Oremus G, Guerrero F D, Alison M W, Kimball M M, Kim J H, Foil L D
Department of Entomology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA.
Vet Parasitol. 2006 Oct 10;141(1-2):156-64. doi: 10.1016/j.vetpar.2006.05.009.
Between 1999 and 2002, the effect of mid-season doramectin treatments on the level of resistance in pyrethroid-resistant horn fly populations was examined at three separate Louisiana State University Agricultural Center research stations. The cattle were treated with pyrethroid ear tags in all years at all farms, and each farm received a mid-season doramectin treatment in 1 year. The number of weeks of control at Red River was 11 weeks higher in the year following the mid-season treatment of doramectin. At Macon Ridge, the number of weeks of control was 2 weeks higher in the year following the doramectin treatment. No change was observed at St. Joseph. The LC50s for fly populations tested at Macon Ridge and St. Joseph were found to increase for pyrethroids from the spring populations to the fall populations between 2000 and 2002. The LC50s for fly populations at Red River followed the same trends except in 2000, the year when the doramectin treatment was administered. Flies collected pre and post-treatment each year from St. Joseph and Red River were assayed for two alleles (kdr and skdr) associated with target site resistance to pyrethroids. Flies collected pretreatment at Macon Ridge in 1999 also were assayed for the kdr and skdr, and this population of flies had a frequency of 85.6% R-kdr alleles. At St. Joseph and Red River there was a general decline in the frequency of homozygous susceptible skdr (SS-skdr) and homozygous susceptible kdr (SS-kdr) individuals, as well as a general increase in homozygous resistant skdr (RR-skdr) and homozygous resistant kdr (RR-kdr) individuals, during the 4-year study. At both sites, the frequency of R-kdr alleles increased significantly in flies collected in the fall compared to flies collected in the spring with the exception of Red River in 2000, when dormacetin was applied. The frequency of the R-kdr alleles was significantly higher in flies collected in the fall compared to flies collected in the spring in the following year at both sites in two out of three comparisons. The frequency of R-skdr alleles was significantly lower in fly populations tested in the spring compared to fly populations tested in the fall at both farms in years when doramectin was not applied but there were no differences in the years when doramectin was applied. The frequency of R-skdr alleles was significantly higher in fly populations tested in the fall compared to in the spring the following year during all three comparisons at Red River and in one of three comparisons at St. Joseph.
1999年至2002年期间，在路易斯安那州立大学农业中心的三个不同研究站，研究了季中使用多拉菌素治疗对拟除虫菊酯抗性厩螫蝇种群抗性水平的影响。所有年份所有农场的牛均使用拟除虫菊酯耳标进行处理，且每个农场在某一年接受了一次季中多拉菌素治疗。在红河地区，季中多拉菌素治疗后的次年，控制周数增加了11周。在梅肯岭，多拉菌素治疗后的次年，控制周数增加了2周。在圣约瑟夫未观察到变化。2000年至2002年期间，在梅肯岭和圣约瑟夫测试的厩螫蝇种群对拟除虫菊酯的半数致死浓度（LC50）从春季种群到秋季种群呈上升趋势。红河地区厩螫蝇种群的LC50遵循相同趋势，但在使用多拉菌素治疗的2000年除外。每年在圣约瑟夫和红河地区治疗前后采集的厩螫蝇，检测与拟除虫菊酯靶标位点抗性相关的两个等位基因（kdr和skdr）。1999年在梅肯岭治疗前采集的厩螫蝇也检测了kdr和skdr，该种群的R - kdr等位基因频率为85.6%。在为期4年的研究中，在圣约瑟夫和红河地区，纯合敏感skdr（SS - skdr）和纯合敏感kdr（SS - kdr）个体的频率普遍下降，纯合抗性skdr（RR - skdr）和纯合抗性kdr（RR - kdr）个体的频率普遍增加。在两个地点，除了2000年使用多拉美丁的红河地区外，秋季采集的厩螫蝇中R - kdr等位基因的频率相比春季采集的显著增加。在三项比较中的两项中，次年秋季采集的厩螫蝇中R - kdr等位基因的频率相比春季采集的显著更高。在未使用多拉菌素的年份，两个农场春季测试的厩螫蝇种群中R - skdr等位基因的频率相比秋季测试的显著更低，但在使用多拉菌素的年份没有差异。在红河地区的所有三项比较以及圣约瑟夫的三项比较中的一项中，次年秋季测试的厩螫蝇种群中R - skdr等位基因的频率相比春季显著更高。
