Predaceous coccinellids can feed on non-prey food, but the ecological value of this feeding to maintain a coccinellid population is not well understood. Prey density can vary greatly in the field, whereas non-prey food sources such as pollen and nectar are more predictable. In the present study, Adalia bipunctata L. (Coleoptera: Coccinellidae) larval performance on pure and mixed diets of a high-quality non-prey food with varying amounts of prey was investigated. Rosy apple aphid, Dysaphis plantaginea Passerini (Hemiptera: Aphididae), served as prey in the experiment and was given to A. bipunctata larvae either ad libitum as a surplus diet or as a limited diet, the amount of which was selected so that it would limit larval development, according to a pilot study. Flowers of buckwheat, Fagopyrum esculentum L. (Polygonaceae), a high-value floral diet, served as the non-prey food. Newly hatched A. bipunctata larvae were reared on each of five diets: (1) flowers only, (2) limited prey only, (3) limited prey plus flowers, (4) surplus prey only, (5) surplus prey plus flowers. Larval survival, developmental time, and adult dry weight were measured. The addition of floral diet had a significant positive impact on A. bipunctata larval survival and development when prey diet was limited, survival ratio was 6× higher and developmental time was 25% shorter. In conclusion, A. bipunctata immature development can benefit from a floral diet supplemented to a prey diet, which indicates that the use of flowers in cropping systems can help to enhance biocontrol services by A. bipunctata.