Stenus (Nestus) delitor, Ryvkin, 2012

Ryvkin, Alexandr B., 2012, New species and records of Stenus (Nestus) of the canaliculatus group, with the erection of a new species group (Insecta: Coleoptera: Staphylinidae: Steninae), European Journal of Taxonomy 13, pp. 1-62 : 32-35

Stenus (Nestus) delitor sp. nov.

( Figs. 5C , 6A , 7A )

Material examined

RUSSIA: Holotype: ♂, ‘ Evenkia , [ Baykitskiy District ,] basin of Podka- | mennaya Tunguska River : Ko- | chumdek River 8–10 km up-stream of mouth |. 70 m a.s.l. [ rill bank , among stones (mosses and litter). (He+Hm+Ho)]. 22–24.VII.1990. A.B. Ryvkin.’ <photo label in Russian>, ‘262’, ‘HOLOTYPUS’ <my standard printed red label>, ‘ Stenus HT | delitor sp. n. | A.B. Ryvkin det., 2008’ <my standard determinative label> ( ZMMU) . – Paratypes: 1♂, together with holotype, ‘262’ ( AR) ; 2 ♂♂, 1 ♀, ‘ Evenkia , [ Baykitskiy District ,] Central Sibe- | rian [Biosphere] Reserve , basin of | Stolbovaya River : [upper reaches of]Raskol Rill (confluent of Dulkuma River), S | slope of Dulkuma | residual mountain . 250–330 [280] m a.s.l. [Bank of rill (left confluent of Raskol Rill): litter under Alnus sp., Abies sibirica , Picea obovata and mosses near water.] 16.VII. | 1991. A.B. Ryvkin’ <photo label in Russian>, ‘132’ ( AR, IRSN) ; 1 ♂, ‘ Tuva, [ Todjenskiy District , ]Azas Nature Reserve , basin | of Azas River : upper reaches of Kara | -Tesh River [(environs of the 3rd hut)]. 1150 m a.s.l. [ Carex spp., mosses and Poaceae with sparse Salix spp. etc. on river bank and near small flood-plain lake .] 06.VI. | 1990. A.B. Ryvkin’ <photo label in Russian>, ‘64’, ‘ Stenus | illusor Ryv. | A.B. Ryvkin det., 1993’ <my standard determinative label> ( AR) ; 1 ♂, ‘ Khamar-Daban Mt. Ridge | pass in upper reaches | of L.[evaya] Mishikha River , 1800 m a.s.l. | foot of glacier | 1.VII. [19]75. Shilenkov’ <photo label in Russian>, ‘ Stenus | latipennis | J. Sahlbg. | det. V.Puthz 1979’ <standard determinative label by Puthz>, ‘ Stenus | illusor A. Ryv. | A.B. Ryvkin det. 1984’ <my standard determinative label> <specimen with endophallus dissected by Puthz> ( AR) . — The paratypes listed above are also provided with both ‘PARATYPUS’ printed red label and my standard determinative label (‘ Stenus | delitor sp. n. | A.B. Ryvkin det., 2008’) for each lot.

Differential diagnosis

Stenus delitor sp. nov. is closely related to both S. (N.) latipennis J. Sahlberg, 1880 and S. (N.) illusor Ryvkin, 1987 ; it can be distinguished from these species by its smaller elytra, by the character of the puncturation and ground sculpture, and by the shape of the aedeagus. External differences from all the known species of the canaliculatus-group are given in the key below.

Etymology

The name of this species is the Latin noun ‘delitor’ (destroyer).

Description

LENGTH. 4.0– 4.6 mm (the latter value for specimens with abdomen extended).

COLORATION. Black, shining, with moderately long and dense greyish-silvery pubescence. Legs black, tibial apices and tarsi sometimes a bit lighter. Anterior margin of labrum nearly sraight, without median notch. Antennae brown to dark brown, with segments 1–2 black to brownish-black; 1st segment of maxillar palpi yellow, 2nd brown with yellowish base, 3rd dark brown, with base a bit lighter.

HEAD. Much broader than pronotum (56:46), as broad as to a bit broader than elytra between humeri (56: 56 in holotype), somewhat narrower than elytra in broadest part (56:62). Front with broad, moderately prominent longitudinal median ridge, obtuse-angled in cross-section, and flanked with two well developed lateral impressions; median elevation more than twice as broad as each of lateral portions in basal part (20:9). Puncturation fairly coarse and dense, irregular, partly nonrugosely confluent in twos to threes; basal part of median elevation punctured somewhat sparser but without conspicuous spots or strips impunctate; average diameter of punctures somewhat larger than basal cross-section of antennal segment 3. Frontal slope before antennal fossae fairly gentle. Antennae moderately long, scarsely reaching middle of pronotum. Length proportions of antennal segments 2–11 = 7:9:7:7:6:6:4:5:5:5; segments of club a little longer than broad (5:3.5, 5:4.5, 5:4).

