Risk of select parasiticides diflubenzuron, eprinomectin, and fenbendazole to dung-associated beetles

Dung-associated beetles provide crucial ecosystem services including reducing pasture fouling and contributing to animal and pasture health. However, parasiticides used on cattle can negatively impact beetles. We assessed the exposure and impact of Clarifly (active ingredient [a.i.] diflubenzuron), LongRange (a.i. eprinomectin), and Safe-guard (a.i. fenbendazole) on beetles and flies. Using high-performance liquid chromatography, we quantified the residual concentrations of these chemicals in cattle feces for 150 d. We found fenbendazole excreted within the first 3 d after treatment, while diflubenzuron and eprinomectin persisted for 8 to 12 wk. To estimate the concentrations of these active ingredients that are toxic to beetles, we dosed cattle dung with diflubenzuron, eprinomectin, or fenbendazole, allowed insects to colonize in the field, and monitored the emergence of beetles. Dung beetle (Scarabaeidae) abundance was negatively impacted by diflubenzuron and eprinomectin while fenbendazole had no negative effects. Predatory beetles, families Carabidae, Histeridae, Hydrophilidae, and Staphylinidae, were unaffected by all chemicals. We found that dung from animals treated with LongRange was toxic to Scarabaeidae for 30 to 90 d after treatment. Similarly, diflubenzuron was toxic to Scarabaeidae when cattle consistently consumed it, although concentration of diflubenzuron in dung varied when cattle were fed using Clarifly. In contrast, the active ingredient in Safe-guard, fenbendazole, was not toxic at 10 mg/kg. Although, we found this product excreted at higher concentrations for 1 d after treatment, it likely poses little risk. Our results suggest that producers who value beneficial beetles as a management goal should avoid eprinomectin and diflubenzuron products that excrete for long periods.