Bembidion aenulum Hayward, 1901

Bembidion aenulum Hayward, 1901 View in CoL

( Figs. 1 View FIGURE 1 A, 4A, 5A, 6A, 7A–C, 8A)

Type material. Holotype female (in MCZ), examined, labelled: "Cedar Co. Iowa, V.31 ['Iowa' machineprinted, remainder handwritten] / Roland Hayward Coll. / Type 2006 ['2006' handwritten, on red paper] / Bembidium aenulum Hayw. [handwritten]"

Nomenclatorial notes. The female holotype of B. aenulum Hayward has all the external diagnostic character states of this western species, including the deeper microsculpture, less angulate humeral angle, distinctive prothorax shape, and wider mentum tooth. While identification of the holotype as a member of the western species would be more certain if the specimen were a male, or was sequenceable, the seven specimens whose DNA were sequenced from the type locality, Cedar County, Iowa, and neighboring Jones County all belong to this species. In addition, our 2003 collections from these two counties yielded 49 additional specimens, all of which show the morphological traits of the western species. Thus, it appears the eastern species does not occur at the type locality, providing further evidence of membership of the holotype in the western species.

Diagnosis. The smallest species of Odontium . Pronotum with hind angles wider than front angles, thus with a trapezoidal pronotum; sides straighter than B. paraenulum , and with less evident laterobasal depressions ( Fig. 5 View FIGURE 5 A). Humeral sulcus of elytron nearly parallel to basal margin of pronotum ( Fig. 5 View FIGURE 5 A). Microsculpture coarse, notably granulate in places, especially at the back of the pronotum. Mentum tooth wider at base, more trapezoidal than in B. paraenulum ( Fig. 6 View FIGURE 6 A).

Additional characteristics. ABL 3.5 to 4.1 mm, with most specimens less than 4.0 mm in length. Dorsal surface of body with metallic reflection, in most specimens golden or coppery. Appendages rufo-testaceous, with terminal two articles of maxillary palps, antennomeres 5–11, tarsi, and ends of tibia infuscated. Chromosome number is 2n = 22+XY ( Maddison, 1985).

Geographic variation. None noted.

Habitat. We have found this species at eight localities in Iowa and Nebraska on pure, often coarse sand of rivers ( Figs. 1 View FIGURE 1 A), in most localities in the company of Bembidion confusum , and less frequently with B. robusticolle Hayward , B. chalceum , etc.

Material examined ( Fig. 9 View FIGURE 9 , stars). In addition to the holotype, 148 specimens were examined, from the following localities (number of specimens seen indicated in parentheses after the locality): IOWA: Clayton Co., Turkey River at Osterdock, 195m, 42.7323°N 91.1602°W (1); Jones Co., Wapsipinicon River W of Oxford Junction, 220m, 41.9913°N 91.0067°W (29); Cedar Co., Cedar River at Rochester, 195m, 41.6715°N 91.1599°W (20); Cedar River at route X 40, 198m, 41.735°N 91.247°W (7); Hardin Co., Iowa River, Steamboat Rock, 290m, 42.4079°N 93.0722°W (6); Webster Co., Des Moines River near Stratford, 275m, 42.3101°N 93.9371°W (37); Linn Co., 3.0 mi N Viola, 4291Cd, 260m (1). NEBRASKA: Keith Co., South Platte River at Brule, 41.0858°N 101.8870°W (43); Cass Co., Louisville, Platte River, 310m, 41.003°N 96.182°W (2); Merrick Co., Central City, Hord Lake (1); Platte Co., Columbus (banks Loup R.) (1). SOUTH DAKOTA: Spink Co., Redfield (1).