Why is there no impact of the host species on the cold tolerance of a generalist parasitoid?

For generalist parasitoids such as those belonging to the Genus Aphidius, the choice of host species can have profound implications for the emerging parasitoid. Host species is known to affect a variety of life history traits. However, the impact of the host on thermal tolerance has never been studied. Physiological thermal tolerance, enabling survival at unfavourable temperatures, is not a fixed trait and may be influenced by a number of external factors including characteristics of the stress, of the individual exposed to the stress, and of the biological and physical environment. As such, the choice of host species is likely to also have implications for the thermal tolerance of the emerging parasitoid. The current study aimed to investigate the effect of cereal aphid host species (Sitobion avenae, Rhopalosiphum padi and Metopolophium dirhodum) on adult thermal tolerance, in addition to sex and size, of the aphid parasitoids Aphidius avenae, Aphidius matricariae and Aphidius rhopalosiphi. Results revealed no effect of host species on the cold tolerance of the emerging parasitoid, as determined by CTmin and Chill Coma, for all parasitoid species. Host species significantly affected the size of the emerging parasitoid for A. rhopalosiphi only, with individuals emerging from R. padi being significantly larger than those emerging from S. avenae, although this did not correspond to a difference in thermal tolerance. Furthermore, a significant difference in the size of male and female parasitoids was observed for A. avenae and A. matricariae, although, once again this did not correspond to a difference in cold tolerance. It is suggested that potential behavioural thermoregulation via host manipulation may act to influence the thermal environment experienced by the wasp and thus wasp thermal tolerance and, in doing so, may negate physiological thermal tolerance or any impact of the aphid host

Early life nutritional quality effects on adult memory retention in a parasitic wasp

Nutritional quality during early life can affect learning ability and memory retention of animals. Here we studied the effect of resource quality gained during larval development on the learning ability and memory retention of 2 sympatric strains of similar genetic background of the parasitoid Trichogramma brassicae: one uninfected and one infected by Wolbachia. Wolbachia is a common arthropod parasite/mutualistic symbiont with a range of known effects on host fitness. Here we studied, for the first time, the interaction between resource quality and Wolbachia infection on memory retention and resource acquisition. Memory retention of uninfected wasps was significantly longer when reared on high quality hosts when compared to low quality hosts. Furthermore, uninfected wasps emerging from high quality hosts showed higher values of protein and triglyceride than those emerging from low quality hosts. In contrast, the memory retention for infected wasps was the same irrespective of host quality, although retention was significantly lower than uninfected wasps. No significant effect of host quality on capital resource amount of infected wasps was observed, and infected wasps displayed a lower amount of protein and triglyceride than uninfected wasps when reared on high quality hosts. This study suggests that the nutritional quality of the embryonic period can affect memory retention of adult wasps not infected by Wolbachia. However, by manipulating the host’s obtained capital resource amount, Wolbachia could enable exploitation of the maximum available resources from a range of hosts to acquire suitable performance in complex environments

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Effects of three insecticides on adult bionomics of the parasitoid Encarsia formosa

Pesticides can negatively affect many life history traits of natural enemies. In this study, we studied the effects of three insecticides with different modes of action on the bionomics of Encarsia formosa, a parasitoid of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Buprofezin (800 mg (a.i.)/L) and pyriproxyfen (50 mg (a.i.)/L) were selected among IGRs, while fenpropathrin (250 mg (a.i.)/L) was selected from the Pyrotheroids. Adults of E. formosa were treated via exposure to residues of insecticides on leaf discs. Our results revealed that buprofezin and pyriproxyfen did not affect longevity and fecundity, while fenpropathrin significantly reduced the longevity and fecundity of treated wasps. Results of logistic regression revealed that control, buprofezin- and pryproxyphen-treated E. formosa was a function of host density and followed a type II functional response. In contrast, E. formosa treated by fenpropathrin showed a type III functional response. Estimated attack rate for buprofezin and pyriproxyfen did not differ significantly from the control, whereas fenpropathrin-treated wasps showed a lower attack rate than the control. According to the obtained results, handling time of fenpropathrin-treated wasps was significantly higher (4.57 ± 0.5) than the control (2.83 ± 0.35). Our results showed that the maximum parasitism rate achieved by control wasps was 8.39, while the rate for buprofezin-, pyriproxyfen- and fenpropathrin-treated wasps was 6.99, 7.69 and 5.25, respectively. Overall, results suggest that buprofezin and pyriproxyfen can be used in an integrated pest management programme or biological control programme without destructive effects on the efficiency of this natural enemy in green houses

