In vivo responses of midgut epithelial cells to ookinete invasion of three different vector–parasite combinations, Aedes aegypti–Plasmodium gallinaceum, Anopheles stephensi–Plasmodiumberghei, and A. stephensi–P. gallinaceum, were directly compared by using enzymatic markers and immunofluorescence stainings. Our studies indicate that, in A. Aegypti and A. stephensiookinetes traverse the midgut via an intracellular route and inflict irreversible damage to the invaded cells. These two mosquito species differ, however, in their mechanisms of epithelial repair. A. stephensidetaches dam-aged cells by an actin-mediated budding-off mechanism when invaded by either P. berghei or P. gallinaceum. In A. aegypti, the midgut epithelium is repaired by a unique actin cone zipper mechanism that involves the formation of a cone-shaped actin aggregate at the base of the cell that closes sequentially, expelling the cellular contents into the midgut lumen as it brings together healthy neighboring cells. Invasion of A. Stephensiby P. Berghei induced expression of nitric oxide synthase and peroxidase activ-ities, which mediate tyrosine nitration. These enzymes and nitro-tyrosine, however, were not induced in the other two vector–parasite combinations examined. These studies indicate that the epithelial responses of different mosquito–parasite combinations are not universal. The implications of these observations to vali-date animal experimental systems that reflect the biology of natural vectors of human malarias are discussed