Autocrates maqueti Drumont, 2006

Cho, Hee-Wook, Kwon, Min Chul, Kim, Sang Ki & Beutel, Rolf Georg, 2022, Morphology of larvae and pupae of the genus Autocrates (Coleoptera: Trictenotomidae) and its phylogenetic implications, Acta Entomologica Musei Nationalis Pragae 62 (1), pp. 197-210 : 199-209

Autocrates maqueti Drumont, 2006

Material examined. Numerous eggs and larvae were obtained from two adults with the following collecting data: 1 female, SOUTH KOREA: GඒൾඈඇGൻඎK Pඋඈඏ.: Yeongyang County, Subi-myeon, Suha-ri, Suha valley, 36°50’14.84”N, 129°16’11.85”E, ca. 320 m, 2.vii.2021, leg. H.-W. Cho; 1 female, same data except 16.vii.2021. For this study, 90 first instar and 2 last instar larvae were fixed and stored in 70% ethanol.

Mitogenome characterization. The complete mitochondrial genome is 15,906 bp in size, containing 13 protein-coding genes, two RNAs, 22 tRNAs, and one control region.

Larval stages. Our breeding experiments and preliminary measurements (head capsule width) revealed an exceptionally high number of 25 larval stages or even more. It is evident that the number of larval instars varies within a species.

Egg ( Figs 2, 3 ). Length 1.84–1.96 mm (mean: 1.92 mm, n = 8) and width 0.38–0.44 mm (mean: 0.41 mm). Egg clusters contained from 95 to 675 eggs. They are elongate-oval, yellowish-white, and covered with an adhesive substance. First instar larva ( Figs 4–13 ). General appearance ( Figs 4, 5 ). Body length 2.57–3.23 mm (mean: 2.96 mm, n = 8), body width 0.43–0.46 mm (mean: 0.44 mm), and head width 0.39–0.40 mm (mean: 0.40 mm). Elongate, parallel- -sided, somewhat flattened dorsoventrally. Ground color of living and alcohol-preserved larvae pale yellowish-white; head, urogomphi and legs yellowish-brown, mandibles dark-brown.

Head ( Figs 8, 9 ). Distinctly prognathous, well sclerotized, brownish, slightly narrower than pronotum, partially retracted into prothorax, sub-parallel, very slightly rounded laterally, slightly widening posteriorly but distinctly narrowing shortly before posterior margin, evenly rounded posterolaterally. Epicranial stem (= coronal suture) very short; frontal arms lyre-shaped, with anterior horizontal section extending to lateral half of head, without reaching antennal articulation area; dorsal median endocarina absent. Fronto-clypeal ridge not recognizable externally, probably absent; clypeo-labral suture distinct. Frons with 5 pairs of setae and 3 campaniform sensilla: median row of 3 setae (Df1–3), 1 seta (Df4) below frontal arms, and 1 seta (Df5) close to antennal base. Clypeus trapezoidal, with 2 setae and 1 campaniform sensillum on lateral region. Labrum semi-circular, with 3 pairs of setae and 2 pairs of campaniform sensilla; epipharynx with 5 pairs of relatively stout setae, 1 pair of long setae on anterior margin, and 1 pair of pointed setae placed medially. Epicranium on each side with a row of 4 small pointed setae (Dp1–4) on vertexal region, 5 dorso-epicranial setae (De1–5), 4 lateral setae (L1–4), and 5 campaniform sensilla. Five stemmata present on each side of head above moderately elevated antennal insertion area, arranged into anterior column of 3 and posterior column of 2. Ventral side of head with 2 setae ( V 1–2) along hypostomal rods, 2 setae ( V 3–4) close to antennal base, and 4 campaniform sensilla. Maxillary grooves deep. Hypostomal ridges long and subparallel; ventral epicranial ridges absent.

