Effects of ivermectin on target and non-target dung-breeding flies (Diptera) in cattle dung pats

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The effects of antiparasitic drug, ivermectin, on the dung-breeding flies were studied in laboratory and field experiments in Hokkaido, Japan. In two pour-on treatments (500μg/kg), ivermectin was excreted in dung for up to 14 and 21 days after treatment, with peaks at 3 days and 1 day, respectively. Dung from treated cattle prevented the larval development of Haematobia irritans and Neomyia cornicina up to 14 days and reduced the larval and pupal survival rates at 21 days after treatment. In the field experiment using emergence traps, the numbers of emerged flies from dung pats were 3,655 (18 families) in control dung and 2,234 (16 families) in treated dung. Especially, Musca bezzii, Ravinia striata, Sepsis duplicata, Sepsis thoracica, Sepsis cynipsea, Sphaeroceridea, Empididae, Sciaridae and Chironomidae were severely reduced in treated dung. Reduction of cyclorrhaphaous flies similarly occurred at 1, 3 and 7 days after treatment, which coincides with high concentrations of ivermectin. Conversely, Ceratopogonidae and Phoridae increased in treated dung, regardless of days (1, 3 and 7) after treatment. Dry weights of flies emerged from dung pats of treated cattle in the field experiment were only 5.8% of those from dung of control cattle, indicating that dung-decomposing activity by fly larvae was supressed in dung of treated cattle.