Trans-generational and within-generational effects of two macrocyclic lactones on tunneller and dweller dung beetles (Coleoptera: Scarabaeidae): A case study

Two distinct experiments were carried out to assess the trans-generational and within-generational effects of the parasiticides ivermectin and moxidectin to dung beetles (Coleoptera: Scarabaeidae). In the first experiment, the fertility of Euoniticellus intermedius (Reiche) (Scarabaeinae) was assessed for individuals developing in dung containing 10 g ivermectin/kg fresh dung, a residue concentration previously shown to be sublethal to larval development. Our results showed that the fertility of adults exposed to these residues as larvae was unaffected. In the second experiment, the fertility of Agrilinus constans (Duftschmid) (Aphodiinae) was determined after females were allowed to feed for three weeks on dung containing different concentrations of moxidectin residues (five concentrations ranging from 0.32-32.00 mg/kg dry dung). The fertility of females was not affected, regardless of the concentration to which they were exposed, even when they were exposed to high moxidectin residues that killed all the offspring. The combined findings of these two experiments emphasise that sublethal effects should be included in models that assess the nontarget effects of faecal residues to insects breeding in dung of livestock treated with veterinary medicinal products.