Feeding specialization shapes the bottom-up effect of arbuscular mycorrhizal fungi across a plant–aphid–parasitoid system

Arbuscular mycorrhizal fungi (AMF) are major root symbionts regulating plant physiology. Their presence affects the performance of aboveground insect herbivores in relation to their feeding strategy and their feeding specialization. For example, the effect of the arbuscular mycorrhizal (AM) symbiosis on chewing insects, positive for specialists and negative for generalists, has been previously demonstrated. Conversely, the impact of AMF on phloem-suckers with relatively different levels of specialization remains unexplored. • We tested the influence of the AM Funneliformis mosseae on the fitness of the specialist aphid Acyrthosiphon pisum and the generalist aphid Myzus persicae on Vicia faba plants. Further, we investigated the effects of AMF on the higher trophic level, the aphid parasitoids Aphidius ervi (specialist) and Aphidius colemani (generalist), by evaluating plant attractiveness and parasitoid fitness. To support the results of behavioral and biological bioassays we characterized the photosynthetic parameters, the volatilome and the transcriptome of tested plants. • Mycorrhizal plants proved unsuitable for the generalist M. persicae but enhanced the fitness of the specialist A. pisum. The AM symbiosis had no effects on the behavioral response of A. colemani and enhanced the attraction and fitness of A. ervi.