Insecticidal and mosquito repellency property of essential oil from hyptis suaveolens leaves

Abstract

Essential oil was extracted from the leaves of Hyptis suaveolens by hydro-distillation by placing 1kg of the washed fresh leaves in round bottom flasks set up with 1liter distilled water. The Mosquitocidal activity, mosquito larvae (larvicidal) and mosquito repellency effect were carried-out using standard modified methods. Percentage yield of the essential oils was gotten as 0.05%. The essential oil showed very strong larvicidal properties against mosquito larvae. There was low mortality rate at lower dose, at a concentration of 6.25ppm the mortality rate was 4% over a period of 6 hours, same concentration at 12 and 24 hours gave mortality rate of 11%. The LC50 and LC 90 at this concentration were 25.21 and 302.67 respectively. At a concentration of 12.50ppm a mortality rate of 4% was also recorded at 6 hours, at 12 and 24 hours 13% mortality were recorded, and same LC50 and LC90 with 6.25ppm. At concentration of 25.00ppm, 20%, mortality rate was recorded for 6 hours and 30% for both 12 and 24 hours, the LC50 and LC90 are 9.575 and 352.458 respectively. There were no significant differences at 50, 100 and 1000ppm, the mortality rate was 100% for the period of 6, 12 and 24 hours with LC50 and LC90 of 0.549 and 0.853 respectively. There was no record of death in the control even after 24 hours. It was observed that the amount of air that enters and leaves the cage affect the rate at which mosquitoes were repelled. In a group of mosquitoes kept in a cage with all sides open (ASO) 65% of the mosquitoes were repelled within 30 minutes while for one side open (OSO) and all sides closed (ASC), 73% and 85% of the mosquitoes were repelled within the same time frame. In a second experiment, 100% of mosquitoes were repelled from the surface of rats with shaven skin where essential oil was applied. The essential oil also demonstrated dose dependent mosquitocidal activity with LC50 and LC90 values of 6 and 21ppm respectively.