The Effects of Diflubenzuron (Dimilin®) on Selected Mayflies (Heptageniidae) and Stoneflies (Peltoperlidae and Pteronarcyidae)

Abstract

Two 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, Sfenacron 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 .O, 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 Pteronarcysproteus (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 ar a food base. Introduction of DFB-treated leaves to headwater streams may adversely affect these organisms.

Nontarget effects of a test application of diflubenzuron to the forest canopy on stream macroinvertebrates

“…the shredder/collector-gatherers Ephemerella dorothea and Eurylophella funeralis, and Heptageniidae (p ϭ 0.096), the mayfly family that included the scraper/collector-gatherer species Stenonema, Epeorus, and Stenacron. Heptageniid mayflies were shown to be sensitive to DFB concentrations in water of 0.6 ppb in an earlier study in our laboratory [15]. Differences in mean density between streams in treatment and reference watersheds were also observed for oligochaete worms and flatworms (Turbellaria).…”

“…Studies by Swift et al [9] and Harrahy et al [15] showed that DFB residues toxic to shredders can remain on leaves in a stream for up to 4 months.…”

“…Chem. 15,1996 M.K. Hurd et al (from 2.0 to 1.1) in treated watersheds in the postapplication period, whereas mean densities in reference streams nearly doubled (1.9-3.7; Fig.…”

“…In a continuous-flow laboratory stream, they determined that a DFB concentration (Ͼ1.0 g/L) required to control chironomids would severely reduce or eliminate Peltoperla, Paraleptophlebia, Ephemerella, and Nemoura. Harrahy et al [15] found that survival rates of several heptageniid mayflies were significantly lower in test concentrations of DFB (as low as 0.6 ppb) than in controls, following a 4-day exposure period.…”

Effect of diflubenzuron on the maturation and reproductive success of the copepod Eurytemora affinis

“…In insects, chitin synthesis can resume following a limited exposure period (Grosscurt and Jongsma 1987). Effects may be either the result of a steady build-up of the contaminant to a threshold level in the organism over time or there may be a latency period prior to the manifestation of effects (Harrahy et al 1994). In the latter case, we may expect latent effects after a certain period of time even if the organisms were removed from the toxicant.…”