Field resistance of codling moth against Cydia pomonella granulovirus (CpGV) is autosomal and incompletely dominant inherited

The current appearance of local codling moth populations with resistance to Cydia pomonella granulovirus (CpGV) is an impediment to continuous CpGV application. Therefore, crossing experiments have been performed in order to gain information about the inheritance of resistance. Evidence is presented that the observed field resistance is stably inherited even under non-selective conditions in the laboratory. Offspring of reciprocal F1 crosses between a susceptible (‘S’) and a resistant (‘R’) strain and backcrosses between F1 and S were bioassayed at different CpGV concentrations. The resistant strain showed 100 times lower susceptibility in 7-day bioassays. The responses of the reciprocal crosses (male S × female R and female S × male R) did not differ significantly, indicating that resistance is autosomally inherited. The median lethal concentration for the F1 progeny was intermediate between those of its parental strains. Mortality data obtained from the backcrosses suggested that inheritance of resistance is due to a non-additive, polygenic trait.