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The occurrence and distribution of resistance of codling moth to Cydia pomonella granulovirus in Europe



Thirty-five codling moth (CM, Cydia pomonella L., Lepidoptera, Tortricidae) populations collected in different commercial orchards in six European countries were tested for their susceptibility to Cydia pomonella granulovirus (CpGV-M). Including previously published data on CpGV-M resistance, a total of 38 CM colonies showed considerably elevated LC50 values, independent of the country origin. When only few test individuals are available, determination of mortality of neonate larvae at a discriminating concentration range of 104 to 106 OB/ml (>log4) as a direct measure of percentage susceptible individuals in a CM population is more advisable than calculation of LC50 values. The >log4 mortality alone or in combination with the LC50 value can be used for identification of resistance in a population. Results indicated a locally separated but widely spread occurrence of CM populations with low susceptibility to CpGV-M. The most plausible hypothesis for the emergence of CpGV-M resistance is its selection by repeated use of CpGV products.