Pyrochroa serraticornis (Scopoli)

Molfini, Marco, Giulio, Andrea Di, Mancini, Emiliano & Bologna, Marco A., 2021, Larval features illuminating adult taxonomy? Case study in the European cardinal beetle species of the genus Pyrochroa (Coleoptera: Pyrochroidae: Pyrochroinae), Zootaxa 4966 (3), pp. 337-348 : 341-345

Pyrochroa serraticornis (Scopoli) ( Figs 1B , 2B, D, F , 3E–H , 4B, D , 5B )

Diagnosis. The most diagnostic characters are structures associated with the highly sclerotized urogomphal plate: lateral lobes acute rounded; sclerotized conical teeth between lateral lobes and the straight parallel urogomphi; urogomphal lip flat, ventrally to the single urogomphal pit with parallel rugulae. Other diagnostic characters vs. P. coccinea are shown in Table 1 .

Description of mature larva. Body length about 2.4 cm (from mesal labral apex to apices of urogomphi) and maximum width about 3.8 mm (across widest portion of urite VIII) ( Fig. 1B ). Body orthosomatic with sides subparallel, moderately sclerotized except much of cephalic capsule, mandibles, and urogomphal plate more heavily sclerotized; body vestiture consisting of short to moderately elongate, scattered setae. Thoracic and abdominal tergites II–VII and IX lacking parabasal ridges; abdominal tergites I and VIII with weakly formed parabasal ridge ( Figs 1B , 4B ). Head and body from light yellowish to darker, melanisation much darker in areas of heavy sclerotization such as mandibles, urogomphi, urogomphal lip and urogomphal pit.

Head. Prognathous, flattened, exserted from prothorax, about 3.3 mm width ( Figs 2B, D ). Epicranial suture lyriform with stem short, frontal arms complete nearly to antennal insertions, endocarinae absent ( Fig. 2B ). Free, symmetrical trilobate labrum with scattered slender setae ( Fig. 2B ). Two pair of stemmata on each lateral side, parallel with antennal insertions. Antennal insertions fully exposed; antennae moderately long, stout, 3-segmented; antennomere I quite straight, narrower in the middle area, wider apically; sensorium of II small, drop-shaped; antennomere III narrower than I–II, about 2/3 the length of II, acutely rounded apically; setae well distributed on all the surface of antennomers. Mouthparts retracted ( Figs 2B, D ). Mandibles heavily sclerotized, movable, asymmetrical, molar area of mandibles well developed; left mandible bigger, bearing a prominent, hooked inwards, molar tooth, apex sub-securiforme with one small subapical expansion; inner surface bearing two longitudinal depressions so as to make it appear tridentate from a ventral view ( Fig. 3F, G ); apex of right mandible securiforme, inner surface concave so as to make it appear bidentate from a ventral view ( Figs 3E, H ). Maxillae ( Fig. 2F ) each with 1-segmented cardo which is diagonally folded upward upon itself toward the stipes and thus appearing 2- segmented; a well-developed, undivided, pad-like maxillary articulating area; ventral surface of stipes bearing few scattered spiniform setae; galea and lacinia fused to form maxillary mala; mala bearing stout apical and adoral spiniform setae and a well-developed pointed uncus at apico-adoral margin; 3-segmented, filiform maxillary palpus, palpomere II about 1.2 times as long as I, palpomere III subequal in length to II, tapering distally, acutely rounded apically. Labium with mentum trapezoidal ( Fig. 2D ); submentum glabrous, shape elongate with sides shallowing sinuate basally, apical margin slightly more heavily sclerotized ( Fig. 2D ); ligula well developed, elongate, almost glabrous, bearing few setae hardly characterized from our samples; each labial palpus short, 2-segmented, palpomere I twice as long as II. Hypostomal rods ( Fig. 2D ) well developed, divergent; gular sutures separate ( Fig. 2D ).

