Toxognathus Fairmaire, 1878

Rosa, Simone Policena, 2014, Phylogenetic analysis and taxonomic revision of Physodactylinae (Coleoptera, Elateridae), Papéis Avulsos de Zoologia (São Paulo) 54 (18), pp. 217-292 : 237-239

Toxognathus Fairmaire, 1878

Toxognathus Fairmaire, 1878: 271 ; Fleutiaux, 1918a: 276; Fleutiaux, 1924: 178; Schenkling, 1927: 509; Fleutiaux, 1940a: 34; Fleutiaux, 1940b: 104; Stibick, 1979: 168; Bouchard et al., 2011: 319.

Type species (by monotypy): Toxognathus costulatus Fairmaire, 1878 .

Diagnosis (male): Integument densely punctate with punctures rasp-like, covered with yellow setae predominantly erect, longer on lateral borders of elytra; pronotum wider than long, elytra parallel-sided on anterior 3/4 with striae deeply impressed with a row of punctures larger than those of pronotum, interstices convex or costate. Mandible short and wide with an oblique ridge on laterodorsal face, labrum subrectangular, concave and declivous anteroventrad. Posterior angles of ventrite 1 without marginal plate, of ventrites 2-4 with acute and produced marginal plates; tarsomeres simple, claws pectinate.

Distribution: SOUTHEAST ASIA.

Redescription (male): Integument bright, light to dark brown, reddish-brown or black; densely pilose, setae short, longer on abdominal ventrites, yellow or golden, erect on dorsal surface, predominantly decumbent ventrally. Total length: 5.0-12.0 mm; elytral base 1.0-1.1x wider than pronotum, elytra 2.5-3.1x longer than pronotum.

Head ( Fig. 9E ) with margins over antennal insertions straight, oblique and convergent to the median straight margin. Frontal carina complete or absent between antennal insertions; frontoclypeal region gradually or steeply declivous to base of labrum about 5x wider than long; punctures coalescent 0.2 diameter apart. Antenna ( Figs. 7E , 9A ) with 11 antennomeres, serrate from antennomere IV, usually flat; antennomeres II and III subequal, III 1.0-1.05x as long as II; IV 1.9-2.5x times longer than III; IV-VI subequal as wide as long; VII-XI increasing gradually in length to apex. IEP usually 0.34-0.39. Labrum ( Fig. 9D ) subrectangular, anterior edge slightly emarginate or straight, concave and declivous anteroventrad, about 3.5x wider than long, coarsely punctate, with long setae. Mouthparts directed anteroventrad. Mandible ( Fig. 9D ) wide and short, unidentate or bidentate, apical tooth short, subapical tooth smaller; laterodorsal face coarsely punctate with an oblique ridge steeply declivous to apical part; lateral edge abruptly curved apicad; mesal margin at base with a row of short setae. Maxilla and labium covered with light-brown setae. Maxilla ( Fig. 9B ) with galea securiform, outer half with long and sparse setae, inner half with dense and short setae; lacinia elongate, elliptical, densely pilose; medistipes trapezoidal longer than wide with several short to long setae; Labium ( Fig. 9C ) with prementum deeply emarginate on anteromedian margin with anterolateral angles rounded, not produced; maxillary and labial palpi densely pilose with apical palpomere elliptical.

Prothorax 1.10-1.25x wider than long, lateral carina complete, entirely lateroventral ( Fig. 8B ) or lateral on posterior region and directed ventrad anteriorly ( Fig. 11C ). Pronotum flattened to convex, densely punctate, punctures rasp-like and umbilicate; posterior angles of pronotum non-carinate. Hypomeron ( Figs. 8C , 11C ) with punctures smaller than those of pronotum, sparse, umbilicate, posterior 1/5 glabrous; posterior margin with an inverted U- or V-shaped short notch adjacent to posterior angle. Prosternal suture ( Figs. 8C , 9G ) curved, marginate by a shiny band along hypomeral margin. Prosternum ( Figs. 8C , 9G ) 1.07-1.20x wider than long, with punctures larger than those of pronotum, 0.5-1.0 diameter apart; anterior lobe truncate, covering mentum. Prosternal process ( Figs. 8C , 9G ) 2.5-2.6x longer than diameter of procoxae, curved between procoxae then straight, ventral surface a little narrower and shorter than the ventral surface forming a subapical tooth ( Fig. 8D ). Procoxae open.

