Molluscicidal Activity of Aqueous Extracts of Selected Medicinal Plants on Fresh Water Snails and Fish

Abstract

Aim: To investigate the molluscicidal activity of aqueous extracts of Phyllanthus niruri  and Euphorbia tirucalli  on fresh water snails Lymnaea (Radix)  acuminata and Indoplanorbis exustus (as target organisms) and on  Channa punctatus fish ( as non target organism),sharing the same habitat. Methodology: The aqueous extracts of the stem bark and leaves of  Phyllanthus niruri ( a tropical small herb, commonly known as a Bhumi Amla), belonging to the family Phyllanthaceae and the aqueous extracts of stem bark and latex of Euphorbia tirucalli (a semi-arid tropical plant, commonly called milk bush) of the family Euphorbiaceae, were investigated as plant origin molluscicides, against freshwater snails, responsible for causing fascioliasis, Lymnaea (Radix) acuminate and Indoplanorbis exustus, as well as on Channa punctatus ,using Singh and Agarwal method and POLO computer program. Results: A significant time and dose-dependent effect of aqueous extracts of both the plants against the freshwater snails were observed. Thus increase in exposure time, the LC50 of Phyllanthus niruri stem and leaf extracts were decreased from 267.89 mg DW/L (24h) > to 180.64mg DW/L (96h) against Lymnaea acuminata and 261.49 mg DW/L (24h)> to 136.40 mg DW/L (96h) against Indoplanorbis exustus. Likewise, the LC50 of aqueous extract of latex of Euphorbia tirucalli were decreased from 1.80 mg DW/L (24h) >to 0.65 mg DW/L (96h) against Lymnaea acuminata and 0.90 mg DW/L (24h)> to 0.28 mg DW/L (96h) against Indoplanorbis exustus, with the increase in exposure time. Its aqueous stem bark extract showed a similar pattern.  These aqueous plant extracts at higher doses were also observed to be lethal to freshwater fish Channa punctatus, which share a common habitat with the freshwater snails, but the doses LC90, (24h) of snails didn’t cause any mortality to these fishes, thus indicating that these plant extracts can be safely used as molluscicides.