Xixuthrus (Xixuthrus) domingoensis Fisher, 1932

Santos-Silva, Antonio & Lingafelter, Steven W., 2012, Morphological Analysis Of Mecosarthron Buquet And Xixuthrus Thomson And Reevaluation Of Generic Assignment Of Xixuthrus Domingoensis Fisher (Coleoptera, Cerambycidae, Prioninae), Papéis Avulsos de Zoologia 52 (27), pp. 315-332 : 318-323

Xixuthrus (Xixuthrus) domingoensis Fisher, 1932 ,

Restored Combination

( Figs. 4, 5E, F , 9 )

Xixuthrus domingoensis Fisher, 1932: 1 ; Blackwelder, 1946: 552 (cat.).

Mecosarthron domingoensis ; Ivie, 1985: 246 (comb. nov.); Chemsak et al., 1992: 14 (cat.); Monné & Giesbert, 1994: 5 (cat.); Monné, 1995: 7 (cat.); Monné & Hovore, 2005: 14 (cat.); 2006: 13 (cat.); Monné, 2006: 54 (cat.); Lingafelter & Woodley, 2007: 173.

Russo (1930) mentioned an undescribed species of Xixuthrus from the Dominican Republic. Fisher (1932) described this species, then known only from two males, as Xixuthrus domingoensis (we provide the first description of females below). Ivie (1985) reconsidered the generic placement and suggested it would be better placed in Mecosarthron . Monné (2006) in his catalog of Cerambycidae of the Neotropical Region, accepted this conclusion. Lingafelter & Woodley (2007), although challenging Ivie’s placement, retained its position in Mecosarthron , pending further research.

Ivie (1985) examined the holotype of Xixuthrus domingoensis and concluded that it should be placed in Mecosarthron Buquet. According to him “ Mecosarthron differs from Xixuthrus by having the profemora longer than or subequal to the mesofemora in males (profemora shorter than mesofemora in Xixuthrus )”. However, males of X. microcerus have the profemora slightly longer than the mesofemora and males of X. helleri have the pro- and mesofemora subequal in length, exactly as in males of M. buphagus . Further, the length of the forelegs in Xixuthrus is allometric and variable ( Yanega et al., 2004). Further, according to Ivie (1985), “the third antennomere [is] distinctly shorter than the first … (subequal in Xixuthrus )”. However, because antennomere III is highly variable in Xixuthrus (e.g., distinctly longer than the first in X. heros and X. terribilis Thomson, 1877 ; distinctly shorter in X. helleri and X. costatus ; and subequal in X. arfakianus ), this is also a spurious character on which to base his decision. Finally, Ivie (1985) wrote: “… the anterior margin of the pronotum [is] acutely indented near the sides and in the middle [ X. domingoensis – holotype] (smoothly bisinuate in Xixuthrus )”. Again, this character is not useful to distinguish Xixuthrus from Mecosarthron because it is variable. For example, X. granulipennis Komiya, 2000 , X. costatus , and X. helleri have the anterior edge of the prothorax very similar to X. domingoensis . Curiously, Ivie (1985) indicated the main difference between Xixuthrus and Mecosarthron , as was pointed out by Lameere (1903b): “ Mecosarthron domingoensis Fisher can be distinguished from M. buphagus Buquet ( Brazil) and M. gounellei Lameere ( Brazil) by the finely punctate pronotum with irregular, smoothly glabrous calli on each side of disk”. This character alone, even without any other, supports keeping Fisher’s species in Xixuthrus , but the form of the protibia and protarsomere I ( Fig. 4 ) is also identical to that found in nearly all species of Xixuthrus (for M. buphagus , see Fig. 2 ).

Based on the morphological characters of the type species of Mecosarthron and Xixuthrus , we return Mecosarthron domingoensis to Xixuthrus (Xixuthrus) , re-establishing the original combination. The arguments used by Ivie (1985) to place this species in Mecosarthron are not supported. However, we need to say that some features found in X. (X.) domingoensis agree better with those found in Dysiatus than in Xixuthrus , as for example, the very distinct sexual punctation in males ( Fig. 5E ) [for males of Dysiatus melas see Fig. 8A ]. The differences pointed out by Pascoe (1869) (“mandibulae crassae, subverticales, productae, rectae, apice abrupte arcuatae, intus bidentatae … Antennae graciles, dimidio corporis longiores; scapo subelongato, depresso, scabro, intus denticulato; articulo tertio multo breviore … Prothorax transversus, utrinque denticulatus, angulis anticis productis, rotundatis, apice bisinuato, basi truncate …”) to separate Dysiatus from Xixuthrus do not really distinguish these genera. Pascoe (1869) separated Xixuthrus and Dysiatus in a key: anterior angles of the prothorax rounded ( Xixuthrus ); anterior angles of the prothorax produced ( Dysiatus ). This feature is variable in the species actually placed in Xixuthrus and does not exclude X. domingoensis from Dysiatus . Pascoe (1869) also wrote: “tarsi antici articulo basali haud elongato”. This is not true: the photographs of the holotype of Dysiatus melas Pascoe ( Figs. 8A, B ) show that tarsomere I is elongate, as in some species of Xixuthrus , although not notably elongate as in X. microcerus and X. domingoensis .

