocharis formosa (Westwood) (Hymenoptera: Eulophidae) are common idiobiont parasitoids of leafminers attacking vegetable crops. They exhibit differing levels of synovigeny, and host feeding enhances their fecundity and longevity. The reproductive systems of these two parasitoids are typical of hymenopteran eulophids, consisting of two ovaries, each usually comprising three polytrophic meroistic ovarioles. Diglyphus isaea possesses two obvious oviduct accessory glands, which are absent in N. formosa. Both parasitoids underwent oosorption when starved, while feeding on host larvae promoted oogenesis and egg maturation. In both, oogenesis and vitellogenesis commenced on the first day of the pupal stage rather than after eclosion. Formation of ovarioles in D. isaea commenced 1 day earlier than in N. formosa. Mature eggs were rarely observed in ovaries of newly emerged D. isaea, but usually a few were present in N. formosa. When hosts (second–third instar Liriomyza sativae larvae) were provided, the number of mature eggs in D. isaea ovaries initially increased and then stabilized, while in N. formosa, the number first increased and then decreased. Diglyphus isaea had fewer but larger eggs than N. formosa did. Thus, synovigenic divergence begins at the pupal stage and may result in different life-history traits of adults.

The evolution of host associations in the parasitic wasp genus Ichneumon (Hymenoptera: Ichneumonidae): convergent adaptations to host pupation sites

BackgroundThe diversification of organisms with a parasitic lifestyle is often tightly linked to the evolution of their host associations. If a tight host association exists, closely related species tend to attack closely related hosts; host associations are less stable if associations are determined by more plastic traits like parasitoid searching and oviposition behaviour. The pupal-parasitoids of the genus Ichneumon attack a variety of macrolepidopteran hosts. They are either monophagous or polyphagous, and therefore offer a promissing system to investigate the evolution of host associations. Ichneumon was previously divided into two groups based on general body shape; however, a stout shape has been suggested as an adaptation to buried host pupation sites, and might thus not represent a reliable phylogenetic character.ResultsWe here reconstruct the first molecular phylogeny of the genus Ichneumon using two mitochondrial (CO1 and NADH1) and one nuclear marker (28S). The resulting phylogeny only supports monophyly of Ichneumon when Ichneumon lugens Gravenhorst, 1829 (formerly in Chasmias, stat. rev.) and Ichneumon deliratorius Linnaeus, 1758 (formerly Coelichneumon) are included. Neither parasitoid species that attack hosts belonging to one family nor those attacking butterflies (Rhopalocera) form monophyletic clades. Ancestral state reconstructions suggest multiple transitions between searching for hosts above versus below ground and between a stout versus elongated body shape. A model assuming correlated evolution between the two characters was preferred over independent evolution of host-searching niche and body shape.ConclusionsHost relations, both in terms of phylogeny and ecology, evolved at a high pace in the genus Ichneumon. Numerous switches between hosts of different lepidopteran families have occurred, a pattern that seems to be the rule among idiobiont parasitoids. A stout body and antennal shape in the parasitoid female is confirmed as an ecological adaptation to host pupation sites below ground and has evolved convergently several times. Morphological characters that might be involved in adaptation to hosts should be avoided as diagnostic characters for phylogeny and classification, as they can be expected to show high levels of homoplasy.

Functional response of the aphelinid parasitoid,Aphytis diaspidis:Effect of host scale species,Diaspidiotus perniciosusandHemiberlesia lataniae

Aphytis diaspidis Howard is an idiobiont parasitoid of the invasive (Diaspidiotus perniciosus Comstock) and usual (Hemiberlesia lataniae Signoret) hosts. The objectives were to study the effect of host scale species on functional response of A. diaspidis and to answer on the question raised whether the killing efficiency of this parasitoid against the invasive host will differ from that of usual host. The parasitoid showed no host species preference with a type II response when offered both hosts at densities of 10–50 insects per patch. The proportion of hosts parasitized exhibited the same characteristic curve for the parasitoid on both hosts: a wave form that appeared to be a composite of a decelerating (type II) response at low host density and an accelerating and a decelerating (type III) response at medium to high densities. I assume that egg limitation, and/or host feeding rather than parasitism may have induced the modified type II response. The number of host parasitized within a 48 h increased with host density with a maximum of 18.3 and 18.6 adults of D. perniciosus and H. lataniae, respectively. However, the proportion of host parasitized significantly decreased with host density. This implies that the wasp seems to be more affective in low host populations. This result has to be considered in rapid population control. Estimated handling times for parasitoid were 0.98 and 1.258 h and attack rates were 0.016 and 0.02 h−1 on H. lataniae and D. perniciosus, respectively. Theoretically, the maximum number of hosts that could be parasitized by a single female within 48 h was 38.16 and 48.97 of D. perniciosus and H. lataniae, respectively. The longer time in handling D. perniciosus by a parasitoid showed that the host has lower quality than the usual host, H. lataniae. The functional response results have to be considered in both mass rearing quality testing and biocontrol programs.

Parasitoid attack of the seed-feeding beetle Bruchus loti enhances the germination success of Lathyrus japonicus seeds

Hard seeds of some legume species can germinate after seed-feeding insects bore through the seed coat and consequently break seed dormancy. Larvae of bruchine beetles are the main seed feeders attacking many legume species. Boring of the hard seed coat by bruchine beetle larvae enhances the germination percentage of legume species, but consuming too much of a single seed may reduce the chances the seed will survive. We hypothesise that the early mortality of bruchine larvae due to parasitism contributes positively to seed germination because larvae are killed before consuming too large a quantity of the seed. Here, we tested this hypothesis using Lathyrus japonicus seeds and Bruchus loti, the main seed feeder attacking this plant. B. loti larvae were mainly parasitised by two species of idiobiont parasitoids—Pteromalus sp. and Dinarmus sp. The seeds from which Pteromalus wasps emerged germinated more successfully than did the seeds from which B. loti adults emerged. B. loti larvae parasitised by the two wasp species consumed the seeds less intensively than did unparasitised larvae. Thus, the results of experiments supported our hypothesis. However, the germination success varied significantly between the seeds from which Pteromalus and Dinarmus wasps emerged. The difference in the size of seeds the two wasp species chose for parasitism may have influenced the germination percentage.

Phenotypic plasticity and fitness in egg parasitoids

Several proxies can be used to estimate the fitness of egg parasitoids: size, longevity, fecundity, mating ability and vagility. All these proxies are positively correlated with the lifetime fitness gain of an individual. However, the phenotypic plasticity, which is the ability of a genotype to produce distinct phenotypes depending on environmental conditions, may alter the value of these proxies. Host related factors (host species and quality), competition and duration of development will influence the proxies expressed by a given phenotype. When the phenotype is modified by the temperature at which an individual develops, the resulting phenotype will vary based on the life history strategy of the parasitoid. While in koinobiont species an increase in size is positively correlated with longevity and fecundity, the reverse occurs with idiobiont parasitoids. Using size as a proxy could thus be misleading depending on the factors that influence the size of the adult.