Geographic variation in chemical composition and bioactivity of Valeriana wallichii root oils: implications for botanical fumigant development against stored-product insects.

Abstract

BACKGROUND Stored-product insects (Sitophilus spp., Plodia interpunctella, Sitotroga cerealella) drive substantial postharvest losses and increasingly resist synthetic fumigants. Valeriana wallichii roots yield volatile oils rich in short-chain acids and sesquiterpenes. We compared gas chromatography-mass spectrometry (GC-MS) profiles and fumigant/contact toxicities of oils distilled from India, China, and Nepal and tested representative constituents to identify bioactive chemotypes for grain protection. RESULTS GC-MS revealed significant geochemical divergence: Indian oil was characterized by a high acidity (isovaleric acid 39.6%; 3-methylvaleric acid 3.1%), whereas Nepalese oil had a greater concentration of 5-methylfurfural (12.45%) and sesquiterpenes. Indian oil was the most effective fumigant (median lethal dose (LD50): 8.65 μg/cm3 (Sitotroga cerealella adults), 25.14 μg/cm3 (Tyrophagus putrescentiae adults), 31.24 μg/cm3 (P. interpunctella adults) - 1.3-3.4 times more potent than other sources; contact bioassays confirmed the same hierarchy. Among the constituents, 5-methylfurfural exhibited the highest toxicity (LD50, 2.19 μg/cm3 for T. putrescentiae; 2.17-9.05 μg/cm3 for Sitotroga cerealella and adult P. interpunctella), followed by 3-methylvaleric acid (3.57 μg/cm3 for mites) and isovaleric acid (5.96 μg/cm3 for mites); β-caryophyllene demonstrated a preference for mites (LD50, 11.81 μg/cm3). Susceptibility ranked T. putrescentiae ≈ Sitotroga cerealella > P. interpunctella > Sitophilus spp. Fumigant bioassay was 1.5 to 4 times more efficacious than contact bioassay. CONCLUSION An acid-dominant Indian chemotype maximizes volatile bioactivity, with short-chain acids and 5-methylfurfural as primary drivers. Species-specific sensitivity supports targeted deployment (e.g., sachet-style emitters for mites/moths) and chemotype standardization. These findings advance botanical fumigant development by pinpointing active classes and geo-source effects, guiding low-residue controlled-release formulations and synergist-augmented strategies for tolerant coleopterans. © 2025 Society of Chemical Industry.