Implications of insecticide resistance for the control of flystrike and lice on sheep

The Australian sheep blowfly (Lucilia cuprina) and the sheep body louse (Bovicola ovis) have both demonstrated their propensity to develop resistance to insecticides used for their control. Most populations of L. cuprina contain individuals resistant to organochlorines and organophosphates. Some are also resistant to benzoylphenyl ureas. Many populations of B. ovis are resistant to pyrethroid insecticides. However, very few populations are resistant to organophosphates. Treatments directed at lice infestations have selected for resistance in sheep blowfly so insecticide treatments need to be considerate of the possible impact on non-target parasite resistance. Flock management plans would assist in identifying options for producers but clearer information on pesticide residue/environmental requirements are needed first.