Antenna. Prominent, 3-segmented, inserted on elevated anterolateral region of head capsule; antennomere I very short, about 3× wider than long, with 4 campaniform sensilla; antennomere II cylindrical, almost 3× longer than basal segment, with 4 setae, 1 campaniform sensillum, and wide but fairly short cupola-shaped sensory appendage; antennomere III subconical, elongate, with 6 setae and 2 campaniform sensilla.

Mouthparts ( Figs 9–11 ). Mandibles asymmetric, heavily sclerotized, roughly triangular, distinctly projecting beyond apical labral margin; each with 2 large apical teeth, one subapical tooth, 2 indistinct teeth closer to molar region, 2 setae, and 3 campaniform sensilla; mola distinctly delimited, covered with tooth-like asperities arranged in rows. Left mandible slightly longer than right, with 1 molar tooth. Maxillary articulatory area well developed, with semi-membranous pad-like structure inserted between cardo and stipital base. Cardo small, obliquely inserted in maxillary groove, with 1 seta. Stipes rather broad and about 3× longer than cardo, distally widening, with 4 setae and 2 campaniform sensilla. Maxillary palp 3-segmented, inserted anterolaterally on stipes on transverse articulatory area; palpifer not recognizable as defined structure; palpomere I short, wider than long, with 2 campaniform sensilla; palpomere II as long as wide, about 2× longer than palpomere I, cylindrical, with 2 setae and 1 campaniform sensillum; palpomere III subconical with 1 seta, 1 digitiform sensillum and 1 campaniform sensillum on sides, and group of short spine-like setae inserted on flattened apical region. Mala firmly fused with stipes mesad articulatory area of palp; with deep distal cleft bearing 3 fixed teeth at inner margin, 6 stout setae at apex, 9–10 stout setae along inner margin, and 2 campaniform sensilla. Submentum completely fused with gula, entire region scarcely defined and weakly sclerotized (gulasubmentum), with single pair of setae; mentum with single pair of setae; prementum broad and short; ligula well developed, covered with spinules apically, with single pair of setae. Labial palp 3-segmented, cylindrical; palpomere I with 1 seta and 1 campaniform sensillum; palpomere II with 1 campaniform sensillum; palpomere III with group of setae at apex and 1 campaniform sensillum.

Prothorax ( Fig. 6 ). Transverse, slightly longer than following thoracic segments. Pronotum lightly sclerotized and divided medially by distinct ecdysial line; with 13 pairs of setae of various lengths, longest ones along margins, and 8–10 pairs of campaniform sensilla. Prosternum divided into 3 parts by 2 longitudinal lines, with 3 pairs of setae; basisternum with 1 pair of setae; pleurites with 2 setae on precoxale and epimeron.

Meso- and metathorax. Distinctly transverse, similar in shape and chaetotaxy. Tergites lightly sclerotized and divided medially by distinct ecdysial line; with 10 pairs of setae of various lengths, longest ones mostly along lateral and posterior margins, and 5 pairs of campaniform sensilla. Basisternum with 2 pairs of ventral setae; pleurites with 3 setae on precoxale and epimeron. Mesothoracic spiracle annular, vertically elliptical, located anterolaterally.

Legs ( Fig. 12 ). Stout, 5-segmented, slightly flattened laterally; all legs similar in shape and chaetotaxy. Coxa broad, with 15 setae of various lengths and 1 campaniform sensillum. Trochanter distinctly widened apically, with 4 setae of various lengths and 5 campaniform sensilla. Femur moderately elongate with 8 setae and 1 campaniform sensillum. Tibiotarsus elongate, with 5 stout setae and several tiny subapical setae. Pretarsal claw about as long as tibiotarsus and apically pointed, with 2 setae inserted at about midlength.

Abdominal segments I–VIII ( Fig. 7 ). Each segment lightly sclerotized; chaetotaxy similar; segments I–VII strongly transverse, gradually broadening; segment VIII narrowed posteriorly. Each tergite with 7 pairs of setae of various lengths, longest ones along lateral and posterior margins, pair of short setae in front of tergite, and 4 pairs of campaniform sensilla. Each sternite with 7 setae of various lengths. Abdominal spiracles on segments I–VIII annular.

