Scaptolenus acrognathus, Champion, 1896

Martínez-Luque, Erick Omar & Johnson, Paul J., 2023, Description of the Female and Redescription of the Male of Scaptolenus acrognathus Champion (Coleoptera: Elateridae), The Coleopterists Bulletin 77 (3), pp. 319-327 : 320-326

SCAPTOLENUs ACROGNATHUs Champion, 1896

Scaptolenus acrognathus Champion 1896: 564 , table XXV, fig. 8, 8a, male (drawing). References: Dalla Torre 1911: 11; Dalla Torre 1913: 11; Blackwelder 1944: 275.

Material Examined (1 ♀; 3 ♂). MEXICO: Querétaro, Huimilpan, Cerro de Capula , (20°20′31.1′′N, 100°17′37.7′′W), oak forest, leaf litter, 2,536 msnm, 14-viii-1997, Col. J. L. Cozar (UAQE-22753: 1 ♀; and UAQE-22754: 1 ♂) ; San Luis PotosÍ, Matehuala , 5-vii-1971, Col. B. K. Dozier ( FSCA: 1♂) ; Estado de México, Valle de Bravo , 17-vi-1961, Col. J. Hendrichs S. ( CNIN-IBUNAM: 1♂) .

Description of Female ( Figs. 11–18 , 20, 22, 24, 26 ). Body 13.8 mm long, 4.7 mm wide; head, mandibles, antennae, pronotum, abdomen, and elytra fusco-rufous, basal part fulvous ( Figs. 11–13 ). Head with setae similar in length to length of penultimate maxillary palp, thin, fulvous-colored, scattered on frons and grouped apically, denser at base of mandibles and antennae. Eye black, small, similar in length to antennomere 1. Antenna with setae similar in length to antennomere 3 and fulvous in color. Pronotal margin setae similar in length to setae on head, setae only on margin of pronotum, densest at anterior and posterior angles. Legs with small setae half the length of setae present on head and fulvous in color. Elytra with setae similar in length to setae present on legs, with thin, fulvous setae on outer marginal part, abundant at base and apically. Abdomen bright fusco-rufous ( Figs. 12, 13 ), with scattered testaceous setae, thin and similar in length to setae present on elytra.

Head 2.2 mm long, 2.2 mm wide, with dense, deep punctation. Front irregularly shaped (not smooth, but distinctive or tubercled). Maxillary palp ( Fig. 26 ) with apical part of palpomere cylindrical, 2.6 times as long as wide, wider at apex than at base; penultimate palpomere cylindrical, 4 times as long as wide, gradually widening apically. Antenna clavate with short, seemingly fused antennomeres ( Fig. 20 ), length ratio of antennomeres 2–11: 0.2:0.2:0.1:0.1: 0.1:0.1:0.08:0.09:0.05:0.1. Pronotum 1.6 times as wide as long; width of pronotum 4.4 mm, length of pronotum 2.7 mm; anterior margin convergent medially, subacute, lateral margins rounded, with carina extending from the posterior angle to more than half of lateral margin, not reaching anterior margin. Pronotum with scattered, shallow punctation; posterior angles divergent and not very acute, exceeding apex of scutellar shield. Scutellar shield subtriangular with rounded edges. Elytra together 8.8 mm long and 4.7 mm wide (across humeri), punctures very similar to punctures of pronotum, gradually sulcate ( Fig. 11 ). Abdomen smooth with a shiny appearance ( Fig. 12 ), with 5 ventrites and with fine, sparse punctuation, each puncture with very thin, decumbent, fulvous seta. Hind wing length 8.11 mm, 2 times as long as wide ( Fig. 14 ). R cell open, r3, r4, RML, MSP, and SS present; basal portion of RP measuring 1.59 mm, MP 3+4 short measuring 1.05 mm; CuA 2 and CAS directly connected with Cu; CuA 1, CuA 3+4, W cell, AA 3, and AA 4 absent. Prosternum wider than long, length 1.3 mm, width of prosternum 1.6 mm, not exceeding coxae, abruptly truncated in anterior part, discal part gradually curved, punctation similar to that of abdomen. Mesoventrite and metaventrite with fine, shallow punctures, each puncture with fulvous seta, similar in length to setae present on head. Metacoxal plate broadly arcuate anteriorly ( Fig. 24 ), strongly narrowing laterally, with 2 acute teeth separated by an emargination over femoral attachment; posterior margin carinate from ectal tooth to lateral apex; coxal plate finely and shallow punctate, each puncture with seta similar in size to setae present on head, setae fulvous. Metanepisternum triangular anteriorly, narrowing to metacoxal angle. Protibia with ectal border with subacute, triangular central tooth ( Fig. 22 ), tibial apex with subacute lateral tooth, tibia with fine, shallow punctures, each puncture with seta. Tibia with setae densely clustered at apical margin; length of the ectal tooth 0.5 mm. Protibial spurs long, equal, 0.5 mm long; nearly straight, gradually curved, apex subtruncate. Average lengths of tarsomeres 1–5, basal to distal: 1.0 mm, 0.5 mm, 0.3 mm, 0.2 mm, 0.5 mm; each robust, subcylindrical, with fine, rigid setae of similar length to setae present on protibiae.

