Abstract
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.
Highlights
Like most insects that feed on plant-phloem, aphids (Hemiptera: Aphididae) host symbiotic bacteria in their tissues that can have significant consequences on their evolutionary ecology (Oliver et al, 2010; Ferrari & Vavre, 2011)
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
Of the 68 citrus aphid colonies sampled at 9 locations in northern Tunisia, we identified 19 colonies of the cotton-melon aphid, A. gossypii, and 49 colonies of the green citrus aphid, A. spiraecola
Summary
Like most insects that feed on plant-phloem, aphids (Hemiptera: Aphididae) host symbiotic bacteria in their tissues that can have significant consequences on their evolutionary ecology (Oliver et al, 2010; Ferrari & Vavre, 2011). Aphids can carry an array of heritable facultative symbionts (e.g. H_defensa, S. symbiotica, R. insecticola, etc.) that occur more sporadically in host insect populations and are maintained in these by vertical transmission and intra- and interspecific horizontal transfers (Sandström et al, 2001; Caspi-Fluger et al, 2011; Gehrer & Vorburger, 2012) These facultative bacterial partners can impart dramatic phenotypic effects to their host, sometimes beneficial and sometimes harmful depending on specific environmental conditions (Oliver et al, 2006, 2010). Since facultative symbionts may have beneficial effects (e.g. defence against parasites, improvement of nutrition, etc.) or detrimental effects on their host (e.g. fitness cost), there is an interest in determining the bacterial partners present in these insects, in particular in species that are crop pests The presence of these bacteria in aphid populations may interfere with control programs, whether biological (e.g. influence on host resistance to parasitoid wasps) or chemicals (e.g. influence on host susceptibility to insecticides) (Skaljac et al, 2018; Vorburger, 2018). These two species of aphid are among the most destructive pests of citrus crops
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