EFFECT OF NUVAN, METHYL PARATHION AND THIMET ON THE MORTALITY, BEHAVIOR AND REPRODUCTIVE-PERFORMANCE OF FRESH-WATER MOLLUSK LYMNAEA-STAGNALIS

When adult Lymnaea stagnalis specimens were treated with aqueous solut ions of nuvan, methly parathion and thimet separately for 30 days, the y displayed hyperirritability after 4+/-2 days, manifested in climbing behaviour at the surface of the water. They remained clinging to the wall of the container for long intervals without feeding. Owing to dec alcification the shell became thin, fragile and semitransparent. The h igher concentration of pesticides resultant into zero percent of fecun dity and viability while in lower concentration the number of egg mass es as well as number of egg capsules/egg mass showed significant decre ase in comparison to the control groups. In higher concentration of pe sticides the development was not proper but irregular and it was arres ted at any stage. On the basis of relative toxicity on the mortality a nd other aspects of reproductive performance these three organophospho rus pesticides could be ranked nuvan >, methyl parathion > thimet.