Clove (Syzygium aromaticum) being a most valuable spice, produce stems and leaves as by-products during processing. This study aimed to valorize these by-products as potential grain protectants against rice weevils since it is a novel approach to reducing the post-harvest loss of rice and minimizing synthetic insecticide usage. The composition of clove stem and leaf essential oils was analyzed using gas chromatography-mass spectrometry. Accordingly, the contact repellent activity and fumigation mortality of essential oils were tested while computing the mortality percentage and LD50 values. The yield of stem essential oil (5.52%) was significantly higher than leaf essential oil (3.92%). Further, stem essential oil with a 100 µL dose showed the highest repellency (100.00 ± 0.00%) and mortality (96.67 ± 3.33%) while 50 and 75 µL doses caused similar mortality (83.30 ± 3.33%) after 5 days. The lowest LD50 (28.06 µL/L) was observed on day 5, indicating the higher toxicity of stem essential oil. Eugenol (73.73 and 82.56%), β-caryophyllene (24.84 and 16.67%), α.-humulene (0.82 and 0.33%), and 1S, CIS-calamenene (0.14 and 0.03%) were detected as the major components responsible for the insecticidal activity of stem and leaf essential oils. Hence, the valorization of clove by-products was successful as potential grain protectants, and clove stem essential oil could be the most effective alternative for rice weevil management.
Keywords: Essential oils; GC–MS; Grain protectants; Sitophilus oryzae; Syzygium aromaticum; Valorization.
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