EFFECTS OF IVERMECTIN AND MOXIDECTIN ON THE INSECTS OF CATTLE DUNG

The numbers of insects colonizing the dung of cattle injected with the anthelmintics ivermectin or moxidectin were compared with the coloniz ation of the dung from control animals given no treatment, in a blind field trial. Dung was collected 2, 7, 14, and 21 days after dosing and set out in a randomized grid of standard 2 kg pats. Pats were retriev ed from each of the three groups group after 7, 14, 21 and 42 days in the field for analysis of insect fauna. There were no significant diff erences in the number of adult Aphodius spp. (Coleoptera: Scarabaeidae ) found in the dung from the three treatment groups with either time o f exposure in the field or time after treatment, showing that adult be etles were attracted to all pats equally. However, dung from animals t reated with ivermectin prevented the development of larval Aphodius sp p. for at least 7 days after treatment. In contrast, the dung from ani mals treated with moxidectin supported the development of Aphodius spp . at all stages after dosing, as did dung from control animals. There were no significant differences in the number of cyclorrhaphous Dipter a larvae in dung from control or moxidectin-treated animals. In contra st, such larvae were largely absent from the dung collected from iverm ectin-treated cattle for up to 14 days after dosing. The results show that moxidectin is less toxic to dung-inhabiting insects than ivermect in following standard injection treatment. The results are discussed i n relation to the effects of anthelmintics on non-target pastureland i nsects.