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Abstract
SUMMARY
Terrestrial gastropods have become considerably as economic pests in Egypt. The control of these snails is of great importance. In this study, the molluscicidal activity of methomyl, urea, and copper hydroxide against the brown garden snail E. vermiculata and the small white garden snail, T. pisana terrestrial snails were investigated. The effect of those compounds on some biochemical systems of the snails were also assayed.
The obtained results of this study could be summarized as follows:-
5.1. Molluscicidal activity of methomyl, urea and copper hydroxide against E. vermiculata and T. pisana
1) Methomyl was found to be the most toxic compound against E. vermiculata followed by copper hydroxide which was followed by urea after 72 hrs of evaluation where LC50 values were 3750, 3310, 40880 ppm, respectively.
2) Methomyl was also the most toxic compound when it was tested against T. pisana followed by copper hydroxide which was followed by urea, with LC50 values of 3760 , 4630, 40130 ppm , in respect.
3) E. vermiculata was more susceptible to methomyl and copper hydroxide than T. pisana. There was no difference in the susceptibility of the two tested snails to urea.
4) The toxicities of the tested compounds against both snails were enhanced as the exposure time, was increased.
5.2. Biochemical studies
1- AChE of E.vermiculata and T. pisana
a. In the kinetic studies, the affinity between the T. pisana AChE and the substrate (or the concentration of the substrate at which v= 1/2 Vmax which is tarmed Km) (Km= 0.042mM) was higher than the affinity between the E. vermiculata AChE (Km= 0.098mM). The Vmax values were 0.042 and 0.052 m mole/min for AChE E. vermiculata and T. pisana, respectively. The specific activity of AchE FOR T. pisana was 1.4 times as the specific activity of E. vermiculata AChE.
b. The in vitro studies revealed that methomyl was more potent as an inhibitor to AChE of T. pisana when it was compared to the AChE of E. vermiculata. The sensitivity of AChE of T. pisana to methomyl was 4.1 times more than that AChE E. vermiculata, with I50 values of 1.3 and 5.3 µM, successively.
c. The in vivo studies revealed that methomyl at concentrations of 375, 750 and 1875 ppm caused 42.3, 51.4 and 75.4% inhibition of E. vermiculata AChE activity, subsequently. On the other hand, methomyl caused inhibition percentages of 88.73, 89.44, and 92.25% for AChE T. pisana when it was tested at the concentrations of 376, 752 and 1880 ppm, in respect. The inhibition of E. vermiculata and T. pisana AChE using methomyl was time and concentration dependents.