Thorax and Abdomen. Thorax flattened, segmentation well developed, sides of prothorax subparallel, meso- and metathorax rounded ( Fig. 1B ); cervicosternum divided into three plates ( Fig. 2D ). Legs well developed, moderately short, 5-segmented including tarsungulus, vestiture consisting of sparse, short setae.Abdomen flattened, sides slightly converging forward, moderately sclerotized, tergites I–VII subequal in length and width; tergite VIII approximately 2.8 as long as each other ( Fig. 1B ). Sternite VIII emarginate apically ( Fig. 4D ). Ventrolateral margins of abdominal laterotergite VIII emarginate, with lanceolate shape, ending with more sclerotized acute apex forming a lateral tooth visible even from dorsal view ( Figs 1B , 4D ). Tergite IX divided into four plates ( Fig. 4B ), hinged, capable of considerable dorso-longitudinal movement, extending ventrally, thus forming the urogomphal plate, widest basally where it forms well developed acute rounded lateral lobes ( Figs 4B, D ); surface of urogomphal plate bearing numerous, well-developed, callosities and several setigerous calli, in particular, long setae are associated with three pair of calli on the dorsolateral surfaces and one pair of calli at the base of urogomphi ( Fig. 4B ); a pair of well developed, highly sclerotized conical teeth between urogomphi and lateral lobes ( Figs 4B, D ); urogomphi heavily sclerotized, long, slender, straight, parallel, tapering and acuminate apically; ventral surface of urogomphal plate sharply excavate basally at articulation with sternites IX–X, excavation narrowing distally to bases of urogomphi and urogomphal lip forming a thin slot ( Fig. 4D ). Urogomphal plate possessing a heavily sclerotized urogomphal lip ventrally ( Figs 4B, D , 5B ), forming the ventral surface of the wide heavily sclerotized single urogomphal pit ( Fig. 5B ), which fills the space between the heavily sclerotized fixed urogomphi, and bear characteristic parallel rugulae. Sternite IX broadly transversely U-shaped ( Fig. 4D ), partially recessed into shallow emargination of sternite VIII, possessing continuous semicircular arch of approximately 32 well-developed asperities along anterior margin; ventrolateral margin heavily sclerotized forming an acute tooth slightly visible even in dorsal view ( Figs 1B , 4D ). Segment X reduced, transversely ovate, basal margin rounded, recessed into emarginations of sternite IX, visible ventrally ( Fig. 4D ).

Spiracles. One pair of well-developed, ovate, thoracic spiracles situated ventrolaterally on laterotergite along anterior end of mesothorax. Paired, sub-ovate abdominal spiracles, subequal in size, located on dorsolateral margin of abdominal tergite I ( Fig. 1B ) and ventrolateral margins of abdominal laterotergites II–VII; paired spiracles of abdominal laterotergite VIII annular-ovate, located ventrolaterally at distal 1/3 of its length ( Fig. 4D ).

Figures

FIGURE 1. Larval habitus: A—habitus of mature larva of Pyrochroa coccinea, dorsal view; B—habitus of pre-mature instar larva of P. serraticornis, dorsal view. Scale bars: A = 5 mm; B = 2.5 mm.

FIGURE 2. Details of cranium: A—cranium of Pyrochroa coccinea, dorsal view; B—cranium of P. serraticornis, dorsal view; C—cranium of P. coccinea, ventral view; D—cranium of P. serraticornis, ventral view; E—right maxilla of P. coccinea, ventral view; F—right maxilla of P. serraticornis, ventral view. Scale bars: A–D = 1.5 mm; E–F = 0.5 mm.

FIGURE 3. Mandibles of Pyrochroa coccinea (A–D) and Pyrochroa serraticornis (E–H): A, E—right mandible, ventral view; B, F—left mandible, ventral view; C, G—left mandible, inner view; D, H—right mandible, inner view. Scale bars: A–H: 0.5 mm.

FIGURE 4. Details of abdomen: A—abdominal urites XIII–IX of Pyrochroa coccinea, dorsal view; B—abdominal urites XIII–IX of P. serraticornis, dorsal view; C—abdominal urites XIII–X of P. coccinea, ventral view; D—abdominal urites XIII–X of P. serraticornis, ventral view. Scale bars: A–D = 1 mm.

FIGURE 5. Details of urogomphal plate: A—urogomphal plate of Pyrochroa coccinea, posterior view; B—urogomphal plate of P. serraticornis, posterior view. Scale bars: A–B = 1 mm.