Regimbartia attenuata ( Fabricius, 1801 )

Minoshima, Yûsuke N. & Hayashi, Masakazu, 2015, Description of the larval stages of the berosine genera Berosus and Regimbartia based on the Japanese species B. japonicus and R. attenuata (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae 55 (1), pp. 47-83 : 62-74

Regimbartia attenuata ( Fabricius, 1801)

( Figs 8–16 , 17C–D )

Material examined. JAPAN: HONSHÛ: Shimane Prefecture: 9 L1 ( HGF, KMNH), Wadakami , Oku-uga-chô, ponding fallow field, 16.vi.2008 (date of fixation), M. Hayashi leg. & reared ; 1 L1 ( KMNH), Wadakami , Oku-uga-chô, ponding fallow field, 13.vi.2008 (date of fixation), M. Hayashi leg. & reared ; 2 L3 ( KMNH), Wadakami , Oku-uga-chô,ponding fallow field, 12.vii.2008, M. Hayashi leg. ; 1 L1, 3 L2 ( HGF, KMNH), Okinoshima, Sono-chô, Izumo-shi , paddy field, 19.vi.2008, M. Hayashi leg. ; 1 L1 ( KMNH), Wadakami , Oku-uga-chô, ponding fallow field, 25.vi.2008 (date of fixation), M. Hayashi leg. & reared ; 2 L1 ( KMNH), Nozato-chô, Izumo-shi , 3.vi.2008 (date of fixation), M. Hayashi leg. & reared. NANSEI ISLANDS: Okinawa Prefecture: 2 L3 ( EUMJ), Sonai, Yonaguni-jima I., 1.viii.1962, M. Satô leg.

Description. General morphology. Third instar ( Figs 8 , 12–15 , 16B ). Larva metapneustic. Body ( Figs 8A–B ) rather slender with strong setiferous projections, nearly parallel-sided; thorax and abdomen bear short to long, membranous projections. Colour greyish white with sclerotised parts brownish, head capsule yellowish brown. One pair of spiracles on mesothorax; eight pairs of spiracles on abdominal segments; spiracles on mesothorax and abdominal segments 1–3 strongly protuberant; those on abdominal segments 4–7 hardly detectable, seem to be reduced; posterior one pair enclosed in spiracular atrium, very large, annular; anterior eight pairs non-functional, posterior pair functional.

Head ( Figs 12A , 13 ). Head capsule subquadrate, attenuated posteriad; cervical sclerites large, subrectangular. Frontal line straight and slightly lyriform, but almost invisible in third instar; posterior end of frontal lines U-shaped; coronal line absent. Surface of head capsule smooth. Six stemmata on each anterolateral corner of head capsule. Clypeolabrum nearly symmetrical ( Fig. 13C ). Nasale weakly convex with strongly serrate anterior margin (bearing many small cuticular teeth on ventral surface of anterior margin). Epistomal lobe very weakly rounded; both lobes with a few to several small cuticular teeth.

Antenna ( Figs 14A–B ) 3-segmented, long, slender. Antennomere 1 longer than antennomeres 2 and 3 combined, with one projection on subapical part of inner face; apical part of projection membranous. Antennomere 2 attenuated basally, narrower than antennomere 1 at base, about as wide as antennomere 1 at apex; apical part of inner face of antennomere 2 weakly projecting anteriorly. Antennomere 3 the narrowest and shortest.

Mandibles ( Figs 15A–B ) rather slender, slightly asymmetrical. Right mandible with two inner teeth, apical one large, projecting apically, and basal one small; basal inner tooth of left mandible with one, closely aggregated associated tooth.

Maxilla ( Figs 14C–D ) 6-segmented, slightly longer than antenna. Cardo small, subtriangular. Stipes the longest and widest, about twice as long as palpomeres 1–4 combined; inner face with few cuticular spines basally; a small cuticular projection present subapically on inner face. Maxillary palpus 4-segmented, palpomere 1 widest, dorsal surface completely sclerotised; palpomere 2 shortest and wider than palpomere 3; palpomere 3 the longest; palpomere 4 narrowest; inner process small, sclerotised.

