Granulosis virus, GV 颗粒体病毒

颗粒体病毒

中文名称：颗粒体病毒
英文名称：granulosis virus;GV
定义：引起颗粒体病的杆状病毒，病毒基因组为双链DNA。在感染细胞内形成颗粒状的包含体，其内通常只含有一个带囊膜的、大小约40nm×260nm的病毒粒子。
应用学科：昆虫学（一级学科）；昆虫病理学（二级学科）
一种寄生在昆虫中的一种杆状病毒，以蛋白质包涵体的形式存在，即蛋白质包含着一个病毒颗粒。核酸为双链DNA。

Any of various baculoviruses in the genus Granulovirus; used in the control of insect pests.

granuloviruses ( Granulosis virus )

Over 150 insect species from the order Lepidoptera have been reported to be susceptible to one or more granulosis virus (GV) isolates. Many of the species are important pests (e.g. codling moth, Cydia pomonella, imported cabbageworm, Artogeia (=Pieris) rapae, greasy cutworm, Agrotis segetum, potato tuber moth, Phthorimaea operculella, Indianmeal moth, Plodia interpunctella, etc.). While the GVs have been little used for insect control since being discovered in the 1920s, research is continuing around the globe. In 1981, codling moth GV became the first and, so far, the only candidate GV for USEPA registration. In Europe, two GVs are registered for use and a third is in the Registration Phase. The GVs are attractive for development as microbial insecticides mainly because of their specificity and safety. Many have been successfully multiplied in vivo, a few in vitro, and, it appears, they may be genetically engineered.

Impact

Significant commercial efforts to develop biopesticides based on GV are under way in Europe, North America and Australia. To date, only a few commercial biological pesticide products based on GVs have been produced and these mainly use the CpGV (Copping, 1998; Moscardi, 1999).

Adoxophana orana, attacked by A. orana GV (Capex 2/Andermat Biocontrol) in Switzerland.

Cydia pomonella, attacked by C. pomonella GV (Madex 3/Andermat Biocontrol in Switzerland; Gramupon/AgrEvo in Germany; Carposin, Agrichem in the Netherlands; Carpovirisine/NPP in France; Virin-Gyap NPO Vector in Russia; Cyd-X/Thermotrilogy in the USA)

Pthorimea operculella, attacked by P. operculella GV (Matapol) in Peru.

However active, programmes to develop other GV as crop protection agents are generally on a much more limited scale than for their relatives the NPVs. In South America there has been a successful project to develop PoGV for controlling potato tuber moth (P. operculella) in potato stores and this has been extended to Egypt and Tunisia. In Brazil programmes to develop the GVs of Erinnyis ello a pest of cassava and Diatraea saccharis a sugarcane pest are also underway and the EeGV has been used on up to 20,000 ha per annum (Moscardi, 1999). Plodia interpunctella GV has been under active development in the USA for control of P. interpunctella (Indian meal moth) in stored products but as yet a product has not yet been registered (Vail et al., 1991). The turnip moth Agrotis segetum has been the target for a number of candidate biopesticides based upon A. segetum GV. Work in both Denmark and Russia resulted in two products being developed (Agrovir and Virin-OS (Winstanley and Rovesti, 1993)) but their current commercial status is unclear.

In China, Pieris rapae GV and Plutella xylostella GV have both been developed for the control of these pests on cabbage (Entwistle, 1998). Since 1978 these GVs have reportedly been used on up to 100,000 ha (Moscardi, 1999) and products are now available based on powder and liquid suspensions of these viruses, sometimes in combination, and such products have also been exported to Vietnam. In India products for the use of GV against the sugarcane pest Chilo infuscatellus have also been commercialized although the scale of its current use is unclear (Puri et al., 1997).

The major attraction of GV is that the viruses are effective against strains of this pest which are resistant to chemical pesticides. One key target pest for GV has been the diamond back moth P. xylostella, which has become resistant to all major groups of chemical pesticides in many areas of Asia.

