Differential Efficacy of Three Commonly Used Pyrethroids for Laboratory and Field-Collected Larvae and Adults of Helicoverpa zea

Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), pyrethroid resistance monitoring programs typically utilize cypermethrin in the adult vial test. Vial bioassays with cypermethrin, esfenvalerate, and bifenthrin were conducted on H. zea third instars and male moths from a susceptible laboratory colony and the F1 generation of a pyrethroid-resistant field population. In the susceptible population, both growth stages were most sensitive to bifenthrin and adults were more sensitive to esfenvalerate than cypermethrin. LC₅₀ resistance ratios for the larvae and adults of the resistant population were approximately two times higher for bifenthrin than cypermethrin or esfenvalerate. For the resistant population, vial assays using either growth stage gave similar resistance ratios for each of the three pyrethroids, respectively, proving the adult vial test accurately reflects larval resistance. However, as resistance ratios varied considerably depending on the pyrethroid used, resistance ratio values obtained with one pyrethroid may not be predictive of resistance ratios for other pyrethroids. Our results suggest that carefully chosen pyrethroid structures diagnostic for specific mechanisms of resistance could improve regional monitoring programs.