On the Andean genus Leschenius (Coleoptera: Curculionidae: Entiminae): Updated phylogeny, with a new species from Ecuador, discovery of males, and larval description of the potato weevil Leschenius vulcanorum

The weevil genus Leschenius del Río (Curculionidae: Entiminae: Naupactini) is distributed in the northern Andes, in Colombia and Ecuador. Among its species, L. vulcanorum stands out as an important pest of potatoes in its parthenogenetic form, which is known as “tiroteador de la papa”. In this study, the adult male and the larval stage (first and mature larvae) of L. vulcanorun are described and illustrated for the first time. A description of the male of Leschenius bifurcatus is also provided. A new bisexual species was discovered, Leschenius ventrilingulatus sp. nov., and is described from Ecuador. An updated phylogenetic analysis was performed, including the new species, with results indicating a sister group relationship between L. ventrilingulatus and L. vulcanorum. They can be distinguished because the former is usually of smaller size and is covered by denser and thicker setae, has shorter antennae, a subcylindrical shape of the pronotum, shorter elytra (about 1.5×longer than wide at base), the female has ventrite 4 with a posterior rounded projection, and posterior margin of ventrite 5 subacute, not excavated. This paper also includes lectotype designations, a revised key to all known species of Leschenius, habitus photos of males and females, illustrations of genitalia, and a distribution map.


INTRODUCTION
The weevils of the South American genus Leschenius del Río (Curculionidae, Entiminae, Naupactini) range in the highlands of Colombia and Ecuador, at approximately 1,800 to 5000 m.a.s.l. (del Río, Marvaldi & Lanteri, 2012). According to the phylogeny of the Naupactini tribe by Lanteri & del Río (2017), the genus Leschenius belongs to the so-called ''Andean group'', a clade of genera distributed in the Andes: (
Immature stages. The slide-mounted larval specimens are deposited at the MLPC, labelled with the data of this article. Techniques for dissection of larvae, terminology and abbreviations herein applied correspond to Marvaldi (1998).
Dissections of genitalia were made according to standard entomological techniques, and characters were drawn using a camera lucida adapted to a stereoscopic microscope (Nikon SMZ800). All measurements were taken with an ocular micrometer attached to the same microscope, and their abbreviations used in the description are as follows: L, maximum length; LA, length of antennae; LB, length of body; LE, length of elytra; LP, length of pronotum; W, maximum width; WRa, width of rostrum measured across apex (excluding scrobes); WRb, width of rostrum at anterior margins of eyes. The terminology used for the morphological structures follows Marvaldi et al. (2014), Lanteri & del Río (2017) and the glossary of weevil characters by Lyal (2021). The terminology used for the sculpture follows that of Harris (1979).
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. The LSID for this publication is: urn:lsid:zoobank.org:pub:348600A7-0721-4BC9-A3FD-CB5CBDC55954. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central SCIE and CLOCKSS.

Phylogenetic analysis
For the phylogenetic analysis of Leschenius, the list of morphological characters and the data matrix by del Río, Marvaldi & Lanteri (2012) were modified to include the new species as a terminal taxon as well as new information about the males of Leschenius vulcanorum and L. bifurcatus.
For the inclusion of the new species in the present analysis, four characters from the list by del Río, Marvaldi & Lanteri (2012) were redefined (chars. 5, 41, 47, and 48), and a new one for the male genitalia was added (Table 1). The new list consisted of 50 morphological characters of the adults, including 36 from the external morphology and 14 from the female (9) and male terminalia (5). The data matrix herein analyzed includes 12 terminal taxa, corresponding to seven species of Leschenius plus five outgroup taxa (Table 2) closely related to Leschenius according to Lanteri & del Río (2017). All characters were treated as non-additive and analyzed under equal weights.
49. Apex of penis, curvature in lateral view: not recurved (0); dorsally slightly recurved (1) dorsally strongly recurved (2). relationship that is supported by several synapomorphies (at least 10 exclusive and one homoplastic character changes, shown in Fig. 1). Leschenius is monophyletic and includes the new species, L. ventrilingulatus, sharing the synapomorphies of the genus: the well-developed pre-epistome (character 10.1); the 'V'-shaped pronotal base (character 17.2); the slightly prominent to absent elytral humeri (character 23.1); and the procoxae almost contiguous with anterior margin of prosternum (character 29.0). Leschenius is also supported by five homoplastic character states: antennal scape slightly exceeding posterior margin of eyes (character 12.2, with reversal to 12.1 in L. nigrans-L.manueli clade); funicle segments 2 and 1 subequal (character 13.2, with reversal to 13.1 in L. vulcanorum and L. rugicollis); elytral base straight to slightly curved backwards (character   1  2  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  6  7  8  9 Melanocyphus lugubris  The genus Leschenius has two main clades, named A and B in Fig. 1. Clade A is well supported and includes the new species, L. ventrilingulatus as sister of L. vulcanorum, a relationship supported by the very short rostrum (character 5.2), the relatively wide pronotum (character 14.1), the short cornu of spermatheca (character 44.0); the penis with its apex tapering into a long acute projection (character 47.0), dorsally slightly recurved (character 49.1), with a long flagelum like sclerotization in the endophallus (character 48.2). Clade B includes the remaining five species of the genus, supported by the rostral sulcus exceeding posterior margin of eyes (character 7.1), corbel of metatibial apex narrow, setose or denuded (character 31.2); penis apodemes half as long as penis body (character 45.1), and by some homoplastic characters such as medium sized body (character 0.1), sides of rostrum slightly convergent towards apex (character 6.0), and presence of apical projection of elytra (character 24.1). In clade B, L. bifurcatus is the sister group of the remaining species, which Most characters of the following larval description, based on specimens of L. vulcanorum, may apply to the genus Leschenius. Terminology as in Marvaldi (1998).

