Insects rely on the innate immune system to defend themselves from pathogens, and are thought to be incapable of mounting adaptive immune response. We investigated whether pre-exposure of adult females to Plasmodium infection could enhance their ability to respond to a second infection. We found adult mosquito females challenged with Plasmodium are able to "learn" and respond more efficiently to subsequent challenges. Preliminary data indicate that the priming response involves hemocyte differentiation. We identified a single QTL in Chr. 13 that confers an African strain of Plasmodium falciparum (GB4) the ability to evade the immune response of An. gambiae (L35) females. In contrast, 98-100% of P. falciparum 7G8 parasites (Brazilian strain) are detected by the mosquito immune system and killed.  The location of the recombination sites flanking the central marker in the QTL was determined by saturating this region with additional microsatellite markers and defines a 171.8 kb region coding for 42 genes. Several complementary strategies to narrow down this region and identify the gene(s) that allow African strains of P. falciparum to evade the immune system and infect mosquitoes will be discussed.