Location: Crop Diseases, Pests and Genetics ResearchTitle: Glassy-winged sharpshooters cease feeding and avoid plants treated with sub-lethal doses of the neonicotinoid insecticide imidacloprid
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2022
Publication Date: N/A
Interpretive Summary: The glassy-winged sharpshooter is an invasive insect that established in California in the late 1980’s. The glassy-winged sharpshooter is a vector of Xylella fastidiosa, a bacterial pathogen that causes numerous economically important plant diseases including Pierce’s disease of grapevine. Since establishment in California, large glassy-winged sharpshooter populations that moved between citrus orchards, an overwintering habitat, and vineyards were associated with multiple Pierce's disease epidemics. The insecticide Imidacloprid is widely applied to control glassy-winged sharpshooters in vineyards and in citrus orchards. Imidacloprid is often applied via drip irrigation systems and is taken up by the plants vascular system, providing systemic control of susceptible insect populations for a period measured in weeks to months. However, recent studies indicate that resistance to imidacloprid is increasing in California populations of glassy-winged sharpshooter. The interaction of glassy-winged sharpshooters with plants treated with sub-lethal doses of imidacloprid were investigated in the laboratory. Glassy-winged sharpshooters were shown to cease feeding on plants treated with imidacloprid and in choice-tests glassy-winged sharpshooter adults avoided imidacloprid treated plants. As glassy-winged sharpshooters must ingest imidacloprid for it to kill them, ability of highly mobile adults to recognize and avoid treated plants suggests that applications of imidacloprid may be more likely to push glassy-winged sharpshooters out of treated habitats rather than kill them. Information regarding interaction of glassy-winged sharpshooters with imidacloprid treated plants is critical to design effective strategies for suppressing glassy-winged sharpshooter populations.
Technical Abstract: Insecticides are a primary means for suppressing populations of insects that transmit plant pathogens. Application of insecticides for limiting spread of insect transmitted plant pathogens is often most effective when applied on an area-wide scale. The glassy-winged sharpshooter is a vector of the bacterial pathogen Xylella fastidiosa, which causes numerous plant diseases including Pierce's disease of grapevine. The glassy-winged sharpshooter has been the subject of an area-wide suppression program in California for nearly two decades. Overreliance on a limited number of active ingredients including the neonicotinoid imidacloprid has resulted in increased levels of resistance to commonly applied products. In California, glassy-winged sharpshooters move between citrus, an important overwintering host, and vineyards. Accordingly, imidacloprid is routinely applied via the irrigation system in vineyards and citrus orchards. For soil applied applications, it may take days to weeks for concentrations in plants to increase to lethal doses. Further, as the dose of imidacloprid required to kill sharpshooters increases due to resistance, so too does the period that sharpshooters are exposed to sub-lethal doses. Response of glassy-winged sharpshooter to cowpea plants treated with sub-lethal doses of imidacloprid was evaluated by conducting no-choice and choice tests. In no-choice feeding assays, glassy-winged sharpshooters caged on plants treated with sub-lethal doses of imidacloprid ceased feeding and produced little excreta. Further, sub-lethal exposure to a range of doses over a 5-day period did not affect viability over a 9-week post-exposure holding period on untreated plants. In choice-tests, glassy-winged sharpshooters avoided treated plants and were observed predominately on untreated plants. Results suggest that application of imidacloprid to vineyards and citrus orchards may push glassy-winged sharpshooters out of treated habitats rather than kill them.