Fourie L J, Kok D J, Horak I G, Van Zyl J M
Department of Zoology and Entomology, University of the Orange Free State, Bloemfontein, South Africa.
Exp Appl Acarol. 1995 Mar;19(3):147-53. doi: 10.1007/BF00046285.
Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.
由血红扇头蜱雌蜱叮咬导致的麻痹是南非大片地区的一个主要问题。由于蜱的生命周期长达2年，因此有人推测，在2年时间内对绵羊进行战略性杀螨剂处理，选择在大多数饱血雌蜱的致死时间进行，应该能显著降低蜱的繁殖潜力。在已知感染血红扇头蜱的两个独立牧场放牧的两群绵羊，在2年时间内分别接受了战略性处理或阈值处理（即仅当蜱的侵害超过了基于麻痹的预定临界水平时）。对与这两群绵羊一起放牧的未处理对照绵羊的蜱负担进行了4年的监测，并确定了其季节动态。两群绵羊蜱虫大量繁殖的时间相似，但两群绵羊的平均蜱负担记录存在显著差异。在试验的第三年和第四年，接受战略性处理的羊群中绵羊身上的蜱虫数量并未如预期那样减少。造成这种情况的可能原因是饲养密度低，尤其是在成年蜱虫数量高峰期，以及存在维持蜱虫种群的野生宿主。
