Distinguishing Orasema (Hymenoptera: Eucharitidae) parasitic on fire ants with molecular and morphological characters

Several species of Orasema are known to attack both Solenopsis and Wasmannia (Myrmicinae), and have been proposed as biological control agents of fire ants (Heraty 1993). Two species complexes are known to attack fire ants; the Orasema xanthopus group attack Solenopsis in southern South America, and species in the costaricensis group are parasitoids of Wasmannia. Few studies have focused on the biology or taxonomy of the group. Species of the group can be separated with some difficulty based on morphology and their geographic distribution in South America. However the similarity between these species is so great that an accurate molecular characterization is necessary for the correct allocation of species, especially in areas of broad sympatry. Genetic ITS2 and 28S-D2 sequences demonstrate fixed differences between species that can be correlated with geography and morphology. Because of the deep level of signal provided by 28S, we are also able to provide a hypothesis of relationships placing the fire ant complex within the subfamily. By using specific morphological and molecular methods for the classification species can be more accurately identified for use in control efforts.