Parasitoid Aphidius Ervi Research Articles

Presence of less-preferred hosts of the aphid parasitoids Aphidius ervi and Praon volucre reduces parasitism efficiency

Parasitoids are characterized by a defined range of hosts, either more specialist or generalist. Under natural conditions, females may encounter different host species on the same plant or in the same location. In this case, their preference for one host could influence their choice. However, the presence of less suitable hosts may also affect their choice and, in some cases, may reduce their interest in a patch where both preferred and less preferred hosts are available. The aim of the present study was to test the consequences of the simultaneous presence of three cereal aphids (Sitobion avenae Fabricius, Metopolophium dirhodum Walker, and Rhopalosiphum padi Linnaeus) on the parasitism by two of their parasitoids, Aphidius ervi Haliday and Praon volucre Haliday. Firstly, in the no-choice experiment, A. ervi parasitized on S. avenae at a significantly higher rate as compared to M. dirhodum, whereas no parasitism on R. padi was observed. P. volucre parasitized the three species of cereal aphids with a significant preference for S. avenae. Interestingly, when two or three host species were offered simultaneously in the same quantity to pairs of parasitoids, the level of parasitism was less than that observed for one host species alone. This observation exhibits a distractive effect on non-host species, from the defense mechanism of a non-suitable host or from the perception of bad quality patches. These results raise the question of the practical application of inundative release of parasitoids for biocontrol when several hosts are available simultaneously.

The aphid Acyrthosiphon pisum exhibits a greater survival after a heat shock when parasitized by the wasp Aphidius ervi

The pea aphid Acyrthosiphon pisum is a common pest of many species of legumes and its parasitoid Aphidius ervi is regarded as a successful biocontrol agent. In this study, we report a greater survival rate of parasitized aphids compared with unparasitized ones, after exposure to a very high temperature (39°C for 30min). After the heat shock, the survival of unparasitized aphids decreases according to their age at the heat shock treatment, suggesting a different adaptation of the aphid life stage to the different microclimatic conditions they experience. Survival of parasitized aphids does not change according to the time of the heat shock treatment, but it is always significantly higher compared with the unparasitized ones. Parasitized aphids are very quickly subjected to a wide range of physiological modifications and the observed increased survival could be a consequence of these modifications before the heat shock treatment. The possible explanations as well as the possible adaptive nature of the observed phenomenon are discussed.

Unintended effects of a Phytophtora-resistant cisgenic potato clone on the potato aphid Macrosiphum euphorbiae and its parasitoid Aphidius ervi

Genetically modified (GM) plants may show unintended differences compared to the original varieties, due to the modification process. Such differences might in some cases affect non-target organisms linked to the crop into an agro-ecosystem. In this paper, we aimed to study interactions of two blight-resistant GM potato clones with the aphid species Macrosiphum euphorbiae Thomas, a non-target arthropod frequently feeding on potato plants and one of the major pests of that crop. One of the potato events used in our experiments caused an increased fertility of the aphids in the first generation, and consequently, a positive effect on the growth of the aphid population was estimated. When a second generation of the aphid was reared on potato leaves of the same GM event, differences in aphid fertility were no longer observed. Behavioural studies conducted in a wind tunnel using the aphid parasitoid Aphidius ervi Haliday indicated that neither of the two tested GM varieties had a significant effect on the attractiveness of potato plants towards the parasitoid. In planta tests proved to be sensitive protocols to detect unintended effects on a non-target arthropod; experimental results, however, indicate that these effects are not expected to be biologically relevant in this tritrophic system, if these GM events become available for commercial use in the future.

