Fig. C37.1, Schiff et al. 2006: 14, 15 (female with black wings and mainly black banded abdomen, habitus)
Fig. C37.2 (female with yellowish brown wings and mainly black banded abdomen, habitus)
Fig. C37.3 (female with black wings and almost completely reddish brown abdomen, habitus)
Fig. C37.4 (female with yellow wings and mainly yellow banded abdomen, habitus)
Fig. C37.5, Schiff et al. 2006: 13 (male habitus)
Fig. C36.1 (live female with yellowish brown wings and mainly black banded abdomen)
Fig. C37.6 (live male)
Figs. C37.8, C37.9 & C37.10 (maps)
Both sexes of Tremex columba have short setae covering the body, e.g., setae of frons about 0.5 times as long as distance between inner edges of the lateral ocelli. Females have the cornus angular in lateral view along its ventral edge near base. Males have metatarsomere 5 as long as metatarsomere 2.
Color. Head mainly reddish brown. Surface around ocelli, often behind dorsal margin of eye, and medially behind ocelli black; antenna light reddish brown, but sometimes blackened in middle (Fig. B1.24); maxillary palp black to reddish brown; mandible mainly black. Pronotum reddish brown and ventrolaterally black; propleuron black; mesonotum mainly reddish brown, black in lateral half of mesoscutum; mesepisternum black and reddish brown over 0.5 to entire lateral surface; metathorax black. Coxae and trochanters black; pro- and mesofemur mostly reddish brown, and metafemur mostly black; tibiae and tarsi pale yellow. Wings almost black, lightly to darkly yellowish brown, or yellow tinted. Tergum 1 or 1 and 2 mostly, terga 2–8 or 3–8 at side, narrowly or broadly across base, tergum 9 from a small lateral spot to most of surface, and tergum 10 completely to mainly reddish brown (Fig. A3.3), remaining surfaces black, or completely reddish brown. Sterna 2–7 black in basal 0.5 and reddish brown in apical 0.5, or completely light reddish brown. Sheath mainly reddish brown.
Head. Frons in lateral view with setae about 0.5 times as long as distance between lateral ocelli (Fig. B3.1), and with mostly contiguous and large pits (diameter about 0.4–0.5 times lateral ocellus diameter), but as a narrow band less dense on gena behind eye (Fig. B3.1). Postocellar region in frontal view scarcely elevated. Antenna clearly shorter than coastal cell length of fore wing; flagellum widened at middle, and with 11–14 flagellomeres (Fig. B1.24).
Thorax. Pronotum in dorsal view with numerous coarse teeth over surface. Mesonotum densely (pits 0.5–1.0 pit diameter apart) and coarsely pitted. Metatarsomere 2 in lateral view with dorsal margin clearly convex, about 3.0 times as long as high (Fig. B3.7), and tarsal pad 0.3 times as long as its ventral length. Fore wing with length of cell 2R1 subequal to cell 3R1 length.
Abdomen. Setae short and present on median region of terga 1, 5 and 6, more widespread on posterior half of terga 7 and 8 and laterally on terga 1–9, dense only medially on tergum 1, scattered elsewhere (distance about as far apart as length of setae). Tergum 9 laterally with surface anterior to each seta slightly raised and smooth (pits not clearly outlined), and distant from other raised surfaces (Fig. B3.5). Median basin of tergum 9 flat, 1.5–1.7 as wide as long, with base (delimited by small longitudinal furrows) 0.8–0.9 times as long as median length, with small teeth present posterolaterally, each tooth with small seta (Fig. B1.30). Tergum 10 in dorsal view about 1.2 times as long as median length of median basin, with teeth over dorsal surface and along lateral edges in apical half, and with round angular projection in basal 0.3 laterally (also visible in lateral view) (Figs. B1.30 & B3.3). Sheath. Basal section 1.15–1.25 times as long as apical section. Apical section about 0.4 times as long as fore wing length. Ovipositor. Lancet with 18–22 annuli, and with annuli outlined only under apical section of sheath (Fig. C37.7). Pitted section about as long as length of apical section (Fig. C37.7); annulus 1 outlined and without or with a very small pit, last annulus before teeth annuli with small pit (Fig. C36.3), preceding annuli each with a well defined pit, and each pit about 0.4 times as long as annulus length; first tooth annulus with sensilla grouped together in a slight impression.
Color. Tibiae and tarsi color pattern variable. In dark specimens, tibiae light reddish brown in basal 0.5 (protibia) to 0.25 (metatibia), and tarsi black dorsally on tarsomeres 1 and 2 of protarsus, completely black on tarsomeres 1–3 of mesotarsus, and on tarsomeres 1–4 of metatarsus; in pale specimens, tibiae and tarsi reddish brown or paler. Abdomen color pattern ranging from mainly black to completely reddish brown. In dark specimens, tergum 1 and most of 2 black, terga 3 and 4 black with reddish-brown transverse band, terga 5–7 black, but pale at side, tergum 8 light reddish brown and reddish brown medially, and sterna 2–8 mainly black; in pale specimens, terga 1–8 and sterna 1–9 completely reddish brown.
