Potencial regulador de parasitoides sobre poblaciones de Aphis gossypii Glover, 1877 (Hemiptera: Aphididae) en laboratorio, bajo condiciones semiáridas

This study aims to evaluate the regulatory potential of Lysiphlebus testaceipes and Aphidius matricariae over Aphis gossypii in semiarid laboratory conditions. Our results showed that the longevity of L. testaceipes females was significantly lower than A. matricariae ones. The daily mummification rate of aphid was more important for L. testaceipes than for A. matricariae and declined with parasitoids age. Overall, both the mummification rates and the emergence rates were the highest in L. testaceipes. A. matricariae offspring developed in a shorter time compared to L. testaceipes ones. The overall sex ratio did not vary according to parasitoid species. From our results L. testaceipes was more effective for the biological control of A. gossypii on potato in the semi-arid agro-ecosystems.Este estudio tiene como objetivo evaluar el potencial regulador de Lysiphlebus testaceipes y Aphidius matricariae sobre Aphis gossypii en condiciones de laboratorio semiáridas. Nuestros resultados mostraron que la longevidad de las hembras de L. testaceipes fue significativamente menor que la de A. matricariae. El porcentaje diario de momificación fue más importante para L. testaceipes que para A. matricariae y disminuyó con la edad de los parasitoides. En general, las tasas de momificación y de emergencia fueron más altas en L. testaceipes. La descendencia de A. matricariae se desarrolló en menos tiempo que la de L. testaceipes. La proporción sexual no varió respecto a las especies parasitoides. Con nuestros resultados, L. testaceipes fue más efectivo para el control biológico de A.&nbsp

Évolution spatiotemporelle de la diversité et du fonctionnement d'une guilde de parasitoïdes

Cette thèse porte sur l analyse des dimensions spatiale et temporelle du fonctionnement et de la diversité taxonomique et fonctionnelle d une guilde. Au sein d une guilde, les espèces exploitent un même type de ressources; pour cette raison, les niches écologiques fondamentales des membres d une guilde sont similaires et une relation de compétition interspécifique se met en place si la ressource partagée est limitante. Quatre questions principales sur le fonctionnement d une guilde ont été abordées : (1) à quelles échelles spatio-temporelles se structurent la guilde et les ressources exploitées, (2) quelles sont les influences respectives des filtres environnementaux et des interactions interspécifiques sur les traits fonctionnels des membres de la guilde, (3) quelle est la stratégie d exploitation de ressources d un membre de la guilde face à une faible disponibilité de ressources et (4) quel est l impact du contexte climatique sur la structure d une guilde et de son réseau trophique, et sur le degré de spécialisation écologique des espèces de la guilde sur la ressource. Le modèle biologique de cette étude a été une guilde de parasitoïdes de pucerons de céréales (Hymenoptera : Braconidae : Aphidiinae). Ces parasitoïdes s attaquent aux pucerons (Homoptera : Aphididae) inféodés aux céréales dans les agroécosystèmes. Les variations d abondance relative des parasitoïdes et de leurs hôtes ont été importantes aux échelles interrégionale et interannuelle, mais très faibles à l échelle intra-régionale. La divergence des traits fonctionnels des parasitoïdes s est maintenue sur trois régions et deux années, et le contexte local a influencé les traits de la guilde dans son ensemble. Pendant la saison hivernale, une période marquée par une faible densité de pucerons, le parasitoïde Aphidius rhopalosiphi a présenté des stratégies contrastées pour maximiser sa fitness en exploitant les hôtes Sitobion avenae et Rhopalosiphum padi, mais une forte spécialisation écologique sur le terrain a été observée en présence d une espèce compétitrice : Aphidius avenae. Cette présence a pu être corrélée à une hausse des températures hivernales.This thesis is an analysis of the spatial and temporal dimensions of the functioning and taxonomic and functional diversity of a guild. In a guild, species exploit the same type of resources; consequently, fundamental ecological niches of guild members are similar and an interspecific competitive relationship is established if shared resources are limiting. Four main questions on the functioning of a guild are addressed: (1) the spatiotemporal scales to which guilds the guild and its exploited resources are structures, (2) the respective weight of environmental filtering and interspecific interactions on the configuration of realized niches of guild members, (3) the strategy of resource exploitation in a guild member facing low resource availability and (4) the impact of climatic context on the structure of a guild and its food web, and the degree of specialisation on resources. The biological model chosen in this study was a cereal aphid parasitoid guild (Hymenoptera: Braconidae: Aphidiinae). Those parasitoids attack aphids (Homoptera: Aphididae) in agroecosystems, which are anthropised environments marked by high disturbance rates and in which host resources are variable in density and in quality. Relative abundance variations in parasitoids and in their hosts were considerable at interregional and interannual scales, but weak at the intra-regional scale. Functional trait divergence in parasitoids was maintained across three regions and two years, and regional and annual environmental contexts influenced guild traits as a whole. In winter, a period marked by low aphid density, the parasitoid Aphidius rhopalosiphi presented contrasted strategies to maximise fitness whilst exploiting Sitobion avenae and Rhopalosiphum padi hosts, but a high degree of ecological specialisation in the field was observed in the presence of a competitive species, Aphidius avenae. This presence was correlated to an increase in winter temperatures.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

