In the present study, detection, characterization and virulence analysis of a field collected nucleopolyhedrovirus isolated from the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) was carried out. The obtained isolate, named SpliNPV-YW, was collected from diseased S. littoralis larvae in El-Menoufia governorate, Egypt. Transmission electron microscopy showed the presence of typical occlusion bodies with average size of (1.06 × 1.19 µm). Upon digestion using two different endonucleases, PstI and ScaI, no clear difference was detected in the collected isolate (SpliNPV-YW) DNA genome pattern compared to the reference strain SpliNPV-AN1956. The evolutionary analysis of the polyhedrin gene's partial nucleotide sequence revealed that SpliNPV-YW isolate was closed and had a genetic origin with the NPV isolate SpliMNPV-A26-5 that belongs to group II NPVs with identity of 99.7%. The median lethal concentration (LC50) and the median lethal time (LT50) values were estimated for second and fourth larval instars of S. littoralis. The LC50 values were 2.8 × 104 OB/ml for second larval instar and 5.2 × 105 OB/ml for fourth larval instar after 10 days of treatment. Regarding the speed of killing of the viral isolate, the results showed that the LT50 value for the second instar larvae (LT50 = 5.5 days) was lower than that of the fourth instar larvae (LT50 = 6.2 days) at concentrations of 4.3 × 1010 (ob/ml) and 1.2 × 1011 (ob/ml) for second and fourth instar larvae, respectively. Host specificity and virulence characteristics make SpliNPV-YW isolate a good potential to be utilized as a candidate biopesticide for the control of S. littoralis population in Egypt.

中文翻译：

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从棉叶虫 Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) 中分离的核多角体病毒的检测、表征和毒力分析

在本研究中，进行了从棉叶虫 Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) 中分离的田间收集的核多角体病毒的检测、表征和毒力分析。获得的分离株，命名为 SpliNPV-YW，是从埃及 El-Menoufia 省患病的 S. littoralis 幼虫中收集的。透射电子显微镜显示存在平均尺寸为 (1.06 × 1.19 µm) 的典型闭塞体。在使用两种不同的核酸内切酶 PstI 和 ScaI 进行消化后，与参考菌株 SpliNPV-AN1956 相比，在收集的分离物 (SpliNPV-YW) DNA 基因组模式中未检测到明显差异。多角体基因的进化分析' 部分核苷酸序列显示，SpliNPV-YW 分离株是封闭的，与属于第二组 NPV 的 NPV 分离株 SpliMNPV-A26-5 具有遗传起源，同一性为 99.7%。估计了 S. littoralis 的第二和第四幼虫龄的中位致死浓度 (LC50) 和中位致死时间 (LT50) 值。处理 10 天后，二龄幼虫的 LC50 值为 2.8 × 104 OB/ml，四龄幼虫的 LC50 值为 5.2 × 105 OB/ml。关于病毒分离物的杀灭速度，结果表明，2龄幼虫（LT50 = 5.5天）的LT50值低于4龄幼虫（LT50 = 6.2天），浓度为4.3×1010（ ob/ml) 和 1.2 × 1011 (ob/ml) 分别用于二龄和四龄幼虫。