Snails of family Lymnaeidae act as an intermediate host of Fasciola species, which caused fasciolosis nearly in all the continents of world. Eugenol and quercetin are active molluscicides against snail Lymnaea acuminata. Laboratory evaluation is done to determine the effect of abiotic factors on the toxicity of these molluscicides in the year 2010-2011. Highest toxicity of eugenol (24 h LC 50 10.03 mg LG 1 ) and quercetin (24 h LC 50 129.13 mg LG 1 ) was observed in the month of May. Significant correlation was observed between LC 50 values of eugenol and quercetin with temperature/pH/dissolved oxygen/carbon dioxide. In vivo acetylcholinesterase (AChE), alkaline phosphatase (ALP) and acid phosphatase (ACP) activity were measured in the nervous tissue of treated snails in each month of year 2010-2011.
Statistical analysis:Results have been expressed as Mean ±SE of six replicates. Rank correlation was applied in between LC 50 and corresponding changes in enzyme activity in different months of the year -2011(Sokal and Rohlf, 1973. One way analysis of variance were applied between enzymatic activity in different month of the year.
RESULTS AND DISCUSSIONThere was significant (p<0.05) variation in the toxicity of eugenol and quercetin against the Lymnaea acuminata in each month of the year 2010-2011. Highest toxicity of eugenol (24 h LC 50 10.03 mg LG 1 ) (Table 1) and quercetin (24 h LC 50 129.13 mg LG 1 ) (Table 2) was observed in the month of May and lowest in the month of January (24 h LC 50 40.69 mg LG 1 ) (Table 1) and quercetin (24 h LC 50 430.67 mg LG 1 ) (Table 2). A significant positive correlation between LC 50 and water pH/carbon dioxide, contrary a negative correlation between LC 50 and dissolved oxygen/temperature was observed in different months of year 2010-2011 (Table 1). There was no marked correlation in between the LC 50 and conductivity of water. The slope values were steep and separate estimation of LC 50 based on each of six replicates was found to be within the 95% confidence limits of LC 50 . The t-ratio is greater than 1.96 and the heterogeneity factor is less than 1.0. The g-value was less than 0.5 at all probability levels. There was a positive rank correlation between LC 50 of eugenol in different months and corresponding AChE/ACP/ALP activity in the nervous tissue of treated snail L. acuminata. No significant rank correlation was observed between LC 50 of quercetin and corresponding ACP/ALP activity in the nervous tissue of treated snail.Maximum inhibition of AChE (52.38% of control) was observed when snails were exposed to 60% 24 h LC 50 of quercetin followed by eugenol (66.66% of control). Maximum inhibition of ALP (60.15% of control) was observed when snails were exposed to 60% 24 h LC 50 of eugenol followed by quercetin (90.73% of control) (Table 3). Maximum inhibition of ACP (82.08% of control) was observed when snails were exposed to 60% 24 h LC 50 of eugenol (Table 3) followed by quercetin (90.
