Occurrence of Resistance to Bacillus thuringiensis in Diamondback Moth, and Results of Trials for Integrated Control in a Watercress Greenhouse

High levels of resistance to Bacillus thuringiensis Berliner in diamondback moth Plutella xylostella (L.), (LC50 more than 280 ppm) was observed in a watercress greenhouse in Osaka Prefecture in 1988. Populations of egg, larva, pupa and adult of diamondback moth were monitored weekly throughout 1988. Population of the larva fluctuated from nearly 0 to 1,300,000. Three control methods were attempted: Insect Killer (high voltage electric shocker with luring purple color lamps), Konagakon (a sex pheromone dispenser), and the vacuum cleaner to suck adult moths. The percentage of moths killed by 24 sets of Insect Killer in the greenhouse was estimated at less than 15% of the emerged adults even in summer. The percentage of mating reduction by Konagakon depended on moth density (more than 90% of mating reduction i f 1 moth/m2; less than 50% if 3 moths/m2). The vacuum cleaner reduced moth population by 50% in every operation. It is therefore possible to reduce the moth density where Konagakon is effective through five or six operations of vacuum sucker.