Among specimens with a lateral longitudinal band on the pronotum and with short setae on the head [caudatus], both sexes of X. melancholicus are recognized by the very small pits (pit diameter 0.1–0.2 times lateral ocellus diameter) and very few pits on the gena between the upper and lower limits of the genal ridge, and the small white spot that usually does not extend to the genal ridge. Females also have completely light reddish brown coxae (except for the black anterior and posterior dorsal edges), and generally longer apical section of the sheath (basal section/apical section ratio more than 0.27 for most specimens). Males of melancholicus cannot be separated from males of caudatus.
Color. Head black except for small white spot behind eye; white spot usually not extending down to genal ridge (Fig. B5.41); antenna black. Thorax black except for white longitudinal band extending from posterolateral to anterolateral angles including vertical portion of anterior angle (Fig. C43.3). Legs light reddish brown but narrowly black at dorsal coxal articulation (Fig. C43.1). Fore and hind wings almost completely clear except for a very lightly tinted darkened band before stigma and in apical 0.25; fore wing very lightly tinted in cell 2CU, costal cell brown and most of surface behind anal cells yellowish brown, veins black (including veins C and R, and vein 1r-rs near junction with stigma) (Fig. B5.17). Abdomen black. Sheath with apical section black and basal section reddish brown.
Head. Eye in lateral view (20 specimens measured) with maximum height 1.37–1.64 times as long as maximum length, and maximum height of eye 0.42–0.51 times as long as maximum height of head (from transverse ridge on gena above mandible to top of head) (Fig. B5.7). Gena in dorsal view with maximum distance between outer edges clearly wider than maximum width between outer edges of eyes (in frontal view outer edges of eyes clearly not intersecting genae) (Fig. B5.4), and in lateral view distance between outer edge of eye and genal ridge 0.48–0.61 times as long as maximum length of eye (as in Fig. B5.27). Transverse ridge above mandible narrow, sharp and mainly smooth (as in Fig. B5.21). Head in dorsal view with pits restricted to vertex (scarcely pitted from dorsoposterior edge of eye to occiput) and postocellar area (scattered or absent on most of median furrow, but a little more widespread near lateral ocelli) (Fig. B5.2), in lateral view pits almost absent on gena ventral to genal ridge, and few and very small (diameter of pit 0.1–0.2 lateral ocellus diameter) between outer edge of eye and genal ridge (mainly near eye) (Fig. B5.43).
Thorax. Fore wing vein 3A absent (73%), reduced to a stump (24%) or rarely extending toward posterior wing edge as a nebulous vein (3%), but not extending along posterior margin of wing.
Abdomen. Median basin of tergum 9 with base (outlined by two lateral black longitudinal furrows) 0.8 times as wide as median length, maximum width of basin 1.6 times as wide as median length, and basin 0.5 times as long medially as median length of cornus (Fig. C39.2). Cornus constricted in dorsal view, its minimum width (at constriction) 0.8 times as wide as maximum width subapically (Fig. C39.2). Sheath. Length 1.2–1.4 times as long fore wing length; basal section 0.24–0.35 times as long as apical section (Fig. C43.4); lateral surface of apical section with well defined ridge (Fig. B5.13, see insert). Ovipositor. Lancet with 25–29 annuli (first 15 annuli hard to see, but still outlined; N = 14) (Fig. B5.15); junction of basal and apical sections of sheath aligned between 2nd and 3rd, at 3rd, or 3rd and 4th annuli; major pits present on 4-5 apical annuli before teeth annuli (Fig. B5.15), and 7–15 preceding annuli with a very small pit (Fig. B5.15).
Color. Coxae, tibiae (except very base) and tarsomeres 1–5 black (apical segments sometimes brown or reddish brown in old or teneral specimens); femora completely or mainly, and extreme base of tibiae (not sharply outlined but gradual shift) reddish brown (Fig. B5.51).
Thorax. Metatibia with shallow notch on dorsal edge in basal 0.25.
Initially we thought that X. caudatus was a well defined and widespread species. We had several barcoded specimens from eastern North America confirming our concept. However, it was not to remain so straight forward. NMS reported a population from the Cascade Mountains, Washington, based on recent DNA barcoded specimens. For more information see “taxonomic notes” under X. caudatus.
