Reduced Susceptibility of Homalodisca vitripennis (Hemiptera: Cicadellidae) to Commonly Applied Insecticides

Abstract

Pest management for the glassy-winged sharpshooter, Homalodisca vitripennis Germar (Hemiptera: Cicadellidae), in Kern County, California relies on the application of insecticides. These treatments have contributed to low H. vitripennis field counts since applications were initiated in 2001. However, densities have been high in recent years despite continued management, prompting efforts to evaluate the susceptibility of current populations to insecticides. H. vitripennis adults were subjected to bioassays with five commonly applied insecticides, and the results were compared to baseline toxicities determined in 2002. Two neonicotinoids, imidacloprid and thiamethoxam, were evaluated using systemic uptake bioassays. Contact toxicities of the neonicotinoid acetamiprid and pyrethroids bifenthrin and fenpropathrin were estimated using leaf dip bioassays. Dose-mortality responses were analyzed by probit analysis. For each compound, there was no significant difference in annual LC50 values determined over 2 yr. Compared to baseline toxicities, acetamiprid and bifenthrin were found to be significantly less toxic to H. vitripennis. The LC50 values of these two compounds increased sevenfold and 152-fold, respectively. Tests with the neonicotinoids revealed a trend of decreasing susceptibility levels within each season followed by reversion back to early season LC50 estimates in the following year. In addition, data showed seasonal and site variation in susceptibility to imidacloprid, possibly due to differential applications in nearby fields.

Xylella fastidiosa and Glassy-Winged Sharpshooter Population Dynamics in the Southern San Joaquin Valley of California

“…Because glassy-winged sharpshooter populations were reduced to undetectable levels from vineyards by applications of a neonicotinoid during spring, most adults present in vineyards in July and August presumably moved into vineyards from surrounding habitats only after neonicotinoid titers in grapevines decreased below a lethal dose. The period that neonicotinoid titers remain high enough to deliver a lethal dose may be declining in the San Joaquin Valley, because recent evidence suggests that glassy-winged sharpshooter tolerance for neonicotinoids may be increasing (Andreason et al 2018). Because X. fastidiosapositive glassy-winged sharpshooters were abundant in July and August and recent evidence suggests limited winter curing of infections that occur in July and August (Daugherty and Almeida 2019), late summer should be considered a period of high risk for spread of X. fastidiosa in the San Joaquin Valley.…”

Sharpshooters: a review of what moves Xylella fastidiosa

“…; Andreason et al . ). In many areas of California, there now appears to be over a thousand‐fold increase in insecticide resistance to neonicotinoids compared to populations surveyed in 2003; the exact mechanism(s) of the resistance is unknown but likely involves cytochrome P450 enzymes (Redak et al .…”

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

“…The intensity of imidacloprid selection was of interest to us since it had been relied upon extensively within the area‐wide treatment programs in the Central Valley and Southern California. In a recent report, bifenthrin (pyrethroid insecticide) resistance was documented in Central Valley populations of GWSS 19 . In that report, Andreason et al 19 .…”