Microvelia (Picaultia) yoshitomii Watanabe, 2023

Watanabe, Kohei, 2023, A new species of the broad-shouldered water strider genus Microvelia Westwood (Hemiptera: Heteroptera: Veliidae) from the Ogasawara (Bonin) Islands, Japan, Zootaxa 5375 (1), pp. 142-150 : 143-149

Microvelia (Picaultia) yoshitomii Watanabe , sp. nov.

[Japanese name: Ogasawara-keshi-katabiroamembo]

( Figs. 1–21 )

Type Material. HOLOTYPE: apterous male ( EUMJ), Minamizaki , Haha-jima, Ogasawara Islands, Japan, N26 37.491 E142 10.600, 25 IX 2012, H. Yoshitomi leg. PARATYPES: 3 apterous males, 1 macropterous male, 20 apterous females, 18 macropterous females ( EUMJ, IIM), same data as holotype .

Description.Apterous male ( Figs. 1 , 5–13 , 15–20 ). Coloration: Head grayish-brown, dorsal midline black, pits of cephalic trichobothria black; buccula dark-orange; labial segments I–III dark-orange, segment IV black; antennal segment I yellowish-brown, with basal part light yellowish-brown, segments II–IV yellowish-brown; circumocular area narrowly silver; eyes dark-red; pronotum grayish-brown, with light-brown transverse band along anterior margin excluding both anterolateral angles, and with blackish-brown transverse band just behind light-brown transverse band, setae on light-brown transverse band silver, midline blackish-brown, punctures blackish-brown; metapleuron grayish-brown; fore, middle, and hind legs mainly yellowish-brown, basal part of femur light-yellowish-brown, apex of femur dark-brown; abdomen mainly grayish-brown, posterolateral portions of mediotergites I–III with uniformly distributed silvery pubescence, middle of mediotergites I–V with mesal blackish-brown patch, middle of mediotergites VI–VII with a mesal blackish-brown longitudinal line; all laterotergites, segment VIII, pygophore (segment IX), proctiger, and parameres brown. Structure: Body elongate-oval, approximately 2.6 times as long as body width. Head ( Fig. 1 ) Short and wide, approximately 1.5 times as wide as its length; eyes with two ocular setae; ocelli absent; antenna approximately 0.5 times as long as body, proportional lengths of antennal segments I–IV 1.1: 1.0: 1.4: 2.1; labium reaching middle of mesosternum. Pronotum broad, approximately1.6 times as wide as its length, with sparse punctures, posterior margin arched posteriad; mesonotum completely hidden under pronotum; metanotum hidden under pronotum except lateral parts. Legs generally covered with many short setae. Fore leg ( Figs. 5, 8, 11 ) short; femur with several long setae apically, setae on inner margin longer than those on outer margin; tibia strongly projected in baculiform at apex, with very short grasping comb apically ( Fig. 8 ) and comb-like setae apicoventrally, short setae more densely distributed ventrally; tarsus with a pair of pretarsal claws subapically ( Fig. 11 ). Middle leg ( Figs. 6, 9, 12 ) long; femur simple, with several long setae apically, setae on apical inner longer than setae on apical outer; tibia covered with long setae in apical 2/5 ventrally and in whole length dorsally, short setae more densely distributed ventrally, and with strong thumb-like projection apicoventrally and short grasping comb apically ( Fig. 9 ); tarsomere I–II setae on outer surface longer than those on inner surface; tarsomere II approximately 1.4 times as long as tarsomere I, with a pair of pretarsal claws subapically; ventral arolium bristle-like. Hind leg ( Figs. 7, 10, 13 ) long; femur simple, with several long setae apically; tibia with short setae densely distributed apicoventrally; tarsomere I–II setae on outer surface longer than setae on inner surface; tarsomere II approximately 1.1 times as long as tarsomere I, with a pair of pretarsal claws subapically; ventral arolium bristle-like. Abdomen slightly narrowed apicad; all mediotergites flat; mediotergites I–VI subequal in length, evidently wider than its length of respective mediotergites; mediotergite VII longest, slightly wider than its length; laterotergites slightly raised. Genital segments ( Figs. 15–20 ): Segment VIII ( Fig. 15 ) approximately 1.1 times as long as its maximum width, symmetrical, covered with many light-brown setae along posterior margin, anteroventral margin strongly concave in M-shape, middle of posterodorsal margin shallowly depressed, tergite longer than sternite; pygophore ( Figs. 18, 20 ) small, rounded ventrally, covered with many light-brown setae except basal part; parameres asymmetrical, right paramere ( Figs. 16–18 ) large, broad in basal part, covered with many erect setae in basal half, slightly sinuate in ventral view, apically rounded in lateral view, abruptly narrowed and obtuse at apex in ventral view, with slightly curved dorsal margin and almost straight ventral margin in lateral view; left paramere ( Fig. 18 ) small, with long setae; proctiger ( Figs. 19−20 ) rounded apically, narrowed near middle, broadened at base, lacking lateral processes, covered with sparse setae on basal half of dorsal surface and many light-brown long setae on apical half of all surface.

