Diversity and Implication of Symbiotic Bacteria in Aphids-Ants Relationships in Madagascar.

Facultative bacteria in aphids provide their hosts with various physiological and ecological adaptations, such as resistance to thermal stress, parasitoids and entomopathogenic fungi. Furthermore, these symbionts possess the capacity to modulate the composition of honeydew, a substance that is particularly favored by numerous ant species. That's why we were interested in determining whether the presence of facultative bacteria in myrmecophilic aphids influences their relationship with mutualistic ants. In the vicinity of Antananarivo (Madagascar), the objectives of the study were to (i) determine the diversity of ants, aphids and symbionts and to (ii) assess the impacts of the identified symbiont on behavioural interactions of ants and aphids. We identified a total of four species (Serratia symbiotica, Rickettsia, Spiroplasma, Hamiltonella defensa) of facultative symbionts present in the three ant species (Camponotus maculate, Monomorium madecassum, Nylanderia gracilis) we tested and a total of six facultative symbionts (Serratia symbiotica, Rickettsia, Spiroplasma, Hamiltonella defensa, Regiella insecticola, Rickettsiella) among three of the five aphid species (Aphis citricidus, Aphis fabae, Aphis spiraecola, Macrosiphum euphorbiae, Rhopalosiphum maidis) we tested. Although our results did not show the involvement of symbionts on ant behaviour or their association with aphids, our study showed that the number of ants increases with the number of interactions, that Nylanderia gracilis are the ants with the most interactions and finally that ants observed on pesticide-treated plots have fewer interactions with aphids.