Faeces from sheep treated with albendazole had no detectable effects on breeding by either flies or beetles. In contrast, faeces voided by sheep treated with controlled-release capsules of ivermectin (CRI) precluded successful breeding by each of the species tested. No fly larvae and almost no beetle larvae survived in faeces collected up to 39 days after capsule administration. Newly-emerged O taurus also suffered significant mortality whereas those that survived underwent delayed sexual maturation. Ivermectin residues had no effect on the survival of sexually mature beetles, but reduced the fecundity of O taurus. A model simulating the effects of drug residues on dung beetle populations indicates that CRIs have the potential to cause substantial declines in beetle numbers, particularly if treatment coincides with spring emergence.

Excreted faecal residues of moxidectin are relatively innocuous to larvae of both M vetustissima and M domestica. Those of ivermectin inhibit survival for 7 to 14 days after treatment and are likely to have adverse effects on non-target organisms.

Females of the Australian sheep blowfly, Lucilia cuprina, exploit sheep dung as a source of protein for egg development. Flies fed on dung collected from sheep 1 to 6 days after being drenched with the broad-spectrum antiparasitic drug ivermectin showed delayed reproductive development and reduced fecundity. Male and female survival was also reduced. Despite these effects, except where the recommended frequency of drenching (1 to 4 times per annum) is greatly exceeded, it is unlikely that ivermectin residues will affect any useful reduction in blowfly populations.

The oral formulation of ivermectin is eliminated more rapidly than the injectable formulation and, as a consequence, is likely to be less harmful to dung-feeding insects. Abamectin and ivermectin appear to equally toxic larvae of M vetustissima.

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