Two new species of the genus Melixanthus Suffrian (Coleoptera, Chrysomelidae, Cryptocephalinae) from China

Abstract Two new species of the genus Melixanthus Suffrian, 1854 are described from China: M.menglaensis Duan, Wang & Zhou, sp. nov. from Yunnan (also in Vietnam, Tonkin) and M.similibimaculicollis Duan, Wang & Zhou, sp. nov. from Yunnan. Another species, M.rufiventris Pic, 1926, is reported for the first time in China. High-quality color images and line drawings of adult habitus, aedeagus, and other important structures are provided for all three species. The types of the new species are deposited in the collection of Institute of Zoology, Chinese Academy of Sciences (IZ-CAS).


Introduction
The leaf beetle genus Melixanthus Suffrian, 1854 (Chrysomelidae, Cryptocephalini) is mainly distributed in the Oriental region and includes approximately 60 species until now; of these, 11 species are known to occur in China (Gressitt and Kimoto 1961;Tan et al. 1980;Tan 1988;Tan and Pu 1992;Lopatin 2005;Schöller et al. 2010). This genus was erected very early on as valid genus-level taxon and can be diagnosed by the following characteristics: antennae rather short, usually reaching humeral region of elytra; apical six segments broadened and flatted, about 1.2-2.2 times as long as wide; claws of all legs usually toothed or thickened basally. Not all Melixanthus species readily show the character of claws with or without teeth, and at least a few of species are not easily included in or excluded from this genus. This has challenged taxonomists studying this group.
The Chinese fauna of the genus was studied by including in a comprehensive study on the family Chrysomelidae (e.g., Chûjô 1954;Gressitt and Kimoto 1961;Tan et al. 1980;Schöller et al. 2010). Kimoto and Gressitt (1981) studied the chrysomelid fauna of Thailand, Cambodia, Laos, and Vietnam (countries near China), and thus their publication is important in identifying the Chinese species. The most recent and comprehensive study of Melixanthus, having excellent species revisions and key to species, was published by Medvedev (2012).
Our present study reports new findings, including the description of two new species of Melixanthus from China.

Materials and methods
Dried specimens were relaxed in hot distilled water at 80 ℃ for about 2 h to soften the body and ease dissection. The abdomen was separated with insect pins from the rest of the body, soaked in 10% KOH solution and then in a hot water bath for 15 min to advance the process. After this, specimens were transferred in distilled water to rinse the residual KOH solution off and stop the bleaching process. Afterwards, the aedeagus, spermatheca and rectal sclerites were prepared. The dissected parts were placed into glycerin for observation and measurement with an apochromatic stereomicroscope Zeiss SteREO V12. Color photographs of the adults and genitalia were captured with an Axio Zoom V16 fluorescence stereo zoom microscope and photomontage was performed in Zen 2012 (blue edition) imaging software. Adobe Photoshop CS6 was used in digital post-processing of the color images, and Adobe Illustrator 2020 was used to make the line drawings.
Materials used in this study are from the collection: IZ-CAS (Institute of Zoology, Chinese Academy of Sciences, Beijing, China).
Measurements are average values calculated from the values of at least five specimens, or all available specimens in case less than five specimens were available. The following abbreviations are used in the text to indicate the measurements of the specimens: BL body length (length from the apex of pronotum to the apex of elytra in dorsal view); BW body width (distance between the humeri, maximal body width); HL head length (length from occiput to the front apex of mandibles); HW head width (distance between the outer margin of eyes in frontal view, maximal head width); PL pronotal length (length from the basal angle to anterior margin, maximal longitudinal length of pronotum); PW pronotal width (distance of the widest portion of the pronotum); EL elytral length (length of the maximal elytral length in dorsal view); AL aedeagus length (length from the apex of aedeagus to the basal margin, maximal aedeagus length); AW aedeagus width (the maximal width of aedeagus); SL spermathecal length (length of the maximal spermathecal length, without duct).
Aedeagus (Figs 4A-C, 5A-C) elongate, about 3.2 times as long as wide, clubbed. Apex of median lobe narrower than middle, acute at apex, slightly curved in lateral view; with several pubescence on each side of apex and upper lateral margins, punctate on ventral side of upper middle part. Median orifice with middle sclerite bending inwards above surface. Upper part of median lobe with a pair of sclerotized prominence, exceeding the median lobe. Inner sac rather narrow, arrow-shaped. Tegmen Y-shaped, weakly sclerotized, almost translucent.
Distribution. China (Yunnan); Vietnam (Tonkin). Etymology. The specific epithet is derived from the name (Pinyin) of the type locality, Mengla.
Diagnosis. This species is similar to M. bimaculicollis Baly, 1865, but can be distinguished from that species in having finer punctures on the head, a narrower pronotum, an impunctate scutellum, and fine puncture rows on the elytra, whereas M. bimaculicollis has the elytra with distinct punctures and a surrounded by dark ring; its claws are not toothed ( Fig. 2A, B) and the basal margin of its prosternum is drawn out into a pair of small, sharp denticles (Fig. 1A, B).
Head with sparsely pubescence, without punctures, flattened in midline, and with longitudinal shallow groove on frons. Eyes kidney-shaped, deeply emarginated; antennal insertions about equally separated with superior eye-lobes. Clypeus trapeziform, anterior margin concave, without punctures. Antennae (Fig. 6C) long and slightly thin, reaching 1/3 region of elytra; 1 st segment clubbed; 2 nd oblong, about 1/2 as long as 1 st ; 3 rd -5 th thin, about equal in length, longer than 2 nd ; 6 apical segments moderately thickened, about 1.7-2.0 times as long as wide, last segment pointed apically. Pronotum (Fig. 6A, B) 1.8 times as wide as long, moderately narrowed and rounded anteriorly; surface strongly convex, impunctate and shining. Scutellum triangular, nearly as long as wide, surface smooth, shining, apically elevated, observable in lateral view. Elytra (Fig. 6A, B) with humeri prominent and glabrous, widest slightly behind humerus, feebly truncated at apex. Disc with regular rows of coarse punctures; interspace of rows without any punctures; epipleura slightly obliquely placed and observable in lateral view.
Aedeagus (Figs 6D-F, 7A-C) elongate, about 2.7 times as long as wide, clubbed. Anterior margin of median lobe nearly straight, middle part papillary protruding, strongly curved in lateral view; with several pubescence on each side of apex and upper lateral margins, punctate on apex of median lobe. Median orifice with middle sclerite bending inwards above surface. Upper part of median lobe with a pair of sclerotized prominence, exceeding the median lobe. Inner sac rather narrow, arrow-shaped. Tegmen Y-shaped, weakly sclerotized, almost translucent.

Distribution. China (Yunnan).
Etymology. The specific epithet is derived from the Latin terms simili-, bi-, maculi-and collis, to indicate the new species near to M. bimaculicollis.
Diagnosis. The new species is similar to M. bimaculicollis Baly, 1865, but can be distinguished from it by the smaller body size; head and scutellum without any punctures; slightly narrower pronotum; elytra with finer punctures, and only basal part punctures surrounded by dark ring; basal margin of prosternum (Fig. 1C, D) drawn out into a pair of small sharp denticles. Melixanthus similibimaculicollis is also similar to M. menglaensis Duan, Wang & Zhou, sp. nov., but can be distinguished by the following characters: head without punctures; claws toothed ( Fig. 2C, D); and body size smaller.