The current study accentuates the use of botanicals as an alternative to the chemical compounds in vector control by estimating the mosquito larvicidal potential of Ocimum gratissimum L. leaf essential oil against the fourth instar larvae of Aedes albopictus Skuse (Diptera: Culicidae). The chemical composition of essential oil from leaves was evaluated using gas chromatography-mass spectrometry (GC/MS) analysis. GC/MS revealed that the essential oil of O. gratissimum contained 51 compounds. The major chemical constituents identified were 3-allyl-6-methoxyphenol (19.30%), 4-(5-ethenyl-1-azabicyclo (2, 2, 2) octan-2) (16.82%), 1-(2, 5-dimethoxyphenyl)-propanol (12.23%) and 1-(1-hydroxybutyl)-2, 5-dimethoxybenzene (5.53%). The essential oil showed pertinent larvicidal effect, and the LC50 value in 24 h was 26.10 ppm (LC90 = 82.83 ppm). Aromatic plants and their essential oils are very important sources of many compounds that are used for different applications, and they are more promising pesticides or insecticides for control of mosquito populations than synthetic ones. The results of the present investigation justify the larvicidal potential of leaf essential oil of O. gratissimum as a safer and more effective larvicide against A. albopictus.

The current investigation emphasizes the crucial role of natural products of plant origin in vector control by evaluating the mosquito larvicidal efficacies of the essential oil from Eryngium foetidum L. (Apiaceae) against the fourth instar larvae of Aedes albopictus Skuse (Diptera: Culicidae). Gas chromatographymass spectrometry analysis was used to reveal the chemical composition of essential oil obtained from aerial parts. The essential oil showed good larvicidal effect and the LC 50 value in 24 h was 33.3 ppm (LC 90 =57.7 ppm). The major chemical constituents found in the essential oil were 2-dodecen-1-al (46.68 %) and caprinic alcohol (14.8 %). Results of this study showed that the leaf essential oil of E. foetidum may be used as a potent source of natural larvicidal principles against A. albopictus.

Hyptis suaveolens and Leucas indica, two common weeds were selected for the present study, to reveal their probable cytotoxic potential. The meristematic root tips of Allium cepa were used for testing the cytotoxic property of the aqueous leaf extracts containing both polar and non-polar compounds, and that containing polar compounds alone, at different concentrations (0.125, 0.25, 0.5, 1 and 2 %) and at different time durations, using distilled water as negative control. Mitotic squash preparations were made using a standard protocol. The mitotic index of the treated root tip cells was found to be decreasing and the abnormality percentage was found to be increasing with increase in extract concentration when compared with the control. Maximum cytotoxicity was observed in the extract containing both polar and non-polar compounds. Both the tested plants were found to be cytotoxic. The abnormalities noticed were of both clastogenic (nuclear lesions, nuclear fragmentation, etc.) and non-clastogenic (aberrant cell wall formation at cytokinesis, ball metaphase, etc.) types. Both plant extracts were found to significantly (P \ 0.05) inhibit root growth of Allium cepa with an EC 50 value of 1.92 % (R 2 = 0.594) for Hyptis and 1.58 % (R 2 = 0.757) for Leucas. The results were also analysed statistically by using analysis of variance followed by appropriate post hoc tests. These two weeds are aromatic plants comprising of essential oils that are volatile, natural complex compounds characterized by a strong odour and formed as secondary metabolites. In nature, essential oils play an important role in the protection of the plants as insecticides by reducing their appetite for such plants. When specifically targeted the concept of effectively exploiting these weeds for the formulation of herbal insecticides/ pesticides may be possible in the near future.

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