Resistance of Heliothis armigera to Insecticides in the Ord Irrigation Area, North Western Australia1

Abstract

Since 1970, Heliothis armigera (Hübner) has replaced H. punctigera (Wallengren) as the dominant Heliothis species attacking cotton in the Ord valley and has become progressively more difficult to control with insecticides. To determine whether insecticidal resistance was occurring, a standard technique of topical application to larvae was used. Compared with H. punctigera, the Ord strain of H. armigera showed a 90-fold tolerance to DDT, a 35-fold tolerance to DDT-toxaphene, a 5-fold tolerance to methyl parathion, and a 4-fold tolerance to endosulfan. H. armigera from unsprayed areas gave variable results which may be due to dispersal of resistant strains. In comparison to the lowest LD₅₀ values obtained, the Ord strain showed a 90-fold resistance to DDT, a 5-fold resistance to DDT-toxaphene, and a 3-fold resistance to methyl parathion. No resistance to insecticides has so far been demonstrated with H. punctigera.