| Abstract
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The biological activity, and morphological, histopathological and molecular features of a single nucleocapsid nuclear polyhedrosis virus (SNPV) and a multiple nucleocapsid NPV (MNPV) isolated from Thysanoplusia orichalcea (Lepidoptera: Noctuidae) in Indonesia were determined. The SNPV (ThorSNPV) has a tetrahedral-shaped occlusion body (OB), while the MNPV (ThorMNPV) has a polyhedral-shaped OB. The virulence of ThorSNPV to third instar soybean loopers Pseudoplusia includens was low, with an LD{50} value of 65,636 OBs/larva. However, the ThorMNPV was highly virulent to third instar soybean loopers with an LD{50} of 242 OBs/larva. Transmission electron microscopy studies showed that many OBs of ThorSNPV did not contain embedded virions. Both ThorSNPV and ThorMNPV had a narrow host range, and only infected one species (soybean looper) of seven noctuid species tested. Both viruses infected primarily the fat body, tracheal epithelium and hypodermis of soybean loopers. The genomic sizes of the ThorSNPV and ThorMNPV were determined to be 135 and 111.7 kbp, respectively. The open reading frames of ThorSNPV and ThorMNPV polyhedrin genes consist of 738, and 735 nt which code for 246, and 245 amino acid residues of the putative polyhedrin protein with estimated molecular weights of 28,778 and 28,705 Da., respectively. The promoter for the ThorSNPV polyhedrin gene is similar in length to the promoter of Spodoptera frugiperda NPV (SfMNPV) and has a 5 nt deletion before the start codon. The promoter for ThorMNPV polyhedrin gene is identical to those of the AcMNPV and Bombyx mori MNPV. Tetrahedral OBs with virions properly occluded were produced when the polyhedrin gene of AcMNPV, whose OBs are polyhedral in shape, was replaced by the polyhedrin gene of ThorSNPV whose OBs are tetrahedral in shape. This work establishes the importance of the polyhedrin protein encoding gene sequence in determining OB shape. Phylogenetic analysis of the polyhedrin protein sequence reveals that ThorMNPV and ThorSNPV belong to Groups I and II of baculoviruses isolated from lepidopteran hosts, respectively. Fibrous sheets, a P10 gene product, were seen in the nucleus and cytoplasm of the tracheal cells of soybean looper infected with ThorMNPV. Aberrant virions of ThorMNPV were observed with curved and elongated shapes.
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