Molluscicides of Plant Origin

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Abstract
Snails are well known as carriers of diseases and vectors of pests. Being largely herbivorous, land snails cause immense damage to both cultivated and useful non-cultivated plants. A large population of snails, however, inhabits freshwaters, where the larvae of parasitic trematodes also pass part of their life. Many aquatic snails act as vectors for the larvae of trematodes and thereby cause a number of diseases. Two diseases carried by aquatic snails, fascioliasis and schistosomiasis cause immense harm to man and his domestic animals. Snails are next only to insects in the harm they cause to mankind. The World Health Organization has tested thousands of synthetic compounds for the eradication of snails. Though effective, these pesticides have so far not proved themselves to be entirely satisfactory. With a growing awareness of environmental pollution which such compounds can cause, efforts are being made to find molluscicidal products of plant origin. Being the products of biosynthesis, these are potentially biodegradable. Several groups of compounds present in various plants have been found to be toxic to snails. Thus, saponins, tannins, miscellaneous alkaloids, alkenyl phenols, glycoalkaloids, flavonoids, sesquiterpenes lactones, terpenoid and phorbol esters have been found to be poisonous to snails at acceptable doses ranging from <1–100 ppm. These molluscicidal compounds come from 56 families of angiosperms. Although the active moiety in many cases has been identified, systematic studies on their long term effects on non-target organisms as well as their structure-activity relationship remains largely unknown. In this review we have tried to assemble all the known information on products of plant origin, which might possibly be used for snail control.