Facultative symbionts associated with aphid populations in citrus orchards in northern Tunisia

Renoz, François [UCL] Pons-Guillouard, Inès [UCL] Noël, Christine [UCL] Lebdi-Grissa, Kaouthar [Laboratory of Entomology and Acarology, National Agronomic Institute of Tunisia (INAT) - University of Carthage, 43 Avenue Charles Nicolle, Cité Mahrajène, 1082 Tunis, Tunisia, e-mail: grissak@yahoo.fr] Foray, Vincent [ Institut de Recherche sur la Biologie de l'Insecte (IRBI), UMR CNRS 7261, 37200 Tours, France; e-mail: vincent.foray@univ-tours.fr] Hance, Thierry [UCL]

Like many insects, aphids (Hemiptera: Aphididae) can host a wide diversity of symbiotic bacteria that can be important drivers of their evolutionary ecology. In addition to the nutritional obligate symbiont Buchnera aphidicola, these phloem-sap feeding insects can host various facultative symbionts whose functional diversity depends on complex interactions with the host genotype and environmental factors. During sampling in citrus orchards in northern Tunisia, we collected aphids on citrus plants. The specimens belonged either to the cotton-melon aphid Aphis gossypii or the green citrus aphid Aphis spiraecola. We analysed the prevalence of Arsenophonus, Serratia symbiotica, Hamiltonella defensa and Regiella insecticola, four facultative symbionts frequently found in the genus Aphis and potentially associated with phenotypic effects related to nutrition, protection against parasites and tolerance of high temperatures. We found that the diversity and prevalence of facultative symbionts differed between these two aphid species that exploit similar ecological niches. In particular, we found a high prevalence of Arsenophonus in A. gossypii populations and that the defensive symbiont H. defensa was only present in A. spiraecola populations. These results are discussed in light of the ecology and life cycles of each of the species of aphid studied.