Studies on the Nutritional Relationship of Larval Aedes Aegypti (Diptera: Culicidae) with Smittium Culisetae (Trichomycetes)

SUMMARY

Axenic larvae of the mosquito, Aedes aegypti, were reared singly on a sterile semidefined medium from which required vitamins and sterols were individually deleted. Trichospores obtained from axenic cultures of the fungus, Smittium culisetae (Trichomycetes), were added to the medium to infest the hindguts of the larvae. First instar larvae invariably became heavily infested from the original spore inoculum, but infestations were often not maintained in the subsequent larval instars. In some instances thalli attached to the external cuticle of living larvae. With the introduction of S. culisetae, larvae were able to attain at least one additional instar when reared without riboflavin, pyridoxine or nicotinamide. No such improvement in larval growth was noted with S. culisetae upon the omission of thiamine or Ca pantothenate. In the absence of sterols larvae did not develop beyond the fourth instar, but following the addition of S. culisetae, one out of 45 larvae pupated. Both the lipid extract and dead whole mycelium of S. culisetae are adequate sources of sterols for larvae, and larvae are able to utilize desmosterol, the predominant sterol in Smittium spp. Sparse free mycelial growth was evident in the medium in those vitamin and sterol tests where larvae demonstrated an improvement in growth; hence the free mycelium may have been serving as a dietary source of nutrients. It is possible that mosquito larvae growing under some conditions of nutritional stress may be provided with required nutrients through infestations of S. culisetae in their guts.