Behavior was altered and survivorship was reduced when parasitoids, Anagyrus pseudococci (Girault) (Hymenoptera: Encyrtidae), were fed flowers from buckwheat, Fagopyrum esculentum L. (Polygonaceae), treated with soil applications of imidacloprid (Marathon 1% G). Parasitoids at 1 d had significantly reduced survivorship of 38 ± 6.7% on label rate and 17 ± 4.2% on twice label rate compared with 98 ± 1.2% on untreated flowers. Parasitoids trembled 88% on label rate and 94% on twice label rate compared with 0% on untreated flowers. Residue analysis on a composite sample of 425 flowers showed that imidacloprid concentration was 6.6 ± 1.0 ppm (16 ppb/flower) in label rate, 12.3 ± 2.7 ppm (29 ppb/flower) in twice label rate, and 0 ppb in untreated flowers. The hydroxy metabolite concentration was 1.1 ppm (2.4 ppb/flower) in label rate, 1.9 ppm (4.4 ppb/flower) in twice label rate, and 0 ppm in untreated flowers. The olefin metabolite concentration was 0.2 ppm (0.5 ppb/flower) in label rate, 0.5 ppm (1.1 ppb/flower) in twice label rate, and 0 ppm in untreated flowers. Soil-applied imidacloprid used at flowering may be translocated to nectar in higher concentration compared with the imidacloprid seed treatment Gaucho. Considerable research has studied effects of Gaucho-treated canola, sunflower, and maize on behavior and mortality of Apis mellifera L. In our laboratory, we showed that translocation of imidacloprid to flowers reduced survivorship and altered behavior of pink lady beetle, Coleomegilla maculata DeGeer (Smith and Krischik 1999) and green lacewing, Chrysoperla carnea Stephens (Rogers et al. 2007).