Type V: A sex-linked crossed resistance to three Cydia pomonella granulovirus isolates, with different levels of dominance

The codling moth (Cydia pomonella), is known to be resistant to many (bio)insecticides, including the Cydia pomonella granulovirus (CpGV). Of the multiple isolates available on the European market, two are already known to have selected resistance: Type I to CpGV-M and type II or III to group E (CpGV-S or -R5). In 2019, a monitoring program revealed three wild populations of insects with reduced susceptibility to the three main used virus isolates (CpGV-M, -R5 and -V15). In this context, our aim was to characterise this new type of resistance, referred to as Type V, and to determine its inheritance pattern and degree of dominance, and to investigate whether and how it differs from previously described resistance mechanisms.

We collected a population previously identified as multiresistant from which several lines were isolated and selected during 13 generations with either CpGV-M, -R5 or no virus. Bioassays clearly showed high levels of resistance to CpGV-M, -R5 and -V15, as well as cross-resistance between the three isolates. Individual crossing experiments showed different inheritance modes for resistance to CpGV-M and CpGV-R in type V. Resistance to CpGV-M appeared dominant Z-linked as in type I, while it was more likely recessive, but still Z-linked for resistance to CpGV-R. Altogether, Type V is a novel type of resistance that cannot be overcome by CpGV-V15, and marked by a distinct inheritance pattern. Further research is needed to understand the relationship between resistance to each isolate, and adapt the future pest management strategies.