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Title: Resistance in Cydia pomonella to the Codling Moth Granulovirus in Europe: Could It Happen Here?

item Lacey, Lawrence

Submitted to: Western Orchard Pest and Disease Management Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/20/2007
Publication Date: 1/4/2008
Citation: Lacey, L.A. 2008. Resistance in Cydia pomonella to the Codling Moth Granulovirus in Europe: Could It Happen Here? Proceedings of the Western Orchard Pest and Disease Management Conference, Portland, OR, January 9-11, 2008. pp. 21-22.

Interpretive Summary: Codling moth is a very serious pest of apple and pear in most countries where pome fruit are grown. It is controlled in conventional orchards through the use of broad spectrum insecticides. In organic orchards the means to control codling moth are limited to non-chemical means. For a variety of safety and environmental reasons, alternatives to broad spectrum insecticides are being developed. One of the safest and most specific control agent of codling moth is a virus discovered in Mexico in 1963. Three commercial products of the codling moth granulosis virus are now being used in the United States. Use of the virus increased considerably in the USA since 2000, especially in organic orchards. Unfortunately, resistance in codling moth to the virus was recently reported in Europe in populations where the virus was used for several years. Susceptibility in some codling moth populations in Germany and France is 1000 times less than in non-resistant populations. Scientists at the USDA-ARS laboratory in Wapato, WA, in cooperation with scientists in Germany at the Agricultural Service Center Palatinate, Phytopathology and Plant Protection Laboratory in Neustadt, Germany are investigating the susceptibility of field populations of codling moth in Washington State that have received regular treatments of the virus over the past 5 years. These scientists will also begin work on a strategy to forestall development of codling moth resistance to the virus. If the activity of the virus is maintained, it will continue to provide an effective means of codling moth control to both conventional and organic growers.

Technical Abstract: One of the most specific control agents of codling moth (CM) is the granulovirus (CpGV) discovered in Mexico in 1963. Although first evaluated in North America, its commercial development and widespread use began in Europe. Use of CpGV has increased considerably in North America since 2000, especially in organic orchards. The virus provides selective control of CM that is safe to beneficial insects including honey bees and natural enemies of CM. Recently, CM resistance to CpGV was reported in Germany and France in organic orchards treated with multiple applications of CpGV over an extended period. Resistance to CpGV has now been found in Switzerland and Italy. Resistance ratios in some CM populations exceed 1000. Laboratory studies reveal that rapid development of extreme resistance (100,000 resistance ratio) is possible due to sex-linked inheritance of dominant resistant genes. Because CpGV is being increasingly used in North America, the potential for development of resistance should be anticipated. An integrated approach that alternates other soft interventions with CpGV should be considered especially when the virus is used extensively within a region. Management strategies that will maintain the efficacy of CpGV are needed before a decline in CM susceptibility is detected. Various factors could influence the probability that resistance in CM to CpGV would develop in North America. In addition to the frequency of genes responsible for resistance in our CM populations, the number of years that CpGV has been used against a given population, the number and frequency of applications per season, the size of virus treated populations and their proximity to CM that are not treated with CpGV, could help to determine if and when resistance will develop.