Molluscicidal activity of Pergularia tomentosa (L.), methomyl and methiocarb, against land snails

The molluscicidal activity of a cardenolide (cardiac glycoside) extract from Pergularia tomentosa (L.) (Asclepiadaceae), methomyl, and methiocarb was evaluated against the land snail Monacha obstructa (Ferussac) at 25 degress C. The LD50 value of the plant extract after 24 h of treatment was 60.9 mug/snail, whereas the LD50 values of the two tested carbamate pesticides after 72 h of treatment were 11.9 and 27.4 mug/snail, respectively. Only contact toxicity tests were used in this study because cardiac glycosides and plants containing them, including P. tomentosa, have a strong antifeedant effect against land snails. Further studies are needed to isolate and identify the molluscicidal compound(s). The possible uses of plants that contain cardenolides, as molluscicides, are discussed.