Labium ( Figs 13B , 15C–D ) well developed. Submentum ( Fig. 13B ) fused to head capsule, large, subpentagonal or subtriangular, wider than mentum. Mentum transverse subrectangular, lateral face weakly convex, widest medially, each anterior corner weakly but distinctly projecting anteriorly; dorsal surface covered with small cuticular spines posterolaterally. Prementum very narrow and long, about two-fifths as width of mentum, and about 2.7 times as wide as long; basal part close to LA8 sensilla partially membranous. Ligula stout, shorter than or as long as labial palpus, weakly curved dorsally; dorsal part of ligula mostly membranous excluding basal margin, ventral surface of ligula sclerotised but lateral part membranous. Labial palpus short, palpomere 1 shorter and slightly wider than palpomere 2.

Thorax. Thoracic membrane covered with fine cuticular pubescence, each apex multi-furcate (e.g., Fig. 8E ) excluding anterior margin which bears fine cuticular pubescence of simple shape; thoracic sclerites bearing densely arranged fine cuticular projections; apex of projections expanded circularly ( Fig. 8C ). Prothorax wider than head capsule. Proscutum formed by one large plate subdivided by fine sagittal line, anterior part rather weakly sclerotised. Prosternal sclerite ( Fig. 12B ) subpentagonal, with long and fine indistinct sagittal line; anterior margin of sclerite with densely arranged short setae. Mesonotum with two sclerites on each side; anterior two narrow, weakly sclerotised and indistinct; posterior sclerites large, subtriangular, both posterior sclerites jointing at anterior margin. Five pairs of setiferous, membranous projections present on dorsal and lateral surfaces; one small on posterior mesonotal sclerite; one small laterodorsal at midlength; three long (e.g., Fig. 8D ) on lateral face. Metanotum with apparently two metanotal sclerites; sclerites very weakly sclerotised and indistinct, subrectangular. One short membranous projection bearing apical seta present posteromesally to lateral sclerite. Eight pairs of setiferous, membranous projections present on dorsal and lateral surfaces; one small very close and posteromesally to metanotal sclerite; three long on lateral surface; remaining ones forming a transverse row behind metanotal sclerite; from mesal to lateral, bearing small, short setiferous projections. Legs ( Fig. 16B ) long, visible in dorsal view, 5-segmented; all three pairs similar in shape.

Abdomen. Abdomen 10 segmented, tapering posteriad ( Figs 8A–B ); segments 1 to 7 similar in shape and size. Abdominal membrane covered with fine cuticular pubescence, each apex multi-furcate ( Fig. 8E ) excluding anterior margin of dorsal surface, ventral surface, and membrane on segment 8, which bears fine cuticular pubescence of simple shape. Segment 1 without dorsal sclerite. Twelve setiferous, membranous projections (e.g., Fig. 8D ) present on each side of dorsal and lateral surfaces; four small on anterior part of segment; two small and four long behind anterior four, mesal pair small, lateral two pairs long; these projections situated between spiracles; two pairs of long projections on lateral surface, ventrally to spiracles, one laterally, one lateroventrally; five pairs forming a transverse row on posterior part; dorsal four pairs small, lateral pair long. Two small setiferous, membranous projections present laterally on ventral surface, one on anterior part, one on posterior part. Segments 2 to 7 similar to segment 1, but dorsal and lateral projections on segment 6 and 7 differ from segment 1. Segment 6 with 11 pairs of setiferous, membranous projections on dorsal and lateral surfaces; four pairs forming a transverse row on posterior part, behind remaining projection on segment 6; dorsal three pairs small, lateral pair long. Segment 7 with nine pairs of setiferous, membranous projections on dorsal and lateral surfaces; four pairs of projections forming a transverse row present at midlength, behind anterior four projections, median two rather short, lateral three long; three pairs of projections forming transverse row in posterior part, lateral pair long, remaining pairs on dorsal surface, small.

