Inheritance and stability of pyrethroid resistance in the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) in Central Africa.

Background: The cotton bollworm Helicoverpa armigera (Hübner) has developed esterase-mediated resistance to pyrethroids in Central Africa. To gain a better understanding of how quickly this resistance can evolve, its genetic basis and stability were examined in a field-derived strain of H. armigera (474-fold resistant to cypermethrin).

Results: Genetic crosses between susceptible, resistant and F(1) hybrids indicated that resistance was inherited as a dominant trait (D(LD) = 0.86) and conferred by a single autosomal gene. The dominance of resistance decreased as the cypermethrin dose increased, so that resistance was incompletely dominant (D(ML) = 0.73) at the highest dose tested. Resistance (DL(50)) of the F(1) hybrid progeny significantly decreased over five generations in the absence of pyrethroid exposure.

Conclusion: Rapid selection of resistance alleles due to dominance supports the ability of H. armigera to develop resistance to pyrethroids in Central Africa. However, associated fitness costs provide useful information for managing the evolution of resistance.