Measurement. See Table 1 .

Apterous female ( Fig. 2 ). Similar to those of apterous male. Body larger than that of male. Body approximately 2.4 times as long as maximum body width. Head approximately 1.5 times as wide as its length; antenna approximately 0.5 times as long as body, proportional lengths of antennal segments I–IV 1.1: 1.0: 1.3: 2.0. Pronotum approximately 1.8 times as wide as its length. Fore and middle tibiae without apical projection and grasping comb ( Fig. 2 ), hind tibia slightly longer than hind femur; middle tarsomere II approximately 1.3 times as long as tarsomere I, hind tarsomere II approximately 1.1 times as long as tarsomere I. Abdominal mediotergites ( Fig. 2 ) flat, mediotergite VII longest, I–VIII wider than long.

Measurements. See Table 1 .

Macropterous male and female ( Figs. 3–4 ). Pronotum large, pentagonal, with developed humeri. Hemelytron ( Fig. 14 ) mainly grayish-brown, surpassing abdominal apex, with four closed cells, most veins brownish, base of An (anal) vein and R (radius) +M (media) +Cu (cubitus) vein creamy white, two basal closed cells mostly creamy white, two middle closed cells with at least one creamy white spot, apical unclosed cell with one creamy white spot, basal 2/3 of anterior margin (Sc: subcosta) and R+M+Cu vein covered with dense blackish-brown setae. Other coloration and structures similar to those of apterous male and female.

Measurements. See Table 1 . The measurements of other structures of the macropterous male and female are almost the same as those of the apterous male and female, except body length and wide and pronotum length and wide.

Etymology. The specific name is dedicated to Dr. Hiroyuki Yoshitomi, who collected all available specimens; a noun in the genitive case.

Diagnosis. This new species belongs to the subgenus Picaultia based on the diagnostic characters, including the grasping comb length of the male fore tibia less than 1/4 of the tibial length; the grasping comb present on the fore and middle tibiae; the male parameres asymmetrical, with the right paramere large and the left paramere distinctly smaller ( Andersen & Weir, 2003; 2004). Microvelia (P.) yoshitomii sp. nov. is similar in general appearance to M. (P.) douglasi , M. (P.) japonica and, M. (P.) pilosa , but can be distinguished by a combination of the following characteristics:

From M. douglasi , proportional lengths of hind tarsomere II/I in both sexes approximately 1.1 (vs. approximately 1.4 in M. douglasi ), apex of male fore and middle tibiae strongly projected ( Figs. 8–9 ) (vs. weakly projected), anteroventral margin of male abdominal segment VIII concave in M-shape ( Fig. 15 ) (vs. shallowly depressed), and right paramere apically rounded and not markedly narrowed in lateral view, with ventral margin almost straight in lateral view ( Fig. 16 ) (vs. apically pointed and markedly narrowed, with ventral margin evenly curved) ( Andersen & Weir, 2003).

