Effects of aerial application of diflubenzuron on emergence and flight of adult aquatic insects

Malaise traps were used to monitor emergence and flight distances of adult Plecoptera and Trichoptera from headwater streams in the Fernow Experimental Forest, West Virginia, before and after application of diflubenzuron. Diflubenzuron was applied to 2 stream catchments in May 1992. Emergence and flight distances in 2 treatment and 2 reference catchments were assessed with 5 traps placed at various distances from each stream during April through September 1991 and 1992. The regression of the number of adults caught in each trap versus distance of the trap from the stream was compared among years and treatments for each species to determine if diflubenzuron affected adult emergence. The emergence of the stonefly, Peltoperla arcuata Needham, during the first 4 mo after treatment was reduced in die treatment catchments compared with the untreated catchments. Adults of other species were not reduced in the treatment catchments during the period of study. However, additional detritivorous species might have shown an adverse effect if the monitoring had been extended through the period after diflubenzuron-treated leaves entered the streams.