Increased voltinism in carrot weevil under a warmer climate

The carrot weevil, Listronotus oregonensis, is an important pest of carrots that causes yield losses of up to 50%. In recent years, control of this pest has become more complex in carrot-producing areas of Quebec, Canada. This situation is explained mainly by an extension of the activity period of adults, which complicates pest control management strategies. The objective of this study was to evaluate the impact of temperature increases on the phenology of carrot weevil. In a field experiment, we observed the activity period of adults, egg-laying duration, and larval development in carrot plots exposed to two different climatic conditions. A plot of carrots was set up under a tunnel to increase the temperature by 1°C in comparison with a control plot without any shelter. Weevil phenology was affected greatly by the increased temperature, as shown mainly by the extension of the egg-laying period. The proportion of mated and sexually mature females was higher at the end of the season under the warmer climatic conditions than under the ambient temperatures. The inhibition of reproductive diapause under warmer conditions can explain why females were still active in the field at the end of the season. In addition, the abundance of the four larval stages of carrot weevil during the growing season demonstrates that two cohorts were present, thus confirming the presence of two generations in northern regions. These results concretely show that the recent increase in temperature is changing the phenology of this pest and will require modifications to pest management strategies.