Elaphidion glabratum (Fabricius)

Ivie, Michael A. & Schwengel-Regala, Michelle L., 2007, The Elaphidion Audinet-Serville of the Puerto Rican Bank: new species, distributions, taxonomic corrections, and a key to species (Coleoptera: Cerambycidae: Elaphidiini), Zootaxa 1503, pp. 55-68 : 61-62

Elaphidion glabratum (Fabricius)

( Figs 16 , 18 20)

Stenocorus glabratus Fabricius, 1775: 180 .

Elaphidion glabratum: Ivie, 1985: 310 . Monné and Giesbert, 1995: 54. Chalumeau and Touroult, 2005: 101. Monné and Hovore, 2005: 65. [For a complete pre-1985 synonymy, see Ivie 1985.]

A complete discussion of the tortured nomenclatural history of this species was given by Ivie (1985).

DIAGNOSIS: The small size (8–19 mm), cinerous to golden pubescence, and relatively long unispinose antennomere 4 will distinguish this species and E. pseudonomon from all other Elaphidion in the area. Although long series of these two closely-related species are obviously distinct to the naked eye when placed next to each other, actual diagnoses of E. glabratum and E. pseudonomon are difficult, and require careful use of details. From E. glabratum , E. pseudonomon , can be distinguished by the male genitalia (see Ivie 1985), somewhat lighter color, details of the antennal configuration and setation. The antennal characters require detailed measurements. In male E. glabratum antennomeres 3 and 4 are subequal (with 4 only rarely more than 1 mm shorter than 3), and 5 is longer (by 1–3 mm) than 3 (i.e. antennomere 4 is greater than 30% total length of 3+4+5). In male E. pseudonomon , antennomere 3 and 5 are subequal, with 5 no more than 1 mm longer than 3, while 4 is at least 2 mm shorter than 3 (i.e. antennomere 4 is less than 30% total length of 3+4+5). In females of both species, antennomere 4 is consistently shorter than 3, and in E. pseudonomon it is slightly more so, but the difference is difficult to quantify. In female E. pseudonomon , antennomere 4 is usually less that 28% of the total 3+4+5, while in E. glabratum it is usually greater than 28%. For unassociated females, the allopatric distribution is helpful, with E. pseudonomon occurring on the Virgin Islands that lie on the Puerto Rican Bank, while E. glabratum occurs from St. Croix and its satellites into the Lesser Antilles.

The elytral setation and punctation are also different, and helpfully not sexually dimorphic. The setae of E. pseudonomon ( Figs 17 , 19) are more golden and individually larger than in E. glabratum ( Figs 16 , 18), covering the elytra and pronotum more uniformly, but not being dense enough to completely obscure the underlying cuticle. The specimen therefore looks uniformly lighter colored to the unaided eye because of the uniform mix of the color of setae and cuticle. In fresh specimens, the humerus is covered in setae ( Fig. 17 ), and at mid-elytron (at the level of the metacoxa) the setae uniformly cover the entire disc except for 2 narrow, indistinct strial lines (Fig. 19). Older rubbed specimens of E. pseudonomon may exhibit bare spots, but never to the extent seen in E. glabratum , and the remaining setal patches are always sparse enough to see through to the surface. This characteristic is always distinguishable at a point just mesad the humeral umbone ( Fig. 17 ), and on the mid-point of the elytron at the level of the metacoxa (Fig. 19). Greasy specimens may appear darker, but this is an obvious artifact of preservation. The setae in E. glabratum are cinerous and narrower, and form dense patches that at least in part completely obscure the cuticle ( Figs 16 , 18), leaving other areas bare except for the single seta associated with each puncture. The difference in setal density of these patches relative to the condition in E. pseudonomon is always distinguishable at a point just mesad the humeral umbo ( Fig. 16 ), and on the mid-point of the elytron at the level of the metacoxa (Fig. 18). The overall effect of this condition is more areas of unobscured cuticle showing to the naked eye, thus making the fresh specimen look darker.

Lastly, post-humeral punctures of E. pseudonomon are usually slightly smaller in diameter, making them seem less dense ( Fig. 21). In E. glabratum the post-humeral punctures of the elytra are slightly larger ( Fig. 20), although there seems to be about the same number of actual elytral punctures in both species.

DISTRIBUTION: St. Croix, Buck Is. (near St. Croix, WIBF), Saba (WIBF), St. Martin, St. Barthelémy, St. Eustatius, Nevis, Antigua, Montserrat, and Guadeloupe, and probably St. Christopher, Dominica and St. Lucia

Figures

FIGURES 16 – 17. Dorsal view of left elytral base (scale bar = 1 mm). 16. E. glabratum; 17. E. pseudonomon. FIGURES 18 – 19. Dorsal view of left mid-elytra (anterior to right) (scale bar = 1 mm). 18. E. glabratum; 19. E. pseudonomon.