Gruner Daniel S, Ram Karthik, Strong Donald R
Bodega Marine Lab and Section of Evolution & Ecology, University of California-Davis, P.O. Box 247, Bodega Bay, CA 94923-0247, USA.
J Invertebr Pathol. 2007 Jan;94(1):12-9. doi: 10.1016/j.jip.2006.08.009. Epub 2006 Sep 26.
We tested for soil substrate effects on the movement and infectivity of naturally co-occurring entomopathogenic nematodes Steinernema feltiae and Heterorhabditis marelatus, alone and in combination. We manipulated the presence and bulk density of soil and added Galleria mellonella baits within capped and perforated 15mL centrifuge tubes. Sampling tubes were then deployed in situ into field and laboratory settings as experimental traps for infective juveniles. In comparisons with standard soil collections from Lupinus arboreus rhizospheres, sampling tubes were equally sensitive to the presence of H. marelatus and more sensitive to S. feltiae. In laboratory microcosms, both EPN species infected Galleria at high frequencies in tubes lacking soil and in the absence of heterospecifics. Infection frequency of S. feltiae was unaffected by the presence of H. marelatus, but it declined with higher soil bulk density inside tubes. In contrast, detectable infection frequency by H. marelatus was reduced only marginally by the presence of soil but severely by the presence of S. feltiae. Thus, the presence of soil in tubes reversed the identity of dominant species infecting Galleria in tubes, an effect magnified when soils were compacted. Moreover, S. feltiae rarely moved into tubes lacking Galleria baits, whereas H. marelatus colonized unbaited tubes 4- to 5-fold more frequently than S. feltiae. In situ, sampling tubes acted as filters to reduce interference and contamination by fungal pathogens common in field soils. The method allows precision sampling with minimal soil disturbance while protecting bait insects from scavengers. Manipulation of tube design may allow selective sampling of EPN species, depending on the abiotic characteristics of soils, and the biology, behavior, and interspecific interactions of coexisting species.
我们测试了土壤基质对自然共生的昆虫病原线虫斯氏线虫（Steinernema feltiae）和马里兰异小杆线虫（Heterorhabditis marelatus）单独及组合状态下的移动性和感染性的影响。我们控制土壤的有无和容重，并在加盖且打孔的15毫升离心管中添加了大蜡螟（Galleria mellonella）诱饵。然后将采样管原位部署到田间和实验室环境中，作为感染性幼虫的实验诱捕器。与从羽扇豆（Lupinus arboreus）根际采集的标准土壤样本相比，采样管对马里兰异小杆线虫的存在同样敏感，对斯氏线虫则更敏感。在实验室微观环境中，如果离心管中没有土壤且不存在异种线虫，两种昆虫病原线虫都能以较高频率感染大蜡螟幼虫。斯氏线虫的感染频率不受马里兰异小杆线虫的影响，但会随着管内土壤容重的增加而下降。相反，马里兰异小杆线虫的可检测感染频率仅因土壤的存在而略有降低，但会因斯氏线虫的存在而大幅下降。因此，离心管中土壤的存在改变了感染大蜡螟幼虫的优势线虫种类，当土壤压实后这种影响会被放大。此外，斯氏线虫很少进入没有大蜡螟诱饵的离心管，而马里兰异小杆线虫在未放置诱饵的离心管中定殖的频率比斯氏线虫高4至5倍。在原位环境中，采样管起到了过滤器的作用，减少了田间土壤中常见真菌病原体的干扰和污染。该方法能够在对土壤干扰最小的情况下进行精确采样，同时保护诱饵昆虫不被捕食者侵害。根据土壤的非生物特性以及共存线虫种类的生物学特性、行为和种间相互作用，对采样管设计进行调整，可能实现对昆虫病原线虫种类的选择性采样。
