Field evaluation of piper guineense and spilanthes mauritiana powder as mosquito larvicides in Kilifi district, Kenya

Abstract

Field tests were conducted in Kilifi District on field populations of anopheline and culicine mosquitoes using Piper guineense and Spilanthes mauritiana powder. A total of 36 aquatic habitats containing mosquito larvae were sampled and the larval populations determined by standard dipping technique before and after the application of the plant powder. Four doses (8.571, 5.714, 2.875 and 1.429 g/l) were used in the fild trials and larval mortality monitored after 24, 48 and 72 hours. Emerging adult mosquitoes were trapped by modified "Saliternick" mosquito cages and wing length measured by occular microscope. Phenotypic changes were noted. The effects of the plant material on larval habitat temperature, conductivity, dissolved oxygen and predatory non-target organisms were also monitored.

Spilanthes mauritiana and P. guineense powder at 8.571 g/l induced highest overall larval mortality of 97.4 + 0.58, 96.2 + 0.34 %, in anophelines and 100, 96.2 + 0.32% in culicines. However, at the lowest tested dose (1.429 g/l) the overall larval mortality reduced substantially to 22.4 + 0.72, 18.5 + 0.82%, and 19.9 + 0.51, 25.1 + 0.68%, for anophelines and culicines, respectively. The LD50 values were calculated at 2.74 and 2.26 g/l for S. mauritiana and P. guineense, respectively, for anophelines. Similarly, LD50 of 2.32 and 164, respectively, for culicines were determined. There was no significant difference between the mean wing length of emergent adults from the treated pools (F1, 40 = 0.771; p = 0.91) and the controls (F1, 60 = 1.183; p = 0.13). Both powders significantly affected the amount of dissolved oxygen in the treated pools as compared to the controls (F1,22 = 10.57, p = 0.0036). In general, there was no significant difference in the mean water conductivity between the treated and control pools (F1,45 = 0.965; p = 0.576). Both plants showed no significant difference in the mean water temperatures between the treated and control pools (F1,37 = 0.738; p = 0.782). The plant materials did not show any negative effect on non-target predatory organisms that also contribute in controlling mosquito larval population densities. The two plants exhibited high larval toxicity and may offer an alternative too for the control of mosquitoes