﻿Revision of the xyleborine ambrosia beetle genus Microperus Wood, 1980 (Curculionidae, Scolytinae, Xyleborini) of Thailand with four new species and four newly recorded species

﻿Abstract Microperus Wood, 1980 ambrosia beetles in Thailand are reviewed. Four species, M.bidentatussp. nov., M.bucolicussp. nov., M.globodeclivissp. nov., and M.serratussp. nov. are described. Four new combinations are given: Microperusarmaticeps (Schedl, 1942) comb. nov., Microperusexsculptus (Eggers, 1927) comb. nov., Microperuspedellus (Schedl, 1969) comb. nov., and Microperusspicatulus (Browne, 1986) comb. nov., stat. res., all from Xyleborus. Two new synonyms are proposed: Microperuscruralis (Schedl, 1975) (= Xyleborusmyllus Browne, 1986 syn. nov.), Microperusexsculptus (Eggers, 1927) (= Xyleborusdentipennis Browne, 1983 syn. nov.). Four species are reported from Thailand for the first time: Microperuschrysophylli (Eggers, 1930), Microperusexsculptus, Microperusnanus (Browne, 1949) and Microperusquercicola (Eggers, 1926). With the inclusion of the Microperus species described and recorded herein, the diversity of Microperus is increased to 35 species, of which 18 are recorded in Thailand. An updated key to the Microperus of the Indochinese Peninsula and China is provided. The taxonomy, diagnostic characters, and distribution of species are briefly discussed.


Introduction
The xyleborine ambrosia beetle genus Microperus was first erected by Wood (1980) for members of the Xyleborus theae Eggers, 1940 species group, but the genus name was initially proposed in an unpublished manuscript by F. G. Browne (Wood 1980). Wood diagnosed Microperus species as slender, at least 2× as long as wide, posterior face of the antennal club with at least one suture visible and apical margin of corneous area never costate, scutellum invisible and strial punctures usually seriate. Later Wood (1986) synonymized Microperus with the similar genus Coptodryas Hopkins, 1915 without comment. Microperus was resurrected and separated from Coptodryas Hopkins, 1915 as a result of a cladistic review of xyleborine taxonomic characters (Hulcr et al. 2007). The genera are distinguished by multiple differences in the antennal characters, and body shape. Subsequent molecular phylogenetic studies including both Coptodryas and Microperus have confirmed that the genera are closely related (Cognato et al. 2011;Mandelshtam et al. 2019). However, Hulcr et al.'s (2007) diagnosis and description of both Coptodryas and Microperus were based on a limited taxon sampling of five species per genus and as a result, did not reflect the full morphological variation exhibited by species within these genera. Smith et al. (2020) recently expanded Hulcr et al.'s (2007) work in a revision of the fauna of Indochina and China and provided revised descriptions and diagnoses. Despite these recent advances, additional revisionary work is required to identify other Microperus species still erroneously placed in Coptodryas.
Microperus currently contains 27 species distributed in Asia from Far East Russia, Korea and Japan, west to Sri Lanka and southeast to Papua New Guinea and Australia. Eighteen species are distributed in Indochina and China, and Thailand has the greatest diversity ). The first Microperus species recorded in Thailand was M. pometianus (Schedl 1939), reported as Xyleborus pometianus (Nunberg and Chûjô 1961). Several researchers have subsequently recorded additional species from Thailand (Browne 1980;Beaver 1999;Hutacharern et al. 2007;Sittichaya et al. 2012). The first synoptic list of Thai Microperus included nine species (Beaver et al. 2014). Smith et al. (2020) added three additional species, increasing the Microperus diversity in Thailand to 12. In this paper, we describe four new species of the genus from Thailand, transfer four species from Coptodryas and Cyclorhipidion Hagedorn, 1912 to Microperus and place two species into synonymy, increasing the total number of Microperus species to 35. We also provide a key to the species of Microperus in the Indochinese peninsula and China updated from that in Smith et al. (2020).

