Food webs centered on aphids contain networks of species, some directly related to prey characteristics, others mediated via the characteristics of the host plant. These tritrophic interactions can be even more extensive and complex when ants are present in aphid colonies. This study investigated how the presence of ants (Cataglyphis aenescens Nylander & Formica cunicularia Latreille) in colonies of a generalist aphid (Myzus persicae Sulzer) can influence (i) the performance of an important generalist aphidophage (the common hoverfly Episyrphus balteatus DeGeer) feeding on aphids growing on two host plants that express different levels of the glucosinolate sinigrin (Brassica napus L. & Brassica nigra L.); and (ii), the oviposition of the aphidophage on ant-free versus ant-tended aphid colonies. Individual fitness was calculated from performance measures, and the number of eggs laid by gravid females used as a measure of preference. Ant presence significantly reduced the survival rate of predator immature stages, but there were no significant effects of host plant (sinigrin content), and host plant did not interact with ant presence. Female fecundity was significantly reduced by ant presence and varied between host plants, but these factors did not interact significantly. Syrphid females avoided ovipositing in the presence of ants, independent of plant species. Overall, the presence of ants in aphid colonies reduced predator performance and reduced oviposition by hoverfly females. Therefore the ant-aphid interaction is important in biological control as it influences the distribution of aphidophagous syrphids within the habitat.

Keywords