Prevention of blowfly strike on sheep by cypermethrin

Merino ewe lambs (n = 500) were used in a trial to assess the efficacy of cypermethrin in preventing blowfly strike on sheep. Three hundred of these lambs were treated with 300 mg cypermethrin each and run as a separate flock. One hundred lambs were used as untreated controls and a further 100 lambs were treated topically with a larval growth regulator as treated control animals. It was found that the synthetic pyrethroid afforded total protection for 3 weeks against strike by Lucilia cuprina. The blowfly challenge was heavy, and 26% of the untreated control animals were struck in the 4 week trial period.