Laboratory feeding studies were conducted to determine the effects on Orius insidiosus nymphs of feeding on 1-d-old European corn borer, Ostrina nubilalis (Hübner), larvae that had ingested a diet containing Bt toxins. A commercial formulation of Bacillus thuringiensis subsp kurstaki (Dipel ES) was incorporated into a meridic diet used to feed European corn borer larvae; they then were offered as food to O. insidiosus nymphs. Immediately after adult eclosion, O. insidiosus sex was determined, body weight and length were measured, and developmental time was calculated. Another feeding study was conducted to determine the effect of Bt corn silk on mortality of immature O. insidiosus. Fresh silks of Bt and non-Bt corn plants were offered to O. insidiosus nymphs until they reached adulthood. Mortality counts were made daily. Finally, visual counts of O. insidiosus were made on Bt and non-Bt corn in fields at three locations in Kansas. The numbers of O. insidiosus nymphs and adults were recorded on 40 plants per location on two sampling dates. No significant differences occurred in developmental time, body weight, or body length of mature O. insidiosus or mortality of immature O. insidiosus when reared on European corn borer larvae that had fed on a diet containing Dipel ES. The nymphs feeding only on Bt or non-Bt corn silk suffered 100% mortality. No significant difference occurred in mortality of immature O. insidiosus when they were fed on Bt or non-Bt silk one day and on corn earworm eggs the next day. Numbers of O. insidiosus adults and nymphs in fields of Bt corn and non-Bt corn did not differ significantly in most cases. Our results suggest that Bt corn does not have a significant effect on the predator O. insidiosus.