Wolbachia impairs post-eclosion host preference in a parasitoid wasp

Host preference behavior can result in adaptive advantages with important consequences for the fitness of individuals. Hopkin’s host-selection principle (HHSP) suggests that organisms at higher trophic levels demonstrate a preference for the host species on which they developed during their own larval stage. Although investigated in many herbivorous and predatory insects, the HHSP has, to our knowledge, never been tested in the context of insects hosting selfish endosymbiotic passengers. Here, we investigated the effect of infection with the facultative bacterial symbiont Wolbachia on post-eclosion host preference in the parasitoid wasp Trichogramma brassicae (Hymenoptera: Trichogrammatidae). We compared host preference in Wolbachia-infected individuals and uninfected adult female parasitoids after rearing them on two different Lepidopteran hosts, namely the flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) or the grain moth Sitotroga cerealella (Lepidoptera: Gelechiidae) in choice and no choice experimental design (n = 120 wasps per each choice/no choice experiments). We showed that in T. brassicae, Wolbachia affects the post-eclosion host preference of female wasps. Wolbachia-infected wasps did not show any host preference and more frequently switched hosts in the laboratory, while uninfected wasps significantly preferred to lay eggs on the host species they developed on. Additionally, Wolbachia significantly improved the emergence rate of infected wasps when reared on new hosts. Altogether, our results revealed that the wasp’s infection with Wolbachia may lead to impairment of post-eclosion host preference and facilitates growing up on different host species. The impairment of host preference by Wolbachia may allow T. brassicae to shift between hosts, a behavior that might have important evolutionary consequences for the wasp and its symbiont

Effect of interference and exploitative competition on associative learning by a parasitoid wasp a mechanism for ideal free distribution?

International audienceCompetition among foraging individuals of the same species occurs for several resources including, but not limited to, food, mates, nesting sites and, in parasitoid wasps, hosts. Individuals should therefore adapt their resource exploitation decisions accordingly and learning ability has been shown to be used in intraspecific competition situations to optimize fitness. We investigated the effect of interference and exploitative competition on aversive learning of a parasitoid wasp Venturia canescens (Hymenoptera Ichneumonidae) as a model. We studied the effect of the presence of one to five competitors and of prior competitors, that is, the presence of parasitized hosts, on olfactory learning of wasps based on a Pavlovian conditioning system. We found that the odour of peppermint, which was previously positively associated with the reward of an oviposition, was rejected by females that experienced this odour while exploiting a patch of unparasitized hosts in the presence of conspecific females. Unexpectedly, the number of competitors in cases of interference did not increase the level of aversion to the peppermint odour. Thus conditioned stimuli previously encountered during the exploitation of a patch of parasitized hosts were rejected when females oviposited in the presence of unparasitized hosts. Our results suggest that intraspecific competition, by interference and by exploitation, acts as motivation for females to avoid stimuli related to competition; this may explain how an ideal free distribution can be reached by learning processes. © 201

Does Wolbachia infection affect decision-making in a parasitic wasp?

International audienceVarious physiological effects of Wolbachia infection have been reported in invertebrates, but the impact of this infection on behavior and the consequences of these behavioral modifications on fitness have rarely been studied. Here, we investigate the effect of Wolbachia infection on the estimation of host nutritive resource quality in a parasitoid wasp. We compare decision-making in uninfected and Wolbachia-infected strains of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) on patches containing either fresh or old host eggs. For both strains, fresh eggs were better hosts than older eggs, but the difference was smaller for the infected strain than for the uninfected strain. Oviposition behavior of uninfected wasps followed the predictions of optimal foraging theory. They behaved differently toward high- vs. low-quality hosts, withmore hosts visited andmore ovipositions, fewer high-quality hosts used for feeding or superparasitism, and a sex ratio that was morebiased toward females in patches containing high-quality hosts than in patches containing low-quality ones. Uninfected wasps also displayed shorter acceptance and rejection times in high-quality hosts than in hosts of lower quality. In contrast, infected wasps were less efficient in evaluating the nutritive quality of the host (fresh vs. old eggs) and had a reduced ability to discriminate between unparasitized and parasitized hosts. Furthermore, they needed more energy and therefore engaged in host feeding more often. This study highlights possible decision-making manipulation by Wolbachia, and we discuss its consequences forWolbachia fitness

