Insecticidal, repellent and oviposition-deterrent activity of selected essential oils against Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus.

Essential oils extracted from 10 medicinal plants were evaluated for larvicidal, adulticidal, ovicidal, oviposition-deterrent and repellent activities towards three mosquito species; Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. The essential oils of Juniperus macropoda and Pimpinella anisum were highly effective as both larvicidal and ovicidal. The essential oil of P. anisum showed toxicity against 4th instar larvae of A. stephensi and A. aegypti with equivalent LD95 values of 115.7 microg/ml, whereas it was 149.7 microg/ml against C. quinquefasciatus larvae. Essential oils of Zingiber officinale and Rosmarinus officinalis were found to be ovicidal and repellent, respectively towards the three mosquito species. The essential oil of Cinnamomum zeylanicum resulted into highest repellent (RD95) values of 49.6, 53.9 and 44.2 mg/mat against A. stephensi, A. aegypti and C. quinquefasciatus, respectively apart from oviposition-deterrent potential.

Piperitenone oxide as toxic, repellent, and reproduction retardant toward malarial vector Anopheles stephensi (Diptera: Anophelinae).

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.

Bioactivities of l-carvone, d-carvone, and dihydrocarvone toward three stored product beetles.

The rice weevil, Sitophilus oryzae L., adults were highly susceptible by contact to l-carvone, d-carvone, and dihydrocarvone when compared with the lesser grain borer, Rhyzopertha dominica F., adults and red flour beetle, Tribolium castaneum (Herbst.). Adults of R. dominica were more susceptible than the other species to fumigant vapors of l-carvone, d-carvone, and dihydrocarvone. The three larval stages (14-, 16-, and 18-d-old) of T. castaneum progressively became more susceptible with age toward contact toxicity of three test compounds but in fumigant toxicity, 16-d-old larvae of T. castaneum were more susceptible to the three compounds. Comparison of contact and fumigant toxicity of the test compounds indicates that l-carvone and d-carvone possess 24 times more fumigant toxicity toward adults of R. dominica than its contact toxicity. Overall order of toxicity was l-carvone > d-carvone > dihydrocarvone. Egg hatching and subsequent larval and adult survival of T. castaneum were significantly reduced when the eggs of T. castaneum were treated with l-carvone, d-carvone, and dihydrocarvone. l-Carvone completely suppressed egg hatching at the concentration of 7.72 mg/cm2. Data on feeding-deterrent indices indicate the high potency of l-carvone as feeding-deterrent in order of S. oryzae adults > T. castaneum adults > R. dominica adults > T. castaneum larvae.

Effect of d-limonene on three stored-product beetles.

d-Limonene was investigated for contact and fumigant toxicity, ovicidal effects, oviposition-deterrent, development inhibition, and feeding-deterrent activities against three stored-product beetles (Coleoptera): lesser grain borer, Rhyzopertha dominica (F.); rice weevil, Sitophilus oryzae (L.); and red flour beetle, Tribolium castaneum (Herbst). Contact and fumigant toxicity decreased as larvae aged. Contact toxicity was similar for adults of the three species tested, but R. dominica was most susceptible to fumigant activity. T. castaneum oviposition decreased as concentration of d-limonene increased and d-limonene reduced oviposition up to 92.3% at the concentration of 2.14 mg/cm2. Hatching of d-limonene-treated eggs of T. castaneum was reduced by 94.5% with no subsequent larval and adult survival at 2.14 mg/cm2 concentration. A flour disc bioassay indicated 87.7 to 96.8% feeding-deterrency by d-limonene toward all three insect species tested at the highest concentration of 60.0 mg/g food. These results suggest that d-limonene can be effectively used to suppress populations of stored-product beetles.

Insect growth inhibitor activity of arjunolic acid isolated from Cornus capitata.

Arjunolic acid (a pentacyclictrihydroxytriterpenic acid) isolated from the stem of Cornus capitata (Cornaceae) exhibited significant inhibitory activity towards 4th instar larvae of Spilarctia obliqua. A dose dependent relationship of both activities was observed. The effective concentration (EC(50)) to reduce feeding and growth of the larvae of S. obliqua was found to be 617.8 and 666.9 ppm, respectively.

Arjunetin from Terminalia arjuna as an insect feeding-deterrent and growth inhibitor.

Crude ethanolic extract of the stem bark of Terminalia arjuna (Combretaceae) and its three compounds namely arjunic acid, arjungenin and arjunetin were evaluated for antifeedant, growth inhibitory and oviposition-deterrent activities against a lepidopterous insect Spilarctia obliqua. The compound arjunetin showed highest growth inhibitory and feeding-deterrent properties with a growth inhibition (GI(50)) and feeding-inhibition (FD(50)) of 188.5 and 287.1 micro g/g diet respectively. Oviposition bioassays indicated no oviposition-deterrence in any of the compounds tested. The structure-activity relationship study indicated the importance of a glycosidation linkage in arjunetin.