Analysis of the frequency of mixed genotype infections in CpGV

The success of biological control of the codling moth, Cydia pomonella, with commercial products based on Cydia pomonella granulovirus (CpGV) isolates relies both on the ingestion of a sufficient amount of occlusion bodies (OBs) between their hatching from the egg and the penetration inside the fruits, and the correct replication of the virus in the insect larvae. Larvae resistant to one isolate, CpGV-M are frequently found in European orchards. In recent years, efforts have been devoted to obtaining virus isolates able to control resistant insects, among them, CpGV-R5. Ingestion of CpGV-M by a resistant larva does not allow replication of CpGV-M. Ingestion of CpGV-R5 results in virus replication and larval death. Ingestion of a mixture of CpGV-M and CpGV-R5 allows replication of both genotypes and better insect control. Both CpGV-M and CpGV-R5 are present in the commercial product Carpovirusine ® Evo 2 (NPP, Arysta LifeSciences). No recent data have been collected concerning the actual amount of virus ingested by the neonate larvae. As mixed infection CpGV-M and CpGV-R5 provide better protection, this is an interesting property to explore to improve the strategy of treatment in orchards. We analysed the distribution of virus droplets on leaves for two orchards using two different dispersion techniques, and leaves sprayed in laboratory conditions. We observed the mortality of larvae allowed to feed on these contaminated leaves for selected amounts of time. We then used High resolution melting (HRM) to estimate the occurrence of each genotype alone and mixed genotypes in individual larvae.