Abdominal segment IX ( Fig. 13 ). Paired fixed urogomphi well-developed, distinctly curved upwards apically; surface somewhat rough, with 10 pairs of setae and 8 campaniform sensilla. Sternite with asperities anteromedially and 4 pairs of setae. Ventral part of tergite IX not subdivided.

Abdominal segment X. Tergite weakly sclerotized, with 4 pairs of setae. Sternite largely membranous with 3 pairs of setae. Pygopod well developed.

Last instar larva ( Figs 14–31 ). General appearance ( Figs 14–16 ). Body length 93.8–112.0 mm (mean: 102.9, n = 2), maximum width 14.2–15.0 mm (mean: 14.6), and head width 11.55–11.65 mm (mean: 11.60 mm). Elongate, parallel-sided, somewhat flattened dorsoventrally. Ground color of living larvae creamy-white to yellowish-white with obscure pale markings; head reddish-brown, anterior part blackish-brown with yellow rhombus-like marking; longitudinal ridges on tergites and sternites, and spiracular peritremes dark-brown; urogomphi darker towards tip; legs pale-brown to reddish-brown with pretarsal claw blackish-brown apically.

Head ( Figs 17, 18 ). Distinctly prognathous, well sclerotized, distinctly narrower than pronotum, partially retracted into prothorax, evenly rounded laterally, strongly narrowing posteriorly; posterior edge of head capsule distinctly emarginate. Surface covered with sparse punctures bearing minute setae. Epicranial stem (= coronal suture) relatively short; frontal arms lyre-shaped, with anterior horizontal section slightly sinuate, reaching lateral margin of antennal articulation area; dorsal median endocarina absent. Fronto-clypeal ridge absent. Clypeo-labral suture distinct. Frons with transverse wrinkles below frontal arms, 8 pairs of setae: median row of 4 setae (Df1–4), 2 setae (Df5–6) below frontal arms, and 2 setae (Df7–8) close to antennal base. Clypeus trapezoidal, divided by median transverse ridge, lower region glabrous, with 3 setae laterally. Labrum transverse, anterior corners strongly rounded, with 5–6 pairs of dorsal setae, and numerous marginal setae; epipharynx with numerous setae and group of sensory papillae placed anteromedially. Epicranium on each side with row of 4 small pointed setae (Dp1–4) on vertexal region, 6 dorso-epicranial setae (De1–6), and 6–7 lateral setae (L1–7). Ventral side of head with 3–4 setae ( V 1–4) along ventral epicranial ridges, 3–4 setae ( V 5–8) close to antennal base, and series of small pointed setae near posterior edge. Maxillary grooves deep. Hypostomal ridges long and subparallel; hypostomal rods absent. Stemmata absent.

Antenna ( Fig. 24 ). Prominent, 3-segmented, inserted on elevated anterolateral region of head capsule; antennomere I longest, distally widening, 2.5× longer than wide, with sparse setae on lateral surface; antennomere II cylindrical, nearly 0.8× as long as basal segment, with sparse setae on lateral and apical surface, and strongly reduced, flat, S-shaped sensory appendage at apex; antennomere III very small, subcylindrical, with group of minute setae at apex.