Light Environments Differently Affect Parasitoid Wasps and their Hosts’ Locomotor Activity

In natural environments, organisms must adapt to changing light conditions. Significant research has been done on diurnal pollinating insects’ vision. However, little is known on parasitoid insects. Here, we studied how locomotor activity of the parasitoid wasp Aphidius ervi and its main host, the pea aphid Acyrthosiphon pisum, is affected under controlled artificial illumination. Using LEDs of 5 different wavelengths (361, 450, 500-600, 626 and 660 nm), we created different artificial light spectra that parasitoids and host aphids can encounter in natural environment including leaf-shade and direct sunlight. We found that pea aphid probability of walking depended on interactions between illumination, developmental stage and genotype as expressed in clonal variation. Artificial light intensity did not affect the parasitoid’s probability of walking as opposed to wavelength, and activity depended on the sex of individuals. Males were more active than females under all monochromatic wavelength spectra tested. Virgin females were much less active under the artificial leaf-shade illumination and artificial sunlight, as compared to males and mated females. Delay before flight for females was favored by sunlight illumination whereas the light environment did not affect flight delay for males. We demonstrated that locomotor activity of A. pisum (walking) and of A. ervi (walking and flight) vary according to the light environment. This study should help develop better understanding of the effects of illumination on host-parasitoid interactions, which in turn may help control insect pest populations.

Nectar bacteria affect life history of a generalist aphid parasitoid by altering nectar chemistry

Abstract Nectar is a crucial energy resource that strongly mediates the interactions between plants and animal pollinators or plant defenders. Previous research has shown that nectar is frequently colonized by microorganisms, most commonly bacteria and yeasts, which can have a strong impact on nectar chemistry. However, at present little is known about the effects of microorganisms on the fitness of animals feeding on nectar. We used three nectar bacteria representing different metabolic groups (Asaia sp., Lactococcus sp. and Rosenbergiella sp.) and the common generalist aphid parasitoid Aphidius ervi (Haliday; Hymenoptera: Braconidae) to test the hypothesis that different nectar‐dwelling bacteria affect nectar consumption and insect longevity differently by altering the chemistry of nectar. Bacteria significantly affected nectar chemistry by altering its acidity, sugar and amino acids composition/concentration and by adding compounds synthesized by the microbes. Although inoculation with bacteria did not affect nectar consumption, a significant difference in insect longevity was observed. The impact on longevity was species specific, with Lactococcus being beneficial and Asaia having a detrimental effect. Bacteria have a strong impact on nectar chemistry and changes in nectar chemistry may not only influence the foraging behaviour of flower‐visiting animals and impact on plant fitness, but also influence the fitness of nectar‐consuming organisms. As effects were species dependent, changes in nectar chemistry induced by different bacteria may have contrasting effects on the interactions between plants and insects. It is therefore essential to know how different microbes alter nectar chemistry to understand the relationships between plants, nectar‐inhabiting microbes and nectar‐consuming animals. A plain language summary is available for this article.

Trichoderma harzianum enhances tomato indirect defense against aphids.

Many fungal root symbionts of the genus Trichoderma are well-known for their beneficial effects on agronomic performance and protection against plant pathogens; moreover, they may enhance protection from insect pests, by triggering plant resistance mechanisms. Defense barriers against insects are induced by the activation of metabolic pathways involved in the production of defense-related plant compounds, either directly active against herbivore insects, or exerting an indirect effect, by increasing the attraction of herbivore natural enemies. In a model system composed of the tomato plant, the aphid Macrosiphum euphorbiae and the parasitoid Aphidius ervi, plant metabolic changes induced by Trichoderma harzianum and their effects on higher trophic levels have been assessed. T. harzianum T22 treatments induce a primed state that upon aphid attacks leads to an increased attraction of aphid parasitoids, mediated by the enhanced production of volatile organic compounds (VOCs) that are known to induce Aphidius ervi flight. Transcriptome sequencing of T22-treated plants infested by aphids showed a remarkable upregulation of genes involved in terpenoids biosynthesis and salicylic acid pathway, which are consistent with the observed flight response of A. ervi and the VOC bouquet profile underlying this behavioral response.

Aphid symbionts and endogenous resistance traits mediate competition between rival parasitoids.

