Biology and Integrated Management of the Cabbage Seedpod Weevil in Prairie Canola Crops

The economic importance of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), increased rapidly in the prairies of western Canada following its discovery in canola near Lethbridge in 1995. Since 1999 outbreaks have occurred almost annually over thousands of hectares of cropland, necessitating applications of vast quantities of chemical insecticide. Both larvae and adults can damage the crop, with larvae developing within pods and feeding on seeds and adults feeding through pod pericarp late in the season to further reduce yield and quality. The development of sustainable control strategies has proceeded in several directions, including chemical, cultural, plant resistance, and biological control, and successes in each area have facilitated development of an integrated management approach for this pest. The chemical insecticide compounds and formulations with greatest effectiveness for reducing both adult and larval densities through foliar sprays and seed treatments were identified. Trap crop technology was tested under prairie field conditions, and seeding date recommendations were determined. New canola germplasm was produced that expresses both antibiotic and antixenotic (non-preference) resistance to the weevil. The mechanism of resistance was unraveled for the new germplasm, and has identified two key glucosinolate compounds that affect weevil behavior; these can drive future plant breeding programs to develop additional weevil-resistant germplasm. The species compositions and impact of indigenous natural enemies of the weevil were determined, and studies were conducted to assess European natural enemies for possible introduction to North America in a classical biological control program. Although the cabbage seedpod weevil remains an important component of the insect pest fauna of prairie canola crops, the knowledge now exists to enable producers to manage this pest in a sustainable manner.