An Exploratory Study on the Influence of Vesicular-arbuscular Mycorrhizal Fungi on the Success of Weed Biological Control with Insects

Abstract

This paper presents the results of an exploratory study to determine whether vesicular-arbuscular mycorrhizal (VAM) fungi affect the success of insects used as weed biological agents. No direct correlation between the colonization by VAM fungi alone and the success of root- and shoot-feeding insects was found. However, in Centaurea diffusa , plants colonized by VAM fungi had a lower shoot root ratio and increased attack and survival of the root beetle, Sphenoptera jugoslavica , in the field. Beetle success was also best on C. diffusa when the plant was growing among determinate grasses that largely cease growing after flowering in the spring or early summer. This is consistent with other reports that VAM hyphae can transfer nutrients between plant species from low to high sinks. From these results and related reports in the literature, it is suggested that plants with many stenophagous root-insects are those in which VAM fungi colonization increases nutrient partitioning to the roots with little or no decrease in plant growth. Root-feeding, rather than foliage- or seed-feeding, insects seem to be particularly effective as biocontrol agents for plants of this type.