A new Cydia pomonella colony resistant to multiple Cydia pomonella granulovirus isolates

Abstract: Repeated treatment to control insect pests can exert strong selective pressure on
individuals, leading to the emergence and spread of resistant phenotypes. The codling moth
(CM), Cydia pomonella, is known to be resistant to many (bio)insecticides, including the ‘M’
isolate of Betabaculovirus cypomonellae, previously known as Cydia pomonella granulovirus (CpGV), which is intensively used as a biocontrol product. Following the spreading of this very strong resistance in Europe two new isolates effective against CpGV-M resistant insects, have been introduced into the French market: CpGV-R5 and CpGV-V15. In this context our first objective was to track the emergence of resistances to these new products in the field to manage them as soon as possible. The second objective was to create a laboratory colony with new types of resistance for better understanding multi-resistance patterns. To these aims, field monitoring was conducted in 2019. CM samples were collected from 36 orchards in France, Germany and Italy and tested for susceptibility to the three commercially available isolates in Europe (CpGV-M, -R5, and -V15). Out of the 29 populations tested, 20 had reduced susceptibility to CpGV-M only, 10 had reduced susceptibility to both CpGV-M and CpGVV15, and 3 had reduced susceptibility to CpGV-M, -V15, and -R5 (i. e., considered as multiresistant). In 2020, one multi-resistant field population was intensively resampled to derive a laboratory colony. Individuals were bred under selective pressure with CpGV-R5 for 16 generations, and the response of this colony to the three commercially available isolates was tested. Results indicated that this colony is highly resistant to these three isolates. Further research is needed to understand the relationship between resistance to each isolate, the mechanisms involved and the genes responsible for these resistances. This also raises questions about pest management practices.