Strain difference in sensitivity to 3,4-dichloroaniline and insect growth regulator, fenoxycarb, in Daphnia magna.

Acute and reproductive toxicity tests were conducted on seven strains of Daphnia magna from six laboratories in five countries. 3,4-Dichloroaniline (DCA) and fenoxycarb were used as test chemicals. Acute toxicity tests revealed that estimated EC(50) (50% effective concentration) values for DCA varied by a factor of 2.1 among strains (310-640 microg/L), whereas the EC(50) values for fenoxycarb varied by a factor of 4 (210-860 microg/L). EC(50) values for reproductive toxicity tests with DCA ranged from 5.9 to 38 microg/L among strains. Fenoxycarb exposure induced the production of male neonates in all the strains used in the present study. Estimated EC(50) values for the induction of male offspring were highly variable among strains: sensitivity to fenoxycarb differed by a factor of approximately 23 overall (0.45-10 microg/L). The present pre-validation tests suggest that induction of male sex in neonates by a juvenile hormone analog is universal among genetically different strains. Decreased total numbers of neonates at increased concentrations of fenoxycarb as well as other juvenoids may, however, obscure the incidence of male neonates production in the 21-day reproduction tests due to the low statistical power.