USDA-ARS, Southeastern Fruit and Tree Nut Research Lab, 21 Dunbar Road, Byron, GA 31008, United States.
J Invertebr Pathol. 2012 Jan;109(1):34-40. doi: 10.1016/j.jip.2011.09.004. Epub 2011 Sep 12.
Entomopathogenic nematodes respond to a variety of stimuli when foraging. Previously, we reported a directional response to electrical fields for two entomopathogenic nematode species; specifically, when electrical fields were generated on agar plates Steinernema glaseri (a nematode that utilizes a cruiser-type foraging strategy) moved to a higher electric potential, whereas Steinernema carpocapsae, an ambush-type forager, moved to a lower potential. Thus, we hypothesized that entomopathogenic nematode directional response to electrical fields varies among species, and may be related to foraging strategy. In this study, we tested the hypothesis by comparing directional response among seven additional nematode species: Heterorhabditis bacteriophora, Heterorhabditis georgiana, Heterorhabditis indica, Heterorhabditis megidis, Steinernema feltiae, Steinernema riobrave, and Steinernema siamkayai. S. carpocapsae and S. glaseri were also included as positive controls. Heterorhabditids tend toward cruiser foraging approaches whereas S. siamkayai is an ambusher and S. feltiae and S. riobrave are intermediate. Additionally, we determined the lowest voltage that would elicit a directional response (tested in S. feltiae and S. carpocapsae), and we investigated the impact of nematode age on response to electrical field in S. carpocapsae. In the experiment measuring diversity of response among species, we did not detect any response to electrical fields among the heterorhabditids except for H. georgiana, which moved to a higher electrical potential; S. glaseri and S. riobrave also moved to a higher potential, whereas S. carpocapsae, S. feltiae, and S. siamkayai moved to a lower potential. Overall our hypothesis that foraging strategy can predict directional response was supported (in the nematodes that exhibited a response). The lowest electric potential that elicited a response was 0.1 V, which is comparable to electrical potential associated with some insects and plant roots. The level of response to electrical potential diminished with nematode age. These results expand our knowledge of electrical fields as cues that may be used by entomopathogenic nematodes for host-finding or other aspects of navigation in the soil.
在觅食时，昆虫病原线虫会对各种刺激做出反应。此前，我们曾报道过两种昆虫病原线虫对电场的定向反应；具体来说，当在琼脂平板上产生电场时，斯氏线虫（一种利用巡航型觅食策略的线虫）会移动到更高的电势，而伏击型觅食者嗜菌异小杆线虫则会移动到更低的电势。因此，我们假设昆虫病原线虫对电场的定向反应在物种间存在差异，并且可能与觅食策略有关。在这项研究中，我们通过比较另外七种线虫物种的定向反应来验证这一假设：异小杆线虫、格鲁吉亚异小杆线虫、印度异小杆线虫、大异小杆线虫、斯氏线虫、瑞氏异小杆线虫和暹罗异小杆线虫。嗜菌异小杆线虫和斯氏线虫也被包括在内作为阳性对照。异小杆线虫倾向于巡航觅食方法，而暹罗异小杆线虫是伏击者，斯氏线虫和瑞氏异小杆线虫是中间型。此外，我们确定了能引起定向反应的最低电压（在斯氏线虫和嗜菌异小杆线虫中进行测试），并研究了线虫年龄对嗜菌异小杆线虫对电场反应的影响。在测量物种间反应多样性的实验中，我们没有检测到除格鲁吉亚异小杆线虫外的异小杆线虫对电场的任何反应，格鲁吉亚异小杆线虫移动到更高的电势；斯氏线虫和瑞氏异小杆线虫也移动到更高的电势，而嗜菌异小杆线虫、斯氏线虫和暹罗异小杆线虫则移动到更低的电势。总的来说，我们的假设即觅食策略可以预测定向反应（在表现出反应的线虫中）得到了支持。引起反应的最低电压为 0.1V，与一些昆虫和植物根的电势相当。对线虫年龄的反应水平随着线虫年龄的增加而降低。这些结果扩展了我们对电场作为昆虫病原线虫可能用于寻找宿主或在土壤中导航的其他方面的线索的认识。
