Does rain reduce the efficacy of Butox 7.5 pour on (deltamethrin) against biting midges (Culicoides specimens)?

Previous studies have shown that cattle and sheep that are treated topically with Butox 7.5 (deltamethrin) on the neck or along the back are protected from biting Culicoides spp. for up to 4 weeks. During these studies, the animals were provided with adequate shelter against the rain. The efficacy of deltamethrin on wet animals was, therefore, not tested. The present experiment was done to determine if thoroughly wetting the test subjects twice a week would affect the efficacy of deltamethrin. Cattle and sheep were treated with Butox 7.5 along the neck or dorsal midline. Test animals were wet thoroughly with tap water twice weekly. Control animals remained dry. Hair was clipped off the legs, near the claws, at day 7, 14, 21, and 28 after treatment of test and control animals. Recently caught C. obsoletus midges were then exposed to the hair for 15, 30, 60, and 120 s. Time taken for the midges to die after exposure was recorded. The product remained effective for at least up to 28 days, although, differences in the time taken to kill the midges were noted. Differences in time taken for the midges to die were also seen between those exposed to treated cattle hair and those exposed to treated sheep hair.