A comparison of the development and survival of the dung beetle, Onthophagus taurus (Schreb.) when fed on the faeces of cattle treated with pour-on formulations of eprinomectin or moxidectin.

Faeces voided by 1-year old cattle at 3-70 days after treatment with a pour-on formulation of moxidectin had no detectable effects on development or survival of the common dung beetle Onthophagus taurus. In contrast, faeces voided by cattle treated with a pour-on formulation of eprinomectin were associated with high juvenile mortality during the first 1-2 weeks after treatment. Increased mortality also occurred among newly emerged beetles fed on faeces collected 3 days after eprinomectin treatment and there was evidence of suppressed brood production among those that survived. This effect was still apparent even after insects fed for a further 10 days on the faeces of untreated cattle. A model simulating the effects of drug residues on dung beetle populations suggests that in the absence of immigration a single treatment of eprinomectin is capable of reducing beetle activity in the next generation by 25-35%. Effects are likely to be greatest when treatment coincides with emergence of a new generation of beetles.