Studies on the effect of Tamarindus indica seeds extract on Biomphalaria pfeifferi and its natural enemies

Abstract

In view of the widespread use of chemical pesticides in the control of schistosomiasis and its negative impact on the environment and living organisms; a series of laboratory and field experiments were designed to test molluscicidal activity of the aqueous extract of T. indica seeds (Ara'daeb) as a natural source to combat the intermediate hosts, and thus to control the disease. The study comprises two parts; in the first part the immediate and long term effects of the extracts on Biom. pfeifferi (egg masses, neonates and adults); as well as the negative impact on water bugs, as one of the natural enemies of the snail, was assessed. In this part, the molluscicidal activity of T. indica seeds were determined using probit regression analysis to calculate the lethal dose that gives 50% and 95% mortalities in 24 hours. The findings indicated that the sensitivity of snails to the Ara'daeb seeds extract is directly proportional to the age of snail. Neonates were more sensitive than adults while egg masses did not show any observable reaction. The immediate and long term effects resulted in a significant reduction in the number and the fecundity of exposed snails (P < 0.05). Water bugs did not show any response to the extract when exposed to Biom. pfeifferi LD100, for 24-hours. In the second part, chemical screening was carried out to determine the constituent of the plant seeds under investigation. Tamarindus indica seeds contain large amounts of nutrients, i.e. carbohydrates, proteins, oils, important minerals as well as small amounts of tannins. The most important active ingredient detected is saponin, which may account for the molluscicidal activity observed. Ara'daeb has all the desirable characteristics of an ideal plant of molluscicidal activity reconciled with environment and humans. Application of the extract in the field conditions showed observable reduction in the snail population in the canals, although quantitative measures were not applied to field trials; and these observations may open a new field of research for future studies.