Trictenotoma formosana Kriesche, 1919

Hu, Fang-Shuo, Pollock, Darren A. & Telnov, Dmitry, 2020, Comparative morphology of immature Trictenotoma formosana Kriesche, 1919 and systematic position of the Trictenotomidae (Coleoptera, Tenebrionoidea), European Journal of Taxonomy 640, pp. 1-22 : 3-17

Trictenotoma formosana Kriesche, 1919

Figs 1–27

Description

Last-instar larva ( Figs 1–17 , 27 )

LARVA. Tenebrionoid. Body elongate (body length: 77.3 mm (74–83 mm, n = 4), from mandibles to posterior extent of urogomphi), parallel-sided, slightly to moderately flattened dorsoventrally; colour pale yellow, darker on anterior half of head (including mouthparts, antennae, maxillary labial palps), tarsunguli and apices of urogomphi. Basal half of head, legs, and bases of urogomphi reddish-brown. Dorsal and ventral surfaces of body (excluding legs) with two distinct types of ornamentation: scattered, elongate setae in a regular pattern on tergites and sternites; and narrow, sclerotized, longitudinally oriented ridges (the latter often very short and tubercle-like, especially on venter of meso- and metathorax) medially on most sternites and tergites.

HEAD ( Figs3–4 , 27 ). Prognathous, exserted from prothorax, with lateral edges slightly and evenly rounded; dorsal surface punctate, somewhat rugose, with sparse, elongate setae; dorsolateral setae as follows: oblique pair laterally on each side of clypeus; single seta on epicranial plate just laterad widest extent of lyriform frontal arms of epicranial suture; transverse pair on frons just anteriad anterior curve in frontal arms; several setae on lateral margins of epicranial plate mainly in anterior half; ventral setae as follows: transverse pair near base of antennae; several setae along moderately raised ventral epicranial ridges; epicranial suture with lyriform frontal arms, extending to just behind antennal insertions; epicranial stem very short; posterior edge of epicranial plate deeply incised medially, margins bisinuate; endocarinae absent; stemmata absent; labrum rectangular, about twice as wide as long, anterior corners rounded, with dense row of relatively stout setae along anterior margin. Mandibles ( Figs 7–9 ) large, heavily sclerotized, asymmetrical, tridentate apically; inner margin of left mandible with distinct premolar tooth, slightly ventral in placement; mola present on both mandibles, larger on left mandible; mola on left mandible with two slightly dentate ridges, anteriormost larger; mola on right mandible with single ridge; molae with transverse ridges without dorsal asperities; dorsal microtrichiae absent; both mandibles with scattered, short setae especially on lateral margins. Maxillae ( Fig. 5 ) with 2-segmented cardo and truncate mala; mala with a row of dense, moderately long spines along inner margin and a long (subequal in length to width across distal end of mala) acute split tooth on inner edge; stipes punctured, apically and on outer margin sparsely spinose. Maxillary articulating area distinct. Maxillary palpi 3-segmented, 2 nd maxillary palpomere longer than 1 st or 3 rd palpomere; distal maxillary palpomere narrowed apically. Labium without suture between gula and submentum (forming ‘gulamentum’); submentum rectangular, slightly longer than wide, with a pair of setae at about midlength; mentum punctured, longer than wide and widest at its midlength, with pair of stiff setae along each lateral margin, suture between prementum and mentum not clear. Ligula absent (present in first instar, see below); labial palpi 3-segmented, 2 nd labial palpomere longer than palpomere 1 or 3; apical labial palpomeres narrowed apically. Hypostomal ridges present; hypostomal rods absent. Antennae ( Fig. 6 ) prominent, 3-segmented; 2 nd antennomere shorter and narrower than basal antennomere; antennomere 3 short and narrow (ratio: 1.61: 1.16: 0.23). Sensorium absent. Antennomeres 1 and 2 with sparse setae especially along inner margins; antennomere 3 with few setae on apex.

