<scp>SYN</scp> ‐A, a naturally derived synergist, restores pyrethroid efficacy against cabbage stem flea beetle but negatively impacts its parasitoid <scp> <i>Microctonus brassicae</i> </scp>

The synergist SYN-A can effectively restore pyrethroid efficacy against metabolic resistant CSFB populations, potentially allowing up to 80% reduction in insecticide application rates while maintaining superior control. However, the severe impacts on beneficial parasitoids highlight the need for careful implementation strategies, including precise timing of applications outside peak parasitoid activity periods and continued evaluation of non-target effects. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.