Rediscovery of Malthesis ater Motschulsky, 1853 and a catalog of the genus Malthesis Motschulsky

Malthesis is a Cantharidae genus with a history of ambiguous systematic placement, being sometimes classified within Malthininae and currently placed in Chauliognathinae, sometimes as a probable synonym of Chauliognathus . Part of the problem is a complete lack of knowledge about the identity of their type species, M. ater , from Colombia. The current generic placement is based on the identity of the subsequently described Malthesis species which, in turn, have never been compared with M. ater . One specimen belonging to the type series of M. ater , here designated as the lectotype, has been located at the Zoological Museum of M. V. Lomonosov State University (Moscow, Russia) and the identities of the species and genus could finally be assessed. Here, M. ater is redescribed in detail based on the study of the aforementioned lectotype and additional specimens from Colombia. The morphological study of the species confirms that most of the subsequently described species are indeed congeneric with M. ater , and enables a reliable placement of the genus within Chauliognathinae: Chauliognathini. In addition, a fully updated catalog of all the 38 currently valid species and subspecies of Malthesis is given to ease their future taxonomic studies.


INTRODUCTION
The systematic position of the genus Malthesis Motschulsky, 1853 within Cantharidae has always been questionable.Part of this uncertainty stems from the dubious original description of the genus and its type species, M. ater Motschulsky, 1853, and from the lack of knowledge about their type specimens.The purpose of this paper is to redescribe M. ater based on their lectotype and additional specimens to address the validity and systematic position of Malthesis.
In the first issue of his series entitled "Études Entomologiques", Motschulsky (1853) introduced morphological and biological observations on the beetle group then called "Malthinides" ("Malacodermes", "Telephorides", currently Cantharidae).The first notes are on the new genus Malthesis which, according to Motschulsky, resembles cerambycids belonging to the group of "Stenopterides" (Cerambycinae: Stenopterini).Malthesis and the single species Malthesis ater were characterized by the head wider than pronotum, which is plane, almost quadrate, obliquely truncate on anterior angles; scutellum quadrate; elytra wider than pronotum, long, a little narrowed posteriorly; wings surpassing the elytra; first antennomere longer than the following two combined; antennomere II very short; antennomere III three times longer than II; antennomere IV half longer than III; tarsal claws simple; pygidial segment bulging (Motschulsky 1853, p. 1).Lacordaire (1857) considered this characterization insufficient to accurately position the genus amongst Cantharidae, though he suggested that the genus might be classified near Malthinus Latreille, 1806 (currently Cantharidae: Malthinini).Kirsch (1865) proposed new species matching Motschulsky's description and added new features for the genus diagnosis, which, according to him, would reasonably locate Malthesis closer to Chauliognathus Hentz, 1830 (currently Cantharidae: Chauliognathini) than to Malthinus.Pic (1926a) presented short descriptions for new Malthesis species as couplets in a dichotomous key primarily based on body coloration.For him, three of the new species resembled the genus Malthinus for having elytra longer and subparallel, almost concealing the wings, anterior region less robust and narrower prothorax, whereas the others resembled Chauliognathus species, which have in common the large head, narrowed posteriorly with protruding eyes; elytra attenuated and a little dehiscent, surpassed by the wings; pronotum subquadrate, slightly longer than wide; legs long; a matt appearance; and apex of abdomen cupuliform in males.
Palabras clave.Catálogo, Chauliognathinae, Colombia, Neotropical, taxonomía Due to this ambiguity, Malthesis kept being considered a member of the tribe Malthinini in subsequent catalogs (Delkeskamp 1939, Blackwelder 1945).Wittmer (1963) formally listed Malthesis within Chauliognathini, as likely a synonym of Chauliognathus, probably after having access to specimens studied by Kirsch and Pic. However, this transfer was based on Kirsch's and Pic's concept of Malthesis that, in turn, was based only on Motschulsky's (1853) original descriptions, not on the study of his specimens.
The type specimens of Malthesis ater were presumably unknown to any other author prior to the present study.
The taxonomy of Malthesis remained stable for almost 70 years, with no taxonomic work being published between Pic's (1947) last species description and Constantin's (2016) revision of French Guiana Chauliognathinae, in which new species, synonyms, and combinations were proposed in the genus.Later, Biffi (2019) transferred Malthesis bicoloricornis (Pic, 1947) from Microdaiphron Pic, 1926.The genus is currently considered valid, with 38 species and subspecies.
One type specimen of M. ater was located in the Zoological Museum of M. V. Lomonosov State University (Moscow, Russia) and sent to me for study.In order to assess the identity of the type species M. ater and to enable a better understanding of Motschulsky's concept of the genus, the species has been redescribed based on their type specimen and additional specimens from Colombia.Furthermore, the morphological study of the type species allows the proposal of a stable systematic positioning for the genus.Finally, I provide an updated catalog of all the current valid species in Malthesis to ease their future taxonomic studies.