Insects use endogenous mechanisms and infection with protective symbionts to thwart attacks from natural enemies. Defenses that target specific enemies, however, potentially mediate competition between rivals and thereby impact community composition. Following its introduction to North America to control pea aphids (Acyrthosiphon pisum), the parasitoid Aphidius ervi competitively displaced other parasitoids, except for the native Praon pequodorum. The pea aphid exhibits tremendous clonal variation in resistance to A. ervi, primarily through infection with the heritable bacterial symbiont Hamiltonella defensa, although some symbiont-free aphid genotypes encode endogenous resistance. Interestingly, H. defensa strains and aphid genotypes that protect against A. ervi, provide no protection against the closely related, P. pequodorum. Given the specificity of aphid defenses, we hypothesized that aphid resistance traits may contribute to the continued persistence of P. pequodorum. We conducted multiparasitism assays to determine whether aphid resistance traits mediate internal competition between these two solitary parasitoid species, but found this was not the case; P. pequodorum was the successful internal competitor across lines varying in susceptibility to A. ervi. Next, to determine whether resistance traits influence competitive interactions resulting in the stable persistence of P. pequodorum, we established replicated cages varying in the proportion of resistant aphids and recorded successful parasitism for each wasp species over time. As expected, A. ervi outcompeted P. pequodorum in cages containing only susceptible aphids. However, P. pequodorum not only persisted, but was the superior competitor in populations containing any proportion (20–100%) of resistant aphids (20–100%). Smaller scale, better replicated competition cage studies corroborated this finding, and no-competition and behavioral assays provide insight into the processes mediating competition. Genetic variation, including that acquired via infection with protective symbionts, may provide a supply of hosts susceptible only to particular enemies, mediating competition with effects on community richness and stability.

Susceptibility of Macrosiphum euphorbiae to the parasitoid Aphidius ervi: larval development depends on host aphid genotype

AbstractThe potato aphid, Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae: Macrosiphini), is a common polyphagous aphid in Europe and North America. However, the factors influencing potato aphid dynamics and susceptibility to natural enemies are largely undescribed, particularly in relation to facultative endosymbiotic bacteria, which can provide protection against parasitism and disease in some aphid species. This study investigated whether potato aphid susceptibility to one of its principal natural enemies, the parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae: Aphidiinae), varied in relation to aphid genotype and/or endosymbiont presence. Parasitism and aphid fitness assays were conducted on clonal lineages of aphids, harbouring their natural endosymbiont infections, collected over 3 years from separate geographic locations. Parasitized aphids were dissected to quantify parasitoid oviposition, larval development, and mummification. Amongst the 19 clonal lines of M. euphorbiae tested, seven aphid genotypes were identified, and 11 lines harboured one or both of the facultative endosymbionts Hamiltonella defensa Moran et al. and Regiella insecticola Moran et al.; H. defensa infections were associated exclusively with two of the seven M. euphorbiae genotypes. Parasitism resistance was detected in clonal lines belonging to a single aphid genotype and resulted from failure of parasitoid eggs to develop into larvae rather than failure of the parasitoid to oviposit. Contrary with studies of several other aphid species, there was little evidence that H. defensa provided strong protection to M. euphorbiae from parasitism by A. ervi. Furthermore, there were no clear fitness costs to the aphid associated with parasitism resistance or with H. defensa infection. The two M. euphorbiae genotypes in which H. defensa occurred, which included the resistant genotype, exhibited faster development, higher survival, and greater fecundity than the other five aphid genotypes. These findings suggest that biological control of M. euphorbiae using A. ervi alone could exacerbate pest problems by selecting for the fittest parasitism‐resistant genotypes.