THORAX ( Figs 11–12 ). Prothorax transverse, subquadrate, approximately as long as combined lengths of meso- and metathorax; several setae on lateral margin and pair of setae near posterolateral corner; meso- and metathorax subequal in length, with inverted ‘V-shaped’ field of short longitudinal ridges along anterior margin, occupying middle ¼ of tergites; behind anterior field of ridges is another group of ridges, extending posteriorly as slightly curved line; dorsal setae of meso- and metathorax in similar positions: several along lateral margin, one near posterolateral angle and one slightly removed from lateral margin at about half length of segment; ventral surface of prothorax flat, with pair of setae near procoxal cavity, lacking longitudinal ridges; meso- and metathorax ventrally with a V-shaped impression at midlength, anterior to which is a dense field of longitudinal ridges (with a few ridges posteriad impressions). Mesothoracic spiracle annular, large and oval, laterotergite not distinctly produced. Legs ( Fig. 10 ) 5-segmented, short, with spine-like, stiff, elongated setae especially on ventral and anterior surfaces; dorsal margin of femora distinctly curved, apex much wider than base; coxa with short setae; tarsungulus relatively short, stout, with constriction at or before midlength, without distinct spine or setae at its base.

ABDOMEN ( Figs 13–17 ). Elongate, segments 1–8 subhexagonal, widest at about midlength; segment 1 slightly shorter than segment 2, segments 2–8 subequal in length and width; tergite 9 ( Fig. 16 ) nearly half-circular (excluding urogomphi); tergite 9 slightly shorter and narrower than tergite 8; tergites 1–8 with distinct sinuous parabasal ridge and narrow ‘V-shaped’ field of moderately long longitudinal ridges; sternites 1–8 with a curved impression, two subparallel median impressions and a relatively dense field of short longitudinal ridges; spiracles annular, ovoid, moderately large. Sternite 9 ( Fig. 15 ) with asperities along anterior margin, forming two slightly arcuate rows of 12–15 asperities each, outermost asperity larger than others; tergite 9 extended ventrally around anus, forming a series of small plates; tergite 9 ( Fig. 16 ) relatively densely punctate medially (especially compared to anterior tergites), with two small U-shaped predistal protrusions, each bearing an inconspicuous erect seta; dorsal setae placed similarly on tergites 2–8: several long setae along lateral margin, pair of setae on each side along posterior margin towards midline; scattered short setae among medial ridges, one or two setae on posterior half of tergites towards posterolateral margin; ventral setae as follows: two short setae on each side medially, near anterior edge of ridge field; one seta just posterior to ridge field, one or two setae near posterolateral corner. Urogomphi ( Figs 15–17 ) short, hook-like, curved dorsally, outer margins subparallel and inner margins divergent posteriorly; several moderately long setae on distal half of urogomphi; urogomphal pit(s) and lip absent.

First-instar larva ( Figs 18–26 )

BODY. Elongate (body length: 1.66 mm (1.47–1.81 mm, n = 20) from mandibles to urogomphi), parallelsided, flattened dosorventrally. Colour translucent-yellow, darker on apices of mandibles; dorsal and ventral surfaces of body (excluding legs) with two distinct types of ornamentation: scattered, elongate setae in a regular pattern on tergites and sternites; and narrow, short spines medially on most sternites and tergites.

HEAD ( Figs 20–21 , 26 ). Prognathous, exserted from prothorax, with lateral edges slightly and evenly rounded; head slightly wider than long; dorsal surface glossy, not punctate, with sparse, elongate setae; dorsolateral setae as follows: six pairs on labrum (two pairs on apex, three pairs on lateral surface, one pair on middle near base), two pairs on each side of clypeus, a pair on frons near base of antennae, a pair on frons just anteriad of anterior curve in frontal arms, a pair in front of stemmatal complex, three pairs behind stemmatal complex, a pair of long setae between frontal arms and stemmatal complex, a pair in middle of epicranial plate, a pair between stemmatal complex and base of head; ventral setae as follows: two pairs on oblique-frontal frons, a pair near base of stipes, another pair below this pair; epicranial suture with short lyriform frontal arms; epicranial stem indistinct; endocarinae absent; 5 stemmata on each side ( Fig. 26 ), forming anterior column of 3 and posterior column of 2; labrum half-circular. Mandibles sclerotized, slightly asymmetrical, tridentate apically; mola not clear on either mandible; both mandibles with an inner tooth. Maxillae with 2-segmented cardo and truncate mala; mala with a row of dense, moderately long spines along inner margin and a truncated tooth on inner edge; few spines on apex of truncated tooth; stipes with four setae on each side. Maxillary articulating area distinct. Maxillary palpi 3-segmented, 2 nd maxillary palpomere longer than 1 st or 3 rd palpomere; apical maxillary palpomere narrowed apically. Labium without suture between gula and submentum (forming ‘gulamentum’); submentum rectangular, slightly longer than wide; mentum wider than long and widest at midlength, with pair of stiff setae in middle; suture between prementum and mentum not clear. Ligula present; labial palpi 3-segmented, 2 nd labial palpomere longer than palpomere 1 or 3. Hypostomal ridges and hypostomal rods absent. Antennae prominent, 3-segmented; 2 nd antennomere longer and wider than basal antennomere; antennomere 3 short and narrow; sensorium absent. Antennomere 1 with single seta on inner margin; antennomere 2 with four apical setae.

