Synonyms and other taxonomic changes
Here's the DSA checklist committee comments (published in October's Argia, although I think it's available online as well):
Sympetrum semicinctum, Band-winged Meadowhawk.
Western populations have been considered a separate species, S. occidentale (Western Meadowhawk), since Walker (1951) distinguished them from the eastern S. semicinctum. Although no published work presented evidence for combining the two species, some North American workers have questioned the separation, and Dunkle (2000), Donnelly (2004), and Abbott (2005) did not recognize occidentale as distinct. Finally, Pilgrim & von Dohlen (2007) presented evidence that populations of semicinctum and occidentale were identical at two genetic loci and that the morphological characters that had been used to distinguish the two species overlapped. They further stated that the subspecies that had been recognized for western populations were not worthy of formal recognition because of much overlap in characters. It should be added, however, that populations that have been considered semicinctum, occidentale, californicum, and fasciatum do in fact possess distinctive characteristics and point to an interesting example of geographic variation in a widespread and common species. This information should not be lost by the suppression of the names.
Pilgrim, E.M. and C.D. von Dohlen. 2007. Molecular and morphological study of species-level questions within the dragonfly genus Sympetrum (Odonata: Libellulidae). Annals of the Entomological Society of America 100: 688–702.
… Jason Forbes, 27 January, 2008