Sub-lethal effects of moxidectin on the Neotropical dung beetle Onthophagus landolti Harold (Coleoptera: Scarabaeinae)

Macrocyclic lactones can have adverse effects in dung beetles exposed to manure containing them. An assessment of the survival and fertility of adult Onthophagus landolti Harold fed with manure from cows treated with moxidectin was performed, as well as the emergence rate of the imagoes from the masses. Three cows (Bos indicus x B. taurus) were subcutaneously injected with 1% moxidectin (0.2 mg kg^?1 b.w.) and another three were injected with 10% moxidectin (1.0 mg/kg^?1 b.w.). Manure was collected from these animals one day prior to moxidectin administration, five days post-treatment in the 1% and 10% treatments, and fourteen days in the 10% treatment. Four bioassays were done: a control using manure without moxidectin; 1% moxidectin at five days post-treatment; 10% moxidectin at five days post-treatment; and 10% moxidectin at fourteen days post-treatment. In each replicate, for each pair of adult O. landolti was daily fed with 30 g manure according to the treatments. No lethal effects were observed in any of the four treatments. Sub-lethal effects (P < .05) were present in the 10% moxidectin treatments at five and fourteen days post-treatment. Fecundity was reduced by 78.2% at five days and 54.9% at fourteen days, and imago emergence was negatively affected at both times. Current moxidectin application methods may have negative effects on the environmental services provided by dung beetles, and therefore need to be modified to minimize any impacts they might have on these vital members of tropical livestock systems.