Control of Aedes larvae using crude extracts of plant mixtures of Capsicum frutescens, Allium sativum and Psophocarpus tetragonolobus

Abstract

Dengue is a vector-borne viral disease transmitted by mosquito species Aedes aegypti and Ae. albopictus. Control of the vector mosquito population is challenging due to human-influenced breeding sites. Larval control is one of the most effective methods compared to other mosquito control methods. In this study, larvicidal activities of hot water, cold water and water:acetone extracts of plant mixtures of Capsicum frutescens (king chilli/ “Naimiris”), Allium sativum (garlic) and Psophocarpus tetragonolobus (winged beans) were tested against third instar larvae of mosquitoes of genus Aedes. Also, red and green C. frutescens were separately added to the plant mixtures to investigate the significant difference in larval mortalities. Stock solutions were prepared using each solvent extract; final concentrations of test solutions were set as 1,000, 2,000, 5,000, and 10,000 mg L⁻¹, while distilled water was used as the control. Larval mortalities were observed after 24 and 48 h exposure periods. Cold water and water:acetone extracts showed 90 and 100% mortality after 24 h, respectively, and 100% larvae mortality after a 48 h exposure period at 10,000 mg L⁻¹. Larval mortalities increased with increasing concentrations and exposure time. The hot water extracts did not show any significant larval mortalities. LD₅₀ values of the mixture, which includes green C. frutescens was relatively low (LD₅₀=2,460.29 mg L⁻¹) compared to that of red C. frutescens (LD₅₀ = 2,577.86 mg L⁻¹). Water:acetone extracts had the highest efficacy against larvae (100% larval mortality). Larvicidal effect of water:acetone extracts of P. tetragonolobus (leaves and pods) alone and a mixture of green C. frutescens and A. sativum showed that the mixture of green C. frutescens and A. sativum has the highest efficacy (100% larval mortality within 9 h). Psophocarpus tetragonolobus pods and leaves showed 30 and 25% mortality after 24 h exposure, respectively, and 70 and 35% mortality after 48 h exposure, respectively. These results revealed that the water:acetone extract of green C. frutescens and A. sativum mixture showed relatively high larvicidal activities against Aedes larvae with the lowest LD₅₀ values (2,051.01 and 1,097.69 mg L⁻¹for 24 and 48 h exposure periods, respectively). The results of the study suggest that the plant mixture of green C. frutescens and A. sativum could be used as an environmentally friendly alternative to chemical insecticides.