The purpose of this research is two fold. First to improve pest management of the sciarid fly (Diptera: Sciaridae) by better defining its relation to mushroom production. Secondly, to explore some of the factors and aspects of the biology of the fly which may increase room to room dispersal rates of adults. The effects of different generations of production room Lycoriella mali Fitch infestations and seasons on yield were explored. In models regressing densities of different generations to mushroom yield, significant negative slopes (p=.05) existed in all models. However, flies did not account for as much yield variance as hypothesized (16.43%). Yield is greatest during the winter months when insect pressure is lowest and decreases in summer months when more insects are present. Diflubenzuron (Dimilin 25 WP, Uniroyal Co.) was tested for its effects on fly emergence and oviposition. Diflubenzuron was effective in suppressing fly emergence and remained effective when treated compost was exposed to phase II peak heating. In production room experiments all fly generations had significantly fewer flies in rooms treated with diflubenzuron at fill. L. mali showed a slight preference to oviposition in diflubenzuron treated compost, indicating a possible attractant effect. A criterion table was developed to estimate the age of L. mali. Both younger and larger L. mali carried more ovarioles. The number of ovarioles that L. mali carry dropped significantly after 48 h; this is likely the time the fly becomes parous. The effects of ambient temperature and distance between production rooms on dispersal were explored. The greatest number of dispersing flies were caught during the summer months. As the daily median temperature increased, the number of dispersing flies increased exponentially. Production room blocks on the perimeter of the farm generally had fewer dispersing flies than centrally located production room blocks indicating that it was unlikely that a reservoir population existed outside the farm. Measurements of wing area and age of L. mali captured while dispersing and not dispersing were compared. Dispersing flies had significantly smaller wings than non-dispersers (p=.000). Wing area for dispersing flies decreased along a density gradient, while wing area for non-dispersers did not. The mean age of dispersing flies was not significantly different (p=.082) from non-dispersers, and neither changed along a density gradient. / Graduation date: 1996