Helochares Mulsant, 1844

Minoshima, Yûsuke & Hayashi, Masakazu, 2011, Larval morphology of the Japanese species of the tribes Acidocerini, Hydrobiusini and Hydrophilini (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae (suppl.) 51, pp. 1-118 : 50-52

Genus Helochares Mulsant, 1844

( Figs. 1 E–F, 6B, 29–43, 44C, 45D, 65C)

Species examined. Helochares (Helochares) pallens ( MacLeay, 1825) (L1–3), Helochares (Hydrobaticus) anchoralis Sharp, 1890 (L1), Helochares (Hydrobaticus) nipponicus Hebauer, 1995 (L1–3).

Diagnosis. The larvae of this genus are similar to those of other genera of the Japanese Acidocerini , but are distinguished from them by the following characters: (1) head capsule with scale-like setae ( Fig. 36 ); (2) nasale with distinct teeth, not serrate or smooth ( Figs. 36C , 42A ); (3) each epistomal lobe with one or two stout, short scale-like setae and two short setae (e.g., Fig. 36C ); (4) antennal sensorium (SE1) rather long ( Figs. 39A , 40B , 42B ); (5) abdominal segments without spinose prolegs.

General morphology. Body slender, almost parallel-sided, tapering posteriad, widest between second and fourth abdominal segments ( Figs. 1 E–F, 6B).

Head (e.g., Fig. 32A , 35A ). Head capsule subquadrate. Frontal lines lyriform, fused at base of head capsule, coronal line short. Surface of head capsule smooth. Six stemmata on each anterolateral portion of head capsule. Clypeolabrum (e.g., Figs. 29C , 33A ) asymmetrical. Nasale asymmetrical, with six teeth, four on right projecting further than two on left. Epistomal lobes rounded, slightly to strongly asymmetrical.

Antenna 3-segmented, short, stout in first instar (e.g., Fig. 30A ) to rather slender in third instar (e.g., Fig. 33B ). Flagellum the shortest.

Mandibles (e.g., Figs. 33 C–D) almost symmetrical, with two inner teeth, distal tooth larger than basal one; inner face of mandible serrate on basal part. Basal tooth of left mandible comparatively smaller than that of right mandible.

Maxilla (e.g., Figs. 33 E–F) 6-segmented (including cardo), distinctly longer than antenna. Cardo small, irregularly shaped. Stipes the longest, longer than palpomeres 1–4 combined; subapical part of inner surface with spine-like cuticular projection; basal part of inner face bearing several cuticular projections. Maxillary palpus 4-segmented; palpomere 1 incompletely sclerotised on dorsal surface; inner process sclerotised.

Labium (e.g., Figs. 29B , 33 G–H) well developed. Submentum fused to head capsule, large, subpentagonal, wider than mentum. Mentum subtrapezoidal in dorsal view, wider than prementum, bearing cuticular spines on dorsal surface. Prementum subquadrate, wider than long. Ligula largely sclerotised, distinctly shorter than labial palpi, longer than labial palpomere 1, with weakly bifid membranous apex. Labial palpi covered with narrow cuticular spines on intersegmental membrane between palpomeres 1 and 2.

Thorax. Prothorax slightly wider than head capsule ( Figs. 1 E–F, 6B). Proscutum formed by large plate subdivided by fine sagittal line, anterior and posterior margins weakly sclerotised; several very long to rather long setae situated on each side, some of them scale-like. Prosternum subpentagonal, incompletely subdivided by fine sagittal line ( Fig. 44C ). Mesonotum subdivided by fine sagittal line, with two dorsal sclerites on each side, anterior one small and narrow, posterior one large, each with very long to rather long setae. Metanotum with one large dorsal sclerite on each side, median part of sclerites sometimes indistinct (looking then as two dorsal sclerites on each side), anterior part larger than posterior part, each sclerite with very long to rather long setae. Legs ( Fig. 45D ) rather short, visible in dorsal view, 5-segmented, bearing several short to long, stout setae, lacking swimming hairs; all three pairs similar in shape.

Abdomen. Abdomen 10-segmented, tapering posteriad, covered with fine pubescence on membranous parts; segments 1 to 7 similar in size and shape, each with dorsal sclerites and small, narrow lateral sclerites; segments 8 to 10 forming spiracular atrium.

Spiracular atrium ( Figs. 32B , 35B , 41B ): Segment 8 with large, oval dorsal plate; posterior edge of plate projecting medially; procercus incompletely sclerotised, with one stout and two rather long setae. Segment 9 trilobed, partially sclerotised; median lobe with one small, incompletely sclerotised projection on each side; each lateral lobe with short, membranous acrocercus; urogomphi short, one-segmented; prostyli reduced.

