LAUSR

To determine the potential long-term risks associated with continual use of pesticides, we investigated (1) whether short-term exposure (48 h) of first generation (1G) Scapholeberis kingi to two acetylcholinesterase-inhibitor insecticides, pyraclofos and pirimicarb, would alter acetylcholinesterase-inhibitor sensitivity (based on immobility) in the second generation (2G), (2) whether acetylcholinesterase (AChE) activity-levels could be related to any observed change in sensitivity, and (3) whether intrinsic growth rates (r) in field cladocerans could vary between generations. We collected field-clone populations of different sensitivities from four sites in an agricultural area. Neonates (< 24 h old) were selected after insecticidal exposure for 48 h, then cultured without insecticide to obtain second-generation neonates. Based on the 48 h EC50 values, 2G neonates in the majority of the selected clones were more sensitive to the insecticides compared to the control groups. Changes in sensitivity could not be explained by AChE activity in the 2G. Although the r values decreased in few selected clones, these values recovered in the 2G suggesting that they could rapidly adapt to insecticidal exposure at the population level. The findings from our study can contribute to a better understanding in the potential risks of insecticides to aquatic organisms.