Dromochorus minimus, Duran & Herrmann & Roman & Gwiazdowski & Drummond & Hood & Egan, 2019

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 : 272-274

DROMOCHORUS MINIMUS DURAN, ROMAN,

HERRMANN & EGAN SP. NOV.

( FIG. 9D )

Common name

Pygmy dromo tiger beetle.

Type locality

SE of Pleasanton , TX. Holotype (deposited in U S N M): 1 ♂, U S A: Te x a s: A t a s c o s a C o./S E o f Pleasanton / 19-VI-2014 /leg D. Duran . Paratypes: 3 ♂ ♂, 3 ♀ ♀, U S A: Te x a s: A t a s c o s a C o./S E o f Pleasanton/19-VI-2014/leg D. Duran. 3 ♂, 4 ♀♀, USA: Texas: Atascosa Co./SE. of Pleasanton/30-V- 2014 / leg D. Sunberg. 1 ♂, 1 ♀, USA: Texas: Atascosa Co./SE. of Pleasanton/02-VI-2015/leg S.J. Roman. 17 ♂♂, 7 ♀♀, USA: Texas: Atascosa Co./SE. of Pleasanton/29-VI-2014/leg D. Brzoska. 1 ♂, USA, Texas: Bexar Co./7 miles S. San Antonio/06-VI-2010/ leg G. Waldren. 1 ♂, USA: Texas: Bexar Co./Loop 1604 Hwy/12-VI-2016/leg J. Back.

Distribution

Central/south Texas, south of the Balcones Escarpment. Currently known only from Bexar, Atascosa and Frio Counties.

Diagnosis

Dromochorus minimus can be separated from all other species, by the presence of a frosted or ashy grey to beige dorsum, sometimes with blue reflections, in conjunction with labial palpi that are all dark (apical segment is not darker than other segments), and sparse erect setae on the pronotum, often irregularly placed throughout.

This species is most likely to be confused with D. pruininus , chaparralensis or welderensis .

Dromochorus pruininus is generally larger ( Fig. 6 ; Table 2), has pale maxillary palps with a contrasting dark apical segment and is also separable by geographic range.

Dromochorus chaparralensis is usually larger ( Fig. 6 ; Table 2), and lacks any prominent frosted texturing on the dorsal surface. The pronotum of D. chaparralensis has setae more regularly arranged, mostly along lateral third.

Dromochorus welderensis is usually larger ( Fig. 6 ; Table 2), and its pronotum has decumbent white setae, mostly along lateral third. The habitat of D. welderensis is Gulf Coast Prairie.

Description

Small- to medium-sized Dromochorus . Body length 10.5–13.7 mm, mean ♀ 12.7 mm, mean ♂ 11.7 mm. Head slightly wider than pronotum. Head predominantly charcoal black with blue to green reflections mostly concentrated near the anterior margin and edges of the supraorbital region. 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 black with bright polished metallic green to violet reflections, with shallow longitudinal striae gradually ending at border of vertex. Clypeus shining black with blue to violet reflections throughout. Male labrum tridentate with 6–8 setae, central area pale ochre-testaceous,

with a thin dark-brown to black border posteriorly and sometimes anteriorly, dark-brown to black laterally; in some populations, the pale central area of the labrum may exist as a small spot, up to one-third of the total labrum surface; 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; 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 dull-textured without metallic reflections and possessing erect setae in apical rings only, covered with fine pubescence throughout.

Thorax: Pronotum 2.4–3.1 mm in length, mean ♀ 2.8 mm, mean ♂ 2.7 mm; width 2.5–3.3 mm, mean ♀ 3.0 mm, mean ♂ 2.7 mm. Pronotum charcoal black, typically with frosty pale grey to brown, or blue to violet sheen, especially along lateral margins, slightly wider than long, widest near anterior margin, width to length ratio 1.0 to 1.1, thin erect setae sparse to irregularly spaced on pronotum; disc finely rugose, with thin but distinct median line, with well-defined shallow sulci present anteriorly and posteriorly; notopleural sutures clearly defined, not visible from dorsal view; proepisternum black with iridescent olive green to violet reflections, glabrous. Elytra elongate, dorsal surface convex, 6.4–8.0 mm length, mean ♀ 7.6 mm, mean ♂ 7.1 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 texture dull, with no pitting present, elytral coloration charcoal black, typically with grey, brown or blue-grey frosted texture along lateral margins, apex with blue or grey frosted texture; elytral maculations absent; subsutural foveae absent.

Legs: Pro-, meso- and metacoxae dark brown with iridescent violet and cupreous reflections, numerous setae on pro- and mesocoxae, sparse on metacoxae; pro- and mesotrochanters with a single erect seta, metatrochanter glabrous, trochanters dark brown-testaceous; femora black with metallic violet and green reflections, densely clothed in decumbent white setae; tibiae testaceous 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 olive green and violet reflections. Decumbent white setae present on ventrite 1. Ventrites 2–6 have sparse short brown erect setae present throughout, but often abraded.

Etymology

Dromochorus minimus is named for its smaller size. On average, this species is the smallest in the genus ( Table 2).

Ecology/natural history

Little is known about this species’ natural history. Adults have been collected from mid-May until late June, but it is possible that the species may be active outside of this window.

Dromochorus minimus occurs in mesquite-chaparral savannah in central/south Texas, just south of the Edwards Plateau, part of the larger Gulf Coastal Plains physiographic province. It has been found in open grassy areas interspersed between mesquite trees and clumps of Opuntia cactus. Adult beetles may be found venturing into the open spaces between clumps of grass, and will rapidly run into vegetation if pursued. Dromochorus minimus appears to be remarkably swift, even compared to other species of Dromochorus .

In direct sunlight, live specimens appear beige-grey to smoky blue-grey.

Figures

Figure 6. Boxplots, by species, from morphometric data used in principal component analyses (PCA) for each of 411 individuals. PCA indicated three measurements: PC1, overall body length; PC2, shape of the pronotum; and PC3, elytral length to body length ratio, to explain 92–95% of the total variation in the dataset. Shown are targeted comparisons among two main phylogenetic groups: 1, the D. minimus–D. velutinigrens–D. welderensis–chaparralensis group; and 2, the D. knisleyi– D. belfragei–D. pruininus clade. Species labelled with the same letters did not differ significantly from each other, species labelled with ‘ab’ did not differ between other species which were significantly different. Percentages are relative contributions per analyses, and group; outliers are shown as black dots.

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.