DOES A REPELLENT EFFECT CONTRIBUTE TO REDUCED LEVELS OF INSECT ACTIVITY IN DUNG FROM, CATTLE TREATED WITH IVERMECTIN

A two-year pitfall trapping study was performed to test the preference of coprophilous beetles (Hydrophilidae, Scarabaeidae, Staphylinidae) for dung from untreated cattle versus dung from cattle treated topical ly one or four weeks previously with a recommended dose of ivermectin in a pour-on formulation. In 1994, significantly more Aphodius fimetar ius (Linnaeus) and A. distinctus (O.F. Muller) at each of two sites we re collected with dung from treated cattle. No differences were detect ed for other taxa. In 1995, significantly fewer individuals of ten tax a, including A. fimetarius and A. distinctus, were collected with dung from treated cattle. No differences were detected for other taxa. A c hange in cattle diet may have altered levels of faecal residues, there by changing beetle preferences between years. Comparisons between peri ods of spring and autumn activity identified a change in seasonal pref erences for at least some species. Similar numbers of Onthophagus nuch icornis Linnaeus and of A. fimetarius were collected in spring with du ng from treated or untreated cattle, but significantly more individual s of both taxa were collected in autumn with dung from untreated cattl e. In contrast, the preference of Aphodius prodromus Brahm for dung fr om treated cattle was unchanged between spring and autumn. These resul ts show that ivermectin therapy does influence the colonization of dun g from treated cattle. However, the nature of this influence is confou nded by extraneous factors. Until such time that these factors can be accounted for, general predictions regarding the effect of ivermectin therapy on the colonization of dung by coprophilous insects are premat ure.