Ecotoxicological Studies of Methyl Parathion on Growth and Reproduction Potential of Some Tropical Earthworms

摘要

The aim of present study was to estimate the effects of different concentrations of Methyl parathion pesticide on the survival, biomass and cocoon production rate of commonly distributed tropical earthworms (Metaphire posthuma (Vaillant), Lampito mauritii Kinberg and Allolobophora parva Eisen) in semi-arid tropic agrosystems of northern Rajasthan. Three different concentrations of methyl parathion via 1.00 (T ), 1.125 (T_2) and 2.250 gm/kg soil (T_3) (total contamination) were used for ecotoxicological testing under laboratory conditions for 60 days. Pesticide caused significant reduction in earthworm population with lowest mortality 10% (of the control) in L. mauritii by T_1, and highest mortality 90% (of the control) in A. parva by T_3 treatment, after 60 days of experimentation. The total mortality in all species studied was strongly correlated with pesticide concentrations. Comparatively the highest biomass reduction in L. mauritii (P < 0.05), M. posthuma (P < 0.05) and A. parva (P > 0.05), was recorded with T_3 treatment. In respect to different concentrations of pesticide, the total individual cocoon numbers fluctuated drastically in all the three earthworm species studied. Dramatically L. mauritii showed a non-significant increase (17 % more than control) in individual cocoon numbers with T_1 treatment, while none the other species/or treatment showed this type of behavior with methyl parathion. Nevertheless, methyl parathion caused significant reduction in total number of cocoon in M. posthuma (about 76.7 % of the control) and A. parva (about 99.3 % of the control) with T_3 treatment. The results of present study suggested a species-specific toxic sensitivity between earthworms and a pesticide sensitivity difference at same concentration of pesticide was also recorded between both endogeics: L. mauritii and M. posthuma. In respect to vital activities M. posthuma appeared to be more sensitive towards the different concentration of pesticide than L. mauritii. Epigeic A. parva led to a lower exposer risk than endogeics and consequently showed lower biomass reduction.