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The antimicrobial activity of the essential oils of Mentha spicata L. and Anethum sowa Roxb. (Indian dill) were studied. The major chemical constituents of the hydrodistilled essential oils and their major isolates from cultivated M. spicata and A. sowa were identified by IR, 1 H-and 13 C-NMR and GC: (S)-( )-limonene (27.3%) and (S)-( )-carvone (56.6%) (representing 83.9% of the spearmint oil) and (R)-(C)-limonene (21.4%), dihydrocarvone (5.0%), (R)-(C)-carvone (50.4%) and dillapiole (17.7%) (together 76.9% in Indian dill oil), respectively. In vitro bioactivity evaluation of the isolated oil components revealed that both the optical isomers of carvone were active against a wide spectrum of human pathogenic fungi and bacteria tested. (R)-(C)-limonene showed comparable bioactivity profile over the (S)-( )-isomer. The activity of these monoterpene enantiomers was found to be comparable to the bioactivity of the oils in which they occurred.

The essential oil of Artemisia annua L. was tested for its toxic repellent and development inhibitory activities against 2 economically important stored product insects: Tribolium castaneum (Herbst) and Callosobruchus maculatus (L.). Adult beetles of T. castaneum were repelled significantly by oil of A. annua at 1% concentration (vol:vol) and above in filter paper arena test. Dose-response relationship of A. annua oil revealed a significant negative correlation between larval survival; pupal survival and adult emergence of T. castaneum (i.e., increase in dose caused decrease in survival and adult emergence). Effective concentration (EC50) to reduce F1 progeny by 50% was calculated to be 2.6 and 4.1 microl/ml solvent against both the insect species, C. maculatus and T. castaneum, respectively. The relationship between bioactivity of oil from A. annua and responses of T. castaneum and C. maculatus is discussed. We found that oil from A. annua was largely responsible for both repellent (behavioral) and toxic (physiological) actions on 2 species of insect tested.

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Anopheles stephensi (Liston) is a well-known vector of malarial parasite in tropical countries. The developing trend of resistance in mosquitoes toward synthetic mosquitocidal agents makes their management extremely difficult. Effectiveness of essential oils with aroma therapeutic values seems to be an emerging tool to combat this vector. Piperitenone oxide isolated from essential oil of a new genotype, Mentha spicata L. variety viridis, has been evaluated for larvicidal, ovicidal, oviposition-deterrent, developmental toxicity, and repellent properties against various stages of A. stephensi. The results indicated the higher efficacy of piperitenone oxide than the crude essential oil of M. spicata variety viridis in all the bioassay experiments. The lethal response of piperitenone oxide and the oil toward fourth instar larvae showed LD50 values of 61.64 and 82.95 microg/ml, respectively. Female adults of A. stephensi exposed to the oil laid approximately 42 times less number of eggs at the dose of 60.0 microg/ml as compared with control, whereas exposure of piperitenone oxide at the same dose completely inhibited the oviposition. Furthermore, piperitenone oxide also completely inhibited egg hatching at the dose of 75.0 microg/ml in ovicidal assay. Developmental toxicity studies showed the significant developmental inhibition potential of the compound and oil. Additionally, piperitenone oxide was found to be highly toxic and repellent toward adults of A. stephensi as compared with oil.