Density-gradient centrifugation of the virions liberated from Rachiplusia ou nuclear polyhedra

Co-occlusion and persistence of a baculovirus mutant lacking the polyhedrin gene

A co-occlusion process was evaluated as a commercially and ecologically acceptable strategy for the development of genetically improved baculovirus insecticides. Coinfection of Spodoptera frugiperda (IPLB-SF-21) tissue culture cells with Autographa californica nuclear polyhedrosis virus (AcMNPV) and an AcMNPV mutant (Ac-E10) lacking the polyhedrin gene resulted in occlusion of both virus types within polyhedra. The amount of occluded Ac-E10 virions in progeny polyhedra populations during serial passage in Trichoplusia ni larvae was evaluated. Maintenance of the mutant in progeny polyhedra required polyhedra inocula containing equal numbers of the two virus types at a high dose. A significant reduction in occluded mutant nucleocapsids occurs with inoculum levels below a 100% lethal dose. At inoculum levels below a 30% lethal dose, the majority of fourth-instar larvae were infected with only one type of virus. The commercial application and ecological advantages of the co-occlusion process are discussed.

Milestones leading to the genetic engineering of baculoviruses as expression vector systems and viral pesticides

The baculovirus expression vector system (BEVS) is widely established as a highly useful and effective eukaryotic expression system. Thousands of soluble and membrane proteins that, in general, are correctly folded, modified, sorted and assembled to produce highly authentic recombinant proteins have been cloned and expressed. This historical chronology and perspective will focus on the original, peer-reviewed discoveries that were pioneering and seminal to the development of the BEVS and that provided the basis for subsequent and more recent developments and applications.

Biological and molecular characterization of a multicapsid nucleopolyhedrovirus from Thysanoplusia orichalcea (L.) (Lepidoptera: Noctuidae)

A multicapsid nucleopolyhedrovirus (ThorMNPV) that was co-isolated with a single nucleocapid ThorSNPV from mixed infected larvae of Thysanoplusia orichalcea L. (Lepidoptea: Noctuidae) is characterized. Scanning electron microscopy of ThorMNPV showed a dodecahedral-shaped occlusion body (OB). The occluded virions contained one to as many as eight nucleocapsids/virion. Virion band profiles in gradient centrifugation were consistent in at least 10 rounds of centrifugation from different virion sample preparations. The ThorMNPV had high virulence to third instar Trichoplusia ni and Pseudoplusia includens with LD50 values of 17 and 242OBs per larva, respectively. However, ThorMNPV did not cause mortality in Spodoptera exigua, Spodoptera frugiperda, Spodoptera eridania, Anticarsia gemmatalis, and Helicoverpa zea. ThorMNPV replicates in cells of various tissues such as the fat body and tracheal epithelium cells. T. ni High 5 cells were permissive to ThorMNPV in terms of infection and viral DNA transfection, but SF-21 was less permissive and the infection process was slower. Production of OBs by ThorMNPV in the nuclei of SF-21 was not well pronounced. The genome size of ThorMNPV was estimated to be 136 kb. The polyhedrin gene open reading frame (ORF) was cloned and completely sequenced. The promoter sequence is identical to that of Autographa californica MNPV. Phylogenetic analyses using partial sequences of the polh, lef-8, and lef-9 revealed that ThorMNPV is a member of the Group I NPVs and is related but distinct from the AcMNPV/Rachiplusia ou NPV/Bombyx mori NPV cluster.

In vivo isolation of baculovirus genotypes

Restriction endonuclease profiles of a wild-type granulosis virus from Artogeia rapae (ArGV3) and a nuclear polyhedrosis virus from Lymantria dispar (LdMNPV) indicated that the preparations were genotypically heterogeneous. Eight constituent genotypes were isolated from ArGV3 by low mortality dose infections of late instar A. rapae and analysis of progeny viral DNA recovered from individual cadavers. Three distinct genotypes were isolated from LdMNPV by the same approach, using L. dispar larvae. These results show that larval mortality can occur as a consequence of productive infection by a single virus particle. Comparative physical mapping of the eight ArGV3 genotypes suggested that their diversity may be partly attributable to recombination during natural coinfection.

Granulosis viruses, with emphasis on the GV of the Indian meal moth, Plodia interpunctella

The granulosis viruses and nuclear polyhedrosis viruses are being considered for use as biological insecticides for control of their insect hosts. Many of these insect species, which include some of the most serious pests of agriculture and forests, have become difficult to control because they have developed resistance to chemical insecticides. Several laboratory and field studies have demonstrated that the baculoviruses (GV and NPV) are promising alternatives to chemicals for the control of economically important insects. These viruses are highly virulent, selective, and stable, and the impact on the environment following their application is minimal. A decision concerning the application of baculoviruses to stored grain and field crops must be based upon a prudent consideration of the benefits to be obtained and the potential risks of their use. Such decisions should be made only after consideration of the physical, chemical, and biological properties of these viruses. In addition, methods must be developed for the unequivocal identification of these viruses, and their effects on nontarget species at the cellular and molecular levels must be investigated. This can best be accomplished if a sufficient body of knowledge regarding the molecular properties of these viruses and their infection process is accumulated by an extensive quantitative approach. Much of this knowledge is lacking because, prior to their consideration for use as insecticides, the baculoviruses appeared to have little medical or economic importance. As a result, interest in studying them was limited. It has become obvious that the molecular properties of these viruses must be investigated if full advantage is to be taken of using them as insect control agents, and if present and future problems concerning their use as insecticides are to be handled properly. Fundamental research on the biochemical and biophysical properties of baculoviruses has concentrated mainly on a variety of nuclear polyhedrosis viruses (Harrap, 1972a,b; Harrap et al., 1977; Summers and Smith, 1975a,b; Arif and Brown, 1975). Much of this progress can be attributed to tissue culture-host cell systems available for the NPVs. The in vitro host system(s) has allowed insect virologists to make phenomenal strides in understanding the cellular and molecular events of virus infection, and, in addition, to enter the era of biochemical sophistication in which animal virology is found at present.(ABSTRACT TRUNCATED AT 400 WORDS)

Applied and molecular aspects of insect granulosis viruses

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