Phaenonotum exstriatum (Say, 1835)

Archangelsky, Miguel, Rodriguez, Georgina, Torres, Patricia L. M., Liesa, Ciemep-Conicet, Dbbe & FCEyN, 2016, Primary chaetotaxy and larval morphometry of Phaenonotum exstriatum and Dactylosternum cacti (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae 56 (1), pp. 167-193 : 181-190

Phaenonotum exstriatum (Say, 1835)

Examined larvae. Seven L1, four L2 and seven L3 reared from the adults collected in the following locality: USA: OKLAHOMA: Latimer Co., vi.1990, K. Stephan lgt.Adults and larvae were reared in laboratory and the complete life cycle was obtained ( ARCHANGELSKY & DURAND 1992).

First instar larva ( Figs 33–43 ). Diagnosis. Head capsule subquadrate to slightly suboval; frontal lines inversely bell-shaped, merging just before occipital foramen, coronal line present, extremely short ( Fig. 33 ); clypeolabrum symmetrical, bearing three short teeth, middle one projecting farther than lateral ones ( Figs 33 , 35 ); lateral lobes of epistome almost symmetrical, projecting farther than nasale, slightly serrated on inner margin, with a sharp short spine on outer angle pointing mediad ( Figs 33 , 35 ); posterior tentorial grooves close to midline, past midlength, just behind submentum ( Fig. 34 ). Cervical sclerites present, narrow and elongate ( Fig. 33 ). Antenna short ( Fig 36 ), basal antennomere the longest, sensory appendage as long as third antennomere. Mandibles symmetrical ( Fig. 37 ), with two inner teeth and inner border serrated. Maxilla ( Figs 38, 39 ) with large stipes, longer than palpus, with strong cuticular spines on outer face dorsally and an apical stout and sharp projection on inner margin; first and fourth palpomeres subequal in length, longer than second and third. Labium with submentum fused to head capsule, subtriangular; mentum slightly wider than prementum, with strong cuticular spines dorsally ( Fig. 40 ); basal palpomere the shortest, membranous area at base of both palpomeres with sharp cuticular spines; ligula twice as long as first palpomere ( Figs 40, 41 ). Pronotal plate large, covering most of pronotum; those of meso- and metathorax shorter (see Figs 4, 6, third instar larva). First abdominal segment dorsally with a pair of narrow, poorly sclerotized sclerites (Figs 4, 6, third instar larva); dorsal plate on abdominal segment eight subdivided (Fig. 4, third instar larva); abdominal segments two to seven ventrally not strongly lobed (Figs 5, 6, third instar larva), with two rows of short spines but not “prolegs”; legs short, five-segmented ( Figs 42, 43 ).

Chaetotaxy. Setae PA8, PA9, PA14, PA16, PA21, PA28, FR6, FR10, FR8 and AN10 branched (as in Fig 8); setae PA7, PA12, PA13 closely aggregated; seta AN9 absent; inner margin of stipes with row of additional bifid setae (gMX2).

Primary chaetotaxy ( Figs 33–43 ). Head capsule ( Figs 33–35 ). Frontale with 30 sensilla: two short setae on basal third, close to frontal lines (FR1); two pores (FR2) and two minute setae (FR3) closer to midline on distal half; five pairs of setae (FR5 short, FR6 short and branched, FR7 short, FR9 short, FR10 short and branched) and two pairs of pores (FR4, FR14) close to base of each antenna; distal area of frontale with two pairs of setae (FR8 short and branched, FR12 very short) and three pairs of pores (FR11, FR13, FR15); nasale with six short and stout setae (gFR1), each epistomal lobe with two anterior setae pointing mediad (gFR2). Each parietale with 30 sensilla. Dorsal surface: with a basal longitudinal row of four very short setae (PA1, PA2, PA4, PA5) and one pore (PA3); one subbasal pore (PA6) close to frontal line; three closely aggregated long setae at midlength (PA7, PA12, PA13); two pores (PA10, PA15) and two setae at distal third (PA11 short, PA14 rather long and branched) in the area surrounding the stemmata; one short branched seta close to frontal line behind antennal socket (PA8) and one pore (PA19) and three setae on anterolateral corner of head capsule (PA9 rather long and branched, PA20 long, and PA21 rather long and branched). Ventral surface with three pores (PA23, PA24, PA25) and one long seta (PA22) on anterolateral corner, close to mandibular acetabulum; two pores (PA17, PA30) and two setae (PA16 rather long and branched, PA18 long) along outer margin; two pores (PA27, PA29) and two setae (PA26 short, PA 28 rather long and branched) forming a longitudinal row closer to midline, PA26, PA27 and PA28 very close together at about midlength, PA29 at basal fourth.

