In spite of its importance as a potential target for disease control, the insect gut has received little attention. Insect-borne parasites of human disease frequently initiate their development in the insect by penetrating its gut. The gut of hematophagous insects is also the site of blood digestion, a process that triggers egg production and ultimately influences insect fitness and reproduction. This proposal is to develop molecular approaches for the study of the Simulium gut, focusing on the above-mentioned processes. Simulium (blackfly) is the vector for onchocerciasis (river blindness), a debilitating disease that affects millions of people in Africa and Latin America. The parasite is ingested by the blackfly with the blood meal from an infected individual. In order to develop, the parasite must penetrate the blackfly gut. Penetration is largely but not entirely hindered by the secretion by the gut epithelium of a thick peritrophic matrix (PM) that surrounds the blood meal. There are reasons to believe that inhibition of PM formation would result in excessive parasite burden which causes fly lethality. One goal of the proposed research is to clone the genes encoding the two major PM components. The structural organization of these genes, including essential promoter elements, Will be defined and factors required for the gut-specific regulation of gene expression will be investigated. A second focus of this research is the investigation of genes which function in the digestion of the blood meal. Two genes which were previously isolated in this laboratory and encode putative proteolytic enzymes, will be similarly characterized. Finally, antibodies to Simulium gut proteins will be produced and used to explore the feasibility of developing immunological approaches to alter the fitness of the fly or to modify its vector capacity. The ultimate goal of these experiments is to provide the means for devising rational approaches of vector and disease control.