Pyractonema nigripennis Solier

Archangelsky, Miguel, 2010, Larval and pupal morphology of Pyractonema nigripennis Solier (Coleoptera: Lampyridae: Photinini) and comparative notes with other Photinini larvae, Zootaxa 2601, pp. 37-44 : 38-41

Pyractonema nigripennis Solier

Description of last larval instar. Length: 15 to 17 mm, width 2.6 to 2.8 mm. Body elongate, almost parallelsided, slightly flattened dorsoventrally ( Fig. 1 ). Color dark brown dorsally, with light brown margins, ventrally light brown except for dark brown sternal plates and dark brown laterotergites.

Head capsule: Length: 1.60 mm; width: 1.35 mm. Prognathous, subquadrate, dorsoventrally flattened, robust ( Fig. 4 ); partially retractable within the prothorax ( Fig. 1 ), leaving only antennae and mouthparts exposed. Head capsule not fused ventrally ( Fig. 5 ), basal part of head softer (white areas on Figs. 4–5 ). Labrum and clypeus fused. Ecdysial line not developed in last instar larva. Head with three internal ridges, one transverse at midlength, the other forming a Y-shaped structure extending from the base of antennae and coming together at middle of transverse ridge. One pair of small lateral stemmata posterior to base of antennae. Epipharynx formed by two oval plates covered with several transverse rows of microtrichiae; hypopharynx as a small triangular sclerite covered by a dense pubescence.

Antennae: Large, three-segmented, partially retractable within membranous base ( Fig. 8 ); originating on lateroapical edges of head capsule ( Fig. 4 ); membranous base with sclerotized area on outer margin, covered by medium length setae. Basal antennomere widest, partially sclerotized, with basal dorsal sclerite separated from rest of antennomere by membranous area, all segments covered by setae, those in the middle larger and stouter than basal and apical ones. Second antennomere narrower, as long as basal one, also covered by setae, carrying across its apex both a large globular sensorium as long as third antennomere and the third antennomere, which is the shortest, with several short setae and three narrow sensoria.

Mandible: Symmetrical, strongly falcate, with an inner channel opening subapically on outer edge ( Figs. 6–7 ). Retinaculum present, forming one sharp inner tooth on apical third of mandible. Inner margin of mandible and base of retinaculum with blunt cuticular projections which become setiform towards base of mandible in dorsal view. Basal half of mandible, in ventral view, with patches of dense pubescence ( Fig. 7 ). One strong dorsal seta close to base of retinaculum. Sensory (hyaline) appendage on outer margin of mandible before channel opening, present in other larval Lampyridae , missing ( Archangelsky & Branham 1998, 2001; Branham & Archangelsky, 2000). Base of mandible with an inner membranous lobe covered by a dense pubescence ( Fig. 6 ).

Maxilla: Long and robust, closely attached along the sides of the stipes to the labium ( Figs. 5 , 9 ). Cardo elongate, irregularly shaped, bearing 13–15 setae on ventral surface; contacting a transverse basal plate. Stipes very broad, surface covered with small setae and bearing 14–15 strong and long setae on ventral and outer surfaces; dorsally with numerous setae and a longitudinal strip of pubescence on disk. Galea large ( Figs. 9– 10 ), two-segmented, basal segment about two times as long as second segment and bearing two setae on outer margin; distal segment short, subconical, bearing five stout setae and two slender apical sensoria. Lacinia large, membranous, twice as long as galea, covered by a dense pubescence. Palpus apparently threesegmented ( Fig. 10 ), basal palpomere largest, subquadrate, longer than other two segments combined, covered with numerous setae; second palpomere ring-shaped bearing several setae; distal palpomere subconical, bearing a globular sensorium-like structure at base on outer margin and four short, slender sensoria on dorsal side. Between second and third palpomeres there is a very small narrow plate dorsally ( Fig. 11 ), bearing 3–4 setae, which could be interpreted either as a subdivision of the second or third segment, or as a vestigial palpomere (in which case the palpus should be considered as four-segmented).

Labium: Closely attached to maxilla, formed by a short and strongly sclerotized prementum, mentum (mostly membranous) and submentum. Prementum heart-shaped, in both dorsal and ventral views with a distal apical cleft ( Figs. 5 , 9 ); bearing numerous setae both dorsally and ventrally, lacking brushes of cuticular spines dorsally. Palpus two-segmented; basal segment short, wider than long, bearing several setae; distal segment longer and narrower, pointed and bearing a large, globose sensorium at base on outer margin ( Fig. 12 ), lacking setae. Submentum longer than wide, strongly sclerotized, with a pair of very large setae on basal half.

