Effect of diflubenzuron on flight of adult aquatic insects (Plecoptera, Trichoptera) following emergence during the second year after aerial application.

With Malaise traps, we monitored the flight of adult Plecoptera and Trichoptera following emergence from headwater streams in the Fernow Experimental Forest, WV, during the second year after application of diflubenzuron. We placed five traps at various distances from each stream during May through September of 1991, 1992, and 1993. We collected pretreatment samples during the first year. In May 1992, diflubenzuron was applied to two watersheds, and the other two watersheds were used as untreated references. The 1992 study tested the effects of diflubenzuron that fell directly into the streams or were washed into the stream during the first year. For 1993, we tested the hypothesis that diflubenzuron affected adult flight following emergence during the year following abscission and possible ingestion of the treated leaves. The analysis compared the regressions of the number of adults caught in each trap versus distance of the trap from the stream among years and between treatments for each species. The flight of the stonefly Leuctra ferruginea (Walker) was reduced in the treatment watersheds compared with the reference watersheds during the year following abscission of the treated leaves. Adult flight of other species did not decrease in the treatment watersheds during 1993. These results show a relatively small effect of diflubenzuron on these aquatic insects; however, our study involved only a single application of diflubenzuron. Additional research may be needed to predict the possible effects of multiple applications of diflubenzuron over several years as often occurs during actual efforts to suppress gypsy moth, Lymantria dispar (L.).