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

Abstract

AbstractAfter 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 azinphosmethyl and phosmet have been selected. Resistance, as expressed in first-instar larvae, was only two- to four-fold to azinphosmethyl or phosmet, but up to 45% fruit infestations have been documented in commercial blocks. Resistance to azinphosmethyl was not well expressed in adult Oriental fruit moths. In tests with larvae, cross-resistance occurred to most other organophosphorus insecticides except acephate and chlorpyrifos. Acephate was more toxic to resistant than to susceptible larvae. Resistance was higher (> 100-fold) to the methyl carbamates carbaryl and carbofuran but was approximately fivefold to the carbamoyl oxime methomyl. Cross-resistance to pyrethroids was not observed. Tests with field-collected material, either from crosses on mating trays in the field or from pupae collected in cardboard bands attached to trees, indicated that resistance was widespread across the Niagara production area but that the resistance was not uniformly expressed at all locations. Resistance was expressed in F1 larvae from crosses of susceptible females with field-collected males, indicating that the genetic change 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 control program indicated that neither chlorpyrifos nor acephate were as effective as a pyrethroid (deltamethrin). The sustainability of these IPM programs and potential resistance management strategies are discussed.