The incidence of resistance is considered to be widespread. On some properties the level of resistance is so severe that this chemical group, whether applied as an off-shears backline, dip or long wool treatment, does not provide effective lice control. The use of synthetic pyrethroids has decreased significantly in recent years. Lice detection Monitoring for lice is a fundamental part of a lice control program, both to assess treatment and for early detection of reinfestation after eradication. The ideal time to look for lice is during the six months before shearing.
Adult lice are only one to two mm long, and are pale brown with dark bands across the body.
They live on the skin surface and along wool fibres, where they feed on the skin debris, wool grease and bacteria. In the first three months, they are mainly found under the neck, especially in long woolled areas. After three months, they become fairly evenly distributed in the fleece. Lice can be seen by parting the wool in good light and by doing at least 10 partings per side to give a high level of assurance of freedom if no lice are found. Lice eradication Eradication is best achieved using chemicals on sheep with short wool as lice numbers are lowest at this time.