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 die tufted apple bud moth, Platynota idaeusalis (Wa lker), were evaluated to test cross-resistance between the organophosp hate insecticide azinphosmethyl versus several types of insect growth regulators (IGRs) and abamectin. Neonates were exposed to surface-trea ted diet for 14 d, then transferred to untreated diet to complete deve lopment. Mortality was assessed at 7 and 14 d, then again at adult ecl osion. Mortality from organophosphate insecticides did not increase af ter 7 d, but the IGRs and abamectin caused additional mortality by 14 d. The IGRs caused additional mortality between 14 d and adult eclosio n. Resistance ratios in the organophosphate resistant strains were 20- fold for azinphosmethyl and ranged from low (< 5-fold) for hexaflumuro n and fenoxycarb, to high (1.5-26-fold) for diflubenzuron. Resistance to malathion was also low and appeared to be negatively correlated wit h azinphosmethyl resistance. High levels of synergism (27-fold) were f ound with die esterase synergist S,S,S-tributylphosphorotrithioate (DE F) 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.