Predicting future cabbage seedpod weevil impacts
Bioclimate simulation models were used to understand how abiotic factors affect canola yield and cabbage seedpod weevil distribution and abundance.
Cabbage seedpod weevil (Ceutorhynchus obstrictus) was introduced to North America from Europe, and was first collected in the Canadian Prairies in southern Alberta in 1995. The most recent survey map posted on the Prairie Pest Monitoring Network shows that it has expanded across the southern Prairies into Saskatchewan and Manitoba.
Canola and other brassicaceous crops are primary hosts for cabbage seedpod weevil. Economic damage occurs when larva feed within pods and destroy developing seeds. The economic threshold for applying insecticides is currently 25 to 49 weevils per 10 sweeps when the crop is at the bud through flowering stages.
A research study was conducted to update a bioclimate model for cabbage seedpod weevil and to develop a new bioclimate simulation model for canola to help understand how abiotic factors (i.e., temperature, soil moisture) affect the distribution and abundance of cabbage seedpod weevil and the yield of canola.
Based on climate inputs, bioclimatic simulation models for cabbage seedpod weevil and canola were updated/developed using CLIMEX 4.1. This model develops ecoclimatic index (EI) values that indicate how species can survive and reproduce on a location-specific basis. An EI value of 0 means no persistence and a value of 100 means optimal establishment. Increasing EI values indicate an increase in abundance and an estimate of potential distribution.
The first CLIMEX model for cabbage seedpod weevil on the Canadian Prairies was developed in 2002. It predicted that the distribution of cabbage seedpod weevil would eventually cover the canola growing area of western Canada. Since then, research has developed a greater understanding of the insect, and better climate data is now available. This research updated the previous CLIMEX model and was validated with worldwide data.
The researchers developed and validated a new bioclimate model for canola in order to analyze the relationship between climate and canola yield on the Prairies. These models were then used to see how cabbage seedpod weevil and canola respond to changes in temperature and precipitation.
The research looked at three scenarios: the current climate; a climate that is warmer and drier; and one that is cooler and wetter. Areas at risk of canola yield loss from cabbage seedpod weevil were defined as areas with above average canola yield with an EI greater than 20 and that overlap with areas of high cabbage seedpod weevil abundance with an EI greater than 20.
Abiotic stresses impact pest risk
Based on current climate averages, the highest canola yields were modelled to be across the central and northern Prairie regions. The highest cabbage seedpod weevil abundance and risk to canola was greatest across the southern and central areas. The overlap between the two shows that the area of highest cabbage seedpod weevil risk to canola production would occur across the central Prairies.
The model predicts that under a warm/dry scenario, the overlap with high canola yield and high cabbage seedpod weevil populations would be limited to small areas in southeastern Manitoba and northeastern Alberta.
With a cooler/wetter climate, the predicted overlap where high yield canola is at risk to cabbage seedpod weevil is limited to southern Alberta and southern Saskatchewan.
Predicted regions of the Canadian prairie agricultural area where CSW poses a risk to canola yield (blue shaded area), where canola is expected to have above average yields (yellow shaded area), and where CSW most threatens canola yield (red shaded area), in (A) the current climate, (B) warmer/drier climates, and (C) cooler/wetter climates.
Source: Weiss et al., 2025
The researchers summarized that “understanding where canola (or rapeseed) production is at the greatest risk of cabbage seedpod weevil damage is important for improving integrated pest management programs for cabbage seedpod weevil. This information can help to guide the development of scouting and monitoring programs, plan ahead for the possibility of insecticide applications, or strategically use crop rotation to avoid growing canola in years of high risk. All of these can help farmers to make the most of their available resources when managing cabbage seedpod weevil.”
The research reported in this manuscript was funded, in part, by the Canadian Agricultural Partnership AgriScience Program, Integrated Crop Agronomy Cluster, a federal, provincial, territorial initiative. CABI is an international intergovernmental organization, and we gratefully acknowledge the core financial support from our member countries.
Ross M. Weiss, Tim Haye, Owen Olfert, Shelley Barkley, John Gavloski, James Tansey, Jennifer Otani, and Meghan A. Vankosky. 2025. Bioclimatic analysis of cabbage seedpod weevil, Ceutorhyncus obstrictus (Marsham) (Coleoptera: Curculionidae) and canola, Brassica napus Linnaeus (Brassicaceae) responses to climate. Canadian Journal of Plant Science. 105: 1-16. OPEN ACCESS https://doi.org/10.1139/cjps-2024-0177
Photo by Jon William, AAFC Saskatoon
