A new method for rearing the sciarid fly, Lycoriella ingenua (Diptera: Sciaridae), in the laboratory: possible implications for the study of fly — fungal interactions

Abstract

A new method for rearing the sciarid fly Lycoriella ingenua in the laboratory has been developed. The flies were reared on pure culture of the fungi Absidia cylindrospora or A. glauca cultivated on malt extract agar in Petri dishes. Adult flies were introduced to plates with fresh culture of fungi, laid eggs there and the larvae fed on fungi. The newly emerged generation of adults was collected and transported to new dishes. The whole development of one generation lasted 18 days at 25 °C and one female laid on average 53 eggs. By this technique more than 30 fly generations were reared without introducing any new material from nature. Using the flies obtained from this rearing system the oviposition attractiveness of 68 species of soil fungi were tested in multichoice stellar preference experiments. The oviposition attraction of individual species varied substantially, the frequency of egg laying was significantly higher than random choice in 18 species, in 14 species proportional to random choice and in 30 species lower than random choice, 10 species of which were never used for egg laying. Taxonomic affiliation did not appear to correspond with the flies' oviposition behaviour. In the next experiment the oviposition attraction of 25 species was compared with the suitability for larval development. A significant proportion of the highly preferred fungi did not offer suitable conditions for larval development. On the other hand, a substantial majority of fungi with lower preferences (selected for oviposition with frequency proportional to random choice) did offer suitable conditions for larval development. This appears to be caused by ambivalent relationships of fungi and flies - not only are fungi important as a food source for fly larvae, but also eggs and trapped adult flies are used by some fungi as a source of nutrients. In other cases the attraction of adult flies can be important for fungal spore dispersal.