Effects of Apple Leaf Allelochemistry on Tufted Apple Bud Moth (Lepidoptera: Tortricidae) Resistance to Azinphosmethyl

The dihydrochalcone glycoside phloridzin is a dominant allelochemical in foliage of apple. This allelochemical varies within and among apple cultivars and can influence distribution and abundance of tufted apple bud moth, Platynota idaeusalis (Walker), in orchards. Laboratory bioassays were used to investigate the influence of phloridzin on tolerance of both susceptible and resistant colonies of P. idaeusalis to the organophosphate insecticide azinphosmethyI. Addition of phloridzin to diet did not influence tolerance of first ins tars of the susceptible strain to azinphosmethyI. Third instars of the susceptible strain exhibited reduced tolerance to azinphosmethyl in the presence of phloridzin, and this response was associated with inhibition of the activities of glutathione transferase, esterase, and aniline hydroxylation enzymes. Neonate larvae of the resistant strain fed on diet with phloridzin were more tolerant to azinphosmethyl at high insecticide concentrations only. Third instars of the resistant strain were equally tolerant to azinphosmethyl in the presence and absence of phloridzin. Although phloridzin inhibited glutathione transferase activity in resistant larvae, as in the susceptible strain, it increased activity of esterases. Our data provide further evidence that both host-plant allelochemistry and insect selection history influence results of pesticide bioassays.