Head. Antenna almost thread-like and clearly shorter than costal cell length of fore wing, and middle flagellomeres in lateral view about 1.5 times as long as wide.
Thorax. Metatibia in lateral view about 5.0 times as long as its maximum width and in cross section about 1.5 times as high as its maximum ventral width. Metatarsomere 1 about 4.0 times as long as high. Metatarsomere 5 as long as metatarsomere 2 (Fig. B3.9).
Abdomen. Sterna completely and quite densely pitted. Sternum 8 with apical widely (about 0.5 times width of apical edge) and deeply indented.
Except for T. maurus, we did not examine the type specimens of the other nominal species of T. columba. To determine the synonymy, we referred to the species descriptions, the type localities, and the available illustrations. All descriptions match our concept of T. columba and each name can be assigned to one of the color forms discussed below.
Bradley (1913) recognized three color forms based mainly on abdominal color patterns. We agree with his concept. The palest form (body reddish brown and wings dark brown) is found mainly in the southeastern states north to southern New York and Illinois (Fig. C37.3). The names T. sericeus and T. servillei match this form (Bradley 1913). The darkest form (abdomen mainly black with yellow markings and wings dark brown to yellowish brown) is widespread in eastern North America and is recorded from Saskatchewan to the Atlantic coast and south to Georgia. Dark-winged specimens are found south of southern New York (Fig. C37.1) but become uncommon northward where they are replaced by specimens with yellowish brown wings (Fig. C37.2). The names S. columba, S. pensylvanicus, S. cinctus, S. americana, T. obsoletus and T. maurus are associated with this form (Bradley, 1913). The moderately dark form (abdomen mainly pale reddish brown with black transverse bands and wings yellow tinted) is found in the prairie region north to the extreme southern portion of the Canadian prairies and as far east as Illinois and southernmost Ontario near Lake Erie and in the Rocky Mountain region south into northern Mexico (Fig. C37.4). The name T. columba aureus applies to this form (Bradley 1913). Specimens with intermediate color pattern are known only from the bordering prairie regions in Saskatchewan and Manitoba. The latter specimens are similar to the eastern form with dark abdomen, but the wings are yellow and the apex of the abdomen in females is often more widely pale. The two forms found in the southern half of eastern United States are sympatric and are part of two discrete color forms. We found one female with the abdomen showing the pattern of the two forms, one on each side of the abdomen. Despite some evidence of gene flow in the northernmost part of its range (in the Canadian prairies), females of the western form remain sharply distinct in central Illinois where all three forms occur. Females probably mimic a common vespid species with a matching body and wing color pattern in each of the regions that are present during the main T. columba flight period. The most likely models commonly flying at the time that females of T. columba are ovipositing probably belong to the genus Polistes (Vespidae). Tremex columba females of the reddish abdomen form are similar to P. perplexus Cresson, P. bellicosus Cresson or P. carolinus (Linnaeus), females of the dark form with black wings are similar to P. annularis (Linnaeus), P. metricus Say, or dark winged (southern) specimens of P. fuscatus fuscatus (Fabricius), females of the dark abdomen form with reddish-brown wings are similar to the pale winged P. fuscatus laurentianus Bequaert, and females of the moderately dark form with yellow wings are similar to P. aurifer Saussure and probably other similarly colored western species. Information from morphology and DNA barcoding shows no difference between the three color forms. Therefore, we treat them as discrete color forms of one species.
Early summaries of the biology of T. columba were given by T. W. Harris (1827, 1857), Thomas (1876), Harrington (1882a,1882b), Saunders 1883, Harrington (1893), Riley (1888), Packard (1890), Ashmead (1900), Felt (1905 – damage and life history), and Herrick (1935). Smith and Schiff (2002) provided a recent synthesis, much of it derived from Stillwell (1964, 1967). They also published the emergence times for both T. columba and one of its parasitoid Ibalia anceps. Females attack dead or weaken limbs of deciduous trees. Oviposition starts in mid August and lasts till late September. Females lay 2–7 eggs in each oviposition hole. The oviposition holes are at about a right angle with the bark and go to a depth of 2–15 mm in the sapwood. Eggs either hatch within 15–30 days or over winter and hatch the following spring.
Newly hatched larvae make their tunnels roughly parallel to the bark at a depth less than 4 cm. Larvae go through at most 11 instar stages. Larval development lasts two or more years in cold temperate regions. Larvae cannot develop without the presence of the wood fungus Cerrena (Daedalea) unicolor Bull. Murr. This fungus is associated with females in all stages of development. Females adults carry the fungal spores in mycangia located in the abdomen anterior to the ovipositor. Eggs pick up the fungus as they pass down the ovipositor and the fungus is also injected into the wood at oviposition and starts developing immediately, so by the time a larva hatches there is plenty of fungus to eat. Female larvae have special hypopleural organs to carry the fungal oidia (Stillwell 1965). This organ is found between the first and second abdominal segments below the level of the spiracle (it is also seen in some specimens between the metathorax and the first abdominal segment). At molting, the fungus in the hypopleural organ is not transferred to the later instar larva, but must be picked up again.
