The effect of climate change on the insecticide reduction goal in Southern Germany using the example of the pollen beetle

Abstract The European Union is debating ambitious biodiversity targets. These measures have seen early adoption in Baden-Württemberg, Germany, with a new law aiming for a 50% reduction in the use of synthetic chemical plant protection products (CPPP) by 2030. Estimating the economic viability of reducing CPPPs without compromising farm revenues is an important step in reaching the goal, but the necessary data are often incomplete, unavailable, or non-existent. We calibrated a coupled crop-insect model using available field data on oilseed rape and its pest pollen beetle, and tested if we could upscale the field data both spatially and temporally. The simulation results show that while the damage threshold of 10 insects per plant is reached currently only in 4–5% of cases, the threshold will be reached in 23–53% of cases in the near future (2040–60), and 37–96% in the far future (2080–2100). Particularly warmer winters favor pollen beetle populations and lead to more cases of explosive population growth. Resulting yield losses may amount to up to 40% in the near, and up to 90% in the far future. Even with CPPP applied, yield losses could not be decreased to satisfactory levels in our simulations, suggesting that current methods of pollen beetle control may have to be adapted in the future. The study highlights the critical interplay between climate change, agricultural practices, and pest management, stressing the importance of data- and model-driven approaches to ensure food security and biodiversity conservation.