RESISTANCE TO INSECTICIDES IN ORIENTAL FRUIT MOTH POPULATIONS (GRAPHOLITA-MOLESTA) FROM THE NIAGARA PENINSULA OF ONTARIO

After about 20 years of wide usage in integrated.pest management (IPM) programs on peach in the Niagara Peninsula of Ontario, populations of Oriental fruit moth, Grapholita molesta (Busck), resistant to azinpho smethyl and phosmet have been selected. Resistance, as expressed in fi rst-instar larvae, was only two- to four-fold to azinphosmethyl or pho smet, but up to 45% fruit infestations have been documented in commerc ial blocks. Resistance to azinphosmethyl was not well expressed in adu lt Oriental fruit moths. In tests with larvae, cross-resistance occurr ed to most other organophosphorus insecticides except acephate and chl orpyrifos. Acephate was more toxic to resistant than to susceptible la rvae. Resistance was higher (>100-fold) to the methyl carbamates carba ryl and carbofuran but was approximately fivefold to the carbamoyl oxi me methomyl. Cross-resistance to pyrethroids was not observed. Tests w ith field-collected material, either from crosses on mating trays in t he field or from pupae collected in cardboard bands attached to trees, indicated that resistance was widespread across the Niagara productio n area but that the resistance was not uniformly expressed at all loca tions. Resistance was expressed in F-1 larvae from crosses of suscepti ble females with field-collected males, indicating that the genetic ch ange in resistant larvae was unlikely the effect of a single recessive gene. Field tests in replicated two-tree plots and in larger (0.25-0. 6 ha) plots treated with up to five applications as a season-long cont rol program indicated that neither chlorpyrifos nor acephate were as e ffective as a pyrethroid (deltamethrin). The sustainability of these I PM programs and potential resistance management strategies are discuss ed.