Effects of ivermectin on two afrotropical dung beetles, Onthophagus gazella and Diastellopalpus quinquedens (Coleoptera: Scarabaeidae).

Subcutaneous injection of 0.2 mg kg-1 ivermectin to heifers negatively affected larvae of the afrotropical dung beetles, Diastellopalpus quinquedens and Onthophagus gazella, developing in the dung. Although closely related, the two species seem to differ in susceptibility; 28% of brood masses made of dung voided 2 days after treatment contained third instar D. quinquedens, whereas O. gazella died as first instars in dung voided up to 8 days after treatment. Folding of the head capsules and lack of mandibular wear in the dead O. gazella larvae suggest that ivermectin could be absorbed through the integument and prevent normal feeding and distension of the head capsule. In addition, the surviving third instar O. gazella in dung voided 16 days after treatment had significantly reduced clypeal and mandibular widths. The dung burial activity, mainly by D. quinquedens, estimated in a field experiment was not affected by ivermectin residues in the dung.