Multiple baculovirus infections in codling moth: CpGV-R5 help to CpGV-M cannot be substituted by CrpeNPV

International audience; The most common resistance to Cydia pomonella Granulovirus in codling moth is the type I resistance, that results in a complete arrest of CpGV-Mexican isolate replication in all cells of resistant larvae. This arrest can be overcome by supplying CpGV-R5, a virus isolate able to replicate in such resistant larvae. Sequential ingestion of the two virus genotypes yields different results in function of the order of ingestion. Experiments were carried out with virus doses high enough to ensure about 80% mortality of larvae with CpGV-R5, and equal amounts of CpGV-M. No CpGV-M replication was observed when this virus was provided first, while double infections were detected if CpGV-R5 was supplied prior to CpGV-M. The delay between ingestion of the two viruses (30 to 240 minutes) did not influence the frequency of double infections. Cryptophlebia pestaltica nucleopolyhedrovirus (CrpeNPV) efficiently replicates in codling moth larvae, susceptible or resistant to CpGV-M replication. Mixed infections can be obtained by feeding susceptible larvae with CpGV-M and CrpeNPV or with CpGV-R5 and CrpeNPV, or by feeding resistant larvae with mixtures of CpGV-R5 and CrpeNPV. However, unlike CpGV-R5, CrpeNPV is not able to lift the restriction on CpGV-M replication in resistant larvae, indicating that the mechanism involved in resistance is specific.