Pterothorax: Mesoventrite with posterior region abruptly inclined ventrad about 30° in relation to anterior region ( Fig. 9I ), with anterior articulating surfaces ( Fig. 9H ) concave bordered posteriorly by oblique carina, borders of mesoventral cavity nearly straight and divergent to mesocoxae then convergent ( Fig. 9H ); floor of cavity with shiny median band. Mesocoxal cavity ( Fig. 9I ) open to both mesepisternum and mesepimeron, trochantin visible; mesepisternum with an oblique carina anteriorly contiguous to the anterior carina of mesoventral articulating surface. Mesometaventral suture distinct. Metaventrite ( Fig. 7B ) 1.4-1.5x wider than long, 1.5-1.8x longer than mesoventrite, with punctation umbilicate, 0.2-1.0 diameter apart; metepisternum about 6.3-7.0x longer than wide. Scutellum abruptly elevated above the level of mesoscutum, pentagonal to subrectangular, longer than wide. Elytra gradually widened from humerus to posterior 1/3-1/4 then gradually rounded to apex; apices conjointly rounded; striae deeply impressed with a row of punctures; interstices convex, punctate, rugose; epipleura abruptly narrowed near metacoxa, slightly widened apicad from ventrite 2. Hind wings ( Figs. 7F , 8E , 9K ) with radial cell 3.75x longer than wide, CuA 1 present; wedge cell absent; apex with median and posterior field sclerotizations, convergent basad and an oblique sclerotization adjacent to the radial cell. Legs, Metacoxa inclined about 24° in relation to transverse axis of body, gradually shortened laterally, median ventral part about 3.5x longer than lateral part; free margin of metacoxal plate absent or short; metatrochanter and metafemur ( Fig. 7I ) weakly convex, metafemur 2.7-3.5x longer than wide. Tibiae ( Figs. 7 G-I; 9J) 1.7-3.5x wider at apex than at base; apices with two subequal spurs longer than setae, with a row of 8-15 spiniform setae along each outer and inner apical border and 2-3 irregular rows of spiniform setae on dorsal margin, spiniform setae shorter than the fine setae. Tarsomeres ( Fig. 9J ) decreasing in length from I-IV, V about 1.2x longer than III and IV together, simple, densely pilose ventrally; claws pectinate (with more than six teeth).

Abdominal ventrites ( Figs. 8F , 9L ) I-IV evenly covered with short setae and punctures 0.5-1.0 diameters apart, apical part of ventrite 5 with punctures coalescent forming longitudinal striae; posterior angles of ventrite 1 right without marginal plate, ventrites 2-4 with triangular marginal plates widened posteriad; ventrite 1 about 3x longer on lateral part than at middle, ventrites 2-4 subequal in length; ventrite 5 subtriangular 1.55-1.95x wider than long, strongly convex posteriorly ( Fig. 9M ). Pregenitalic segments and aedeagus covered with brown setae. Sternite VIII ( Fig. 10A ) subrectangular, 1.7-2.0x wider than long, bilobed posteriorly, with a pair of light sclerotizations on lateral lobes and a dark T-shaped sclerotization on anteromedian margin; posterior margin of lobes with long brown setae; tergite VIII ( Fig. 10B ) evenly sclerotized with short and long brown setae on lateroposterior margin; sternite IX ( Fig. 10C ) with anteromedian margin rounded or acute, produced and curved dorsad, with a longitudinal dorsal apodeme, posterior part covered with brown setae longer on lateroposteri- or and apical margin; sternite and tergite IX fused near the anterior margin; tergite IX ( Fig. 10D ) with anterior margin bisinuose or straight, posterior lobes acute with long brown setae; tergite X ( Fig. 10D ) suboval with long brown setae on posterior border, apical margin membranous fringed by minuscule setae.

