Interaction of Methomyl with Brown Garden Snail, Eobania vermiculata (Müller), and White Snail, Theba pisana (Müller) Acetylcholinesterase Activity

Abstract

Comparative toxicity of methomyl against two land snails Eobania vermiculata and Theba pisana was investigated. The Michaelis constant(Km) and maximal velocity(Vmax) valuesof E. vermiculata and T. pisana AChE were compared. Finally, the in vivo and in vitro inhibition of E. vermiculata and T. pisana acetylcholinesterase by methomyl was studied. Results revealed that, the median lethal concentrations (LC50s values) of methomyl against T. pisana were 58.85, 18.71 and 3.87 % after 24, 48 and 72hrs post-treatment,respectively. On the other hand, LC50s values of methomyl against E. vermiculata were 2.94, 0.92 and 0.38 % after the same time, respectively. The Km values were 0.098 and 0.042 mM and Vmax values were 0.042 and 0.052 mmole/min for E. vermiculata and T. pisana AChE, respectively. Specific activity of T. pisana AChE is 1.43 times the E. vermiculata AChE specific activity. When T. pisana was exposed to methomyl at concentrations of 375, 750 and 1875 ppm the inhibition percentages of AChE were 88.74, 89.44 and 92.25%, respectively. On the other hand, methomyl revealed inhibition percentages of 42.3, 51.4 and 75.3% of E. vermiculata AChE activity at concentrations of 37.6, 75.2 and 188.0 ppm, respectively. The in vitro studies showed that, the sensitivity of T. pisana AChE (I50 = 1.3 µM) is 4.1 times more than the sensitivity of E. vermiculata AChE (I50 = 5.3 µM) to methomyl.