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Revision of the World species of Xeris Costa (Hymenoptera: Siricidae)
CJAI 28 -- September 25, 2015
doi: 10.3752/cjai.2015.28
Henri Goulet1, Caroline Boudreault1 and Nathen M. Schiff2

7. Xeris indecisus (MacGillivray)

Fig. C7.1, (female with reddish-brown abdomen, habitus); Schiff et al. 2006: 84, 85

Fig. C7.2, (female with black abdomen, habitus); Schiff et al. 2006: 95, 96

Fig. C7.3, (male with reddish-brown abdomen, habitus); Schiff et al. 2006: 83

Fig. C7.4, (male with black abdomen, habitus); Schiff et al. 2006: 91

Fig. C7.5 (live male with dark abdomen)

Fig. C7.6 (live female with dark abdomen)

Urocerus indecisus MacGillivray, 1893: 243. Holotype male (INHS, Webb 1980), not examined. Type locality, near Olympia, Washington. Frison, 1927: 268 (type); Schiff et al., 2012: 253.

Xeris morrisoni; Konow, 1898b: 226 (not Cresson, 1880: 35). Bradley, 1913: 24; Essig, 1926: 774–775 (hosts); Bedard, 1938: 194 (host); Hedicke, 1938: 23 (catalog); Ries, 1951: 84 (catalog), Middlekauff, 1960: 69 (taxonomy, hosts and parasitoids); Morris, 1967: 60–62 (host).

Xeris morrisoni indecisus; Maa, 1949: 85 (change in combination and rank). Burks, 1958: 17 (catalog); Smith, 1979: 129 (catalog); Taeger et al., 2010: 105 (catalog).

Xeris spectrum townesi Maa, 1949: 88. Holotype female (USNM), examined by D. R. Smith and H. Goulet. Type locality: “Hoquiam [Washington]”. Burks, 1958: 17 (catalog), Burks, 1967: 27 (catalog); Smith, 1979: 129 (catalog); Taeger et al., 2010: 105. Synonymized by Schiff et al., 2012: 253.

Xeris indecisus; Schiff et al., 2012: 253 (change in rank).

Diagnostic combination

Among specimens without a longitudinal band on the lateral margin of the pronotum and with dense pits between dorsoposterior edge of eye and occiput outside postocellar area [indecisus, cobosi, degrooti, himalayensis, morrisoni, tarsalis and tropicalis], X. indecisus is recognized in both sexes by the wide gena (in frontal view maximum width between the outer edges of eyes clearly less than maximum width between genae), the narrow, sharp and mainly smooth transverse ridge above the mandible, the reddish-brown or black abdomen and, in females, by the lightly tinted wings with darkly tinted apical and median bands and by the light reddish-brown flagellum or apical 0.3 of flagellum. However, females and males of X. indecisus with reddish-brown abdomen from the central Rocky Mountain region can only be distinguished from those of X. degrooti by their barcodes.



Color. Head black except for large white spot on gena dorsal to middle of eye extending down to genal ridge (Fig. B2.46); flagellum black but reddish brown on 8–12 apical flagellomeres (black abdomen form) (Fig. B2.51), or completely light reddish brown (reddish-brown abdomen form, but unusually also for the black abdomen form) (Fig. B2.52); last maxillary palpomere reddish brown (at least at base) or black. Thorax completely black (Fig. B2.57) or with small to large white spot on vertical surface near anterolateral angle of pronotum (spot absent in dorsal view, or present and very narrow) (as in Figs. B2.54 and Fig. B2.55). Legs above coxae light reddish brown (Figs. C7.1 and Fig. C7.2); coxae almost all light reddish brown except on surface at dorsal angle (especially in specimens with reddish-brown abdomen) to brown (Fig. B2.53), or black with reddish-brown apex (Fig. C7.2). Fore and hind wings lightly tinted brown but fore wing with a clearly outlined darker band below base of stigma in cells 1R1, 1M and 2CU and in apical 0.25 (Fig. B2.66) or rarely wing darkly tinted (as in Fig. B2.65); costal cell brown (as in Fig. B2.39); veins dark brown or black (including veins C and R, and base of stigma around junction with vein 1r-rs) (as in Fig. B2.39). Abdomen segments 1 or 1 and 2 black, and segments 2–10 or 3–10 reddish brown (pale form) (Fig. B2.60), or abdomen black (Fig. B2.61). Sheath with apical section black and basal section reddish brown.