Altruistic defence behaviours in aphids

Background: Altruistic anti-predatory behaviours pose an evolutionary problem because they are costly to the actor and beneficial to the recipients. Altruistic behaviours can evolve through indirect fitness benefits when directed toward kin. The altruistic nature of anti-predatory behaviours is often difficult to establish because the actor can obtain direct fitness benefits, or the behaviour could result from selfish coercion by others, especially in eusocial animals. Non-eusocial parthenogenetically reproducing aphids form colonies of clone-mates, which are ideal to test the altruistic nature of anti-predatory defence behaviours. Many aphids release cornicle secretions when attacked by natural enemies such as parasitoids. These secretions contain an alarm pheromone that alerts neighbours (clone-mates) of danger, thereby providing indirect fitness benefits to the actor. However, contact with cornicle secretions also hampers an attacker and could provide direct fitness to the actor. Results: We tested the hypothesis that cornicle secretions are altruistic by assessing direct and indirect fitness consequences of smearing cornicle secretions onto an attacker, and by manipulating the number of clone-mates that could benefit from the behaviour. We observed parasitoids, Aphidius rhopalosiphi, foraging singly in patches of the cereal aphid Sitobion avenae of varied patch size (2, 6, and 12 aphids). Aphids that smeared parasitoids did not benefit from a reduced probability of parasitism, or increase the parasitoids' handling time. Smeared parasitoids, however, spent proportionately more time grooming and less time foraging, which resulted in a decreased host-encounter and oviposition rate within the host patch. In addition, individual smearing rate increased with the number of clone-mates in the colony. Conclusions: Cornicle secretions of aphids were altruistic against parasitoids, as they provided no direct fitness benefits to secretion-releasing individuals, only indirect fitness benefits through neighbouring clone-mates. Moreover, the use of cornicle secretions was consistent with their altruistic nature, because the occurrence of this behaviour increased with the size of indirect fitness benefits, the number of clone-mates that can benefit. This study provides evidence for a case of kin-directed altruistic defence outside eusocial animals

Conditional Reduction of Predation Risk Associated with a Facultative Symbiont in an Insect

International audienceSymbionts are widespread among eukaryotes and their impacts on the ecology and evolution of their hosts are meaningful. Most insects harbour obligate and facultative symbiotic bacteria that can influence their phenotype. In the pea aphid Acyrthosiphon pisum, an astounding symbiotic-mediated phenotype has been recently observed: when infected with the symbiotic bacteria Rickettsiella viridis, young red aphid larvae become greener at adulthood and even darker green when co-infected with Rickettsiella viridis and Hamiltonella defensa. As body colour affects the susceptibility towards natural enemies in aphids, the influence of the colour change due to these facultative symbionts on the host survival in presence of predators was tested. Our results suggested that the Rickettsiella viridis infection may impact positively host survival by reducing predation risk. Due to results from uninfected aphids (i.e., more green ones attacked), the main assumption is that this symbiotic infection would deter the predatory ladybird feeding by reducing the profitability of their hosts rather than decreasing host detection through body colour change. Aphids coinfected with Rickettsiella viridis and Hamiltonella defensa were, however, more exposed to predation suggesting an ecological cost associated with multiple infections. The underlying mechanisms and ecological consequences of these symbiotic effects are discussed

Patch exploitation strategies of parasitic wasps under intraspecific competition. Behav Ecol.

