Peltochares atropiceus (Régimbart, 1903)

Minoshima, Yûsuke N., Fikáček, Martin & Liu, Hsing-Che, 2023, Larval morphology of Crephelochares and Peltochares (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 63 (2), pp. 305-322 : 312-319

Peltochares atropiceus (Régimbart, 1903)

( Figs 5–10 )

First instar larva. General morphology (compared with second instar larva). Similar to second instar larva ( Figs 5A, D ). Antenna ( Fig. 7A ) proportionally stouter than that of second instar larva; subapical projection of antennomere 1 projected more strongly than in second instar larva. Anterior corners of mentum projected more strongly than in second instar larva; projections pointed apically ( Fig. 7F ).

Primary chaetotaxy of head. Frontale ( Figs 6A, C ). Central area with three pairs of sensilla diverging posteriad; FR1 long seta, close to frontal line; FR2 pore-like, between FR1 and FR3; FR3 very short seta, situated anterior to FR2. Setae FR5 and FR6 behind antennal socket; FR5 very short, behind FR6; FR6 short, paddle-shaped. Short seta FR7 on inner margin of antennal socket. FR4, and FR9–10 close and mesal to antennal socket; FR4 pore, behind FR10; FR10 short seta, mesal to FR9; FR9 long, paddle-shaped seta. Pore FR14 anterior to FR7. Very short seta FR12 and pore-like sensilla FR11 and FR13 on inner margin of epistome, forming small triangular group; FR12 lateral to FR11, FR13 behind FR11 and FR12. Long seta FR8 and pore-like sensillum FR15 on mesal part behind nasale; FR15 anterior to FR8. Nasale with group of six short, stout dorsal setae and two very short ventral setae (gFR1); dorsal setae equidistant, lateralmost ones shorter than mesal ones; ventral setae anterior to FR15. Epistome with four setae (gFR2) on anterior margin; two small setae on inner area of epistome; two short scale-like setae on median area of epistome.

Parietale ( Figs 6A–B ). Dorsal surface with basal longitudinal row of five sensilla (from posterior to anterior, PA1–5) at midwidth between coronal line and lateral margin; PA3 pore-like, remaining four very short setae. PA6 pore-like sensillum, close to coronal line. Three setae (PA7, PA12–13) at midlength of head capsule, anterior to PA5; PA7 long, paddle-shaped, mesal to PA12 and PA13; PA13 very long, behind PA12; PA12 short. Very long, paddle-shaped seta PA14 anterolateral to PA12, equidistant between PA12 and PA10. Pore-like sensillum PA10 anterior and slightly mesal to PA14. Long, paddle-shaped seta PA8 behind antennal socket, close to frontal line. Long, paddle-shaped seta PA9 on outer margin of antennal socket. Anterolateral corner of head capsule with one pore-like sensillum (PA19) and three setae (PA20–22) on lateral area and three pore-like sensilla (PA23–25) close to ventral mandibular acetabulum. PA19 dorsal to PA20; rather long seta PA20 and very long, paddle-shaped seta PA21 lateral; PA20 dorsal to PA21; very long seta PA22 on lateroventral face. PA23 lateral to PA24 and PA25, PA24 between PA23 and PA25. Short seta PA11 between PA19 and PA14. Two pore-like sensilla (PA15, PA17) and very long, paddle-shaped seta PA16 on anterior fourth of lateral face; PA15 dorsal, PA17 ventral, PA16 between PA15 and PA17. Very long seta PA18 at midlength of lateroventral face. Pore-like sensillum PA30 lateroventral, on posterior fifth of parietale. Two setae (PA26, PA28) and one pore-like sensillum PA27 ventral, at midlength of parietale; PA26 very long, anterior to PA27 and PA28; PA27 between PA26 and PA28; PA28 very long, paddle-shaped. Pore-like sensillum PA29 posteromesal to PA28.

