Arixyleborus silvanus, Smith & Beaver & Cognato, 2020

Smith, Sarah M., Beaver, Roger A. & Cognato, Anthony I., 2020, A monograph of the Xyleborini (Coleoptera, Curculionidae, Scolytinae) of the Indochinese Peninsula (except Malaysia) and China, ZooKeys 983, pp. 1-442 : 1

Arixyleborus silvanus sp. nov. Fig. 29C, D, J

Type material.

Holotype, female, Thailand: Chiang Mai, Doi Pui, 1400 m, 20.xii.2004-10.i.2005, W. Puranasakul, ex EtOH trap (NHMUK). Paratypes, female, as holotype (MSUC, 1); as previous except: 8-10.xi.2004 (QSBG, 1); as previous except: 10-31.i.2005 (RABC, 2); China: Guangxi, Shangsi, Shiwandashan, 27.iii.20017, Y. Li, ex Liquidambar formosana (IZAS, 1); Hainan, Wu-zhi-shan Town, 18.902N, 109.663E, 703 m, 2.xii.2016, Tian-Shang & Lv-Jia (RABC, 1).

Diagnosis.

1.65-1.8 mm long (mean = 1.72, n = 5); 2.6-2.7 × as long as wide. This species is distinguished by its elongate form and steeply sloping declivity; posterolateral margin with a series of granules; pronotal summit distinctly anterior to middle; elytral disc with striae impressed on posterior part; and interstriae 1-3 extending to apex of declivity, armed with uniseriate granules.

Arixyleborus silvanus is distinguished from A. mediosectus by its less elongate form (2.9-3.3 × as long as wide in mediosectus ), and less elongate pronotum (1.1-1.2 × longer than wide vs. 1.3 × in mediosectus ), the more coarsely granulate interstriae, and more deeply impressed striae at the apex of the elytral disc, and the presence of fine hair-like setae on the declivity rather than coarse setae. It can be further distinguished from the closely related A. crassior by the more elongate form (2.5 × as long as wide in A. crassior ), more stout pronotum (1.1-1.2 × longer than wide vs. 1.3 × in A. crassior ), the more coarsely granulate interstriae, and weakly impressed striae at the apex of the elytral disc, and the presence of fine hair-like setae on the declivity rather than coarse setae.

Similar species.

Arixyleborus crassior , A. mediosectus , A. phiaoacensis .

Description

(female). 1.65-1.8 mm long (n = 5); 2.6-2.7 × as long as wide. Body uniformly red-brown. Legs and antennae yellow-brown. Head: epistoma entire, transverse, lined with a row of hair-like setae. Frons slightly convex from epistoma to upper level of eyes; surface alutaceous, shiny, sparsely punctate; punctures above epistoma large, coarse, shallow; punctures decreasing in size, coarseness, and depth from epistoma to upper level of eyes. Eyes deeply emarginate above level of antennal insertion, upper portion of eyes smaller than lower part. Submentum deeply impressed, very narrow, triangular. Scape short and thick, approximately 3/4 length of club. Pedicle as long as funicle. Antennal funicle 4-segmented, segment 1 shorter than pedicel. Club wider than long and asymmetrical, club type 1; obliquely truncate, segment 2 not visible on posterior face; segment 1 covering posterior face, its margin completely costate; segment 2 narrow, pubescent with corneous part, visible on anterior face only. Pronotum: 1.33 × as long as wide. In dorsal view long and rounded frontally, type 7, sides parallel in basal 2/3, rounded anteriorly; anterior margin without serrations. Pronotum with disc much longer than anterior slope, type 7, summit low. Surface shagreened, anterior 1/2 finely asperate, asperities close, arranged in concentric rings from midpoint of pronotum to anterior margin; anterolateral areas unarmed; disc minutely and sparsely punctate; glabrous. Lateral margins obliquely costate. Base weakly bisinuate; setal tuft absent. Elytra: 1.53 × as long as wide, 1.32 × longer than pronotum. Scutellum moderately sized, linguiform, flush with elytra, flat. Elytral base weakly bisinuate, edge oblique, humeral angles rounded, sides straight from base to apical 1/2 of declivity, then rounded to apex. Disc longer than declivity, distinctly separated, shiny; striae impressed, punctures on basal 1/2 larger and deeper than those on apical 1/2; interstriae minutely, finely uniseriate punctate from base to midpoint, moderately setose, basal 1/2 of interstriae shagreened, dull, becoming sharply carinate, denticulate. Declivity obliquely truncate, strongly shagreened, dull; striae punctate, punctures large, shallow, glabrous; interstriae tuberculate, tubercles small, each bearing a fine hair-like seta, less than the distance between tubercles in length; interstriae 1-3 extending to apex of declivity, armed with uniseriate granules. Posterolateral declivital margin carinate, tuberculate to interstriae 7. Legs: Protibiae slender, broadest at apical 1/3; posterior face inflated, tuberculate; outer margin of apical 1/2 with five small socketed denticles. Meso- and metatibiae flattened, outer margin evenly rounded with seven socketed denticles; posterior face unarmed.

Etymology.

L. silvanus = associated with forests. An adjective.

Distribution.

China (Guangxi, Hainan), Thailand.

Host plants.

This species is only recorded from Liquidambar formosana ( Altingiaceae ).

Figures

Figure 29. Dorsal, lateral and declivital view of Arixyleborus setosus holotype, 2.5 mm (A, B, I), A. silvanus holotype, 1.65 - 1.8 mm (C, D, J), A. sittichayai holotype, 2.3 mm (E, F, K), and A. suturalis, 1.5 - 1.7 mm (G, H, L).