Dromochorus velutinigrens, Johnson, 1992

Duran, Daniel P., Herrmann, David P., Roman, Stephen J., Gwiazdowski, Rodger A., Drummond, Jennifer A., Hood, Glen R. & Egan, Scott P., 2019, Cryptic diversity in the North American Dromochorus tiger beetles (Coleoptera: Carabidae: Cicindelinae): a congruence-based method for species discovery, Zoological Journal of the Linnean Society 186, pp. 250-285 : 276-278

DROMOCHORUS VELUTINIGRENS JOHNSON, 1991

( FIG. 9G )

Common name

Velvet tiger beetle.

Type locality

‘10 km east of Riviera, Kleberg Co, Texas’. Syntypes (3) in USNM, Washington DC.

Distribution

Dromochorus velutinigrens is currently known from south and west Texas, from the Gulf Coast south of Corpus Christi, west to Dimmit County. Few localities are known ( Fig. 3 ), and gaps between the known occurrences may be due to a lack of sampling in the intervening areas. It is likely that D. velutinigrens also may be found in adjacent areas of Tamaulipas, Mexico.

In the vicinity of LaSalle and Dimmit Counties, D. velutinigrens and D. chaparralensis come in close proximity, and are sympatric in at least one site.

Diagnosis

This is a very distinctive species of Dromochorus . Dromochorus velutinigrens can be diagnosed by having strong blue, violet or green reflections throughout the entire dorsal surface, especially towards lateral margins, in conjunction with a narrow gracile body form and a pronotum with few to no setae. Males are unique among Dromochorus for having an all dark labrum.

The only species that could potentially be confused with D. velutinigrens is D. welderensis .

Dromochorus welderensis is black dorsally, with a faint dark-blue sheen. It has scattered to regular white decumbent setae present on the disk of the pronotum, especially along lateral margins. Males have a pale central spot on the labrum. Body form is more robust than D. velutinigrens .

Description

Medium- to large-sized Dromochorus . Body length 11.4–14.9 mm, mean ♀ 13.3 mm, mean ♂ 12.7 mm. Head slightly wider than pronotum. Head charcoal black with velvety violet to blue sheen, with bright violet, blue or greenish reflections in supraorbital areas and anterior margin. Fine rugosity often present on the frons and vertex. All head portions glabrous except for two supraorbital setae next to each eye. Frons concave in median area, especially in male, bulging towards slightly convex near anterior margin, clearly delimited from clypeus, gradually blending into vertex. Genae bright polished metallic blue to violet, blending to violet posteriorly, with shallow longitudinal striae gradually ending at border of vertex. Clypeus bright metallic blue and violet. Male labrum tridentate with 6–8 setae, entirely dark-brown to black with polished metallic cupreous to green reflections, rarely with a faint ochre-testaceous spot in centre; female labrum tridentate with 6–8 setae, entirely dark-brown to black with polished metallic cupreous to green reflections. All segments of maxillary and labial palpi consistently darkbrown with metallic violet and green reflections; apical segment is not darker than other segments. Antennae normal length, reaching back to

humerus and basal third of elytron, slightly longer in male than female; scape dark testaceous to black with metallic reflections of violet, cupreous and green, with 2–3 apical setae; pedicel dark testaceous with metallic reflections of violet, cupreous and green, lacking any setae; flagellum dark testaceous, antennomeres 3–4 with metallic violet and green reflections, densely clothed in short, white setae, antennomeres 5–11 dulltextured without metallic reflections and possessing erect setae in apical rings only, covered with fine pubescence throughout.

Thorax: Pronotum 2.2–3.1 mm in length, mean ♀ 2.8 mm, mean ♂ 2.7 mm; width 2.3–3.2 mm, mean ♀ 2.9 mm, mean ♂ 2.7 mm. Pronotum charcoal black, with velvety violet to blue sheen, slightly wider than long, widest near anterior margin, width to length ratio 0.9 to 1.1, pronotal setae absent or with few, irregular, long setae scattered throughout disk; disc smooth, with thin but distinct median line, shallow sulci present anteriorly, and present but less well-defined posteriorly; notopleural sutures clearly defined, not visible from dorsal view; proepisternum metallic blue to violet reflections, glabrous. Elytra elongate, 6.7–9.0 mm length, mean ♀ 8.2 mm, mean ♂ 7.7 mm, shape similar in both sexes, but slightly wider in female, especially toward apical third; sutural spine absent, microserrations not present on elytral apices; elytral dorsal surface convex, texture dull throughout, elytral coloration charcoal black with velvety violet to blue sheen, lateral margins and apex with shining blue, violet or green reflections; elytral maculations absent; infuscations absent; subsutural foveae absent.

