Gregarine host specificity has been the cornerstone of gregarine taxonomy for nearly a century. Several laboratory experiments have accepted strict host specificity by failure to cross-infect distantly related hosts with unrelated gregarine species. These empirical studies are not feasible for all gregarine hosts, especially nondomesticated groups. Additionally, studies of gregarine distributions have always focused on insect hosts of disparate groups, rather than targeting potential hosts species within a single genus and their congeneric gregarines. This study addresses host utilization of nubenocephalid gregarines parasitizing the odonate genus Argia (Odonata: Zygoptera: Coenagrionidae). Populations of 9 species of adult Argia were collected, dissected, and observed for gregarine infection during the April–September flight seasons in 2007 from 17 localities in the central United States. On average, 2.5 species of Argia were collected at each locality. A species of Nubenocephalus—Nubenocephalus nebraskensis, Nubenocephalus secundus, or Nubenocephalus spp.—was collected from every infected population of Argia except for the Argia vivida population at Prairie Dog Town Fork-Red River, Randall County (Co.), Texas, U.S.A. Nubenocephalus secundus utilizes at least 7 of the 9 argid hosts sampled whereas N. nebraskensis was collected from only 2 argid species. Only Argia translata was observed to host both N. secundus and N. nebraskensis. These patterns of host utilization by nubenocephalid gregarines represent an ecotypic gregarine assemblage rather than a vicariant assemblage, demonstrating that nubenocephalid gregarines do not differentiate between species of Argia as hosts.