Antenna ( Fig. 7A ). Antennomere 1 with five pore-like sensilla (AN1–5).AN1 situated dorsolaterally on posterior third; AN2 dorsal, at midlength; AN3–5 apical; AN3 on outer face, AN4 on inner face, AN5 ventral. Antennomere 2: pore-like sensillum AN6 dorsal and subapical. Six sensilla (AN7–11, SE1) on intersegmental membrane between antennomeres 2 and 3. Antennal sensorium SE1 and setae AN7–9 on outer face; SE1 slender, rounded apically, as long as antennomere 3; AN7 short, between SE1 and AN8; AN8 very short, posterior to AN7; AN9 small, dorsal to AN8. Long, paddle-shaped seta AN10 and very short seta AN11 on inner face. Antennomere 3 bearing group of sensilla (gAN) on apical membranous area; gAN with two long setae and four short sensilla.

Mandible ( Figs 7B–C ) with five primary sensilla (MN1–5). MN1 long, on posterior two-fifths of outer face. Pore-like sensilla (MN2–4) dorsal, between midlength and posterior two-fifths. MN2 anteromesal to MN1, between MN1 and MN3; MN3 mesal to MN2; MN4 at midlength, on outer face. Seta MN5 very short, subapical, on outer face. MN6 undetectable.

Maxilla ( Figs 7D–E ). Cardo with one long ventral seta ( MX 1). Stipes with five stout dorsal setae ( MX 7–11) on inner face; MX 7 short, basal; MX 8–10 short, bearing one small subapical tooth; MX 11 much longer and narrower. MX 2 and MX 3 pore-like sensilla, subbasal, on ventral face; MX 2 on outer part, MX 3 on inner part. Ventral face bearing three subapical sensilla ( MX 4–6) laterally; MX 4 pore-like, behind MX 6; MX 5 very long paddle-shaped seta, mesal to MX 4 and MX 6; MX 6 very long seta. Palpomere 1 with three setae ( MX 13, MX 14, MX 16) and three pore-like sensilla ( MX 12, MX 15, MX 17). MX 16 short seta, dorsal on inner area, on membrane. MX 12–14 on apical margin of sclerite; MX 12 and very long seta MX 13 on lateroventral face; very long seta MX 14 on inner face. MX 15 and MX 17 on intersegmental membrane behind inner appendage; MX 17 dorsal, MX 15 ventral.Appendage with one long paddle-shaped seta, one short seta, and few small sensilla (gAPP). Palpomere 2 with two pore-like sensilla ( MX 18–19); MX 27 undetectable. MX 18 on lateroventral face, close to apical borderline of sclerite; MX 19 dorsal, on inner face of intersegmental membrane between palpomeres 2 and 3. Palpomere 3 with two setae ( MX 21, MX 23) and two pore-like sensilla ( MX 20, MX 22); MX 20 apical, on lateroventral face; MX 23 long, dorsolateral, close to apical margin of sclerite; rather long seta MX 21 ventral, on inner face, close to apical margin of sclerite; MX 22 behind MX 21. Palpomere 4 with two pore-like sensilla ( MX 25–26) apically on outer face and long seta ( MX 24) at base of inner face; MX 25 dorsal, digitiform; MX 26 ventral. Apical membranous area of palpomere 4 with several small sensilla (gMX).

Labium ( Figs 6B , 7F–G ). Submentum with very long seta LA1 on lateral corner and very short seta LA2 on anterior corner. Mentum with two pairs of ventral sensilla (LA3–4) on lateral face. Short seta LA3 on posterior third; pore-like sensillum LA4 slightly anterior to midlength. Dorsal face of prementum with pair of subbasal pore-like sensilla (LA8) on central part of sclerite. Pore-like sensillum LA9 lateral, on membrane between prementum and palpi. Long seta LA10 at base of ligula. Ventral face of prementum with three lateral sensilla (LA5–7); LA5 very short seta, basal; LA6 long seta, anteromesal to LA5; LA7 pore-like, on margin between sclerite and membrane. Ligula with one pair of small sensilla (LA12) on apical membranous area and one pair of ventral pore-like sensilla (LA11) at base of ligula. Labial palpus with three sensilla (LA13–15) and group of apical sensilla (gLA). Palpomere 1 with very short seta LA13 and pore-like sensillum LA14; LA13 ventral and basal; LA14 dorsal, on intersegmental membrane between palpomeres 1 and 2. Palpomere 2 with subapical pore-like sensillum LA15 on outer face; gLA composed of setae of variable length on apical membranous area.

