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PhD Thesis: Bahavioural, ecological and genetic determinants of mating and gene flow in African malaria mosquitoes

October 27, 2010 - 14:39 -- Kija Nghabi

Kija R.N. Ng’habi

Malaria is still a leading threat to the survival of young children and pregnant women, especially in the African region. The ongoing battle against malaria has been hampered by the emergence of drug and insecticide resistance amongst parasites and vectors, respectively. The Sterile Insect Technique (SIT) and genetically modified mosquitoes (GM) are new proposed vector control approaches. Successful implementation of these approaches requires a better understanding of male mating biology of target mosquito species. This thesis explored the potential behavioural, ecological and genetic determinants of mating and gene flow in the major African malaria vector Anopheles gambiae s. l.

This thesis specifically investigated (i) the effect of larval density and nutrition on the mating competitiveness of adult male Anopheles gambiae s.s mosquitoes (ii) compared the physiological fitness of male Anopheles gambiae mosquitoes between laboratory and field populations, (iii) the potential for establishing a self-replicating Anopheles arabiensis population in an enclosed semi-natural environment and observing its genetic variation over time, (iv) the development of a PCR-based method for assessing male mating success among inseminated female An. gambiae and (v) the population genetic structure of An. gambiae s. l. along the Kilombero valley (southern Tanzania).

Results indicated that environmental factors experienced during larval development, affect adult male mating behaviour. These factors can be experimentally manipulated during mass-rearing to enhance male mating success. Laboratory reared males are physiologically different from wild males. Field males have more lipids than laboratory-reared males. This thesis also reports the first ever establishment of an Anopheles population in an enclosed seminatural environment. Conditions within the system were suitable for maintaining the genetic variation which is frequently lost under traditional laboratory cage conditions. The newly developed PCR-based method to assess insemination success will help to understand the mating biology and ecology of An. gambiae mosquitoes within the enclosed semi-field system. Results also show that the An. arabiensis populations of the Kilombero valley display a population substructure whereas An. gambiae s. s. showed no population substructure.

It is concluded that environmental factors, such as crowding and larval nutrition can be manipulated in the laboratory to enhance male mating success. Given the successful establishment of a semi-field mosquito population and the evidence that it does maintain more genetic variation than laboratory colonies, I suggest that studies aimed at exploring male mating biology /ecology and feasibility of SIT/GM can be executed in an enclosed semifield environment. Information obtained in the semi-field system may be more representative of field mosquitoes than that from caged colony mosquitoes. The results of this thesis, therefore, provide useful information to strengthen current and future vector control approaches.

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