Decreased susceptibilities of four field populations of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), to acetamiprid.

The efficacy of acetamiprid, a neonicotinoid insecticide, against four field populations of the diamondback moth, Plutella xylostella (L.), from Aichi, Hyogo and Kagoshima Prefectures in Japan was determined using the leaf-dipping method. The data obtained indicated that, compared to the reference Osaka susceptible strain (OSS), the four field populations were tolerant to the insecticidal effect of acetamiprid, displaying LC50 resistance ratio (RR) of 4.5-9.0 Maintaining the population from Aichi Prefecture in the laboratory without exposure to acetamiprid resulted in a decline of the LC50 RR from 9.0 to 1.6 over seven generations, suggesting that acetamiprid-resistance is not stable.