Commercial Use of Entomopathogenic Viruses

Several strategies have been followed for the commercial use of insect viruses as biological control agents of pests. The selection of the most suitable strategy depends on the target species, in terms of feeding habits, behavior and the type of damage caused. The goal expected after the application of the viral agent should also be taken into account, such as reducing the plant damage (in terms of yield or cosmetic damage) or the elimination of the insect pest population.

The inoculation strategy is widely used to induce artificial epizootics on the natural pest population by the introduction of viral inocula. If successful, the pest population densities will decrease before the pest reaches its economic threshold. This strategy is based on the presumption that the virus is already present in the environment, either because it is part of the natural biotic factors or because it was introduced earlier. In this case, its natural levels are too low to start an epizootic, and an application of high levels of inocula may trigger the epizootic. This strategy has proven to be useful in forest environments, where a basal inoculum remains in the soil until the next season which complements the effect of an early application. Some examples where this strategy has been used include: the control of the gypsy moth (Lymantria dispar) in Northeast United States, Central and East Europe, the Mediterranean region and Japan using the product Gypchek; the control of the Douglas-fir tussock moth (Orgya pseu-dotsugata) in the USA using TM-Biocontrol-1; and the control of the European pine sawfly (Neodiprion sertifer) using Neochek-S on more than 20 000 ha over the last 30 years in the USA.88 Considering all the forest pests, inundative applications of these products are out of the question and therefore planned applications on specific areas are used to trigger early epizootics in large areas of forest.

Viruses have also been used under the classical biological control strategy. After the introduction of a virus into the susceptible pest population, the virus may colonize and become established as a regulating biotic factor of the pest population, without requirement of further virus releases. One example where this strategy has been successful is in the control of the rhinoceros beetle (Oryctes rhinoceros) in several South Pacific islands with Nudivirus.89 Indeed, the strategy was so successful that the pest has been eradicated in many of these islands, eliminating the damage caused to coconut and oil palms.75 As with classical strategies, the inoculative release of the virus inocula can be carried out: either by simple spraying of the product (similar to the inundative strategies described below); by releasing infected hosts to contaminate healthy individuals; or by releasing contaminated parasitoids or predators (including birds) whose contaminated droppings will spread the inocula onto the pest's food. The use of contaminated baits is another technique for spreading the inocula, as adults may become contaminated and later transfer the infection to their offspring and mates. Contamination of seedlings may be another approach to spreading the viral infection, by stressing the insect population (e.g. by using a low-dose insecticide application), a sublethal or a covert infection may emerge as a lethal factor.89

The inundative strategy is based on the use of the virus as a bioinsecticide. That is, the virus is produced at industrial levels and is applied every time the pest is causing (or is expected to cause) economic damage. This strategy has been successfully incorporated into IPM programs, as long as basic information of the pest's biology, population density, economic threshold, etc. is known, in order to optimize its application and to program other control alternatives. This strategy has the advantage of using the same application technology used for the spraying of chemical insecticides, such as additives, spraying techniques, machinery (i.e. ground or aerial), etc., so no additional or special equipment is required.

Although the inundative strategy is used worldwide, the development of viral bioinsecticides has occurred mostly in Europe and North America, as the first viral insecticide, Elcar, was used in the United States against the cotton boll-worm, Helicoverpa zea. Today there are further CpGV (granulovirus obtained from Cydia pomonella) products on the European market: Granupom (Probis GmbH), Carpovirusine (Arysta LifeScience) and Cyd-X (Certis). In Europe, CpGV is successfully applied on more than 100 000 ha per year in organic and integrated pome fruit production. In spite of some constraints regarding the use of viral insecticides, a lack of technical information about the potential of these control agents and some reticence to use unknown agents in the field, a few Latin American countries have also developed some viral bioinsecticides. Countries such as Brazil, Peru and Bolivia produce and use their own viral bioinsecticides. In fact, one of the most successful cases for the use of baculoviruses is the control of the velvet caterpillar, Anticarsia gemmatalis (Lepidoptera: Noctuidae), in Brazil using its own NPV. For more than 20 years, this pest has been kept under the economic threshold almost exclusively by the spraying of the AgNPV (Baculovirus anticarsia EM ), on an average of two million ha of soybean, annually.90

Another example is the control of potato tuberworm, Phthorimaea operculella, with granulovirus, PoGV, in Peru.91 This pest is highly harmful to potato crops as it feeds on the aerial part of the plant, as well as on the tubers (see Figure 8.6). The International Potato Center (CIP) has coordinated the production of the PoGV, especially for the use of low income producers in the Andean highland territories. Its use is focused on the protection of the tuber "seeds" by covering them with a dust formulation ("Baculovirus de la polilla de la papa'') before storage.92

Figure 8.6 Phthorimaea operculella feeds on the potato tubers. In Peru the potato tuberworm, Phthorimaea operculella (Lepidoptera: Gelechiidae), has been efficiently controlled with its own GV (PoGV). Producers dust potatoes just after harvest and before storage with a dry formulate of PoGV, provided mostly by government agencies.

Figure 8.6 Phthorimaea operculella feeds on the potato tubers. In Peru the potato tuberworm, Phthorimaea operculella (Lepidoptera: Gelechiidae), has been efficiently controlled with its own GV (PoGV). Producers dust potatoes just after harvest and before storage with a dry formulate of PoGV, provided mostly by government agencies.

One of the best known examples for the commercial use of a baculovirus-based bioinsecticide is the successful control of the Heliothis-Helicoverpa complex by the commercial product Elcar, based on the Heliothis virescens NPV, HvNPV. This is an important complex of pests because of its wide host range, which includes cotton, soybean, maize, sorghum, tomato, tobacco, among others.89 Elcar was the first viral insecticide registered in the USA. Another baculovirus widely used as a bioinsecticide is the Autographa californica NPV, AcNPV, mostly used against the cabbage looper, T. ni (Lepidoptera: Noctuidae) in crops such as broccoli, cabbage, cauliflower, and lettuce, among others.92 This is the only species of baculovirus known to have a wide host range, which includes 23 species of Lepidoptera, most of them within the family Noctuidae. This is the main reason for its potential as a bioinsecticide. In fruit-producing systems, the Cydia pomonella granulovirus, CpGV, has been developed to control this important pest of apples, which has proven to be effective on codling moth larvae from USA, Canada, Europe and Australia. Several insect viruses have been developed and registered for use as insecticides. Most are specific to a single species or a small group of related forest pests, for example the gypsy moth, Douglas-fir tussock moth, spruce budworm and pine sawfly. They are not commercially available but are produced and used by the United States Forest Service. Other insect viruses investigated for use as insecticides include those that infect the alfalfa looper, soybean looper, armyworms, cabbage looper and imported cabbageworm. Although some of these viruses have been formulated and applied in field tests, none has been registered or sold commercially. Both the codling moth GV (Decyde®) and the Heliothis NPV (Elcar®) were at one time registered by the US EPA and produced commercially, but these products are no longer registered or available.

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  • Merimac
    What is entomopathogenic viruses?
    2 years ago

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