Larvicidal efficacy of selected medicinal plant extracts against larvae of medically important malaria and arbovirus vectors

Abstract Background & Objectives : Mosquitoes transmit serious human diseases, causing millions of deaths every year. The development of resistance to chemical insecticides has resulted in rebounding vectorial capacity, meaning that plants may serve as viable alternative sources of mosquito control agents. The present study critically tested the larvicidal activities of four candidate medicinal plant species: Ocimum forskolei , Gymnema sylvestre , Lippia javanica, and Datura stramonium . These species are traditionally used for mosquito control and are reported to be effective against larvae of mosquito vectors of malaria and arboviral diseases in Ethiopia. The extracts were evaluated against late third to early fourth instar larvae of Anopheles arabiensis, Anopheles stephensi , and Aedes aegypti. Methods : Dried parts of the four selected medicinal plants were extracted using polar (80% methanol) and non-polar (n-hexane) solvents. The extracts were evaluated for larvicidal activities against late 3 rd to early 4 th instar larvae of An. arabiensis , An. stephensi , and Ae. aegypti mosquitoes. Larval mortalities were recorded after 24 hours of exposure following standard WHO bioassay guidelines. Results : All n-hexane crude extracts showed varying degrees of larvicidal activity against An. arabiensis. The highest activities were observed in the n-hexane extracts of G . sylvestre and L . javanica , achieving 100% and 99.7% larval mortality at 2000 ppm, respectively. At 500 ppm, n-hexane crude extracts of G. sylvestre and L. javanica caused mortality rates ranging from 14.7% to 56.7%, whereas O. forskolei and D. stramonium at 1000 ppm caused mortalities ranging from 64.3% to 64.7%. N-hexane crude extracts of G. sylvestre and L. javanica at 2000 ppm concentration had similar effects to the standard larvicide temephos (100% mortality). Additionally, n-hexane crude extracts of L. javanica at 2000 ppm caused 100% Ae. aegypti and G. sylvestre 100% An. arabiensis larval mortality receptively. Probit analysis revealed that G. sylvestre and L. javanica were extremely potent against An. arabiensis larvae, with LC 50 values of 921.00 ppm (LC 90 = 1340.30 ppm) and 659.42 ppm (LC 90 = 1034.47 ppm), respectively. L. javanica also exhibited strong potency against Ae. aegypti larvae with an LC 50 of 1005.50 ppm and LC 90 of 1503.90 ppm. Conclusion : N-hexane crude extracts of the evaluated medicinal plants possess strong potential for use as eco-friendly botanical larvicides against An. arabiensis and Ae. aegypti . Further studies to isolate, identify, and formulate the specific active compounds are highly recommended.