THORAX ( Figs 22–23 ). Prothorax transverse, subquadrate, approximately as long as combined lengths of meso- and metathorax; dorsolateral setae and spines as follows: pair of long setae on anterior one fourth of prothorax, pair of short spines near this pair of setae; pair of setae on antero-lateral part of prothorax; two pairs of setae on lateral margin of prothorax; pair of setae on posterior-lateral part of prothorax; pair of setae on base of prothorax; three pairs of short spines near frontal margin of mesothorax; two pairs of setae on lateral margin of mesothorax; pair of setae on base of mesothorax; two pairs of short spines on frontal margin of metathorax; pair of setae on antero-lateral part of metathorax; two pairs of setae on lateral margin of metathorax; pair of setae on base of metathorax; ventral spines as follows: five pairs of spines spread on frontal half of prothorax; a pair of short spines on frontal margin of mesothorax and metathorax. Mesothoracic spiracle annular and round. Legs 5-segmented, with spine-like, stiff, elongated setae especially on ventral and anterior surfaces.

ABDOMEN ( Figs 22–25 ). Elongate, segments 1–8 subhexagonal, length and width similar in all segments; tergite 9 ( Fig. 24 ) nearly half-circular (excluding urogomphi); tergite 9 slightly longer and narrower than tergite 8; dorsolateral setae and spines of tergites 2–8 ( Fig. 22 ) as follows: two pairs of spines near middle of tergites; with pair of setae near lateral margin of tergites on both sides; pair of long setae on lateral margin of tergites; a pair of long setae on lateral-posterior part of tergites; ventral setae and spines on sternites 2–8 ( Fig. 23 ) as follows: six pairs of spines or setae spread on each sternite; a pair of spines on posterior-lateral parts of sternites; a pair of long setae on lateral margins; segment 9 with paired urogomphi, about 1.5 × as long as segment 8, hook-like and curved dorsally; urogomphal pit(s) and lip absent; dorsolateral setae of tergite 9 and urogomphi ( Fig. 24 ) as follows: a pair on frontal-lateral margin of segment 9, a pair between posterior margin of segment 9 and urogomphi, a pair on midlength of urogomphi, a pair of short setae on apex of urogomphi, sternite 9 with a half-circular ridge; ventral setae of sternite 9 and urogomphi ( Fig. 25 ) as follows: two pairs on frontal margin of sternite 9, a pair of setae on middle plate of sternite 9, a pair of long setae on lateral sternite 9, a pair of short setae at ¼ length of urogomphi, a pair of long setae near midlength of urogomphi, a pair of long and a pair of short setae near apex of urogomphi.

Description of the pupa ( Figs 28–36 )

PUPA. Adecticous-exarate, whitish to creamy with reddish to orange spiracles and darker mandibular apices. Body slightly to moderately flattened dorso-ventrally, with two distinct types of ornamentation: scattered, elongate setae on spherical protrusions and tergites; and extremely fine setae medially on most sternites and tergites ( Figs 35–36 ).

HEAD. Deflexed ventrally, not visible in dorsal view. Eyes large and reniform, narrow, broadly shallowly emarginate anteriorly and posteriorly. Frons dorsally shallowly impressed, delicately transversely wrinkled between antennal insertions. Clypeus and labrum delicately transversely wrinkled. Mandibles externally semioval, apices pointed, internally sinuous. Antennae long, extending to third abdominal ventrite.

THORAX. Pronotum trapezoidal, with moderately curved lateral and anterior margins; lateral margins irregularly carinate; disc with two median longitudinal carinae. Mesonotum with scutellar shield; mesonotum with irregularly wrinkled median protrusion; elytra well developed. Metathoracic notum oval, longer than mesothoracic notum and abdominal ventrites 1–6; anterior margin with semicircular groove.

