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Abstract
The occurrence of codling moth populations in European apple orchards that were not
controlled by Cydia pomonella granulovirus (CpGV) is the first reported case of field
resistance against a baculovirus control agent. A monogenic dominant sex-linked mode
of inheritance was previously demonstrated in single-pair crosses between a homogeneous
resistant (CpRR1) and a susceptible (CpS) laboratory strain of codling moth. However,
resistant field populations (CpR) are more heterogeneous in their levels of resistance,
and the possibility that they could harbor different resistance genes to CpRR1 had
not been directly addressed. Here we report single pair crossing experiments using
a resistant codling moth strain collected from an apple orchard in the southwest of
Germany. Single-pair crosses within the field strain revealed a genetic basis to the
heterogeneity of CpR concerning CpGV resistance. Hybrid crosses to a susceptible laboratory
strain and backcrosses of the F1 generation to the resistant CpR strain confirmed
that the homogeneous CpRR1 and the heterogeneous field strain CpR share the same mode
of inheritance. Thus the variable levels of CpGV resistance in field populations is
likely due to frequency differences of the same resistance-conferring gene, rather
than different genes, which will facilitate future efforts to monitor and manage resistance.