Many aquatic snails act as intermediate hosts for the larvae of trematodes, Fasciola hepatica and Fasciola gigantica, which cause the diseases fascioliasis and schistosomiasis. The WHO has tested several thousands of synthetic compounds for the control of the snail host. Although effective, these molluscicides have so far not proved themselves to be entirely satisfactory. With a growing awareness of environmental pollution, efforts are being made to discover molluscicidal products of plant origin. Being products of biosynthesis, these are potentially biodegradable in nature. Several groups of compounds present in various plants have been found to be toxic to target organisms at acceptable doses ranging from <1 to 100 ppm. Common medicinal plants, i.e. Thevetia peruviana, Alstonia scholaris (Family; Apocynaceae), Euphorbia pulcherima and Euphorbia hirta (Family; Euphorbiaceae), have potent molluscicidal activity against freshwater snails. The toxicological actions of Thevetia peruviana may be due to the presence of apigenin-5-methyl ether (flavonoid) and triterpenoid glycosides, while a number of alkaloids (pseudo-akuammigine in addition to betulin, ursolic acid and beta-sitosterol), steroids and triterpenoids are present in Alstonia scholaris and the diterpenoids, pulcherrol, beta-sitosterol, hentriacontane, ellagic acid and beta-amyrin are present in Euphorbia hirta and in Euphorbia pulcherima. Although, at present very little literature is available on the control of vector snails through plant origin pesticides, an attempt has been made in this review to assemble all the known information on molluscicidal properties of common medicinal plants of eastern Uttar Pradesh, India, which might be useful for the control of harmful snails.
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