Based upon laboratory and field studies, and examination of more than 3,500 museum specimens, Diabrotica longicornis barberi Smith and Lawrence is elevated to species rank. Diabrotica barberi and D. longcornis (Say) are distinct species whose ranges overlap in the central plains of the United States. Adults of D. longicornis are characterized by piceous antennae, tibiae, tarsi, and clypeus and are collected from cucurbits. Diabrotica barberi is commonly collected in cornfields and , where it is sympatric with D. longicornis, has yellow to testaceous antennae, tibiae, tarsi, and clypeus. The distinguishing colors prevailed in progeny of field-collected beetles fed from egg hatch to adulthood on a common diet. Sex pheromone extracts which attract D. barberi males did not attract D. longicornis males, and males of each species were attracted by conspecific virgin females but not by females of the other species. In caged sexual compatibility experiments, mating success was asymmetrical.Discrimination analysis of 14 morphometric characters failed to discriminate completely between D. barberi and D. longicornis. Chromatic variation within D. barberi is geographically complex. The distribution of the two taxa is presented