Spiracular atrium ( Fig. 12C ). Segment 8 with large oval dorsal plate covered with fine cuticular projections and setae of variable length; dorsal surface of segment 8 tetralobate, median two lobes very large, covered with short pubescence, lateral ones small, indistinct. Segment 9 trilobed, partially sclerotised; urogomphus large, bearing one very long seta and a few short setae; procercus rather long, partially sclerotised, with one long and two short setae apically; median lobe of spiracular atrium partially sclerotised, with four long setae on posterior margin; lateral lobe of spiracular atrium partially sclerotised composed by inner sclerite and outer sclerite, bearing several setae of variable length; acrocercus and prostylus undetectable, absent.

Second instar. Very similar to third instar larva; sclerites on meso- and metathorax and abdominal segments more weakly sclerotised than in third instar.

Head. Head capsule. Frontal lines clearly visible. Epistomal lobe very weakly projecting anteriorly, similar to that of first instar ( Fig. 9C ). Ventral cuticular teeth on nasale much sparsely arranged than in third instar, rather similar to those in first instar.

Antenna (e.g., Figs 14A–B ) proportionally stouter than in third instar.

Labium (e.g., Figs 15C–D ). Mentum subtrapezoidal, widest basally; lateral face of mentum slightly convex; anterior corners of mentum slightly projecting anteriorly.

Thorax and abdomen. Arrangement of cuticular projections and pubescence on thorax and abdomen similar to but finer than in third instar. Apex of cuticular pubescence and projections similar to but more simple than in third instar; setiferous, membranous projections on thoracic and abdominal segments proportionally smaller than in third instar, but more similar to third instar than to first instar.

First instar ( Figs 9–11 , 16A ). Similar to second instar larva; sclerites on meso- and metathorax more weakly sclerotised than in second instar.

Head. Head capsule ( Fig. 9 ). Epistomal lobe hardly detectable or absent ( Fig. 9C ). Nasale very weakly convex anteriorly, nearly straight; ventral cuticular teeth on nasale sparsely arranged.

Antenna ( Figs 10A–B ) proportionally stouter than in second and third instars.

Maxilla ( Figs 10C–D ) proportionally stouter than in third instar.

Labium ( Figs 11C–D ). Anterior margin of mentum rounded in dorsal view, without anterior corners and projection; prementum about 3.1 times as long as wide but about half the width of mentum.

Thorax and abdomen. Arrangements of cuticular projection and pubescence on thorax and abdomen similar to third instar but projection and pubescence finer than in second instar. Apex of cuticular pubescence or projections simple; setiferous, membranous projections on thoracic and abdominal segments proportionally smaller than in second instar, the number of the projections less than in third instar. Prothorax as wide as or slightly wider than head capsule.

Chaetotaxy of head. Primary chaetotaxy ( Figs 9–11 ). Frontale ( Figs 9A, C ). Very short seta FR1 on about midlength of frontale rather close to frontal line. Pore-like sensillum FR2 anteromesal to FR1, posteromesal to inner margin of antennal socket. Short seta FR5 and rather long seta FR6 posteromesal to antennal socket, lateral to FR2; FR5 mesal to FR6. Pore-like sensillum FR4 mesal to antennal socket, anterior to FR5–6. Three sensilla (FR3, FR8, FR15) situated mesally behind nasale, FR3 rather short, stout seta, FR8 long seta, FR15 pore-like; FR3 mesal to FR8, FR8 posterior to FR15. Short seta FR10 between FR7 and FR8. Four sensilla (FR7, FR9, FR12–13) forming longitudinal row between inner margin of antennal socket to lateral portion of nasale; FR7 very short seta, FR9 very long seta, FR12 rather short and stout seta, FR13 pore-like sensillum; FR7 mesal and close to inner margin of antennal socket, FR9 between FR7 and FR13, FR13 between FR9 and FR12, FR12 anterior to remaining sensilla (FR7, FR9, FR13). Pore-like sensillum FR11 on anteromesal portion of epistome, posterior to mesal-most seta of gFR2. Pore-like sensillum FR14 lateral and close to FR9. Nasale with group of six short setae, and with (at least) two short ventral seta and four small pore-like sensilla (gFR1) ( Fig. 9C ); median two dorsal setae very short, shorter than other ones, next ones rather short, longer than other ones, lateral ones short; median two pairs of dorsal setae closely aggregated. Pore-like sensillum on lateral part of nasale, close to FR12; a pair of ventral setae and ventral pore-like sensilla situated mesally close to median four setae of gFR1. Each epistomal lobe with three rather short, stout but somewhat slender setae (gFR2).

