Deretus spinicollis Schawaller, 2004

Purchart, Luboš, Nabozhenko, Maxim V. & Ras, Kola Scientific Centre, 2012, Figures 1 – 7. Habitus, Dorsal View. 1 In Revision Of The Genus Adelostoma (Coleoptera: Tenebrionidae). Part 1: Subgenus Zarudnionymus Semenov & amp; Bogatchev, 1947, Acta Entomologica Musei Nationalis Pragae 52, pp. 295-302 : 296-300

Deretus spinicollis Schawaller, 2004

( Figs. 1–16 )

Larva. The description is based on a later instar larva 26 mm long, 2.8 mm wide, head capsule 2.3 mm broad.

Body ( Fig. 1 ). Brownish-yellow with blackish mandibles; cuticle sclerotized, with shiny and weakly rugose surface of tergites and sternites.

Head ( Figs. 2–6 ). Prognathous, oval, slightly tilted downward; seams very weakly visible; vertex with two and forehead with four long erect setae. Clypeus convex in lateral view, transverse, trapezoidal and with two long setae on each side, anterior margin somewhat hollowed. Labrum transverse, its dorsal surface slightly convex in lateral view, with eight marginal and two discal setae; marginal setae form three groups (3+2+3); discal setae slightly longer than marginal. Epipharynx with ten long marginal and two short discal setae; marginal setae form three groups (4+2+4); basal part with two longitudinal rows of brush-like setae. Antennae trimerous; antennomere I wider than long; antennomere II two to three times longer than the first one, slightly narrowed in middle; antennomere III slender, with four setae apically. Mandibles asymmetrical, strongly sclerotized apically and at molar part; both mandibles in dorsal view with long seta at their base and two setae laterally; mandible apices distinctly bifid (bidentate); left mandible with triangular tooth between apical tooth and molar part dorsally. Maxilla consisting of primary cardo, stipes, maxillary palpus and lacinia; the latter with two rows of short and thick setae on its inner margin; maxillary palpus three-segmented, bearing several long setae, all segments longer than wide, with last segment sub-conical. Labium with distinct prementum, mentum and submentum; prementum centrally with pair of long setae; ligula with two short thick setae; mentum subcylindrical, slightly widened in middle, with three pairs of long setae situated latero-medially and close to anterior and posterior margin respectively; submentum centrally with a pair of setae.

Thorax. Prothorax slightly longer than wide; mesothorax approx. twice as broad as long; metathorax approximately 1.5 times broader than long; prothorax with two pairs of setae situated close to anterior margin; meso- and metathorax with a pair of setae situated centrolaterally; all thoracic segments with four to seven setae laterally.

Legs ( Figs. 7–8 ). Forelegs somewhat longer and stouter than mid- and hindlegs; trochanter elongated, covered with differing number of strong setae; femur and tibiotarsus covered sparsely with varying number of spines and setae; claws brown apically, their length about half length of tibiotarsus.

Abdomen ( Figs. 9–10 ). Abdominal tergites 1–7 with several setae dorso-laterally; cuticle very slightly wrinkled transversally; spiracles small, more or less circular, slightly longer than wide; abdominal tergite 8 with large deep rounded holes, with two small spines situated dorso-laterally, with one small tooth in posterior corners and with relatively large and somewhat bidentate protuberance in the middle of posterior margin, this protuberance is smooth and bears two spines at its base projecting back obliquely upward; abdominal tergite 9 transverse in dorsal view, apically rounded and with 12 setae forming three groups (5+2+5) – two well separated groups of setae situated laterally and one group of setae situated in the middle of apex; abdominal tergite 9 also with prominent, projecting urogomphi apically strongly sclerotized, vertical and slightly bent forward, with three setae situated dorsally, one seta situated dorso-laterally on the outer side of each urogomphus and one seta situated at anterior base of each, lateral parts of abdominal tergite 9 also with one small projecting tooth horizontal and bent forward.