Head. Distance between nearest eye edge and lateral ocellus edge about 1.1–1.5 times as long as distance between inner edges of lateral ocelli (as in Fig. C1.5). Setae on clypeus about as long as diameter of a lateral ocellus (Fig. B2.77). Eye in lateral view (N = 20) with its maximum height 1.36–1.67 times as long as its maximum length (Fig. B2.77), and maximum height of eye 0.42–0.50 times as long as maximum height of head (from transverse ridge on gena above mandible to top of head) (as in Fig. B2.77, measurements as in Fig. B2.8). Gena in dorsal view with maximum distance between outer edges clearly wider than maximum distance between outer edges of eyes (B2.41) (in frontal view outer edges of eyes clearly not intersecting genae) (as in Figs. B2.5); in lateral view with distance between outer edge of eye and genal ridge 0.50–0.64 times as long as maximum length of eye (Fig. B2.77), with almost no pits ventral to genal ridge, and with many medium size pits (diameter of pit 0.2–0.25 times lateral ocellus diameter) between outer edge of eye and genal ridge (mainly near eye) (Fig. B2.77). Transverse ridge above mandible narrow, sharp and mainly smooth (Fig. B2.77). Vertex quite densely pitted and pits medium in size (diameter of pit about 0.3 times lateral ocellus diameter), pits present from dorsoposterior edge of eye to occiput outside postocellar area, absent on most of postocellar area (B2.41); pits dense, narrowly distributed and medium in size along median furrow (not sharply outlined), a little more widespread near lateral ocelli (as in B2.41).

Thorax. Pronotum in lateral view with coarse polygonal pits on 0.1–0.7 (commonly 0.2 to 0.3) of posterior surface (as in Fig. B2.97). Propleuron in lateral view with medium size polygonal pits on most of surface (as in Fig. C12.7); in ventral view with scattered to moderately dense small teeth with smooth surface in between (as in Fig. B2.22). Transcutal furrow of mesonotum clearly outlined  and finely sculptured, thus mesoscutum and axilla clearly distinct (as in Fig. C5.2). Fore wing in middle 0.3 of vein 2A diverging very rarely slightly (as in Fig. C11.6) to usually considerably (as in Fig. C12.6) away from wing edge, and then more (as in Fig. C11.6) or less (as in Fig. C12.6) abruptly curved away from wing edge; vein 3A absent (81%), reduced to a stump (18%), or rarely extending slightly as a nebulous vein (1%), but not extending along posterior margin of wing.

Abdomen. Tergum 9 with meshes of microsculpture on ventral half below and above longitudinal furrow near center not well impressed and sculpticells clearly flat (slightly raised as scale above furrow) (as in Fig. B2.93, insert); median basin with base (outlined by two lateral black longitudinal furrows) 0.7 times as wide as its median length, with maximum width of basin 1.3 times as wide as its median length, and median length 0.5 times as long medially as median length of cornus (measurements as in Fig. A3.2). Cornus constricted in dorsal view, its minimum width (at constriction) 0.8 times as wide as maximum width of cornus subapically; with large teeth in apical 0.3 (as in Fig.B2.110). Sheath. Basal section 0.20–0.31 times as long as apical section (N = 60) (Figs. C7.1 and C7.2); lateral surface of apical section with well-defined ridge (as in Fig. B2.13, insert); length 1.2–1.5 times as long as fore wing length. Ovipositor. Lancet with 26–33 annuli (first 15 annuli difficult to see, but still outlined; N = 15); junction of basal and apical sections of sheath aligned between 2nd–3rd annuli, at 3rd annulus or between 3rd–4th annuli; major pits present on last 4–6 apical annuli before teeth annuli and with a very small pit on at most each of the 6 preceding annuli (as in Fig. C1.18).


Color. Head with dorsal spot behind as large as in females (Figs. C7.3 and C7.4). Antenna, coxae, femora (pro– and mesofemur black in most specimens to mainly reddish brown in some), tibiae (except for diffused brown spot at very base in some specimens) and tarsi (except reddish-brown tarsomeres 3–5 or 4 and 5) black. Pronotum in dorsal view black (Fig. B2.57) or with white spot extending at most toward posterolateral angle (as in Figs. B2.55 and B2.58). Fore wing basically clear (Figs. C7.3, and C7.4). Abdomen black on segments 1 and 2 and laterally on terga 3–8, and reddish brown elsewhere (pale form) (Fig. C7.3), or completely black (dark form) (C7.4).

Thorax. Metatibia with shallow notch on dorsal edge in basal 0.25 (Fig. B2.68).

Taxonomic notes

The holotype of Urocerus indecisus was not examined. The description (especially the femora and pronotal color pattern) matches our concept for this species.

Xeris spectrum townesi specimens share with X. indecisus the large spot size on the gena, and the denser pits on the gena and vertex; females share the flagellum and the pronotum color, and males share the pronotum and metafemur color. Males of the pale abdomen form match the description of the type of U. indecisus, and females of the black abdomen form match Xeris spectrum townesi. Both sexes of both color forms are easily associated. Both color forms have the same range and adults are often found together. The pale abdomen and dark abdomen forms were classified until now as two species (Maa 1949, Ries 1951, Middlekauff 1960, Smith 1979). Information from morphology and DNA barcoding confirms that the two color forms belong to the same species.

Xeris indecisus has been ranked as a subspecies of X. morrisoni (Maa 1949, Middlekauff 1960, Smith 1979). However, the information from morphology and DNA barcoding confirms that the two populations are distinct (Schiff et al. 2012).

