Syzeton Blackburn 1891
Creators: name: Gompel, Nicolas
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Aderidae
Syzeton

description: Taxonomic status of Syzeton Blackburn, 1891
Werner (1990) treated the species discussed in this paper as part of the genus Zonantes Casey, 1895 (type-species: Xylophilus subfasciatus Leconte, 1855). In his monography, however, Báguena Corella (1948) considered the North American genus Zonantes a subgenus of the Australian genus Syzeton Blackburn, 1891 (type species: Syzeton laetus Blackburn, 1891, fixed by Nardi (2007)). A superficial overview of species respectively assigned to each of these two genera shows a great degree of morphological similarities. Dr. Traci Grzymala confirmed this impression in her doctoral thesis (2016) by revisiting the taxonomic status and investigating the phylogenetic relationships of these two genera. She concluded:
“ The genus Zonantes was recovered as a clade within Syzeton in the concatenated analysis, rendering Syzeton paraphyletic. No single gene analysis recovered Syzeton and Zonantes as distinct clades and there are no consistent morphological differences found between these two taxa”.
She therefore proposed Zonantes as a synonym of Syzeton. Her doctoral work not being formally published as required by the ICZN, this synonymy is not effective. I therefore propose to validate it here by confirming that Zonantes Casey, 1895 is a junior synonym of Syzeton Blackburn, 1891, syn. nov.
Consequently, all North American species treated by Werner (1990) as Zonantes are now placed in Syzeton, as detailed hereafter.
The genus is characterized by the following morphological features (see also Grzymala (2016) for an extensive description): elytral pubescence generally well developed, uniseriate (Figure 1a); head transverse, bean-shaped in dorsal view, with base both truncated and concave (Figure 1b); anterior margin of pronotum broadly convex, formed from two segments converging in an obtuse angle toward the head (Figure 1c); antennomere 3 longer than the pedicel (Figure 1d); ♀♀ with a setose pit on the last abdominal ventrite (Figure 1e, f); mesothoracic tarsi with a ventral brush of long setae in both sexes (Figure 1g); presence of a small, basal, ventral, setae-filled excavation on hind femora of both ♂♂ and ♀♀ (Figure 1h, i); ♂ hind femora devoid of large pads of setae (contrasting with, for instance, ♂♂ of Elonus Casey, 1895).
Most species exhibit distinct but moderate sexual dimorphism, such as the size of the eyes (enlarged in ♂♂) or the conformation of the antennae (shorter in ♀♀).
Male aedeagus broadly cylindrical, moderately curved in lateral view, generally well sclerotized; phallobase not distinctly separated from apicale by a suture, as seen in other genera such as Mixaderus Collado &Alonso-Zarazaga, 1996 (Gompel, 2021) or Cobososia Collado & Alonso-Zarazaga, 1996 (Telnov & Gompel, 2021); apicale devoid of paired accessory lobes (Grzymala, 2016) as often found in Pseudoanidorus Pic, 1893 or Anidorus Mulsant & Rey, 1866 (N. Gompel & Barrau, 2002); ventral side of the phallobase with a large oval opening that never reaches the base of the aedeagus; a set of complex sclerotized internal plates often present in the aedeagus and visible with retrolighting.
Syzeton species are broadly distributed around the world, except in Europe and North-Africa. Syzeton specimens are typically collected by sweeping grass or beating the foliage of shrubs and hardwood trees. They are also often attracted to lights or obtained from flight intercept traps and Malaise traps, in forests or grasslands.
