Cybister occidentalis Aubé, 1838

Miller, Kelly B., 2013, Review of the Genus Cybister Curtis, 1827 (Coleoptera: Dytiscidae: Dytiscinae: Cybistrini) in North America, The Coleopterists Bulletin 67 (4), pp. 401-410 : 407

Cybister occidentalis Aubé, 1838 Figs. 4 , 12–15, 19

Cybister occidentalis Aubé, 1838: 67 . Chevrolat 1863: 202; Sharp 1882a: 733; Zimmermann 1920: 263; Blackwelder 1944: 80; Epler 1996: 3:39, 2010: 5.51.

Cybister (Nealocomerus) occidentalis . Young 1953: 7, 1955: 121; Brinck 1945: 13.

Diagnosis. This species is uniquely characterized by the nearly right-angled ( Fig. 6 ) to slightly rounded ( Fig. 7 ) apicoventral angle of the metafemur combined with the presence of extremely large marginal lobes on the median lobe of the aedeagus in males (Fig. 12–14). This species differs from C. explanatus in having the apicoventral angle of the metafemur nearly right-angled and often slightly rounded (as in Fig. 6 ) rather than acuminately produced ( Fig. 7 ) and the presence of extremely large marginal lobes on the median lobe of the aedeagus in males (Fig. 12–14). Cybister occcidentalis can only be confidently separated from C. fimbriolatus by characteristics of the male median lobe. In C. fimbriolatus , the ventral sclerite is long and relatively slender, extending to near the apex of the median lobe (Figs. 8–10). In C. occidentalis , the ventral sclerite is much shorter and broader, ending well short of the apex of the median lobe (Figs. 12–14).

Measurements. TL = 27.6–33.7 mm, GW = 14.4–18.2 mm, TL/GW = 1.8–1.9.

Variation. The main variation within this species is in size, though it is not extreme (30– 34 mm). Also, some specimens have the lateral yellow stripes on the elytra shorter, not extending to the apex of the elytra.

Taxonomy. Aubé (1838) described this species based on specimens from Cuba (type locality = “ Cuba, Havana ”) . The type specimen was not examined, but there can be little doubt as to the identity of this species from Cuba .

Distribution. This species is found mainly in the Bahamas and Cuba ( Fig. 19 ). The species has also been collected from Big Pine Key from extreme southern Florida ( Young 1953, 1954; Epler 2010). Turnbow and Smith (1983) recorded the species also from Crisp County, Georgia. This is some distance outside the expected range of the species, and Young (1954) did not find the species anywhere else in the southeastern mainland, suggesting that this record could be erroneous.

Natural History. This species is found in ponds and ditches ( Young 1953, 1954).

Figures

Figs. 1–7. Cybister species. 1) C. fimbriolatus, male, base of left metacoxa, metatrochanter, and metafemur showing position of stridulatory ridges on the metacoxa; 2) C. fimbriolatus, California; 3) C. fimbriolatus, Florida; 4) C. occidentalis, Bahamas; 5) C. explanatus, California; 6) C. fimbriolatus, right metatrochanter and metacoxa; 7) C. explanatus, right metatrochanter and metacoxa.

Fig. 19. Distribution of Cybister species in North America and Mexico.