Parietale ( Figs 9A–B, D–E ). Dorsal surface with a group of five sensilla (PA1–5) forming irregularly longitudinal row at midwidth in posterior part of parietale; PA1–2 and 4–5 short setae, PA3 pore-like. PA6 pore-like, located posteromesally close to posterior end of frontal line, close to posterior margin of head capsule. Very long seta PA9 behind lateral margin of antennal socket; long setae PA7–8 close to frontal line, posterior to lateral part of antennal socket; PA8 posterolateral to PA7, between PA9. Pore-like sensillum PA10 between mesal stemmata of anterior and posterior rows. Two rather short setae (PA12–13) posterior to PA9–10, PA12 between PA5 and PA9, PA13 posterolateral to PA12. Short seta PA11 and very long seta PA14 located inside of line connecting stemmata; PA14 lateral to PA11. PA 19–22 in anterior corner of head capsule; PA19 pore-like sensillum, PA20–22 very long setae; PA19–21 very closely aggregated on laterodorsal face, PA19 dorsal to PA20–21; PA20 between PA19 and PA21; PA21 ventral to PA19–20; PA22 lateroventral. Pore-like sensilla PA23–25 situated behind ventral mandibular articulation, PA23 lateral to PA24–25, close to PA22; PA24–25 very close to each, PA25 anterior to PA24. Four sensilla (PA15–18) on lateroventral surface ( Figs 9B, D–E ), PA15–17 on anterior third, PA18 slightly posterior to midlength; PA16 and PA18 long setae, PA15 and PA17 pore-like sensilla; PA16 and PA17 anterior to PA15, closely aggregated, PA17 mesal to PA16; PA15 between PA16 and PA18. Two long setae (PA26 and PA28) and pore-like sensillum PA27 aggregated on median part of ventral surface of parietale, slightly more mesal to midwidth; PA26 anterior to PA27–28, PA27 between PA26 and PA28, PA28 posterior to PA26–27. Two pore-like sensilla (PA29–30) in posterior portion of ventral surface of parietale; PA30 close to posterior corner, PA29 mesal to PA30, on about midlength between PA30 and gular sulcus.

Antenna ( Figs 10A–B ). Antennomere 1 with five pore-like sensilla (AN1–5); AN1–2 situated dorsally on posterior fourth to fifth, AN1 posteriorly to AN2, AN3 subapically on lateroventral face, AN4 on inner projection, AN5 ventrally on median portion of anterior margin of sclerite. Antennomere 2 with one pore-like sensillum (AN6) situated dorsally on subapical part of sclerite; very short seta AN7 and sensorium SE1 on lateral face of intersegmental membrane between antennomeres 2 and 3, AN8–9 absent. SE1 slender, about as long as antennomere 3. Setae AN10–11 aggregated on inner face of intersegmental membrane between antennomeres 2 and 3, AN10 very long, AN11 short. Antennomere 3 with apical sensilla (gAN) in apical membranous area; gAN with two very long setae and a few short setae of variable shape.

Mandibles ( Figs 11A–B ). Mandible with two setae (MN1 and MN5) and four pore-like sensilla (MN2–4 and MX 6). MN1 and MN4 on median part of outer face; MN1 rather short, posterior to MN4. MN2–3 on median part of mandible; MN3 posteromesal to MN1–4, MN2 between MN3 and MN4; minute seta MN5 on apical third of outer face; MN6 very small and indistinct, subapical on inner face.

