THE EFFECTS OF DIFLUBENZURON (DIMILIN(R)) ON SELECTED MAYFLIES (HEPTAGENIIDAE) AND STONEFLIES (PELTOPERLIDAE AND PTERONARCYIDAE)

Two types of laboratory toxicity tests (exposure in water and feeding) were conducted to determine the effects of diflubenzuron (DFB) on non target aquatic insects. The mayflies Cynygmula subaequalis, Stenacron interpunctatum, Stenonema meririvulanum, and Stenonema femoratum (Hept ageniidae) and the stonefly Peltoperla arcuata (Peltoperlidae) were ex posed to DFB in water for 96 h, then transferred to pesticide-free wat er and observed for 36 d. The mayflies were exposed to 0, 0.6, 5.6, 55 .7, or 557.2 ppb and the stoneflies to 0, 1.0, 10.2, 101.5, or 1,015 p pb DFB in water. The mayflies were found to be sensitive to DFB in wat er at concentrations as low as 0.6 ppb. The stonefly was less sensitiv e to DFB in water. In our feeding studies, Peltoperla arcuata and Pter onarcys proteus (Pteronarcyidae) were fed DFB-treated yellow poplar le aves for 24 d, then observed for 60 and 90 d, respectively. Survival o f treated Peltoperla was significantly different from the controls at day 60. Survival of treated Pteronarcys was not significantly differen t from the controls during the 90-d test period, although the low numb er of molts that occurred during that time may have influenced these r esults. Future studies should use early life stages that coincide with leaf fall, when treated leaves would be introduced to headwater strea ms. The life histories of many aquatic insects are timed to make maxim um use of leaf detritus as a food base. Introduction of DFB-treated le aves to headwater streams may adversely affect these organisms.