Is the endophyte‐based plant protection against aphids mediated by changes in the insect microbiome?

Abstract

Aphids are important herbivores in natural and managed environments. Westudied the response of aphids and their associated microbiota to the presence of the fungalendophyte Epichloë sp. LpTG-3 strain AR37, and the AR37-derived alkaloids in plants.We hypothesized that AR37 and/or AR37-derived alkaloids would reduce the aphid performance,and that this reduction would be associated with endophyte-mediated changes inthe abundance, composition, and diversity of beneficial bacterial endosymbionts of aphids(e.g., Buchnera). Plants of Lolium perenne associated with AR37 variants able (wild typeand idtA) and unable (idtM) to produce indole diterpene alkaloids were challengedwith Rhopalosiphum padi aphids. We measured aphid population size, plant biomass, andthe abundance, composition and diversity of the aphid’s bacterial microbiota. The presenceof AR37 increased the resistance of plants against R. padi aphids via the productionof indole diterpene alkaloids, and this effect was independent of the plant biomass. Theendophyte-mediated reduction in aphid performance was not associated with changes inthe abundance, composition and diversity of the insect’s bacterial microbiota. However, wecannot rule out that the reduction in aphid performance could be associated with a putativeendophyte effect on the bacterial provision of benefits to aphids. Our study highlighted theprotective role of endophyte-derived indole diterpene alkaloids against aphids. Further investigations will be needed to determine if there is a link between the endophyte-mediatedaphid resistance and the integrity of the insect’s bacterial microbiota.