Thorax: Three-segmented. Pronotum subcircular, wider at base, containing retracted head in repose ( Fig. 1 ). Meso- and metanotum suboval, wider than long, with rounded margins. Thoracic tergites subdivided by sagittal line (that of pronotum incomplete), with one clear line on each side, subparallel to sagittal line ( Fig. 2 ). Lateral areas of meso- and metathorax formed by two laterotergites, anterior one of mesothorax bearing a biforous spiracle ( Fig. 1 ). Prosternum subtrapezoidal, poorly sclerotized, extending above and to the sides of coxae, carrying a large episternum and a narrow epimeron. Meso- and metasternum subdivided by a transverse fold into an unsclerotized anterior basisternum, and a poorly sclerotized sternellum, subdivided into three plates, lateral ones carrying the episterna and epimera, medial one elongate, as an inverse Y.

Legs: Five-segmented, coxae long and robust, subtriangular; trochanters smaller, subtriangular in lateral view; femora larger than trochanters, subtrapezoidal, with a long seta in medial inner portion; tibiotarsi as long as femora, tapering towards distal end, with a double row of strong setae on inner margin; pretarsi strong, simple, with a pair of stout basal setae.

Abdomen: Ten-segmented, tapering towards posterior end ( Fig. 1 ). Segments one to seven similar in shape, subrectangular, wider at posterior end; segment eight subquadrate, narrower than preceding segments; segment nine subquadrate, smaller than preceding segment; segment ten interpreted as the narrow ring surrounding anal region and carrying holdfast organ. Tergites one to eight with sagittal line, tergites one to seven with one clear line on each side, subparallel to sagittal line, segments eight and nine evenly dark.

Sternites one to nine small, subquadrate, dark colored except for lightly colored sternite eight. Pleural areas well developed, segments one to seven subdivided, upper plate (laterotergite) large, suboval, carrying spiracles, lower plate (laterosternite) small, narrowly subtriangular, that of segment seven very narrow; pleura eight membranous, bearing a round photic organ ( Fig. 1 ); pleural areas of segments nine and ten reduced. Biforous spiracles present on pleurites one to eight.

Description of pupa. Length: 13.5 mm, maximum width: 3.9 mm at base of pronotum. White in color, strongly curved, ventrally concave ( Fig. 3 ).

Head: Completely covered by pronotum in dorsal view ( Fig. 3 ). Eyes small, on sides of head; antennae inserted in front of eyes, extending to distal end of mesotibiae.

Thorax: Pronotum large, subcircular, covering head. Meso- and metanotum shorter, subrectangular, carrying wing pads on sides; wingpads reaching distal end of second abdominal segment. First and second pair of legs fully visible in ventral view; third pair of legs partially covered by wingpads. One pair of spiracles present on pleura of mesothorax.

Abdomen: Tergites one to seven subtrapezoidal, wider than long; segment eight subquadrangular; segments one to eight with posterolateral projections directed posteriorly. Sternite one reduced, sternites two to eight subrectangular, becoming narrower towards end, with posterolateral corners projected posteriorly. Spiracles present on abdominal pleural areas of segments one to eight. Photic organs present on margins of segment eight, functional.

Figures

FIGURES 1 – 3. Pyractonema nigripennis. 1 — Last larval instar, lateral view; 2 — Last larval instar, detail of thoracic dorsal coloration; 3 — pupa, lateral view. Scale bars: 1 mm.

FIGURES 4 – 7. Pyractonema nigripennis, last larval instar. 4 — Head capsule, dorsal view; 5 — Head capsule, ventral view; 6 — Mandible, dorsal view; 7 — Mandible, ventral view. Scale bars, Figs. 4 - 5: 1 mm; Figs. 6 - 7: 0.2 mm.

FIGURES 8 – 12. Pyractonema nigripennis, last larval instar. 8 — Antenna, dorsal view; 9 — Maxillolabial complex, ventral view; 10 — Maxillary palpus and galea, ventral view; 11 — Maxillary palpus, dorsal view; 12 — Apical sensorium of labial palpus, ventral view. Scale bars: Figs. 8 – 9: 0.2 mm; Figs. 10 – 11: 0.1 mm.