Mouthparts ( Figs 23, 26–31 ). Mandibles asymmetric, heavily sclerotized, roughly triangular, each with 3 large apical teeth, several setae inserted between condyle and mola, and group of setae on lateral surface; molae asymmetric, very strongly sclerotized, with distinct parallel ridges; molar protuberances prominent medially on left mandible, basally on right mandible; left mandible very slightly longer than right one, with 1 premolar tooth. Maxillary articulatory area well-developed, with pad-like structure inserted between cardo and stipital base. Cardo small, obliquely inserted in maxillary groove, with 1 seta. Stipes rather broad and about 3× longer than cardo, distally widening, with numerous stout setae on inner and outer surface. Maxillary palp 3-segmented, inserted anterolaterally on oblique stipital articulatory area; palpifer not recognizable as defined structure; palpomere I cylindrical, slightly longer than wide, with moderately dense setae on lateral surface; palpomere II cylindrical, longer and narrower than palpomere I, with moderately dense setae on lateral and apical surface; palpomere III cylindrical, slightly narrowing apically, with several setae on inner surface; group of minute setae inserted on flattened apical region. Mala firmly fused with stipes mesad articulatory area of palp; with deep distal cleft bearing 3 fixed teeth at inner margin, numerous stout setae on apical and inner surface, and several stout setae on dorsal and lateral surface. Submentum completely fused with gula (gulasubmentum), lightly sclerotized posteriorly, with two pairs of setae; mentum with dense setae on lateromedial surface; prementum broad and short; hypopharynx strongly sclerotized, with sharply pointed V-shaped tip; above rounded part with 3 pairs of setae; ligula absent. Labial palp 3-segmented, cylindrical; palpomere I wider than long, with several setae; palpomere II 2× longer than palpomere I, with sparse setae; palpomere III small, with group of setae at apex.

Prothorax ( Figs 19, 20 ). Transverse, lateral sides distinctly rounded, with notch before base; wider and longer than other thoracic segments; surface strongly rugose; longitudinal ridges absent. Pronotum lightly sclerotized and divided medially by distinct ecdysial line; with 9–10 pairs of setae of various lengths, longest ones along lateral margin. Sternum without transverse depression medially, with 3 pairs of setae. Pleurites with 4 setae.

Meso- and metathorax. Distinctly transverse, strongly rugose, similar in shape and chaetotaxy. Tergites lightly sclerotized and divided medially by ecdysial line obliterating near posterior margin; with 8–9 pairs of distinct major setae and scattered minute setae on anterior and anterolateral surface; series of irregular, longitudinal ridges of various length arranged in 2 rows, transverse row present on both tergites, inverted U-shaped row on mesotergum and V-shaped row on metatergum. Sternites with depressed transverse arch on middle half; anterior and posterolateral surface of depression densely covered with short longitudinal ridges; with 9–10 pairs of scattered setae. Mesothoracic spiracle annular, vertically elliptical, located anterolaterally, and almost 2× longer than abdominal spiracles.

Legs ( Fig. 25 ). Stout, 5-segmented, somewhat cylindrical, with moderately dense setae of various lengths; all legs similar in shape and chaetotaxy. Coxa broad, widely separated from each other. Trochanter and femur distinctly widened apically. Tibiotarsus cylindrical, slightly narrowed apically. Pretarsal claw much shorter than tibiotarsus, apical half heavily sclerotized, bent, and tapered.

Abdominal segments I–VIII. Each segment lightly sclerotized, strongly rugose; segments I–VII similar in shape and chaetotaxy; segment I distinctly transverse, smaller than other segments; segments II–VII weakly transverse; segment VIII gradually narrowing. Each tergite with 11–13 pairs of setae of various lengths, longest ones along lateral margin, and several scattered minute setae on lateral surface; sternite with 10–12 pairs of short setae. Tergites I–VII with series of variously long, irregular, longitudinal ridges arranged in 2 rows, obtuse-angled row and acute- -angled row, both located outside V-shaped depression; tergite VIII with 1 or 2 pairs of small longitudinal ridges medially. Sternite I with median transverse depression; sternites II–VIII with median transverse depression, 1 pair of oblique depressions, and numerous short longitudinal ridges around depressions. Abdominal spiracles on segments I–VIII annular.

Abdominal segment IX ( Figs 21, 22 ). Strongly rounded posteriorly. Tergite with 1 pair of small U-shaped ridges anterior to urogomphi. Paired fixed urogomphi short, slender, distinctly curved upwards apically, with 6 pairs of setae. Sternite with asperities anteromedially. Ventral portion of tergite IX indistinctly subdivided.

Abdominal segment X. Weakly sclerotized, with few setae. Pygopod not developed.

