Two mechanisms regulate mosquito host-seeking behavior after a blood meal. Distention-induced inhibition is a neural mechanism that prevents host seeking as long as the abdomen is distended beyond a critical volume. Oöcyte-induced inhibition is a humoral mechanism, initiated by the ovaries, but resulting from a substance apparently produced by the fat body during vitellogenesis. Optimal conditions in the laboratory generally result in the overlap of these mechanisms, so that mosquitoes feed on blood only once during each gonotrophic cycle. However, circumstances that arise in the field, such as suboptimal larval and adult nutrition, an aged population, or a delay in mating, can affect the two mechanisms so that the chances for multiple host contacts during a single gonotrophic cycle increase.