In the prepupa, a wax-like substance covers the oidia held in the hypopleural organ. After molting, the spores are introduced into the mycangia of the newly emerged female. Galleries are filled with sawdust and frass and may extend for 1–3 m. Pupae are found in the sapwood to as deep as 30 cm in the heartwood. It takes 3–5 weeks for the pupa to complete its development.
In Canada, emergence of new adults starts in mid August, reaches a peak in early September, and ends in early October. Males start their emergence about one week before females. Females may have to tunnel up to 1 m to emerge. Under such condition a female may lay several hundreds eggs on the way out. These unfertilized eggs will become males. Mated females produce offspring of both sexes. An amazing density of 162 specimens in a small 20” by 10” (50 cm by 25 cm) portion trunk was reported by Laurent (1931). Damage by larvae was described by Thomas (1881).
The main parasitoids are Ichneumonidae (Megarhyssa atrata (Fabricius), M. greenei Viereck and M. macrura (Linnaeus)) and Ibaliidae (Ibalia anceps Say). Species of Megarhyssa are keyed in Townes and Townes (1960), and those of Ibalia in Smith and Schiff (2002).
Tremex columba has been reared from a wide variety of angiosperm trees (T. W. Harris 1827, T. W. Harris 1841, Fitch 1858a, 1857, 1859, Clementi 1868, Walsh and Riley 1868, Riley 1870, Thomas 1876, Thomas 1881, Harrington 1882a, Harrington 1882b, Saunders 1883, Dimmock 1885, 1887, Packard 1881, Packard 1890, Lintner 1897, Fyles 1917, Blackman and Stage 1924, Essig 1926, Davis 1932, Herrick 1935, Smith 1943, Beal and Massey 1945, Middlekauff 1960, Smith 1979: 129, Smith and Schiff 2002). The main hosts are hickories, maples, and elms (83% of records). Based on 218 reared and confirmed specimens, hosts are: Acer sp. (16) , Acer negundo (1), Ac. rubrum (31), A. saccharum (3), Betula sp. (Herrick 1935), Carpinus sp., Carya sp. (86), C. illinoensis (1), Castanea dentata (1), Celtis sp. (3), C. laevigata (4), C. occidentalis (1), Fagus grandifolia (4), Fraxinus sp. (1), Juglans cineria (1), Malus sp., Nyssa sylvatica (2), Platanus sp. (1), Populus sp. (8), Pyrus sp., Quercus sp. (8), Robinia sp. (3), Salix sp. (1), Ulmus sp. (35), U. americanus (6), U. glabra (1). Three host records gymnosperms are unlikely: Picea abies (1), Pinus resinosa (1) (Pinaceae), and Helianthus (2) (Asteraceae).
Based on 126 field-collected specimens, the earliest and latest capture dates are June 3 and October 10. The main flight period is from the second half of July to the first half of October with a peak in the first half of August Stillwell (1964, 1967). Adults of T. columba were not captured at hill tops, but we observed several hundreds specimens swarming around an old dying sugar maple tree. Most specimens were out of reach, above 4–5 m.
CANADA: AB, NB, NS, ON, QC, SK. USA: AL, AR, CA (probably adventive), CO, CT, DC, FL, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NV, NY, OH, PA, RI, TN, TX, UT, VA, VT, WI, WV, WY. Tremex columba is recorded in southern Canada from Alberta to Nova Scotia south to Arizona and Florida (Bradley 1913, Rohwer 1928, Ries 1951, Middlekauff 1960, Stange 1996, Smith 1979) (Figs. C37.8, C37.9 & C37.10). Specimens originating from Mexico were intercepted at entry ports along the United States and Mexico border.
Specimens studied and included for the distribution maps: 955 females and 323 males from BYUC, CASS, CNC, CUCC, CUIC, DEBU, EDUM, FRLC, FSCA, GLFC, LEMQ, MNRQ, NCSU, NFRC, OSAC, UASM, UCRC, USGFS–GA, and USNM.
Specimens for molecular studies: 21 specimens. See Fig. E2.2.
CANADA. Ontario: 2007, SIRCA 023, 604; 2007, SIRCA 025, 618; 2007, SIRCA 026, 619; 2007, SIRCA 027, 624; 2007, SIRCA 028, 624. USA. Arkansas: 1999, CBHR 110, 658. Georgia: 2006, CBHR 573, 658. Illinois: 2006, CBHR 373, 658. Michigan: 2007, CNCS 1047, 616; 2007, CNCS 1048, 557; 2007, CNCS 1050, 596; 2007, CNCS 1051, 628; 2007, CNCS 1052, 609. Minnesota: 2008, CBHR 1464, 597. Mississippi: 1997, CBHR 5, 658; 2002, CBHR 131, 658; 2002, CBHR 132, 658. Montana: 2006, CBHR 370, 658. New York: 2005, CBHR 201, 658. Oregon: 2008, CBHR 400, 658. South Carolina: 2006, CBHR 892, 508.