From M. japonica , proportional lengths of hind tarsomere II/I in both sexes approximately 1.1 (approximately 1.5 in M. japonica ); apex of male fore and middle tibiae strongly projected ( Figs. 8–9 ) (vs. weakly projected), anteroventral margin of male abdominal segment VIII concave in M-shape ( Fig. 15 ) (vs. shallowly depressed), and right paramere apically rounded and not markedly narrowed in lateral view, with ventral margin almost straight in lateral view ( Fig. 16 ) (vs. apically pointed and markedly narrowed, with ventral margin evenly curved) ( Esaki & Miyamoto, 1955).

From M. pilosa , proportional lengths of hind tibia/femur in both sexes approximately 1.0–1.1 (vs. approximately 1.3–1.4 in M. pilosa ), proportional lengths of hind tarsomere II/I in both sexes approximately 1.1 (vs. approximately 1.4), apex of male fore and middle tibiae strongly projected ( Figs. 8–9 ) (vs. weakly projected), anteroventral margin of male abdominal segment VIII concave in M-shape ( Fig. 15 ) (vs. shallowly depressed), and right paramere apically rounded and not markedly narrowed in lateral view, with ventral margin almost straight in lateral view ( Fig. 16 ) (vs. apically pointed and markedly narrowed, with ventral margin evenly curved) ( Matsushima et al., 2021).

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

Biology. Microvelia yoshitomii sp. nov. was collected from a small pool in primary forest ( Fig. 21 ).

Remarks. Microvelia douglasi has been recorded in the Ogasawara Islands based on specimens collected from Haha-jima, Chichi-jima, and Kitaiou-jima Islands ( Tomokuni & Satô, 1978; Shimamoto & Ishikawa, 2023). These specimens might represent this new species; thus, re-examination is necessary to verify their identities.

The sex ratio of Veliidae is suggested to be related to mate-guarding behavior, an important behavioral ecological aspect (e.g., Arnqvist et al., 2007; Watanabe et al., 2023). The type series of M. yoshitomii sp. nov. collected on the same day and at the same locality had a substantially high number of females (male: female = 5:38). The sex ratio of M. iriomotensis of the same subgenus was almost equal in captivity (male: female = 118:108) (Watanabe et al., 2023). In contrast, some veliid species are known to be markedly male-biased in natural populations, such as Phoreticovelia rotunda Polhemus & Polhemus, 2000 and P. disparate Polhemus & Polhemus, 2000 ( Arnqvist et al., 2007). The sex ratio bias of M. yoshitomii sp. nov. may be related to its unique ecology, and future research on this subject is required.

The ratio of apterous to macropterous individuals of the type series was 23:19. The habitat of this species is a small water pool ( Fig. 21 ), which can easily disappear without rainfall for duration. The higher ratio of macropterous to apterous individuals may be attributed to their habitat in an unstable small pool, which creates the requirement for frequent flight.

Figures

FIGURE 21. Pool in the forest at the type locality of Microvelia yoshitomii sp. nov. Photograph by Dr. Hiroyuki Yoshitomi.

FIGURES 1–4. Microvelia yoshitomii sp. nov., dorsal aspect. 1, 3, male; 2, 4, female. 1, Holotype; 2–4, paratypes. 1–2, Apterous; 3–4, macropterous.

FIGURES 5–13. Legs of Microvelia yoshitomii sp. nov. male. 5, 8, 11, fore leg; 6, 9, 12, middle leg; 7, 10, 13, hind leg. 5–7, Femur; 8–10, tibia; 11–13, tarsus. Scale bars = 0.05 mm.

FIGURES 14–20. Fore wing, abdominal segment VIII, pygophore, and proctiger of Microvelia yoshitomii sp. nov. 14, Left fore wing (female); 15, abdominal segment VIII, ventral view; 16–17, right paramere, lateral (16) and ventral (17) views; 18–19, pygophore (segment IX), proctiger, parameres, dorsal (18) and lateral (19) views; 20, proctiger, ventral view. Scale bars for 14 = 0.5 mm, for 15–20 = 0.05 mm.