Entomology and Nematology Department, University of Florida, Lake Alfred, FL 33850-2299, USA.
J Invertebr Pathol. 2012 Oct;111(2):126-35. doi: 10.1016/j.jip.2012.07.006. Epub 2012 Jul 25.
Entomopathogenic nematodes (EPNs) are promising biological control agents of soil-dwelling insect pests of many crops. These nematodes are ubiquitous in both natural and agricultural areas. Their efficacy against arthropods is affected directly and indirectly by food webs and edaphic conditions. It has long been suggested that a greater understanding of EPN ecology is needed to achieve consistent biological control by these nematodes and the development of molecular tools is helping to overcome obstacles to the study of cryptic organisms and complex interactions. Here we extend the repertoire of molecular tools to characterize soil food webs by describing primers/probe set to quantify certain free-living, bactivorous nematodes (FLBNs) that interact with EPNs in soil. Three FLBN isolates were recovered from soil baited with insect larvae. Morphological and molecular characterization confirmed their identities as Acrobeloides maximum (RT-1-R15C and RT-2-R25A) and Rhabditis rainai (PT-R14B). Laboratory experiments demonstrated the ability of these FLBNs to interfere with the development of Steinernema diaprepesi, Steinernema riobrave and Heterorhabditis indica parasitizing the weevil Diaprepes abbreviatus (P<0.001), perhaps due to resource competition. A molecular probe was developed for the strongest competitor, A. maximum. We selected the highly conserved SSU rDNA sequence to design the primers/probe, because these sequences are more abundantly available for free-living nematodes than ITS sequences that can likely provide better taxonomic resolution. Our molecular probe can identify organisms that share ⩾98% similarity at this locus. The use of this molecular probe to characterize soil communities from samples of nematode DNA collected within a citrus orchard revealed positive correlations (P<0.01) between Acrobeloides-group nematodes and total numbers of EPNs (S. diaprepesi, H. indica and Heterorhabditis zealandica) as well as a complex of nematophagous fungi comprising Catenaria sp. and Monachrosporium gephyropagum that are natural enemies of EPNs. These relationships can be broadly interpreted as supporting Linford's hypothesis, i.e., decomposition of organic matter (here, insect cadavers) greatly increases bactivorous nematodes and their natural enemies.
昆虫病原线虫（EPNs）是许多作物土壤栖居性害虫的有前途的生物防治剂。这些线虫在自然和农业区域中无处不在。它们对节肢动物的功效直接和间接受到食物网和土壤条件的影响。长期以来，人们一直认为，需要更深入地了解 EPN 生态学，才能实现这些线虫的持续生物控制，并开发分子工具来帮助克服对隐生生物和复杂相互作用研究的障碍。在这里，我们通过描述用于量化与土壤中 EPN 相互作用的某些自由生活的捕食线虫（FLBN）的引物/探针集来扩展分子工具的范围，以描述土壤食物网。从用昆虫幼虫诱饵的土壤中回收了三种 FLBN 分离物。形态和分子特征确认它们是 Acrobeloides maximum（RT-1-R15C 和 RT-2-R25A）和 Rhabditis rainai（PT-R14B）。实验室实验证明，这些 FLBN 能够干扰寄生在象鼻虫 Diaprepes abbreviatus 上的 Steinernema diaprepesi、Steinernema riobrave 和 Heterorhabditis indica 的发育（P<0.001），这可能是由于资源竞争。针对最强劲的竞争者 A. maximum 开发了一种分子探针。我们选择高度保守的 SSU rDNA 序列来设计引物/探针，因为这些序列比可能提供更好分类分辨率的 ITS 序列更丰富地用于自由生活的线虫。我们的分子探针可以识别在该基因座上具有 ⩾98%相似性的生物体。在从柑橘果园中收集的线虫 DNA 样本中使用这种分子探针来描述土壤群落，发现 Acrobeloides 组线虫与 EPN 总数（S. diaprepesi、H. indica 和 Heterorhabditis zealandica）以及包括 Catenaria sp. 和 Monachrosporium gephyropagum 在内的线虫捕食真菌的复杂体之间存在正相关（P<0.01），EPNs 的天敌。这些关系可以广泛解释为支持 Linford 的假说，即有机物质（此处为昆虫尸体）的分解大大增加了捕食线虫及其天敌的数量。
