The molluscicidal efficacy of methanol extracts of Pterocarpus angolensis, Sclerocarya birrea, Pappea capensis and Commiphora africana against Lymnaea natalensis and Helisoma duryi

Abstract

Tropical plants have been shown to contain compounds that have some molluscicidal activity against snail intermediate hosts of parasitic trematodes. Dried methanol extracts of Pterocarpus angolensis, Sclerocarya birrea, Pappea capensis and Commiphora africana were screened for molluscicidal activity against Lymnaea natalensis and Helisoma duryi. The freshwater snail L. natalensis is the intermediate host of fascioliasis in Zimbabwe, whereas H. duryi is a related non-vector snail. Of the four plant extracts studied, P. angolensis was the most effective with a 48 h LC₅₀ of 34 mg l⁻¹, whilst C. africana was the least effective with a 48 h LC₅₀ of 53 mg l⁻¹ for L. natalensis. The extract of P. angolensis was selectively toxic to L. natalensis, its LC₅₀ being three times higher for H. duryi than for L. natalensis. These plant extracts are a potential source of lead compounds in the development of highly selective and environmentally friendly molluscicides. Further studies to isolate the active principles in these extracts are recommended.