DETERMINATION OF THE TOXICITY OF FECES OF CATTLE TREATED WITH AN IVERMECTIN SUSTAINED-RELEASE BOLUS AND PREFERENCE TRIALS USING A DUNG FLY,NEOMYIA-CORNICINA

The toxicity of dung from cattle treated with an ivermectin sustained- release bolus was estimated in terms of ivermectin or ivermectin equiv alents, using a laboratory bioassay with the dung fly Neomyia cornicin a Fabricius (Diptera, Muscidae). The mortalities of flies measured 7 d ays after feeding for 24 h on dung containing known concentrations of ivermectin (between 0.125 and 1 mu g ivermectin per gram fresh dung) w ere compared with the mortalities of insects fed for 24 h on dung from cattle treated 21 days previously with an ivermectin sustained-releas e bolus. The toxicity of the bolus dung was equivalent to dung contain ing 0.66 mu g ivermectin per gram fresh dung. To determine whether ins ects could differentiate between control dung and dung from bolus-trea ted cattle, choice-chamber tests were carried out. There was no signif icant difference in the percentage of females that chose either dung t ype, suggesting that they were unable to distinguish the dung of bolus -treated cattle from control dung. Results are discussed in relation t o the impact that bolus use can have on the insect fauna of cattle dun g.