Primary chaetotaxy of head. Frontale altogether with 44–46 sensilla ( Figs. 29A, C , 36A, C ). Central part with three pairs of sensilla divergent posteriad (FR1–3); FR1 rather long seta close to frontal line; FR2 pore-like; FR3 short seta situated more anteriorly than FR2. Three setae (FR5–7) situated posteriorly to antennal socket, FR6 between FR5 and FR7, FR7 close to inner margin of antennal socket. FR4 pore-like, slightly digitiform, situated posteromesally to antennal socket. Nasale with a group of six stout, short setae and a few sensilla (gFR1). Epistomal lobes with three to four short setae each (gFR2). Pore-like sensillum FR15 placed posteriorly to median portion of nasale; long seta FR8 behind FR15. Two setae (FR9–10) and one pore-like sensillum (FR14) situated medioanteriorly to antennal socket; one long seta (FR9) and one rather short seta (FR10) situated mesally to antennal socket. Two pore-like sensilla (FR11 and FR13) and one short seta (FR12) on inner part of epistomal lobe; FR11 close to each lateral seta of gFR1.

Parietale with 30 sensilla each ( Figs. 29 A–B, 36A-B). Dorsal surface with a group of five sensilla (PA1–5) situated posteriorly at midwidth, forming irregular to slightly irregular longitudinal row; PA1–2 and PA4–5 short setae, PA3 pore-like sensillum. PA6 pore-like, located posteromesally close to joint of coronal and frontal lines, about same distance from posterior margin of head as PA1. PA7 and PA12 on median part of dorsal surface of parietale, between PA5 and PA10; PA12 situated slightly anteromesally to PA7; seta PA8 very long, situated posteriorly to antennal socket, close to frontal line; pore-like sensillum PA10 situated between PA7 and PA8, but laterally of line connecting PA7 and PA8. Seta PA9 long, scale-like, close to outer margin of antennal socket. Very long setae PA13 and PA14 located laterally of PA7 and PA12, at midlength of laterodorsal part; PA14 between PA11 and PA13. PA11 rather short seta at about midlength between PA14 and PA20. anterior corner of epicranium with one pore-like sensillum (PA19) and three long trichoid setae (PA20–22); PA19 situated dorsally to PA20–22; PA20 rather to moderately long, PA21 very long, PA22 long; PA20 between PA19 and PA21; PA 22 situated ventrally to remaining sensilla. Two pore-like sensilla (PA15 and PA17) and one narrow scale-like seta (PA16) situated on about anterior third of lateral surface of parietale; PA15 situated more dorsally than PA16; PA17 situated more mesally than PA16; one very long seta (PA18) at midlength of lateral surface of parietale. Ventral surface with three pore-like sensilla (PA23–25) on anterior margin close to ventral mandibular acetabulum; PA23 situated close to PA22, more distant from PA24–25 than the latter from each other. Two very long setae (PA26 and PA28) and one pore-like sensillum (PA27) located at midlength of parietale, slightly laterally of midwidth of parietale. PA27 between PA26 and PA28. Two pore-like sensilla (PA29–30) located ventrally in posterior part of parietale; PA29 behind PA28; PA30 situated posteriorly to PA18.

Antenna ( Fig. 30A , 37A ): Antennomere 1 with five pore-like sensilla (AN1–5); AN1 at midlength, AN2 on distal third, AN3–5 on distal margin, AN4 dorsal, AN3 and AN5 ventral. Antennomere 2 with one pore-like sensillum (AN6) situated dorsally on subapical part of sclerite, and five setae (AN7–11) situated subapically on intersegmental membrane between antennomeres 2 and 3. SE1 rather long, slender, about as long as antennomere 3. Antennomere 3 with apical sensilla (gAN) on apical membranous area; gAN with two long trichoid setae and a few short setae.

Mandible ( Figs. 30 B–C, 37B–C) with six sensilla; MN1 seta, MN2–4 and MN6 pore-like, MN5 seta or pore-like. MN1 rather long, on outer face of mandible. Sensilla MN2–4 forming a triangular group in median area of dorsal surface. MN5 situated subapically on outer face of mandible. MN6 situated subapically on inner face of mandible.