Pupa ( Figs 32–34 ). General appearance. Body length 54.8 mm and maximum width 16.5 mm (n = 1). Exarate, broad anteriorly, narrowing posteriorly, and moderately flattened dorsoventrally. Ground color of living pupa creamy-white to yellowish-white; apices of mandibular teeth and spiracular peritremes brown, apices of urogomphi dark-brown.

Head. Bent ventrad, invisible from above, distinctly narrower than pronotum, and sparsely covered with minute setae. Surface with transverse wrinkles, becoming wider and denser towards anterior side. Frons distinctly depressed at anterior margin. Fronto-clypeal ridge not recognizable externally. Labrum trapezoidal with setose anterior margin. Median epicranial region on each side shallowly depressed. Eyes large, strongly transverse and elongated, widening laterally.Antennae placed on femur of fore and middle legs, reaching apex of abdominal segment II. Mandibles well developed, symmetric, semicircular, each with 1 apical tooth.

Thorax. Tergites with wrinkles with varying orientation, sparsely covered with minute setae, divided medially by distinct ecdysial line. Pronotum transverse, convex dorsally; lateral margins with large postmedian protrusion and several sinuous notches; anterior margin deeply emarginate. Mesonotum distinctly shorter than other thoracic segments. Elytral and hind wing sheaths bent ventrad, reaching apex of abdominal segment III.

Abdomen. Surface with widely separated wrinkles, sparsely covered with minute setae. Tergites I– VI strongly transverse, each with 1 pair of lateral protrusions and 1 pair of sublateral protrusions, those of 2nd to 4th segments prominent. Tergite VII narrow trapezoidal with conspicuous emargination. Sternite VIII narrowed posteriorly, with 2 small apical protrusions. Tergite IX disk-shaped, with short, paired, 1-segmented urogomphi. Abdominal spiracles on segments I– VI annular, with well sclerotized peritreme.

Discussion

Number of larval instars. As shown by our breeding experiments accompanied by measurements of the head capsule, the postembryonic development of Autocrates is characterized by an enormously increased number of 25 larval instars. The presently available information on the life cycle and postembryonic development of cucujiform beetles is very scarce, with the exception of the intensively investigated model Tribolium castaneum (Herbst, 1797) (e.g. Pඈංඇඍൾඋ et al. 2021) and a few other species. Nevertheless, this remarkable phenomenon deserves attention. The condition observed in Autocrates is in stark contrast to the presumptive ancestral number of three larval stages in Coleoptera (e.g. Cඋඈඐඌඈඇ 1981, Bൾඎඍൾඅ et al. 2014). Even though the number of instars is also distinctly increased in examined species of Tenebrionidae , six in Tribolium castaneum (e.g. WൺඅඌKං et al. 2016) and eight in Alphitobius diaperinus (Panzer, 1796) (Fඋൺඇർංඌർඈ & Dඈ Pඋൺൽඈ 2001), the case we documented in Autocrates is remarkable. It appears plausible to assume that this is related to a phytophagous diet and very large body size. However, the true mechanism is unknown at present. Gaining more information on the number of larval stages in various groups of Coleoptera and the exploration of the biological, genetic and phylogenetic background would be an intriguing field for future studies.

Phylogenetic position of Trictenotomidae . In contrast to suggested close phylogenetic affinities with Cerambycidae (e.g. Fൾඋඋൾඋ & Dඋඎආඈඇඍ 2003), recent studies based on morphological features (Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005, Hඎ et al. 2020) or molecular data (BൺඍൾඅKൺ et al. 2016; Mർ- Kൾඇඇൺ et al. 2015, 2019; ZHൺඇG et al. 2018) converge upon a robust placement in the “salpingid group” sensu Wൺඍඍ (1987), which now contains the families Boridae , Pyrochroidae , Salpingidae , Pythidae , and Trictenotomidae (e.g. PඈඅඅඈർK & Tൾඅඇඈඏ 2010, Hඎ et al. 2020). Below, we interpret larval features with respect to the systematic placement of Trictenotomidae .