MATERIAL AND METHODS
The morphological terminology and orientation of aedeagus used in the descriptions follow Biffi (2016).Photographs were taken with a Canon EOS Rebel T3i camera, equipped with a Canon MP-E 65mm macro lens, attached The type specimens of all Malthesis species have been examined.The distribution of the species given in the catalog is based on data from their original descriptions, the type specimens' labels, and from subsequent published sources.It should be noted, however, that localities given in the original publications and labels are sometimes unclear or extensive territories (e.g., "Amazon", Peru).At other times, they are misleading, as in the many species described or labeled as from "Bogota", which might refer to the commercial origin of the specimens rather than the actual collecting locality (c.f.Paynter 1997, Forero 2006).

Distribution: Colombia (Cundinamarca).
Remarks: One male syntype of M. ater found in ZMUM  is herein designated as a lectotype.It is not clear whether the original type series comprised further specimens.The specimen is incomplete, missing most parts of both antennae, some legs, and palpi, and in poor condition of preservation, covered in mold and with an oxidized pin.Due to its fragility, the specimen and its broken remaining pieces were mounted on card boards.

A CATALOG OF MALTHESIS
A full revision of Malthesis, including some species currently allocated to Chauliognathus, is necessary to clearly define the morphological boundaries of the genus and the identity of the 38 currently valid species and subspecies.Despite being described in scattered publications, most of the type specimens are grouped in their authors' collections.The types of Kirsch's species are deposited in MTKD, whilst those of Pic and Constantin are housed in MNHN.The only exceptions are 1 syntype of Malthesis hickeri Pic, 1926 (currently Chauliognathus hickeri) and 1 syntype of M. subcyanipennis Pic, 1935 Pic, 1926Malthesis bahiensis Pic, 1926a: 15;Delkeskamp 1939: 245 (catalog);Blackwelder 1945: 370 (checklist);Delkeskamp 1977: 460 (catalog); Biffi c2022 (checklist).