Second instar larva (compared with third instar larva). Similar to third instar larva ( Fig. 5B ). General morphology. Frontal lines, gular sulcus and submental sulcus clearly visible (see Fig. 6A ). Frontal lines lyriform, strongly curved at midlength. Prothorax slightly wider than head capsule.

Chaetotaxy. Head capsule. Similar to third instar but bearing fewer secondary sensilla as follows. Frontale. One short seta in front of FR1. Parietale. Three short setae along base of frontal line; one sensillum (possibly seta) between PA8 and PA9; one short seta between PA19 and PA9. Antenna ( Fig. 8A ). Antennal sensorium SE1 shorter than antennomere 3. Mandible ( Fig. 8B ). One small seta in front of MN4. Two small setae behind MN1. Three rather short basal setae on lateral face. Maxilla ( Figs 8C–D ). Stipes with two subapical setae on inner face, one dorsal, one ventral; one long seta close to MX 6; four rather long setae on outer face. Labium ( Figs 8E–F ). Mentum bearing four pairs of short, stout dorsal setae; two at midlength on lateral face, one on anterior corner and one apical on mesal part. Ventral face with one very short secondary seta on anterior corner.

Third instar larva. General morphology. Body ( Fig. 5C ) slender, widest at abdominal segments 2 and 3, then tapering posteriad.

Colour of fixed larvae light yellowish white with orange-coloured head and sclerotized parts on thorax and abdomen ( Fig. 5C ); living larvae with sclerotized parts reddish brown, body partly transparent with digestive tract partly visible ( Fig. 5E ).

Head capsule subquadrate ( Fig. 9A ). Frontal lines vestigial, only posterior part recognizable, converging at base; coronal line short. Six stemmata closely aggregated on each anterolateral corner of head capsule. Clypeolabrum ( Fig. 9B ) nearly symmetrical. Nasale with distinct teeth; most lateral teeth larger, six small teeth present between large lateral teeth. Lateral lobe of epistome almost symmetrical, projecting further than nasale and rounded. Gular sulcus only visible basally, submental sulcus hardly visible ( Fig. 9D ). Posterior tentorial pits oblong oval, near presumable junction of gular sulcus and submental sulcus ( Fig. 9D ). Cervical sclerites subquadrate ( Fig. 9A ).

Antenna ( Fig. 10A ) 3-segmented, slender, moderately long. Antennomere 1 longest and widest; small subapical membranous projection present on inner face of antennomere 1. One minute structure present laterally at base of antennomere 2. Antennomere 3 elongate, shortest and narrowest.

Mandibles ( Fig. 10B ) symmetrical. Mandible with two inner teeth at about midlength of mandible, distal one larger.

Maxilla ( Figs 10C–D ). Counting cardo, 6-segmented, distinctly longer than antenna. Cardo small, irregularly triangular. Stipes cylindrically sclerotized, longest and widest segment, slightly longer than twice length of palpomeres 1–4 combined. Palpomere 1 wider than other palpomeres, incompletely cylindrically sclerotised dorsally. Palpomere 2 shortest, as wide as palpomere 3 or slightly wider. Palpomere 3 longest, longer than palpomeres 1 and 2 combined. Palpomere 4 narrowest, slightly longer than palpomere 1.

Labium ( Figs 9D , 10E–F ) well developed. Submentum large, subtriangular. Mentum subhexagonal, wider than long; anterior corner of mentum projected anteriorly; dorsal surface bearing small but strong cuticular teeth on basal half. Prementum trapezoid, longer than wide. Ligula cylindrically sclerotized, moderately stout, distinctly shorter than labial palpus. Labial palpus slender, similar to prementum in length; palpomere 1 short, palpomere 2 long.

Thorax. Prothorax slightly wider than head capsule ( Fig. 5C ). Proscutum formed by one large plate divided by fine sagittal line, anterior and posterior areas weakly sclerotised. Prosternum ( Fig. 9E ) subpentagonal, with incomplete sagittal line posteriorly. Mesonotum with pair of narrow transverse sclerites anteriorly and large, subquadrate plate divided by fine sagittal line behind narrow sclerite ( Fig. 5C ). Metanotum with pair of small anterior transverse oval sclerites and large irregular plate, anterior part subquadrate, divided by fine sagittal line, posterior part smaller, subtriangular. Legs ( Figs 5C , 9F ) well developed, visible in dorsal view, 5-segmented, bearing setae of variable length and pores but without swimming hairs; trochanter with one very long seta.

