The insecticide, endosulfan, is still an effective weapon in the arsenal against Hellothis pest species. It fs used extensively in spring and summer as a cheap alternative to the synthetic pyrethroids. This is despite the recurrence of endosulfan resistance first observed in the 1970's (Kay et aL 1983). According to the monitoring data obtained by Neil Forrester ( 1992), NSW Agriculture & Fisher1es, endosulfan resistance was present at levels of 10- 30% in the Namoi Valley during years 1986-1989. However, in the past two years resistance has undergone a sudden increase, with frequencies of up to 50% during summer. A similar pattern was observed in Emerald, although resistance frequencies are higher than in the Namoi Valley (Forrester 1992).