The life cycle, morphology, and potential of Diomus terminatus Say (Coleoptera: Coccinellidae) to control the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), were examined in the laboratory. The morphologies of first and fourth instars are described and illustrated, with emphasis on characters of first instar that differ from those of later instars. Dramatic differences exist in the relative size and abundance of specialized setae between early and late instars. Field-collected late instars of D. terminatus were successfully reared to adult stage at 26°C by using M. sacchari feeding on small pieces of sugarcane {Saccharum, spp.) leaves. The eggs laid on the sugarcane leaves hatched in 4.5 ± 0.1 d. Larval and pupal stages lasted an average of 6.8 ± 0.6 and 4.9 ± 0.2 d, respectively. D. terminatus required 12.1 ± 0.6 d from egg hatch to adult emergence. The adult longevity test with single adults in petri dishes revealed that D. terminatus remained alive for 26 ± 1.9 d when feeding on aphids of mixed ages. The larvae consumed a total of 30 ± 1.8 aphid nymphs, with a daily consumption rate of 4.7 ± 0.4. The adult voracity test showed that D. terminatus could consume as many as 19 ± 0.9 aphids per d. These results are discussed with respect to their implications for aphid control in Louisiana sugarcane.