In 2004, specimens of Sirex noctilio Fabricius were discovered in New York State (Hoebeke et al. 2005). The species is known to cause major damage to pine plantations in South America, South Africa, Australia and New Zealand. The news of its establishment in North America was taken seriously by Canadian and American authorities and major surveys were started (and are ongoing). Hundreds of sampling sites in United States from Michigan to New Hampshire and in Canada from the eastern region of Lake Superior to New Brunswick were visited weekly and Siricidae extracted from cut logs placed in rearing containers.
With this sudden interest in horntail wasps, taxonomists got involved because adults of S. noctilio are not obviously distinguishable from those of some of the native species in eastern North America. It was known that species close to S. noctilio belong to two species complexes, the cyaneus and californicus complexes, but further work was needed to resolve the taxonomic problems. Therefore, more or less independently, the first three authors concluded that the North American species required revision. N. M. Schiff studied mitochondrial DNA (cytochrome oxidase 1 – CO1) of most North American and central European species, and provided information about ecology, sampling techniques and associated fungi; H. Goulet studied the species and higher classification based mainly on morphological information, wrote the identification keys and checked several type specimens; and D. R. Smith prepared parts of the introduction and a section on specimens intercepted in North America, refined nomenclatural information, studied type specimens, prepared the reference section and was the main editor. C. Boudreault was responsible for statistics, illustrations, plate design and HTML programming for the web version.
Because Siricidae are large, usually showy insects, most collections have specimens, but because standard collecting methods rarely work to capture adults only a few collections have large numbers of specimens, obtained mostly by rearing. Malaise traps catch a few adults; sweeping and the use of yellow pan traps do not catch any. Adults are most easily collected by rearing from trunks of dead or dying trees. Adults of some species go to the top of hills (Chapman 1954), and if the vegetation is low enough they can be sampled with a net; others are attracted to fire in fire-prone forests and may be hand collected on trunks and stumps.
The 3000-4000 adults of Siricidae in the Canadian National Collection of Insects, Ottawa were almost entirely obtained by Canadian Forest Service staff. Over 70% of the specimens had been reared. This gave us good series of reared specimens from known hosts which greatly helped to resolve taxonomic problems in the Nearctic region. As the work progressed we decided to treat all Western Hemisphere species and world genera. We could not treat the world fauna at species level because most of the species are centered in Asia, a region poorly represented in North American collections.
Viitasaari (1984, 1988) and Midtgaard and Viitasaari (1989) provided us with the main clue to solving species complexes using adult morphology. In their works, ovipositor features were covered systematically. Amazingly, the ovipositor pits (very likely of S. noctilio not S. juvencus as stated) were illustrated much earlier (Hartig 1837), and females of almost every species of Sirex in the New World appear to have a unique set of ovipositor features. The character has not been as significantly useful at species level in other genera but each had a unique combination of other features. Other characters such as larvae (Hartig 1837, Yuasa 1922 [excellent illustrations of the larva of T. columba and many other structures]), male genitalia (Crompton 1919, Chrystal 1928), fine structures of the last tarsomere (Holway 1935), adult spiracles (Tonapi 1958), fore wing cenchrus coupling (Cooley 1896), internal thoracic musculature (Daly 1963), and larval digestive system (Maxwell 1955) were not studied by us. Larvae were not identified by us using morphology; instead, they were more easily and accurately identified using DNA barcodes.
Linnaeus (1758) described the first Siricidae, Sirex juvencus, Urocerus gigas and Xeris spectrum (originally as Ichneumon juvencus, I. gigas and I. spectrum) from the Old World. Sirex juvencus has been intercepted many times at North American ports. In the New World, the first valid species described was Tremex columba (Linnaeus 1763) (originally as Sirex columba), the first of 56 names proposed for our 28 native species. We summarize in 25-year periods the species names proposed and treated as valid here. From 1758–1775, three names were proposed; only T. columba is still in use. 1776–1800, five names were proposed; four are still in use, Sirex cyaneus Fabricius, S. nigricornis Fabricius, Urocerus albicornis (Fabricius) and U. flavicornis (Fabricius). From 1801–1825, two species names were proposed; neither is in use today. From 1826–1850, five names were proposed; Sirex nitidus (T. W. Harris) is in use. From 1851–1875, 17 taxa were proposed; seven species names are in use here, Sirex areolatus (Cresson), S. varipes Walker, Teredon cubensis (Norton), Urocerus californicus Norton, U. cressoni Norton, Xeris caudatus (Cresson), and X. melancholicus (Westwood). Norton and Cresson had good collections at their disposal and together they contributed 38% of the names in use here. From 1876–1900, 13 names were proposed; four are in use here, Sirex behrensii (Cresson), Xeris indecisus (MacGillivray), X. morrisoni (Cresson), and X. tarsalis (Cresson). From 1901–1925, eight species names were proposed; three are in use here, Sirex californicus (Ashmead), S. obesus Bradley, and Urocerus taxodii (Ashmead). By the end of this period, 90% of the named New World species were known. From 1926–1950, two names were proposed; one, Sirex longicauda Middlekauff, is in use here. From 1951–1975, no names were proposed. From 1976–2000, one name was proposed and is still in use; Sirotremex flammeus Smith.
In summary, Cresson proposed nine names, Westwood eight, Ashmead five, Fabricius four, and Kirby four. Of the names proposed by Cresson 67% are valid, by Westwood 12%, by Ashmead 40%, by Fabricius 100%, and by Kirby 0%. The best contributors of valid names are Linnaeus, Fabricius, Walker, Middlekauff, and Smith with 100% success, and Cresson and Norton with 67% success. These seven authors described 76% of the names in use today. Of the 56 species proposed, 22 are still in use in this paper. In this work we add six new species bringing the total number of native species to 28.