Nontarget effects of ivermectin on coprophagous insects in Japan

Effects of the antiparasitic drug ivermectin on the dung-breeding flies and beetles Liatongus minutus (Motschulsky) were studied in laboratory and field experiments in Hokkaido, Japan. Ivermectin was detected in dung from 1 to 21 d after treatment, with a peak at the first day after treatment in two pour-on administrations (500 µg/kg). Laboratory bioassays were performed on the flies Musca bezzii Patton and Cragg and Scatophaga stercoraria L. and on the beetle Liatongus minutus. Dung from treated cattle inhibited larval development of M. bezzii from 1 to 14 d and pupation rate was reduced 21 d after treatment. In S. stercoraria, pupation and emergence rates were reduced for up to 14 and 28 d, respectively. In laboratory experiments of the dung beetle L. minutus, no significant difference was found in numbers of brood balls constructed per female between dung from treated and control cattle, whereas in field experiments, numbers of brood balls recovered in treatment were more abundant than that of control at 14 d after treatment. However, emergence rates of L. minutus were significantly reduced in dung from treated cattle for up to 14 d after treatment in both laboratory and field experiments. In a field experiment using emergence traps, numbers of flies emerged were 10,494 (18 families) in dung from untreated control cattle and 9,348 (17 families) in dung from treated cattle. Emergence of Paregle cinerella (Fallén), Neomyia cornicina (Fabricius), Ravinia striata (Fabricius), Sepsis latiforceps Duda, Sepsis duplicata Haliday, Sphaeroceridae spp., and Empididae spp. was reduced severely in dung from treated cattle. Conversely, numbers of Ceratopogonidae and Psychodidae increased in dung from treated cattle. Total dry weights of flies emerged from 48 dung pats in field experiments was 5,849.7 mg in dung from control cattle and 1,268.2 mg in dung from treated cattle, showing a 79.3% reduction in treated dung.