The primary Amazonian malaria vector Anopheles darlingi has the ability to adapt quickly to micro- geographic changes resulting from novel environmental conditions such as those encountered in agricultural settlements. Therefore, it is a substantial health threat in Latin America. This proposal examines three understudied aspects of An. darlingi to identify the main mechanism responsible for its success in transmission: broad plasticity or genetic specialization. First, we will test the Frontier Malaria Hypothesis (FMH), tht settlement age predicts malaria incidence, by explicitly separating the effects of settlement age and forest cover. We will use a state-of-the art ecologically-based experimental design that compares environmental variables in three levels of forest cover and two habitat types in both new and old settlements in two regions of Amazonian Brazil. Entomological metrics, most notably the entomological inoculation rate (EIR), will be compared among 12 settlements. We anticipate that a modified FMH, that accounts for both age and forest cover, will provide stronger predictive power for the invasiveness of An. darlingi and other vectors in a wide range of fragmented landscape types. Secondly, we will compare population genomics of An. darlingi exposed to (i) different levels of Plasmodium in the endemic Amazonian region versus southern Brazil where malaria is rare, and (ii) environmental variables in multiple Amazonian settlements. Development of SNPs across the An. darlingi genome will allow us to determine whether populations of An. darlingi differ in their genetic capacity to resist Plasmodium and to discover genomic signatures of selection among populations and regions. Thirdly, we will conduct life-history experiments that focus on the reaction norms to temperature of traits that are directly linked to vectorial capacity. We will test for regional genetic variation for traits and their plasticities, and evaluate whether there has been selection for these differences. By providing original data on the genotypic and phenotypic characteristics integral to the rapid response of An. darlingi to landscape fragmentation, our work will have a significant impact on frontier malaria in the Amazon and in other similar settings. The proposed work is conceptually innovative because it links landscape fragmentation, genetics and life-history traits with the precise localities that are likely to become foci of increased transmission. It is technically innovative because of the use of a next-gen RADseq method to evaluate populations of An. darlingi from localities with varying exposure to Plasmodium. Our long-term goal is to predict where and when An. darlingi populations will expand, resulting in new foci of malaria risk.