Gressitt (1959) also separated Xixuthrus from Dysiatus in a key, using the form of anterior angles of prothorax: rounded in the species of Xixuthrus from New Guinea and projected forward in Dysiatus . However, this character does not distinguish the genera, and reveals a mistake: the anterior angles of Xixuthrus (Daemonasthra) helleri , a species that occurs in New Guinea and was mentioned by Gressitt (1959), are as in Dysiatus . Furthermore, other species recently described, such as X. lameerei Marazzi et al. (2006) , also from Papua New Guinea, have the anterior angles of the prothorax as in Dysiatus .

Similarly, the characters used by Lameere (1903b) are inadequate to distinguish Xixuthrus from Dysiatus : “Antennes à 3 e article notablement plus court que le 1 er; mandibles renflées à la base; tarses antérieurs à 1 er article non allongé”, for Dysiatus ; and “Antennes à 3 e article au moins presque aussi long que le 1 er; mandibules non renflées à la base tarses antérieurs à 1 er article allongé”, for Xixuthrus .

The shape and punctation of the prothorax in males, type of mandible, and length of antennomere III is very similar in D. melas and X. domingoensis , but the length and shape of the protibia and tarsomere I (longer and finer) and the presence of elytral pubescence [absent in males of D. melas ], allow the exclusion of Fisher’s species from Dysiatus . According to Lameere (1912) the females of D. melas have the elytra slightly pubescent.

The geographical isolation of X. (X.) domingoensis suggests that the species may have been introduced. However, no known species of Xixuthrus in the Pacific Islands (its geographic center of diversity) match this species. Thus, it is most likely a native species, although it is challenging to explain the presence of a species of Xixuthrus on an Atlantic island, while it doesn’t occur in Africa or North, Central, or South America.

The original description of the male ( Figs. 4 A-C, 9) is detailed and needs few additional comments. Nevertheless, Fisher (1932) recorded some features that do not agree with the holotype or with the specimens more recently collected: “Elytra five times as long as pronotum” (actually just longer than four times); and “eyes … separated from each other on the top by about the width of the upper lobe” (actually, the distance between upper lobes is equal to about 1.5 X the width of the lobe, and a little greater than its length). Since the original description was based only on males, we present the first description of the female below, followed by comments on sexual dimorphism in this species.

Description (female, Fig. 4 D-F): Integument reddish-brown, mostly matte due to pubescence; darker on head, pronotum, venter, and appendages than on elytra; mostly covered with very short, fine, translucent to slightly golden pubescence.

Head coarsely and confluently punctate between the eyes; punctures of differing sizes; area between the posterior edge of eyes and occiput densely punctate-granulate; punctures becoming less dense on antennal tubercle; pilosity short and moderately dense between eyes, with equal abundance, density, and length between eyes and occiput. Labrum centrally strongly concave, arcuate at base; pilosity long, moderately dense, projecting forward. Eyes large, with only slight indention near antennal tubercle; from lateral view, eye extends the entire height of head from vertex to gula, somewhat broader ventral to tubercle than dorsally; from ventral view, eye extends nearly length of head from posterior margin to just before mandible base. Minimum distance between upper eye lobes about 2/3 length of antennomere III; distance between lower lobes greater, but less than length of antennomere III. Area around eye margin not sulcate; strongly depressed between eyes and antennal tubercles with central sulcus extending from between antennal tubercles to occiput. Gula between ventral lobes of eyes strongly vermiculate, lacking pubescence. Gena strongly produced anteriorly into broad, but blunt tooth below mandibular insertion. Mandibles ventrally projecting, from 0.5 to 0.6 times the length of the head; with strong, acute, broad apical tooth, smaller tooth at middle, and weak tooth at base; coarsely, confluently punctate on outer surface, except for teeth (anterodorsally); mostly smooth on underside (posteroventrally); pilosity short, sparse, limited to margins and base. Antennae reaching about middle of elytra or slightly surpassing middle. Scape about as long as antennomeres II-III-IV together (about length of head); dorsally flat, coarsely, shallowly, sparsely punctate, otherwise smooth and shiny, without denticles; neither vermiculate or asperate.