Materials and methods
Specimens were collected from 27 study sites in 24 conservation areas across all regions of Thailand. Southern Thailand was sampled between 2014-2015 and the North, Northeast and East were sampled between 2019-2020 ( Fig. 1). In Southern Thailand 20 ethanol-baited flight intercept traps were deployed in each study site, whereas five  Photographs were taken with a Canon 6D digital Camera with a Canon MP-E 65 mm Macro Photo Lens (Canon, Tokyo, Japan) and StackShot-Macrorail (Cognisys Inc, Michigan, USA). The photos were then combined with Helicon Focus 6.8.0. (Helicon Soft, Ukraine); all photos were improved with Adobe Photoshop CS6 (Adobe Systems, California, USA). The antennal and pronotum types and characters follow those proposed by Hulcr et al. (2007) and subsequently elaborated upon by . Length was measured from pronotum apex to the apex of the declivity and width was measured at the widest part of specimen.

Taxonomic treatment
Microperus Wood, 1980Microperus Wood, 1980 Type species. Xyleborus theae Eggers, 1940(= Xyleborus myristicae Schedl, 1939; original designation. Diagnosis. This genus is distinguished by the following combination of characters: small to minute size, 1.2-3.1 mm long and cylindrical and elongate form, 1.9-3.2× as long as wide; antennal club truncate or flattened, segment 1 costate, segment 2 or segments 2 and 3 visible on anterior side small and appearing soft, segment 2 or segments 2 and 3 visible on posterior side (types 2, 3, 4 of Hulcr et al. 2007 and; elytral base sinuate, rarely transverse, with a dense tuft of setae present along elytral base associated with an elytral mycangium; scutellum minute or not apparent; strial and interstrial punctures arranged in parallel rows, striae punctate, prominent; pronotum from lateral view taller than basic (type 2 of Hulcr et al. 2007) or with pronotal disc longer than anterior slope (type 7); pronotum from dorsal view basic and parallel-sided (type 2), or subquadrate (type 3), and anterior margin of pronotum without a row of serrations. . This species is distinguished by its cylindrical appearance, elytral disc shining and convex, declivity steep, declivital interstriae 1 and 2 flat, slightly impressed, declivital interstriae 3-6 convex on basal half, with a pair of prominent tubercles on interstriae 3, apical half flattened. This species differs from M. recidens by the elytral disc more flattened, declivital summit less steep, declivital face more flattened and broader, and declivity armed with a pair of prominent tubercles on interstriae 3 (those much smaller in M. recidens).
Etymology. L. bi = two, dentatus = toothed, the name refers to the two prominent denticles on each declivital interstriae 3. An adjective.
Etymology. L. bucolicus = rural, rustic. In reference to the agrarian habitat in which the species was collected. An adjective.
Similar species. M. pedellus. Description (female). Appearing bicolored, moderately setose: head, anterior slope of pronotum and elytra dark brown, remainder of pronotum, antennae, and legs light brown. Head: epistoma entire, transverse, with a row of dense hair-like setae. Frons weakly convex to upper level of eyes, shagreened lower part densely covered with long erect hair-like setae, punctate, punctures shallow and bearing a long, erect hairlike seta. Eye shallowly emarginated just above antennal insertion, upper and lower parts subequal. Submentum medium in size, distinctly triangular, shallowly impressed. Antennal scape short and thick, as long as club. Pedicel as wide as scape, shorter than funicle. Funicle 4-segmented, segment 1 shorter than pedicel. Club circular, broader than tall; type 3; segment 1 corneous covering about half of posterior face, anterior face costate concave, narrow; segment 2 narrowly corneous on anterior face, posterior face fully visible, segment 3 soft, visible on posterior face. Pronotum: 1.08× as long as wide. In dorsal view basic type 2; lateral side parallel to anterior two thirds; anterior margin round without medial serrations. Base weakly bisinuate, posterior angles acutely rounded. In lateral view type 7, disc slightly longer than anterior slope; disc convex, summit at apical 2/5; anterior slope densely covered with asperities; disc shagreened, impunctate; pronotum sparsely covered with moderately long hair-like setae, lateral margins obliquely costate. Elytra: 1.62× as long as wide, 1.5× as long as pronotum. Scutellum minute, convex, slightly raised above elytral surface. Elytral mycangium indicated by a disperse median setal tuft along elytral base. Base shallowly sinuate, edge oblique, humeral angles rounded. Lateral margins parallel beyond basal half, apex broadly attenuated at apical 4/5, apex broadly rounded. Declivity gradually commencing, broadly convex without posterolateral carina; elytra setose, elytral disc shinning, flat near scutellum broadly convex beyond, striae punctate, parallel laterally, puncture small, round moderately deep, punctures with shorter hair-like setae, interstriae flat, impunctate bearing a row of long erect hair-like setae, setae on disc and declivity equal in length. Legs: procoxae contiguous, prosternal coxal piece short, inconspicuously covered with a tuft of long hair-like setae. Protibiae slender, broadest at the middle; posterior face smooth; margin armed with six small socketed denticles. Meso-and metatibiae inflated; outer margin evenly rounded with seven and six small socketed denticles, respectively.
Distribution. Northern Thailand (Payao Province). Host plants. Unknown. . This species is distinguished by elytral disc convex, posterior half of elytra striae impressed with large round punctures, impression increased posteriorly, interstriae costate with strong interstrial spines posterior to declivital summit, declivity steep, shallowly impressed on the middle to interstriae 2, interstriae 3 with small but prominent tubercles.