Specimens of X. indecisus from the central Rocky Mountain region with reddish-brown abdomen and in females with darkly tinted wings could be confused with those of X. degrooti. Adults of both species cannot yet be segregated on structures. See “Taxonomic notes” under X. degrooti.

Though the side of the vertex is densely pitted in X. himalayensis and X. cobosi, females of these two species have a black flagellum whereas those of X. indecisus have the apical 0.3 or all of the flagellum light reddish brown. Males of X. himalayensis (male unknown in X. cobosi) have a clearly outlined yellowish-white spot at the base of the metatibia whereas those of X. indecisus have a dark brown poorly defined spot at the base of the metatibia or have a completely black metatibia.

Geographical variation

Adults of X. indecisus have two distinct color forms: the abdomen is either mainly reddish brown or completely black. Both color forms are known from the coastal and interior regions of British Columbia south to California. We cannot recognize any geographical variation pattern between these two color forms.

Less obvious are variations in ovipositor length. The basal section of the sheath is proportional to body size, but the apical section is not. We calculated the ratio between the basal and apical section as a general measure of relative size for the ovipositor. Females (N = 10) from Lake Tahoe, California, have a ratio of 0.20–0.25 (mean = 0.23). In Oregon and British Columbia, females (N = 44) have ratios of 0.20– 0.32 (average 0.25). Therefore specimens from California have a relatively longer apical section of the sheath. DNA barcodes based on 21 specimens from regions with long and short ovipositors do not segregate specimens into two groups. We see no reasons to recognize subspecies.

However, in the central Rocky Mountain region, there are no specimens of X. indecisus with a black abdomen. All specimens have a reddish-brown abdomen and wings of females are darkly tinted. We do not want to officially recognize this population as subspecifically distinct because the sample is rather small and the females of this species and X. degrooti cannot be recognized except by their DNA barcodes.

Hosts and phenology

Xeris indecisus has a wide host range (Bedard 1938 – under X. morrisoni, Cameron 1965, Morris 1967). Based on 121 reared and confirmed specimens, all but one host are Pinaceae: Abies sp. (13), A. concolor (17), A. grandis (10), A. lasiocarpa (8), A. magnifica, Larix occidentalis (12), Picea sp. (1), P. sitchensis (10), Pinus contorta (2), P. ponderosa, Pseudotsuga menziesii (28),and Tsuga heterophylla (20). There is only one record from Calocedrus decurrens (Cupressaceae).

Based on 24 field-collected specimens, the earliest and latest capture dates are May 18 and September 11. The main flight period is from the first half of June to the first half of September.


Canada: Britsh Columbia. United States: California, Colorado, Idaho, Montana, Nevada, Oregon, South Dakota, Utah, Washington. Xeris indecisus, a widespread western species in forested regions, is recorded from British Columbia, Montana, and South Dakota to California, Arizona and Colorado(Burks 1967, Cameron 1965, Smith 1979) (see map C42.6 in Schiff et al. 2012). The specimens of X. indecisus recorded by Burks (1967) under X. spectrum townesi from Arizona need confirmation as they could be specimens of X. chiricahua. One female from the west coast of the United States was intercepted in Osaka, Japan (Okutani 1965). We have seen a female intercepted in New Zealand (FRNZ and PANZ) and one more intercepted at Slough (near Windsor, England) as an infestation in a control laboratory (BMNH).

Specimens studied and included for distribution map: 234 females and 113 males BYUC, CFIA, CNC, DEBU, EDUM, MTEC, OSAC, PFRC, ROME, UASM, UCRC, USFS–GA, USFS–MS, and USNM.

Specimens for molecular studies: 29 specimens from Canada (British Columbia) and United States (California, Colorado, Oregon and Washington). See Fig. D1.2c. For each specimen the following is recorded: country, year, state/province, specimen code (in italics), and number of base pairs.

CANADA. British Columbia: 2006, CBHR 418, 658; 2006, CBHR 419, 658. USA. California: 1999, CBHR 33, 658; 1999, CBHR 98, 658; 2007, SIR 075, 421; 2007, SIR 076, 600; 2007, SIR 077, 586; 2007, SIR 078, 654. Colorado: 2005, CBHR 189, 658. Oregon: 1999, CBHR 108, 658; 2006, CBHR 385, 658; 2006, CBHR 1078, 658; 2007, SIR 074, 421; 2007, SIR 080, 615; 2007, SIR 081, 421. South Dakota: 2007, CNCHYM 02489, 422; 2007, CNCHYM 02493, 422; 2007, CNCHYM 02492, 129; 2007, CNCHYM 03050, 410; 2007, CNCHYM 03051, 374. Utah: 2008, CNCHYM 03047, 382. Washington: 2005, CBHR 210, 658; 2005, CBHR 215, 658; 2005, CBHR 216, 658; 2005, CBHR 228, 658; 2005, CBHR 235, 658; 2005, CBHR 239, 658; 2005, CBHR 254, 658; 2008, CBHR 1310, 658.

Table of contents Abstract Introduction Materials and Methods Biology Hosts Parasitoids Morphology Key DNA References Citation Appendices PDFs