N-Hexane Fraction of Shorea macrophylla Bark Extract as a Repellent against Tribolium castaneum (Herbst)

The red flour beetle Tribolium castaneum is a major stored-product pest affecting food security and postharvest quality. Plant-derived repellents offer a lower-risk alternative to synthetic chemicals, particularly when grounded in locally available resources and traditional knowledge (e.g., Dayak uses of Shorea macrophylla). We evaluated the behavioral repellency of an n-hexane fraction of S. macrophylla bark extract against adult T. castaneum using a Y-tube olfactometer. Six concentrations (0–100%; 100% defined as 0.150 mL extract) were tested. Insect choices were recorded at 60, 120, 180, 240, 300, and 360 min. Treatment effects were compared using Duncan’s test. Repellency became statistically significant from 180 through 360 min (p < 0.05) and increased with both concentration and exposure duration, indicating a clear dose– and time-dependent response. The strongest avoidance behavior was observed at the highest concentration and the longest exposure intervals. The n-hexane fraction of S. macrophylla bark exhibits behaviorally mediated repellency to T. castaneum under laboratory conditions, consistent with activity from volatile secondary metabolites (e.g., terpenoids and aromatic compounds). These findings support the potential of S. macrophylla as a locally sourced botanical repellent for stored-product protection. Further studies should (i) characterize active constituents (e.g., GC–MS), (ii) test additional storage pests and commodities, (iii) evaluate residual efficacy and formulation stability, and (iv) assess safety and practicality for field application.