Field and laboratory observations on the substrates of the mushroom fungus gnat Lycoriella auripila (Diptera: Sciaridae)

SUMMARY Observations in mushroom houses showed that the number of larvae of L. auripila in the casing was higher than in the compost throughout the post‐casing phase of culture. The intestines of larvae from casing contained both peat and fungal material. Choice of oviposition site was accordingly non‐specific. Females from cropping houses appeared to consist of a mixture of monogenic (predominantly unsexual) and digenic (bisexual) strains. Males matured c. 2 days before females at 20 °C; such protandry appeared to be related to sexual differences in the extent of migration undertaken by the dimorphic sexes. Sciarids were reared from egg to adult equally effectively on (a) detached sporophores or on portions of (b) pileus, (c) stipe or (d) gills, all placed on moist peat, or on detached sporophores placed on a variety of inert substrates. Development was completed where sporophore material was the only food source and also occurred on peat to which only protein, particularly egg albumin, had been added. Hence, assuming no protein metabolism by a third organism, for development in the casing layer to occur, the mushroom need contribute only such proteins. However, their replacement by amino acids was not successful in limited tests. Addition of increasing amounts of the fungal metabolites mannitol and calcium oxalate to compost delayed development, and the accumulation of these materials during fungal growth may be responsible for the antagonism between mycelial and sciarid development which results in subsequent migration of emerging adults.