Molecular characterization and biological activity of native Spodoptera littoralis nucleopolyhedrovirus isolate

Reem M. Abd El-Maksoud,Norhan Yasser,Aziza Abdelal,Engy Osman,Samy Sayed,Lamiaa El-Gaied,El Shaimaa Naguib,Wael Elmenofy

doi:10.1186/s41938-021-00433-2

Abstract

BackgroundSpodoptera littoralis nucleopolyhedrovirus (SpliNPV) is considered a promising biocontrol agent that can be used for the effective control of the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), which is an economic pest on many cultivated plants and crops in tropical and sub-tropical regions. The genome of the SpliNPV-AN1956 isolate has been fully sequenced, providing a reference strain for comparison of new isolates. In this study, identification, biological activity, and genetic characterization of a field collected SpliNPV isolate were carried out.ResultsThe examination of viral occlusion bodies (OBs) by TEM showed a typical baculovirus OBs of type nucleopolyhedrovirus (NPV) with polyhedral structures. The phylogenetic analysis of the late expression factor- 5 (lef-5) gene as well as the restriction profile analysis confirmed the identity of SpliNPV as a variant isolate. Digestion with ScaI endonuclease showed that 4 fragments of 50, 35, 27, and 13 kb were detected but 3.2 kb was absent in SpliNPV-Cab3 pattern compared to the reference strain. Meanwhile, upon digestion with PstI and HindIII endonucleases, no differences were observed in both isolates’ pattern. Moreover, the virulence evaluation against S. littoralis 1st instar larvae indicated that LC50 value of SpliMNPV-Cab3 was higher than that estimated for the reference strain. Also, ST50 of SpliNPV-Cab3 (120 h) was significantly different with that of the reference strain (132 h).ConclusionThe host specificity based on virulence parameters make SpliNPV-Cab3 isolate a potential candidate to be involved in the integrated pest management strategies for the control of S. littoralis population with a prospect to biopesticide development.

Highlights

Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) is considered a promising biocontrol agent that can be used for the effective control of the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), which is an economic pest on many cultivated plants and crops in tropical and sub-tropical regions
SpliNPV-Cab3 occlusion bodies (OBs) EM examination Typical viral infection symptoms were detected 5–7 days post infection, using purified viral OBs suggested the specificity of the collected isolate to S. littoralis larvae
Transmission electron microscopic analysis revealed that the examined viral OBs are a typical baculovirus OBs of type nucleopolyhedrovirus (NPV) with polyhedral structures (Fig. 1)

Summary

Introduction

Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) is considered a promising biocontrol agent that can be used for the effective control of the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), which is an economic pest on many cultivated plants and crops in tropical and sub-tropical regions. Different bio-insecticides such as fungi, bacteria, and viruses have been used for many years for insect pest control. Among these bio-insecticides are baculoviruses (Mahendra and Avinash, 2012). The Baculoviridae family taxonomically is sub-divided into four genera; Alpha- and Betabaculovirus which are specific for Lepidoptera, Deltabaculovirus specific for Diptera, and Gammabaculovirus specific for Hymenoptera (Harrison et al, 2018). Such viruses are highly specific to their hosts and do not cause any pollution to the environment and do not leave residues on fruits which are an important issue of most people (Wang and Hu, 2019). The baculovirus expression vector system is nowadays widely used for production of different recombinant protein in insect cells (Elgaied et al, 2017)

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