Is a specialist root-feeding insect affected by arbuscular mycorrhizal fungi?

Abstract

Arbuscular mycorrhizal fungi (AMF) are known to reduce the growth of generalist root-feeding insects, but whether the same is true for a specialist insect is unknown. White clover ( Trifolium repens) was inoculated with the AM fungi Glomus fasciculatum and Glomus mosseae individually and in combination, and larvae of the clover root weevil ( Sitona lepidus) reared on mycorrhizal and non-mycorrhizal plants. On emergence, adult weevils were weighed and the percentage of larvae surviving to adulthood was calculated for each treatment. Larval survival to adulthood was increased by both species of fungi, but weight was unaffected. Larval feeding reduced foliar biomass, but had no effect when two fungi colonized the root system. Although larval survival was greatest in the dual fungal treatment, the proportion of grazed root nodules was lower, suggesting that AMF may improve root quality for the herbivore. Root feeding caused an increase in arbuscular colonization in the dual fungal treatment, and this may have enabled plants to tolerate herbivory, through enhanced mycorrhizal benefit. We conclude that a specialist root feeder is less affected by the presence of AMF than are generalist species. However, AMF enable a plant to tolerate the effects of root loss, and this is dependent on the number of mycorrhizal species in the root system.