Detection of insecticide resistance in Plutella xylostella (L.) (Lepidoptera: Plutellidae) populations in South Australian crucifer crops

In response to reports of failures of sprays to control Plutella xylostella infestations in vegetable-growing areas around Adelaide in 1991, the extent of resistance to six insecticides in several South Australian populations of P. xylostella was determined. Populations sampled from vegetable crops in the Adelaide region were five- to 200-fold resistant to organophosphates (chlorpyrifos, methamidophos and mevinphos), eight- to 400-fold resistant to pyrethroids (esfenvalerate and permethrin) and six-fold resistant to the carbamate methomyl compared with a susceptible strain. Mevinphos and esfenvalerate were the most effective of the tested insecticides. These, together with Bacillus thuringiensis products, have continued until 1998 to be used almost exclusively for the control of P. xylostella in South Australian vegetable crops in the absence of any resistance management strategy.