A plesiomorphic feature of larval Trictenotomidae is likely the lyriform shape of the frontal sutures, which occurs in many families of Tenebrionoidea (Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005) and also in some other groups of beetles (e.g. Lൺ- ඐඋൾඇർൾ et al. 2011). That they end distinctly before they reach the antennal foramina is arguably an autapomorphy of the genus Autocrates , but only expressed in early instars. Other plesiomorphic character states within Tenebrionoidea are the absence of a dorsal endocarina, asymmetric triangular mandibles with a mola, well-developed 5-segmented legs, and paired fixed urogomphi.

An entire series of derived larval features of Trictenotomidae is shared with families of the “salpingid group” and some other groups of Tenebrionoidea . This includes a pronouncedly prognathous head and a distinctly flattened body with widely separated relatively stout legs ( Figs 4–7 , YඈඎඇG 1991, Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005, Hඎ et al. 2020). These features are apparently adaptations for life under bark and have certainly evolved several times independently, for instance in Prostomidae (SർHඎඇGൾඋ et al. 2003, Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005). Another presumably derived feature characteristic for tenebrionoid larvae is a pad-like sclerotized maxillary articulation area, present in larvae of Trictenotomidae ( Fig. 9 : ps, Hඎ et al. 2020), Boridae , Pythidae , Salpingidae (YඈඎඇG 1991, Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005), and some other groups, for instance Prostomidae (SർHඎඇGൾඋ et al. 2003). Another derived feature of the maxilla occurring in Tetratomidae ( Fig. 9 ) and other tenebrionoid families, for instance Pythidae and Salpingidae (Othniinae) , is the uncus, a tooth-like projection of the mala. However, this process has likely evolved several times independently, for instance in Protocucujidae (Bൾඎඍൾඅ & ŚඅංඉංŇඌKං 2001) and Oedemeridae (Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005), or even belongs to the groundplan of the superfamily. Other features common in tenebrionoid groups including Trictenotomidae (Lൺඐඋൾඇർൾ 1991, Bൾඎ- ඍൾඅ & FඋංൾൽඋංർH 2005) are the presence of a single molar tooth and of a hypopharyngeal sclerome, which interacts with the mola. As in the case of the previous characters the phylogenetic assessment is difficult at present (Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005).

A derived condition shared by Pythidae , Boridae , Othniinae , Pyrochroidae and last instar larvae of Trictenotoma (Hඎ et al. 2020: fig. 2) is the subdivision of the anterior prosternal plate into several subunits by longitudinal lines. A distinctive feature found in Trictenotomidae (Lൺඐඋൾඇർൾ 1991, Hඎ et al. 2020) and some other families including for instance Pythidae , Boridae and Salpingidae is a plate-like tergum IX extending onto the ventral side of the segment (Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005). A highly unusual, derived condition shared only by Trictenotomidae (Hඎ et al. 2020) and Pythidae (Lൺඐඋൾඇർൾ 1991, YඈඎඇG 1991, Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005) is the subdivision of the ventral part of tergum IX into several plates. Even though this condition is not visible in first instars larvae of Autocrates ( Fig. 12 ), it is recognizable (though quite indistinct) in the last instar and thus appears to be a synapomorphy of the two families. Another feature shared by larvae of the two families is the presence of ventral epicranial ridges ( Fig. 9 ). These structures also occur in Ciidae and some Tenebrionidae (Lൺඐඋൾඇർൾ 1991, Lൺඐඋൾඇർൾ & Sඉංඅආൺඇ 1991, Bൾඎඍൾඅ & FඋංൾൽඋංർH 2005), apparently the result of parallel evolution.

Despite an obviously high degree of homoplasy, larval features clearly confirm the placement of Trictenotomidae in the “salpingid group” of Tenebrionoidea . Especially the unique feature of tergum IX, shared only with Pythidae , is strong evidence for this phylogenetic hypothesis. However, the possible sister group relationship between the two families remains to be tested in future molecular investigations into the phylogeny of Tenebrionoidea .

