Gall insects: Plant mediated interactions impact insect preference and performance

While perhaps not as intuitive, indirect species interactions can have just as profound an effect on community structure as direct interactions. The strength of plant-mediated indirect interactions between insects depends upon how plants respond to the stress of herbivory. Specialized herbivores such as gall insects provide well-suited systems with which to evaluate indirect interactions between insects that are mediated by plant resource allocation and volatiles. Gall insects are ubiquitous in the natural world, often acting as agricultural pests or biological control agents. Two biocontrol agents have recently been approved for Russian knapweed: the gall wasp, Aulacidea acroptilonica (Cynipidae), and the gall midge, Jaapiella ivannikovi (Cecidomyiidae). We expected competitive plant-mediated indirect interactions between insect species; however, in greenhouse studies we found evidence for facilitation when insect species share a common host plant. This interaction may allow insects to coexist when both attacking Russian knapweed.