Geostiba (Sibiota) silvigena Gusarov,

Gusarov, Vladimir I., 2002, A revision of Nearctic species of the genus Geostiba Thomson, 1858 (Coleoptera: Staphylinidae: Aleocharinae), Zootaxa 81, pp. 1-88: 72-75

publication ID 10.5281/zenodo.155701

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Geostiba (Sibiota) silvigena Gusarov

sp. n.

14. Geostiba (Sibiota) silvigena Gusarov  , sp. n. ( Figs. 321­335View FIGURES 321 ­ 326View FIGURES 327 ­ 335)

Type material. Holotype ,, UNITED STATES: California: Mendocino Co.: Mendocino [39 ° 18 ' 28 "N 123 ° 47 ' 53 "W], ex moss in bed of dried up woodland pool, Berlese funnel (J.R.Helfer), 1.x. 1954 ( CNCI).

Diagnosis. Geostiba silvigena  can be distinguished from other Nearctic species of Geostiba  by having large eyes (temple length to eye length ratio 2.3), pronotal pubescence of type V, well developed wings, long elytra (pronotum length to elytron length ratio 1.0), the presence of two short parallel carinae in the middle of male abdominal tergum 7 in front of posterior margin, and the shape of the aedeagus ( Figs. 323­335View FIGURES 321 ­ 326View FIGURES 327 ­ 335).

Geostiba silvigena  is very similar to eastern Nearctic G. appalachigena  , and differs only in having the apex of median lobe less bent ventrally (in lateral view) ( Figs. 325 ­326View FIGURES 321 ­ 326, 36­ 37View FIGURES 34 ­ 37), and longer and more narrow apex of paramere ( Figs. 334View FIGURES 327 ­ 335, 50View FIGURES 38 ­ 50).

Geostiba silvigena  differs from G. impressula  , another western Nearctic species, in having pronotal pubescence of type V, well developed wings, longer elytra, aedeagus with more narrow apex of the median lobe (in ventral view) ( Figs. 323­324View FIGURES 321 ­ 326, 310­ 312, 315View FIGURES 310 ­ 315), elytral suture slightly raised behind scutellum, and in males lacking the medial pronotal impression.

Description. Length 2.4 mm. Body reddish brown, antennae, legs and mouthparts brownish yellow. Body parallel­sided.

Head as wide as long, surface on disk with fine isodiametric microsculpture, puncturation very fine and weak, distance between punctures equal to 2­3 times their diameter. Temple length to eye length ratio 2.3. Antennal article 2 longer than article 3, article 4 transverse (width to length ratio 1.6), articles 5­10 strongly transverse, last article as long as 9 and 10 combined (as in Fig. 17View FIGURES 8 ­ 17).

Pronotum slightly transverse, width 0.41 mm, width to length ratio 1.0, wider than head (pronotal width to head width ratio 1.1); microsculpture and puncturation as on head. Pronotal pubescence of type V. Elytra measured from humeral angle longer than pronotum (pronotal length to elytral length ratio 1.0), wider than long (1.3), with weak and fine isodiametric microsculpture and fine, somewhat asperate puncturation, distance between punctures equals 2­3 times their diameter. Elytral suture behind scutellum raised. Wings fully developed.

Abdominal terga with fine microsculpture of transverse meshes, with fine and sparse puncturation, puncturation becoming finer towards abdomen apex, on terga 3­5 distance between punctures equals 3­5 times their diameter. Tergum 7 with white edge.

Male tergum 7 with two medial carinae in front of posterior margin. Male tergum 8 with four small carinae in front of posterior margin, posterior margin slightly convex ( Fig. 321View FIGURES 321 ­ 326). Male sternum 8 with convex posterior margin ( Fig. 322View FIGURES 321 ­ 326).

Aedeagus as in Figs. 323­335View FIGURES 321 ­ 326View FIGURES 327 ­ 335. Apex of median lobe in lateral view bent ventrally ( Figs. 325­326View FIGURES 321 ­ 326), distal diverticula of internal sac in ventral view wide ( Figs. 329­330View FIGURES 327 ­ 335).

Female unknown.

Discussion. Geostiba silvigena  has fully developed wings and it is probably widespread along the Pacific coast of North America. The species may not be active in summer when most collections in the area have been made (see the above discussion of natural history of G. impressula  ). Although G. silvigena  is closely related to the eastern Nearctic G. appalachigena  , the westernmost locality of G. appalachigena  is in Wisconsin ( Figs. 336­ 337View FIGURE 336View FIGURE 337). Considering the gap between the ranges of the two species and the minor difference in male genitalia the separate status of the two seems justified.

Distribution and variability. Known only from Mendocino, California ( Fig. 336View FIGURE 336).

Natural History. The only known specimen of G. silvigena  was collected in moss in the bed of a dried up woodland pool.

Etymology. The specific name is derived from the Latin noun silva (forest, woodland) and the verb gigno (to be born, to arise). It refers to the habitat where the species presumably occurs.


Canadian National Collection Insects