Pronotum much broader posteriorly than anteriorly; strongly multispinose on lateral margins (10-15 well defined spines), with well-defined spines at anterolateral and posterolateral corners; densely punctate; punctures mostly confluent but of different sizes; weakly depressed at middle with small, shiny, impunctate region just anteromedially, extending in a partial medial line posteriorly, but not attaining posterior margin; pronotal sculpturing forming several incomplete, elevated ridges laterally on disk. Most pronotal punctures each bear a single, short, inconspicuous, translucent seta, but otherwise the pronotum appears shiny and glabrous. Prosternum moderately but shallowly punctate-vermiculate, becoming less dense at sides and base of prosternal process. Prosternal process wide, slightly narrowed between procoxae; widened again and rounded on apex. Pubescence of prosternum short, sparse, but more conspicuous than on pronotum.

Elytra with mostly matte finish, but with shiny areas around base, suture, and costal ridges; mostly covered with very short, fine, translucent to slightly golden pubescence; very finely punctate; each micropuncture bearing a single, short, translucent seta. Elytra each with three incomplete costae equally spaced between suture and lateral margin; integument with microrugulae throughout, visible under high magnification.

Femora and tibiae mostly smooth but with scattered asperites throughout and microspinules irregularly scattered along inner margin; protibiae each with two confluent spurs apicomesally and a spine apicolaterally. Protibiae slightly curved laterad from base to apex. All femora about as long as tibiae; overall length of legs similar, but middle legs slightly shorter.

Dimensions in mm (female, n = 4): Total length (including mandibles), 60-85; length of prothorax, 9-13; width of prothorax between bases of posterolateral spines, 16-23; width of prothorax between bases of anterolateral spines, 8-11; body width at humeri, 19-27; elytral length, 43-62.

Remarks on sexual dimorphism: Sexual dimorphism in X. domingoensis is most apparent in the structure of the forelegs, pronotum, antennae, and mandibles. The legs (especially protibiae and profemora) are strongly spinulose and asperate in males and very weakly so in females. The protibiae of males are slightly but distinctly curved mesally toward apex (inward curvature) while in females they are outwardly curved toward apex. The protibiae in males are distinctly longer than the profemora (ratio of 1.2-1.3), while in females, they are of approximately the same length. The pronotum in males is very evenly, densely, confluently punctate and lacking ridges. There are 4 small, shiny, semi-impunctate regions on the disk in males: 1 on either side and just anterior to middle, and one posterolateral to that, on each side. In females, the pronotum is as described above, with punctures mostly confluent but of different sizes and with a small, shiny, impunctate region anteromedially, extending into a partial median line posteriorly. The antennae of females reach to approximately the middle of the elytra, while in males, the antennae reach to approximately the apical fourth of the elytra. In females, the mandibles are approximately half the length of the head, while in males, the mandibles are greatly enlarged and nearly as long as the head.

Geographical distribution: Xixuthrus domingoensis is known only from the Dominican Republic (Provinces of Santiago, San Pedro de Macorís, and Altagracia) on the island of Hispaniola.

Type data: Holotype male ( Fig. 9 A-C), from Dominican Republic (Santiago), collected by Giuseppe Russo Gounelle, in 1926, deposited at USNM.

Material examined: All DOMINICAN REPUBLIC: La Altagracia Province, Punta Cana near Ecological Reserve , 0.5 meters, 18°30.477’N, 68°22.499’W: 2-7 July 2005, S.W. Lingafelter (1 female, USNM) ; 2-7 July 2005, N.E. Woodley (1 female, USNM) ; 3 July 2005, Charyn J. Micheli (1 female, USNM) ; 14-17 June , 2010, S.W. Lingafelter (1 female, USNM) .

Figures

FIGURE 2: Mecosarthron buphagus Buquet. A. dorsal habitus, male; B. ventral habitus, male; C. lateral habitus, male; D. dorsal habitus, female; E. ventral habitus, female; F. lateral habitus, female.

FIGURE 4: Xixuthrus domingoensis Fisher. A. dorsal habitus, male; B. ventral habitus, male; C. lateral habitus, male; D. dorsal habitus, female; E. ventral habitus, female; F. lateral habitus, female.

FIGURE 5: Pronota of Mecosarthron and Xixuthrus: A. M. buphagus Buquet, male; B. M. buphagus Buquet, female; C. X. microcerus (White), male; D. X. microcerus (White), female; E. X. domingoensis Fisher, male; F. X. domingoensis Fisher, female.

FIGURE 8: Dysiatus melas Pascoe, holotype (male). A. dorsal habitus; B. ventral habitus; C. holotype labels.

FIGURE 9: Xixuthrus domingoensis Fisher, holotype (male). A. dorsal habitus; B. ventral habitus; C. holotype labels.