Osoriinae, Erichson, 1839

Pandolfi, Alessandra, Kelly, Sandor, Irmler, Ulrich & Bohlen, Patrick, 2024, First record of Mimogonus fumator (Fauvel, 1889) (Coleoptera: Staphylinidae: Osoriinae) in the USA, with a synopsis of the Osoriinae of the Southeastern USA, Zootaxa 5477 (2), pp. 136-146 : 142-143

Key to Osoriinae of the Southeastern USA

A key to genera and species is provided and is adapted from Newton et al. 2000 (genera), Irmler 2003 ( Clavilispinus ), Notman 1925 and Irmler 2014 ( Osorius and Molosoma ), Chapin 1928 ( Holotrochus and Mimogonus ), Ferro 2015 ( Thoracophorus ), and Newton 2017 ( Clavilispinus and Prolibia ).

1 Membranous suture present between each abdominal tergum and sternum; pronotum gradually but strongly narrowed toward base for basal 1/3 or more (triangle-like shape); body very flat................................................. 2

- Abdominal tergum and sternum of each of segments III–VII fused into complete ring; pronotal shape diverse, rarely gradually and strongly narrowed toward base (trapezoid-like shape); body flat to convex or cylindrical......................... 3

2 Head without groove near dorsal edge of eye; pronotum longer than wide (rarely only as long as wide), with sides subparallel for the anterior 2/3; elytron with sutural stria................................... Renardia nigrella (LeConte, 1863)

- Head with groove extending posteriorly from dorsal edge of eye; prontum distinctly wider than long, with sides subparallel for at most the anterior 1/2; elytron without sutural stria................................ Eleusis pallida (LeConte, 1863)

3 Procoxa with deep groove and carina on mesal surface; protibia with inner edge concave and bearing ctenidium; abdominal segment VIII (last visible) with “extra” tergite at apex; body convex, often nearly cylindrical......................... 4

- Procoxa with or without carina on mesal surface; protibia with inner edge straight, without ctenidium; abdominal segment VIII without “extra” tergite at apex (but part of eversible genital segment may be visible); body generally more or less flat.... 11

4 Antenna geniculate; scape about as long as or longer than next three antennomeres combined; external edge of protibia strongly convex, strongly spinose............................................................................... 5

- Antennae not geniculate; scape about as long as next 2 antennomeres combined; external edge of protibia straight to slightly convex, at most with a few slender spines................................................................. 9

5 Length 6 mm or greater................................................................................ 6

- Length 5.5 mm or less................................................................................. 8

6 Clypeus strongly emarginate.................................................... Osorius politus LeConte, 1877

- Clypeus truncate or subtruncate......................................................................... 7

7 Head distinctly narrower than the pronotum; pronotum and elytra shiny and densely punctured; length 6 mm ...................................................................................... Osorius parviceps Notman, 1925

- Head not narrower than the pronotum; pronotum and elytra dull and not densely punctured; length 7–8 mm ...................................................................................... Osorius planifrons LeConte, 1877

8 Second antennal segment subequal in length to third, following segments approximately quadrate; thoracic and elytral punctures in general coarser and more numerous; length 5–5.5 mm ....................... Molosoma latipes (Gravenhorst, 1806)

- Second antennal segment distinctly longer than third, following segments transverse; thoracic and elytral punctures in general sparser and finer; length 3.5–4 mm ........................................ Molosoma brevicorne (Notman, 1920)

9 Pronotum in front of posterior edge deeply emarginate, posterior angles with depression; pronotum and elytra pubescent; body reddish-brown, elytra slightly lighter reddish; introduced in Florida ................ Mimogonus fumator ( Fauvel, 1889)

- Pronotum in front of posterior edge not emarginate, posterior angles without depression; pronotum and elytra glabrous; body dark brown, elytra same color of the rest of the body........................................................ 10

10 Length of pronotum greater than length of elytral suture, sides explanate; elytra rugose-punctate; body relatively robust, length 2.7 mm ............................................................. Holotrochus brachypterus Fauvel, 1905

- Length of pronotum equal to length of elytral suture, sides narrow, not explanate; elytra simply punctate; body relatively slender, length 2.5 mm ................................................... Holotrochus parvulus Chapin, 1928

11 Procoxae separated ventrally by a flat or convex process of prosternum......................................... 12

- Procoxae contiguous................................................................................. 13

12 Abdominal segments with coarse diagonal to nearly longitudinal strigae, at least ventrally... Lispinus obscurus LeConte, 1863

- Abdominal segments without coarse strigae...................................... Nacaeus tenuis (LeConte, 1863)

13 Procoxal fissure open, trochantin exposed................................................................ 14

- Procoxal fissure closed, trochantin concealed.............................................................. 16

14 Head (including eyes) about 2/3 as wide as combined elytral width; pronotum widest in middle third; pronotosternal suture solid, present as a fine external carina; abdominal tergum VIII (last visible) entire, separated laterally from sternum VIII by suture................................................................. Prolibia laevicauda (LeConte, 1866)

- Head (including eyes) more than 4/5 as wide as combined elytral width; pronotum widest in anterior third; pronotosternal suture absent; abdominal sternum VIII extended dorsally in front of tergum VIII and fused to it near midline................. 15

15 Red; dorsal microsculpture deep and distinct, microsculpture on abdomen as deep and distinct as that of elytra; length greater than 2.5 mm ......................................................... Clavilispinus rufescens (LeConte, 1863)

- Yellow; dorsal microsculpture relatively less deep and distinct, microsculpture on abdomen not as deep and distinct as that of elytra; length 1.9–2.1 mm ............................................... Clavilispinus exiguus (Erichson, 1840)

16 Elytra (sometimes also head or pronotum) costate; body surfaces generally roughly sculptured and microsculptured, dull; abdominal sternum VIII extended dorsally in front of tergum VIII............................................. 17

- Elytra not costate; body coarsely punctate or not, with or without depressions along midline of pronotum but otherwise without rough sculpture, more or less shining; abdominal sternum VIII normal, not visible from above.................................................................................... Espeson Schaufuss, L. W., 1882 (undescribed sp.)

17 Eyes visible from above; combined length of pronotum and elytra <0.7 mm; pronotal disc with 2 sublateral ridges; restricted in the US to Florida ................................................ Thoracophorus guadalupensis Cameron, 1913

- Eyes not visible from above; combined length of pronotum and elytra> 0.8 mm; pronotal disc with 2 apically bifurcated, sublateral ridges, or pronotal disc with 4 ridges; widespread.................................................. 18

18 Pronotal disc with 2 apically bifurcated, longitudinal ridges; vertex of head with 2 irregular carinae..................................................................................... Thoracophorus brevicristatus (Horn, 1871)

- Pronotal disc with 4 longitudinal ridges; vertex of head with 4 complete carinae.... Thoracophorus costalis (Erichson, 1840)