Hook-shaped end leaf beetle (Arthrotus hamatus) and black spot leaf beetle (Arthrotus oculatus)

NEWS - Researchers describe hook-shaped end leaf beetle (Arthrotus hamatus sp. nov.) and black spot leaf beetle (Arthrotus oculatus sp. nov.), along with 17 other species and one newly recorded species in China: Arthrotus kalimponganus Kimoto 2004, all from Nanling, China.

Arthrotus Motschulsky 1857 with Arthrotus niger 1857 from Japan as the type species encompasses 48 species distributed in the Eastern and Palearctic regions. Now researchers describe specimens collected from Nanling, including 2 new species and one new record, bringing the total to 50 species worldwide, with 31 species in China.

The genus is characterized by body oblong. Vertex with median furrow, postantennal tubercle well developed, with a longitudinal furrow between postantennal tubercles; a ridge-like convex located between antennae; antennae longer than half the length of the body; in both sexes, antennomere II shortest, antennomere III second shortest, antennomere IV longer than the sum of antennomeres II+III.

Pronotum wider than long, bordered all around; convex disc with or without punctures. Scutellum triangular and convex dorsally. Elytra narrow at base, widening after middle; humeral calli protruding, disc with coarse and deep punctures; epipleura wide at base, gradually narrowing to apex.

The front coxal cavities are closed, the tarsal claws appendiculate. Last sternite of male trilobed; in female, last sternite with no incisions. The genera Arthrotus and Dercetina are very similar, with no significant difference in male external genitalia.

A. hamatus has a body length of 7.5-8.5 mm. Body blue with purple metallic luster; eyes greyish-white; antennae blackish-brown, antennomeres I & II metallic blue; pro- and mesothorax black; yellowish-brown abdomen; tarsomere I black, the rest brown. Vertex with fine punctures and irregularly scattered slender setae, postantennal tubercle square with a transverse groove behind.

Antennae about 9/10 length of body, antennomeres IV to XI densely covered with short setae, antennomeres II and III shortest and subequal, antennomeres IV longest, antennomeres V to convex disc with fine punctures; scutellum triangular, scattered with small punctures.

Elytra with prominent humeral calli, lateral margins slightly concave at basal 1/4, disc densely punctate, distance between punctures about twice the diameter of the punctures; epipleura wide at base, narrowing and end at middle; legs slender, length of tarsomere I of hind leg longer than sum of tarsomeres II+III.

Aedeagus slender and nearly parallel-sided, only slightly narrowed at middle and subapical region; apex rounded with a hook-shaped end; the primary endophallus sclerite about 0.5× as long as aedeagus, sclerite bifurcate from base to basal 1/4, constricted greatly at basal 1/2 and subapical region, apex covered with densely setae, a small sclerite located above the primary one, hook-shaped on lateral view and arrow-shaped on ventral view.

The new species is similar to A. hijau Mohamedsaid 2001 from Malaysia. However, A. hamatus has antenomere I longer and narrower; setae on antenomeres III-XI shorter and denser; antenomere IV is the longest; lateral edge of pronotum straight; aedeagus more elongated, slightly narrowed at subapical region and has a hook-shaped structure at the tip.

While in A. hijau, antenomere I is slightly shorter and wider; setae on antenomeres III-XI are longer and slightly less frequent; antenomeres V are the longest; lateral edges of pronotum are slightly curved; aedeagus is shorter and wider, broad at the tip, not tapering in the subapical region, more slender at the apex, not hooked at the tip.

The specific name is derived from the Latin word “hamatus” referring to the hook-shaped tip of the aedeagus. Distribution in Guangdong (Ruyuan) and Hunan (Yizhang).

A. oculatus has a body length of: ♂ 4.9–5.1 mm; ♀5.1 mm. Head brown; antennae black-brown, except antennomeres I and II yellowish brown; pronotum yellowish brown; scutellum yellow; elytra pale yellow, with a pattern of greyish and black markings, humeral calli covered with a black spot, another black spot located at apical 1/3, scutellum around and basal 1/2 near mesal suture dark brown mixed with black.

Epipleura black from base to apical 1/3; a greyish transverse band cross both elytra with middle narrowed greatly, expanding alone the mesal suture, fading and disappearing at apex. The single female specimen shows a second black spot near middle band, not obvious; ventral side of body, coxa, trochanter and femur yellowish-brown, tibia and tarsus black-brown.

Vertex convex and impunctate; postantennal tubercle well developed and subtriangular, surface smooth and impunctate; antennae shorter than body length, antennomeres II and III shortest and subequal, antennomeres IV longest, twice as long as sum of antennomeres II+III, antennomeres V–VIII equal, shorter than antennomeres IV, antennomeres IX–X equal, shorter than antennomeres VIII, antennomeres XI slightly shorter than antennomeres X.

Pronotum 2× wider than long, anterior angle distinctly protruding, disc covered with sparse inconspicuous punctures, with a slight depression in central region; scutellum triangular, smooth and impunctate; humeral calli of elytra protruding, disc with middle region moderately convex, with densely coarse punctures.

Epipleurae begin to narrow between coxae of mid and hind legs, reaching to apex; length of tarsomere I of hind-leg equal to the sum of tarsomeres II+III. Aedeagus slender, nearly parallel-sided with middle slightly narrowed and basal widened, apex rounded; tectum membranous, covered with tiny and stout setae; moderately curved in lateral view; endophallus sclerite 0.5× as long as aedeagus, apex trifurcated, with densely setae near apex.

Female sternite VIII weakly sclerotized, apical region fan-shaped with truncate apex, apical margin with sparse long setae; spiculum extremely long and slender. receptacle of spermatheca moderately swollen; pump slender and slightly curved, apex rounded; proximal spermathecal duct sclerotized, wide and long. Gonocoxae are connected from basal and bifurcate at the middle, with one longest hair at the apex and several additional hairs at the apical region.

This species is similar to A. yangi Lee, but A. oculatus has more obvious punctures on the elytra, and the spacing between the punctures is significantly narrower than in A. yangi. The apex of the elytra is not black, but has a black spot that does not reach the edge (vs. the edge of the elytra is all black, and the black area is narrow at the base and wide at the apex, the disc has no free black spots in A. yangi).

The spicule of sternite VIII in females is longer and slender; the spermathecal receptacle is more swollen, the apex of the aedeagus is rounded (vs. the apex of the aedeagus is more pointed, sternite VIII with relatively shorter spicules, and the spermathecal receptacle is slightly swollen in A. yangi).

The specific name is derived from the Latin word “oculatus” which refers to the black spot on the white area at the apex of the elytra, shaped like a cat's eye. Distribution in Guangdong (Ruyuan).

Original research

Jian Shen, Hai-Dong Yang, Chang-Ping Ding & Mei-Xia Yang (2024). Notes on Arthrotus Motschulsky, 1857 from Nanling region of China (Coleoptera: Chrysomelidae), with descriptions of two new species. Zootaxa 5528 (1): 744–757, DOI:10.11646/zootaxa.5528.1.50

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