EVALUATION OF COMBINED MOLLUSCICIDAL PLANT EXTRACTS FOR CONTROL OF THE BIOMPHALARIA SNAIL (Biomphalaria pfeifferi)

Abstract

The need to search for better and ecofriendly alternative molluscicide, as a result of high cost of synthetic molluscicide, their environmental toxicity to non target organism and their chemical residue in the environments, propelled this study to elucidate the mono and combined molluscicidal efficacy of Vernonia amydalina, Calotropis procera and Amaranthus hybridus ethanolic extracts. The phytochemical constituents of the single and combined plant extract was determined using standard procedure. The molluscicidal bioassay against Biomphalaria pfeifferi using graded concentrations of the extract ranging from 50 to 400 mg/l was performed following standard protocol. Mortality was recorded after 24, 48, and 72 hrs exposure period. The effect of the plants on the snail architecture was determined histopathologically. The lethal doses was estimated using probit linear regression analysis. The result indicated that the three plants possess bioactive secondary metabolite including flavonoids, alkaloids, tannins and saponins. V. amygdalina has more phytochemical constituent than other plants. Molluscicidal activities increases with increase in extract concentrations and exposure period. Amongst the plants, Vernonia amygdalina showed the highest molluscicidal activities with LC50 of 183.33 mg/L, after 24 hrs exposure period. However the combined extract of V. amydalina and C. procera was most potent with an LC50 (53.65 mg/L) value better than the application of only V. amygdalina with LC50 of 183.33 mg/L, after 24hrs which show synergestic effect. The histopathological results showed that the extract caused mild and severe cytoplasmic fragmentation and vacuolization in the snail digestive and excretory cells, which is more pronounced in the combined extracts. Findings of this study suggest the combinatorial application of V. amydalina and C. procera extracts as an alternative agents in the control of snail intermediate host of schistosomiasis.