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Variable impacts of prevalent bacterial symbionts on a parasitoid used to control aphid pests of protected crops
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International audience. The ecological role of bacterial symbionts associated with insects is increasingly recognized. Notably, aphids are known to harbour facultative bacterial symbionts that influence their phenotypes like conferring a protection against natural enemies. The most well-known Gamma-Proteobacteria Hamiltonella defensa can provide a defence against hymenopteran parasitoids to their aphid hosts. Aphidiine parasitoids are broadly used as biological control agents in inundative releases against aphids of various greenhouse crops so that defensive symbionts can potentially compromise efficiency of the released parasitoids. Here, we first measured the prevalence and spatiotemporal dynamics of bacterial symbionts infecting eight aphid species colonizing protected strawberry crops in France. Considering the three major aphid pest species of strawberry crops (Acyrthosiphon malvae (Mosley), Macrosiphum euphorbiae (Thomas) and Rhodobium porosum (Sanderson)), we then estimated their possible effects on protection against Aphidius ervi (Haliday), a parasitoid species currently used as a biological control agent. Both symbiotic composition and symbiont prevalences highly differed between aphid species. In the three dominant aphid species, many individuals were single infected or co-infected with H. defensa and Regiella insecticola. Prevalences of these bacterial symbionts highly varied across French regions. Parasitism experiments showed that infection with R. insecticola did not provide any protection against parasitoids while infection with H. defensa would be associated with a strong reduction of parasitism in A. malvae only. These results are valuable to understand the implications of defensive symbionts in the effectiveness of biological control.
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