The outcome of competition between two parasitoid species is influenced by a facultative symbiont of their aphid host

Summary Symbiotic bacteria can act to protect their host against natural enemies. Where this protection is asymmetric against different natural enemies, protection conferred by symbionts has the potential to mediate interactions between natural enemies, as well as between enemies and the host. In pea aphids (Acyrthosiphon pisum), resistance against parasitoid wasps can be conferred by facultative symbiotic bacteria. We investigated whether the outcome of competition between two parasitoid species can be influenced by the presence of a defensive symbiont in the host. We exposed pea aphids from a single clonal line, with and without a strain of the protective endosymbiont Hamiltonella defensa, to multiparasitism by the parasitoid wasps Aphelinus abdominalis (Aphelinidae) and Aphidius ervi (Braconidae), and recorded the outcome. The symbiont strain is known to impact A. abdominalis more strongly than A. ervi. We found that the presence of a strain of the protective endosymbiont H. defensa can reverse the outcome of competition between the wasps. In the absence of the symbiont, A. ervi gains very little success when attacking an aphid previously parasitized by A. abdominalis. However, where the aphids possessed the symbiont, A. abdominalis did not develop successfully, and the success rate of A. ervi was significantly increased. Our results show that defensive facultative symbionts are able to influence community interactions at the trophic level above their host. A lay summary is available for this article.

Combining lacewings and parasitoids for biological control of foxglove aphids in sweet pepper

AbstractThe role of natural enemy diversity in biological pest control has been debated in many studies, and understanding how interactions amongst predators and parasitoids affect herbivore populations is crucial for pest management. In this study, we assessed the individual and combined use of two species of natural enemies, the parasitoid Aphidius ervi Haliday, and the predatory brown lacewing Micromus variegatus (Fabricius), on their shared prey, the foxglove aphid, Aulacorthum solani (Kaltenbach), on sweet pepper. We hypothesized that the presence of intraguild predation (IGP) and predator facilitation (through induced aphid dropping behaviour) might have both negative and positive effects on aphid control, respectively. Our greenhouse trial showed that overall, the greatest suppression of aphids occurred in the treatment with both the parasitoid and the lacewing. While the combination of lacewings and parasitoids significantly increased aphid control compared to the use of parasitoids alone, the effect was not significantly different to the treatment with only predators, although there was a clear trend of enhanced suppression. Thus, the combined effects of both species of natural enemies were between additive and non‐additive, suggesting that the combination is neither positive nor negative for aphid control. High levels of IGP, as proven in the laboratory, were probably compensated for by the strong aphid suppression provided by the lacewings, whether or not supplemented with some level of predator facilitation. For aphid management over a longer time scale, it might still be useful to combine lacewings and parasitoids to ensure stable and resilient aphid control.

Adult Parasitoids of Honeydew-Producing Insects Prefer Honeydew Sugars to Cover their Energetic Needs.

To meet their carbohydrate requirements, adult parasitoids exploit a broad range of sugar resources, including floral and extrafloral nectar and honeydew. Although honeydew might be the predominant sugar source, especially in agricultural systems, it often is nutritionally inferior to sugar sources like nectar. Given its broad availability, it may be expected that sugar-feeding insects have evolved specialized adaptations to deal with this typically inferior sugar source. This would apply especially to organisms that have a close association with honeydew producers. Here, we hypothesized that parasitoids of honeydew-producing insects should show a pronounced response to sugars, such as fructose, sucrose, melezitose, and trehalose, and to a lesser extent glucose. To test this hypothesis, we investigated sugar consumption, feeding behavior and survival of the aphid parasitoid Aphidius ervi on several sugars (equiweight solutions). Our results show that A. ervi adults consumed typical honeydew sugars (sucrose, fructose, trehalose, and melezitose) the most, while consuming considerably less glucose or melibiose. Rhamnose, which does not occur in aphid honeydew, was not, or was only marginally, consumed. When different sugars were provided at the same time, A. ervi adults preferred sucrose or fructose over glucose or melezitose. Furthermore, pre-exposure to sucrose or fructose significantly reduced subsequent intake of glucose, suggesting an acquired distaste for glucose after being previously exposed to highly preferred sugars such as sucrose and fructose. Altogether, this study shows that A. ervi adults prefer sugars (fructose, melezitose, trehalose, and sucrose) that are overrepresented in aphid honeydew and show a lower preference to one (glucose) that is underrepresented in honeydew.

