Cross-resistance and synergism in azinphosmethyl resistant and susceptible strains of tufted apple bud moth (Lepidoptera: Tortricidae) to various insect growth regulators and abamectin

Various strains of the tufted apple bud moth, Platynota idaeusalis (Walker), were evaluated to test cross-resistance between the organophosphate insecticide azinphosmethyl versus several types of insect growth regulators (IGRs) and abamectin. Neonates were exposed to surface-treated diet for 14 d, then transferred to untreated diet to complete development. Mortality was assessed at 7 and 14, then again at adult eclosion. Mortality from organophosphate insecticides did not increase after 7 d, but the IGRs and abamectin caused additional mortality by 14 d. The IGRs caused additional mortality between 14 d and adult eclosion. Resistance ratios in the organophosphate resistant strains were 20-fold for azinphosmethyl and ranged from low (<5-fold) for the hexaflumuron and fenoxyearb, to high (15-26-fold) for diflubenzaron. Resistance to malathion was also low and appeared to be negatively correlated with azinphosmethyl resistance. High levels of synergism (27-fold) were found with the esterase synergist S.S.S.-tributylphosphorotrithioate (DEF) to diflubenzuron in a resistant field population but synergism was only 2.2-fold to azinphosmethyl. Synergism with diethyl ester of malic acid (DEM) or piperonyl butoxide (PBO) was absent or very low.