Behavioral effects of acute sublethal exposure to dimethoate on wood mice, Apodemus sylvaticus: II--Field studies on radio-tagged mice in a cereal ecosystem

The effects of direct exposure to an organophosphate (OP) pesticide, dimethoate, were examined in free-living wood mice, Apodemus sylvaticus, in a wheat field. Male mice were radio-tagged at night and followed during 2-3-d periods, before and after an intraperitoneal injection of 50 mg/kg dimethoate which previous laboratory studies had demonstrated causes a maximum depression in brain acetylcholinesterase (AChE) activity of 75% relative to non-exposed mice. In subsequent weeks, survival was estimated by tracking and trapping data. Exposure to dimethoate significantly decreased locomotor activity in the first 6 h after administration resulting in a significant decrease in the area over which animals moved. These effects were limited to the night of treatment and disappeared 24 h later. The transient behavioral impairment of the dimethoate-treated animals appeared to have no effect on medium-term survival. Direct exposure to OPs sufficient to cause 75% depression of brain AChE is unlikely to be hazardous to wood mice if exposure is transient, as in the present study; it would be expected that sustained exposure sufficient to cause such behavioral effects would, however, be detrimental.