Discoderus obsidianus Casey, 1914

Waite, Evan Storm, Hays, Brennan T. & Johnston, M. Andrew, 2024, Discoderus LeConte Species Exhibit Episodic Emergences in both Urban and Natural Environments of Arizona, USA (Coleoptera: Carabidae), The Coleopterists Bulletin 78 (1), pp. 1-8 : 3-5

Discoderus obsidianus Casey, 1914 ( Fig. 1A )

Discoderus obsidianus Casey 1914: 158 ; Bousquet 2012: 1150; Larochelle and Larivière 2003: 241; Noonan 1985: 49.

Discoderus sp. UASM son-3 [in part]: Shpeley and Van Devender 2022: 90.

Diagnosis. This is one of the few readily identi- fiable species given the current state of knowledge of the genus. We are aware of an ongoing revision of the genus that will change our understanding of the genus from what we present here; however, as the genus currently stands, this is an accurate review of the currently accepted species. The pronotum of D. obsidianus is characterized by the lateral margins being relatively straight and convergent in the posterior half. Most Discoderus species have distinctly arcuate pronota, either evenly or subcordate. The species with the most similar pronotal shape to D. obsidianus are Discoderus pinguis Casey, 1884 and Discoderus subviolaceus Casey, 1914 , both known from Arizona, which can be separated as follows. Discoderus pinguis has the pronotum proportionately broader than D. obsidianus and sides evenly curved (distinctly convergent in D. obsidianus ). Discoderus subviolaceus is the most similar and has the posterior third of the pronotum laterally straight and convergent with the middle third distinctly arcuate (posterior half straight in D. obsidianus ), the pronotum is roughly as long as wide (pronotum longer than wide in D. obsidianus ), and is a larger species at around 10 mm in body length (6–8 mm in D. obsidianus ).

Type Material. Female syntype from Arizona ( Fig. 3C ) . Casey (1914: 158) remarked that the type locality is “probably Southern” Arizona.

Specimens EXamined (73). USA: ARIZONA: Gila Co.: Payson, E. Tahoe Vista, C. Beier, 28 June 2022 ( ASUHIC: 4: 2♂, 2♀); Pinto Springs, Miles Ranch Trailhead, 33.439°, −111.065°, 24 June 2022, E. R. Wright ( ERWC: 1) ; Maricopa Co.: ASU, Alameda Natural History Collections Building ,

33.40087°, −111.95024°, 26 June 2022, E. Makings ( ASUHIC: 2); Chandler , 2 July 1984, C. Allen ( UAIC: 2: 1♂, 1♀) ; Mesa, residential area, 33.4241°, −111.8571°, 06 July 2022, M.A. Johnston ( ASUHIC: 10: 6♂, 4♀) ; Tempe, University Dr./S. Dorsey Ln. 33.4209°, −111.9202°, 01 July 2022, E. S. Waite ( EWIC: 10: 3♂, 7♀) ; Tempe, Selleh Park, 33.4030°, −111.9031°, 28 June 2022, E. S. Waite ( EWIC: 3: 1♂, 2♀) ; Tempe, S. Hardy Dr./W. Alameda Dr., ASU Natural History Collections back patio, 33.4007°, −111.9503°, 06 July 2022, E. S. Waite ( PWMC: 10: 7♂, 3♀) ; Phoenix, E. Carson Rd. , 33.38357°, −111.99640 °, 23 June 2022, E. Makings ( ASUHIC: 1); same but 25 June 2022 ( ASUHIC: 1); Phoenix , W. Indian School Rd. /N. 15th Ave., 33.4946°, −112.0924 °, 02 July 2022, B. Hulstedt ( ASUHIC: 14: 6♂, 8♀) ; Sand Tank Mountains , Bender Spring, 32.6786°, −112.3657 °, 15 July 2022, M. A. Johnston ( ASUHIC: 1); Scottsdale , residential area, 33.5757°, −111.9077 °, 30 June 2022, M. A. Johnston ( ASUHIC: 2: 1♂, 1♀) ; Pima Co.: Santa Rita Experimental Range Reservation , 27 May 1976 ( UAIC: 1: 1♀) ; Tucson, in cooler, 2 July 1984 ( UAIC: 1: 1♀) ; Santa Rita Experimental Range, 03 May–26 July 2023 ( NEON: 9); Pinal Co.: Casa Grande , night light , 10 August 1993, Blaine Mathison ( UAIC: 1: 1♀) .

Distribution. Figure 2 shows the currently documented range from available online records and vouchers examined during this study. Without viewing the specimen, we cannot verify the Texas record.

Figures

Fig. 1. Discoderus obsidianus emergence in 2022. A) Dorsal habitus, female from Mesa, AZ (scale bar 5 mm), B) Accumulation of suspected D. obsidianus in Scottsdale, AZ on a front porch over a single night.

Fig. 3. Syntype specimens of Discoderus species described by Casey from Arizona. All scale bars 5 mm. A) D. aequalis Casey, 1914, B) D. congruens Casey, 1914, C) D. obsidianus Casey, 1914, D) D. papagonis Casey, 1924, E) D. hesperus Casey, 1914, junior subjective synonym of D. parallelus, F) D. pinguis Casey, 1884, G) D. subviolaceus Casey, 1914, H) D. symbolicus Casey, 1914.

Fig. 2. Distribution map of Discoderus obsidianus. Localities based on digital records from SCAN (circles), GBIF (triangles), BugGuide (diamonds), and physical specimens from this event (squares). The Texas record is an outlier for which the identification was not confirmed by the authors.