Environmental Aspects of Use of Ivermectin and Abamectin in Livestock: Effects on Cattle Dung Fauna

Abstract

The impact of ivermectin and abamectin on the insect fauna of cattle dung is reviewed: the 9 studies on this topic cited have involved ivermectin in formulations administered orally (daily), injected sc or im, in a sustainable-release bolus or as a pour-on, and abamectin injected sc and by bolus. All have shown some, often considerable effect on either the coprophagous larvae of Diptera or of dung beetles and some dosages have reduced the dung ball formation activity by adult dung beetles (Onthophagus gazella and O. bicornis) but not adult survival of those beetles. Effects of treatment on adult populations of Haematobia irritans, H. thirouxi potans, Stomoxys calcitrans, Musca autumnalis, M. domestica, M. vetustissima and M. xanthomelas are detailed, and could be considered beneficial, but the practical impacts under field conditions remain to be determined. Effects against dung beetles and other organisms which contribute to dung breakdown before Diptera of economic importance can complete their preimaginal development in it or which thus accelerate nutrient recycling to soils, may be considered adverse, as too would be reduction of hymenopteran parasitoids of undesirable Diptera or of various insect predators in the dung. Difficulties in evaluating these impacts are compounded by the many other variables contributing to dung degradation in different parts of the world. A fortunate finding is that ivermectin concentrations lethal to earthworms (LC50 = 300 p.p.m.; no-effect level from one study, 12 p.p.m.) would appear too high to be approached in nature. The author considers that usage of ivermectin and abamectin is an improbable threat to dung beetle populations; he nevertheless cites T.J. Ridsdill-Smith (1988) [see Journal of the Australian Entomological Society, 27: 175-178], who suggests replacing abamectin with a non-insecticidal anthelmintic from September to November, the main breeding season of O. bicornis and other dung beetles in south-western Australia.