Lethal and sublethal effects of ivermectin on the dung-breeding beetles Euoniticellus intermedius (Reiche) and Onitis alexis Klug (Coleoptera, Scarabaeidae)

The lethal and sublethal effects of ivermectin residues in cattle dung on the two dung-breeding beetles Euoniticellus intermedius (Reiche) and Onitis alexis Klug were bioassayed in the laboratory. A single standard injection of cattle with ivermectin (200 μg kg-1) prevented adult emergence of E. intermedius from dung collected 2-7 days after treatment. Fewer beetles emerged from the dung of treated animals compared with the dung of control animals, collected 1 and 14 days after ivermectin injection. Adult emergence of O. alexis was reduced between 2 and 7 days after treatment. Dung from treated cattle prolonged the development of E. intermedius for 28 weeks and that of O. alexis for up to 21 weeks after injection. Specimens of E. intermedius that developed in dung collected 1 and 14 days after treatment were less productive than their controls in their first breeding week but not thereafter. It is suggested that cattle should be treated with ivermectin before or after the peak activity period of dung beetles to reduce effects on dung beetle populations.