ABSTRACT
In tropical and subtropical regions, mosquitoes serve as vectors of life threatening diseases such as malaria, lymphatic filariasis, dengue, yellow fever and encephalitis. Effects of these diseases have prompted the search for eco-friendly control measures for mosquito larvae. This study was carried out to determine the larvicidal activities of the Calopogonium mucunoides leaf and Chrysophyllum albidum seed extract against 2nd and 3rd larval instars of Aedes aegypti.
The leaves and seeds of the plant samples were shade-dried, ground to powder and macerated using ethanol. Stock solutions were prepared from the crude and partitioned extract. Larvicidal bioassay was done on triplicate of ten laboratory reared larvae of Aedes aegypti. The dead and moribund larvae were recorded at different concentrations of 250 ppm, 500 ppm, 750 ppm and 1000 ppm with a simultaneous control at 24, 48 and 72 hours of exposure. The percentage mortality was calculated, LC50 and LC90 values were obtained by probit analysis using SPSS version 21.0 at 95% confidence limit (CL).
Phytochemical screening revealed the presence of alkaloids, terpenoids, tannins and saponins in both Calopogonium mucunoides leaves and Chrysophyllum albidum seeds extracts. The larvicidal bioassay of C. mucunoides extract varied significantly with concentration and exposure time (p<0.05). The lowest mortality rates (1.33 ± 0.88, 1.67 ± 0.88) (mean ± SE ) were recorded at 72 hours and at 250 ppm and 1000 ppm respectively for 2nd and 3rd larval instars. C. albidum seed extractshowed a significant difference (p<0.05) with concentration and time of exposure. The lowest mortality rates (0.67 ± 0.67, 0.00 ± 0.00) were recorded at 24 hours while the highest mortality rates (8.67 ± 0.88, 7.67 ± 0.33) were recorded at 72 hours and at 250 ppm and 1000 ppm respectively for 2nd and 3rd larval instars. Lethal concentration (LC50 and LC90) for C. mucunoides were 2.935 ppm and 7.608 ppm, 2.096 ppm and 6.302 ppm, and 1.626 ppm and 5.866 ppm for 24, 48, and 72 hours respectively for 2nd instar larvae. For, 3rd instar larvae, LC50 and LC90 were 2.923 ppm and 11.067 ppm, 2.096 ppm and 9.686 ppm, and 2.033 ppm and 6.946 ppm respectively. C. albidum exhibited an LC50 and LC90 values of 3.231 ppm and 7.393 ppm, 2.755 ppm and 6.123 ppm, and 2.278 ppm and 4.584 ppm at 24, 48 and 72 hours respectively for 2nd instar larvae. LC50 and LC90 values for 3rd instar larvae were 3.731 ppm and 7.021 ppm at 24 hours, 2.843 ppm and 4.526 ppm at 48hours and 2.774 ppm and 4.202 ppm at 72 hours respectively. There was no significant difference in the effect of the ethanolic extract on 2nd and 3rd instar larvae. The chloroform fraction of C. mucunoides partitioning, gave a 100% mortality of 3rd instar larvae unlike the C. albidum. It was observed that C. mucunoides leaf extract was more potent than C albidum seed extract though both showed good larvicidal activity, they should be further explored for the control of mosquito larvae.
