Previous identifications in North America of Trichomalus perfectus (Walker, 1835) and Mesopolobus morys (Walker, 1848) (Chalcidoidea: Pteromalidae), the principal chalcid parasitoids of the cabbage seedpod weevil (Ceutorhynchus obstrictus Marsham, 1802) in Europe, are shown to be misidentifications of Trichomalus lucidus (Walker, 1835) and Mesopolobus (Xenocrepis) moryoidessp. nov., respectively. Necremnus duplicatus Gahan, 1941 (Chalcidoidea: Eulophidae) is synonymized formally under Necremnus tidius (Walker, 1839) syn. nov., confirming a previous, tentative synonymy. Both sexes of N. tidius, M. moryoides, and T. lucidus are illustrated and compared with those of similar species using macrophotography and scanning electron microphotography. Hypotheses are offered to explain why the principal chalcid parasitoids of the cabbage seedpod weevil differ between North America and Europe and how the three treated species came to be in North America.