The effects of diflubenzuron (Dimilin®) on selected mayflies (heptageniidae) and stoneflies (peltoperlidae and pteronarcyidae)

Abstract

AbstractTwo types of laboratory toxicity tests (exposure in water and feeding) were conducted to determine the effects of diflubenzuron (DFB) on nontarget aquatic insects. The mayflies Cynygmula subaequalis, Stenacron interpunctatum, Stenonema meririvulanum, and Stenonema femoratum (Heptageniidae) and the stonefly Peltoperla arcuata (Peltoperlidae) were exposed to DFB in water for 96 h, then transferred to pesticide‐free water 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 ppb DFB in water. The mayflies were found to be sensitive to DFB in water at concentrations as low as 0.6 ppb. The stonefly was less sensitive to DFB in water. In our feeding studies, Peltoperla arcuata and Pteronarcys proteus (Pteronarcyidae) were fed DFB‐treated yellow poplar leaves for 24 d, then observed for 60 and 90 d, respectively. Survival of treated Peltoperla was significantly different from the controls at day 60. Survival of treated Pteronarcys was not significantly different from the controls during the 90‐d test period, although the low number of molts that occurred during that time may have influenced these results. Future studies should use early life stages that coincide with leaf fall, when treated leaves would be introduced to headwater streams. The life histories of many aquatic insects are timed to make maximum use of leaf detritus as a food base. Introduction of DFB‐treated leaves to headwater streams may adversely affect these organisms.