ABDOMEN. Ventrites 1–6 subrectangular (tergite 6 broadly rounded posteriorly); widest at segment 3, narrowest at segment 6; segments each with a lateral ridge which has a spherical protrusion (weakly developed on segments 1 and 2) ( Fig. 34 ); tergites 2–7 with second spherical protrusion ( Fig. 34 ) on postero-lateral margin (weakly developed on tergite 2); 2–5 long setae on each spherical protrusion. Tergites 1 and 2 laterally wrinkled in dorsal view; tergites 2 and 3 with a median longitudinal groove; sternite 7 subrectangular, with four small protrusions on posterior margin; tergite 7 subpentagonal, with some longitudinal wrinkles; group of about 70 extremely fine setae medially on tergites 1–6 ( Fig. 35 ), about 30 on tergite 7; about 70 extremely fine setae on sternite 3 (first visible)–6; setae on sternite separated into 3 distinct groups, a grouping of about 30 setae on each side of sternite and about 10 setae spread medially on sternite ( Fig. 36 ). Sternite 9 with two oval, wrinkled and flake-like lateral protrusions; protrusion apex narrow and spherical. Urogomphi ( Figs 31–33 ) short and columnar.Abdominal spiracles ( Fig. 34 ) oblong, prominent, with strongly sclerotized peritreme, present on segments 1–6.

Figures

Figs 1–2. Habitus of last-instar larva of Trictenotoma formosana Kriesche, 1919. 1. Dorsal view. 2. Ventral view. Scale bar: 20 mm.

Figs 3–10. Head and fore leg of last-instar larva of Trictenotoma formosana Kriesche, 1919. 3. Head, dorsal view. 4. Head, ventral view. 5. Right maxilla, ventral view. 6. Left antenna, dorsal view. 7–9. Mandibles (7 = ventral view, 8 = dorsal view, 9 = mesal view). 10. Left prothoracic leg. Scale bars: 3–4 = 3 mm; 5, 7–9 = 2 mm; 6, 10 = 1 mm.

Figs 11–17. Thorax and abdominal segments 5 and 9 of last-instar larva of Trictenotoma formosana Kriesche, 1919. 11–12. Thorax (11 = dorsal view, 12 = ventral view). 13. Tergite 5. 14. Sternite 5. 15. Sternite 9. 16. Tergite 9. 17. Abdominal segment 9, posterior view. Scale bars: 3 mm.

Figs 18–19. Habitus of first-instar larva of Trictenotoma formosana Kriesche, 1919. 18. Dorsal view. 19. Ventral view. Scale bar: 0.5 mm.

Figs 20–21. Head of first-instar larva of Trictenotoma formosana Kriesche, 1919. 20. Dorsal view. 21. Ventral view. Scale bars: 0.1 mm.

Figs 22–23. Thorax and abdominal segments 4–5 of first instar larva of Trictenotoma formosana Kriesche, 1919. 22. Dorsal view. 23. Ventral view. Scale bars: 0.2 mm.

Figs 24–25. Abdominal segments 8–9 of first instar larva of Trictenotoma formosana Kriesche, 1919. 24. Dorsal view. 25. Ventral view. Scale bars: 0.1 mm.

Figs 26–27. Head of larva of Trictenotoma formosana Kriesche, 1919 in lateral view. 26. First-instar larva; arrows indicate the 5 stemmata. 27. Last-instar larva. Scale bars: 26 = 0.1 mm; 27 = 3 mm.

Figs 28–30. Pupa of Trictenotoma formosana Kriesche, 1919. 28. Dorsal view. 29. Lateral view. 30. Ventral view. Scale bar: 10 mm.

Figs 31–34.Abdominal segment 9, spherical protrusions and spiracles of pupa of Trictenotoma formosana Kriesche, 1919. 31–33. Abdominal segment 9 (31 = dorsal view, 32 = lateral view, 33 = ventral view). 34. Spherical protrusions and spiracles on segments 4–6, lateral view. Abbreviations: sp = spiracle; lsp = lateral spherical protrusion; ssp = second spherical protrusion. Scale bars: 31–33 = 3 mm; 34 = 2 mm.

Figs 35–36. Extremely fine setae on abdominal segments of pupa of Trictenotoma formosana Kriesche, 1919. 35. Setae on tergites 4–5. 36. Setae on sternites 4–5. Scale bars: 3 mm.