Poor adult nutrition impairs learning and memory in a parasitoid wasp

International audienceAnimals have evolved cognitive abilities whose impairment can incur dramatic fitness costs. While malnutrition is known to impact brain development and cognitive functions in vertebrates, little is known in insects whose small brain appears particularly vulnerable to environmental stressors. Here, we investigated the influence of diet quality on learning and memory in the parasitoid wasp Venturia canescens. Newly emerged adults were exposed for 24 h to either honey, 20% sucrose solution, 10% sucrose solution, or water, before being conditioned in an olfactory associative learning task in which an odor was associated to a host larvae (reward). Honey fed wasps showed 3.5 times higher learning performances and 1.5 times longer memory retention than wasps fed sucrose solutions or water. Poor diets also reduced longevity and fecundity. Our results demonstrate the importance of early adult nutrition for optimal cognitive function in these parasitoid wasps that must quickly develop long-term olfactory memories for searching suitable hosts for their progeny

Wolbachia manipulate fitness benefits of olfactory associative learning in a parasitoid wasp

International audienceUpon encountering a host, a female parasitoid wasp has to decide whether to learn positive or negative cues related to a host. The optimal female decision will depend on the fitness costs and benefits of learned stimuli. Reward quality is positively related to the rate of behavioral acquisition in processes such as associative learning. Wolbachia, an endosymbiotic bacterium, often plays an impressive role in the manipulation of its arthropod host’s biology. Here we studied the responses of two natural Wolbachia infected/uninfected Trichogramma brassicae populations to theoretically high- and low- reward values during a conditioning process and the consequences of their responses in terms of memory duration. According to our results, uninfected wasps showed an attraction response to high value rewards, but showed aversive learning in response to low value rewards. Memory span of uninfected wasps after conditioning by low-value rewards was significantly shorter compared to high-value rewards. As our results revealed, responses to high quality hosts will bring more benefits (bigger size, increased fecundity and enhanced survival) compared to low-quality hosts for uninfected wasps. Infected wasps were attracted to conditioned stimuli with the same memory duration after conditioning by both types of hosts. This was linked to the fact that parasitoids emerging from both types of hosts present the same life-history traits. Therefore, these hosts represent the same quality reward for infected wasps. According to obtained results it can be concluded that Wolbachia manipulates the learning ability of its host resulting in the wasp responding to all reward values similarly

Biosynthesis of Silver Nanoparticles Using Pine Pollen and Evaluation of the Antifungal Efficiency

Background: Nanoparticles have been applied to medicine, hygiene, pharmacy and dentistry, and will bring significant advances in the prevention, diagnosis, drug delivery and treatment of disease. Green synthesis of metal nanoparticles has a very important role in nanobiotechnology, allowing production of non-toxic and eco-friendly particles. Objectives: Green synthesis of silver nanoparticles (AgNPs) was studied using pine pollen as a novel, cost-effective, simple and non-hazardous bioresource. The antifungal activity of the synthesized AgNPs was investigated in vitro. Materials and Methods: Biosynthesis of AgNPs was conducted using pollen of pine (as a novel bioresource) acting as both reducing and capping agents. AgNPs were characterized using UV-visible spectroscopy, X-ray diffraction and transmission electron microscopy. In evaluation for antifungal properties, the synthesized AgNPs represented significant in vitro inhibitory effects on Neofusicoccum parvum cultures. Results: Pine pollen can mediate biosynthesis of colloidal AgNPs with an average size of 12 nm. AgNPs were formed at 22°C and observed to be highly stable up to three months without precipitation or decreased antifungal property. AgNPs showed significant inhibitory effects against Neofusicoccum parvum. Conclusion: The first report for a low-cost, simple, well feasible and eco-friendly procedure for biosynthesis of AgNPs was presented. The synthesized AgNPs by pine pollen were nontoxic and eco-friendly, and can be employed for large-scale production. The nanoparticles showed strong effect on quantitative inhibition and disruption of antifungal growth