EFFECTS OF EXPOSURE TO VEGETATION SPRAYED WITH DIMETHOATE OR CHLORPYRIFOS ON MALLARD DUCKLINGS (ANAS-PLATYRHYNCHOS)

Broods of day-old mallard (Anas platyrhynchos) duckings were led throu gh 200 m of grassland vegetation that had been sprayed with emulsifiab le formulations of either dimethoate (480 g a.i. ha(-1)) or chlorpyrif os (420 g a.i. ha(-1)) or left unsprayed (control). The broods were su bsequently observed on a pond during four 2-3 h periods over the next 2 days and their activities systematically recorded. The brain acetylc holinesterase (AChE) activities of the ducklings were determined at 6, 24 and 48 h after exposure. There were no differences in the behaviou ral activities of the duckling broods at any time after exposure. The mean brain AChE activities did not differ among the treatment groups, although one dimethoate-exposed and one chlorpyrifos-exposed duckling exhibited activity depression of approximately 20% from the mean contr ol value; the level indicating some exposure to anticholinesterase ins ecticides.