Insecticide resistance in California populations of the glassy-winged sharpshooter Homalodisca vitripennis.

BACKGROUND: The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is a primary vector of Pierce's disease of grapes in California. Systemic imidacloprid treatments have been the mainstay of area-wide treatment programs that were established in the Central Valley (Kern and Tulare Counties) and Southern California (Riverside County) during the 1990s to combat the pest. The programs helped to suppress populations on citrus, a major sharpshooter host, to levels that significantly reduced migration into adjacent vineyards. However, beginning in 2012, there has been a resurgence of glassy-winged sharpshooter populations in Kern and Tulare counties, and hitherto successful treatment strategies have not been as effective. This study investigated the possibility that insecticide resistance was a contributing factor to the population resurgence.
RESULTS: Topical application bioassays detected high levels of resistance to imidacloprid in Kern and Tulare populations, and lower levels of resistance (perhaps due to cross-resistance) to the foliar neonicotinoid acetamiprid (20-fold), the pyrethroid fenpropathrin (7.4-fold), and the butenolide flupyradifurone (4-fold). Samples of glassy-winged sharpshooters from citrus groves under organic management also exhibited high levels of imidacloprid resistance.
CONCLUSION: The long-term use of imidacloprid has selected for resistance in glassy-winged sharpshooters. The most resistant populations also exhibited resistance to the foliar neonicotinoid acetamiprid, the pyrethroid fenpropathrin, and the butenolide flupyradifurone. High levels of imidacloprid resistance in insects sampled from organic groves indicate that resistant insects are migrating from nearby conventional groves, which could compromise the control of sharpshooters in organic systems with insecticides affected by cross-resistance.