Sphaeroderma komiana Kato, 2025

Kato, Makoto & Imada, Yume, 2025, Diversity and host plant utilization of leaf-mining beetles of Chrysomeloidea (Coleoptera) in Japan, ZooKeys 1238, pp. 209-268 : 209-268

Sphaeroderma komiana Kato sp. nov.

Fig. 16 K – Z

Type locality.

Japan: Okinawa Pref., Iriomote Is., Komi.

Type material.

Holotype: • ♂, Komi , Iriomote Is., Yaeyama, Okinawa Pref. (24.319°N, 123.910°E, 4 m above sea level), 16-III-2018 (collected as larva on Ixeris japonica by M. Kato), emerged on 15-V-2018 ( NSMT -I-C-200350 ) . Paratypes: • 3 ♂ 1 ♀, same data with holotype, emerged on 11–15-V-2018 ( NSMT -I-C-200351 –200354) ; • 3 ♂ 2 ♀, Shirahama , Iriomote Is., Yaeyama, Okinawa Pref., 16-III-1999 (as larva on Lactuca indica ), emerged on 21–25-IV-1999 ( NSMT -I-C-200355 – 200359) .

Diagnosis.

The species is a small oblong-oval, strongly convex beetle (length 1.8–1.9 mm) with a shiny, completely reddish brown body, elytra, and legs. The head features a pair of distinctly delimited frontal tubercles that contact each other at postero-inner angles. The inter-antennal area is raised and fusiform. The male genitalia exhibit a laterally uncurved aedeagus. The larva mines the leaves of Asteraceae plants including Ixeris japonica , Lactuca indica , and Youngia japonica .

Description.

Adult male (Fig. 16 K – Q ). Habitus. The body is oblong-oval and strongly convex on the dorsal side, measuring 1.8–1.9 mm in length (Fig. 16 K, N ). It is reddish brown, with black eyes. The antennae are dark brown, and the four basal segments, pronotum, and elytra are reddish brown (Fig. 16 N ).

Head. The head has a smooth, shiny, impunctate vertex. The frontal tubercles are transverse and posteriorly delimited by a nearly straight, deep, sharp sulcus, with antero-inner and antero-outer angles produced below, well-delimited behind by a sharp furrow, almost contacting each other at postero-inner angles (Fig. 16 O ). The inter-antennal area is raised and fusiform, with the diameter of the raised area narrower than that of the antennal socket. The eyes are strongly convex, with their transverse diameter in frontal view being 0.8 - fold wider than the inter-ocular distance. The clypeus has an entire anterior fringe. The antennae are half as long as the body. The proportional lengths of antennomeres 1–11 are as follows: 1: 0.50: 0.38: 0.51: 0.65: 0.65: 0.65: 0.65: 0.69: 0.69: 0.91.

Thorax. The pronotum is transverse, 1.7 - fold as wide as long, with the widest point located slightly before basal angles, and broadly arched at the posterior margin, with roundly produced anterior angles. The disc is evenly convex, sparsely covered with small punctures and interspaced with smooth and shining areas. The scutellum is rounded and triangular in shape, flat, impunctate, and as long as wide. The elytra are oblong and strongly convex, each measuring 2.1 - fold as long as wide, widest at the basal one-fourth area and then rounded and narrowed toward the apex (Fig. 16 K ). The disc is densely covered with 11 partially irregular, longitudinal striae of small punctures. The epipleura are wide at the base, with gradual narrowing and disappearance before the apex. The epipleural disc is impunctate and smooth. The prosternum is narrow with a stout longitudinal carina as wide as the length of the 10 th antennal segment (Fig. 16 L ).

Abdomen. The fifth visible abdominal sternite is densely covered with punctures bearing long hairs and is weakly concave apically, with a dark median longitudinal line. The legs are stout, with the first tarsal segments being moderately enlarged but distinctly narrower than the third segment. The hind legs have significantly enlarged femora.

Genitalia. (Fig. 16 P, Q ) The aedeagus is lanceolate in dorsal view, 3.6 - fold longer than its width, almost parallel-sided, and narrowed to a rounded triangular apex. Slightly curved in lateral view, with the ventral surface almost flat. The ostium is membranous, containing an inverted V-shaped sclerotized area.

Female. The body is slightly enlarged, ~ 2.0– 2.2 mm in length.

