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Molluscicidal Efficacy of Croton or Toba Plant (Croton tlgilium Linnaeus) Seed Extract Against Radix (Lymnaea) Quadrasl Moellendorff and Oncomelania Quadrasl Moellendeforff Under Laboratory Conditions
Thesis Abstract:
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. Seven hundred and twenty catfish (Clarias batracus) and 80 mice (Swisswebster) were also used for the bioassay studies. Quantitative toxicity of toba against the snaiIs, mice, and fishes was determined using Probit Analysis.
Time-concentration relationship tests showed that toba obtained the LC90 values for 24-hour exposures of 20.317 ppm against R. (L.) quadrasi, 12.889 ppm against G. convexiusculus, and 32.835 ppm against 0. quadrasi. Toba's LC90 values for the test snai ls were much lower at 24 hours than at 6- and 1-hour exposures.
Toba is less mo llu sc icidal than the commercial molluscicide NaPCP. The stage-size array susceptibilities of R. (L.) quadrasi and G. convexiusculus showed that snail eggs' hatchability were not affected by toba. The LC90 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. Toba's molluscicidal efficacy decreased under working dilution after two and four days of storage at room temperature and on its LC90 values (24-hour exposure) for the test snails, and after 90 days of storage also at room temperature.
When exposed to toba, the snails' 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, MgS04, and CaCI, of up to 200 ppm in water, pH of 5.5-8.0, water temperature of soc to 35°C, and boiling temperature for 30 minutes did not inactivate toba as a molluscicide. Tests on these different factors consistently demonstrated 100 percent efficacy for toba against R (L.) quadrasi and G. convexiusculus. However, efficacy of toba was reduced in 0. quadrasi. Moreover, its efficacy was almost lost against the three species of snails when heated at 95°C for 24 hours.
Toxicity study of toba to mice showed LCso and LC90 values for the 90-day feeding trials of 13,433.112 ppm ( 13.433 g) and 674,610.095 ppm (674.61 0 g), respectively. Thus, it appeared that mice have high tolerance to toba. Toxicity evaluation of toba to catfish (hito) disclosed LC50 and LC90 values for 24-hour exposure of 1.879 ppm and 2.81 ppm, respectively. The toxicity oftoba on catfish are 0.538 for R. (L.) quadrasi, 2.128 ppm for G. convexiusculus, and 0.998 ppm for 0. quadrasi.
Based on these findings, toba could be used as a molluscicide against R L. quadrasi, G. convexiusculus, and 0. quadrasi, the common vectors of economically important parasites of man and animals.
