Activity and mating competitiveness of gamma HCH/dieldrin resistant and susceptible male and virgin female Anopheles gambiae and An.stephensi mosquitoes, with assessment of an insecticide-rotation strategy.

The effects of gamma HCH/dieldrin resistance genes on flight activity and mating competitiveness were investigated in males from backcrossed strains of Anopheles gambiae Giles and An.stephensi Liston. Activity of males and virgin females of both species, as recorded in an acoustic actograph, occurred mainly at dusk (the E peak). The activity pattern of An.gambiae males was not affected by resistance genes; in mating competition and predator avoidance experiments, however, RR males were less successful than RS males which were less successful than SS males. The activity pattern of An.stephensi differed from An.gambiae in that the E peaks of RR males and females in a gradual dusk regime were out of synchrony with those of SS and RS, the E peaks of RR occurring slightly later. Thus, RR males and females tended to mate assortatively in mate competition experiments. When a sudden dusk regime was substituted for the gradual dusk regime, activity of RR An.stephensi became synchronized with SS and RS activity, but in mating competition experiments RR still tended to mate assortatively. Estimates of male competitiveness, together with previously-obtained estimates of female fitness, were included in population genetics models. Computer simulations showed that the frequency of resistance in populations of An.gambiae and An.stephensi should decrease in the absence of insecticide at a rate comparable with known field reversions.