Loss of host fidelity in highly inbred populations of the parasitoid wasp Aphidius ervi (Hymenoptera: Braconidae)

Inbreeding frequently reduces the fitness of organisms, but little is known about how this phenomenon can affect the biological control. Host fidelity provides an adaptive advantage to aphid parasitoids, allowing females to find their aphid host more quickly in heterogeneous environments. This trait is mediated by the learning of signals, mainly chemical cues emitted from the host in which parasitoids developed (natal). This article is aimed at studying whether host fidelity can be altered after many generations of inbreeding reproduction in caged laboratory populations, for which host preference and fitness parameters were measured in the parasitoid wasp Aphidius ervi. Also, the effect of the natal/non-natal hosts was studied, using parasitoids originated from the pea aphid (Acyrthosiphon pisum) and the grain aphid (Sitobion avenae). We observed a loss of host fidelity in the studied A. ervi populations, irrespective of their natal aphid host, which contrasts with previous reports showing preference for natal hosts in outbred laboratory populations. The loss of host fidelity is discussed in terms of the origin of populations; the sex ratio was strongly biased toward males and long-time maintenance under laboratory conditions. Our results highlight the need for controlling the genetic diversity of caged parasitoids before they are released into fields, as a long period of inbreeding could negatively affect the biological control.

Plant and insect microbial symbionts alter the outcome of plant–herbivore–parasitoid interactions: implications for invaded, agricultural and natural systems

Summary Understanding how soil microbial communities influence plant interactions with other organisms, and how this varies with characteristics of the interacting organisms, is important for multiple systems. Solanum spp. are a suitable model for trophic interactions in studies of agricultural and natural systems and can also provide useful corollaries in invaded systems. This study examined the influence of soil mutualist arbuscular mycorrhizal (AM) fungi on growth of different Solanum types fed on by the potato aphid, Macrosiphum euphorbiae, in relation to the presence of the aphid facultative endosymbiont Hamiltonella defensa. Four Solanum types comprising two wild species, S. berthaultii and S. polyadenum, and two accessions of S. tuberosum, were grown with or without AM fungi and infested with one of four clonal lines of a single M. euphorbiae genotype (two with and two without H. defensa). Two experiments were conducted to (i) characterize plant responses to AM fungi and aphids and (ii) assess whether soil AM fungi could influence the success of the parasitoid wasp Aphidius ervi when attacking aphids reared on each Solanum type. In both experiments, similar patterns of plant biomass were observed in relation to AM fungal and aphid treatments. Solanum biomass depended on plant type and aphid infection with H. defensa. Plants exposed to aphids harbouring H. defensa had smaller root biomass, and therefore total plant biomass, compared to plants infested with H. defensa‐free aphids. M. euphorbiae performance varied with aphid clonal line, Solanum type and the presence of AM fungi. Parasitoid success, measured as the proportion of aphids from which a wasp emerged, was highest from aphids that had fed on plants colonized by AM fungi, although this result also varied with Solanum type and aphid clonal line. Synthesis. The presence of soil AM fungi, combined with within‐species plant and insect variation in key traits, can have subtle – but significant – effects on plant fitness and insect success. This study highlights the importance of exploring genotypic variation in plant and pest responses to soil microbiota to identify suitable biocontrol options.

The influence of a parasitoid's response to temperature on the performance of a tri‐trophic food web

1. Food web interactions are complex and can respond to environmental changes in unpredictable ways that do not necessarily equate to the individual responses of each of the components of the food web.2. Biomass can be used to evaluate the productivity of the three individual trophic levels, in the form of the Net Generational Productivity (NGP) and the performance of the entire food web with the newly developed tri‐trophic food web performance ratio (ϕ3t).3. These parameters were used to evaluate the performance of nine plant‐based tri‐trophic food webs composed of: potato, Solanum tuberosum L. and two cultivars of bell pepper Capsicum annuum L; three biotypes of the aphid Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and the parasitoid wasp Aphidius ervi (Haliday) (Hymenoptera: Braconidae).4. The NGP showed that the thermal window for biomass productivity for each trophic level is different and is reduced by approximately 4 °C with respect to the inferior level. Aphidius ervi had the smallest thermal window for biomass productivity and development.5. The present results showed that the performance (ϕ3t) of the tested food webs is influenced in a top‐down fashion, where the intra‐specific variation of the food web, namely the host plant, played a major role in the productivity of each of the subsequent trophic levels.6. The ϕ3t suggested that exposure to high and low temperatures might severely affect the effectiveness of A. ervi as a biocontrol agent of the aphid M. euphorbiae in bell pepper and potato crops.

