Risk of 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 days. We found fenbendazole excreted within the first 3 days
after treatment (DAT), while diflubenzuron and eprinomectin persisted
for 8-12 weeks. 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 DAT. Similarly, diflubenzuron was toxic
to Scarabaeidae when cattle consistently consumed it, although
the 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 DAT, 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.