Combined effect of methanolic extracts of Senna occidentalis (Fabaceae) and Khaya senegalensis (Meliaceae) collected in the far-north region (Cameroon) on adults of Anopheles gambiae senso stricto GILES 1902

Abstract

Malaria remains a significant public health burden in sub-Saharan Africa, primarily due to the presence of its primary vector, Anopheles gambiae . The increasing resistance to synthetic insecticides has necessitated the exploration of environmentally friendly alternatives, such as plant-derived bioactive compounds. This study investigated the adulticidal activity of methanolic extracts from the leaves of Senna occidentalis (Fabaceae) and Khaya senegalensis (Meliaceae) against A. gambiae , a primary malaria vector, in a laboratory experiment conducted from January to February 2020 at the Entomology Laboratory, University of Ngaoundéré, Adamaoua Region, Cameroon. The extraction yields were 17.8 % for S. occidentalis and 14.9 % for K. senegalensis . Phytochemical analysis revealed that S. occidentalis leaves contained 21.55 mg gallic acid equivalent (GAE)/100 g of polyphenols and 24.88 mg quercetin equivalent (QE)/100 g of flavonoids, whereas K. senegalensis leaves contained 18.34 mg GAE/100 g of polyphenols, 34.34 mg QE/100 g of flavonoids, and 27.56 mg catechin equivalent (CE)/100 g of tannins. Bioassays conducted according to World Health Organization (WHO) protocols demonstrated synergistic insecticidal effects between the extracts against A. gambiae . The lethal concentration (LC 50 ) values were 0.87 g/L for S. occidentalis and 1.07 g/L for K. senegalensis , with half-lethal time (HL 50 ) values of 2 h 48 min and 2 h 14 min, respectively. The most effective combination ( S. occidentalis [75 %] + K. senegalensis [25 %]) achieved an LC 50 of 0.98 g/L and HL 50 of 1 h 45 min. These results highlight the potential of S. occidentalis and K. senegalensis extracts as sustainable biocides for controlling A. gambiae ss populations. Their synergistic efficacy and high phytochemical content support further development into eco-friendly vector control tools, aligning with global efforts to combat insecticide resistance. • Combinations of Senna occidentalis and Khaya senegalensis leaf extracts exhibit adulticidal effects against Anopheles gambiae ss. • P1 75 % + P2 25 % combination is the most effective, with LC 50 and HL 50 values of 0.98 g/L and 1 h 45 min, respectively. • Concentration- and time-dependent mortality rate inidcate potential for natural biocide development. • Phytochemical analysis confirms presence of insecticidal secondary metabolites. • Natural extracts offer promising alternative for malaria vector control.