Maxilla ( Figs. 30 D–E, 37D–E): Cardo with one very long, trichoid ventral seta ( MX 1). Stipes with a row of five rather short, stout setae ( MX 7–11) situated dorsally along inner face; MX 7–11 almost equidistant, each with subapical tooth, distance between MX 8 and MX 9 slightly shorter than distance between MX 10 and MX 11. Ventral surface of stipes with three pore-like sensilla ( MX 2–4) and two setae ( MX 5–6); MX 2 on basal fourth of sclerite; MX 3 on basal two-fifths of sclerite; MX 4–6 on outer face of apical part of sclerite; MX 5 very long scale-like seta; MX 6 very long trichoid seta situated more distally than MX 4–5. Palpomere 1 with four sensilla on sclerite ( MX 12–14 and MX 16); one moderately short spiniform seta ( MX 16) situated basally on dorsal inner face; MX 12–13 on lateral surface, MX 14 on ventral surface; MX 12 pore-like sensilla, MX 13–14 long setae. Two pore-like sensilla ( MX 15 and MX 17) on membrane behind inner appendage; MX 17 dorsal, MX 15 ventral. Inner appendage with one rather long scale-like seta and a few rather short to very short setae (gAPP). Palpomere 2 with two pore-like sensilla ( MX 18–19) and one minute seta ( MX 27); MX 18 situated ventrally on outer portion of sclerite, MX 19 on inner face of intersegmental membrane between palpomeres 2 and 3; MX 27 at base of outer face. Palpomere 3 with two long setae ( MX 21 and MX 23) and two pore-like sensilla ( MX 20 and MX 22). Palpomere 4 with one long seta ( MX 24) on basal portion of inner face, and with a digitiform sensillum ( MX 25) and a pore-like sensillum ( MX 26) on subapical portion of outer face, MX 25 dorsal, MX 26 ventral. Apical membranous area of palpomere 4 with several minute setae (gMX).

Labium ( Figs. 30 F–G, 37F–G): Submentum with two pairs of setae (LA1–2); LA1 long in lateral corners, LA2 short on anterior lobes. Ventral surface of mentum with one pair of rather short setae (LA3) and one pair of pore-like sensilla (LA4) situated anterolaterally; LA4 located close to distal margin of sclerite, anteriorly to LA3. Dorsal surface of prementum with one pair of pore-like sensilla (LA8) on median part of sclerite. Ventral surface of prementum with three pairs of sensilla (LA5–7) on lateral portion; seta LA5 short on basal margin of sclerite; LA6 very long, located between LA5 and LA7, slightly mesally of line connecting LA5 and LA7; LA7 pore-like, on borderline of sclerite and membranous area between prementum and palpi. Membranous area between prementum and palpi with one pair of long setae (LA10) and small pore-like sensilla (LA9); LA10 close to base of ligula, LA9 on median portion of membranous area. Ligula with two pairs of pore-like sensilla (LA11 and LA12); LA12 situated dorsally on apical membranous area, LA11 situated ventrally at base of ligula. Palpomere 1 with one minute seta (LA13) ventrally; LA13 close to basal margin of sclerite; LA14 on dorsal side of intersegmentary membrane between palpomeres 1 and 2. Palpomere 2 with one pore-like sensillum (LA15) situated subapically on lateral face of sclerite. Apical membranous area of palpomere 2 with one long seta and several rather long to short setae (gLA).

Figures

Fig. 1. Habitus of the third instar larvae of Acidocerini and Hydrobiusini. A – Agraphydrus narusei (Satô, 1960), dorsal and lateral view; B – Enochrus (Holcophilydrus) simulans (Sharp, 1873), dorsal view; C – E. (H.) umbratus Sharp, 1884, dorsal view; D – E. (Methydrus) japonicus (Sharp, 1873), dorsal view; E – Helochares (Helochares) pallens (MacLeay, 1825), dorsal view; F – H.(Hydrobaticus) nipponicus Hebauer, 1995, dorsal view; G – Hydrobius pauper Sharp, 1884, dorsal and ventral view.

Fig. 36. Head capsule of Helochares (Hydrobaticus) anchoralis Sharp, 1890, first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 42. Helochares (Hydrobaticus) nipponicus Hebauer, 1995, third instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 39. Head appendages of Helochares (Hydrobaticus) nipponicus Hebauer, 1995, first instar.A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 40. Helochares (Hydrobaticus) nipponicus Hebauer, 1995, second instar. A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view: G – labium, dorsal view; H – labium, ventral view.

Fig. 32. Helochares (Helochares) pallens (MacLeay, 1825), third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 35. Helochares (Hydrobaticus) anchoralis Sharp, 1890, first instar.A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 29. Head capsule of Helochares (Helochares) pallens (MacLeay, 1825), first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 33. Helochares (Helochares) pallens (MacLeay, 1825), third instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 30. Head appendages of Helochares (Helochares) pallens (MacLeay, 1825), first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 44. Prosterna of Acidocerini species, third instar, ventral view. A – Agraphydrus narusei (Satô, 1960); B – Enochrus umbratus Sharp, 1884; C – Helochares nipponicus Hebauer, 1995.

Fig. 45. Mesothoracic legs of Acidocerini species, third instar, anterior view.A – Agraphydrus narusei (Satô, 1960); B – Enochrus umbratus Sharp, 1884; C – Enochrus japonicus (Sharp, 1873); D – Helochares nipponicus Hebauer, 1995.

Fig. 41. Helochares (Hydrobaticus) nipponicus Hebauer, 1995, third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 37. Head appendages of Helochares (Hydrobaticus) anchoralis Sharp, 1890, first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.