Host adaptation of the leek‐associate <scp>L2</scp> lineage of <scp> <i>T</i> </scp> <i>hrips tabaci</i> : fitness divergence and molecular mechanisms on cabbage and onion

Abstract Background Thrips tabaci (Thysanoptera: Thripidae) is a globally important agricultural pest with strong host plasticity. The leek‐associated thelytokous (L2) biotype of T. tabaci can infest multiple crops, but the molecular mechanisms underlying its adaptive response to novel host plants remain poorly understood. This study aimed to characterize the biological performance and molecular regulatory responses of L2 biotype T. tabaci during host shift from red cabbage to onion across three successive generations. Results T. tabaci completed its life cycle on both hosts, but age‐specific survival rate ( S xj ), fecundity ( m x ), and maternity ( l x m x ) were significantly higher on red cabbage than on onion. The onion‐reared F 1 generation showed drastically reduced S xj and lower m x / l x m x peaks, with this fitness disadvantage persisting over three generations. Transcriptomic analysis identified 3862, 6549, and 9484 differentially expressed genes (DEGs) in F 1 , F 2 , and F 3 generations reared on onion, respectively, enriched in cytochrome P450‐mediated detoxification and insect hormone biosynthesis pathways; furthermore, eight gene expression patterns were clustered, forming a core regulatory set associated with host shift adaptation. Conclusion A stable rearing system for the L2 biotype of T. tabaci on onion bulbs was established in this study. This study reveals the dynamic biological and transcriptomic adaptation process of T. tabaci during short‐term host shift from red cabbage to onion, highlighting the key roles of detoxification and hormone metabolism in mediating its host plasticity, and provides candidate molecular targets and a foundational framework for future research on this pest's multi‐host adaptation. © 2026 Society of Chemical Industry.