Canadian Journal of Arthropod Identification

Taxonomic revision of the Nearctic erosa species group of Phymata Latreille, 1802 (Heteroptera: Reduviidae: Phymatinae)

CJAI 41 -- October 1, 2020

Paul Masonick & Christiane Weirauch

| Abstract | Introduction | Checklist | Materials & Methods | Species Key | Taxonomy | Acknowledgments | References | PDF | Cite |
| Appendix |

Phymata americana Melin, 1931
    Figs 3A–F, 20A, 21A–D. Map 1.

Phymata americana Melin, 1931
Melin, 1931: p6 (original description); Kormilev, 1953: p66 (taxonomy); Kormilev, 1962: p412 (revision); Henry and Froeschner, 1988: p601 (catalog); Froeschner and Kormilev, 1989: p44 (catalog)
Phymata americana wisconsina Melin, 1931
Melin, 1931: p6 (original description)
Phymata americana coloradensis Melin, 1931 syn. nov.
Melin, 1931: p7 (original description); Henry and Froeschner, 1988: p603 (catalog); Froeschner and Kormilev, 1989: p45 (catalog)
Phymata americana ottawensis Melin, 1931
Melin, 1931: p7 (original description)
Phymata pennsylvanica americana Melin, 1931
Evans, 1931: p715 (revision)
Phymata americana americana Melin, 1931
Kormilev, 1953: p66 (taxonomy); Kormilev, 1962: p412 (revision); Henry and Froeschner, 1988: p601 (catalog); Froeschner and Kormilev, 1989: p44 (catalog)

Diagnosis: Recognized from other species of the Nearctic erosa group by the following combination of characters: (1) the relatively large size (~8–11 mm), (2) integument lacking elongated setaceous granulation, (3) lateral margin of anterior pronotal lobe never keeled, (4) lateral and posterior pronotal angles prominent and often acute, (5) posterior pronotal disk punctate, (6) connexiva of abdominal segments 3–4 pale, each usually with a dark marginal spot (may be absent in teneral forms), (7) lateral margins of connexiva of abdominal segments 4–5 more or less straight, and (8) wing membrane brownish.

Redescription: Male: Medium to large, total length: ~8.15–9.15 mm; width across lateral angles of pronotum: ~3.08–3.67 mm. STRUCTURE: HEAD (Fig. 3B): distiflagellomere shorter in length than pedicel + basiflagellomere (dflg : pd + bflg = ~0.89). THORAX (Fig. 3E, 20A): thoracic surface matte; anterior pronotal disk without elongated setaceous granulation; posterior pronotal disk punctate; area between lateral pronotal notch and longitudinal carina of the posterior pronotal lobe either with diffuse granulation (most eastern populations) or without granulation (most western populations); longitudinal carina with or without prominent knoblike tubercle; lateral margin of anterior pronotal lobe not keeled; lateral notch of medium depth; lateral margin of pronotum from lateral notch to lateral angle smooth or with light crenulation; lateral angle prominent and acute; posterior angle prominent and acute; lateral surface of forefemur smooth or sparsely granulated; lateral surface of thorax smooth or sparsely granulated; forewing membrane brown, cloudy, not hyaline. ABDOMEN (Fig. 3C): posterior corners of connexiva of abdominal segments 2–4 weakly serrate or dentiform; lateral margins of connexiva of abdominal segments 4–5 more or less straight; lateral margins of connexiva of abdominal segments 3–6 with or without fine granulation; connexivum of abdominal segment 5 less than twice as wide as connexivum of abdominal segment 4; connexivum of abdominal segment 6 rhomboidal, anterior and posterior margin roughly the same width. COLORATION (Figs 3A-E): variable; anterior pronotal lobe usually with dark marking; forefemur pale, never darkened; corium with a conspicuous transverse band; lateral thoracic surface predominantly black, with light-colored granulation; connexiva of abdominal segments 3–4 usually with dark basal spots; spiracle of abdominal segment 6 usually not enclosed by dark pigmentation. Female: Large, total length: ~9.59–10.73 mm, width across lateral angles of pronotum: ~3.38–4.31 mm. COLORATION (Figs 3A,F): variable; generally much lighter in color overall than males; pronotum with large light-colored areas interspersed with brown markings; lateral thoracic surface predominantly light in color; lateroventral surface of abdominal sternites 5–7 without brownish coloration.

Biology: Phymata americana is typically found in open grasslands and shrublands and has been collected from a wide variety of flowering plants, particularly many species of Asteraceae. The presence of P. americana on flowering vegetation has been shown to affect the behavior of pollinators and other floral visitors (Elliott and Elliott 1991). The life history and broad predatory habits of P. americana were documented by Balduf (1939, 1940, 1941, 1943). Differences in feeding behavior and morphology of males and females were documented by Mason (1977). Ambush site selection (patch choice) of P. americana has also been examined (Greco and Kevan 1995; Kevan and Greco 2001).