The optimal residence time of a forager exploiting a resource patch in the absence of competitors has been much studied since the development of the marginal value theorem. However, several foragers are frequently observed exploiting the same patch simultaneously, and patch residence time has been surprisingly little studied in such competitive situations. The few theoretical models developed on this topic predict that foragers should engage in a war of attrition and stay in the patch longer than when foraging alone. We tested this prediction in Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae), a solitary parasitoid species in which females are known to defend the hosts they are exploiting via intraspecific fighting. By measuring the effect of direct (i.e., presence of conspecifics) and indirect (i.e., presence of already-parasitized hosts) competition on patch exploitation strategies, we revealed an apparent polymorphism of strategies. Indeed, in competitive situations, some members of the population tended to retreat almost immediately from the patch whereas other members tended to remain, further exploit the patch, and be more involved in interactions with conspecifics. The proportion of ''retreaters'' strongly depended on competition intensity and prior experience of competition. The forager's physiological state (age) also affects patch exploitation strategy and the intensity of interactions between competing females. Our results highlight the necessity for further theoretical studies that consider cases where contests between foragers are costly and take into account prior experience of competition and the forager's physiological state

Spatiotemporal variations in aphid-parasitoid relative abundance patterns and food webs in agricultural ecosystems

Understanding the stability of communities is fundamental in theoretical and applied ecology. Organisms atop trophic chains are particularly sensitive to disturbance, especially when they are dependent on a specific trophic resource subject to strong fluctuations in density and quality, which is the case of parasitoids. We investigated the (1) variability in spatiotemporal relative abundance patterns of a cereal aphid parasitoid community, determining at what scales such patterns vary in agrosystems. We also investigated whether (2) parasitoid relative abundances are strongly influenced by host relative abundances and if (3) different host species are exploited at distinct rates. Aphid parasitoid populations were monitored in three remote agricultural regions in France between 2010 and 2012. Five parasitoid species (Hymenoptera: Braconidae: Aphidiinae) and three aphid species (Hemiptera: Aphididae) were identified in each of those three regions. Fields sampled in one region in a single year exhibited similar relative abundance patterns, with aphid parasitoid communities varying across regions and years. All parasitoid species were able to exploit each monitored host species. Metopolophium dirhodum Wlk was consistently a more frequent species among parasitized aphids than among living aphids, indicating that this aphid species was exploited at a higher rate than the other two aphid species found (Sitobion avenae F and Rhopalosiphum padi L). Those findings suggest the cereal aphid-parasitoid network is not strictly determined by the intrinsic permanent environmental characteristics but partially varies from one year to another. The similarity in abundance patterns in different fields of a region in a given year suggests the existence of a mechanism allowing a rapid synchronisation of the relative abundance patterns at an intra-regional scale. This phenomenon could be useful in predicting host-parasitoid communities and bear important consequences for the ecosystem service provided by parasitoids

Influence of Microbial Symbionts on Plant–Insect Interactions

International audienceThere is growing evidence that microorganisms are important ‘hidden players’ in insect–plant interactions. Insect symbionts can directly affect these interactions by providing insects with key nutrients or by interfering with the plant to modulate food provisioning to insects and plant defences. Insect symbionts can also have indirect cascading ecological consequences at the community level through insect- and plant-mediated effects that include their impact on insect reproduction, on natural enemies of herbivores or on plant-associated microorganisms. Identification of symbiotic communities associated with insects, characterization of transmission and acquisition patterns as well as understanding of molecular mechanisms underlying these plant–insect–microbe interactions have important ecological and evolutionary consequences. This review highlights the excitement that surrounds these investigations and the promise they hold for a better understanding of the functional, ecological and evolutionary impacts of symbionts on plant–insect interactions, with implications and relevance for both applied and fundamental researches

