Diamondback moth, Plutella xylostella (L.), resistance management in Hawaii

Resistance to spinosad insecticide in field populations of diamondback moth was discovered at Kunia, Hawaii, in November 2000, about two and a half years after its introduction. Leaf-dip assays of field populations from the islands of Oahu, Maui and Hawaii confirmed moderate to high levels of resistance compared with pre-introduction baselines. Resistance occurred despite label restrictions that were designed to prevent overuse. A major contributing factor was the lack of suitable alternatives and the unsynchronised use of pesticide classes that led to continuous population exposure. Region-focused resistance management plans were implemented by growers and University of Hawaii extension advisers in an IRAC sponsored program. The two goals were to mitigate resistance to spinosad and avoid resistance to emamectin benzoate and indoxacarb. The use of emamectin benzoate and indoxacarb was limited to month-long windows that were rotated. There was a ban on spinosad use in crucifer production until regional DBM LC50 decreased to a 5 ppm level.