Montoring of resistance allele frequencies in glassy-wing sharpshooter Homalodisca vitripennis, the destructive pest of grape

The Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis is a major vector of the strain of Xylella fastidiosa causing the deadly Pierce’s disease in grapes. Increased applications of pesticides for control seem to select for insecticide resistance. To evaluate the frequency of potential tolerant alleles in field populations of GWSS, we reared laboratory colonies from adult GWSS collected from vineyards of North Florida. Adult GWSS were exposed to residues of insecticides coated inside glass vials and their responses were recorded 6 hours later. Mortality of GWSS was the highest with the carbamate carbaryl (LC₅₀ = 0.04 μg/vial) and higher for the organophosphate malathion (LC₅₀= 0.09 μg/vial) than either the pyrethroid cypermethrin (LC₅₀ = 0.14 μg/vial) or the cyclodiene endosulfan (LC₅₀ = 0.14 μg/vial). Diagnostic concentrations needed to separate susceptible genotypes from tolerant individuals were determined to monitor for tolerant allele frequencies in GWSS.  The seasonal patterns of response to insecticides in field collected GWSS indicated that resistance to malathion is evolving in GWSS populations collected in Tallahassee, FL.