Maxilla ( Figs 10C–D ). Cardo with one moderately short ventral seta ( MX 1). Stipes with five setae ( MX 7–11) situated dorsally along inner face; MX 7–9 moderately short and stout, MX 10 very short, MX 11 long and trichoid; MX 7–9 in basal fourth, MX 10 at midlength of sclerite, MX 11 on apical fourth. Two setae ( MX 5–6) on subapical portion of outer face of sclerite; MX 5 very long, MX 6 long; MX 6 anterior and dorsal to MX 5. Pore-like sensillum MX 4 posterior to MX 5–6. Pore-like sensilla ( MX 2–3) on ventral surface, MX 2 on posterior fourth, MX 3 on posterior two-fifths. Dorsal surface of palpomere 1 with one long, slightly stout, trichoid seta ( MX 16) situated basally on inner face; ventral surface of sclerite with three sensilla ( MX 12–14) close to distal margin of sclerite; MX 12 pore-like on lateral part, MX 13 very long seta posterior to MX 12, MX 14 long seta mesal to MX 12–13. Pore-like sensilla ( MX 15 and MX 17) on membrane behind inner appendage; MX 17 dorsal, MX 15 ventral. Inner appendage with one long seta and a few short setae (gAPP). Palpomere 2 with two pore-like sensilla ( MX 18 and MX 19) and one minute seta ( MX 27); MX 18 situated ventrally on median part of sclerite; MX 19 on inner face of intersegmental membrane between palpomeres 2 and 3; MX 27 at base of outer face of sclerite. Palpomere 3 with two very long setae ( MX 21 and MX 23) and two pore-like sensilla ( MX 20 and MX 22); MX 20 and MX 23 on outer face close to distal margin of sclerite, MX 20 ventral to MX 23; MX 21 on lateral to median part of ventral surface, closer to distal margin of sclerite or on borderline between sclerite and intersegmental membrane; MX 22 situated dorsally on lateral part close to distal margin of sclerite. Palpomere 4 with one long seta ( MX 24) situated basally on inner face, and with digitiform ( MX 25) and pore-like ( MX 26) sensilla apically on outer face of sclerite; MX 25 dorsal, MX 26 ventral. Apical membranous area of palpomere 4 with several minute setae (gMX).

Labium ( Figs 11C–D ). Submentum with two pairs of setae (LA1–2) on each lateral portion; LA1 very long, LA2 short; LA2 anterior to LA1. Ventral surface of mentum with one pair of rather long setae (LA3) and pore-like sensillum (LA4) on anterior margin of sclerite; LA4 posterolateral and close to LA3. Prementum with three pairs of sensilla (LA8–10) situated dorsally and three pairs of sensilla ventrally (LA5–7). LA8 pore-like, situated basally; LA9 pore-like but weakly projecting sensillum, situated subapically on dorsolateral face; LA10 long seta, at base of ligula. LA5 minute seta, situated basally on lateral part, closer to basal margin of sclerite; very long seta LA6 and pore-like sensillum LA7 subapical on lateral part, LA6 posterior to LA7. Ligula with two pairs of pore-like sensilla (LA11–12); LA12 apical, LA11 ventral and basal. LA13 minute seta situated ventrally on basal margin of sclerite of palpomere 1; pore-like sensillum LA14 situated dorsally on intersegmental membrane between palpomeres 1 and 2, LA15 subapically on outer face of palpomere 2. Apical membranous area of palpomere 2 with several setae of variable length and shape (gLA).

Second instar. Primary sensilla similar to first instar.

Parietale (e.g., Figs 13A–B ) with five secondary setae, two dorsal, three lateral. One short between PA6 and PA7, close to frontal line; one short between PA8 and PA9; one short lateral to PA16; one short close to PA16; one rather short mesal to PA15 and PA18.

Antenna (e.g., Figs 14A–B ). SE1 shorter than antennomere 3.

Mandibles (e.g., Figs 15A–B ). Basal half of outer face of mandibles with about 10 secondary sensilla; basal five sensilla short, remaining ones minute.

Maxilla (e.g., Figs 14C–D ). Stipes with six long to rather short secondary setae on outer surface; one long situated apically close to MX 4–6; four rather short setae situated lateroventrally on median to posterior portions.

