Extreme heat reduces insecticide use under real field conditions

Insecticide use and its adverse environmental and health effects are expected to further increase in a warming climate. We here show that farmers' insecticide use, however, declines substantially when facing extreme heat. Using the example of Colorado potato beetles (Leptinotarsa decemlineata) in Switzerland, we find an 11.5% reduction of insecticide use for each day and degree that maximum temperatures exceed 34 °C in the potato growing season. Importantly, our analysis accounts for farmers' behavior under real field conditions, considering the potential adaption of farming practices to extreme heat. It, therefore, highlights how to combine methods to assess and improve our knowledge on the combined major challenges of reducing pesticide risks and coping with the effects of climate change on agriculture while accounting for human behavior. In the analysis, we provide various robustness checks with regard to the definition of temperature extremes, pesticide use indicators, and the chosen statistical model. We further distinguish the principal drivers of the identified effect and find strong evidence that insecticide use reductions are mainly driven by heat-induced decreases in pest pressure rather than heat-induced yield losses that render insecticide applications too expensive. We conclude that similar investigations for other crops and countries are required to assess and understand farmers changing pesticide use decisions under climate change.