Influence of habitat diversity on biological control of Erythroneura leafhoppers in California vineyards

Local and landscape habitat diversification can influence biological control of the Western grape leafhopper (Erythroneura elegantula Osborn) by its key parasitoids Anagrus erythroneurae S. Trjapitzin & Chiappini and A. daanei Triapitsyn in wine grape vineyards. At the landscape scale, Anagrus rely on non-crop habitat outside of the vineyard to successfully overwinter while at the local scale vineyard diversification can provide resources like shelter and floral nectar that can potentially improve parasitoid performance. At the same time, increased habitat diversity can present a challenge to crop production and in some cases has been linked with changes in crop vigor that ultimately effect pest densities. Between 2010-2013 we conducted a series of studies to evaluate the relative influence of flowering summer cover crops, natural habitats, and crop vigor on biological control of E. elegantula in vineyards. While flowering cover crops did attract a large number of natural enemies, this never led to increased populations in the crop canopy itself, much less any increase in biological control of E. elegantula. Rather, vineyards in diverse landscapes had higher early-season abundance of Anagrus spp., which was then linked to increased parasitism and decreased late-season populations of E. elegantula. Leafhopper densities were also influenced by crop vigor, regardless of landscape or cover crops.