Intrafamiliar relationships and immature stages. The description of the larva and pupa of the genus Autocrates allows a comparison with the other genus Trictenotoma and a preliminary assessment of the relationships within the family. The first instar larvae of both genera are very similar in their morphology, sharing an entire series of nearly identical features: a largely unpigmented postcephalic body, parallel-sided and flattened, with stout thoracic legs, and very long setae; a head distinctly prognathous, well-sclerotized, very slightly rounded laterally, with lyre-shaped frontal arms obliterating anterolaterally; five pairs of stemmata; mandibles asymmetric with 2 apical teeth, one subapical tooth, and a single small tooth on the left mola; fixed urogomphi of abdominal tergite IX well-developed, apically upturned, with a rough surface; lack of longitudinal ridges on the thoracic and abdominal tergites and sternites. Distinct differences in chaetotaxy are found between the first instar larvae of the two genera: pronotum with 13 pairs of setae of various lengths in Autocrates , in contrast to 7 pairs in Trictenotoma ; each tergite of meso- and metathorax with 10 pairs in Autocrates , versus 6 pairs in Trictenotoma ; each tergite of abdominal segments II–VIII with 7 pairs in Autocrates , but only 5 pairs in Trictenotoma .

The last instar larva of Autocrates is almost identical with Trictenotoma in body shape and coloration. The head is distinctly prognathous, evenly rounded laterally, and strongly narrowing posteriorly. The frontal arms are lyre-shaped, reaching the lateral margin of the antennal articulation area, in contrast to the condition in the 1st instar. Stemmata are absent in larvae of both genera, and the mandibles asymmetric, with 3 large apical teeth and a coarsely ridged mola. The abdominal tergite IX bears a pair of small U-shaped ridges, the urogomphi are short, slender, and distinctly curved upwards apically. The presence of longitudinal ridges on the thoracic and abdominal tergites and sternites is another feature shared by the larvae of both genera. However, the longitudinal tergal ridges of Autocrates are much denser and more widely distributed than those of Trictenotoma . The first instar larvae of both genera are characterized by the presence of stemmata and absence of longitudinal ridges on thoracic and abdominal segments, whereas the last instars display the reversed character states.

The pupae of both genera share many features: a similar general appearance, irregularly carinate lateral pronotal margins, abdominal tergites with lateral and sublateral protrusions, sternite VIII with 2 small apical protrusions, and an extended tergite IX with paired short urogomphi. The key diagnostic character for adults can also be used to identify the pupae: a large postmedian protrusion (spine in adults) is present on the lateral pronotal margins in Autocrates , whereas it is absent in Trictenotoma . Additionally, the lateral and sublateral protrusions on the abdominal tergites are only slightly produced in Autocrates , but conspicuous and spherical in Trictenotoma .

As mentioned above, the larva and pupa of Autocrates and Trictenotoma are very similar and both genera share almost all characteristics except for the mentioned diagnostic features. The pattern of longitudinal ridges of mature larva and protrusions of the pupal pronotum and abdomen are the most important diagnostic characteristic of these two genera. In contrast, the first instar larva of Autocrates is distinguished from that of Trictenotoma only by the chaetotaxy of the thorax and abdomen, without any other detectable morphological differences. Our results are based on the morphology of immature stages available for one species of Autocrates and two species of Trictenotoma , among a total of 18 known species of the family Trictenotomidae . Additionally, we carried out a preliminary phylogenetic analysis of trictenotomid species using two mitochondrial genes (16S and COI) obtained from two species of Autocrates and one species of Trictenotoma ( Fig. 35 ). It is evident that further investigations including morphological and molecular data of more species are required to confirm our results.

Distribution. Autocrates maqueti was described from Guizhou and Guangxi Provinces of China based on several specimens collected in 2001–2004, and it was also found in Qinghai Province (Lංඇ et al. 2007). A male of A. maqueti (misidentified as A. aeneus ) was collected in Yeongyang County, Gyeongbuk Province, South Korea in 2001, and the species has now been found in the eastern areas of Gyeongbuk and Gangwon Provinces (M.C. Kwon, unpubl. data). It is noteworthy that the Korean population of A. maqueti is very distant from the previously known distributional range of the family Trictenotomidae in the Oriental Region and the southern border of the Palaearctic Region in China. The cause of this disjunct distribution remains unsolved yet.

