Toxicity of methyl parathion on growth and reproduction of three ecologically different tropical earthworms

This work illustrates the toxicological impact of pesticide methyl parathion (MP) (dust-2 % active ingredient, a.i.) on growth and reproduction performance in tropical earthworms: Metaphire posthuma (endogeic), Lampito mauritii (anecic) and Allolobophora parva (epigeic). A total of three concentrations (a.i. g kg(-1) dry test soil), 1.00 (T-1), 1.125 (T-2) and 2.25 (T-3) of MP, were applied in test substrate to examine the impact on mortality, individual live weight changes and reproduction patterns in test species over 60 days under laboratory conditions. MP caused significant mortality in all tested species, and median lethal dose (LD50) for L. mauritii, M. posthuma and A. parva was 24.85, 23.64 and 22.67 mg a.i., respectively. The individual live weight loss was 27.0-37.0 % in L. mauritii, 36.0-57.1 % in M. posthuma and 1.2-11.0 % in A. parva in different test concentrations. The pesticide-exposed worms produced less cocoons than control, but in L. mauritii, an unusual reproduction (hormesis) was recorded. Results suggested the species-specific toxicity of MP against tropical earthworms.