Aedeagus ( Figs. 10E, F ): Phallobase M-shaped with lateroposterior parts parallel-sided or divergent posteriorly. Parameres usually not contiguous ventrally (fused basally in T. costulatus ), with apex securiform, partly membranous, with short and long brown setae. Penis tapering to apex, dorsal articulation with a short and narrow process between the basal struts fused to the parameres; basal struts 0.28-0.34x shorter than the total length of penis; ventral sclerite present.

Remarks: Toxognathus shares with “Physodacylinae” genera the widened tibiae and the prosternal anterior margin truncate, and can be easily recognized by its pectinate claws. Toxognathus is also similar to Melanotini ( Elaterinae ) genera by its pectinate claws, with more than six teeth. Toxognathus species differs from the majority of the species of Melanotini in (the later in parentheses): mesocoxal cavity open to mesepimeron and mesepisternum (open to mesepimeron only) and anterior prosternal margin short and truncate (rounded and produced). Toxognathus also differs from North American and Australian species of Melanotus in the phallobase with anterior edge notched (truncate or rounded) and by the absence of wedge cell on hind wing (present) ( Quate & Thompson, 1967; Calder, 1983). Nevertheless, some Palearctic species have phallobase more similar to that of Toxoganathus species ( Kabalak & Sert, 2011). Mouthparts and hind wings have been studied only for a few species of Melanotus , therefore the apparent synapomorphies found in these structures of Toxognathus could not be compared with those of other Melanotini genera.

Hayek (1990) revised the Melanotus group of genera and showed that the majority of species have mesocoxal cavity open to mesepimeron, although the length of the suture that separates the mesepisternum from the coxal cavity is variable and at least one species of Priopus Laporte, 1840 have mesocoxal cavity open to both mesepimeron and mesepisternum. Toxognathus can be separated from species of this genus by its posterior angles of prothorax shorter and not strongly pointed sharply in ventral view and the tibiae widened apically. Hayek (1990) presented a key to elaterid genera with pectinate claws in which she separated Toxognathus from the other genera with “procoxal cavity wide open posteriorly” and “mesepisternum separated from the metasternum by the mesepimeron” by the following combination of characters: mandible unidentate, anterior margin of prosternum truncate and pronotum without basal lateral incisions. Nevertheless, some species of Toxognathus have mandibles bidentate and a pair of short lateral incisions on pronotum, therefore they can be recognized only by the anterior prosternal margin truncate.

Figures

FIGURE 7: Toxognathus bakeri. A, pronotum; B, metaventrite; C, D, aedeagus (dorsal, ventral). Toxognathus beauchenei. E, antenna; F,hind wing; G, H, I, pro-, meso- and metathoracic leg (without tarsi); J, K, aedeagus (dorsal, ventral).

FIGURE 8: Toxognathus coomani. A, mandible (ventral); B, C, D, prothorax (dorsal, ventral, lateral); E, hind wing; F, abdomen (ventral); G, H, aedeagus (dorsal, ventral).

FIGURE 9: Toxognathus costulatus. A, antenna, B, maxilla; C, labium; D, labrum and mandibles; E, head (dorsal); F,pronotum; G, prosternum; H, mesoventrite; I, mesoventrite, pleural sclerites and mesocoxa (lateroventral); J, protibia and tarsus; K, hind wing; L, M, abdomen (ventral, lateral). Abbreviations: ala, anterolateral angle; as, articulating surface; abp, abdominal marginal plate.

FIGURE 10: Toxognathus costulatus. A, sternite VIII; B, tergite VIII; C, sternite IX; D, tergites IX and X; E, F, aedeagus (dorsal, ventral).

FIGURE 11: Toxognathus dohertyi. A, B, aedeagus (dorsal, ventral). Toxognathus fairmairei. C, hypomeron; D, pronotum and head. Toxognathus mouhoti. E, pronotum; F, G, aedeagus (dorsal, ventral).