Impact of climate change on phenology and sustainable management of the codling moth (Cydia pomonella)

Abstract: Current and projected global warming will have direct impacts on agricultural cropping systems (e.g. productivity), as well as indirect effects through changes in the phenology and life-history adaptation in many species. Hitherto these changes were not easy to simulate for actual phenologies because of the rough temporal (season) and spatial (regional) resolution of climate model projections. We evaluated the impact of climate change on phenology and prospective diapause induction in a global insect pest – the codling moth, Cydia pomonella. Seasonal and regional climate change signals were downscaled to the hourly temporal scale of a pest phenology model and the spatial scale of pest habitats using a stochastic weather generator operating at daily scale in combination with a re-sampling approach for simulation of hourly weather data. Under future conditions of increased temperatures (2045-2074), the present risk of below 20% for a pronounced second generation (peak larval emergence) in Switzerland will increase to 70-100%. The risk of an additional third generation will increase from presently 0-2% to 100%. We identified a significant two-week shift to earlier dates in phenological stages, such as overwintering adult flight. The magnitude of first generation pupae and all later stages will significantly increase. Additionally first generation pupae and later stages will be prolonged. Also a significant decrease in the length of overlap of first and second generation larval emergence was identified. Such shifts in phenology will ultimately induce changes in life-history traits regulating the life cycle. An according life-history adaptation in photoperiodic diapause induction to shorter day-length is expected and would thereby even more increase the risk of an additional generation. With respect to codling moth management, the shifts in phenology and voltinism projected here will require adaptations of plant protection strategies to maintain their sustainability.