Yoder Corrie A, Grewal P S, Taylor R A J
Department of Entomology, Ohio State University, OARDC, Wooster, Ohio 44691, USA.
J Parasitol. 2004 Dec;90(6):1229-34. doi: 10.1645/GE-3315.
Nonfeeding infective juvenile (IJ) entomopathogenic nematodes (EPNs) are used as biological agents to control soil-dwelling insects, but poor storage stability remains an obstacle to their widespread acceptance by distributors and growers as well as a frustration to researchers. Age is one factor contributing to variability in EPN efficacy. We hypothesized that age effects on the infectiousness of IJs would be evident within the length of time necessary for IJs to infect a host. The penetration behavior of "young" (<1-wk-old) and "old" (2- to 4-wk-old) Heterorhabditis bacteriophora (GPS 11 strain), Steinernema carpocapsae (All strain), and Steinernema feltiae (UK strain) IJs was evaluated during 5 "exposure periods" to the larvae of the wax moth, Galleria mellonella. Individual larvae were exposed to nematode-infested soil for exposure periods of 4, 8, 16, 32, and 64 hr. Cadavers were dissected after 72 hr, and the IJs that penetrated the larvae were counted. Larval mortality did not differ significantly between 72- and 144-hr "observation periods," or points at which larval mortality was noted, for any age class or species. However, age and species effects were noted in G. mellonella mortality and nematode penetration during shorter time periods. Initial mortality caused by S. carpocapsae and H. bacteriophora IJs declined with nematode age but increased with S. feltiae IJ age. Young S. carpocapsae IJs penetrated G. mellonella larvae at higher rates than old members of the species (27-45% vs. 1-4%). Conversely, old S. feltiae IJs had higher penetration rates than young IJs (approximately 8 to 57% vs. 4 to approximately 31%), whereas H. bacteriophora IJs had very low penetration rates regardless of age (3-5.6%). Our results show that the effect of age on IJ infectiousness can be detected in IJs aged only 2 wk by a 4-hr exposure period to G. mellonella. These results have important implications for storage and application of EPNs and suggest the possibility of shortening the time required to detect nematodes in the soil.
不取食的感染期幼虫（IJ）昆虫病原线虫（EPNs）被用作生物制剂来防治土壤栖息昆虫，但较差的储存稳定性仍然是其被经销商和种植者广泛接受的障碍，也让研究人员感到沮丧。年龄是导致EPNs功效变异性的一个因素。我们假设，在IJ感染宿主所需的时间长度内，年龄对IJ感染性的影响将是明显的。在对大蜡螟（Galleria mellonella）幼虫的5个“暴露期”内，评估了“年轻”（<1周龄）和“年老”（2至4周龄）的嗜菌异小杆线虫（Heterorhabditis bacteriophora，GPS 11菌株）、小卷蛾斯氏线虫（Steinernema carpocapsae，All菌株）和长尾斯氏线虫（Steinernema feltiae，英国菌株）IJ的穿透行为。将单个幼虫暴露于感染线虫的土壤中，暴露期分别为4、8、16、32和64小时。72小时后解剖虫尸，对穿透幼虫的IJ进行计数。对于任何年龄组或物种，在72小时和144小时的“观察期”或记录幼虫死亡的时间点之间，幼虫死亡率没有显著差异。然而，在较短时间段内，在大蜡螟死亡率和线虫穿透方面观察到了年龄和物种效应。由小卷蛾斯氏线虫和嗜菌异小杆线虫IJ引起的初始死亡率随线虫年龄下降，但随长尾斯氏线虫IJ年龄增加。年轻的小卷蛾斯氏线虫IJ比该物种的年老成员以更高的速率穿透大蜡螟幼虫（27 - 45%对1 - 4%）。相反，年老的长尾斯氏线虫IJ比年轻的IJ具有更高的穿透率（约8%至57%对4%至约31%），而嗜菌异小杆线虫IJ无论年龄如何都具有非常低的穿透率（3 - 5.6%）。我们的结果表明，通过对大蜡螟4小时的暴露期，可以在仅2周龄的IJ中检测到年龄对IJ感染性的影响。这些结果对EPNs的储存和应用具有重要意义，并表明有可能缩短在土壤中检测线虫所需的时间。
