Mutants showed normal exflagellation numbers and developed into mature ookinetes in vitro and in the midgut of A. stephensi mosquitoes. Ookinetes did not show any morphological differences from wild-type parasites. Mutant ookinetes cannot invade midgut epithelial cells as was shown by light microscopic analysis. Ookinetes cannot rupture the cell membrane of the midgut epithelial cell as was shown by electron microscopic analysis. Analysis of ookinete invasion/traversal showed that wild type ookinetes had invaded the midgut epithelium, and over half of them were attached to the basal lamina. The epithelial cells initially invaded by ookinetes were heavily damaged. They were characterized by high electron density staining, protrusion from the epithelium, absent or scant microvilli, and degeneration of cytoplasmic organelles such as mitochondria. In contrast, mutant ookinetes were found neither in the cytoplasm of the midgut epithelial cell nor beneath the basal lamina. All of the mutant ookinetes were located outside the epithelium, and over the half of them adhered to the membrane of the epithelial cell, attaching their apical tip to epithelial cell surface. The epithelial cell surface where the ookinete attached was invaginated toward the cytoplasm, but no apparent breakage was observed in the extended cell membrane. The attached epithelial cells were kept intact, as shown by staining of normal electron density, dense microvilli, retention of the complex structure of the basal membrane labyrinth, and intact cytoplasmic organelles.

No oocysts are formed. Mutant ookinetes cannot invade and traverse midgut epithelial cells (see phenotype 'Fertilization and ookinete').