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This study investigates the chemical constituents of essential oils and their anti-microbial activity of Alpinia scabra and Alpinia murdochii, two wild Zingiberaceae species. The essential oils were obtained by hydrodistillation and the chemical components of the oils were determined by GC-FID (retention indices, RI) and GC/MS analysis. The major components of Alpinia scabra rhizome oil are γ-selinene (33.45%), α-selinene (3.64%) and α-terpineol (3.55 %) while the major components of the leaves are β-pinene (63.37%), α-pinene (6.58 %) and borneol (3.20 %). The major compounds of Alpinia murdochii rhizome oil are γ-selinene (15.51 %), (E,E)-farnesyl acetate (6.56 %), terpinen 4-ol (5.58 %) and α-terpineol (5.04 %). The monoterpenes; β-pinene (23.83 %), sabinene (23.76 %) and terpinene-4-ol (10.49 %) were the major components in the leaf oil of A. murdochii. The lowest MIC values were recorded for the rhizome essential oils of both Alpinia species against all Staphylococcus aureus strains (coded as MSSA, MRSA, Sa7, VISA24, VRSA156) with MIC values ranging from 0.04 mg/mL to 2.50 mg/mL. The rhizome oils of both species also showed a broad spectrum of anti-microbial activity as compared to the leaf oils.

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The insecticidal activities of extracts from 22 Malaysian medicinal plant extracts from 8 botanical families were tested against rice weevil: Sitophilus oryzae (L.) and lesser grain borer: Rhyzopertha dominica (F.). The extracts were obtained using hexane, methanol, and dichloromethane to extract potential biopesticides from dried leaves. The toxicity levels were examined periodically based on antifeedant activity and contact toxicity assays using treated grain assay. Hexane extracts of Alpinia conchigera, Alpinia scabra, Curcuma mangga, Curcuma purpurascens, Goniothalamus tapisoides, Piper sarmentosum, and methanol extracts of Curcuma aeruginosa, C. mangga, and Mitragyna speciosa were the most potent extracts against S. oryzae and R. dominica with lethal concentration (LC50) values of ≤ 0.42 mg/mL and ≤ 0.49 mg/mL, respectively. The contact toxicity test results showed that methanol extracts of C. aeruginosa and C. mangga, dichloromethane extracts of Cryptocarya nigra, and hexane extracts of C. mangga, and C. purpurascens resulted in 100% mortality of both pests within 28 days exposure of 5 mg/cm2 concentration.