Influence of flowering cover crops and landscape diversity on biological control in vineyards

Previous studies have demonstrated that increasing habitat diversity within an agroecosystem (field-scale, on-farm diversity) can influence biological control of pests while more recently other studies have shown that the area and diversity of natural habitats surrounding an agroecosystem (landscape-scale diversity) can influence natural enemy populations and biological control of pests. As such, it has been suggested that the ability of on-farm habitat diversification to enhance biological control may be contingent upon the type of landscape within which the farm is situated (e.g. low vs. high diversity landscape). A two-year study to evaluate this hypothesis in California wine grape vineyards was conducted in 2012-2013. Paired plots with and without flowering summer ground covers were established in a number of vineyards representing a continuum of landscape diversity (ranging from low to high diversity landscapes). Biological control of a key wine grape pest, the western grape leafhopper (Erythroneura elegantula), was then monitored in these plots over 2 growing seasons. The goal of this study was to determine whether or not landscape context effected how these flowering summer ground covers influenced biological control of E. elegantula.