To date there have been no reports of resistance developing to GV but this may reflect the limited usage of GVs in pest control. A lack of susceptibility in some host populations to the GV of P. operculella has been reported (Briese, 1982).

An important characteristic of GVs is their specificity though this can be seen as both an advantage and a drawback. GV specificity means these pathogens are safe to most other insects and so are completely compatible with other biological control options. These viruses have no direct adverse effect on beneficial insects, predators or parasites. Their use therefore will not produce any of the secondary pest problems encountered when broad-spectrum chemicals are used. Its specificity also means it is safe to humans and can be sprayed onto crops right up to the time of harvesting with no residue problems. The drawback, however, is that one species/strain of GV will kill only a narrow spectrum of susceptible host species. The GV of P. xylostella will kill this pest on cabbage but not affect any other Lepidopteran cabbage pests such as Hellula undalis or Crocidolomia binotalis that can also attack these crops (Abdul-Kadir, 1992).

Another limiting property of some GVs is their speed of action. Some GVs are acutely lethal and resemble NPVs in their pathology, examples of these are the P. xylostella GV or Cydia pomonella GV, both of which have been investigated extensively as microbial control agents (Asayama and Osaki, 1970). Such fast acting GVs have been extensively studied and several commercial pesticides have been developed from CpGV. However, a number of other GV species cause chronic infections that kill hosts relatively slowly and these may have a more limited potential as biological insecticides. Even in the acutely lethal GVs, such as those of C. pomonella and P. xylostella, cessation of feeding and death rarely occurs before 4-5 days after infection. The infective dose needed to kill a larva also increases greatly as the larva grows. The combination of these two factors means that GV are successful only as pest control agents if application is able to target early instars. Later instars can be successfully infected but often require high application rates which can be uneconomic. More importantly, later instars, even if successfully infected, can cause unacceptable crop damage before they die.

Another limitation of GV as insecticides is their limited environmental stability especially to UV light. Although the granulin coating helps to protect the virus particle, its stability under UV exposure is very short. Thus, GV sprayed on leaf surfaces exposed to direct sunlight is often inactivated rapidly and little residual activity can remain on exposed surfaces more than a day after application.

Hosts / species affected

The granuloviruses (GV) are, like the better know nucleopolyhedroviruses (NPV), a genus of insect pathogens in the family Baculoviridae. At least 135 species of insects are known to be susceptible to infection with GV, almost all Lepidoptera but a few Hymenoptera (Murphy et al., 1995). Like their close relatives the NPV most GVs are highly specific and generally infect a single or a few closely related species usually in the same genus. The viruses are named after the insect in which they were first isolated and identified thus the GV from the codling moth (Cydia pomonella) is C. pomonella GV or CpGV. GVs differ from NPVs in that only one virus particle or virion is found in each infective particle, the occlusion body (OB) or granule. In this virus the single rod-shaped particle of DNA, 250 x 50 nm, is encased in a crystal matrix composed of a protein called granulin. This is structurally very similar to the closely related polyhedrin of NPV and provides the viral particle with a degree of protection during its passage between hosts. The OBs of GV containing only the one virion are, at 0.3-0.5 mm in length, much smaller than the NPV occlusion bodies (ranging from 1 to 15 mm) that contain many virions. This small size means they are just discernable with a light microscope using phase contrast or preferably incident dark field microscopy at x200-400.

A few of the most important hosts in the crop protection context are listed below but for a fuller list the Index virium website (http://life.anu.edu.au/viruses/Ictv/index.htm) or Murphy et al. (1995) should be consulted.

In all host species the larval stages are the primary target of infection, with early instars being most susceptible: Artogeia rapae [Pieris rapae], Cydia pomonella, Chilo infuscatellus, C. sacchariphagus, C. suppressalis, Choristoneura fumiferana, Cryptophlebia leucotreta, Harrisina metallica (brillians), Helicoverpa armigera, Mamestra brassicae, Phthorimaea operculella, Pieris brassicae, P. rapae, Plodia interpunctella, Plutella xylostella, Spodoptera littoralis and Trichoplusia ni.