As more specimens from western North America became available, we noticed that the eastern population had a shorter apical section of the sheath relative to the basal section. We carefully measured all the available specimens and confirmed a marked difference in the sheath length between the eastern and western populations. We also measured the basal and apical sections of the sheath. To insure an accurate measurement of the apical section we had to consider two situations. If the apical section covered the ovipositor we recorded its length because the apical section is straight or almost so, but if the apical section was separated from the ovipositor we measured its length up to the end of the ovipositor because the ovipositor is straight whereas the apical section of the ‘detached’ sheath is curved and therefore gives a shorter (and inaccurate) length measurement. The ratio derived from the basal section length relative to that of the apical section for the eastern unit (42 specimens) gave a mean = 0.295 (standard deviation = 0.031) and the western unit (73 specimens) gave a mean = 0.237 (standard deviation = 0.016). There is a difference of 1.25 standard deviations between the mean of the two populations. Based on a difference of two standard deviations, the overlapping zone is 0.25–0.27. Therefore, 75% of the females of each population could be segregated correctly, and specimens with values between 0.25 and 0.27 are of uncertain status. Moreover, in Alberta both populations exist sympatrically. Therefore, we consider the eastern and western populations as specifically distinct.
Two names apply to this complex. Cresson’s type of U. caudatus is a female from Colorado and is associated with the western species. Cresson’s name is older, However, we do not know if the eastern species is named or not. We could not assign the male holotype of S. melancholicus to this species with certainty because we did not have a diagnostic character for distinguishing males of the western X. caudatus from those of the eastern species. The male of S. melancholicus is probably a specimen from a region east of the Rocky Mountains because most of Westwood’s new species of Siricidae are from eastern North America. If so, Westwood’s type would match the eastern species. However, we are not certain because Westwood did describe one western species of Siricidae. In spite of this and to avoid creating a synonym, we decided to assign Westwood’s name to X. melancholicus rather than describing it with a new name.
Specimens of X. melancholicus like X. caudatus are quite easily distinguished from other New World species of Xeris using the key. We discussed under X. caudatus the differences between X. caudatus and named species of the X. spectrum species complex from Eurasia. The discussion about the Eurasian species and X. melancholicus is the same as that given under X. caudatus and so is not repeated.
Males and females of X. melancholicus were observed aggregating at the highest point of Mount Rigaud, Quebec. Though mating was not observed then, we assume that both sexes get together for this purpose.
Xeris melancholicus has a wide host range (Middlekauff 1960, Stillwell 1960, Cameron 1965, Morris 1967, Kirk 1975). Based on 24 reared and confirmed specimens, all are Pinaceae: Abies balsamea (15), Larix occidentalis, P. glauca (4), and Pinus banksiana (5).
Based on 155 field-collected specimens, the earliest and latest capture dates are June 12 and August 18. The main flight period is from the second half of June to the first half of August with a peak in the second half of July. We collected 11 specimens (3 females and 8 males) though more were seen at the summit of Mount Rigaud, Quebec, between June 15 and June 27 (1985 to 2011).
CANADA: AB, BC, MB, NB, NS, ON, QC, SK. USA: CT, ME, MI. Xeris melancholicus, a widespread species, is recorded from the central Alaska, northernmost British Columbia and central Alberta to Newfoundland, Michigan and Connecticut (Fig. C40.6).
Specimens studied and included in the distribution map: 126 females and 54 males from BDUC, CNC, FRLC, GLFC, LEMQ, MNRQ, NFRC, UAM, USFS–AK, USFS–GA, USFS–MS, and USNM.
Specimens for molecular studies: 13 specimens. See Fig. E2.3.
CANADA. Alberta: 2008, CNCS 1086, 576; 2008, CNCS 1087, 563; 2008, CNCS 1088, 515; 2008, CNCS 1089, 579. Nova Scotia: 2006, CBHR 297, 658; 2005, CBHR 300, 658. Ontario: 2007, SIRCA 041, 624; 2007, SIRCA 042, 616. USA. Michigan: 2005, CBHR 203, 658. Minnesota: 2008, CBHR 1375, 658; 2008, CBHR 1461, 534; 2008, CBHR 1462, 578. New York: 2006, CBHR 603, 658.