Entomopathogenic nematodes (EPNs) Steinernema and Heterorhabditis and their symbiotic bacteria, Xenorhabdus and Photorhabdus, have been successfully used for the control of insect pests. The objectives of this study were to survey the EPNs and symbiotic bacteria in the agricultural areas of the Phitsanulok province, Thailand, and to study the association between the soil parameters and presence of EPNs. We collected 200 soil samples from 40 soil sites in agricultural areas (field crops, horticulture crops and forest). The prevalence of EPNs was 8.0% (16/200). Fifteen of the EPN isolates were molecularly identified (based on 28S ribosomal DNA and internal transcribed spacer regions) as Steinernema siamkayai. Seven isolates of Xenorhabdus stockiae were identified using recombinase A sequencing. Phylogenetic analysis revealed that all the Steinernema and Xenorhabdus isolates were closely related to S. siamkayai (Indian strain) and X. stockiae (Thai strain), respectively. Significantly more EPNs were recovered from loam than from clay. Although the association between soil parameters (pH, temperature and moisture) and the presence of EPNs was not statistically significant, the elevation levels of the soil sites with and without EPNs were found to be different. Moreover, statistical comparisons between the agricultural areas revealed no significant differences. Therefore, we concluded that S. siamkayai is associated with X. stockiae in agricultural areas and that there is no association between the soil parameters of agricultural areas and presence of EPNs, except for soil texture and the elevation. Steinernema siamkayai may be applied as a biocontrol agent in agricultural areas.

中文翻译：

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泰国北部农区昆虫病原线虫及其共生菌的调查

昆虫病原线虫 (EPN)施泰内马和异形线虫和它们的共生细菌，异虫和光杆状体，已成功用于防治害虫。本研究的目的是调查泰国彭世洛省农业区的 EPNs 和共生细菌，并研究土壤参数与 EPNs 存在之间的关联。我们从农业区（大田作物、园艺作物和森林）的 40 个土壤站点收集了 200 个土壤样本。EPN 的患病率为 8.0% (16/200)。15 个 EPN 分离株被分子鉴定（基于 28S 核糖体 DNA 和内部转录间隔区）为暹罗丝虫. 七株病原菌使用重组酶A测序鉴定。系统发育分析表明，所有施泰内马和异虫分离株密切相关S. siamkayai（印度菌株）和X. stockiae（泰国菌株），分别。从壤土中回收的 EPN 明显多于从粘土中回收的 EPN。尽管土壤参数（pH、温度和湿度）与 EPNs 存在之间的关联在统计学上不显着，但发现有和没有 EPNs 的土壤站点的海拔水平是不同的。此外，农业区之间的统计比较显示没有显着差异。因此，我们得出结论S. siamkayai与....关联X. stockiae在农业地区，除了土壤质地和海拔之外，农业地区的土壤参数与 EPNs 的存在之间没有关联。暹罗丝虫可用作农业领域的生物防治剂。