Essential oil fractions from dried seed powder of Piper guineense were analyzed by gas chromatography-mass spectrometry (GC-MS) and evaluated for their insecticidal effects on Sitophilus oryzae L. The GC-MS analysis showed quantitative and qualitative differences between the oil fractions. Chromatographic results revealed chemical constituents like eugenol, piperanol, pinene, carene, copaene with insecticidal properties. New chemotypes were seen in the different fractions. Instead of β-caryophyllene reported in literature, α-caryophyllene was found in all the different fractions. Caryophyllene oxide, an oxygen-containing sesquiterpene was present in all fractions except n-hexane. In addition to α-phellandrene present in all, β-phellandrene, a monoterpene hydrocarbon was found in the n-Hexane fraction. Contact toxicity on wheat grains showed that all fractions caused significant (P < 0.001) mortality of the weevils. The oil fractions also showed variable contact toxicity on impregnated filter paper. All doses of the n-hexane fraction were very toxic to the test insect than the control, causing 100% mortality after five days of exposure. All the fractions produced a strong repellent activity against the test insect. These results suggest that P. guineense has potentials for development as an organic insecticide against S. oryzae and other pests of stored grains.
Key words: Piper guineense Schum. et Thonn., essential oil fractions, chemotypes, toxicity, repellency, Sitophilus oryzae (L.).
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