Entomology and Nematology Department, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850-2299, USA.
J Invertebr Pathol. 2012 Jan;109(1):134-42. doi: 10.1016/j.jip.2011.10.012. Epub 2011 Oct 29.
Greenhouse experiments were conducted to assess the influence of soil texture on the persistence, efficacy and plant protection ability of entomopathogenic nematodes (EPNs) applied to control larvae of the Diaprepes root weevil (DRW), Diaprepes abbreviatus, infesting potted citrus seedlings. Seedlings were grown in pots containing either coarse sand, fine sand, or sandy loam. Three DRW larvae were added to each of 80 pots of each soil type. 24 h later, 20 pots of each soil type that had received weevil larvae were inoculated with EPN infective juveniles (IJs) of one of the following species: Steinernema diaprepesi, Steinernema riobrave and Heterorhabditis indica. Pots of each soil without EPNs were established as controls with DRW and controls without DRWs. Subsequently, pots with larvae received three additional larvae monthly, and the experiment continued for 9 months. Plant root and top weights at the end of the experiment were affected by both soil (P≤0.0001) and nematodes (P≤0.0001), and nematode species protected plants differently in different soils (interaction P≤0.0001). Soil porosity was inversely related to plant damage by DRW, whether or not EPNs were present; and porosity was directly related to the level of plant protection by EPNs. Mortality of caged sentinel weevil larvae placed in pots near the end of the experiment was highest in pots treated with S. diaprepesi. In a second, similar experiment that included an additional undescribed steinernematid of the Steinernema glaseri-group, soil type affected root damage by DRW and root protection by EPNs in the same manner as in the first experiment. Final numbers of S. diaprepesi and Steinernema sp. as measured by real-time PCR were much greater than those of S. riobrave or H. indica in all soils. Across all treatments, the number of weevil larvae in soil at the end the experiment was inversely related to soil porosity. In all soils, fewer weevil larvae survived in soil treated with S. diaprepesi or Steinernema sp. than in controls with DRW or treatments with S. riobrave or H. indica. The results of these experiments support the hypothesis that EPNs provide greater protection of seedlings against DRW larvae in coarse textured soil than in finer textured soil. However, less vigorous growth of the control without DRW seedlings in the two finer textured soils suggests that unidentified factors that stressed seedlings in those soils also impaired the ability of seedlings to tolerate weevil herbivory.
温室实验旨在评估土壤质地对应用于控制 Diaprepes 根象甲（DRW）幼虫的昆虫病原线虫（EPNs）的持久性、功效和植物保护能力的影响，DRW 是 Diaprepes abbreviatus，它侵害盆栽柑橘幼苗。幼苗在含有粗砂、细砂或砂壤土的盆中生长。在每种土壤类型的 80 个盆中添加 3 只 DRW 幼虫。24 小时后，在每种土壤类型的 20 个盆中接种一种以下物种的 EPN 感染性幼虫（IJs）：Steinernema diaprepesi、Steinernema riobrave 和 Heterorhabditis indica。未接种 EPN 的盆作为带有 DRW 的对照和不带 DRW 的对照设立。随后，每月向带有幼虫的盆中再添加 3 只幼虫，实验持续 9 个月。实验结束时，植物根和顶部的重量受到土壤（P≤0.0001）和线虫（P≤0.0001）的影响，线虫物种在不同土壤中以不同的方式保护植物（相互作用 P≤0.0001）。土壤孔隙度与 DRW 对植物的损害呈负相关，无论是否存在 EPN；而孔隙度与 EPN 对植物的保护程度呈正相关。实验结束时，放在靠近实验结束的盆附近的笼养哨兵象甲幼虫的死亡率在施用 S. diaprepesi 的盆中最高。在第二个类似的实验中，包括 Steinernema glaseri 组中另一种未描述的 Steinernema，土壤类型以与第一个实验相同的方式影响 DRW 对根的损害和 EPN 对根的保护。在所有土壤中，通过实时 PCR 测量的 S. diaprepesi 和 Steinernema sp. 的最终数量远大于 S. riobrave 或 H. indica 的数量。在所有处理中，实验结束时土壤中象甲幼虫的数量与土壤孔隙度呈负相关。在所有土壤中，用 S. diaprepesi 或 Steinernema sp. 处理的土壤中存活的象甲幼虫比有 DRW 或用 S. riobrave 或 H. indica 处理的对照土壤中的幼虫少。这些实验的结果支持了这样一种假设，即在粗质地土壤中，EPNs 为幼苗提供了比在细质地土壤中对 DRW 幼虫更大的保护。然而，在两种质地较细的土壤中，没有 DRW 幼苗的对照生长不旺盛，这表明在这些土壤中使幼苗受到压力的未知因素也损害了幼苗耐受象甲取食的能力。
