Koppenhöfer A M, Jaffee B A, Muldoon A E, Strong D R, Kaya H K
Department of Nematology, University of California, Davis 95616-8668, USA.
J Invertebr Pathol. 1996 Nov;68(3):246-52. doi: 10.1006/jipa.1996.0092.
We determined whether nematode-trapping fungi may influence the dynamics of a coastal shrub community. The food chain interactions in the shrub community involve the dominant plant species, its major insect herbivore, and an entomopathogenic nematode, Heterorhabditis hepialus. Of the 12 nematode-trapping fungi previously isolated from soils at the study site, 5 were selected for this study. Arthrobotrys oligospora, Geniculifera paucispora, Monacrosporium eudermatum, and Monacrosporium cionopagum efficiently trapped and colonized H. hepialus on agar; in contrast Nematoctonus concurrens trapped but did not infect or colonize the nematode on agar. To determine whether these fungi can suppress H. hepialus in soil, we added the fungi in the form of fungal-colonized nematodes to pasteurized (2 hr at 62 degrees C) and raw (nontreated) soil from the study site. Suppression was measured by comparing nematode invasion into a wax moth larva in fungus-treated and untreated soil in vials at 20 degrees C. Fungal population density in soil was estimated using dilution plating and most probable number procedures. All fungi suppressed H. hepialus if the wax moth larvae were added 4 days after the nematodes. Suppression ranged between 37 and 54% and did not differ among fungi. Suppression was usually greater in raw than in pasteurized soil. Raw soil contained a constant background of nematode-trapping fungi, and A. oligospora was the most common among these; no background was detected in pasteurized soil. The presence of background fungi in raw soil may explain the higher suppression in raw than in pasteurized soil. Fungal propagule densities in our laboratory experiments were similar to those observed in the field, suggesting that nematode-trapping fungi may influence the dynamics of the plant, insect herbivore, and entomopathogenic nematode in the coastal ecosystem.
我们研究了捕食线虫真菌是否会影响沿海灌木群落的动态。灌木群落中的食物链相互作用涉及优势植物物种、其主要食草昆虫以及一种昆虫病原线虫——斯氏线虫。在先前从研究地点的土壤中分离出的12种捕食线虫真菌中，选择了5种用于本研究。少孢节丛孢、少孢膝梗孢、真厚顶单顶孢和食虫单顶孢能在琼脂上有效地捕获并定殖斯氏线虫；相比之下，并发线虫杀手能捕获但不能在琼脂上感染或定殖该线虫。为了确定这些真菌是否能在土壤中抑制斯氏线虫，我们将真菌以定殖真菌的线虫形式添加到来自研究地点的经过巴氏消毒（62摄氏度下2小时）和未处理（生土）的土壤中。通过比较20摄氏度下小瓶中经真菌处理和未处理土壤中线虫对大蜡螟幼虫的侵染情况来测量抑制效果。使用稀释平板法和最大可能数法估计土壤中的真菌种群密度。如果在接种线虫4天后添加大蜡螟幼虫，所有真菌都能抑制斯氏线虫。抑制率在37%至54%之间，不同真菌之间没有差异。生土中的抑制效果通常比巴氏消毒土壤中的更好。生土中含有稳定的捕食线虫真菌背景，其中少孢节丛孢最为常见；在巴氏消毒土壤中未检测到背景真菌。生土中存在背景真菌可能解释了生土中抑制效果高于巴氏消毒土壤的原因。我们实验室实验中的真菌繁殖体密度与田间观察到的相似，这表明捕食线虫真菌可能会影响沿海生态系统中植物、食草昆虫和昆虫病原线虫的动态。
