We examined rates of late-season parasitism of larvae of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), by native species of Bracon F. (Hymenoptera: Braconidae) over 8 years in Montana and North Dakota, United States of America. We found that rates of parasitism of larvae in diapause chambers reached a maximum of 46%, exceeding the previously reported maximum of 2.5% in 75% of sites and years examined. In contrast to previous work, our results demonstrate that C. cinctus larvae are suitable hosts for braconid parasitoids, even after the formation of diapause chambers, and suggest that parasitism rates may be underestimated if stems are sampled prior to harvest.