With a sudden interest in horntails following the accidental introduction of the European Sirex noctilio Fabricius into northern New York State (Hoebeke et al. 2005), there was a need to resolve numerous taxonomic problems, which resulted in a revision of the Western Hemisphere Siricidae (Schiff et al. 2012). In the latter paper, while attempting to understand Maa’s (1949) concept of the North American Xeris spectrum spectrum, we had to study the European populations of X. spectrum as well as other subspecies of X. spectrum and remaining Eurasian species. Surprisingly, the North American population of X. spectrum spectrum was not X. spectrum but consisted of two species not found in Eurasia. Moreover, we discovered that the Eurasian X. spectrum was a complex of two species in Europe and four species in Asia, so no species are shared between North America and Asia. Moreover, there were still some nomenclatural problems with Eurasian species. We recently found another cryptic North American species of Xeris that was not included in Schiff et al. (2012). After further study of the above species complexes, based on over 2400 specimens, we felt confident doing this revision.
Adults of Xeris are usually large and elegant insects. Most collections have specimens. However, standard collecting methods rarely work to capture adults and only a few collections have large numbers of specimens. Adults are best collected by rearing from short sections of boles of dead trees. Adults have been found at the top of hills with short vegetation, others were attracted to fire in fire-prone forests, and some have been hand collected on trunks and stumps. As taxonomists are usually poorly equipped to collect Siricidae high in trees, our best friends are forest entomologists who have reared successfully Siricidae from sections of identified tree boles usually during their main research that often involves cerambycid or buprestid beetles.
Adults of Xeris are easily distinguished from other Siricidae. In both sexes, there is a small vertical ridge on the gena posterior to the eye. In addition, the metatibia has one spur at the apex and the hind wing has no anal cell. Females of almost all species are recognized by the unusually long ovipositor. Schiff et al. (2012) provide more information about their recognition and their phylogenetic position among the Siricidae see .
Through 2014, seventeen names have been proposed for Xeris. The first species described was Ichneumon spectrum Linnaeus, 1758, based on a female. By 1800 two more species, based on males from northern Europe, were described, Sirex nanus O. F. Müller, 1776, and S. emarginatus Fabricius, 1793. Both have been treated as synonyms of X. spectrum. No new taxa were then proposed until 1865, when the area of study shifted to North America as western North America became accessible to entomologists. Five species were described from 1865–1900, Urocerus caudatus Cresson, 1865, Sirex melancholicus Westwood, 1874, Urocerus morrisoni Cresson, 1880, Urocerus tarsalis Cresson, 1880, and Urocerus indecisus MacGillivray, 1893. All five are still recognized here. During the period 1901–1950 Bradley (1913) published the first North American revision of Xeris and described X. macgillivrayi, a synonym of X. tarsalis (Schiff et al. 2012). Bradley (1934) described X. himalayensis from northern India, and Maa (1949) described X. spectrum malaisei from Taiwan and X. spectrum townesi from western North America. The latter was considered as a synonym of X. indecisus (Schiff et al. 2012). After 1950 three more taxa were described, X. spectrum cobosi Viedma and Suárez, 1961, from Morocco, Neoxeris melanocephala Saini and Singh, 1987, from India, here considered as a synonym of X. himalayensis, and X. indianus Vasu and Saini, 1999, from India, also considered here as a synonym of X. himalayensis. Since the year 2000 two new species were added, X. chiricahua Smith, 2012, from southwestern United States and X. tropicalis Goulet, 2012, from southernmost Mexico (Schiff et al. 2012).
Of the 17 names previously proposed six are here considered as synonyms leaving 11 valid species. None were retained as subspecies. We add five new species, one from the central Rocky Mountain region of USA, another from Europe, one from Laos, and two from China (Yunnan).
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