Pupa. Body ( Figs. 11–13 ). Body length 16.5–18.2 (2.5–2.8) mm, body width 5.4–5.6 mm (n=3), white with darker apices of spines on lateral processes and urogomphi, with brown claws and mandible apices and with black eyes; body very sparsely setose, setae whitish-yellow; lateral processes of abdominal tergites well developed, bearing two fine setae; abdominal tergite 9 with pair of reflexed urogomphi.

Head ( Fig. 16 ). Smooth, concealed (not visible in dorsal view), with two setae on forehead, with further two setae between eyes and with two setae behind each eye, the latter with two setae on its anterior margin; clypeus transversely wrinkled with two setae on each side; labrum smooth, sparsely setose.

Thorax. Pronotum transverse, slightly transversely wrinkled and with strongly protruded anterior angles, each with one to two spines, anterior pronotal margin with 4 spines, sides of pronotum slightly convex, with three to five spines in middle, posterior angles of pronotum with one spine, each half of pronotum with one spine situated before posterior pronotal margin, all pronotal spines bearing one seta; hypomeron smooth and glabrous; elytral and metathoracic wing sheaths glabrous, the latter shorter apically; mesonotum slightly longer than metanotum, both shorter than first abdominal tergum, meso- and metanota with two pairs of setae; meso- and metaventrite glabrous, the latter slightly longer than metacoxa.

Abdomen ( Figs. 14–15 ). Abdominal spiracles ovate, present on segments 1–6; tergites 1–8 with 4–5 pairs of setae, tergite 8 also with two tubercles laterally, each bearing one seta; lateral processes of abdominal segments 1–7 with two apically sclerotized spines with one seta before each spine; abdominal ventrite 2 glabrous, ventrite 3 with one pair of setae, ventrites 4–6 with five pairs of setae and ventrites 7–8 with three pairs of setae; tergite 9 with one pair of strongly developed, apically sclerotized urogomphi with several setae at base.

Legs. Same colour as body; procoxae with one to two setae; femora sparsely covered with several setae; tibiae and tarsi glabrous, the latter with brown claws.

Remarks. Spines on lateral processes of the abdomen and urogomphi on abdominal tergite 9 present in pupae of Deretus spinicollis serve as antipredator devices ( STEINER 1995; BOUCHARD & STEINER 2004). Such structures, together with protective setae, spines as well as cryptic, aposematic and mimetic colours and shapes form a group of passive antipredator device and can be found in many insect pupae ( BOUCHARD & STEINER 2004). In some cases also non-passive antipredator devices as stridulatory organs or so called ‘gin traps’ can be observed ( HINTON 1955). In tenebrionid pupae, both these defence mechanisms can be observed frequently. The list of known tenebrionid pupae possessing antipredator devices is presented by BOUCHARD & STEINER (2004). According to this list, pupae of the genus Helops Fabricius, 1775 and Tarpela Bates, 1870 are the only known representatives of the tribe Helopini with antipredator structures. Helops possess the same structures as Deretus , while in Tarpela pupae gin traps and paired urogomphi are present.

Structures present in pupae seem to be very useful for phylogeny of Tenebrionidae . However, as only few representatives have been studied so far, there is no doubt that more taxonomic, ecological and behavioural studies are needed to fully understand their phylogenetic and evolutionary importance ( BOUCHARD & STEINER 2004).

Figures

Figs. 1–8. Deretus spinicollis Schawaller, 2004; larva. 1 – habitus in lateral view; 2 – clypeus, labrum and antennae in dorsal view; 3 – epipharynx in ventral view; 4 – head in ventral view; 5 – left mandible; 6 – right mandible; 7 – front leg; 8 – mid leg.

Figs. 9–16. Deretus spinicollis Schawaller, 2004; 9–10 – larva; 11–16 – pupa. 9 – abdominal segments 7–9 in dorsal view; 10 – same in lateral view. 11 – habitus in dorsal view; 12 – same in ventral view; 13 – same in lateral view; 14 – abdominal segments 7–9 in dorsal view; 15 – same in lateral view; 16 – head.