Field evaluation of synthetic aphid sex pheromone in enhancing suppression of aphid abundance by their natural enemies

The effects of lures containing aphid sex pheromone components (4aS,7S,7aR)-nepetalactone and (1R,4aS,7S,7aR)-nepetalactol on abundance of pea aphid, Acyrthosiphon pisum Harris, aphid parasitoids, predators and hyperparasitoids in alfalfa fields were investigated over three years. Although aphid abundance was variable among years, pheromone lure treatment significantly decreased aphid abundance. Among natural enemies of the aphids, only parasitism by the aphid parasitoids Aphidius ervi Haliday and Praon barbatum Mackauer was affected by pheromone lure treatment, with parasitism rates being significantly increased. In contrast, no pheromone lure effects on abundance were detected for predacious species and hyperparasitoids. These results indicate that slow-release formulations of synthetic aphid sex pheromone can attract primary aphid parasitoids and enhance their ability to suppress aphid abundance in the field, and that negative effects on biological control by hyperparasitoids and intraguild predation are not promoted by pheromone lure treatment.

Extracellular matrix degradation via enolase/plasminogen interaction: Evidence for a mechanism conserved in Metazoa.

While enolase is a ubiquitous metalloenzyme involved in the glycolytic pathway, it is also known as a multifunctional protein, since enolases anchored on the outer surface of the plasma membrane are involved in tissue invasion. We have identified an extracellular enolase (Ae-ENO) produced by the teratocytes, embryonic cells of the insect parasitoid Aphidius ervi. We demonstrate that Ae-ENO, although lacking a signal peptide, accumulates in cytoplasmic vesicles oriented towards the cell membrane. Ae-ENO binds to and activates a plasminogen-like molecule inducing digestion of the host tissue and thereby ensuring successful parasitism. These results support the hypothesis that plasminogen-like proteins exist in invertebrates. Interestingly the activation of a plasminogen-like protein is mediated by a mechanisms involving the surface enolase/fibrinolytic system considered, until now, exclusive of vertebrates, and that instead is conserved across species. To our knowledge, this is the first example of enolase mediated Plg-like binding and activation in insect cells, demonstrating the existence of an ECM degradation process via a Plg-like protein in invertebrates.

Signatures of genetic bottleneck and differentiation after the introduction of an exotic parasitoid for classical biological control

As biological invasions, intentional introductions often result in a loss of genetic diversity in the new founder populations. In classical biological control programs, natural enemies introduced into novel environments are likely to suffer from population bottlenecks. Unlike invasive populations, individuals for biological control are typically kept in quarantine during several generations before being released in the field. This procedure reduces further the effective population size of the introduced populations, which thus increases the effects of inbreeding and genetic drift, resulting in a greater loss of genetic diversity. This study addresses the genetic consequences of the introduction of the parasitoid wasp Aphidius ervi, a successful biocontrol agent of important aphid target-pests in Chile. This was assessed by examining the genetic diversity and differentiation at nuclear and mitochondrial genetic markers in terms of (1) the magnitude of the genetic diversity loss after 38 years of the introduction of A. ervi, (2) the current level of genetic differentiation between Chilean introduced populations and putative native populations from France, and (3) the genetic relationships and magnitude of the genetic diversity loss between introduced populations of A. ervi in Chile compared to those introduced in North America. The results provide evidence that parasitoid populations suffered the effects of a moderate genetic bottleneck during the introduction, showing further a strong geographical genetic differentiation between populations in the natal and novel environments. In addition mtDNA sequences analysis showed evidence of a single main event of introduction in Chile, unlike the North American situation, where there is evidence for multiple introductions. The significance of the loss of genetic diversity during introductions related to the success of parasitoids as biocontrol agents in classical biological control programs is discussed.

