Effect of diazinon on life stages and resting egg hatchability of rotifer Brachionus plicatilis

The effects of organophosphate pesticide, diazinon, on life history parameters and hatchability of resting eggs of rotifer Brachionus plicalitis were assessed. Newly hatched (<1h-old) neonates were individually cultured in six varying concentrations (0/control, 0.1, 1.0, 2.5, 5.0 and 10.0 mg/L) of diazinon. The life history parameters such as time (h) the rotifers bear first egg and release first neonate, reproductive period, net reproductive rate, mixis, intrinsic rate of population increase, and life span were evaluated. Results showed that among the life history parameters, the time the rotifers took to release neonates is the most sensitive, giving the lowest EC50 value of 1.24 mg/L. The fecundity of maternal females, amictic and mictic daughters was also investigated. Rotifers exposed to 10.0 mg/L produced significantly fewer amictic daughters, and at this concentration, rotifers did not produce any mictic daughter. At 5.0 mg/L, the number of male offspring was significantly lower than the control. Furthermore, the hatchability of resting eggs produced by the rotifers was evaluated when exposed to diazinon: from birth until they produced resting eggs (early development); during late developmental stage of resting eggs (before diapause); and during diapausing stage. The hatchability of the resting eggs was not affected when exposure was timed at late developmental and diapausing stages. Overall results showed that even though amictic females reproduced normally in the presence of low concentration of diazinon, sexual reproduction is severely affected, especially the hatchability of resting eggs when the exposure was timed on its early developmental stages. This provides another evidence that production of resting eggs is particularly sensitive to the presence of xenobiotics in the environment