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Diabrotica barberi Smith and Lawrence and D. longicornis (Say) are currently recognized as closely related chrysomelid species. Morphological and genetic data support that the two species are sister taxa, and hybridization has been proposed to occur. The objectives of this work were to: 1) assess life history parameters of both taxa and hybrids, 2) compare mating behavior, pheromone response, and spermatophore transfer of both taxa and hybrids, and 3) examine genetic and morphological data for evidence of introgression. Using lab-reared individuals, fitness parameters and potential for population growth were assessed. D. barberi and D. longicornis differed in longevity and fecundity. Hybrids of a D. longicornis mother, D. barberi father, were as viable as individuals of either parental species, but hybrids of a D. barberi mother, D. longicornis father, demonstrated consistently poor fitness. Studies of reproductive characteristics demonstrated that F1 hybrids (D. longicornis mother, D. barberi father) are reproductively fit and that the two parental taxa exhibit numerous small differences in reproduction. The genetic and morphological data provided evidence for gene flow between the two taxa, which prevents population differentiation. This research demonstrates that hybridization most likely occurs under field conditions, and that the relative fitness of hybrids of a D. longicornis mother, D. barberi father, is comparable to the parental taxa. Greater work on the ecology of both taxa is needed to assess the degree of ecological separation. Currently available data support a reevaluation of the current taxonomic status; redesignation of the taxa as subspecies may be most appropriate.