SummaryHistological studies were made of larvae ofApis melliferawhich had been fed sucrose solution containing spores ofAscosphaera apis.Germinated spores were seen in the lumen of the ventriculus. Hyphae developing from these did not colonize the gut contents extensively, but grew directly through the peritrophic membrane and gut epithelium. Unlike the situation in other genera of mycopathogens, the peritrophic membrane did not appear to provide a barrier to infection byA. apis.Subsequently, the mycelium spread throughout the haemocoel, and after 3 days, the first hyphae were seen to penetrate the integument and grow aerially.