Author : Ramis, Godofredo Z.

Summary : The molluscicidal efficacy of Croton or toba (Croton tigilium) was evaluated under laboratory conditions against three species of snails, namely: Radix (Lymnaea) quadrasi, 6,694 pieces; Gyraulus convexiusculus, 6,706 pieces; and Oncomelania quadrasi, 5,700 pieces. Some 720 catfish (Clarias batracus), and 80 mice (Swisswebster) were also used for the bioassay studies. Quantitative toxicity of toba against the snails, mice and fishes was determined using Probit Analysis. Time-concentration relationship tests showed that toba obtained the LC (subscript 90) values for 24-hour exposures of 20.317 ppm against R. (L.) quadrasi, 12.889 ppm against G. convexiusculus, and 32.835 ppm against O. quadrasi. Toba's LC (subscript 90) values for the test snails were much lower at 24 hours than at 6- and 1- hour exposure. Toba is less molluscicidal than the commercial molluscicide NaPCP. The stage-size array susceptibilities of R (L.) quadrasi and G. convexiusculus showed that snail eggs' hatchability are not affected by toba. The LC (subscript 90) values for 24-hour exposure required to kill the newly hatched, juveniles, adolescents, and mature snails progressively increased in amount with older and larger snails. Tobas's molluscicidal efficacy reduced under working dilution after two and four days of storage at room temperature and on its LC (subscript 90) values (24-hour exposure) for the test snailes, and after 90 days of storage also at room temperature. When exposed to toba, the snail's protective behavior surfaced; they crawled out of the containers, contracted into their shells, and their shells discolored (from dark brown to light yellowish brown). Artificial irradiation and natural sunlight, rice paddy mud of up to 1.5 percent solutions, MgSO (subscript 4), and CaCl (subscript 2) of up to 200 ppm in water, pH of 5.5-8.0, water temperature of 5 degree C to 35 degree C, and boiling temperature for 30 minutes did not inactivate toba as a molluscicide. Tests on these different factors consistently demonstrated 100.