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

This paper reports the findings of two trials into the effects of the treat ment of cattle with ivermectin slow-release (SR) bolus on the larval develo pment of the dung beetle Aphodius constans 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 bolu s. Faecal ivermectin concentration reached a peak at 63 days post-treatment (1427 ng.g(-1)) and ivermectin was detected up to 147 days post-treatment in the first trial (7.2 ng.g(-1)). First stage larvae of A. constans were r eared with control or contaminated dung and adult beetles were counted afte r emergence. In the first trial, the comparison of pairwise samples showed that ivermectin prevented the development of larval A. constans until day 1 05, while at day 135 the rate of emergence was still significantly lower th an the corresponding series of control (p < 0.05). In the second trial, the difference between control and treated series remained significant until 1 43 days post-treatment, with no emergence until 128 days post-administratio n of SR bolus to cattle. These results show the negative effect of ivermect in on the development of larval A. constans, even at a low concentration (3 8.4 ng.g(-1)). 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 pe riod.