FIELD EFFECTS OF IVERMECTIN RESIDUES ON DUNG BEETLES

1. The effects and the persistence of a single injection of ivermectin (Ivomec(R);) to steers, at the recommended dose rate of 200 mug kg-1 body weight, were studied in spring field experiments (Spanish conditi ons). 2. Elimination of ivermectin by cattle (faecal route) was rapid (12 days), with a peak in day 5. The persistence of ivermectin in drop ped dung was low under field conditions (<6 days). 3. The drug itself did not increase attraction of beetles to dung. The attraction of beet les to dung from treated animals increased after day 5 until day 17, b eyond the time when ivermectin was available. The hypothesis made was that ivermectin modified the gut flora of treated cattle after the pea k of elimination. Watering of pats did not influence results. 4. Iverm ectin concentration in dung dropped on days 1 and 10 post-treatment in hibited the development of larvae of the dung-dwelling Diptera Neomyia cornicina. At the former concentration, it inhibited the development of the dung beetle Euoniticellus fulvus whereas, for the latter, a sli ght delay in development was observed. 5. The consequences of routine treatment of cattle with ivermectin on non-target organisms are discus sed. The risks for the environment are different according to insect g roups and countries, mainly due to differences in conditions of temper ature and degradation of ivermectin.