Malaria threatens the health of more than 2 billion people in tropical areas of the world. In India and other western Asian countries, the most common mosquito vector of human malaria is Anopheles stephensi. New and improved methods are needed for personal protection from bites by An. stephensi and the malaria parasite it transmits to humans. In this study, Indian, ARS, and Chinese scientists determined the mosquitocidal and repellent effects of essential oil of vetiver (a type of grass) against An. stephensi. Larvicidal activity of the essential oil was modest but when vetiver oil was applied to skin at between 0.5 and 1.5 mg/cm2, it completely prevented mosquito biting for up to 5 h. The result suggest that vetiver crude oil extract warrants further testing and development for use as a topically-applied repellent to protect humans from the bites of malaria mosquito.

Technical Abstract: Essential oil extracted by steam distillation of Vetiveria zizanioides (L.) Nash (Poaceae) was evaluated for larvicidal and adult repellent activity against the malaria vector Anopheles stephensi (Liston). Median lethal concentrations (LC50) at 24 h post treatment for instars 1-4 were, respectively, 281, 356, 389, and 475 mg/L. The repellency of topically applied vetiveria oil tested at rates of 0.5 mg/cm2, 1 mg/cm2, and 1.5 mg/cm2 was 100% for 2, 4, and 5 h, respectively. After 12 h, the level of protection from mosquito bites provided by V. zinzanoides essential oil was 52% at the 0.5 mg/cm2 rate, 62% at the 1 mg/cm2 rate, and 76% at the 1.5 mg/cm2 rate. The results indicate that V. zinzanoides essential oil is larvicidal and repellent to An. stephensi adults and that further study and development of this botanical insecticide as a mosquito control and/or personal protection agent is warranted. From the result it can be concluded the crude extract of V. zinzanoides essential oil was an excellent potential for controlling larvicidal and adult repellent activity against the malaria vector mosquitoes.