Legs: Pro-, meso- and metacoxae black with iridescent blue, violet and green reflections, with numerous setae, fewer on metacoxae; pro- and mesotrochanters with a single erect seta, metatrochanter glabrous, trochanters dark brown-testaceous; femora metallic violet to blue, with green reflections, densely clothed in decumbent white setae; tibiae brown, clothed with setae of two types: sparser brown-testaceous long setae and dense short decumbent white setae; two tibial spines present; tarsi brown-testaceous, first three dilated protarsomeres in male with dense greyish-white setal pad.

Abdomen: Venter black with metallic violet to greenish reflections throughout most surfaces. Decumbent white setae present on ventrite 1. Ventrites 2–6 have scattered short brown recumbent setae present throughout, but often abraded.

Ecology/natural history

Adults are active earlier than other species in the genus. Records are from mid-April through late June, but year to year, emergence dates are highly variable relative to congeners and may be more dependent on spring rainfall patterns.

Our limited knowledge of habitat associations for Dromochorus velutinigrens is based on two populations. The type locality is a Texas A&M University– Kingsville’s Site 55 Biological Research Station ( Johnson, 1991) on the northern shore of Baffin Bay in Kleberg County, TX. Much of the habitat along the northern banks of the bay has been destroyed by agricultural use, primarily heavy grazing. Johnson (1991) reported that the species can be found associated with sandy road paths and grassy areas along semi-forested areas through the sites. Our team observed adults in sandy, vegetated backshore regions near the bay just below shrubby clay dunes (lomas). Individuals can be found running in and around bunches of cord grass ( Spartina spartinae ) and in relatively open sandy areas not far from the water’s edge. The adults of D. velutinigrens are by far the most sand-tolerant of the known Dromochorus , as indicated by their presence also on sandy backshore areas near vegetated dunes.

Clay lomas are prevalent along the southern Texas coast from St. Charles Bay through northeastern Mexico along the coast of Tamaulipas to Rancho Tepehauje ( Tunnell et al., 2002). Future surveys need to focus around clay dune formations in t h e s e r e g i o n s w h e r e t h e b e e t l e i s c u r r e n t l y undocumented.

Dromochorus velutinigrens also occurs more i n l a n d, a s f a r w e s t a s C h a p a r r a l W i l d l i f e Management Area in Dimmit and LaSalle Counties. In these areas, we believe that the species’ presence may be explained by the Dilley soil series. These orange/reddish soils are classified as fine sandy loams and are darker in contrast to the type locality in Kleberg County. Extreme soil colour variability has also been observed across the ranges of D. belfragei and D. pruininus . The Dilley series extends to the North into Zavala County. Although unconfirmed, the range for D. velutinigrens will likely extend into this county as well.

This location is part of the greater Gulf Coastal Plain physiographic province, and may explain historical connectivity between inland and coastal populations of D. velutinigrens . It is probable that this inland population is not disjunct but, instead, that there has not been sufficient sampling in the intervening areas. Targeted surveys may yield other populations in sandy formations in Mexico and southern Texas.

Adults can be found among ghost crab ( Ocypode quadrata ) colonies, which D. velutinigrens may use for escape when pursued. The ability to hide in cracks for escape appears to be widespread throughout the genus.

Figures

Figure 3. Distributionof sampled Dromochorus populations.Colours correspondto those used in Figure 1. Green = D.pilatei, pink = D. welderensis sp. nov., sky blue = D. velutinigrens, red = D. chaparralensis sp. nov., blue = D. pruininus, lime green = D. knisleyi sp. nov., orange = D. minimus sp. nov., black = D. belfragei.

Figure 9. Dorsal habitus for species of Dromochorus. A, D.pruininus; B, D.belfragei; C, D. knisleyi sp. nov.; D, D. minimus sp. nov.; E, D. chaparralensis sp. nov.; F, D. welderensis sp. nov.; G, D. velutinigrens; H, D. pilatei.