Luctithonus Lingafelter, 2020

Lingafelter, Steven W., 2020, New genera, species, and records of Acanthocinini (Coleoptera: Cerambycidae: Lamiinae) from Hispaniola, Insecta Mundi 754, pp. 1-23 : 6-8

Luctithonus Lingafelter , new genus

( Fig. 4–6 )

Diagnosis. This genus is recognized by the presence of a basal elytral crest with a small tuft of setae (at arrow in Fig. 4c , from anterior view in Fig. 4e ); a pronounced depression behind the elytral crest; pronotal disc nearly impunctate except for row of small, well-defined punctures along posterior constriction ( Fig. 4g ); pronotum without dorsal tubercles and with broad lateral tubercles positioned posteromedially and apices elevated ( Fig. 4a, g ); very broad mesosternal process that is as wide as mesocoxa ( Fig. 4f ); greatly expanded prosternal process with apex wider than the mesosternal process, closing the procoxal cavities posteriorly ( Fig. 4f ); scape which is mostly evenly cylindrical for the apical ¾ ( Fig. 4b ); absence of erect setae or additional setal tufts on the elytra, legs, antennae, and venter; absence of an elytral carina ( Fig. 4c, e ); and long first metatarsomere that is nearly the length of the remaining tarsus and pale except for extreme apex ( Fig. 4d ). Justification for proposing this new genus is presented in the Remarks, along with comparison to other genera of Acanthocinini .

Description. Length: 6.1–8.8 mm; width: 2.4–3.5 mm.

Head: Covered in vestiture of short, dense, appressed setae; impunctate. Median-frontal line well delineated and complete from clypeus to occiput. Antenna: Long, slender, extending beyond elytral apices by 4–6 antennomeres. Antennomeres with short pubescence only, mostly darker apically, pale basally. Antennal scape long, slender, reaching to near posterior margin of pronotum, narrowed basally but cylindrical at apical ¾, not swollen at middle, approximately as long as third antennomere, constricted at base. Eye: lower eye lobe large, quadrate to rectangular, over twice as long as gena and about twice as long as upper eye lobe; lobes connected by 4–5 rows of ommatidia. Upper eye lobes separated by about basal width of scutellum. Mouthparts: labrum, clypeus, and palpi very pale tan, much lighter in color than head and mandibles.

Thorax: Pronotum covered in short, appressed pubescence, mostly impunctate except for transverse row of punctures along posterior constriction. Pronotum without tubercles dorsally and with single, broad, lateral tubercle, posterolaterally positioned with subacute apex slightly elevated dorsally. Scutellum moderately pubescent, darker at sides than at apex and middle; broadly rounded posteriorly. Prosternal process almost 1/2 width of procoxa at narrowest point, broadly expanded at apex to about midpoint of each procoxa, apex about equal to width of procoxa, closing procoxal cavities posteriorly. Mesosternal process between mesocoxae very broad, approximately 1.5 times width of prosternal process and slightly less than width of mesocoxa. Metasternum mostly impunctate with very shallow metasternal sulcus. Elytra: each with pronounced mediobasal pubescent tubercle with distinct depression posterior to it, otherwise covered in dense, appressed pubescence and lacking erect setae. Large punctures most evident on basal half. No distinct costae or carinae present, although the epipleural region is abruptly vertical from disk. Apices truncate to produced apicolaterally into a very weak spine-like process. Legs: metatibia distinctly longer than metafemur with very darkened apical third to half; first metatarsus elongate, slightly shorter than remaining metatarsomeres combined, pale except for extreme apex and tarsomeres 2–4) that are darkened.

Abdomen: mostly impunctate and covered in fine, appressed pubescence. Terminal ventrite about 1.5 times length of penultimate in both sexes. Median basal carina present in females.

Etymology. Luctithonus is formed from the Latin (lucti -), meaning struggle, truncated and appended to the genus name Tithonus to refer to its similarity to that genus and the difficulty in assigning it to any other existing genus in Acanthocinini . The genus name is masculine.

Remarks. Miguel Monné, in several works, divided the Neotropical Acanthocinini into groups to facilitate identification. His first treatment, Monné (1990), provided a key to the genera with a centrobasal crest and scattered stiff, erect setae on the elytra. Of the genera treated in Monné (1990), only Lithargyrus Martins and Monné (originally Cometochus Villiers, 1980 ), Tithonus Thomson (now Leptocometes Thomson ), and Oedopeza Audinet-Serville are known from the Caribbean islands. Running this taxon through that key to genera, one arrives at couplet 12, Oedopeza Audinet-Serville (antennomere IV without a setal tuft, metatibiae cylindrical, each elytron with only one centro-basal crest, antennae and legs without long, erect setae, elytra without longitudinal carinae, mesosternal process as wide as mesocoxa, venter and tarsi without long setae). However, the absence of stiff, erect setae on the elytra actually would preclude us from using this key and arriving at Oedopeza or the other genera treated.

In a later work, Monné (2001), reviewed the genera of Acanthocinini with a basal elytral crest, lateral elytral carina, but without erect elytral setae. The genera included in that group are known only from South America. Running this taxon through the key, we arrive at couplet 1, Acanthodoxus Martins and Monné. However , the absence of a lateral elytral carina would exclude Acanthodoxus or any other treated genera as possibilities.

The works on the Cerambycidae of Puerto Rico ( Micheli 2010), Lesser Antilles ( Chalumeau and Touroult 2005), and Cuba ( Zayas 1975; Devesa et al. 2019, although lacking a key to Acanthocinini genera of Cuba) were also consulted in an attempt to assign this taxon. Running it through the various keys, one arrives at Alcidion Sturm in couplet 7 of the Acanthocinini genera key in Micheli (2010), Trypanidius Blanchard in couplet 8, with some difficulty, in Chalumeau and Touroult (2005), and Lethes Zayas in couplet 9 of Zayas (1975). However, these genera share very few characters with this new taxon and as those keys are limited in scope, their utility for showing generic affiliation is minimal.

Superficially, species in this taxon are most similar to Lithargyrus guadeloupensis (Villiers) , but lack anteromedial pronotal tubercles (the disc of the pronotum is evenly convex), lack erect setae on the elytra, and have elytral apices that are truncate to moderately produced apicolaterally (not spined). Species in the new taxon are also similar to Leptocometes hispidus Bates (1881) , but that species has weakly spined elytral apices externally, weakly produced anteromedial pronotal tubercles, and long, erect elytral hairs. Therefore, given that the suite of characters in this taxon does not conform to any genera or generic groups, I propose the new genus, Luctithonus.

Type species. Luctithonus aski Lingafelter , new species, by present designation.

Figures

Figure 4. Luctithonus Lingafelter, new genus. a) Head, anterior view. b) Antennal scape. c) Elytron showing location of basal crest. d) Hind tibia and tarsus. e) Anterior view of elytra showing location and extent of tufts. f) Prosternum and mesosternum. g) Pronotum.

Figure 5. Luctithonus species. a) L. aski Lingafelter, new species, holotype male. b) L. aski Lingafelter, new species, paratype female. c) L. pantherinus (Zayas), d) L. pantherinus (Zayas), holotype male. e) L. duartensis Lingafelter, new species, holotype male, dorsal. f) L. duartensis Lingafelter, new species, paratype female, ventral. g) L. duartensis Lingafelter, new species, paratype female, ventral view of sternites.

Figure 6. Distribution map of Luctithonus species known from Hispaniola.