Biology. Preliminary observations on feeding and oviposition behaviors of Autocrates maqueti suggest a great similarity with Trictenotoma formosana , which is the only species of Trictenotoma with well-known biology and immature stages. The hatched larvae of A. maqueti stayed together for 3–4 days devouring their own eggshells, then were all scattered in the breeding box. They actively moved on the surface, grooves and crevices of the bark. Their elongate and flat body, and well-developed legs and pygopod are well suited for bark-related microhabitats. The number of larval instars of Trictenotoma is unknown because of the habit of devouring the exuviae after molting and the cryptic lifestyle in soil (Lංඇ & Hඎ 2019). Alternatively, we measured the head width from digital images and counted the hard parts of exuviae like the head capsule that were not eaten by the larvae. The last larval stage of A. maqueti are determined as approximately 25th instar. Such large numbers of larval instars are unusual in the superfamily Tenebrionoidea . The first adult eclosion occurred 405 days after oviposition, whereas most individuals are still in late larval instars. Although the growth rate varies greatly between individuals, it is predicted that the duration of the life cycle of A. maqueti from eggs to adults in our breeding facilities is 405–520 days. The detailed life history, behavior and morphology of all larval instars need to be presented separately.

Figures

Figs 1–3. Adults and eggs of Autocrates maqueti Drumont, 2006. 1 – male (right) and female (left); 2 – egg cluster under the bark; 3 – eggs at high magnification.

Figs 4–7. First instar larva of Autocrates maqueti Drumont, 2006. 4 – dorsal habitus; 5 – ventral habitus; 6–7 – scanning electron micrographs of head, thorax and abdominal segment I (6) and abdominal segments II–IX (7).

Figs 8–9. First instar larva of Autocrates maqueti Drumont, 2006. 8 – head in dorsal view; 9 – head in ventral view.Abbreviations: C – cardo; De – dorsoepicranial seta; Df – dorsofrontal seta; Dp – dorsoposterior seta; Es – epicranial stem; Fa – frontal arms; Gu – gula; Hyr – hypostomal ridge; L – lateral seta; Lb – labrum; Ma – mala; Md – mandible; Pmt – prementum; Ps – pad-like structure; Smt – submentum; V – ventral seta.

Figs 10–13. First instar larva of Autocrates maqueti Drumont, 2006. 10 – right mandible in ventral view; 11 – left mandible in ventral view; 12 – foreleg in lateral view; 13 – abdominal segments VIII–X in lateral view.Abbreviations: Mo – mola; Mot – molar tooth; s VIII/IX/X – sternum VIII/IX/X; t VIII/ IX/X – tergum VIII/IX/X; Ug – urogomphi.

Figs 14–16. Last instar larva of Autocrates maqueti Drumont, 2006. 14 – dorsal habitus; 15 – ventral habitus; 16 – lateral habitus.

Figs 17–22. Last instar larva of Autocrates maqueti Drumont, 2006. 17–18 – head in dorsal (17) and ventral views (18); 19–20 – thorax & abdominal segments I–II in dorsal (19) and ventral views (20); 21–22 – abdominal segments VIII–IX in dorsal (21) and ventral views (22).

Figs 23–31. Last instar larva of Autocrates maqueti Drumont, 2006.23 – maxillae and labium in dorsal view; 24 – antennomeres II–III; 25 – foreleg in lateral view; 26–28 – right mandible in ventral (26), dorsal (27), and mesal views (28); 29–31 – left mandible in dorsal (29), ventral (30), and mesal views (31).

Figs 32–34. Pupa of Autocrates maqueti Drumont, 2006. 32 – dorsal habitus; 33 – ventral habitus; 34 – lateral habitus.

Fig. 35. Bayesian inference tree of trictenotomid species based on combined COI and 16S sequences.