The University of Queensland, School of Veterinary Science, Qld, Australia.
Vet Parasitol. 2010 Apr 19;169(1-2):157-64. doi: 10.1016/j.vetpar.2009.12.026. Epub 2009 Dec 29.
A farmlet study was conducted over 4 years in which three treatments were applied to six groups of Holstein dairy calves. Calves in each group were infested with equal numbers of N-strain (susceptible) and Ultimo strain (amitraz and synthetic pyrethroid resistant) tick larvae to establish self-sustaining populations with an initial, measurable level of resistance to amitraz. Standard counts of all ticks between 4.5 and 8.0mm diameter on one side of each animal were made each week and treatment was applied when tick numbers exceeded a threshold of 25 engorged adults per side. The three treatments were: 1, spinosad spray whenever tick numbers exceeded the threshold; 2, amitraz spray whenever tick numbers exceeded the threshold; 3, spinosad whenever tick numbers exceeded the threshold for the first 2 months, then amitraz for 2 months, with alternation every subsequent 2 months. Engorged adult female ticks were collected from each treatment group on 10 or 11 occasions during the study and tested using the larval packet test bioassay (LPT) for acaricide resistance. Spinosad 250ppm provided effective control of amitraz-resistant tick populations in the field, using a similar number of treatments as in the amitraz and rotation groups. The initial infestations of all of the groups resulted in the establishment of populations with in vitro evidence of resistance to amitraz using the LPT. Treatment with spinosad or with a rotation between spinosad and amitraz every 2 months resulted in reduced levels of resistance to amitraz according to the LPT. The animals treated with amitraz alone showed increasing resistance to amitraz according to the LPT each summer and autumn with a return to full or almost full susceptibility to amitraz in early spring in all years. This pattern suggests a relative lack of fitness of amitraz-resistant ticks that might be exploited by using an acaricide rotation strategy.
一项为期 4 年的农舍研究中，对 6 组荷斯坦奶牛犊牛应用了 3 种处理方法。每组犊牛均感染了等量的 N 株（敏感型）和 Ultimo 株（对甲氨基阿维菌素苯甲酸盐和合成拟除虫菊酯具有抗药性）的蜱幼虫，以建立具有初始、可衡量的抗甲氨基阿维菌素苯甲酸盐水平的自维持种群。每周在每只动物一侧直径为 4.5 至 8.0 毫米的所有蜱虫进行标准计数，当蜱虫数量超过每侧 25 只饱血成虫的阈值时进行处理。3 种处理方法如下：1. 当蜱虫数量超过阈值时，使用多杀菌素喷雾；2. 当蜱虫数量超过阈值时，使用甲氨基阿维菌素苯甲酸盐喷雾；3. 在前 2 个月内，当蜱虫数量超过阈值时，使用多杀菌素喷雾，然后在接下来的 2 个月内使用甲氨基阿维菌素苯甲酸盐喷雾，每 2 个月交替一次。在研究期间，从每个处理组收集了 10 或 11 次饱血雌蜱，并用幼虫包测试生物测定法（LPT）测试其对杀螨剂的抗药性。多杀菌素 250ppm 在田间有效控制了对甲氨基阿维菌素苯甲酸盐具有抗药性的蜱虫种群，使用的处理次数与甲氨基阿维菌素苯甲酸盐和轮换组相似。使用 LPT，所有组的初始感染均导致建立了具有体外抗甲氨基阿维菌素苯甲酸盐证据的种群。使用多杀菌素或每 2 个月在多杀菌素和甲氨基阿维菌素之间轮换处理，根据 LPT，导致对甲氨基阿维菌素苯甲酸盐的抗药性降低。每年夏秋季，单独使用甲氨基阿维菌素苯甲酸盐处理的动物根据 LPT 显示出对甲氨基阿维菌素苯甲酸盐的抗药性增加，而在所有年份的早春，对甲氨基阿维菌素苯甲酸盐的敏感性又恢复到完全或几乎完全。这种模式表明，对甲氨基阿维菌素苯甲酸盐具有抗药性的蜱虫的适应性相对较差，这可能可以通过使用杀螨剂轮换策略来加以利用。