A facultative endosymbiont in aphids can provide diverse ecological benefits.

Ecologically important traits of insects are often affected by facultative bacterial endosymbionts. This is best studied in the pea aphid Acyrthosiphon pisum, which is frequently infected by one or more of eight facultative symbiont species. Many of these symbiont species have been shown to provide one ecological benefit, but we have little understanding of the range of effects that a single strain can have. Here, we describe the phenotypes conferred by three strains of the recently discovered bacterium known as X‐type (Enterobacteriaceae), each in their original aphid genotype which also carries a Spiroplasma symbiont. All comparisons are made between aphids that are coinfected with Spiroplasma and X‐type and aphids of the same genotype that harbour only Spiroplasma. We show that in all cases, infection with X‐type protects aphids from the lethal fungal pathogen Pandora neoaphidis, and in two cases, resistance to the parasitoid Aphidius ervi also increases. X‐type can additionally affect aphid stress responses – the presence of X‐type increased reproduction after the aphids were heat‐stressed. Two of the three strains of X‐type are able to provide all of these benefits. Under benign conditions, the aphids tended to suffer from reduced fecundity when harbouring X‐type, a mechanism that might maintain intermediate frequencies in field populations. These findings highlight that a single strain of a facultative endosymbiont has the potential to provide diverse benefits to its aphid host.

Patch Experience Changes Host Acceptance of the Aphid Parasitoid Aphidius ervi

We investigated patch quality assessment by the parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae) when exploiting colonies of the lettuce aphid Nasonovia ribisnigri Mosley (Hemiptera: Aphididae). Three host patches of different qualities were sequentially offered to a naive female parasitoid. High quality patches (HQ) consisted of 20 N. ribisnigri reared on susceptible lettuce; low quality patches (LQ) consisted of 20 N. ribisnigri reared on partially resistant lettuce and mixed quality patches (MQ) consisted of equal numbers (10) of aphids reared on both lettuce types. Parasitized aphids were reared until parasitoid emergence; number of mummies and sex ratio were noted. On the first host patch encountered, the mean number of A. ervi mummies produced was significantly higher for HQ host patches (X ± SD; 7.1 ± 5.0) than for LQ host patches (3.8 ± 4.5). This suggests that female A. ervi do not need prior experience to assess patch quality; females probably using an innate estimate of patch quality when encountering a first host patch. This initial patch quality assessment can be modified with experience. When females encountered a MQ patch, they kept their exploitation level constant on the following patch, whatever its quality. Females increased their level of host acceptance on the third patch when three LQ patches were offered successively; accepting low-quality hosts could be preferable when better hosts are not currently available in the habitat. These results suggest that A. ervi females behave in a manner consistent with a Bayesian updating process when foraging for hosts.

Does sex-biased dispersal account for the lack of geographic and host-associated differentiation in introduced populations of an aphid parasitoid?

Host recognition and use in female parasitoids strongly relies on host fidelity, a plastic behavior which can significantly restrict the host preferences of parasitoids, thus reducing the gene flow between parasitoid populations attacking different insect hosts. However, the effect of migrant males on the genetic differentiation of populations has been frequently ignored in parasitoids, despite its known impact on gene flow between populations. Hence, we studied the extent of gene flow mediated by female and male parasitoids by assessing sibship relationships among parasitoids within and between populations, and its impact on geographic and host-associated differentiation in the aphid parasitoid Aphidius ervi. We report evidences of a high gene flow among parasitoid populations on different aphid hosts and geographic locations. The high gene flow among parasitoid populations was found to be largely male mediated, suggested by significant differences in the distribution of full-sib and paternal half-sib dyads of parasitoid populations.