Distribution: Widespread, ranging across southern Canada, northeastern US, Great Lakes region, Great Plains, westward to the Rocky Mountains, and into the deserts and shrublands of the southwestern US and northern Mexico. While this species is found primarily east of the Rocky Mountains, specimens have been found as far west as Arizona. Based on our survey of museum material and iNaturalist observations, P. americana appears to be largely absent from the southeastern United States. Most erosa group specimens examined from this region fit the revised descriptions of other taxa (i.e., either P. pennsylvanica, P. fasciata, or P. mystica) more closely than the description of P. americana above.

Discussion: Phymata americana is one of the most common ambush bug species in North America and its broad geographic range has presumably resulted in morphological variation. Froeschner and Kormilev (1989) recognized four subspecies of P. americana. Molecular analyses have subsequently revealed that P. americana sensu lato consists of three distinct groupings, one that includes the nominate subspecies, P. americana coloradensis, and P. pennsylvanica, a second that consists of P. americana metcalfi and P. pacifica stanfordi, and a third represented by P. americana obscura, a species restricted to the northern Great Basin and Palouse region. Phymata arctostaphylae also renders P. americana sensu lato paraphyletic with it being more closely related to western P. americana subspecies (metcalfi and obscura) than eastern taxa. Given their divergent morphologies and distinct geographic ranges, we treat each of these groupings as a separate species and hereby synonymize P. americana coloradensis with the nominate subspecies. The main differences between these geographical varieties is coloration and the presence or absence of a prominent knoblike tubercle on each of the longitudinal carinae of the posterior pronotal lobe with the former (western populations) exhibiting lighter coloration and larger protuberances than the latter.Despite that molecular data sequenced to date have yet to clearly separate P. americana and P. pennsylvanica (see Masonick and Weirauch, 2020), we treat them as different species due to size and morphological differences (refer to Fig. 23). Punzalan and Rowe (2017) suggested that these two taxa likely engage in hybridization where they come into contact and may give rise to individuals that exhibit intermediate forms of the two phenotypes.

Identification remarks: Phymata americana typically lacks a very dense granulation patch (like that of P. fasciata or P. pacifica) between the lateral notch and longitudinal carina of the posterior pronotal lobe. Granulation is usually present and diffuse here on many specimens from the eastern United States and Canada (see pronotum of male and female specimens in Figs 3E–F). Specimens from western populations tend to lack granulation in this area. Some male specimens (particularly those from western North America) have serrate or dentiform connexiva on abdominal segments 2–4 and may exhibit relatively dilated abdomens that resemble P. mystica (see male P. americana specimen in Key(2) Couplet 17). The following characteristics of P. americana help to separate it from P. pennsylvanica: (1) males witha distiflagellomere that is shorter than the pedicel and flagellomere combined, never distinctly longer, (2) pronotum usually with large, conspicuous light colored markings (dark pigmentation of pronotum of P. pennsylvanica is typically more uniform and widespread), (3) transverse band on corium light in color, (4) uneven margins of connexiva of abdominal segments 2–4, (5) connexivum of abdominal segment 5 not abruptly dilated in males, (6) dark colored ventral region of pro- and mesopleura in males, (7) lack of dark pigmentation encircling spiracle on sternite 6, (8) presence of peaks or protuberances along the longitudinal carinae of the posterior pronotal lobe (these are especially prominent among western populations, see Key(2) Couplets 8’ and 17 for examples of P. americana specimens with prominent peaks), and (9) presence of long and prominent multibranched preocellar and ocellar processes (these processes tend to be slightly smaller in P. pennsylvanica).

Type information: Melin’s type series of P. americana, P. americana coloradensis, P. americana ottawensis, and P. americana wisconsina are deposited in the Swedish Museum of Natural History, Stockholm, Sweden. We here designate one of these specimens to serve as a lectotype for P. americana. As only images of a few specimens from these type series were examined for this study, we were unable to verify if the remaining syntypes are actually conspecific. Images of the following specimens were examined:
LECTOTYPE: (Phymata americana Melin, 1931): Male: [country not specified]: Ottawa, Johansen, (UCR_ENT 00123195) (NHRS-GULI000075674 (NRM). Fig. 21A. Image:
SYNTYPE: (Phymata americana coloradensis Melin, 1931): Male: USA: Colorado, Morrison, (NRM). Fig. 21B. Image:
SYNTYPE: (Phymata americana ottawensis Melin, 1931): Female: [country not specified]: Ottawa, Johansen, (NRM). Fig. 21C. Image:
SYNTYPE: (Phymata americana wisconsina Melin, 1931): Female: USA: Wisconsin, Kumlien, (NRM). Fig. 21D. Image:

Additional material examined: See Appendix; 1,265 specimens, including 755 adult males and 503 adult females.