EFFECTS OF DIFLUBENZURON ON THE REPRODUCTIVE SUCCESS OF THE BLUEGILL SUNFISH, LEPOMIS-MACROCHIRUS

Exposure to diflubenzuron concentrations of 2.5 mu g/L reduced growth of young-of-the-year (Y-O-Y) bluegill by 56 and 86% in replicate enclosures and by 88 and 97% at 30 mu g/L. An adult bluegill reproduction study was conducted in six littoral enclosures located in a 2-ha pond near Duluth, Minnesota. Decreased growth of Y-O-Y-bluegill resulted from the reduction or elimination of preferred invertebrate prey items by diflubenzuron that led to different and/or less Y-O-Y food consumption. Adult bluegill behavior and spawning, embryo hatching, larval survival until swim-up, and Y-O-Y biomass were also studied. Before the first two diflubenzuron applications, spawning occurred in all enclosures; following the first application, spawning occurred in both control enclosures and one 30-mu g/L enclosure. Successful embryo hatching and larval swim-up occurred in all enclosures prior to the first application, and in one control and one 30-mu g/L enclosure following application. The Y-O-Y growth was the most sensitive end point, and Y-O-Y biomass was among the least sensitive end points for bluegill reproductive success. The Y-O-Y bluegills (and potentially other fish species) that are exposed to diflubenzuron concentrations of greater than or equal to 2.5 mu g/L may experience reduced growth, which can result in greater starvation, increased predation, reductions in over-winter survival, and diminished to poor recruitment.