Antenna ( Fig. 36 ). A1 bare, with five pores, four on dorsal face (AN1 basal on outer margin, AN2 at midlength, AN3 distally on outer margin, AN4 distally on inner margin) and one on ventral face (AN5 on inner distal margin). A2 with one dorsal pore (AN6) on distal half, two subapical setae (AN7 short, AN8 minute) on outer margin close to base of SE1, and two subapical setae on inner margin (AN10 long and branched, AN11 short); AN9 absent. A3 with a group of at least six setae (two long, one short and three very short).

Mandible ( Fig. 37 ) with six sensilla, one short seta on outer face at basal third (MN1), one minute seta on outer margin at distal quarter (MN5), and three dorsal pores at level of distal retinaculum (MN2, MN3, MN4). MN6 minute, difficult to see, located subapically close to inner margin.

Maxilla ( Figs 38–39 ). Cardo with one rather long seta ( MX 1). Stipes with a row of 14 short and stout setae, distal 13 (gMX2) bearing a subapical spine and separated by a longer distance, becoming closer to each other basally, basal seta simple (homologous to MX 7) slightly more distant from others; apical outer face of stipes with two long setae ( MX 6 dorsal, MX 5 ventral) and one pore ( MX 4 ventral); ventral face with two pores ( MX 2 at midlength closer to outer margin, MX 3 more distally and closer to inner margin). MP1 dorsally with one subbasal rather long seta ( MX 16) on inner margin and one pore close to base of appendage ( MX 17); ventrally with two long subapical setae ( MX 13, MX 14) and two pores ( MX 12 on outer margin, MX 15 at base of appendage); inner appendage with at least three sensoria (gAPP, one rather long seta, one short branched seta, one short stout seta). MP2 with two pores, one dorsal and apical on inner margin ( MX 19) and one ventral on outer margin ( MX 18), and one minute seta basally on outer margin ( MX 27). MP3 with two rather long setae and two pores, one seta dorsal, on outer margin ( MX 23), the other ventral on inner margin ( MX 21); both pores on ventral surface, one close to outer margin ( MX 20) the other ( MX 22) close to seta MX 21. MP4 with one rather long basal seta dorsally on inner margin ( MX 24) and two subapical pores on outer margin ( MX 25 digitiform and dorsal, MX 26 ventral); a group of six or seven short setae constitute gMX.

Labium ( Figs 34 , 40–41 ). Submentum with two pairs of setae on anterior margin ( Fig. 34 ), one long (LA1), the other minute (LA2). Mentum with two long setae (LA3) and two pores (LA4) on ventral surface, LA4 close to anterior margin, anterior to LA3. Prementum ventrally with two pairs of setae (LA5 minute and basal, LA6 long at midlength) and one pair of subapical pores (LA7); dorsally with one basal pair of pores (LA8) and one pair of minute seta-like sensilla (LA9) on membrane connecting with labial palpi and ligula. Ligula with one pair of long setae at the base (LA10) and two pairs of sensilla (LA12 cone-like, apical on dorsal face and LA11 pore-like, at midlength on ventral face). LP1 with one minute seta (LA13, ventral) and one distal pore (LA14 dorsal) on membrane connecting with LP2; LP2 with one subapical pore on outer face (LA15) and a group of at least nine setae at the apex constitute gLA, three setae minute, four setae short, one rather long and one long seta.

