PYRETHROID RESISTANCE MECHANISMS IN AUSTRALIAN HELICOVERPA-ARMIGERA

In 1983, at the onset of pyrethroid resistance in Australian Helicoverpa armigera, three resistance mechanisms were identified. They were: a strong nerve insensitivity (Super-Kdr), penetration resistance (Pen), and a factor which was overcome by piperonyl butoxide (PBO). Super-Kdr nerve insensitivity appeared to be a major cause of pyrethroid resistance and contributed to high-order resistance (> 100-fold). From 1987 to 1990, to monitor the effect of the Australian Helicoverpa insecticide resistance management strategy on insecticide resistance, we conducted a survey of the frequencies of these mechanisms in field-collected H. armigera. The relative importance of the Pen and Pbo mechanisms in resistant H. armigera have increased but Pen and Pbo confer only low order (approximately 20-fold) resistance. We found no evidence of the 1983 Super-Kdr mechanism in the latest samples, but, instead, found another distinct Kdr-type mechanism. This mechanism was correlated with very low-order nerve insensitivity and was of little toxicological significance. The impact of the Helicoverpa insecticide resistance management strategy on pyrethroid resistance in H. armigera is discussed.