Female Terminalia. Tergite VIII ( Fig. 15 ) widening apically in basal third, then gradually narrowing apically; apex broadly rounded with long, thick setae, similar in length to setae present on head; base with deep median emargination, each basolateral lobe extended, punctation dense and deep along entire length of tergite. Sternite VIII ( Fig. 16 ) broadly subtriangular, punctate with thin setae, similar in length to setae present on tergite VIII, located on lateral margin, with 2 groups of setae in apical fifth; basal angles slightly extended, with carinate margin running medially from lateral margin of basal fifth of sternite and merging with base of spiculum ventrale; basodiscal area of sternite translucent, difficult to delimit; spiculum ventrale (broken in figure) very long, 3.16 times as long as sternite. Ovipositor ( Figs. 17, 18 ) baculum 4.04 times length of gonocoxites; base of ovipositor 1.98 mm wide, tapering to dorsoventrally compressed gonocoxites, each 0.63 mm wide.

Redescription of Male ( Figs. 1–10 , 19, 21, 23, 25 ). Body 13.2–16.0 mm (x = 14.8, n = 3) long, 5.6–6.2 mm (x = 6.0, n = 3) wide; Dorsum brown ( Fig. 1 ), thoracic venter and femora fulvous; abdominal ventrites, femora, tibiae, tarsomeres, and claws fuscous in color ( Figs. 2, 3 ). Head black with anterior setae similar in length to antennomere 3, decumbent and fulvous. Eyes black, longer than half the length of antennomere 1. Antennae brown with setae fulvous, setae similar in length to antennomere 3. Pronotum dark brown with long, fine, fulvous-colored setae similar in length to antennomere 6 ( Fig. 1 ). Legs with coxae and femora fulvous, with long, thin decumbent setae and similar in length to antennomere 6. Tibiae, tarsomeres, and claws fuscous with decumbent setae similar in length to antennomere 6 ( Figs. 2, 3 ). Elytra fuscous with shorter fulvous setae similar in length to antennomere 3, concentrated on the lateral margin ( Fig. 1 ). Abdomen fuscous on all segments, with testaceous, decumbent, evenly spaced, short, scattered setae ( Fig. 2 ).

