Larvicidal effects of Selected Medicinal Plant Extracts against Anopheles arabiensis, Anopheles stephensi, and Aedes aegypti

ABSTRACT Background: The emergence of resistance, along with their harmful effects on human health, non-target organisms, and the environment, of synthetic insecticides necessitate the development new complementary insecticides that are effective, environmentally friendly, biodegradable, and target-specific. This study was undertaken to evaluate larvicidal activities of 80% methanol and n-hexane extracts of four plants that are traditionally used by communities against mosquitoes. Methods: The dried leaves of Ocimum lamiifolium, Amaranthus hybridus and Premna schimperi, and seeds of Lepidium sativum were extracted with 80% methanol and n-hexane solvents. Larvicidal activities of these extracts were evaluated under laboratory condition in the range of 62.5 to 2000 ppm against the late 3rd - early 4th instar larvae of An. arabiensis, An. stephensi and Ae. Aegypti mosquitoes. Larvae mortality was observed after 24 h of exposure. The mortality data were subjected to probit analysis to determine LC50 and LC90 values. Results: At 2000 ppm concentration, the n-hexane extract of the tested plants: Ocimum lamiifolium against An. arabiensis, An. stephensi and Ae.aegypti, and Amaranthus hybridus against An. stephensi and Ae. aegypti, Lepidium sativum and Premna schimperi against An. Arabiensis exhibited 100%, larvicidal activity with LC50 and LC90 values of 666.07, 1278.22, 713.25 & 1920.82, 2139.91 & 988.90; 874.78, 636.761 and 1426.03, 1122.94; 412 & 1222.62, and 736.150 & 1120.67 respectively. All the n-hexane extracts showed larvicidal activity whereas, all the 80% methanol crude extracts were not selected and subjected to dose-response bio-assay, yielding the mortality of larvae< 40% after 24 h during the preliminary screening at 2000 ppm. Conclusion: The n-hexane crude extracts of the tested plants have the potential to be used as larvicides against larvae of An. arabiensis, An. stephensi and Ae. Aegypti. Therefore, it is necessary to undertake studies that focused on bioassay-guided isolation, purification & structural elucidation of active compound (s) from the most active n-hexane fractions of tested plants to develop a product that complement the current existing vector control tools.