Summary

Description

In June 1992, we collected 52 plasma samples from nestling redwinged blackbirds Age latus phoeniceus, house sparrows Passer domesticus, and brownheaded cowbirds Molothrus ater at 5 study sites near the town of Ada in northwestern Minnesota. Three sites were adjacent to sugar beet fields that were likely to be treated with Lorsban an organophosphate insecticide for control of sugar beet root maggots Tetanops myopaeformfs, and 2 sites were distant from fields likely to be treated reference sites, Application of Lorsban in fields surrounding study plots was monitored through contact with landowners and direct observations. Cholinesterase ChD activity levels total cholinesterase TChD, acetylcholinesterase AChE, and butyrylcholinesteraseBChE in nestling plasma were measured and tested TChE and AChE for reactivation in the presence of 2PAM, an indication of exposure to organophosphate insecticides. In addition, 11 nestlings were euthanized and in these samples we measured brain ChE activity and reactivation, and we analyzed gastrointestinal tracts and carcass washes for Lorsban residues. Total ChE and BChE activity were lowest in similaraged nestlings at sites adjacent to treated beet fields TChE, t 2.51, d. f. 21, P 0.033; BChE, t 2.56, d.f. 21, P 0.043. Nestlings from sites that were near fields where Lorsban was applied were more likely to exhibit plasma AChE reactivation than nestlings from reference sites where OP or carbamate insecticide application was improbable Xsquare 3.805, df. 1, Pz 0.05. The magnitude of plasma ChE reactivation was highest within 13 days of insecticide application, although significant reactivation was measured up to 11 days after application of Lorsban. Plasma AChE reactivation appeared to be a more sensitive indicator of exposure to ChEinhibiting insecticides than absolute TChE or BChE activity levels. The occurrence of Lorsban residue in gastrointestinal tracts and carcass washes suggested that nestlings were exposed to insecticides through prey delivery andor physical contact with adults.