Larvicidal and Ovicidal Effects of Leucas stachydiformis Leaf Extract and Fractions Against Anopheles arabiensis Patton

Several species within the genus Leucas have demonstrated significant anti-mosquito properties, including ovicidal, larvicidal, pupicidal, adulticidal, and/or repellent effects. The present study aimed to evaluate the larvicidal and ovicidal potential of crude extracts and solvent fractions derived from the leaves of Leucas stachydiformis (Hochst. ex Benth.) Briq (Family: Lamiaceae). The crude leaf extract of L. stachydiformis was prepared using the maceration method with 80% methanol, followed by solvent partitioning with solvents of increasing polarity: n-hexane, chloroform, and n-butanol. Larvicidal activity of the hydroalcoholic extract and its solvent fractions was assessed against fourth instar larvae of Anopheles arabiensis, using a concentration range from 6.25 ppm to 400 ppm. Ovicidal activity was tested on freshly laid eggs of An. arabiensis by incubating them with test solutions at similar concentrations for 72 hours. Results showed that the 80% methanol extract, along with the chloroform and n-hexane fractions, exhibited strong larvicidal activity (81 - 100%) at 400 ppm after 48 h. The n-butanol fraction displayed moderate activity (50 - 80%). Notably, the chloroform fraction demonstrated the highest larvicidal potency, with LC₅₀ values of 28.9 ppm and 26.8 ppm after 24 and 48 h, respectively. Regarding ovicidal activity, the 80% methanol extract was markedly more effective than the solvent fractions, with IH₅₀ and IH₉₀ (50% and 90% hatching inhibition concentrations) values of 39.3 ppm and 194.9 ppm, respectively. The findings of this study provide strong evidence that the leaves of L. stachydiformis possess genuine insecticidal properties. These results support the continued exploration of natural compounds from medicinal plants as viable alternatives to synthetic insecticides and repellents.