Spradbery J P, Tozer R S, Drewett N, Lindsey M J
Aust Vet J. 1985 Sep;62(9):311-4. doi: 10.1111/j.1751-0813.1985.tb14913.x.
An in vitro technique for screening systemic insecticides against larvae of the screw-worm fly, Chrysomya bezziana is described. Susceptibilities of screw-worm larvae of different ages to ivermectin (MK-933) were determined. Based on 24 h larval mortality, the LD50 of 1-,2-,3-,4- and 5-day larvae was 0.01, 0.02, 0.03, 0.2 and 0.4 ppm of ivermectin. LD50 based on adult emergence following treatment of 4- and 5-day larvae was 0.02 and 0.05 ppm. The LD99.9 for 4-day larvae based on 24 h larval mortality and adult emergence was 11.0 and 0.15 ppm respectively and for 5-day larvae, was 44.3 and 0.4 ppm respectively. Pen and field trials with cattle infested with screw-worm fly demonstrated the potential of ivermectin as a systemic insecticide. Dosages of 50, 100 and 200 micrograms/kg, of ivermectin administered subcutaneously to experimentally infested cattle gave complete control for 6, 12 and 14 days respectively. Ivermectin at 200 micrograms/kg caused 100% mortality of screw-worm larvae up to 2 days old at the time of treatment with 70, 64 and 21% mortality of 3-, 4- and 5-day old larvae at the time of treatment. The residual protection from a single dose of 200 micrograms/kg was 16 to 20 days. When bull calves were treated with ivermectin at a dose of 200 micrograms/kg at the time of castration and branding, none of the 77 treated animals sustained a screw-worm strike in the scrotal area compared with 47 strikes (44%) in the 106 control cattle.
本文描述了一种体外筛选针对螺旋锥蝇（Chrysomya bezziana）幼虫的全身性杀虫剂的技术。测定了不同龄期螺旋锥蝇幼虫对伊维菌素（MK - 933）的敏感性。根据24小时幼虫死亡率，1日龄、2日龄、3日龄、4日龄和5日龄幼虫的伊维菌素半数致死剂量（LD50）分别为0.01、0.02、0.03、0.2和0.4 ppm。基于对4日龄和5日龄幼虫处理后的成虫羽化情况，其LD50分别为0.02和0.05 ppm。基于24小时幼虫死亡率和成虫羽化情况，4日龄幼虫的LD99.9分别为11.0和0.15 ppm，5日龄幼虫的LD99.9分别为44.3和0.4 ppm。对感染螺旋锥蝇的牛进行的圈舍和田间试验证明了伊维菌素作为全身性杀虫剂的潜力。对实验性感染的牛皮下注射50、100和200微克/千克剂量的伊维菌素，分别可实现6、12和14天的完全控制。在处理时，200微克/千克的伊维菌素可导致处理时2日龄及以下的螺旋锥蝇幼虫100%死亡，3日龄、4日龄和5日龄幼虫的死亡率分别为70%、64%和21%。单次注射200微克/千克剂量的伊维菌素的残留保护期为16至20天。当公牛犊在去势和打烙印时用200微克/千克剂量的伊维菌素进行处理时，77头处理过的动物中没有一头在阴囊部位遭受螺旋锥蝇叮咬，而106头对照牛中有47头（44%）被叮咬。
