Department of Plant Pathology Physiology and Weed Science, Virginia Tech, 119 Price Hall, Blacksburg, VA 24061, USA.
Vet Parasitol. 2010 May 28;170(1-2):78-87. doi: 10.1016/j.vetpar.2010.01.026. Epub 2010 Jan 25.
Observations were made on vertical migration patterns of Haemonchus contortus infective larvae on Cynodon dactylon (bermudagrass) and Paspalum notatum (bahiagrass) pastures under summer climatic conditions typical of East Texas. Ten thousand H. contortus infective larvae (L3) were introduced to 100 cm(2) subplots of each pasture species within a plot area of 1m(2). Subplots were inoculated with larvae by applying them in an aqueous medium to the soil or mat beneath the vegetation. Herbage from the inoculated areas was harvested on 5 sampling days over a span of 21 days. L3 recoveries were observed and recorded each day on four herbage strata viz. 0-5, 5-10, 10-20 and >20 cm from ground level. The log transformed larval recovery data were analyzed for effect of day, stratum, and day x stratum interaction for each grass species during two separate experimental periods. Precipitation, relative humidity and temperature during the study were subjected to correlation and multiple regression analyses with the larval counts. Significant (P</=0.0017) differences were found for the effect of day on larval recoveries. No significant differences were detected for stratum or day x stratum interaction effects, though stratum provided a strong indication of influencing larval recovery. A high positive correlation (>or=0.93) between rainfall and total average daily larval counts was apparent. The multiple regression analysis did not show significant results for any of the climatic factors tested. This study showed that the H. contortus infective larvae can survive beyond 21 days in the soil and infest pasture grasses when the climatic conditions are favorable. Avoiding use of H. contortus contaminated pasturelands in summer at the onset of rainfall following a dry spell may effectively reduce nematode loads in susceptible farm animals. Additional studies should focus on factors affecting long term L3 survivability, migrational pattern on these and other plant species and the relationship between climatic factors and larval migration patterns throughout the year. Total larval recovery of H. contortus in this study was greater in bahiagrass than bermudagrass. While the design of this study did not allow for testing one pasture species against another, studies with potted plants would allow for some valid comparisons. Soil characteristics may also play a role in L3 survival and subsequent migration.
在德克萨斯州东部典型的夏季气候条件下，对 Cynodon dactylon（百慕大草）和 Paspalum notatum（bahiagrass）牧场上旋毛虫感染幼虫的垂直迁移模式进行了观察。在 1m2的试验区内，将 10000 条旋毛虫感染幼虫（L3）引入到每个牧草物种的 100cm2亚区中。通过将幼虫施用到土壤或植被下的基质中的水介质中，将幼虫接种到接种区域。在 21 天的时间跨度内，在 5 个采样日收获接种区域的草料。每天观察和记录 L3 的回收情况，记录四个草料层（离地 0-5、5-10、10-20 和>20cm）的 L3 回收情况。对每个草种在两个独立实验期间的天、层和天×层相互作用对幼虫回收的影响进行了对数转换后的幼虫回收数据的分析。用幼虫计数对研究期间的降水、相对湿度和温度进行了相关性和多元回归分析。发现天对幼虫回收的影响存在显著差异（P</=0.0017）。未检测到层或天×层相互作用效应的显著差异，但层对幼虫回收有明显影响。降水与总平均日幼虫计数之间存在高度正相关（>or=0.93）。多元回归分析未显示出测试的任何气候因素的显著结果。本研究表明，在气候条件有利的情况下，旋毛虫感染幼虫可以在土壤中存活 21 天以上，并感染牧草草。避免在干旱期后降雨开始时使用受旋毛虫污染的牧场，可以有效降低易感家畜的线虫负荷。进一步的研究应集中于影响 L3 长期存活率、这些和其他植物物种上的迁移模式以及全年气候因素与幼虫迁移模式之间的关系的因素。本研究中，bahia 草中旋毛虫的总幼虫回收率高于百慕大草。虽然本研究的设计不允许一种牧草与另一种牧草进行对比测试，但盆栽植物的研究将允许进行一些有效的比较。土壤特性也可能在 L3 存活和随后的迁移中发挥作用。
