Larval antibiosis to cabbage stem flea beetle ( <scp> <i>Psylliodes chrysocephala</i> </scp> ) is absent within oilseed rape ( <scp> <i>Brassica napus</i> </scp> )

BACKGROUND: Insect pests present a global threat to crops, with plant resistance representing a key breeding goal. The cabbage stem flea beetle (Psylliodes chrysocephala; CSFB) is a key pest of oilseed rape (Brassica napus; OSR) in Europe; however, CSFB resistance is yet to be found in B. napus. To address this, we examine CSFB larval development over time, explore antibiosis across a genetically diverse B. napus panel, and test whether larvae can develop in model Brassicaceae species (Brassica rapa and Arabidopsis thaliana). RESULTS: CSFB larvae completed development from 4 weeks post-infestation, undergoing a 20-fold size increase, with larval recovery after 2 weeks allowing semi-high-throughput resistance phenotyping. Applying this method to 98 Brassicaceae genotypes (97 B. napus and 1 Sinapis alba), we found weak evidence for genotype effects on larval survival. However, phenotype validation with 'resistant' and 'susceptible' B. napus genotypes showed no differences in larval survival or adult emergence. Larval antibiosis was consistently observed in S. alba. Finally, we showed that model B. rapa and A. thaliana genotypes represent suitable hosts for CSFB, with larvae increasing eight to ten times in size after 2 weeks. CONCLUSION: CSFB larval antibiosis appears absent in B. napus, possibly because of bottlenecks experienced during domestication. However, larval antibiosis is present in S. alba, and future work should study the basis of this resistance. Further, CSFB larval screening in Brassicaceae model species presents an opportunity to explore CSFB resistance genetics, informing breeding progress for insect resistance in B. napus. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.