Monitoring acetamiprid resistance in the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae)

Acetamiprid resistance in the diamondback moth (DBM) Plutella xylostella (L.) from cabbage fields of Iwaoka-cho, Kobe City, where acetamiprid is the primary insecticide for DBM control, was monitored from 1999–2001. The results showed only a slight change in the susceptibility of the population over the monitoring period, considering the LC50 values and their corresponding resistance ratios (RRs). However, the LC95 values showed a significant shift towards acetamiprid resistance, suggesting that the population could develop higher levels of resistance to the insecticide in the future. To retard the progress of acetamiprid resistance, growers rotate acetamiprid with other insecticides. We thus evaluated the efficacy of five other insecticides to identify efficacious products to be used with acetamiprid. Results indicated that the population was moderately resistant to esfenvalerate and phenthoate, and tolerant to cartap. The population was, however, susceptible to chlorfluazuron and a preparation of Bacillus thuringiensis (btk). Incorporating chlorfluazuron and btk into the resistance management tactic adopted in Iwaoka-cho is thus a sound option.