Microperus serratus
This species is related to M. undulatus and similar species, but elytral disc is convex, lacking a transverse or saddle-like impression.
Etymology. L. serratus = toothed like a saw. In reference to the serrate margin of the elytral declivity. An adjective.

Remarks. A dorsal habitus image of the lectotype (NMHW) was examined by all authors and the species is transferred from
Cyclorhipidion to Microperus because of the following characters: dense tuft of setae present along elytral base associated with an elytral mycangium; elytral bases broadly V-shaped, costate; scutellum minute, convex and slightly raised above elytra; pronotum from dorsal view basic and parallel sided (type 2), from lateral view disc longer than anterior slope (type 7), and pronotal base weakly sinuate. This species is a probable synonym of M. exsculptus (Eggers, 1927) but has larger denticles along the declivital margin. Additional investigations are needed to assess intraspecific variation and clarify species limits.
Remarks. The holotype of Xyleborus dentipennis (NHML) and images of the M. exsculptus lectotype (NMNH) have been examined and compared by RAB and determined to be conspecific. Accordingly, X. dentipennis is here placed in synonymy. The species is transferred to Microperus based on the characters given for M. armaticeps. (Schedl, 1969), comb. nov. Schedl, 1969: 231. Coptodryas pedellus (Schedl, 1969): Wood and Bright 1992: 826. Remarks. The paratype deposited in NHMW was examined by the senior author. This species is included in Microperus with the following combination of characters: antennal club truncate, type 2, segment 2 visible on posterior side, dense tuft of setae present along elytral base associated with an elytral mycangium; elytral bases broadly V-shaped, costate; scutellum minute, convex and slightly raised above elytra; pronotum from dorsal view basic and parallel sided (type 2), from lateral view disc longer than anterior slope (type 7), and pronotal base weakly sinuate.
Host plants. This species is polyphagous and has been recorded from Cinnamomum (Lauraceae) (Murayama 1952), Diospyros (Ebenaceae), Fraxinus (Oleaceae), Carpinus (Betulaceae) (Mandelshtam et al. 2018) and "oak trees" (Fagaceae) (Eggers 1926). Declivital interstrial granules dispersed, separated by the width of at least three granules; posterolateral margin of declivity weakly carinate and granulate; interstrial vestiture consisting of short semi-erect bristles, shorter in length than the width of an interstria; smaller, 1.2-1.7 mm ....... pometianus -Declivital interstrial granules dense, separated by the width of one granule; posterolateral margin of declivity strongly carinate; interstrial vestiture consisting of long semi-erect hair-like setae, longer in length than the width of an interstria (easily abraded); larger, 1. Our study increased the diversity of Microperus to 35 species of which 18 are recorded in Thailand. Since 2010, Microperus has received considerable attention with eight species described and 12 species transferred from a diversity of genera including Xyleborus, Coptodryas and Cyclorhipidion (Beaver and Liu 2010;Hulcr and Cognato 2013;Beaver et al. 2014;Smith et al. 2018;Park et al. 2020;Smith et al. 2020). However, the faunal emphasis in these studies has largely focused on the faunas of Papua New Guinea, Indochina and the Palearctic. Three of the four new species described herein, and 14 of the 18 Thai species are recorded from the Southern Region (Table 1) which is characterized by species with affinities to the Indo-Malayan and Malayan faunas (Beaver et al. 2014). Based on our findings the Microperus faunas of these regions are in need of considerable revision and are undoubtedly more diverse than currently known.

Key to
Princess Maha Chakri Sirindhorn Year 2019 and Thailand Research Fund (TRF), project number DBG-6180023 to WS and SMS was funded in part, by a Cooperative Agreement (AP21PPQS&T00C034) from the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS). It may not necessarily express APHIS' views.