Head 1.5–1.7 mm (x = 1.5, n = 3) long, 1.4–1.7 mm (x = 1.5, n = 3) wide, with dense, deep punctation with setae. Maxillary palp ( Fig. 25 ) with length of penultimate palpomere 0.4–1.0 mm (x = 0.6, n = 3), length of last palpomere 0.4–1.0 mm (x = 0.7, n = 3). Antennomeres 4–10 serrate ( Fig. 19 ), length ratios of antennomeres 2–11: 0.1:0.3:0.7:0.7:0.6: 0.6:0.6:0.6:0.6:0.6:0.7. Pronotum 1.6× wider than long; width 3.5–3.8 mm (x = 3.6, n = 3), length 2.1–2.2 mm (x = 2.2, n = 3); discal punctation dense and deep, slightly sparser and shallower than on head; lateral margins convergent anteriorly from mid-length, anterior angles subacute, lateral margins rounded, without carina; posterior angles widely divergent, elongate, apically acute. Scutellar shield subtriangular. Elytra together 9.5–12.0 mm (x = 11.0, n = 3) long and 5.6–6.2 mm (x = 6.0, n = 3) wide across humeri, with punctures similar to those of the head, striae shallowly sulciform. Abdomen with 5 ventrites, punctation fine, sparse, each puncture with a fine, decumbent seta. Hind wing length 12.73 mm, 2.1× as long as wide ( Fig. 4 ). Support sclerites (SS) V-shaped; R cell 4.56 times as long as wide; r3, r4, RML, MSP, MP 1+2, MP 3+4 present; MP 3+4 short, 1.53 mm; basal portion of RP 3.76 mm; CuA 1 joining CuA 2; W cell present, 2.6× as long as wide; CuA 3+4, CAS, AA 4, AA 3, AA 3+4 and AP 3+4 present. Prosternum 1.1 mm (x = 1.1, n = 3) long, 1.3 mm (x = 1.3, n = 3) wide, short and not reaching coxae, anterior margin truncate, with disc convex, with fine, shallow and very dispersed setate punctation. Mesoventrite and metaventrite with fine, shallow punctures, each puncture with a long, fine seta similar in length to the setae of the pronotum. Metacoxal ventral plate broad medially, with 3 subacute to acute teeth at coxal base covering metafemoral insertion, then gradually tapering laterally ( Fig. 23 ), with fine, shallow, setate punctation, seta longer than length of antennomere 6. Metanepisternum triangular, broad anteriorly, narrowing to metacoxal angle. Protibial dorsal angle with subacute triangular tooth near midlength ( Fig. 21 ), apex with large, subacute lateral tooth, protibial surface with fine, shallow, setate punctures, setae dense on the upper and lower faces; length of the ectal tooth 0.4–0.5 mm (x = 0.5, n = 3). Protibial spurs long, subacute, shallowly curved inner spur 0.6–0.7 mm (x = 0.6, n = 3); length of outer spur 0.7 mm (x = 0.7, n = 3); apices semi-acute and curved. Length ratios (in mm) of tarsomeres 1–5: 1.3:0.8:0.7:0.6:0.9; tarsomeres slender, subcylindrical, with stiff, fine, long setae.

Male Terminalia. Trilobed aedeagus ( Figs. 6, 7 ): phallobase 1.1 times longer than wide, curved laterally, with a semi-rectangular emagination at its base and a posterior internal emargination narrower than that at base. Median lobe fusiform in dorsal aspect, wide at base, narrowing, then widening after midlength, apically tapering to a narrowly obtuse apex gradually curved ventrally, length 1.5–1.8 mm (x = 1.6, n = 3); parameres divergent basally, gently curved at midlength, subparallel apically, with apices obliquely subtruncate, length 1.3–1.7 mm (x = 1.5, n = 3),

5) Sternite VIII. Aedeagus: 6) Ventral view; 7) Dorsal view. 8) Sternite IX; 9) Tergite IX and X; 10) Tergite VIII.

14) Hind wing; 15) Tergite VIII with spiculum ventrale; 16) Sternite VIII; 17) Ovipositor; 18) Gonocoxites.

central elevation in apical third of paramere with thin, decumbent setae. Sternite VIII ( Fig. 5 ) 1.7 times as wide as long, broader at base than at apex; basal margin straight, with rounded corners; medio-basal part gradually translucent, difficult to delimit; setae thin, longer than antennomere 6, concentrated at margins; distal margin sinuately bilobed.Sternite IX ( Fig.8 ) 2.5 times as long as wide, straight from base to two-thirds length; distal third narrowing, with broadly rounded apex, with translucent discal area in basal third, with rounded angles, setae thin and longer in length than antennomere 6, grouped in apical third. Tergite VIII ( Fig. 10 ) triangular, 1.07 times as wide as long; base with tubercles on margin, stippled on apical two-thirds, setae long, slender, decumbent. Tergite IX ( Fig. 9 ) gradually narrowing distally, posterior margin strongly notched at middle, posterolateral angles rounded, sparsely punctate, and with setae thin and longer in length than antennomere 6, located on distal and apical margins. Tergite X reduced ( Fig. 9 ), no setae or punctation, apex truncate.

Distribution ( Fig. 27 ). Champion (1896) described this species from the state of Guerrero, Mexico. Here we report this species for the states of Estado de México, Querétaro, and San Luis PotosÍ, which represent new state records.

Sexual Dimorphism. Scaptolenus acrognathus shows well-marked sexual dimorphism, with the main differences in the total lengths and relative sizes of the appendages, the female being smaller and with shorter appendages. These differences in sizes are more evident in certain appendages such as the tarsomeres ( Figs. 1–3 , 11–13 ), tibiae ( Figs. 21, 22 ) and in the antennae ( Figs. 19, 20 ), which only reach the apical part of the pronotum. The pronotum is wider than long in the male ( Fig. 1 ). The elytra of the female only cover the first four abdominal segments ( Fig. 13 ), while in the male the elytra cover the entire abdomen ( Figs. 1–3 ). There are also differences in the shape of the metacoxal plates ( Figs. 23, 24 ) and in the complexity (number of veins present) of the wing venation, with the female wing venation being the simplest ( Fig. 14 ).

