AbstractIn haematophagous insects digestion of the blood meal provides nutrients for survival and essential components for egg production. We have isolated and partially characterized two gut‐specific genes from the black flySimulium vittatum. Sequence analysis revealed that both are highly similar to digestive proteases, one to trypsins and the other to carboxypeptidases. RNA blot analysis indicates that the expression of these two genes is regulated in a sexspecific manner; when fed the same sucrose‐based diet, expression in males is substantially lower than in females. In females, expression of both genes is strongly induced by a blood meal. At 6 h after the blood meal the trypsin‐like gene product was immunolocalized to the midgut epithelium and to the outer layers of the peritrophic m