Larvae found infesting fruit from a Carpathian walnut, Juglans regia L., tree in Missouri were confirmed by DNA analysis to be those of pecan weevil, Curculio caryae (Horn) (Coleoptera: Curculionidae). The infested walnut tree occurs in the midst of pecan weevil-infested pecans, Carya illinoinensis (Wang.) K. Koch; the larval haplotypes were found to be identical to pecan weevil larvae from the region, indicating that the walnut infestation arose by association with infested pecan. This is the first confirmed DNA analysis showing pecan weevil attacks J. regia and the second report that J. regia may be at risk of infestation by pecan weevil. Further study indicates this infestation on walnut is established and ongoing. The pecan weevil is a key pest of pecan and seems capable of inflicting similar damage to walnut if spread to commercial areas that produce J. regia.