Wageningen University, Laboratory of Virology, P.O. Box 629, 6700 AP Wageningen, The Netherlands; CABI, P.O. Box 8, Rawalpindi, Pakistan.
Wageningen University, Laboratory of Virology, P.O. Box 629, 6700 AP Wageningen, The Netherlands.
J Invertebr Pathol. 2018 Mar;153:20-29. doi: 10.1016/j.jip.2018.01.009. Epub 2018 Feb 6.
The cotton leafworm Spodoptera litura is a polyphagous insect. It has recently made a comeback as a primary insect pest of cotton in Pakistan due to reductions in pesticide use on the advent of genetically modified cotton, resistant to Helicoverpa armigera. Spodoptera litura nucleopolyhedrovirus (SpltNPV) infects S. litura and is recognized as a potential candidate to control this insect. Twenty-two NPV isolates were collected from S. litura from different agro-ecological zones (with collection sites up to 600 km apart) and cropping systems in Pakistan to see whether there is spatial dispersal and adaptation of the virus and/or adaptation to crops. Therefore, the genetic make-up and biological activity of these isolates was measured. Among the SpltNPV isolates tested for speed of kill in 3rd instar larvae of S. litura, TAX1, SFD1, SFD2 and GRW1 were significantly faster killing isolates than other Pakistani isolates. Restriction fragment length analysis of the DNA showed that the Pakistan SpltNPV isolates are all variants of a single SpltNPV biotype. The isolates could be grouped into three genogroups (A-C). The speed of kill of genogroup A viruses was higher than in group C according to a Cox' proportional hazards analysis. Sequence analysis showed that the Pakistan SpltNPV isolates are more closely related to each other than to the SpltNPV type species G2 (Pang et al., 2001). This suggests a single introduction of SpltNPV into Pakistan. The SpltNPV-PAK isolates are distinct from Spodoptera littoralis nucleopolyhedrovirus. There was a strong correlation between geographic spread and the genetic variation of SpltNPV, and a marginally significant correlation between the latter and the cropping system. The faster killing isolates may be good candidates for biological control of S. litura in Pakistan.
棉铃虫 Spodoptera litura 是一种多食性昆虫。由于转基因为抗棉铃虫的棉花的出现，减少了农药的使用，它最近又重新成为巴基斯坦棉花的主要害虫。棉铃虫核多角体病毒（SpltNPV）感染 S. litura，被认为是控制这种昆虫的潜在候选者。从巴基斯坦不同农业生态区（采集地点相距高达 600 公里）和种植系统中收集了 22 个 SpltNPV 分离株，以观察病毒是否存在空间扩散和适应性，以及对作物的适应性。因此，测量了这些分离株的遗传结构和生物活性。在测试的 SpltNPV 分离株中，TAX1、SFD1、SFD2 和 GRW1 对 3 龄幼虫的致死速度最快，明显快于其他巴基斯坦分离株。对 DNA 的限制性片段长度分析表明，巴基斯坦 SpltNPV 分离株均为单一 SpltNPV 生物型的变体。这些分离株可分为三个基因群（A-C）。根据 Cox 比例风险分析，A 组病毒的致死速度高于 C 组。序列分析表明，与 SpltNPV 类型物种 G2（庞等人，2001）相比，巴基斯坦 SpltNPV 分离株彼此之间的关系更为密切。这表明 SpltNPV 是单一引入巴基斯坦的。SpltNPV-PAK 分离株与 Spodoptera littoralis 核多角体病毒不同。SpltNPV 的地理分布与其遗传变异之间存在很强的相关性，与种植系统之间也存在边缘显著相关性。致死速度更快的分离株可能是巴基斯坦控制 S. litura 的良好候选者。
