Bembidion ampliatum, CASEY, 1918

Sproul, John S. & Maddison, David R., 2018, Cryptic species in the mountaintops: species delimitation and taxonomy of the Bembidion breve species group (Coleoptera: Carabidae) aided by genomic architecture of a century-old type specimen, Zoological Journal of the Linnean Society 183, pp. 556-583 : 575-576

BEMBIDION AMPLIATUM CASEY

( FIGS 1B, 8C, D, 10B, 11B, 12D, 15A)

Bembidion ampliatum Casey, 1918: 24 . Lectotype male, designated by Lindroth (1975: 117), in USNM, labelled ‘Col’ [white paper], [male symbol, hand drawn on white paper], ‘CASEY bequest 1925’ [white paper], ‘TYPE USNM 36828’ [red paper], ‘ampliatum Csy. ’ [white paper, handwritten], ‘ LECTOTYPE ampliatum Csy. By C.H. Lindroth’ [white paper, partly handwritten]. Type locality: Colorado. Examined, including genitalia.

Bembidion improvisum Casey, 1918: 24 . Lectotype male, designated by Lindroth (1975: 117), in USNM, labelled ‘Col’ [white paper], [male symbol, hand drawn on white paper], ‘CASEY bequest 1925’ [white paper], ‘TYPE USNM 36832’ [red paper], ‘improvisum Csy. ’ [white paper, hand written], ‘ LECTOTYPE improvisum Csy. By C.H. Lindroth’ [white paper, partly handwritten]. Type locality: Colorado. Examined, including genitalia.

Diagnosis: This medium-sized species is parallel-sided with a distinctly flat pronotum. Forebody and hindbody black or very dark brown, often with aeneous or metallic hue. Pronotum relatively flat; hind angles obtuse; widest anterior to middle with broad lateral explanation and weak laterobasal carina (as the basal fovea beside it is not as deep, and thus the carina does not stand out so prominently); not sinuate laterally ( Figs 11B, 12C). Elytra are more or less parallel-sided and broadly rounded at apex; elytral disc with smooth appearance (particularly in California and Oregon), in part due to weak striae and weakly foveate dorsal punctures ( Fig. 1B) which are not easily observed without magnification. Microsculpture meshes moderately etched in females, but weakly or at least unevenly etched in most males, often partially disappeared (13D). Male genitalia with the ventral portion of sclerite ‘St’ angled anteriorly such that the ventral extremity is even with, or anterior to, the dorsal extremity; flagellum short and somewhat sinuate ( Figs 8C, 13D, 10B).

Comparison with similar species: Most easily confused with B. lividulum from which it can be distinguished by having a flatter pronotum with weak laterobasal carina (especially reliable in California), less pronounced elytral striae with weakly foveate dorsal punctures and a smooth elytral disc in the basal third anterior to the dorsal punctures (though often less so in specimens east of California and Oregon), and the male genitalia having a more laterally expanded sclerite ‘St’ with the ventral portion angled anteriorly. May also be confused with B. laxatum from which it can be separated through the weakened elytral microsculpture in both sexes, by having a flatter pronotum with obtuse hind angles and weakened laterobasal carina, and lacking the U-shaped recurvature in sclerite ‘St’ of the male genitalia.

Geographic distribution: Throughout the Sierra Nevada and White Mountains in California and north throughout the eastern mountains of Oregon (Steens and Wallowas) to Alberta. Easterly through the Great Basin and Rocky Mountains to Montana, Wyoming, and Colorado, south to New Mexico and Arizona. The only breve group species known from Utah, Wyoming, Colorado, New Mexico and Arizona ( Fig. 15A). A single questionable specimen is reported from Washington (see note below about ‘Geographic variation’) .

Habitat: Open alpine slopes, commonly below patches of melting snow.

Geographic variation: Specimens east of California and Oregon (e.g. Great Basin and Rocky Mountains) are generally smaller-bodied, especially males, and show more intraspecific variation in external structures. Notable within-population size variation has been observed in the Manti La Sal Mountains of eastern Utah, and the Sangre de Cristo Mountains of New Mexico. The single specimen from Washington reported herein (DNA3321) is a morphological and molecular outlier that we doubtfully include within this species .