For insects, peptides play a dominant role in the control of foraging, digestion, and metabolism. Peptidergic cells are widespread in the nervous and the digestive system. However, we still know very little about the specific functions of the peptides from enteroendocrine cells. AstA and MIP, two peptide families produced by enteroendocrine cells in the Drosophila midgut. In my PhD project, I concentrate on the functional characterization of these two peptide families and try to find out whether and how they may regulate foraging as well as digestion of Drosophila.