Arcastes Baly, 1865

Hazmi, Izfa Riza & Wagner, Tomas, 2010, Revision of Arcastes Baly, 1865 from the Oriental Region (Coleoptera, Chrysomelidae, Galerucinae), ZooKeys 42 (42), pp. 79-99 : 81-86

Redescription Arcastes Baly, 1865

Type species. Arcastes biplagiata Baly, 1865 by original designation.

Total length. 4.45–7.35 mm (mean: 5.67)

Head. Brownish-red to red. Very finely punctuated, with significant transverse impression between posterior third of eyes. Eyes large, strongly convex (Fig. 1). Labial palpi slender and maxillary palpi enlarged, occasionally dark brown to black ( Fig. 2a ). Labrum pale to dark brown and occasionally blackish in middle. Mandible pale yellow to dark brown and blackish towards apex. Antennae elongated, extended to apical third of elytra (Fig. 1); third to terminal antennomere densely covered by bristle-like setae. First to eighth or ninth antennomeres black, two to three terminal antennomeres contrasting pale yellow to yellowish-brown, only in A. dimidiata two basal antennomeres also yellowish. First antennomere club-shaped, second shortest, third antenno-

Figure |. Arcastes biplagiata Baly, 1865 . Dorsal colour pattern. scale bar: 1 mm (same for all following Figures)

mere about two times longer than second; ratio length of second to third antennomere 0.50–0.57 (mean: 0.54); third to seventh antennomere broad, significantly enlarged, ratio length of third to fourth antennomeres 0.60–0.70 (mean: 0.65), eighth to eleventh antennomeres much slenderer ( Figs 8, 14, 20).

Thorax. Pronotum transverse, very broad, broadest in middle, anterior angle significantly protruding, posterior angle slightly marked, pronotum with deeply impressed line along lateral margins (Fig. 1). Brownish-red to red as head, shiny, smooth, and finely punctuated, without transverse depression. Pronotal width 1.55–2.25 mm (mean: 1.90), ratio length to width 0.48–0.57 (mean: 0.53). Scutellum large, triangular, impunctate, brownish, red or black. Procoxal cavities partly open ( Fig. 2b ). Meso- and metathorax reddish-brown to black. Metasternum broad ( Fig. 2c ). Elytra elongated, either black throughout, or black with longitudinal yellowish-red spot on disc of each elytron, or black with yellowish to reddish suture that in some species reaches

b

up to one third of each elytron, or basal third completely red and apical two thirds black. Elytra shiny, punctation fine, irregular, slightly coarser and denser than that of pronotum. Elytral length 3.80–5.90 mm (mean: 4.73), maximum width of both elytra together 1.50–4.00 mm (mean: 2.79), ratio of maximum width of both elytra together to length of elytra 0.61–0.72 (mean: 0.66). Alae fully developed ( Fig. 4 ). Legs long and slender, basi-metatarsus elongated ( Fig. 5 ), coxa and trochanter reddish like underside, femur, tibia and tarsus black throughout, tibia with dense and fine setae.

a

b

c

Abdomen. Pale yellow to reddish-brown, occasionally darker in middle, and seventh sternite usually dark brown to black. Last visible sternite in females rounded at apex, and in males with two deep, parallel-sided incisions ( Fig. 3 ).

Male genitalia. The outer shape of median lobe is symmetrical, strongly sclerotized, apex tapered, slightly rounded and not incised. Orifice wide, more or less circular to slightly rectangular. Endophallic structures asymmetrically arranged, ventral spiculae hammer-like, median spiculae narrower, slender, lateral spiculae enlarged and slender, with claw-like small spine medially and tube-like, curved spines. Tectum not incised at apex, almost reaching apex of the median lobe, constricted at middle part and enlarged at base ( Figs 9 , 15, 21).

A. dimidiata A. biplagiata I 2–3 4–6 7–I3

Female genitalia. Spermatheca with oval to slender and elongated nodulus. Middle part long and slightly curved, cornu long and curved (Figs 10, 16, 22). Without stronger sclerotized bursa sclerites.

Distribution. The species are restricted to South-East Asia and up to now only recorded from Singapore, Malaysia (Peninsular) and Indonesia (Borneo, Sumatra), southwards to Java ( Figs 6, 17).

Diagnosis. Beetles of the genus Arcastes are medium sized Galerucinae with strongly elongated basi-metatarsus, without pronotal impressions, reddish head and pronotum and usually contrasting black antennae, legs and elytra, the latter often with yellowish to red spots, suture or base. The significantly enlarged third to eighth antennomeres are very characteristic. Arcastes is the most similar to Neolepta Jacoby, 1884 , with the type species, Neolepta biplagiata Jacoby, 1884 , looking very similar to Arcastes biplagiata at the first glance. Antennae of these beetles are similar with slightly to strongly enlarged antennomeres in the middle, while terminal antennomeres in Neolepta are also black, the basal two antennomeres are reddish, and much slenderer than in Arcastes . The dorsal coloration is also similar, but N. biplagiata posses a pale yellowish transverse band or nearly circular spot in the middle of each elytron. The genitalic patterns of both sexes possess very strong differences. Asymmetric endophallic spiculae of certain shape ( Figs 9 , 15, 21) as in Arcastes are a unique pattern in oriental galerucines with elongated basi-metatarsus, while the median lobe in Neolepta , as in Monolepta , and Candezea , is narrower and has symmetrically arranged endophallic spiculae which are much smaller (cf. Wagner 2001, Wagner and Kurtscheid 2005). The shape of spermatheca of Arcastes resembles that of Monolepta , but in Arcastes it lacks sclerotized bursa-sclerites, while in Monolepta there are two distinct types of this structure. Also Neolepta and Candeza have strongly sclerotized bursa-sclerites.

The pronotum of Arcastes (ratio length to width 0.48–0.57), is on average broader than in Monolepta and Neolepta (0.52–0.65), and within the range of Candezea (0.42– 0.59). Procoxal cavities are similarly structured (partly open) in all these genera. The third antennomere of Arcastes is roughly twice as long as the second (ratio length of second to third antennomere: 0.50–0.57), which is similar to Candezea (0.49–0.63) but different from Neolepta and Monolepta which both have the second and third antennomere of about equal length (0.82–1.10). While Candezea have strongly elongated, slender antennomeres, Arcastes species can be clearly differentiated by the enlarged median ones.

Redescriptions of species

Figures

Figure 2. Arcastes biplagiata Baly, 1865. a Head b prothorax c meso- and metathorax, ventral view.

Figure 3. Arcastes biplagiata Baly, 1865. Abdomen, ventral a male b female.

Figure 4. Arcastes biplagiata Baly, 1865. Hindwing, right, dorsal view.

Figure 5. Arcastes biplagiata Baly, 1865. Legs: a prothoracic b mesothoracic c metathoracic.

Figure 9. Arcastes biplagiata Baly, 1865. Median lobe: a dorsal b lateral c ventral.