What is it and how does it work? The virus (NPV) is one of a variety of naturally occurring infectious diseases of the gypsy moth. The disease is often referred to as 'wilt' due to the soft, limp appearance of the diseased larvae. The moth larvae ingest the viral occlusion bodies along with foliage, and the rod shaped virus particles are liberated as the polyhedral protein matrix dissolves in the gut. These particles invade through the gut wall and attack internal tissues and organs of the larvae, eventually causing a general viral infection. The virus multiplies rapidly in cell nuclei, eventually causing disintegration of internal tissues and death of the larvae. The entire process takes 10 to 14 days, depending upon the size of the larvae, virus dose, and ambient temperature. Effectiveness In the natural environment, the virus persists in the soil and in low density gypsy moth populations causing little mortality. The infection is probably initiated at these low densities and as the host density increases, it spreads due to density dependent processes reaching epizootic (outbreak) proportions. These outbreaks result from increased transmission rates, within and between generations of the moth. Small larvae become infected and die on leaves in the crowns of trees, thus serving as inocula for healthy, feeding larvae. Adult moths may deposit egg masses on NPV-contaminated surfaces, thereby placing hatching larvae at high risk. Birds and mammals have the ability to pass and disperse active gypsy moth NPV, and parasites and invertebrate predators may play a role. In many dense gypsy moth populations, the virus kills up to 90 percent of the larvae and reduces populations to levels where they cause only minimal defoliation and tree damage the following year. On the average, at least 50% of larvae die. The virus will persist at high levels in soil, litter and on bark for at least 1 year following a natural outbreak. Exposure to ultraviolet rays in sunlight is the major cause of NPV degradation. Gypchek Research was begun in the late 1950's by the U.S. Forest Service to explore the feasibility of developing a product containing the virus to use as an alternative to chemical insecticides for suppressing gypsy moth populations. The resulting product, Gypchek, was registered with the U.S. EPA in 1978 as a general use pesticide for aerial and ground application to control the gypsy moth, In the 1990's it satisfied U.S. EPA reregistration requirements. Canada has developed a similar product, Disparvirus. Although current labeling does not require use under U.S. Forest Service supervision, the service continues to control its use and application. Gypchek is primarily produced by processing water extracts of infected gypsy moth larvae (in vivo production). The final product is a finely ground substance containing approx. 15% of viral occlusion bodies with the inert ingredients consisting of extracted material and parts from the insects. Research is continuing on developing strains for cell culture production (in vitro production) facilitating commercial scale production. The application range of Gypchek is between 1.3% to 13% of normal environmental virus levels. Aerial spraying is preferred for forest use. Ground spraying is more convenient for effective control in young plantations, parks and beside roads. The target population is the 1st or 2nd instar larvae. Gypchek is not considered to be very effective in low density gypsy populations, although this is still being studied. It is considered to be most effective in moderate to high density populations. Human Health Considerations There are no reports of acute poisoning from Gypchek. Because Gypchek contains gypsy moth parts, irritation of eyes, skin and respiratory tract may occur. However, these reactions also occur with exposure to gypsy moth parts in the natural setting. In dispersal, the insect matter corresponds to approx. 667 caterpillars per acre compared with 10,000-100,000 caterpillars per acre during heavy infestations. Workers are more likely to be affected than the general public due to greater exposure. The virus represents a complex of 10 closely related genotypic variants. Based upon biochemical and biophysical analyses, serological and immunological testing, and enzymic analysis of viral DNA, these variants have been shown to be unrelated to human and other mammalian viruses and only distantly related to other insect viruses. All known arthropod-borne viruses and other viruses infecting humans have been found to be serologically unrelated to gypsy moth NPV. Environmental Factors Baculoviruses, which attack arthropods and which group includes the gypsy moth NPV, are found wherever insects exists. Being readily carried by wind and rain, it is likely that every piece of land and body of water contains some virus particles and most produce probably is 'contaminated'. This may be considered indirect evidence for the safety of these agents. Testing on laboratory animals, wild mammals, birds and fish revealed no effects with one exception. Massive amounts applied to rabbit eyes produced irritation, caused by the insect parts. It is extremely unlikely that any mammalian or avian species would encounter such high dosages. Testing on aquatic and terrestrial invertebrates confirm the extremely narrow host range of gypsy moth NPV. The virus is non-pathogenic to beneficial insects. Gypsy moth parasitoids may be indirectly affected due to loss of their host. It has no effect on soil organisms and is not a plant virus. Changes in forest condition, water quality, microclimate, and soil productivity and fertility will be minimal compared with those that otherwise would occur from feeding by the gypsy moth. Gypchek is practically insoluble in water, potential for leaching is very low, it is not a volatile liquid, and burning vegetation would destroy the virus rather than releasing anything to the air. The inert material is natural. The dispersal concentration is low. Availability According to Kevin Thorpe, Insect Biocontrol Lab, USDA Agricultural Research Service, Gypchek is only available for research and for sensitive areas where there are, for example, endangered species. Because the production is labor-intensive, the product is expensive. However, there are indications that this will change. Pros 1. Natural to the environment 2. Species specific- not harmful to non-target organisms 3. Works well in moderate to heavy gypsy moth densities 4. Remains in the environment to help "trigger" future outbreaks Cons 1. Cost 2. Not as effective in low density gypsy moth populations 3. Research is still being done to refine application amounts Shirley Kristensen Sources 1 . Gypchek - The Gypsy Moth Nucleopolyhedrosis Virus Product, Forest Health Technology Enterprise Team-, Reardon, R.C., Podgwaite, J., Zerillo, R., Morgantown, WV, 1996.  2. Gypsy Moth Nucleopolyhedrosis Virus, Pesticide Fact Sheet, Information Ventures, Inc., prepared for USDA, Forest Services, 1995.  3. 1995 Environmental Impact Statement - USDA Forest Service - portions from the Web.  4. Kevin Thorpe, Insect Biocontrol Lab, USDA Agricultural Research Service, Beltsville, MD 20705 - phone conversation.