Effects of generalist root feeders (Agriotes spp. larvae, Coleoptera: Elateridae) on grassland plant communities

Background/Question/Methods

Generalist root feeders likely influence plant community structure because (i) they may preferentially feed on certain plant species and (ii) plant species may differ in their ability to cope with the root herbivore attack. Additionally, root herbivore effects on plants may change as well as depend on the abiotic and biotic soil environment. We conducted two greenhouse experiments to identify how widespread insect generalist root herbivores, Agriotes spp. larvae (Coleoptera, Elateridae), affect grassland plant community structure. Above- as well as belowground responses to root herbivory were determined for eight common grassland plant species that were grown separately with or without Agriotes larvae. Interactive effects of the root herbivore and the soil environment were determined for a community of six common grassland plants species that was grown either with or without Agriotes larvae,  in a first phase with two different soil biota communities, and in a second phase with these communities and their soil substrates that had either been Agriotes trained or not.

Results/Conclusions

In single plants the larvae removed more root biomass from larger root systems. Their growth was positively correlated with root biomass, but did not depend on plant species identity. Relative changes in total plant biomass varied for different plant species, but were not related to plant size. In a plant community the root herbivore effect depended on the original soil biota community or/and the herbivore training of the soil substrate for two plant species, while for a third species the effect was independent of these factors. The Agriotes training of the soil substrate additionally determined plant community productivity and the root length colonized by arbuscular mycorrhizal fungi in a model plant species. We conclude that Agriotes spp. larvae may change interspecific plant competition by feeding on the roots that are most abundant. The magnitude of their effect on the plant community may be generated through the ability of the dominant plant species (based on root biomass) to cope with the herbivore damage. However, their impact may vary depending on the background soil biota community and the herbivore history of the soil.