Dromochorus pilatei

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 : 278-279

DROMOCHORUS PILATEI GUÉRIN- MÉNEVILLE, 1845

(FIG. 9H)

Common name

Cajun tiger beetle.

Type locality

‘Velasco, Texas’ (translation). Holotype probably in MHNP, Paris ( Bousquet, 2012).

Synonymy

Cicindela maga LeConte, 1875: 161 . Type locatity ‘near Lake Ponchartrain, Louisiana’. Syntypes (2) in MCZN. Synonymy established by Sallé (1877).

Taxonomic history

This is the type species for the genus Dromochorus , as described by Guérin-Méneville (1845). Two remarkably green specimens were collected by LeConte and described as Cicindela maga (1875) from the vicinity of Lake Ponchartrain, LA.

Distribution

Dromochorus pilatei is known from south-east Texas in the vicinity of the Brazos River east to the Mississippi River in Louisiana, north to Natchitoches, LA. The Lake Ponchartrain record is uncertain. This flightless beetle has otherwise never been found east of the Mississippi River except for LeConte’s specimens. There have been multiple attempts to find the beetle in this area ( Graves & Pearson, 1973; D.P. Duran, pers. obs.), but these have been unsuccessful. We regard this record as a potential error until further verification.

Diagnosis

This species cannot be confused with any other Dromochorus . The distinctive body form, elytral coloration with bronze and green reflections, prominent green subsutural foveae and complex surface texturing are diagnostic. Some individuals have a strong green-bronze sheen over all surfaces, and this trait appears to be more prevalent towards the eastern part of the species range.

Description

Small- to medium-sized Dromochorus . Body length 10.5–14.7 mm, mean ♀ 13.3 mm, mean ♂ 12.4 mm. Head slightly wider than pronotum. Head predominantly brown with cupreous to brassy reflections, green to blue to violet reflections mostly concentrated near the anterior margin and edges of the supraorbital region. In some specimens, bright green to green-blue reflections present throughout. 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 males, bulging towards slightly convex near anterior margin, clearly delimited from clypeus, gradually blending into vertex. Genae metallic blue to violet, with

shallow, longitudinal striae gradually ending at border of vertex. Clypeus bronze with green to blue reflections throughout; female clypeus more extensively greenblue to blue-violet. Male labrum tridentate with 6–8 setae, entirely pale ochre-testaceous, with a thin darkbrown to black border; female labrum tridentate with 6–8 setae, entirely dark-brown to black with polished metallic cupreous to green reflections. Maxillary palpi pale yellow-ochre; apical segment dark-brown to black, often with metallic purple and green reflections. Labial palpi coloured similarly to maxillary palpi. 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 1.8–3.2 mm in length, mean ♀ 2.8 mm, mean ♂ 2.6 mm; width 2.3–3.4 mm, mean ♀ 2.9 mm, mean ♂ 2.7 mm. Pronotum brown with cupreous, brassy or violet reflections; some specimens with green to green-blue reflections throughout, slightly wider than long, widest near anterior margin, width to length ratio 1.0 to 1.2, setae sparse to regularly spaced, mostly present along lateral third of dorsal surface; 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 weak to strong iridescent violet reflections, glabrous. Elytra elongate, dorsal surface convex, 6.4–9.0 mm length, mean ♀ 8.2 mm, mean ♂ 7.6 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 surface dull with complex texturing and infuscations, with regular small pits present throughout disk, as well as larger foveae. Bright green or blue reflections generally present in most to all pits and foveae.

Legs: Pro-, meso- and metacoxae dark-brown to black, may have iridescent blue reflections, scattered setae on pro- and mesocoxae, fewer on metacoxae; pro- and mesotrochanters with a single erect seta, metatrochanter glabrous, trochanters dark brown-testaceous; femora dark-brown black with metallic violet and bronze 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 mostly dark-brown to black with faint violet reflections. Erect brown setae present on ventrite 1. Ventrites 2–6 have sparse short, brown, erect setae present throughout, but often abraded.

Ecology/natural history

Adults appear to be active from mid-May to mid-July. Dromochorus pilatei can be found in significant numbers during peak adult activity (early to mid-June), along shaded, dark soil trails in riparian zones or near the banks of bayous, lakes and salt marshes. Of the Dromochorus , pilatei has the strongest affinity for heavily forested areas. The species is tightly associated with blackish, rich soils with high humus content, which are produced in the forest via decaying vegetation. In contrast, D. pruininus and D. belfragei are associated with disturbed clay deposits that contain less organic matter (red iron oxidized clays or black clay loam). In our observations, D. pilatei apparently avoids the lighter coloured soils that can also be present in its habitat.

This species can be found foraging/mating along man-made trails, disturbances or semi-open vegetated areas of applicable forest. Beetles appear to be concentrated on the edges of trails, sometimes with moderate to thick vegetation. Dromochorus pilatei is the only member of the genus that has been collected at lights at night (J. Back, pers. comm.). However, it was collected in small numbers, and it is likely that its presence was due to a high density of prey in the area, created by the lights. Traditionally thought to be crepuscular and perhaps nocturnal ( Graves & Pearson, 1973) in this habit, we now know this species is active throughout the day in well-shaded areas.