Abstract:

The knowledge of reproductive fitness in susceptible and resistant mosquitoes could be important in planning and implementing mosquito control programs. The laboratory studies were carried out to reveal the variations in the reproductive fitness of parent (AnS) and resistant (AnR) strains of malarial vector Anopheles stephensi originating from Delhi, India on selections with deltamethrin (AnD_L) or the combination of deltamethrin and PBO (1∶5) (AnD_P) at the larval stage and selections with deltamethrin at the adult stage (AnD_A). The reproductive fitness was evaluated in terms of the fecundity, fertility, egg hatchability and the length of gonotrophic cycles. The AnR strains exhibited 60%-73% reduced duration of the gonotrophic cycles when compared with AnS strain. There was a considerable decrease in the egg production, ranging from 14.5% to 37.9% in AnR strains as compared to the AnS strain. The maximum reduction was observed in AnD_L40 strain with the highest levels of deltamethrin resistance. The results indicate the possible positive correlation between the levels of deltamethrin resistance and the reproduction disadvantage. This correlation was further confirmed by 19.4% to 30.9% decrease in the hatchability of eggs of the AnD_L40 strain with respect to that of the parent strain. A worth mentioning observation of the reduced reproductive fitness in RD_p strains suggests the efficacy of synergized deltamethrin selections in not only decreasing the deltamethrin resistance levels but also reducing the frequency of resistant individuals. The diminished reproductive fitness in adult-selected strains possessing negligible resistance to deltamethrin implicates the higher usefulness of deltamethrin as an adulticide in comparison to as a larvicide against An. stephensi. The results suggest that the reduced reproductive fitness of resistant genotypes in the population can eliminate heterozygotes and resistant homozygotes by implementing different resistancemanagement strategies against An. stephensi.

Key words: Anopheles stephensi, deltamethrin resistance, piperonyl butoxide, reproductive fitness, fecundity, egg hatchability, gonotrophic cycle, reproductive disadvantage