Abstract Bacterial endosymbionts can increase aphid tolerance to environmental stressors, including natural enemies, but the mechanisms remain unclear. Macrosiphum euphorbiae , which frequently feeds on Solanum species, forms a facultative association with Hamiltonella defensa . Parasitoid wasps use volatile cues from aphid honeydew to locate hosts, yet the role of endosymbionts in shaping honeydew attractiveness to parasitoids has been little studied. We compared honeydew production from clonal lines of M. euphorbiae with and without H. defensa across two aphid genotypes, collecting and analysing the composition of volatile organic compounds (VOCs) and testing parasitoid ( Aphidius ervi ) behavioural responses to honeydew presented in a choice assay. Honeydew production differed between genotypes, and H. defensa‐ infected aphids produced more honeydew in the choice assay. Parasitoids were more attracted to honeydew from infected aphids, although VOC profiles showed minimal differences between infected and uninfected aphids. These results suggest that facultative endosymbionts may influence aphid honeydew production and indirectly affect parasitoid foraging, highlighting the importance of mechanistic studies of symbiont‐mediated tritrophic interactions.
Macheda et al. (Thu,) studied this question.