Ecological Notes. Few prior works provide biological notes for any species in the genus other than their edaphic habits and occurrence during intense summer rains ( Fall 1932; Werner 1969), and we feel that habitat information is essential for Scaptolenus species. Recently, MartÍnez-Luque et al. (2022) described an ephemeral lifespan for males of an undescribed Scaptolenus species (less than 24 hours after their emergence from the ground). Immature stages develop underground, but nothing is known of their feeding habits. Copulation takes place at the ground surface with the female within her burrow and abdomen available to the male. For these edaphic animals, it may be important to study soil characteristics and their ecological associations to better define the habitats where each species is found.

The specimens from Querétaro were collected in the Sierra de Amealco Natural Region with an altitude of 1,200 –2,800 m in oak forests surrounded by agricultural areas ( Bayona-Celis 2016a; GarcÍa-Sánchez and Meraz 2016). In this region there is a sub-humid temperate climate with summer rains providing an average annual precipitation of 861.5 mm, May to October, with periodic well-marked periods of drought ( Bayona-Celis 2016a; Luna-Soria and Suzán-Azpiri 2016). The average annual temperature recorded is 14.4 °C with a minimum temperature between 3.8 and 9.8 °C and maximum temperatures from 19.2 °C to 24.8 °C (Luna-Soria and Suzán-Azpiri 2016). The soil at the sampling locality belongs to the Feozems group, which is characterized by being dark-colored with porous properties and is rich in organic matter ( Bayona-Celis 2016b).

The locality in the Estado de México is in the Valle de Bravo basin, in the physiographic province Eje Neovolcánico Transversal. This region has a temperate sub-humid climate with summer rains, with well-marked dry and rainy seasons ( INEGI 1977). The average annual rainfall ranges from 1,310 to 1,500 mm. The main type of vegetation is pine-oak forest ( Rzedowski 1981). This type of vegetation is associated in this region with an altitude of 2,200 –3,000 m. Predominant soil in the basin is Andosol, which is formed from volcanic ash and glass, and is dark in color, porous, and very fertile ( INEGI 2015).

The record of S. acrognathus in San Luis PotosÍ lacks specific geographic location data or other habitat information for its collecting site. The municipality of Matehuala is located in the northern part of the state, in the area of the Altiplano Mexicano ( Pedraza-Montes 1994). This municipality presents a topography mainly of undulating plains, with scattered hills and ravines. These conditions correspond to sub-humid temperate climates, located at altitudes of 1,200 –2,100 m, where we find associated pine-oak vegetation ( Rzedowski 1960, 1965). Unfortunately, this vegetation is currently considered an isolated relict within the municipality of Matehuala. In San Luis PotosÍ, these forests are in the northern part, on the eastern slope of Sierra de Catorce, and extend to the southeast of the state, in a portion of the Sierra Madre Oriental ( INEGI 2002).

In the case of the type locality, this was recorded by Champion (1896) as Omilteme, Guerrero. This locality corresponds to the community of Omiltemi located to the west of the municipality of Chilpancingo de los Bravo in the center of the state of Guerrero in southeastern Mexico. This locality has a very rugged topography with elevations of 1,900 –2,800 m ( GarcÍa-Rendón 1988). At the highest points, there is a sub-humid temperate climate, with average annual temperatures of 15 °C to 24 °C. The average annual rainfall is 1,650 mm, with well-marked wet and dry seasons (Miranda and Sharp 1950). The type of vegetation is pine-oak forest, with soil of volcanic origin ( Meave et al. 1992).

Figures

Figs. 11–18. Scaptolenus acrognathus (female). 11) Dorsal habitus; 12) Ventral habitus; 13) Lateral habitus;

Figs. 19–26. Scaptolenus acrognathus. Antenna: 19) Male; 20) Female. Protibia: 21) Male; 22) Female. Metacoxal plate: 23) Male; 24) Female. Maxillary palp: 25) Male; 26) Female.

Figs. 1–10. Scaptolenus acrognathus (male). 1) Dorsal habitus; 2) Ventral habitus; 3) Lateral habitus; 4) Hind wing;

Fig. 27. Distribution of Scaptolenus acrognathus.