Striking the right balance: Can insecticidal control of a vineyard insect pest, Homalodisca vitripennis, be optimized to conserve predatory insects?

Background/Question/Methods

The glassy-winged sharpshooter (Homalodisca vitripennis Germar) is an exotic agricultural insect pest in southern California. It has had devastating impacts in the wine grape-growing region of Temecula, California where it vectors a bacterial pathogen, Xylella fastidiosa. The bacterium blocks movement of plant sap within the xylem, resulting in eventual death of the grapevine. Systemic insecticides (e.g. imidacloprid) have been widely used in the control of H. vitripennis, with some success. Vineyards throughout the Temecula Valley vary in their approach to control and management of this pest, with some organic vineyards applying no pesticides of any kind and others applying imidacloprid yearly or only intermittently. 

Results/Conclusions

Analysis of sticky trap surveys indicates that vineyards applying imidacloprid intermittently (less than once per year) have similarly low densities of H. vitripennis present in contrast to high densities of untreated sites. Concomitantly, disease surveys indicate similar low disease prevalence in all intermittent or yearly treated sites. However, foliage tap samples revealed that intermittently and yearly treated vineyards also have similar low species richness and densities of predaceous and parasitoid insects in contrast to the greater predator and parasitoid diversity of untreated vineyards. The results of these combined studies demonstrate that effective control of H. vitripennis can be achieved with minimal use of insecticides, and that increased use may actually counteract other methods of control (e.g. predation, parasitism).