CAGE AND FLIGHT PEN EVALUATION OF AVIAN REPELLENCY AND HAZARD ASSOCIATED WITH IMIDACLOPRID-TREATED RICE SEED

A series of cage and flight pen trials evaluated the responses of male red-winged blackbirds (Agelaius phoeniceus) to rice seed treated with imidacloprid, a systemic insecticide. In two-cup trials, when both th e treated and untreated seed was either dyed or undyed, individually c aged redwings consistently avoided rice seed treated with 833 and 2500 mg kg-1 imidacloprid but not 278 mg kg-1. When birds had a choice bet ween undyed, untreated rice and dyed imidacloprid-treated rice, consum ption of treated seed was suppressed at all levels. In a one-cup trial , rice consumption during the 4-day test phase was reduced relative to that during the 4-day pretest period at 833 and 2500 mg kg-1 of imida cloprid but not at 0 and 278 mg kg-1. During 4-day trials in a 0.2 ha flight pen, six different ten-bird flocks removed an average of 41.1% of the untreated rice seed on sample quadrats compared with 8.8% lost from plots having 2500 mg kg-1 imidacloprid-treated seed. On the basis of residues from whole seeds and from hulls of rice seed eaten by tes t birds, it is estimated that redwings ingested 13-16% of the imidaclo prid initially present on the seed. Thus, even at 2500 mg kg-1, red-wi nged blackbirds feeding at an average rate of six seeds min-1 acquired only a fraction of the imidacloprid calculated to be a lethal dose. I midacloprid appears to be an effective bird repellent seed treatment w ith minimal avian hazard.