Elucidation of a novel mode of resistance of codling moth against Cydia pomonella granulovirus by homogenization experiments

Abstract: Since 2005, codling moth (CM, Cydia pomonella) populations with a reducedsusceptibility to Cydia pomonella granulovirus (CpGV, Baculoviridae) products have beenreported from about 40 European orchards. The resistance could be traced back to a single,dominant, sex-linked gene. Currently, resistance management strategies are based on theapplication of improved CpGV products containing resistance-overcoming CpGV isolates.Recently, two CM field populations (NRW-WE and SA-GO) with a reduced susceptibility toeven these improved CpGV products were found. First single pair crossing experiments betweenindividuals of these resistant field colonies and a susceptible laboratory CM strain (CpS)indicated that the inheritance of resistance of these populations did not follow the previouslydescribed pattern of Z-linked, dominant resistance. In single-dose bioassays the susceptibility ofneonates of the resistant CM colonies NRW-WE and SA-GO to different CpGV isolates (CpGVM,-S, -V15 and -E2) was estimated. The aim of the current study was the genetichomogenization of the genetically heterogeneous field populations NRW-WE and SA-GO by twodifferent methods: (i) repeated single pair crossings followed by family selection and (ii)successive mass crossing experiments under virus pressure. The resulting homogenous strains ofNRW-WE and SA-GO with fixed resistance will be used for backcrossing experiments with CpSto elucidate the mode of inheritance of their resistance.