Sexual ecology of transgenic mosquitoes Stegomyia (Aedes) aegypti

Abstract

Aedes aegypti is the main vector of the virus that causes dengue fever and its more severe form dengue hemorrhagic fever. As traditional control methods have been unable to prevent its global re-emergence as a significant threat to human health, the development of new control methods is gaining importance. One possibility is a genetics-based control strategy modelled on the traditional sterile insect technique (SIT). The RIDL system (Release of Insects carrying a Dominant Lethal) is such an approach, and has been engineered in Ae. aegypti with tetracycline-dependent repression of a dominant lethal gene construct. This thesis examines some of the aspects of Aedes aegypti mating ecology and behaviour that are relevant for the implementation of SIT-based control programmes, focusing on the competitive fitness of the genetically modified males. The transformed mosquitoes differed from unmodified mosquitoes with a similar genetic background with regard to several life history traits. Though the modified mosquitoes pupated earlier - which may be useful in the mass-rearing of such insects - most of the differences suggest reduced competitive performance of the modified males. These included reduced larval survival, adult longevity, insemination capacity and flight ability. In caged mating trials the modified males were less competitive than their wild type counterparts in direct competition for females. Genetically modified mosquitoes were generally smaller than unmodified mosquitoes reared at high larval densities, highlighting the value of optimising rearing conditions as females preferentially selected larger males for mating. Females exhibited no propensity to re-mate over several gonotrophic cycles, unless they had been mated to sperm-depleted males, in which case secondary insemination was common. In conclusion, genetic manipulation reduced the performance of mosquitoes. However, their competitive disadvantage could be compensated for by high over-flooding ratios upon release. Therefore, accurate estimates of competitive ability, as presented in this thesis, are essential if this control strategy is to prove successful.