Yadav Arun K
Department of Zoology, North-Eastern Hill University, Shillong, 793-022 India.
J Parasit Dis. 2012 Apr;36(1):94-8. doi: 10.1007/s12639-011-0076-x. Epub 2011 Oct 13.
Entomopathogenic nematodes (EPNs) are obligate parasites of insects that are widely distributed in soils throughout the world. They have great potential for use as biological control agents for insect pests. It is known that strains of Steinernema and Heterorhabditis isolated from different geographical regions exhibit differences in their ecological traits, such as infectivity, establishment, survival, reproduction, etc. A precise knowledge of these factors is therefore an essential pre-requisite for devising successful strategies to use these nematodes in biological control programmes. The present study investigated the effect of soil moisture on the activity (as measured by number of nematodes established in hosts) of three entomopathogenic nematode species (Heterorhabditis indica Poinar, Karunakar & David; Steinernema thermophilum Ganguly & Singh; Steinernema glaseri Steiner), isolated from forest soils in Meghalaya, India, under laboratory conditions. The experiments for EPNs were conducted at 25 ± 2°C (30 ± 2°C for S. thermophilum) in a sandy loam soil (85% sand, 12% silt and 3% clay, pH 6.54). Last instar larvae of wax moth, Galleria mellonella served as the experimental insect host. The soil moistures tested were 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22 and 25% (w/w). The study revealed that soil moisture has marked influences on establishment of infective juveniles of different nematode species in insect host. While, S. thermophilum showed establishment at 4% and above soil moistures, H. indica and S. glaseri showed establishment at 5% and above soil moistures. The optimum soil moisture for different nematode species were noted as: H. indica 8-18%, S. thermophilum 6-20%, and S. glaseri 8-25%. Further, a minimum of 6% soil moisture was noted to be essential for achieving 100% host mortality for all the three nematode species.
昆虫病原线虫是昆虫的专性寄生虫，广泛分布于世界各地的土壤中。它们作为害虫的生物防治剂具有巨大潜力。已知从不同地理区域分离出的斯氏线虫属和异小杆线虫属菌株在其生态特性上存在差异，如感染力、定殖能力、存活率、繁殖能力等。因此，准确了解这些因素是制定成功策略以在生物防治计划中使用这些线虫的必要前提。本研究在实验室条件下，调查了土壤湿度对从印度梅加拉亚邦森林土壤中分离出的三种昆虫病原线虫（印度异小杆线虫Poinar、Karunakar和David；嗜热斯氏线虫Ganguly和Singh；格氏斯氏线虫Steiner）活性（以在宿主体内定殖的线虫数量衡量）的影响。昆虫病原线虫的实验在25±2°C（嗜热斯氏线虫为30±2°C）的砂壤土（85%砂、12%粉砂和3%黏土，pH 6.54）中进行。大蜡螟的末龄幼虫作为实验昆虫宿主。测试的土壤湿度为3%、4%、5%、6%、8%、10%、12%、14%、16%、18%、20%、22%和25%（重量/重量）。研究表明，土壤湿度对不同线虫种类的感染性幼虫在昆虫宿主体内的定殖有显著影响。虽然嗜热斯氏线虫在土壤湿度4%及以上时表现出定殖，印度异小杆线虫和格氏斯氏线虫在土壤湿度5%及以上时表现出定殖。不同线虫种类的最佳土壤湿度为：印度异小杆线虫8 - 18%，嗜热斯氏线虫6 - 20%，格氏斯氏线虫8 - 25%。此外，注意到至少6%的土壤湿度对于三种线虫实现100%的宿主死亡率至关重要。
