In vitro assay for permethrin persistence and interference with bloodfeeding of Culicoides (Diptera: Ceratopogonidae) on animals.

Permethrin (65% AI) was applied to the dorsum of 3 goats (3-4 ml/animal). Hair clippings were taken before treatment and 4-6, 18-20, 39-41 and 67-69 days after treatment. Culicoides variipennis fed upward through a thin layer of hair and through a membrane on an artificial feeder containing cattle blood. Midge knockdown was usually complete after the 45 min exposure period, but many bloodfed first. Belly hair residues did not statistically reduce engorgement beyond 4-6 days. Head hair residues reduced engorgement by up to 98% at 18-20 days, but did not significantly reduce engorgement at 67-69 days. Back hair residues significantly reduced engorgement for the entire period (99-100% through day 39-41 and 66% by day 67-69). Partial engorgement was higher in the treatments.