Essential oil was extracted from the fresh fruit of Piper retrofractum Vahl by water distillation method. The yield of extraction was estimated at 0.125%. Adulticidal activity was tested against 2-5 days-old non-blood-fed female Aedes aegypti and Culex quinquefasciatus by topical application. Six concentrations of essential oil dissolved in acetone were prepared in 5%, 7%, 9%, 11%, 13% and 15%. The solution (0.5 μL) was on the pronotum of mosquito, and mortality was observed after 24 hours of exposure. The LD50 and LD99 of essential oil in acetone against Ae. aegypti (8.86%, 23.21%) and Cx. quinquefasciatus (6.95% and 17.35%,) was measured. This is the first report of adulticidal activities of essential oil from P. retrofractum against mosquito vectors.

Plants contain numerous bioactive compounds that can be used to develop environmentally-safe insect control agents. Castor oil is a vegetable oil derived from the seeds of castor bean and is widely used as an industrial lubricant and medicinal purgative. In search of an alternative natural insecticide, the objective of this study was to evaluate the larvicidal and adulticidal activities of castor oil against the important dengue vector, Ae. aegypti. Larvicidal and adulticidal bioassays were conducted following the World Health Organization methods. Larvicidal activity was observed at castor oil concentrations of 10, 25, 50, 75, and 100 ppm; larval mortality was checked after 48 h of exposure and the lethal concentration (LC) at LC50 and LC90 were 51.38 and 116.26 ppm, respectively. Adulticidal activity was determined by topical application at the concentrations of 1, 5, 10, 15, and 20 µg/ mg on female mosquitoes and the mortality was checked after 24 h of exposure. The effective adulticidal activity was apparent with the LD50 and LD90 values of 6.03 and 25.07 µg/mg against female mosquitoes. The results indicated that castor oil has potential in the practical control of both immature and adult stages of the mosquito vector.