Systematics and host relationships of North American ant parasitoids in the genus Orasema

Orasema (Hymenoptera: Eucharitidae) is a genus of ant-parasitizing wasps with a nearly worldwide distribution. Adults oviposit away from the host in plant tissue and the first-instar larvae must gain access to the host brood. They are specialists on the larvae and pupae of myrmicine ants, with all substantiated North American host records from the genera Pheidole and Solenopsis. Orasema coloradensis Wheeler is the only species documented parasitizing both of these ant genera and the only species with a potential association with the genus Formica (Formicinae). The coloradensis species-group is currently composed of two described North American species, O. coloradensis and Orasema violacea Ashmead. Orasema coloradensis has the largest known geographic distribution of any species in the genus, ranging from central Mexico to southern Canada and from Florida to California. This species is highly variable in its morphology, however, early molecular analyses from 6 genes and 18 specimens across North America suggest that O. coloradensis has not speciated despite its large range of hosts and morphology. Very little information is known about O. violacea except that it is restricted to northern Florida and has not been collect since the 1980’s. A grade of undescribed South American species related to O. coloradensis suggest that the coloradensis species-group has an independent North American origin to the rest of the North American Orasema. The coloradensis species group is ideal for a case study on the effects of host choice (plant and ant) on morphology, genetics, and biogeography.