Surfactant toxicity and synergistic activity with pyrethroids in managing resistant <i>Listronotus maculicollis</i> Kirby populations

Abstract This study investigates the efficacy of surfactants as a means to manage the annual bluegrass weevil, Listronotus maculicollis , particularly in populations demonstrating resistance to pyrethroids. Laboratory assays evaluated L. maculicollis adult mortality when exposed to 13 unique turfgrass surfactant classes alone and in combination with a low rate of bifenthrin. Results from dose–response assays suggest that the alkylpolyglucoside (Alypso), organosilicone (Silwet), anionic blend (Pervade), and the anionic + nonionic blend (Duplex) surfactants were acutely toxic to adults. When combined with low rates of pyrethroid, additive effects were seen with each of these classes plus the block copolymer + alkylpolyglucoside (Dispatch), which was non‐toxic in the absence of pyrethroids. The top four surfactant classes were further examined for their ability to depress cytochrome P450 enzyme activity, an enzyme family suspected to confer resistance within L. maculicollis . Only the block copolymer + alkylpolyglucoside blend showed a notable decrease in P450 activity, suggesting a potential mechanism for overcoming insecticide resistance in populations where enhanced enzymatic activity is responsible for pyrethroid resistance. However, the enzyme activity in the tested population of moderately resistant weevils did not show a significant increase, indicating that resistance to pyrethroids in L. maculicollis involves mechanisms other than enhanced enzymatic detoxification. Further research is needed to elucidate additional mechanisms of resistance as well as confirm the benefits of incorporating surfactants into L. maculicollis management strategies in the field.