Diestota (Diestota) ogasawarana Hashizume & Kishimoto, 2025

Hashizume, Takuto & Kishimoto, Toshio, 2025, Discovery of the aleocharine tribe Diestotini in Japan, Ogasawara Islands, with description of a new species of the genus Diestota Mulsant & Rey (Coleoptera: Staphylinidae), Zootaxa 5660 (4), pp. 581-586 : 583-585

Diestota (Diestota) ogasawarana Hashizume & Kishimoto , sp. nov.

( Fig. 1 )

[Japanese name: Ogasawara-kawari-hanekakushi]

Type materials. Holotype: male, JAPAN: “ Ogasawara Islands / Haha-jima Is . / Sekimon / 3. vii. 1997 / T. Kishimoto leg.” ( SPMN) . Paratypes: JAPAN: Ogasawara Islands : Haha-jima : 2 males, 3 females, same data as holotype ( SPMN) ; 3 males, 2 females, same data, but 5 VII 1997 ( SPMN) ; 1 male, 3 females, same data, but 8 VII 1997, by Tullgren extractor ( SPMN) ; 2 males, Sakaigatake , 5 VII 1997, T. Kishimoto leg. ( SPMN) ; 1 male, Sakaigatake– Sekimon , 9 III 1999, T. Kishimoto leg. ( SPMN) ; 9 males, 5 females, Mt. Chibusa-yama , 6 VII 1997, T. Kishimoto leg. ( SPMN) .

Diagnosis. This species is somewhat similar to Diestota ming Pace, 2004 , described from Hong Kong, China, in the appearance and the shape of the spermatheca, but it can be distinguished by the smaller elytra and the smaller widely coiled portion of the spermatheca. This species also similar to D. tongana Pace, 1993 , described from Tonga, but it can be distinguished by the smaller elytra, the longer processes of the male tergite VIII, the larger basal bulb of median lobe of aedeagus.

Description. Measurements (n = 5): BL: 1.82–2.00; FBL: 0.83–0.86; HW: 0.33–0.36; PL: 0.28–0.31; PW: 0.39–0.43; EL: 0.32–0.34; EW: 0.44–0.47.

Relative length of antennomeres 1–11 (n = 1): 26: 19.1: 17.9: 11.7: 10: 10.7: 11.1: 11.5: 12.5: 12.3: 33.2. Ratio of length/width of antennomeres 1–11 (n = 1): 2.14, 1.68, 1.68, 0.96, 0.77, 0.72, 0.63, 0.68, 0.65, 0.58, 1.65.

Body ( Fig. 1A ) yellowish to reddish brown, antennomeres 4–11 and abdomen somewhat darker.

Head almost circular, sparsely punctured with fine punctures, without microsculpture; setae suberect and directed anteromedially. Eyes small, almost as long as temporal length. Antennomeres 1–3 and 11 longer than wide, 4 as long as wide, 5–10 wider than long. Labium ( Fig. 1B ) with ligula slender, divided in basal 2/5, approximately 1/2 times as long as labial palpomere 1; two medial setae of prementum arranged transversely, close each other; medial pseudopore field narrow, without pseudopores. Labial palpus ( Fig. 1B ) moderately long, with two palpomeres; palpomere 1 somewhat longer than 2. Mentum trapezoidal, anterior margin deeply emarginate, lateral margin slightly sinuate.

Thorax. Pronotum transverse, 1.29–1.38 times as wide as long, widest around anterior 2/5, densely covered with punctures larger than those of head, without microsculpture; 1.15–1.17 times as broad as head, with shallow posteromedian transverse impression; setae on disc suberect and directed posterolaterally. Elytra transverse, 1.36– 1.45 times as wide as long, 1.04–1.15 times as long as pronotum, 1.10–1.19 times as wide as pronotum, puncturation sparser than pronotum with punctures larger than those of pronotum, without microsculpture; posterior margin distinctly sinuate; setae suberect and directed posteriorly. Hind wings reduced, approximately as long as elytra.

Abdomen sparsely punctured with fine punctures; tergites III–V with basal impressions; impression of tergite IV with a few short longitudinal keels; anterior area of tergites V–VII with several longitudinal keels, usually ten or more keels on tergite VI; setae suberect, longer and sparser than those of forebody.

Male. Sternite VII with small medial lobate projection on posterior margin ( Fig. 1C ). Tergite VIII ( Fig. 1D ) with eight processes on posterior margin, outer ones sharp and slightly curved, second outer ones longer than the others. Parameres of aedeagus ( Fig. 1E ) with broad apical lobe. Median lobe of aedeagus ( Figs. 1F, G ) with moderately large basal bulb; apical process narrow and sinuate in lateral view; copulatory piece simple.

Female. Sternite VII and tergite VIII not modified. Spermatheca ( Fig. 1H ) extremely long, coiled narrowly at the proximal part, coiled widely near distal end; distal portion ( Fig.1I ) slightly thickened, its terminal part round and flattened.

Distribution. Japan ( Ogasawara Isls : Haha-jima Is.).

Etymology. Named after the Ogasawara Islands , which include Haha-jima Island, where all specimens were collected.

Remarks. In referring to the key to subgenera provided by Pace (1986), this species is considered to belong to the subgenus Diestota because the anterior margin of the mentum is deeply emarginate.

The soil ecosystem of the Ogasawara Islands has suffered catastrophic decline due to predation by the nonnative terrestrial nemertean (ribbon worm), Geonemertes pelaensis Semper, 1863 ( Shinobe et al. 2017). Geonemertes pelaensis has also invaded Haha-jima Island, and, like many other soil-dwelling arthropods, Diestota ogasawarana sp. nov. is likely at high risk of extinction due to predation by G. pelaensis . In Haha-jima, Platydemus sp. , a terrestrial flatworm, which is not known whether alien or native in the Ogasawara Islands , is also known to prey on terrestrial insects ( Shoji & Karube 2023), and the impact of this terrestrial flatworm is also a concern.

Figures

FIGURE 1. Diestota (Diestota) ogasawarana Hashizume & Kishimoto, sp. nov. A, habitus in dorsal view; B, labium; C, male abdominal segment VII (arrow indicates medial lobate projection of sternite VII); D, male tergite VIII; E, right paramere of aedeagus; F, median lobe of aedeagus, lateral; G, ditto, ventral; H, spermatheca; I, distal portion of spermatheca. Scale bars: 1.0 mm for A; 0.1 mm for B–I.