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Abstract

During the period from 1986 to 2004, the susceptibility to insecticides of the diamondback moth (DBM) in Iwaoka, Kobe City, Hyogo Prefecture, was determined using 3rd-instar larvae by the leaf dipping method. Moths were collected from a cabbage field every year in Iwaoka. The efficacy of the field's insecticides in that area was also evaluated every year. According to the leaf dipping test results, before 1995, DBM's susceptibility was remarkably low to acephate, phethoate, permethrin, chlorfluazuron, cartap and BT kurstaki. After 1996, the activity of all these insecticides against DBM seemed to improve, however, in the meantime, some newer insecticides marketed after 1996, such as chlorfenapyr, emamectin-benzoate, spinosad and BT aizawai, have remained highly active in laboratory tests throughout the monitoring period. According to the field test results in 2003 and 2004, phethoate, cartap and BT kurstaki showed good efficacy against DBM. The field efficacy of acephate and chlorfluazuron seemed to improve but they are still insufficient to control DBM at present. The field efficacy of permethrin, however, has continued to be low. On the other hand, some insecticides marketed after 1996 such as chlorfenapyr, emamectin-benzoate, spinosad and BT aizawai, has remained excellent throughout the monitoring period. Upon reviewing prior research, it appears that most insecticides introduced before 1994 lost their practical efficacy within a few years of being placed on the market. However, to dates, insecticides newly marketed after 1996 do not seem to have apparent resistance problem. Therefore, we can surmise that before 1995 and after 1996, a dramatic change has occurred in the area of insecticide resistance problems.