Key to US Syzeton species (modified and expanded from Werner, 1990)
1. Anterior tibiae angularly bowed (♂ of some species, Figure 5a–c)............................................. 2
– Anterior tibiae straight or weakly curved (Figure 5d–l)...................................................... 4
2(1). Posterior femora abruptly expanded dorsally from near middle to apex (Figure 5o). Elytra with broad black midband not interrupted at suture (Figure 2b).............................................................. ♂ S. fasciatus
– Posterior femora not so expanded, black midband of elytra, when present, narrower, rarely expanded anteriorly toward the scutellum (Figure 2a, c, m–n).......................................................................... 3
3(2). Elytra with brown to black adscutellar zone and broad dark median band, sometimes broken into 2 blotches on each elytron (Figure 2c, n)............................................................................ ♂ S. hubbardi
– Elytra all pale across base, entirely pale on disc (Figure 2a), or with a transverse postmedial mark, interrupted at suture (Figure 2m). Texas to Florida, north to Oklahoma ................................................ ♂ S. ouachitanus
4(1). Elytra and whole body brown to black, devoid of markings, or with narrow reddish windows on disc (some specimens of S. ater) (Figure 2e,–f).................................................................................. 5
– Elytra paler, orange or yellow, uniformly pale, or with makings defined by sharp boundaries....................... 7
5(4). Body black (occasionally with reddish windows on the elytra). Eyes smaller, their posterior edge remote from posterior head margin in side view (Figure 4d).................................................................... S. ater
– Body brown. Eyes large, distance between the posterior eye edge and the head margin in side view equivalent to 2–3 ommatidial diameters (Figure 4h)......................................................................... 6
6(4). Elytra and appendages uniformly brown, pronotum dark-brown (as in Figure 2a). Head coarsely punctate. Texas to Florida, north to Oklahoma ............................................................... some ♀♀ S. ouachitanus
– Elytra light-brown, progressively darker toward the apex. Pronotum and head black.Appendages uniformely yellow-orange, contrasting with the darker body color (Figure 2f). Head punctures small and superficial. Arizona ........ S. gruberi n. sp.
7(6). Elytra with broad midband not interrupted at suture (Figure 2b, c)............................................. 8
– Elytra with at most a midband that is interrupted at suture, or with dark blotches or spots in midzone, to entirely pale (Figure 2d, g–l)........................................................................................... 9
8(7). Midband very broad (Figure 2b), its posterior margin not cut into two lobes on each elytron, often continuing forward along suture and merging with broad adscutellar zone and scutellum. Pronotum entirely black................... S. fasciatus
– Midband moderately broad, its posterior edge sinuate (Figure 2c) or cut into 2 lobes on each elytron, the lateral lobe shorter, often isolated from quadrate dark adscutellar zone and scutellum (Figure 2n). Pronotum often paler with dark blotches............................................................................................. S. hubbardi
9(7). Base of elytra with at least some dark markings (Figure 2d, l, n–o)........................................... 10
– Whole base of elytra and scutellum pale (Figure 2g –k).................................................... 12
10(9). Dark marking at base of elytra reduced to a small spot centered midway between the pale scutellum and the humerus of each elytron; midzone of each elytron with a pair of sharply demarcated dark spots, the lateral the more anterior (Figure 2l)........................................................................................ some S. signatus
– Adscutellar area, and usually scutellum black. Midzone with a dark band, interrupted at suture, the midband sometimes reduced to two blotches on each elytron................................................................ 11
11(9). Midzone of elytra with a pair of narrow diagonal dashes, nearly touching at suture at apical 2/3–3/4, and forming a 30–40º angle (Figure 2o). Palest individuals with a brown pronotum have the dashes disconnected from the side margin, and have the adscutellar area only vaguely darkened. Darkest individuals with a black pronotum have dark elytral markings reaching the lateral margin where they merge with markings extending anteriorly almost to humeri. Head black..... most S. nubifer
– Midzone of elytra with a similar pair of narrow dashes, but these less diagonal, forming a 20º angle (Figure 2n). These may be connected to a lateral dark mark from near the front, and the lateral mark to the margin, but sides not dark much anterior to level of front of dashes. Pronotum usually pale with a pair of dark blotches. Scutellum pale, often flanked by dark spots..................................................................................some ♀♀ S. hubbardi
12(10). Pronotum with a pair of dark blotches. Markings otherwise as in couplet 11.................... a few ♀♀ S. hubbardi
– Pronotum entirely pale.............................................................................. 13
13(12). Moderately slender. Elytra width/length=0.54–0.6, elytra sides more parallel. Mostly distributed between Texas and Florida ................................................................................................ 14
– Relatively stout species. Elytra width/length=0.66–0.7, elytra sides more rounded............................... 15
14(13). Dark midband weak, transverse, slightly postmedian, and vaguely interrupted at suture. Texas to Florida, north to Oklahoma ............................................................................... ♀♀ S. ouachitanus
– Dark midband usually broken into 2 blotches on each elytron, separated at suture by pale zone only slightly wider in front. (See couplet 11. Can be mistaken for S. subfasciatus).................................. a very few ♀♀ S. hubbardi
– Dark midband slightly postmedian, sometimes broken into 2 blotches on each elytron, divided at suture by 30º triangular zone. (See couplet 11)................................................................ a very few S. nubifer
15(13). Each elytron with 2 small, nearly circular isolated dark spots in midzone, the lateral one the more anterior, and a black mark at base, on each side of scutellum (Figure 2l). ♂ genitalia: Figure 3l ............................... most S. signatus
– Elytra with dark blotches or a band across midzone, or entirely pale, but not with small, isolated round spots, or with round spots on elytral disc but with base of elytra entirely pale.................................................... 16
16(15). Elytra entirely pale (Figure 2g, h)..................................................................... 17
– Elytra with dark markings, sometimes extremely faint (Figure 2i–k).......................................... 19
17(16). Dorsal pubescence short and appressed (Figures 4a, 5q). Eyes small, devoid of notch near the antennal insertion (Figure 4a). Arizona .............................................................................. S. arizonae n. sp.
