Bioactive volatiles of Allium sativum and Brassica juncea for management of Tribolium castaneum and Corcyra cephalonica: Comprehensive in-silico and in-vitro analysis

Stored grain insects, Tribolium castaneum (red flour beetle) and Corcyra cephalonica (rice moth) pose significant threats to global food security. In spite of effectiveness of the conventional fumigants, huge concerns raised for adverse effect on environmental and human health, thereby prompting interest in exploitation of plant-derived volatile oils (VOs) as eco-friendly alternatives. The present study aimed to evaluate fumigant toxicity of nine VOs of Myrtus communis (McEO), Citrus sinensis (CsEo), Melaleuca alternifolia (MaEO), Eucalyptus globulus (EgEO), Alllium sativum (GEO), and Brassica juncea (MEO) (four varieties individually) against T. castaneum and C. cephalonica. The fumigant toxicity of VOs varied in the order of GEO > MEO > CsEO > McEO > EgEO > MaEO. Fumigant action of GEO exhibited significant mortality against adults of T. castaneum (LC₅₀ 1.05 μL/L air, 24 h) followed by MEO (LC₅₀ 4.90–20.27 μL/L air, 24 h), CsEO (LC₅₀ 11.92 μL/L air, 24 h), and McEO (LC₅₀ 28.10 μL/L air, 24 h). In case of C. cephalonica larvae, MEO (LC₅₀ 9.52–21.55 μL/L air, 72 h) showed the highest response, followed by McEO (LC₅₀ 33.76 μL/L air, 72 h), CsEO (LC₅₀ 41.47 μL/L air, 72 h), and GEO (LC₅₀ 29.16 μL/L air, 72 h). Gas-Chromatography-Mass-Spectrometry (GC-MS) analysis of the most effective GEO revealed presence of diallyl disulfide (62.02 ± 2.48 %) and allyl monosulfide (36.84 ± 2.64 %), whereas MEO indicated abundance of 2-pentenenitrile (78.23 ± 2.69 % to 92.99 ± 2.10 %) in PM 28 (PM28-MEO), PM 30 (PM30-MEO), Pusa Karishma (PK-MEO), and Pusa Jagannath (PJ-MEO), along with trace amounts of allyl isothiocyanate (AITC), 1-butene-4-isothiocyanate, and 5-cyano-1-pentene. The McEO mainly consisted of α-pinene (48.21 ± 2.65 %) and 1,8-cineole (26.86 ± 2.33 %), whereas CsEO was predominantly made up of l-limonene (92.27 ± 3.08 %). In silico modelling depicted favourable binding affinity of AITC with arylalkylamine N-acyltransferase (AANAT, −16.06 kcal/mol) of T. castaneum supported by a hydrogen bond, π-sulfur, π-alkyl, and two alkyl-alkyl interactions. Whereas, 2-pentenenitrile interacted with juvenile hormone esterase (JHE, −15.87 kcal/mol) of C. cephalonica attributed to a π-alkyl, alkyl-alkyl, and two hydrogen bonds, thus explaining remarkable fumigant action of MEO. Further, allyl monosulfide interacted with JHE (−10.25 kcal/mol) of C. cephalonica via five alkyl-alkyl interactions and l-limonene with AANAT (−14.87 kcal/mol) of T. castaneum through two π-alkyl, and six alkyl-alkyl interactions, both resulting in target protein inhibition. These findings highlight the potential of GEO and MEO as natural fumigants for their inclusion in integrated pest management strategies, offering effective and environmentally sustainable solutions for protecting stored grains.