Comparative insecticide resistance of New Zealand and North American populations of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

The susceptibility of two New Zealand populations of diamondback moth, Plutella xylostella, to insecticides from three classes was compared with the susceptibility of a standard North American population (Geneva 88) in laboratory assays at the New York Experiment Station during 1993. Leaf dip assays showed that the New Zealand populations had developed moderate resistance to permethrin compared with the Geneva 88 population, but were still susceptible to methamidophos, Bacillus thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai. One of the New Zealand populations, Pukekohe 1, was 10 times more resistant to permethrin at the LC50 compared to the Geneva 88 population. This level of resistance was consistent with the greater use of synthetic pyrethroids, particularly permethrin, compared with other insecticides on vegetable brassicas at Pukekohe. Use of the Pukekohe 1 population as a standard for resistance assays in New Zealand indicated that diamondback moth from a reported control failure in Pukekohe were 4.9 times more resistant to lambdacyhalothrin, and may be as resistant to synthetic pyrethroids as the most resistant North American populations reported in Shelton et al. (1993b).