Mosquitoes are responsible for the transmission of agents of disease to hundreds of millions of people each year. Their large populations are the result of an efficient reproductive system that converts the protein contained in the blood that the female mosquito ingests into eggs. When they mate with females, male mosquitoes transfer sperm as well as substances from their accessory reproductive glands and these substances alter the female's physiology. Among their many effects, the male accessory gland substances prevent the females of most species from ever mating again. After the first mating, sperm are stored in a special sac, the spermatheca, for the rest of her life and these are released to fertilize each batch of eggs as it is laid. Recent work in this laboratory has demonstrated that in the most important mosquito vector of malaria, Anopheles gambiae, male accessory glands do not control mating behavior as they do in other mosquito species. Mating does, however, somehow alter the female's behavior and the hydrocarbon composition of her cuticle, which may be the cue that males of this species use to distinguish unmated or previously mated females. Preliminary experiments suggest that sperm contained in the spermatheca of the female may prevent her from remating. Another interesting difference that emerged from this work was the demonstration of a sperm polymorphism in male An. gambiae; unlike most other mosquito species, male gambiae produce sperm of considerably variable lengths, but only the longer sperm end up in the female's spermatheca.
The goals of this project are to examine the mechanism of cuticular alteration in An. gambiae, its role in mating, and the possible reasons for the varying types of sperm produced by the male. The change in cuticular hydrocarbons of female mosquitoes will be assessed by gas chromatography after various experimental treatments and the degree to which mating is prevented will be determined. Sperm that are produced by males after various treatments such as hormone administration will be examined microscopically and measured for length and presence of a nucleus, both within the genital tracts of the male and female.
The long-term importance of this project is that it will provide much needed information about the mating systems of the most important mosquito vector in the world. If, using tools of genetic engineering, new genes are to be introduced into mosquito populations to prevent them from transmitting infectious agents, the basic mechanisms of mating by which those genes are to be introduced must be better understood.