The development of high synthetic pyrethroid resistance in Bovicola (Damalinia) ovis and the implications for resistance management.

A field strain of the sheep body louse, Bovicola (Damalinia) ovis, was tested in vitro against a range of synthetic pyrethroids (SP) and demonstrated a degree of resistance 80 to 900 times that of a susceptible strain. The dose response of this strain was compared with that of other strains showing low and intermediate resistance. These data, and those from other reported cases suggest that SP resistance in sheep lice develops sequentially through a low level stage with resistance factors of 20 or less. Further selection results in the development of strains with resistance factors of up to several hundred. The implication is that preventing or managing resistance requires proper lice control management including choosing a chemical capable of eradicating lice populations.