– Dorsal pubescence long, and semi-erected (Figures 4b, 5p)................................................. 18
18(17). ♂ genitalia long and simple (Figure 3h); ♀ antennae short, antennomeres transverse (Figure 5m). Texas, Oklahoma, Florida .................................................................................... S. belovi n. sp.
– ♂ genitalia shorter, broad, with a complex ventral process (Figure 3i); ♀ antennae longer, antennomeres 4–8 as long as wide or slightly wider than long (Figure 5n)....................................................... some S. pallidus
19(16). Dark elytral markings slightly oblique, converging apically, not divided into blotches, but often evanescent, sometimes hardly visible, their lateral edge centering slightly posterior to middle of elytron, (Figure 2i),. Head pale to reddish. Eyes relatively small, distance between eyes in ♂♂ 40% of head width (Figure 4e). ♂ genitalia: Figure 3i. ♂ foretibia weakly bowed, with a slight kink at apex of inner side (Figure 5i)............................................ S. pallidus
– Lateral part of dark elytral markings centering very close to midpoint of elytron. Head brownish to black............. 20
20(19). Band on elytra consisting of two, usually broadly connected, blotches on each elytron, the one nearer the suture centering slightly anterior to the one nearer the side (Figure 2j). Head usually black. ♂ genitalia: Figure 3j. Widespread and common...................................................................................... S. subfasciatus
– Band on elytra with lateral blotch centering slightly anterior to one nearer the suture, the blotches almost always separate (Figure 2k). Head orange, or slightly darkened but never dark brown. ♂ genitalia: Figure 3k. Texas to Florida ................................................................................................... S. floridanus
Separation of S. hubbardi (Casey, 1895), S. subfasciatus (LeConte, 1875) and S. nubifer (LeConte, 1878)
Syzeton nubifer exists in two forms, sometimes found in sympatry: a dark form (Figure 2d), with a black pronotum, darken mid- and hind femora, and well developed elytral markings extending along the lateral margins, and a pale form, with a brown pronotum, legs entirely orange, and elytral markings reduced to a single oblique stripe on each side, often interrupted before the lateral margin. The latter can easily be mistaken for S. hubbardi (Werner, 1990) or S. subfasciatus (LeConte, 1875). In ♂♂, the curvature of the foretibiae (Figure 5c, d, j) and the shape of the aedeagus, particularly in ventral view with the asymmetrical apicale (Figure 3c, d, j) make the distinction unambiguous. In ♀♀, however, the separation is more subtle: ♀♀ of S. subfasciatus (LeConte, 1875) are generally stouter, with ovoid elytra. The elytral markings are variable, from a solid transverse band of black pigmentation, to blotches, and to nearly no markings at all in exceptional cases. Females of the pale form of S. nubifer (LeConte, 1878) often look similar to S. subfasciatus (LeConte, 1875) with a solid transverse band of black pigmentation, but the band always centers slightly posterior to middle of elytron in S. nubifer (LeConte, 1878) (Figure 2o) while it is always centered near the midpoint of the elytra in S. subfasciatus (LeConte, 1875). In females of S. hubbardi (Werner, 1990), the markings form an horizontal transverse band, or, when separated in blotches, the blotches closer to the elytral suture are strongly oblique, nearly parallel to the elytral suture, forming a 20º angle (Figure 2n). In S. nubifer (LeConte, 1878), the inner blotches are less strongly oblique, forming a 30–40º angle together (Figure 2o). Isolated females of these three species may be difficult to name with certainty.
description: Published as part of Gompel, Nicolas, 2022, The genus Syzeton Blackburn, 1891 (Coleoptera, Aderidae) in the United States of America, pp. 243-267 in Zootaxa 5162 (3) on pages 244-246, DOI: 10.11646/zootaxa.5162.3.3, http://zenodo.org/record/6810142