Hydrocanthus debilis Sharp, 1882

Urcola, Juan I., Alarie, Yves, Benetti, Cesar J., Torres, Patricia L. M. & Michat, Mariano C., 2022, Description and chaetotaxic analysis of the larval instars of Hydrocanthus debilis Sharp, 1882 (Coleoptera: Noteridae), Zootaxa 5196 (1), pp. 135-144 : 136-142

Description of the larvae of Hydrocanthus debilis Sharp, 1882

Diagnosis. Within Hydrocanthus , larvae of H. debilis can be distinguished by the following combination of characters: smaller species ( Table 1 ), dorsal surface of body maculate ( Figs 1 , 21, 23 ); egg bursters relatively more separated from each other (EBD/FRL = 0.14–0.16) (instar I); seta PA13 shorter than seta PA14 (instar I) ( Fig. 2 ); setae MX 7 and MX 11 very short ( Fig. 8 ); and anterior surface of trochanter with three spinose setae ( Figs 11 , 18 ).

Instar I ( Figs 1–16 ; Table 1 )

Colour ( Fig. 1 ): Testaceous with dark maculae of different shapes and sizes on dorsal surface.

Body ( Fig. 1 ): Elongate, broadest at middle region, narrowing toward abdominal apex. Measurements and ratios that characterize body shape are shown in Table 1 .

Head ( Figs 2–10 ): Prognathous; cephalic capsule ( Figs 2–3 ) broader than long; maximum width at level of posterior stemmata; slightly narrowed posteriorly, occipital foramen large; coronal suture not distinguishable, ecdysial sutures U-shaped; posterior tentorial pits conspicuous, well separated from each other, not connected to occipital foramen; six lateral stemmata arranged in two curved vertical rows at each side. Frontoclypeus subovate, with two spine-like egg bursters on posterior region; anterior margin rounded, somewhat projected forward.Antenna ( Figs 4–5 ): Short, robust, shorter than HW, composed of four antennomeres; A3 longest, with a rugged area on distal portion; A2 somewhat shorter than A3; A4 somewhat shorter than A2; A1 shortest, approximately one third length of A3. Mandibles ( Fig. 6 ) symmetrical, short, basal half robust, inner margin with strong subrectangular process, distal half curved inwards, slender, narrowing to pointed apex, inner margin smooth. Maxilla ( Figs 7–8 ): Cardo small, subovate; stipes well developed, subrectangular; bearing a galea on distal inner margin and a palpus on distal outer margin; galea well developed, second galeomere slender, about twice as long as first galeomere; palpifer not clearly differentiated from stipes, more evident in ventral view; palpus short, robust, composed of three palpomeres, MP1 and MP2 shortest, MP3 longest. Labium ( Figs 9–10 ): Prementum well developed, broader than long, anterior margin deeply indented medially; palpus short, robust, composed of two palpomeres, LP2 more than twice longer than LP1.

Thorax ( Fig. 1 ): Terga fully sclerotized, convex; pronotum about as long as meso- and metanotum combined, meso- and metanotum subequal in length, wider than pronotum; protergite subrectangular in dorsal view, lateral margins rounded, more developed than meso- and metatergite; ecdysial line absent on three tergites; meso- and metatergite with anterotransverse carina; prosternum with a slightly sclerotized plate between coxae; meso- and metathorax with minute non-functional spiracles. Legs ( Figs 11–12 ): Short, robust, composed of six articles, L1 shortest, L3 longest; coxa broad, elongate, trochanter lacking annulus, femur, tibia and tarsus short, subcylindrical, pretarsus with two long, slender, slightly curved claws, posterior claw shorter than anterior claw.

Abdomen ( Fig. 1 ): Eight-segmented; segments I–VII completely sclerotized, ring-like (except segment I membranous ventrally), progressively narrowing to apex, with minute, non-functional spiracles lateroventrally on anterior half; sclerites I–VII with anterotransverse carina; segment VIII ( Figs 13–14 ) the longest and narrowest, completely sclerotized except for a U-shaped wavy membranous area ventrally contiguous to urogomphi; sclerite VIII with anterotransverse carina; siphon short, slightly protruding. Urogomphi ( Figs 15–16 ): Very short, subcylindrical, slightly visible in dorsal view; not fused to each other proximally along inner margin.

Chaetotaxy: Similar to that of H. sharpi ( Urcola et al. 2019c) except for the following features: seta PA13 shorter than seta PA14 ( Fig. 2 ), setae MX 7 and MX 11 very short ( Fig. 8 ); anterior surface of TR with three spinose setae (TR2 and two additional setae) ( Fig. 11 ).

Instar II. As for instar I except for the following features:

Body: Measurements and ratios that characterize body shape are shown in Table 1 .

Head: Egg bursters absent; A2 somewhat longer than A3; mandible more robust.

Chaetotaxy: Frontoclypeus with 3–4 minute secondary setae on anterior portion and 3–5 minute secondary setae on posterior portion; dorsal surface of parietal with 1–2 secondary setae on anterior portion and 3–5 minute secondary setae on posterior portion; ventral surface of parietal with two hair-like secondary seta near seta PA18, three minute secondary setae on anterior portion, and two minute secondary seta near seta PA12; secondary leg setation detailed in Table 2 ; abdominal segments I–VII with several secondary setae; dorsal surface of abdominal segment VIII with three elongate hair-like secondary setae on anterior portion, one minute secondary seta near pore ABa and 3–4 minute secondary setae on posterior portion; ventral surface of abdominal segment VIII with three elongate hair-like secondary setae on anterior portion, one secondary pore near seta AB11 and three very slender hair-like secondary setae near lateral margin.

