Sex-linked inheritance of endosulphan resistance in Helicoverpa armigera

Endosulphan resistance is common in Australian populations of Helicoverpa armigera (Hübner), but resistance frequencies have not increased above 10–40% of the population, despite widespread use of this insecticide. We examined the inheritance of endosulphan resistance as part of a study of its evolution. Two field-resistant strains were selected in the laboratory. Results from a series of F 1 s and backcrosses in both larvae and adults indicated that resistance was sex-linked, with almost complete dosage compensation in the hemizygous females. In males, resistance was partially dominant in fourth instar larvae but semi-recessive in adults. Estimates of resistance factors depended on the life stage and instar tested and on the bioassay method used. In larvae, resistance factors were highest in neonates (14-fold) and then declined to twofold in fifth instar larvae. Our results indicate that the genetic basis of resistance should enhance the rate of evolution in field populations compared with an autosomal locus.