Retrachydes thoracicus (Olivier, 1790)

Casari, Sônia A. & Albertoni, Fabiano F., 2017, Immatures of Cerambycinae (Coleoptera, Cerambycidae) collected in Litchi chinensis Sonn. (Sapindaceae) in Brazil, Zootaxa 4254 (2), pp. 240-254: 247-252

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Retrachydes thoracicus (Olivier, 1790)


Retrachydes thoracicus (Olivier, 1790) 

( Figs 29View FIGURES 29 ‒ 39 ‒59)

Description of larva. Length: 10‒50 mm.

Coloration yellowish cream ( Figs 40‒42View FIGURES 40 ‒ 42). Head yellowish and brown at exposed area, cream at remainder areas; mouth frame from dark reddish-brown to black; mandibles black; maxillae, labium and antennae partially brown. Prothorax yellow in two transverse dorsal bands near anterior margin, one patch on each alar lobe and two clearer ventral patches. Pubescence long, dense and brown; pubescence longer and denser on anterior half of pronotum, alar lobes and anterior 2/3 of mediopresternum. Meso-, metathorax and abdomen densely setose on laterodorsal and lateroventral lobes.

Head ( Figs. 29, 30View FIGURES 29 ‒ 39, 40‒43View FIGURES 40 ‒ 42View FIGURES 43 ‒ 50) extensible, deeply retracted into prothorax; glabrous except for lateral and anterior regions; prognathous, moderately convex dorsally and flattened ventrally. Head capsule wider than long, narrowed anteriad; hind angles widely rounded; posterior margin slightly emarginate in middle. Median frontal line and endocarina moderately short, 1/3 of capsule cephalic length, not reaching anterior margin; dorsomedian cranial duplicature weakly marked. Epistomal margin ( Figs 29, 33View FIGURES 29 ‒ 39, 43View FIGURES 43 ‒ 50) emarginated in middle, strongly sclerotized, with one pair of setae on each side. Each epicranial half, with three dorsal pairs of setae (except two epistomal): one near median frontal line, one at same level, but more laterally and one below and between previous; many setae near lateral margins, below antennae. Stemmata absent. Occipital foramen very large, divided into two portions: pars minor rounded, and pars major wider than long, with lateral margins rounded. Ventrally, each side of head capsule with several short setae below antennae, one pair near anterior margin and three short setae on each side of gular area (one pair below mouth frame). Gular line absent. Antennae ( Figs 31, 32View FIGURES 29 ‒ 39, 43View FIGURES 43 ‒ 50) moderately short, extensible, with antennifer long and membranous; with three elongate antennomeres: basal with five dorsal and two ventral campaniform sensilla on anterior fourth; median, with two campaniform sensilla and six long dorsal setae on distal third, and three campaniform sensilla, two setae and two tiny and stout ventral setae near apex; apex of median antennomere with one short membranous conical sensorium and distal antennomere; distal antennomere narrower and shorter than previous, with three long and two short and stout setae at apex. Clypeus ( Fig. 33View FIGURES 29 ‒ 39) membranous, band-shaped and extremely narrow and short, one fourth of epistomal margin length, located at emargination of epistomal margin. Labrum ( Fig. 33View FIGURES 29 ‒ 39) circular with diameter wider than clypeus width, with numerous setae distributed by whole surface except on basal region. Epipharynx ( Fig. 36View FIGURES 29 ‒ 39) rounded on anterior 1/4; bulging on posterior 3/4; with stout and moderately short setae near anterior margin, towards middle; below anterior setae, near middle of bulging area, numerous long and fine setae, backwardly directed, and lateral microspines; each side with one triangular elongate sclerite near middle; numerous campaniform sensilla on posterior half. Mandibles ( Figs 44‒50View FIGURES 43 ‒ 50) slightly asymmetrical, varying slightly in size and shape; wide, concave at mesal area with cutting edge widely rounded; one semicircular transverse groove dorsal and one ventral on distal third, longer on right ventral mandible; basal margin of groove more prominent forming a tooth-shaped; external face with 4-6 setae near base. Maxilla ( Figs 34, 37View FIGURES 29 ‒ 39) partially membranous; stipes with wide brown, inclined transversal band near middle and numerous long setae, more concentrate near lateroexternal margin; cardines and maxillary articulating areas fused to postmentum; mala wide and rounded with numerous long and stout ventral setae, forming a band near distal margin; dorsally mala with setae inwardly directed near distal margin, and microspined laterointernally; mala covering laterodorsal area of labium (like Fig. 37View FIGURES 29 ‒ 39); palpifer partially membranous, ventrally with long setae near lateral and internal margins and dorsally, with microspined transversal area near middle; long setae laterally and on microspined area. Maxillary palpi with three palpomeres: basal wider than long, ventrally with numerous long setae near anterior margin and one campaniform sensillum near middle, and dorsally, with long lateroexternal setae and one transverse microspined band near anterior margin; median palpomere longer than wide, ventrally with some long setae and one campaniform sensillum near anterior margin, and dorsally, three lateral long setae and a narrow microspined basal band; palpomere distal elongate, narrower than previous, with one lateroexternal campaniform sensillum, one subapical seta and several peg-shaped sensilla at apex. Labium ( Figs 34, 37, 38View FIGURES 29 ‒ 39): dorsally partially covered by mala (separated on Fig. 34View FIGURES 29 ‒ 39); submentum membranous, with numerous moderately long setae; mentum wider than long, trapezoidal, with a transverse narrow sclerite near middle, and numerous long setae on almost whole surface; prementum wider than long, with numerous long setae, more concentrate near anterior margin; ligula narrow, shorter than basal palpomere, with apex rounded bearing two setae. Labial palpi with two elongate palpomeres: basal palpomere, with numerous long setae near anterior margin; distal palpomere with one campaniform sensillum dorsal and several peg-shape sensilla at apex. Hypopharynx ( Figs 37, 38View FIGURES 29 ‒ 39) membranous, narrowed apicad with rounded apex; bulging and microspined with numerous short and stout setae on anterior third of microspined area; stout long setae near apex; long and fine setae from middle to basal fourth and campaniform sensilla near basal fourth.

