Analysis of the ribosomal DNA sequences of the microsporidia Thelohania and Vairimorpha of fire ants.

Sequences of the 16SrRNA gene of three microsporidia pathogenic to imported fire ants, Solenopsis invicta and Solenopsis richteri, were determined and compared to each other and 15 other species of microsporidia. The sequences of 2 Thelohania species are nearly identical (99.2% identity), supporting light-microscopic and ultrastructural evidence that Thelohania solenopsae and Thelohania sp. are closely related but probably not conspecific. Sequence comparisons further revealed that Vairimorpha sp. has a sequence identity of about 73% with the two Thelohania species and Vairimorpha necatrix, the type species of the genus Vairimorpha. This, together with information on spore morphology, suggests that Vairimorpha sp. represents a genus distinct from that of the fire ant Thelohania. Its placement in the genus Vairimorpha must also be reevaluated. Two new sister taxa, one containing T. solenopsae and Thelohania sp. and one containing Vairimorpha sp., were found to have diverged early in the microsporidian lineage.