Labium (e.g., Figs 15C–D ). Dorsal surface of mentum with two pairs of short, stout secondary sensilla along anterior margin, one pair on median part, another pair on anterior corner; ventral surface with one short secondary seta on each lateral part.

Third instar ( Figs 13–15 ). Similar to second instar.

Antenna ( Figs 14A–B ). Antennomere 2 with one minute secondary sensillum situated subbasally on inner face, often absent.

Mandibles ( Figs 15A–B ). MN2 situated on or slightly anteriorly to the line connecting

MN1 and MN3.

Egg-case. Egg-cases were laid on substrate ( Fig. 17C; HAYASHI 2009a).

GOPALASWAMY and HANUMANTHA RAO (1975) reported the egg-laying behaviour of R. attenuata and mentioned that the specimens carried egg-cases under their abdomen. However, R. attenuata lays egg-case on substrate such as leaves ( HAYASHI 2009a; Fig. 17C ) like other Berosini (e.g., ARCHANGELSKY 1997, 2004, 2008; Figs 17A–B ). This confusing observation of GOPALASWAMY and HANUMANTHA RAO (1975) seems to be actually caused by a misidentification, as they likely observed specimens of the genus Helochares Mulsant, 1844 . The carrying of the egg-case under abdomen has been observed in the species of the genera Helochares , Helobata Bergroth, 1888 , and Radicitus Short & García, 2014 (all Hydrophilidae : Acidocerinae ), and in hydrophiloid families Epimetopidae and Spercheidae ( BØVING & HENRIKSEN 1938, ARCHANGELSKY 1997, HANSEN 2000, SHORT & GARCÍA 2014). This behaviour is not known for any genus within the Hydrophilinae , including all berosine genera.

Figures

Fig. 8. Third instar larva of Regimbartia attenuata (Fabricius, 1801). A–B – habitus, dorsal (A) and ventral (B); C – cuticular projection on pronotum, dorsal; D – lateral setiferous projection, dorsal; E – cuticular projections on abdominal segment, dorsal.

Fig. 9. First instar larva of Regimbartia attenuata (Fabricius, 1801), head capsule. A–B – head capsule, dorsal (A) and ventral (B); C – anterior margin of head capsule, dorsal; D–E – variation of sensilla PA15–18, ventral.

Fig. 10. First instar larva of Regimbartia attenuata (Fabricius, 1801), head appendages. A–B – antenna, dorsal (A) and ventral (B); C–D – maxilla, dorsal (C) and ventral (D).

Fig. 11. First instar larva of Regimbartia attenuata (Fabricius, 1801), head appendages. A–B – mandible, dorsal; C–D – labium, dorsal (C) and ventral (D).

Fig. 12. Third instar larva of Regimbartia attenuata (Fabricius, 1801). A – head, dorsal; B – prosternal sclerite, ventral; C – spiracular atrium, dorsal.

Fig. 13. Third instar larva of Regimbartia attenuata (Fabricius, 1801), head capsule.A–B – head capsule, dorsal (A) and ventral (B); C – anterior margin of head capsule, dorsal.

Fig. 14. Third instar larva of Regimbartia attenuata (Fabricius, 1801), head appendages. A–B – antenna, dorsal (A) and ventral (B); C–D – maxilla, dorsal (C) and ventral (D).

Fig. 15. Third instar larva of Regimbartia attenuata (Fabricius, 1801), head appendages. A–B – mandible, dorsal; C–D – labium, dorsal (C) and ventral (D).

Fig. 16. Regimbartia attenuata (Fabricius, 1801), mesothoracic leg, anterior view. First (A) and third (B) instar.

Fig. 17. A–B – Egg-case of Berosus (Berosus) japonicus Sharp, 1873, wild (A) and rearing (B); C – egg-case of Regimbartia attenuata (Fabricius, 1801), rearing; D – egg of R. attenuata. FigsA, C modified after HAYASHI (2009a). Photos by M. Hayashi.