Evaluation of leaf extracts of Vitex negundo L. (Family: Verbenaceae) against larvae of Culex tritaeniorhynchus and repellent activity on adult vector mosquitoes

Petroleum ether (60-80°C) extracts of the leaves of Vitex negundo (Verbenaceae) were evaluated for larvicidal activity against larval stages of Culex tritaeniorhynchus in the laboratory. Larvae of C. tritaeniorhynchus were found more susceptible, with LC₅₀ and LC₉₀ values of 2.4883 and 5.1883 mg/l, respectively. Human volunteers wearing special terricot (68:32) fabrics, in the form of armbands, anklets, headbands, collar, and shoulder and pocket strips impregnated with V. negundo leaf extract were used, to test their repellent efficacy at two concentrations viz., 1.5 and 2.0 mg/cm² under the field conditions. At 1.5-mg/cm² concentration, more efficacies were found and 6-h complete protection against mosquito bites was provided. Complete protections for 8 h were found at 2.0 mg/cm² against mosquitoes bites. These results clearly reveal that the V. negundo leaf extract served as a potential larvicidal agent against Japanese encephalitis vector C. tritaeniorhynchus and additionally acted as a promising repellent against various adult vector mosquitoes.