Leveraging floral resources to promote biological control requires carefully screening prospective floral species for their suitability not just for natural enemies, but also for targeted pests. Here we examined the influence of access to various sugar resources on Cephus cinctus Norton (Hymenoptera: Cephidae), a major pest of wheat in the northern Great Plains of North America. We conducted greenhouse studies to examine the effect of access to a honey–sucrose solution, three flowering plant species, and aphid honeydew, on the longevity and potential fecundity of C. cinctus. Cephus cinctus longevity increased significantly (females living 1.18–1.25 times as long) in treatments with buckwheat (Fagopyrum esculentum Moench (Polygonales: Polygonaceae)) flowers compared with controls. In contrast, there was no significant effect of two additional mustard species (Capparales: Brassicaceae) tested, canola (Brassica napus L.) and white mustard (Sinapis alba L.), or aphid (Myzus persicae Sulzer (Hemiptera: Aphididae)) honeydew on C. cinctus longevity. Access to buckwheat did not significantly increase the cumulative number of eggs laid by C. cinctus, suggesting that sugar feeding on this plant is unlikely to increase pest impacts. To our knowledge, this is the first published experimental evidence that access to floral resources can increase the adult lifespan of C. cinctus. The results re-inforce previous observations that sugar feeding may be common in Cephus spp. and other Cephidae. Our results further suggest that screening prospective floral species being considered for conservation biological control programs against both C. cinctus and potential parasitoids will be an important precautionary measure in future work.