This study evaluated, using replicated laboratory bioassays, the toxicities of the ethanolic extracts ofDalbergia sissoo (family Leguminosae) fruits, leaves, roots and stem bark against adult Biomphalaria alexandrina, the snail intermediate host of Schistosoma mansoni in Egypt and their egg masses. Adult snails (6 to 8 mm in diameter) and viable 24 h-old embryonated egg masses were separately exposed to seven different concentrations (6.25 to 400 ppm) of extracts for 24 h. The LC50 and LC90 values of test extracts for adult snails and egg masses were calculated by probit analysis. The activities of the tested extracts were concentration-dependent. However, only the ethanolic extract of the fruits demonstrated significant activity on both adult snails and egg masses (24 h-LC90 value 34.4 and 38.6 ppm, respectively). Mortalities of eggs were manifested at the gastrula/exogastrula and or the pre-hatch snail stage of development. Ethanolic extract of the fruits was the most active with 100% mortality at 50 mg/l, followed by those of the leaves (at 100 mg/l), roots (at 200 mg/l) and stem bark (at 400 mg/l). Their respective 24 h-LC50 and LC90 values for B. alexandrina egg masses were 10.8 and 38.6 ppm, 18.5 and 68.3 ppm, 20.4 and 88.4 ppm, 36.8 and 144.6 ppm. The percentage of dead embryos at all stages increased with increasing concentration of extract. Lethality of the ethanolic extract of D. sissoofruits to embryonated egg masses of B. alexandrina is an added advantage to its potential development for use as a plant molluscicide, as the overall efficacy of a molluscicide is greatly enhanced if it also shows significant toxicity towards snail eggs.
Key words: Dalbergia sissoo, Biomphalaria alexandrina, Schistosoma mansoni, egg masses.
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