EFFECTS OF LONG-TERM AND SHORT-TERM EXPOSURE TO CARBARYL ON SURVIVAL, GROWTH AND REPRODUCTION OF DAPHNIA-AMBIGUA

In laboratory experiments a cladoceran, Daphnia ambigua, was exposed for six instars to the insecticide carbaryl at five different concentrations (1,2,3,4, 5-mu-g litre-1) or received short-term (10-h) exposure to 5-mu-g carbaryl litre-1 at different life stages of the animal. In the long-term exposure experiments carbaryl at 1-mu-g litre-1 did not have any detectable effects on the animals, whereas 2-mu-g litre-1 reduced the survival, growth and reproduction of the animals, and higher concentrations killed all the animals examined before they grew to the fifth instar. These results indicate that the range of sublethal concentrations of carbaryl for D. ambigua is narrow. In the short-term exposure experiments the animals did not suffer any damage when they were exposed to the chemical during the egg stage. However, their growth and egg production were reduced when the short-term exposure was conducted during the life stages from the final embryo stage to the third instar. The effect was most marked when the animals were treated during the first instar, indicating that this is the stage when the animals are most sensitive to the chemical.