Scanning electron microscopy was used to study the morphology of the chorionic surface of two pyralids that feed on Opuntia cactus. The chorionic surface of Cactoblastis cactorum has a reticulate pattern due to the ridges on the surface and aeropyles. The chorionic surface has a granular appearance at low magnifications and rugose at high ones. The micropylar area has a central depression with the micropyles and is surrounded by irregularly shaped polygonal cells. The tertiary cells have aeropyles associated with the cells, and these aeropyles have mesh-like extensions that cover their openings. The general appearance of the chorionic surface of Melitara prodenialis is similar to C. cactorum, but the micropylar region differs in that primary cells surrounding the micropylar depression are looping cells of varying sizes. Also, no aeropyles are associated with the looping cells around the micropylar region.