Pronotum wider than long, strongly convex and declivous anteriad; median line, lateral furrow and postnotal fold distinct; with two large shiny lobes near base; eusternum forming two small lobes; sternellum distinct and with one pair of legs. Leg ( Figs 39View FIGURES 29 ‒ 39, 41, 42View FIGURES 40 ‒ 42) short and 4-segmented: coxa wider than long, with numerous long setae forming irregular transverse row; femur wider than long, with long setae near anterior margin; tibiotarsus elongate with a row of long setae near anterior margin; pretarsus elongate and narrowed apicad, imbricately spinose. Meso- and metathorax band-shaped, together as long as pronotum; weakly furrowed longitudinal medially with one transverse elliptical ampulla dorsal and one ventral; ampullae with transverse furrow medially. Mesothorax with a large transverse elliptical lateroventral spiracle ( Figs 35View FIGURES 29 ‒ 39, 42View FIGURES 40 ‒ 42).

Abdomen: segments I ‒VI increasing in length and decreasing in width to apex direction; segments VII ‒VIII widest; segment VIII slightly narrowed at apex; segment IX narrow, band-shaped; segment X rounded and apical, with trilobed apex; segments I ‒VII furrowed longitudinal medially and with one elliptical ampulla dorsal and one ventral; each ampulla furrowed transversally near middle; ampullae furrowed longitudinal-medially and near lateral margins, forming large tubercles; segments I ‒VIII with one elliptical transversal spiracle each side, decreasing in size to apex direction.

Description of pupa ( Figs 51‒53View FIGURES 51 ‒ 53, 59). Length: 30‒35 mm.

Coloration yellowish. Head partially visible dorsally, concave between antennae.

Pronotum wider than long, with anterior margin prominent; fore and hind angles prominent and rounded; lateral margins with one rounded lobe near middle; discal area with two weak rounded tubercles on basal third; tiny sparse microspines scattered by whole surface. Mesonotum: scutellar area triangular and very prominent in middle, almost reaching apex of metanotum.

Abdomen: segments I ‒VI band-shaped, furrowed longitudinal medially and microspined dorsally: segment I with two transverse rows of microspines, one on each side of longitudinal furrow; segments II ‒VI each with two circular microspined areas; basal rows of spines larger; segment VII longer than previous, slightly narrowed at apex, with apical margin rounded and margined by large, black spines; numerous spines of varied sizes distributed on whole surface, being a median circle with larger spines; segment VIII narrow, short and partially visible dorsally with spines near middle; segment IX band-shaped with a pair of spines in middle of distal margin and one spine on each side, near base; segment X reduced, rounded and ventral, surrounded by segment IX, with bilobed apex and two apical spines and one spine on each side; segments I ‒V with dorsolateral spiracles; spiracles of segments VI ‒VII apparently non-functional.

Material examined. BRAZIL. São Paulo: Biritiba-Mirim , in Litchi chinensis  , 07.VII.2008, P.K. Wanishi col., 2 pupae, 3 larvae fixed; idem  , 11.II.2009, F.F.Albertoni & D. Catosso, 5 larvae, 4 adults fixed; idem, 12.II.2009, 5 eggs fixed (from breeding in lab); idem, 12.III.2009, D.O. Catosso col., 3 larvae fixed (1 large; 2 small); idem, 24.IV.2009, D.O. Catosso col., 1 larva fixed (MZSP-10343).

Remarks. Comparing the larva of Retrachydes thoracicus  with the descriptions of other species of Trachyderina  , we verified that they are different especially in relation to stemmata number and abdominal tubercles.

The larva of Metopocoilus quadrispinosus  is distinctly different from the others, and presents three pairs of stemmata, segment IX transverse with a row of about six sclerotized moniliform tubercles and segment X bearing two large unciform tubercles; Trachyderes succinctus  presents one pair of stemmata and abdomen with nontuberculate and micro-granulate ampullae; Trachyderes mandibularis  and Retrachydes thoracicus  have epistoma emarginated behind clypeus, anterior margin of hypostoma bearing four tubercles and ampullae tuberculate and non-granulate. The labrum presents varied shapes among species: cordate, broadly oval to sub-orbicular or rounded.

The pupae of only two species are described in this tribe. Comparing the descriptions with R. thoracicus  , it was observed that they present glabrous heads. The pronotum is variable: presents a few scattered microspines and sides with antero-basal blunt tooth in Metopocoilus quadrispinosus  ; is glabrous with sides tuberculate and disc with three pairs of rounded tubercles sublaterally in Trachyderes succinctus  ; presents tiny microspines scattered on entire surface, fore and hind angles prominent and rounded, sides with a median rounded lobe and discal area with two weak rounded tubercles in Retrachydes thoracicus  . The meso- and metanotum are glabrous in all species, except for a few inconspicuous spinules; the scutellar area is extremely elongate in Trachyderes succinctus  and Retrachydes thoracicus  . In all species, the abdomen presents transverse groups of ferrugineus spines, each with one basal seta, and functional spiracles on segments I ‒V.