Insecticide resistance in diamondback moth, Plutella xylostella (L.), in southern Australia

Synthetic pyrethroids have been the most widely used insecticide group for control of Plutella xylostella in southern Australia since the early 1980’s. Insecticide resistance in Australian populations of P. xylostella was first confirmed in Queensland in 1987. Since then, resistant populations have developed throughout southern Australia with reports of insecticide control failures coming from South Australia (1990), Victoria (1993), New South Wales (1993), Tasmania (1995) and Western Australia (1995). Leaf dip bioassays were conducted to determine the toxicity of permethrin to 21 populations of P. xylostella collected from brassica crops grown in Victoria, Western Australia, South Australia, Tasmania and Queensland. High levels of resistance to permethrin (13 to 62 times greater than susceptible laboratoryreared populations) were found in populations collected from brassica crops where growers had experienced difficulties in controlling P. xylostella with synthetic pyrethroids. Preliminary testing with methamidophos suggests that resistance levels of P. xylostella populations in southern Australia to this insecticide are not as high as those to permethrin. Low levels of resistance (two to 12.5 times greater than susceptible laboratory-reared populations) were recorded from three field populations.