Effectiveness of Root-Boring Knapweed Weevil (Cyphocleonus achates Fåhr.) Herbivory on Spotted Knapweed (Centaurea stoebe Lam.) in Kamloops, BC: A Five-year Review
2025
Troy, Lisa | Tarasoff, Catherine
Spotted knapweed (Centaurea stoebe) is an Eurasian plant now invasive across North America. The root-boring knapweed weevil (Cyphocleonus achates) is one of 13 approved biocontrol agents. In 2017 and 2018, root-boring knapweed weevils were released at 15 sites across Kamloops, BC, Canada. This study is a five-year follow-up on the possible effects of C. achates on spotted knapweed density, distribution, and vigour. The presence of weevils was determined by destructive sampling that included plant extraction and root dissection. Plant height, number of stems, flowers, and buds was also recorded per plant. At the population level, infestation size and plant density was recorded. There was no consistent effect found at the individual plant level between those attacked by the weevil versus those unattacked. Additionally, there was no change in population size or density when compared to parameters from 2017/18. These lack of results is likely due to the short time frame of this study. The sites studied may be too different from those that have shown to be successful in other studies. Further research is required to better understand how spotted knapweed can be effectively controlled in the Kamloops area.
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