A new CpGV isolate overcoming Cydia pomonella resistance to Granulovirus: improvement of the virus efficiency by selection pressure on resistant hosts

Abstract: Since 2004, some codling moth (Cydia pomonella) populations resistant to the Mexican isolate of Cydia pomonella granulovirus (CpGV-M) were detected in different organic orchards in Western Europe. A resistant laboratory colony of codling moth (RGV) was built by introgression of the resistance character in a susceptible laboratory colony (Sv). The resistance of the RGV colony to the CpGV-M came over 60,000-fold when compared to the susceptible laboratory colony (to Sv). To overcome this resistance, the efficiency of CpGV isolates from various origins was investigated. Two of them (I12 and NPP-R1) presented an increased activity on RGV larvae. NPP-R1 reduces the resistance factors of RGV to 7-fold and 46-fold at the LC50 and LC90. Genetic characterization showed that NPP-R1 is a mixture of at least two prevalent genotypes, one of them being similar to CpGV-M. The 2016-r8 isolate obtained from eight cycles of selection of NPP-R1 on RGV larvae had a sharply reduced proportion in the CpGV-M genotype and an increased efficiency on RGV. Carpovirusine samples were formulated with these isolates for field experiment. Results from Germany, Italy and France gave promising results, showing that the 2016-r8 isolate is a good candidate to control CpGV-M resistant codling moth populations.