Leschenius nigrans
Description of larvae. Mature larva. Body robust, widest at thorax and first abdominal segments. Cuticle asperities present on ventral areas and absent on lateral and dorsal areas. Head ( Fig. 2A). Deeply retracted into thorax, longer than wide; posterior margin ogival; posterior half unpigmented, with softer integument and without setae; all setae shifted anteriorly, placed on anterior third. Epicranial line more than 0.5 x the length of head capsule. Frontal lines and endocarina absent. Hypopharyngeal bracon with paramedian maculae. Postoccipital condyles obtuse, hyaline. Setae ( Fig. 2A): fs4,5, des5, and les2 long, subequal situated on anterior cephalic fifth; des1, des3 shorter but well developed; fs1,2,3, des4, pes1-4 minute; les1 reduced; vcs1 longer than vcs2, both short. Stemmata absent. Antenna (Fig. 2B) with sensorium about 2.5 x wider than long, truncate at apex. Labrum (Fig. 2C) with lms1,2,3, subequal, lms1 slightly less widely separated than lms2. Epipharynx (Fig. 2D) with mes1 less separated than mes2; epipharyngeal sensilla as single units (not as sensillum clusters), one pair between mes1 and mes2 but closer to mes2, and another pair close to bases of labral rods; labral rods ( Fig. 2D) ax shaped, bifurcate, with one arm reaching mes1 and the other mes2. Mandibles (Fig. 2E) with mds1 slightly longer than mds2, both transversely placed within the scrobe; mds2 exterior and slightly basal to mds1. Maxillae (Figs. 2F-2G) with spinules on dorsal surface of external margin of stipes and below mala and palpus; maxillary mala with a row of eight dms and with four vms. Labium (Fig. 2F) with premental sclerite well sclerotized, with posterior extension truncate and expanded at apex, anterior extension slender. Thorax (Fig. 3A). Spiracle (Fig. 3E) ellipsoidal, without airtubes. Pronotum (Fig. 3A) with nine setae. Meso-and metathorax with pds3 distinctly longer than others; alar area with two as. Pedal areas of thoracic segments (Figs. 3A-3B) each with nine setae: seta z conspicuous; setae x and y subequal; u smaller than v; v smaller than w; seta v' present and rather conspicuous; small x' distinct; a pair of additional anterosternal microsetae occasionally present in front of each pedal area. Abdomen (Figs. 3A, Figs. 3C-3D): Spiracles (Fig. 3E) elliptical, 2x smaller than thoracic one, without airtubes. Segments AI-VII (Figs. 3A, 3C) with five pds, pds3 and pds5 the longest; spiracular area with only ss2 distinct and progressively placed closer to postdorsum, ss1 vestigial or absent. AVIII with four pds, lacking the homologous pds2 of preceding segments; ss indistinct. Abdominal apex (Fig. 3D) modified, with transverse posterior sclerotized ridges on dorsum, pleura and sternum of AIX; AIX with four ds including a seta ds', placed lateral to ds1; laterally with two ls strongly unequal, the longest on sclerotized ridge; AX terminal, four-lobed, each lateral anal lobe with three minute setae, the outermost larger. First instar larva (Figs. 2H-2J, 3F). Head (Figs. 2H-2I) only slightly retracted into thorax, slightly longer than wide; major cephalic setae placed on anterior half, des2 and les1 less reduced than in older larvae; des1 minute (smaller than in mature larvae). Frontal lines weakly distinct. Anterior and posterior stemmata distinct, as dark pigmented spots. Antennal sensorium prominent and projected outwards. Mandibles (Fig. 2J) with mds1,2 strongly unequal, mds1 about 5x longer than mds2. Thorax. Spiracle (Fig. 3F) bicameral with annulated airtubes; pedal area with setae z, and v' relatively small, seta w relatively very long and spatulate or blunt at apex. Abdomen. Spiracles (Fig. 3F) bicameral, with airtubes having a smaller number of rings than thoracic one; abdominal apex not distinctly sclerotized. Remarks. The characters mentioned above for the first larva, newly hatched, are exclusive of the first instar (see also Marvaldi & Loiácono, 1994). Additional differences between early and older instar larvae involve relative dimension of structures, like the antennal sensorium, which are relatively much larger in the first instar; the pigmentation and level of sclerotization of body areas tend to increase in successive instars; there are larger differences in length between setae of different body areas in early instars. Comparative notes. The larval characters given herein for the genus Leschenius are in full agreement with those defining the tribe Naupactini (Marvaldi & Loiácono, 1994) or Naupactus and allied genera (Marvaldi, 1998). Two apparently distinct features of the mature larva studied of L. vulcanorum are the head capsule with des1 well developed (in known mature larvae of other Naupactini des1 is minute or very small); also, setae x and y of pedal areas of thoracic segments are subequal (in other Naupactini as Naupactus, seta x is distinctly smaller than y). Larval characters deemed as diagnostic for the species are given below.  (Fig. 4D), syn. n.