The Mode of Infection of the Insect Pathogenic Fungus Culicinomyces in Larvae of the Mosquito Culex Fatigans.

The initiation and morphological development of infection by Culicinomyces in C. fatigans larvae was followed by means of observations of dissections and stained histological sections of infected specimens. The infection sites are the foregut and hindgut regions of the digestive tract, unlike those of most other insect-parasitizing fungi, which invade through the exterior integument. The penetration of the gut wall and growth in the haemocoel is described, as well as sporulation of the fungus after death of the larvae. The first stage in infection is the firm adherence of the fungal spore to the gut cuticle. This occurs before the spore germinates, and there is evidence to suggest that it may be excited by a thigmotropic stimulus. The penetration of the gut wall does not involve the formation of an appressorium, though this does not preclude mechanical penetration. The penetration of the exterior cuticle, which occurs after death of the insect and initiates conidiophore formation, involves a typical appressorium and mechanical force.