Effects of avermectin residues in cattle dung on dung beetle (Coleoptera: Scarabaeidae) reproduction and survival

Abstract

Scarabaeine dung beetles feeding on dung from cattle treated with an injection of avermectin at a therapeutic dose to control internal parasites, show larval mortality, mortality of immature adults, reduced egg production, and inhibited ovariole development for periods of 1–4 weeks following treatment. In winter rainfall regions of Australia, feeding by newly emerged adults of an introduced species, Onthophagus binodis, resulted in shredding of cattle dung between December and May. Production of brood masses and eggs resulted in dung being buried from September to November. Feeding by newly emerged adults of a native species, Onthophagus ferox, resulted in dung being buried in May and June, and production of brood masses for breeding resulted in dung burial between September and November. There are thus 2–6 months of the year when injection of cattle with avermectin would affect mortality of newly emerged beetles, and 3 months of the year when avermectin treatment of cattle would affect dung beetle oviposition or larval survival. Beetles were attracted to fresh dung for 2–4 days, and most had left the pad within a week. There are no data to indicate the effects of avermectin residues in dung on dung beetle populations and on beetle fitness. Tests should be done to determine if avermectins in slow release devices have a greater effect on dung beetles than injections, and to determine what effects both have on dung beetle populations.