Larvicidal and synergistic toxicity of Ficus sycomorus and Calotropis procera leaf extracts against malarial vector Anopheles gambiae complex from Kano-Nigeria: A green Bio-control approach

Abstract

Plant phytochemicals appeared to be a promising tool to address resistance and environmental problems posed by synthetic insecticides. This study explored the larvicidal effects, and synergistic toxicity of Ficus sycomorus and Calotropis procera leaves on African malaria vector, Anopheles species sourced from agricultural fields in Kano-Nigeria. The qualitative and quantitative phytochemicals were determined using standard methods. Late third Instar larvae (L3) of Anopheles mosquitoes were subjected to bioassay at various concentrations (0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 mg/mL) of ethanol extracts using the WHO standard protocol with some modifications. The synergistic potential was predicted using mathematical model. The extract of F. sycomorus revealed the highest concentration of flavonoids, alkaloids, saponins and phenols, while C. procera extract had high concentration of glycosides and tannins. However, only alkaloids concentrations (15.41 mg/mL and 7.7 mg/mL) was statistically significant between the two plants (p <0.05). The bioassays show high percentage mortalities in both plants with C. procera extract being more toxic (LC50=0.51 mg/mL; ꭓ2=0.83; 95% confidence limits, CI: 0.30-0.84; p>0.05) on Anopheles larvae than F. sycomorus extract (LC50=1.01 mg/mL; ꭓ2=0.920; 95% confidence limit, CI: 0.50-2.05; p>0.05). The binary combination (concentration LC25:LC25) of the two plants produced promising results of higher mortality than individual highest extract concentrations (LC50=0.38 mg/mL; ꭓ2=0.72; 95% confidence limits, CI: 0.23-0.61; p>0.05) due to possibly synergistic effect of the two plants (X2=13.33). The percentage mortalities in all the crude extracts tested were concentration dependent. It is evident from this study that crude extracts of F. sycomorus and C. procera have promising individual and synergistic larvicidal bioactivities and hence, can be employed in integrated approach for vectors resistance management.