Macrocyclic lactones: impact on non-target fauna in pastures

The endectocides (avermectins and milbemycins) comprise a group of highly e fficacious, broad-spectrum parasiticides, widely used throughout the world for the control of livestock parasites. Endectocides are excreted mainly in faeces, and to a large extent as unaltered drug. Because of this, these dr ugs have the capacity to exert adverse effects on insect populations associ ated with animal dung. Fears have been expressed that this reduction in fau na could have an adverse effect and potentially delay dung degradation, lea ding to fouling of pastures. Two experiments with treated cattle and sheep were designed to compare the effects of moxidectin and ivermectin on the ny Neomyia cornicina F. (Diptera) and the dung beetles Aphodius haemorrhoidal is (L.) and A. constans Duft. (Col. : Aphodiidae). Larvae of Aphodiidae spe cies and flies were bred in dung collected daily from day 0 to day D+38 pos t-treatment and the rate of emergence of adults was calculated. In the catt le experiment, no significant differences were observed in the emergence of A. haemorrhoidalis fed with dung from controls or cattle treated with moxi dectin (Cydectine(R)1% injectable solution; 0.2 mg per kg body weight) or i vermectin (Ivomec(R) 1% injectable solution; 0.2 mg per kg b.w.). For flies , the rate of emergence of N. cornzicina with moxidectin was significantly lower than control until D+10 post-treatment, not different from control af ter D+16. The mortality was absolute (100%) until D+20 with ivermectin and the rate of emergence remained lower than control up to D+34. In the sheep experiment, a significant difference in A. constans rates emergence was obs erved between control and moxidectin for the first 2 days following treatme nt (Cydectin(R) 0.1% oral drench, 0.2 mg moxidectin per kg b.w.). In the iv ermectin group (Oramec(R) 0,088% oral drench at 0.2 mg ivermectin per kg b. w.), the differences with control were significant for 6 days post-treatmen t. Moxidectin was shown to be safe for N. cornicina development after 3 day s post-treatment. In the ivermectin group, differences with control for N. cornicina were significant for 6 days, with null emergence for 5 days post- treatment.