Abstract
We conducted acute toxicity tests using a calanoid species (Eodiaptomus japonicus) and two cyclopoid species(Mesocyclops pehpeiensis, Thermocyclops taihokuensis)of different life stages(nauplius and adult)and assessed their sensitivities to the insecticide diazinon and carbaryl.
The EC50 values of nauplii of the three species ranged between 2.8 and 4.1 ppb for diazinon and between 9.9 and 19.7 ppb for carbaryl, which were in the similar range of the EC50 values of neonates of the cladoceran Daphnia for the same insecticides. In contrast, adults of the copepod species showed much higher tolerance to the chemicals; their EC50 values were in a range between 30.6-46.8 ppb for diazinon and between 785.7-1190.0 ppb for carbaryl, which were 10-70 times higher than the values of nauplii. The difference in the sensitivity to the chemicals between neonates and adults was much larger in the copepods than in Daphnia. This suggests that the copepod populations are controlled mostly by the mortality of nauplii if they are exposed to insecticides.
