The Larvicidal and Repellent Effect of Bush Mint Plant ( Hyptis suaveolens ) and Hairy Sicklepod ( Senna hirsuta ) Extracts against the Larvae and Adult of Culex quinquefasciatus

The efficacy of hexane leaf extracts of Hyptissuaveolens  and Senna hirsuta  as a larvicide and repellent against the 4 th  instar larvae and adult of Culexquinquefasciatus  was investigated. Extraction was done using Soxhlet apparatus. Twenty fourth instar larvae of Culexquinquefasciatus  were exposed to various concentrations (5%, 10%, 15%, 20%, 30% and control) and observed over 3 hours for mortality. Repellency against the adult mosquito was investigated on five human volunteers who did not use any lotion, soap or perfume on the arm. The experiment was carried out during the day in a dark shade. Percentage repellence was recorded every 10minutes for a period of 1 hour. Lethal concentration 50% (LC 50 ) which is the concentration required to kill half the members of the tested population after 3 hours of exposure was used to assess the larval mortality. Result indicated the combined extract with LC 50 6% gave a higher mortality than the individual extract of Hyptis suaveolens  (LC 50  6.4%) and Senna hirsuta  (LC 50  7.5%). Similarly, repellence was highest in the combined extract with 75% repellency than in the extracts of Hyptis suaveolens  (70%) and Senna hirsuta  (50%). The result observed in the study was analyzed using Analysis of Variance. There was a significant difference from the use of individual extracts (P< 0.05). From the result of the study, it was deduced that the efficacy of the treatments increased with an increasing exposure time and concentration. The findings of the study revealed the efficacy of hexane leaf extracts of Hyptis suaveolens  and Senna hirsuta  as good larvicide and repellent against Culex quinquefasciatus  especially in the synergistic state.