Reproductive development and survival of Lucilia cuprina Wiedemann when fed sheep dung containing ivermectin.

When fed dung from sheep treated with ivermectin 24 h previously, Lucilia cuprina adults exhibited reduced survival, delayed ovarian development and reduced egg production. These effects were absent in dung produced 2 or more days after ivermectin treatment. Such transient toxicity is ideal to restrict the evolution of resistance to this drug. This situation may change if the current practice of oral treatment is replaced by a slow-release system of administering avermectins. The avoidance of coincidental evolution of resistance is critical to the long-term welfare of the Australian sheep industry as the avermectins represent an important, and as yet unexploited, insecticide for the treatment of flystrike caused by Lucilia cuprina.