Saliva of blood-feeding arthropods contains a variety of enzymes and other proteins that facilitate feeding by inhibiting host hemostatic defenses. As these proteins are injected into the host, they elicit an immune response, potentially including the production of neutralizing antibodies. This aspect of the interaction between blood-feeder and host suggests that antigenically novel alleles may confer a fitness benefit by allowing more efficient feeding. This may be expected to lead to the accumulation of greater allelic diversity than is seen in housekeeping genes. To test this hypothesis, we are assaying allelic diversity of four single-copy genes (apyrase and three members of the D7 family), encoding secreted salivary proteins, from the Yellow Fever mosquito Aedes aegypti. Mosquitoes have been sampled from colonies founded from 13 collection sites, distributed across Africa, Southeast Asia, and South and North America. Results will be analyzed for within- and between-colony allelic diversity, as well as geographical trends indicating panmixis or barriers to gene flow.