Genitalia. (Fig. 16 R ) The spermatheca is brown and sclerotized, consisting of a proximal swollen receptacle and a distal strongly curved slender pump, with the apex attenuated and curved inward. The receptacle and pump exhibit many transverse wrinkles. The spermathecal duct is proximally sclerotized, connecting to a thin transparent duct. The distal portion of the sclerotized spermathecal duct carries a globular ramus.

Distribution.

The only known distribution is on Iriomote Island, Japan.

Host plant.

Asteraceae : Ixeris japonica (Burm. f.) (Fig. 16 T – X ), Lactuca indica L., Youngia japonica (L.) (Fig. 16 Y, Z ). Ixeris japonica grows on sandy beaches along coral reefs and mangroves (Fig. 16 S ). Lactuca indica and Y. japonica grow along margins of rice field paddies.

Leaf mine.

Full depth linear mines on mature leaf, without crossing, backtracking, or branching (Fig. 16 T – W, Y, Z ). Typically, the mine is initiated near the midrib, seldom adjoining other mines. Minute granular frass is linearly deposited along the subcentral line of the mine. Upon reaching maturity, the larva exits the mined leaf in autumn and drops to the ground, where it pupates beneath the soil surface.

Etymology.

The species name refers to the village name of the type locality, which is also the original name of Iriomote Island (Komi).

Japanese name.

Komi-tamanomi-hamushi.

Remarks.

This newly identified species resembles asterid-associated S. balyi in terms of size, habitus, punctuation of elytra, and frontal tubercles of the head. However, it is distinctly differentiated from the latter by the reddish-brown color of the elytra (black in S. balyi ), parallel-sided and dorso-ventrally flattened aedeagus (aedeagus in the latter having lateral constriction in the middle and strongly curved in lateral view; Kimoto and Takizawa 1993: pl. 84, fig. 9), host plant genera ( Ixeris , Lactuca , and Youngia vs Farfugium , Parasenecio , and Petasites ), and mining pattern without adjoining trajectories (the mine of the latter is characterized by adjoining meandering trajectories; Fig. 16 B, E, I ).

This new species also resembles Clematis - associated Sphaeroderma species ( C. unicolor and yellow form of C. uenoi ) in terms of habitus and body color. However, it is distinguished from the latter by the darker color of elytra compared to their yellowish color in C. unicolor and yellow color in C. uenoi , a pair of frontal tubercles contacting each other compared to distinct tubercles in the latter ( Takizawa 2021: figs 7, 10), and laterally almost uncurved aedeagus of the male genitalia compared to the significantly aedeagus in the latter ( Takizawa 2021: figs 12, 15).

Fifteen species of Sphaeroderma have been recorded from Taiwan, 13 of which are endemic to the region ( Kimoto and Takizawa 1997; Lee 2023). The newly identified species resembles Sphaeroderma hsui Lee, 2023 , a Taiwanese species, in terms of its habitus and small size. However, it can be differentiated from the latter based on its dark brown antennae compared to the yellowish-brown antennae in the latter, transverse frontal tubercle compared to the rounded or subsquare frontal tubercle in the latter, laterally uncurved aedeagus of male genitalia compared to the laterally moderately curved aedeagus in the latter, and a slender spermathecal pump with an apical tubular appendage compared to a short pump without apical appendage in the latter.

Among 21 Sphaeroderma species recorded from Japan ( Takizawa 2021), the following five species have no known host plants ( Hayashi et al. 1984; Kimoto and Takizawa 1993):

Sphaeroderma atrum Jacoby, 1885

Sphaeroderma kuroashi Kimoto, 2000

Sphaeroderma morimotoi Chûjô & Ohno, 1964

Sphaeroderma obscurum Ohno, 1964

Sphaeroderma rubidum (Graells, 1858)

Figures

Figure 16. Adult morphology, behavior, and leaf mines of Asteraceae - associated Sphaeroderma species A – J S. balyi K – Z S. komiana sp. nov. A, D, F adult habitus in dorsal view G, O frontal view of head H, X adult feeding behavior L – N ventral, lateral, frontal view P – Q male genitalia R female spermatheca S landscape of the habitat at type locality B, C, E, I, J, T – W, Y, Z leaf mines. Host plants A – C Petasites japonicus at Ukawa, Kyôtango, Kyôto Pref. D, E Parasenecio kamtschaticus at Tôbai, Nemuro, Hokkaido F – J Farfugium japonicum at Kobukei, Nichinan, Miyazaki Pref. T – X Ixeris japonica at Komi, Iriomote Island, Okinawa Pref. Y – Z Youngia japonica at Hoshidate, Iriomote Is., Okinawa Pref.