PRONOTUM. About 1/5 to 1/6 longer than broad (54: 46 in holotype), broadest near middle, narrowed convexly towards anterior margin and concavely towards posterior one. Deep median longitudinal furrow well developed over almost entire length of disk. Laterobasal depressions very shallow, though laterobasal prominences evident. Puncturation fairly coarse, irregular, somewhat greater in middle of lengh, partly transversely confluent; punctures much greater than those of head.

ELYTRA. As broad as to a bit broader than long (62: 61 in holotype), distinctly longer than pronotum (61: 54 in holotype), although a bit shorter than pronotum (52: 54 in holotype) by suture. Humeral angles short but evident, lateral sides uniformly moderately divergent posteriorly (56:62). Humeral and sutural depressions very feeble, visible near base only. Puncturation deep, more regular and evidently larger in average diameter than that of pronotum, partly confluent, but not forming long furrows.

LEGS. Moderately long; metatibia nearly ½ longer than metatarsus (54:37); 1st segment of metatarsi a bit longer than 5 th segment (11:10.5).

ABDOMEN. Moderately convex, with well developed paratergites and two pairs of keels at bases of anterior visible tergites. Lateral sides of abdomen nearly parallel, feebly convergent in apical part. Tergite 7 with well developed light fringe at posterior margin. Puncturation of tergites fairly dense, on anterior visible tergites irregular, distinctly sparser medioposteriorly, on preapical tergites more scattered medially; average diameter of punctures on anterior visible tergite about equal to that of median elevation of head.

MICROSCULPTURE. Very fine and dense mesh-like ground sculpture well developed throughout but entirely absent in some areas both on head and pronotum and, mainly, on varnish shining interstices between punctures of elytra and along midline of anterior visible abdominal tergites; abdominal tergites 7–10 with evident reticulation. This character seems to be fairly variable in different populations.

MALE. Meso- and metatibiae without specific characters; abdominal sternites 6–7 slightly depressed along midline and cut medioposteriorly; 8th abdominal sternite with fairly broad but not deep, angularlyrounded emargination of posterior margin and with flat depression in posterior half; abdominal sternite 9 as in Fig. 5C ; aedeagus as in Figs. 6A , 7A.

FEMALE. Abdominal sternite 8 with broad, rounded apical margin.

Remarks

Until recently I have interpreted this species as being a western form of S. illusor Ryvkin, 1987 . The specimen from the Khamar-Daban was not included in the type series of the latter owing to evident differences in both external appearance and the shape of the aedeagus. Study of the material from Middle Siberia and Tuva demonstrates that S. delitor is a valid new species.

Figures

Fig. 5. ♂ copulative structures. A–E: Abdominal sternite 9. A. Stenus (Nestus) latipennis J. Sahlberg, 1880 (Russia: Krasnoyarsk Territory: Mirnoye). B. S. (N.) illusor Ryvkin, 1987 (Russia: Magadan Area: 2 km W of Splavnaya). C. S. (N.) delitor sp. nov. (holotype). D. S. (N.) canosus sp. nov. (holotype). E. S. (N.) canalis sp. nov. (holotype). F. S. (N.) caseyi Puthz, 1972 (U.S.A.: Michigan: Berrien Co.). Aedeagus, ventral view. – Scales = 0.1 mm.

Fig. 6. Aedeagus, ventral view. A. Stenus (Nestus) delitor sp. nov. (holotype). B. S. (N.) sphaerops Casey, 1884 (U.S.A.: New York: Albany Co.). – Scales = 0.1 mm.

Fig. 7. ♂ copulative structures. A–I, K: Aedeagus, ventral view. J: Abdominal sternite 9. A. Stenus (Nestus) delitor sp. nov. (holotype). B. S. (N.) illusor Ryvkin, 1987 (Russia: Amur Area: Angelokit River). C–H: S. (N.) latipennis J. Sahlberg, 1880. C. (Russia: SW Taimyr: Ladannakh Lake). D. (Russia: Taimyr: Kotuy River). E. (Russia: Putorana: Ayan Lake). F–G. (Russia: Evenkia: Kruten’kiy Stream). H. (Russia: Magadan Area: ‘Aborigen’). I–J. S. (N.) sphaerops Casey, 1884 (U.S.A.: New York: Albany Co.). K. S. (N.) melanopus Marsham, 1802 (Ukraine: Odessa Area: Krinichnoye). – Scales = 0.1 mm.