DISCUSSION
The generic concept of Malthesis, as interpreted by Kirsch and Pic in their species descriptions was solely based on Motschulsky's original description of the genus.The examination of the lectotype of M. ater and comparison against the other species in the genus confirms that those authors were correct in their interpretation.Furthermore, Malthesis can be reliably classified within Chauliognathinae: Chauliognathini based on a series of features, such as the distinct fronto-clypeal suture, absence of tibial spurs, oblong and convex ventrite VIII, asymmetrical aedeagus with longitudinally twisted median lobe, rather long elytra, almost concealing the abdomen and wings, among others (cf.Brancucci 1980).
In the current classification (Magis and Wittmer 1974, Brancucci 1980, Motyka et al. 2023), two lineages of genera are recognized in Chauliognathini.In the first, the elytra are extremely reduced, covering up to two abdominal tergites and exposing most of the hind wings, e.g., Maronius Gorham, 1881, Paramaronius Wittmer, 1963, Lobetus Kiesenwetter, 1852, Macromalthinus Pic, 1919, etc. (c.f. Brancucci 1981, Biffi 2015, 2020, Biffi and Constantin 2018).In the second group, composed of Chauliognathus Hentz, 1830, Malthesis Motschulsky 1853, Malthopterus Motschulsky 1853, Psilorrhynchus Gemminger and Harold 1869, Daiphron Gorham, 1881, and Microdaiphron Pic, 1919, the elytra are longer, covering more than three abdominal tergites to completely concealing the abdomen and hind wings.Brancucci (1981) produced an identification key to genera of Chauliognathini, but grouped all the long-elytra genera in the same couplet due to their weak definition.Although some of these problems have been tackled with the recent taxonomic revisions of Psilorrhynchus (Biffi 2017, Biffi et al. 2022) and Microdaiphron (Biffi 2019), the classification of the remaining genera remains confusing, with numerous species incorrectly assigned to each one of them.Constantin (2016) presented a key to Chauliognathinae genera occurring in French Guiana, part of which is recorded for Colombia.
Psilorrhynchus can be distinguished by the head forming an elongate rostrum in front of the eyes, the typical trapezoidal pronotum, the last abdominal ventrite of females with lyriform notches, and the aedeagus, particularly the shape of left paramere and the digitiform and flap-like projections in the apex of the median lobe (Biffi 2017, Biffi et al. 2022).The genus Daiphron groups species with Lycidae-like features, such as serrate antennae, elytra widening posteriorly, sometimes with costae, and especially the yellow-and-black aposematic coloration (Biffi 2019, Biffi andRosa 2019).The study of the circumscribed species suggests Daiphron as a heterogeneous and artificial group in need of revision.Malthopterus comprises only one species, but numerous species await description (Biffi in prep.).Malthopterus species can be briefly diagnosed by the eyes bulging, the head (including eyes) wider than the pronotum, the pronotum with margins parallel, and the aedeagus with a cuticular projection on the median lobe.
Chauliognathus is the most problematic genus, including about 550 species from heterogeneous lineages grouped by the absence of obvious diagnostic features.Many species currently assigned to Chauliognathus need to be distributed through Malthopterus, Malthesis, Daiphron, and new genera.Species of Microdaiphron have a typical square to trapezoidal pronotum with the presence of two longitudinal sharp carinae (Biffi 2019).They resemble those of Daiphron for the aposematic color pattern but have more morphological features in common with Malthesis.
Unlike in most Chauliognathinae genera, the aedeagi in Malthesis, Microdaiphron, and some species currently classified in Chauliognathus are rather uniform, only slightly differing in size, shape, and texture, making them hard to interpret as species-level characters (see Biffi 2019).
The same occurs in the last ventrite of females, whose distal border is entire with a shallow median fold, not variously notched as most of the Chauliognathinae species.
Other similarities between Malthesis and Microdaiphron include the sexually dimorphic head shape, which is wider and flat posteriorly in males and narrower in females, and the abdomen weakly sclerotized, with a broad membranous area between the ventrites.The main differences between both genera lie in the antennae, shape of pronotum and elytra, and width of head in comparison with pronotum.The antennomeres of Malthesis are always cylindrical or slightly widened distally, whereas in Microdaiphron the antennae are always serrate or subserrate and dorso-ventrally flattened.In Malthesis the head is very wide, sometimes wider than the pronotum, which is subquadrate, usually as long as wide or slightly longer than wide, with its lateral margins slightly sinuous, narrowed posteriorly.
In Microdaiphron the pronotum is broader, wider than the head, with lateral and anterior margins broadly arched and a pair of longitudinal sharp keels forming a dorsal flat elevation.The elytra in Malthesis are shorter and narrowed posteriorly, usually exposing the apex of wings and last abdominal tergites, while in Microdaiphron they are longer -usually concealing wings and abdomen -, and broad, parallel-sided or slightly broader posteriorly.Some Malthesis species show strong sexual dimorphism that hampers the direct association of males and females for each species.Such differences are found especially in the diagnostic features of the genus, like the shape of the head (narrower in females), pronotum (broader, with lateral margins arched, not sinuated), and elytra (not narrowed, concealing wings and abdomen).Furthermore, unpublished photographic records of Malthesis in copula show also strong chromatic dimorphism.Thus, there might be cases where males and females have been described as distinct species, or even in distinct genera, so a number of synonymies are expected in a future revision of the genus if such strong dimorphism is addressed.Malthesis ater is an example of a species known only to males.It is possible, however, that their females have been described under a different species name.Even with our limited knowledge about the morphological boundaries between Malthesis species, males of M. ater can be tentatively distinguished from their congeners by the almost entirely black body, except for the testaceous yellow markings at mandibles, in the area between the eyes and the base of mandibles, extending to the antennal sockets anteriorly, margins of hypomeron, anterior portion of epipleura, internal margins of metanepisternum, and dark-orange to light-brown spots on the posterior corners of pronotum.The other Malthesis males show various combinations of bicolored pronotum and elytra, longitudinal or bands, spots, well-defined pronotal and elytral margins, among others, usually in shades of yellow, orange, black, and, sometimes, gray.So far, Malthesis species are best distinguished by their color patterns in combination with the shapes and proportions of length and width of antennomeres, head, pronotum, and elytra.Other characteristics, such as aedeagus structures, hind wings, and female genitalia are potentially useful for diagnosis but require a thorough comparative study, for which a series of each species will be needed.
Prior to this work, M. ater was known simply as from "Colombia", according to the original description.One additional specimen was located at UNAB, providing a more precise locality record.It was collected in Quipile, in the vicinity of Bogotá (Cundinamarca department), at the Cordillera Oriental montane forests.ical region, and for the formation of a generation of students and researchers that will keep his legacy alive.I am indebted to the collection curators for loaning and granting access to specimens under their care: Nikolai Nikitsky (ZMUM), Francisco Serna and Erika Valentina Vergara-Navarro (UNAB), Thierry Deuve, Antoine Mantilleri and Azadeh Taghavian (MNHN), Olaf Jäger (MTKD), Max Barclay (BMNH), Matthias Borer, Eva Sprecher and Isabelle Zürcher (NMB).Thanks to Max Barclay (BMNH) and Juan Pablo Botero (MZUSP) for their logistical support to get the specimens to me, to Michael Geiser for proof reading, and to Dimitri Forero and one anonymous reviewer for the contributions to the improvement of the manuscript.This study was supported by grants from São Paulo Research Foundation (FAPESP -2013/08966-1; 2015/21273-0), University of São Paulo Support Foundation (FUSP 3587 -ITV/MZ) and Fundação Guamá (Pará, Brazil).