Instar III ( Figs 17–23 ). As for instar II except for the following features:

Body ( Figs 21–23 ): Measurements and ratios that characterize body shape are shown in Table 1 .

Head ( Fig. 17 ): Mandible more robust.

Chaetotaxy: Frontoclypeus with 2–3 minute secondary setae on anterior portion and 4–5 minute secondary setae on posterior portion; dorsal surface of parietal with 1–2 minute secondary setae on anterior portion and 1–2 minute secondary setae on posterior portion; secondary leg setation detailed in Table 2 and Figs 18–19 ; abdominal segments I–VII with several secondary setae.

Habitat. Adults and larvae of H.debilis were collected in a puddle near a trail at Iberá National Park, approximately 700 m from Provincial Road No. 40 ( 28°33′7.84″S, 57°12′47.58″W, elevation 67 m a.s.l). The sampling site was totally exposed to sunlight, had muddy bottom, shallow depth, and abundant emergent vegetation ( Fig. 24 ).

Comments regarding chaetotaxy

We were unable to find primary seta MX 16 on the galea in H. debilis . This small chaetic sensillum is present in both H. sharpi and H. socius , as well as in the noterid genera Suphis and Suphisellus Crotch, 1873 ( Urcola et al. 2020a, 2020b). Given the small size and position of this sensillum (near the apex of the galea), it is likely present in H. debilis although extremely difficult to observe. Similarly, the small campaniform sensillum located in the tarsus near the base of seta TA1 was not detected in H. debilis ; however, as this sensillum is present in both H. sharpi and H. socius ( Urcola et al. 2019c, 2020a), it is likely present in H. debilis as well. Finally, the primary pore MXd is present in larvae of H. debilis , located at the limit between the first and second galeomeres ( Fig. 8 ). Contrary to what was previously suggested ( Urcola et al. 2019a, 2019c, 2020a, 2021), this pore is also present (in about the same position as in H. debilis ) in H. sharpi , H. socius , and in the genera Suphisellus and Liocanthydrus Guignot, 1957 , but was erroneously coded as absent in these taxa. With regards to Suphis , according to Urcola et al. (2019b) pore MXd is present in a dorsal position towards the apex of the galea. However, we found this to also be a misinterpretation since the pore is present in the same position as in the other studied species. The sensillum coded as MXd in Urcola et al. (2019b) is most likely a different structure (probably the pore coded as MXh in other adephagans).

Figures

FIGURE 24. Habitat of Hydrocanthus debilis Sharp, 1882: puddle in Iberá National Park, Corrientes Province, Argentina.

FIGURES 1–3. Hydrocanthus debilis Sharp, 1882, instar I: (1) habitus, dorsal aspect; (2) cephalic capsule, dorsal aspect; (3) cephalic capsule, ventral aspect. Numbers and lowercase letters indicate primary setae and pores respectively. EB, egg burster; FR, frontoclypeus; PA, parietal; TP, tentorial pit. Scale bars = 0.50 mm for Fig. 1 and 0.10 mm for Figs 2–3.

FIGURES 21–23. Hydrocanthus debilis Sharp, 1882, instar III, habitus: (21) dorsal aspect; (22) ventral aspect; (23) lateral aspect. Scale bar = 0.50 mm.

FIGURES 4–10. Hydrocanthus debilis Sharp, 1882, instar I: (4) left antenna, dorsal aspect; (5) right antenna, ventral aspect; (6) left mandible, dorsal aspect; (7) right maxilla, dorsal aspect; (8) left maxilla, ventral aspect; (9) labium, dorsal aspect; (10) labium, ventral aspect. Numbers and lowercase letters indicate primary setae and pores respectively. AN, antenna; LA, labium; MN, mandible; MX, maxilla. Scale bars = 0.04 mm.

FIGURES 11–12. Hydrocanthus debilis Sharp, 1882, instar I: (11) left metathoracic leg, anterior aspect; (12) right metathoracic leg, posterior aspect. Numbers and lowercase letters indicate primary setae and pores respectively. CO, coxa; FE, femur; PT, pretarsus; TA, tarsus; TI, tibia; TR, trochanter. Scale bar = 0.10 mm.

FIGURES 17–20. Hydrocanthus debilis Sharp, 1882, instar III: (17) head, dorsal aspect; (18) left prothoracic leg, anterior aspect; (19) right prothoracic leg, posterior aspect; (20) abdominal segment VIII, dorsal aspect. Numbers and lowercase letters indicate primary setae and pores respectively. Scale bars = 0.20 mm.

FIGURES 13–16. Hydrocanthus debilis Sharp, 1882, instar I: (13) abdominal segment VIII, dorsal aspect; (14) abdominal segment VIII and urogomphi, ventral aspect; (15) urogomphi, dorsal aspect; (16) urogomphi, ventral aspect. Numbers and lowercase letters indicate primary setae and pores respectively.AB, abdominal segment VIII; U, urogomphus. Scale bars = 0.10 mm for Figs 13–14 and 0.04 mm for Figs 15–16.