Species-specific responses of a root- and shoot-feeding insect to arbuscular mycorrhizal colonization of its host plant

The responses of root-feeding black vine weevil (Otiorhynchus sulcatus) larvae and leaf-feeding adults to colonization of strawberry (Fragaria x ananassa) plants by one or two species of arbuscular mycorrhizal fungi are reported here. Glomus mosseae and Glomus fasciculatum were isolated from a commercial field and used to colonize strawberry plants, singly and in combination. Vine weevil larvae were reared on roots of colonized and uncolonized plants. When the larvae were mature, leaves from all plants, with and without larvae, were fed to adult weevils. Colonization by either fungus reduced larval survival and biomass. However, colonization by both fungi had no effect on the larvae. These effects were manifested in changes in plant performance; weevil feeding decreased plant foliar and root biomass as well as runner production, but only when mycorrhizas were absent or inoculated together Mycorrhizas also mitigated the effects of larval feeding on adult weevils. The response of root-feeding insects to arbuscular mycorrhizal colonization depends on which fungi are present in the root system. Furthermore, arbuscular mycorrhizal fungi might play a critical role in mitigating interactions between phytophagous insects. (C) New Phytologist (2001).