Adults of full-sib Colorado potato beetle families were separated into three groups fed on different diets: transgenic potato foliage, potato foliage treated with a foliar formulation of B. thuringiensis endotoxin (12.37 ?g of Cry3A d-endotoxin per 1?l of mixture), and untreated potato foliage. After feeding for 3 hours, all the beetles were placed on a computer-linked flight mill system. The number of beetles that flew, duration of each flight, and the number of flights for each beetle were recorded. Feeding on transgenic foliage had a strong negative effect on the proportion of beetles that flew, as well as the average number of flights per flying beetle. Mean flight duration was not influenced by the beetle diet, but interaction between family and diet was highly significant, with pronounced family effects observed for the beetles fed on standard and treated foliage. Beetles from families that performed the longest flights when fed on untreated foliage performed the shortest flights when fed on transgenic foliage. Suppression of beetle flight as a result of endotoxin ingestion could keep beetles within transgenic fields, thus increasing selection pressure towards development of physiological resistance. One possible way to reduce this pressure is to provide refugia for susceptible beetles in close association with fields planted to transgenic potato. [Full Text]