The eubacteria associated with the cabbage aphid (Brevicoryne brassicae): Their community composition and influence on aphid performance

Aphids harbour symbiotic bacteria that can have positive or negative effects on their survival and performance. These bacteria are split into two groups: the primary obligate endosymbiont, Buchnera aphidicola, and the secondary endosymbionts. In pea aphid (Acyrthosiphon pisum) the secondary symbionts have been shown to confer various fitness traits to their aphid hosts. To investigate whether endosymbiont composition influences trophic interactions in other aphid species we have used molecular methods to characterise the eubacteria associated with a Scottish arable pest, the cabbage aphid (Brevicoryne brassicae), and we are testing their impact on aphid-parasitoid interactions. Molecular cloning and sequencing and T-RFLP were used to analyse the community composition of several different cabbage aphid lines. The results that we have generated for cabbage aphid indicate that there are at least three different community types: (1) aphid lines dominated by one bacterial type; (2) aphid lines dominated by a second bacterial type; and (3) aphid lines in which no eubacteria other than Buchnera have been detected. Based on the molecular results we have devised aphid performance experiments to test the influence of bacterial composition on trophic interactions, with a particular focus on the success of hymenopteran parasitism. The truly multitrophic nature of cabbage aphid population dynamics in arable systems is highlighted by this study.