Larvicidal and Repellent Effects Against Vector Mosquitoes Anopheles stephensi and Aedes aegypti (Diptera: Culicidae) for Alstonia scholaris Linn R Br Flower and Prospective Characterisation of Bioactive Extract.

Malaria and dengue are among the most widespread vector-borne diseases globally. This study evaluated the larvicidal and repellent characteristics of Alstonia scholaris (Apocynaceae) flower extracts against the Anopheles stephensi and Aedes aegypti vectors. The crude methanolic extract was sequentially fractionated into ethyl acetate, n-butanol and aqueous fractions. Four different fractions were tested against Anopheles stephensi and Aedes aegypti at concentrations ranging from 78 to 1092 ppm and 625-6250 ppm, respectively. Larval mortality was observed after 24 h and analysed using probit analysis to estimate lethal concentrations (LC50). Repellency duration was assessed for adult Aedes aegypti using the various solvent extracts. The methanolic extract exhibited high efficacy against both Anopheles stephensi and Aedes aegypti larvae, with LC50 of 312 and 960 ppm, respectively. The ethyl acetate extract showed strong repellent activity, which is persistent up to 9 h (posttreatment) against adult Aedes aegypti. FTIR analysis of the methanolic extract identified functional groups such as aldehyde, amide, alkyl and carbonyl. GC-MS analysis revealed five major components: ursolic acid methyl ester (12.42%), lupeol (53.86%), lupeol acetate (10.95%), cycloeucalenol (2.62%) and hentriacontane (2.64%). These findings indicate that A. scholaris flower extracts in different solvents show potential larvicidal and mosquito repellent activity for the control of malaria and dengue.