Legs ( Figs 42–43 ). The number and position of pores are the same in pro-, meso-, and metathoracic legs. Coxa with 2 pores (1 anterodorsal, 1 posterior) and 14 setae (12 anterior, 2 posterior); trochanter with 8 pores (5 anterior, 3 posterior) and 9 setae (5 anterior, 4 posterior); femur with 2 pores (1 anterior, 1 posterior) and 10 setae (5 anterior, 5 posterior); tibiotarsus with 2 pores (1 anterior, 1 posterior) and 17 setae (8 anterior, 9 posterior); pretarsus with two setae (1 anterior, 1 posterior).

Morphometry. See Table 2.

Second instar larva. Chaetotaxy more similar to the third instar than to the first. Head capsule. Frontale lacking secondary setae; parietale bearing four small secondary sensilla in similar positions than those of third instar (except for the one close to the frontal line that is absent). Antenna. Without secondary sensilla. Mandible with five or six short secondary sensilla on outer face. Maxilla. Stipes with 12–13 stout secondary setae on dorsal surface and one branched ventral secondary seta close to MX 4 and MX 6; gMX2 with ca. 13 setae. Labium. Mentum with one pair of long secondary setae dorsally on distal half. Number and distribution of pores and setae in legs similar to first instar larva.

Morphometry. See Table 2.

Third instar larva ( Figs 44–52 ). Lateral lobes of epistome projecting slightly farther than nasale, slightly serrated on inner margin but with spine on outer angle much smaller.

Chaetotaxy. Head capsule ( Figs 44–46 ). Frontale without secondary sensilla. Parietale with five secondary sensilla, one ventral seta close to PA18, one dorsal pore near PA19 and two dorsal setae, one close to PA8, the other close to frontal line, near pore FR2; PA21 apparently simple in examined specimens (branched in first and second instars). Antenna ( Fig. 47 ) without secondary sensilla. Mandible ( Fig. 48 ) with four short basal secondary setae close to outer face, and three or four minute secondary setae close to MN1. Maxilla ( Figs 49–50 ). Stipes with ca. 17 stout secondary setae on dorsal surface and one branched ventral secondary seta between pore MX 4 and seta MX 6; gMX2 with 13–14 setae. Labium ( Figs 51–52 ). Mentum with one pair of long secondary setae dorsally on distal half. Number and distribution of pores and setae in legs similar to first instar larva.

Morphometry. See Table 2.

Figures

Figs 33–34. Phaenonotum exstriatum (Say, 1835), chaetotaxy of the head capsule of the first instar larva. 33 – dorsal view; 34 – ventral view. Scale bar = 0.1 mm.

Figs 35–37. Phaenonotum exstriatum (Say, 1835), chaetotaxy of first instar larva. 35 – detail of clypeolabrum; 36 – left antenna, dorsal view; 37 – right mandible, dorsal view. Scale bars = 0.05 mm.

Figs 38–41. Phaenonotum exstriatum (Say, 1835), chaetotaxy of first instar larva. 38–39 – maxilla (38– dorsal view; 39 – ventral view). 40–41 – labium (40 – dorsal view; 41 – labium, ventral view). Scale bars = 0.05 mm.

Figs 42–43. Phaenonotum exstriatum (Say, 1835), prothoracic leg of first instar larva. 42 – anterior view; 43 – posterior view. Scale bar = 0.05 mm.

Figs 44–45.Phaenonotum exstriatum (Say, 1835), chaetotaxy of the head capsule of the third instar larva. 44 – dorsal view; 45 – ventral view. Scale bar = 0.2 mm.

Figs 46–48. Phaenonotum exstriatum (Say, 1835), chaetotaxy of third instar larva. 46 – detail of clypeolabrum; 47 – left antenna, dorsal view; 48 – right mandible, dorsal view. Scale bars:Figs 46, 48 = 0.1 mm, Fig.47 = 0.05 mm.

Figs 49–52. Phaenonotum exstriatum (Say, 1835), chaetotaxy of third instar larva. 49–50 – maxilla (49 – dorsal view; 50 – ventral view); 51–52 – labium (51 – dorsal view; 52 – ventral view). Scale bars = 0.1 mm.