LITERATURE CITED
to a StackShot macro-rail.Multi-focal images were processed with the software ZereneStacker version 1.04, and edited in Adobe Photoshop CS6.Line drawings were produced in Adobe Illustrator CS6.The acronyms of institutions cited in the text are given belowde Agronomía, Universidad Nacional de Colombia, Bogotá, Colombia; ZMUM: Zoological Museum of M. V. Lomonosov State University, Moscow, Russia.
Other examined material: COLOMBIA, Cundinamarca, Quipile, Casco urbano, 4˚44'37.8"N 74˚32'01.82"W, 1262 m a.s.l., 8. ii.2011,J. Romero leg., en suelo, captura manual [on the ground, manual capture](1 male UNAB) (Figs 15-20).Redescription (males): Length (from mandibles to apex of elytra): 7.5 mm.Body predominantly black, pale-yellow spots at genae in front of eyes and antennal sockets, basal two-thirds of mandibles, margins of hypomeron, base of trochanters, anterior portion of epipleura, internal margins of metanepisternum, and dark-orange to light-brown spots at posterior corners of pronotum; abdomen dark brown, pale yellow at membranous distal margins of ventrites.Head (Figs. 15-18) smooth, densely covered in fine and short golden setae; occipital region flat, vertex convex, with barely visible muscular markings, frons convex, longitudinally elevated in the middle, lowered laterally; gular sutures confluent, well visible; genae short in front of eyes, parallel; clypeus V-shaped, fronto-clypeal suture broadly arched in the middle, obliquely straight laterally; anterior margin notched in the middle, forming two rounded lobes, and obliquely straight laterally, parallel to fronto-clypeal suture; paraclypeal lobes elevated, as long as genae; clypeus covered with short setae on its dorsal surface, longer on anterior margin and a pair of long tufts of setae on anterior rounded lobes.Eyes small, not prominent, almost globose, 1.3 times longer than wide, broadly separated.Antennae (Figs. 15, 20) broadly separated; distance between antennae about 3 times width of antennal insertions;antennomere I elongate, narrowed at base, slightly swollen at apex; antennomere II short, nearly as long as wide, narrowed at base; antennomere III twice longer than antennomere II, slightly widened apically; antennomere IV longest, almost cylindrical; antennomere V nearly as long as I, slightly widened apically; antennomere VI slightly concave on its internal surface; antennomeres VII-X similar in shape, progressively smaller toward the apex; antennomere XI cylindrical, apex rounded; antennae densely covered with very short and fine setae and some sparse longer setae.Maxillae: stipes with a row of long basal se-

Fig. 21 .
Fig. 21.Collecting localities of Malthesis ater in Colombia.The red circle indicates the dubious locality record of the lectotype (Bogotá).