Abdomen ten-segmented, mostly membranous; segment 1 with two pairs of sclerites on anteromedial part; anterior one smaller than posterior one. Ventral surface of abdomen without prolegs.

Spiracular atrium ( Fig. 9G ). Segment 8 with suboval dorsal plate with partly membranous posterior margin, borderline between plate and membrane hardly recognizable. Posterior margin of segment 8 strongly projected, trilobate. Procercus short, partly sclerotised with two short and one long seta. Segment 9 trilobed, partly sclerotized, median lobe of spiracular atrium large; lateral lobes smaller than median lobe. Acrocercus membranous, rather short, visible in dorsal view. Urogomphi short, one-segmented, sclerotized.

Chaetotaxy (compared with first instar larvae). Distribution of secondary setae as follows. Frontale ( Figs 9B–C ). Two short setae in front of FR1. Parietale ( Figs 9C–D ). Six to seven short setae along coronal and posterior half of frontal line. One very short and one short seta behind antennal socket, between PA8 and PA9. One very short seta and one pore-like sensillum on anterior corner, between PA9 and PA19.Anterolateral corner bearing two very short setae behind PA21 and PA22. Anterior half of parietale bearing seven setae laterally. One short seta behind PA14. One short seta between PA14 and PA15. One short seta behind PA15, close to PA18. One short seta anterior to PA17. One short seta lateral to PA16 and PA17. One short seta posterior to PA17. One short seta mesal to PA18. Mandibles ( Fig. 10B ) similar to second instar but bearing additional setae; one small seta between MN1 and MN4; four small setae behind MN2; five rather short on basal part of outer face. Maxilla ( Figs 10C–D ) similar to second instar but stipes bearing seven setae on outer face. Labium ( Figs 9D , 10E–F ) similar to second instar but dorsal surface of mentum with seven setae on right margin and eight on left in illustrated specimen.

Biology. Peltochares atropiceus inhabits low-altitude ponds with rich aquatic vegetation and can be collected in Taiwan throughout the year. We observed that females of P. atropiceus carry the egg-case under the abdomen, confirming the egg-carrying behaviour of Peltochares reported by WATTS (2002).

Remarks. The general morphology of larvae of P. foveicollis , described by WATTS (2002) corresponds well with that of P. atropiceus larvae. For the Peltochares larvae described by BERTRAND (1962), see Discussion.

Figures

Fig. 5. Larvae ofPeltochares atropiceus (Régimbart, 1903). A – first instar larva, dorsal view; B – second instar larva, dorsal view; C – third instar larva, dorsal, lateral, ventral view; D – first instar larva, alive individual; E – third instar larva, alive individual.

Fig. 6. Head capsule of first instar larva of Peltochares atropiceus (Régimbart, 1903). A – dorsal view; B – ventral view; C – detail of anterior margin, dorsal view.

Fig. 7. Head appendages of first instar larva of Peltochares atropiceus (Régimbart, 1903). A – antenna, dorsal view; B, C – mandibles, dorsal view; D, E – maxilla, dorsal view (D) and ventral view (E); F, G – labium, dorsal view (F) and ventral view (G).

Fig. 8. Head appendages of second instar larva of Peltochares atropiceus (Régimbart, 1903). A – antenna, dorsal view; B – mandible, dorsal view; C, D – maxilla, dorsal view (D) and ventral view (E); E, F – labium, dorsal view (F) and ventral view (G).

Fig. 9. Third instar larva of Peltochares atropiceus (Régimbart, 1903). A – head, dorsal view; B – anterior margin of head capsule; C – head capsule, dorsal view; D – head capsule, ventral view; E – prosternum, ventral view; F – prothoracic leg; G – spiracular atrium, dorsal view.

Fig. 10. Head appendages of third instar larva of Peltochares atropiceus (Régimbart, 1903). A – antenna, dorsal view; B – mandible, dorsal view; C, D – maxilla, dorsal view (D) and ventral view (E); E, F – labium, dorsal view (F) and ventral view (G).