The negative effects of the residues of ivermectin in cattle dung using a sustained-release bolus on Aphodius constans</it> (Duft.) (Coleoptera: Aphodiidae)

This paper reports the findings of two trials into the effects of the treatment of cattle with ivermectin slow-release (SR) bolus on the larval development of the dung beetle Aphodius constans</it> Duft. Rectal faecal samples were collected prior to treatment and every 3 and 2 weeks in a first and second trial, respectively, and up to 156 days post-administration of the SR bolus. Faecal ivermectin concentration reached a peak at 63 days post-treatment (1427 ng<formula notation="TeX">$\cdot$</formula>g<formula notation="TeX">$^{-1}$</formula>) and ivermectin was detected up to 147 days post-treatment in the first trial (7.2 ng<formula notation="TeX">$\cdot$</formula>g<formula notation="TeX">$^{-1}$</formula>). First stage larvae of A. constans</it> were reared with control or contaminated dung and adult beetles were counted after emergence. In the first trial, the comparison of pairwise samples showed that ivermectin prevented the development of larval A. constans</it> until day 105, while at day 135 the rate of emergence was still significantly lower than the corresponding series of control (<formula notation="TeX">$p < 0.05$</formula>). In the second trial, the difference between control and treated series remained significant until 143 days post-treatment, with no emergence until 128 days post-administration of SR bolus to cattle. These results show the negative effect of ivermectin on the development of larval A. constans</it>, even at a low concentration (38.4 ng<formula notation="TeX">$\cdot$</formula>g<formula notation="TeX">$^{-1}$</formula>). The administration of ivermectin sustained-release bolus to cattle was highly effective in killing dung beetle larvae for approximately 143 days after treatment. The results were similar when dung was obtained from a single animal kept alone, or from a blending of faecal pats obtained from a group of animals kept in field conditions during the whole trial period.