Arts, Humanities, and Cultural Affairs Act: Section-By-Section Analysis (1976): Report 01

Microsatellite Ae33 sequence of Aphidius erv

Facultative Symbiont Infections Affect Aphid Reproduction

Some bacterial symbionts alter their hosts reproduction through various mechanisms that enhance their transmission in the host population. In addition to its obligatory symbiont Buchnera aphidicola, the pea aphid Acyrthosiphon pisum harbors several facultative symbionts influencing several aspects of host ecology. Aphids reproduce by cyclical parthenogenesis whereby clonal and sexual reproduction alternate within the annual life cycle. Many species, including the pea aphid, also show variation in their reproductive mode at the population level, with some lineages reproducing by cyclical parthenogenesis and others by permanent parthenogenesis. While the role of facultative symbionts has been well studied during the parthenogenetic phase of their aphid hosts, very little is known on their possible influence during the sexual phase. Here we investigated whether facultative symbionts modulate the capacity to produce sexual forms in various genetic backgrounds of the pea aphid with controlled symbiont composition and also in different aphid genotypes from natural populations with previously characterized infection status and reproductive mode. We found that most facultative symbionts exhibited detrimental effects on their hosts fitness under sex-inducing conditions in comparison with the reference lines. We also showed that the loss of sexual phase in permanently parthenogenetic lineages of A. pisum was not explained by facultative symbionts. Finally, we demonstrated that Spiroplasma infection annihilated the production of males in the host progeny by inducing a male-killing phenotype, an unexpected result for organisms such as aphids that reproduce primarily through clonal reproduction

Capacité discriminatoire et exploitation des colonies d'hôtes chez un parasitoïde solitaire. Ecologie comportementale et modélisation

Diplôme : Dr. d'UniversiteChez les parasitoïdes solitaires, l'hôte ne permet le développement que d'un seul parasite et les individus surnuméraires sont éliminés au cours de leur développement. Les femelles devraient donc éviter le superparasitisme, c'est-à-dire pondre dans les hôtes parasités. Pour cela, la femelle doit être capable de distinguer un hôte sain d'un hôte parasité, c'est la capacité discriminatoire. Cette capacité a été étudiée chez A. rhopalosiphi, un parasitoïde de pucerons. Cet Hyménoptère ne serait pas capable de reconnaître un hôte parasité depuis peu de temps. Cependant, le comportement de défense des hôtes peut partiellement compenser ce défaut de discrimination. La capacité discriminatoire d'A. rhopalosiphi est limitée et affecte donc le succès reproducteur des femelles. Un modèle a été développé afin d'expliquer l'imperfection de la capacité discriminatoire. Il repose sur un compromis entre la reconnaissance d'un hôte et le risque encouru lors de sa manipulation. Au cours d'une attaque, le puceron peut émettre des sécrétions corniculaires pouvant engluer le parasite. Le durcissement rapide de ces sécrétions nécessite ensuite un long toilettage. Le modèle montre que le coût en temps consécutif à l'engluement peut être une contrainte suffisamment importante pour réduire l'intérêt de la discrimination. Face à ce défaut de discrimination, nous nous sommes intéressés au comportement d'exploitation des colonies d'hôtes chez A. rhopalosiphi. Ce parasitoïde serait très fidèle aux parties riches de son habitat malgré le risque de superparasitisme. Cependant, cette stratégie évolue selon l'expérience de la femelle et son état physiologique. Notamment, une femelle disperse plus ses pontes dans son habitat lorsqu'elle a déjà pondu beaucoup d'oeufs. Enfin, on note que les comportements de défenses des pucerons limitent significativement l'efficacité parasitaire de ce parasitoïde. L'intérêt fondamental et appliqué de ce travail est discuté et replacé dans un contexte plus général