Enochrus (Methydrus) vulgaris (Steinheil, 1869)

Byttebier, Barbara & Torres, Patricia L. M., 2009, Description of the preimaginal stages of Enochrus (Hugoscottia) variegatus (Steinheil, 1869) and E. (Methydrus) vulgaris (Steinheil, 1869) (Coleoptera: Hydrophilidae), with emphasis on larval morphometry and chaetotaxy, Zootaxa 2139, pp. 1-22 : 13-16

Enochrus (Methydrus) vulgaris (Steinheil, 1869)

( Figs. 2 , 7–10 , 18–21 , 24–25 , 28–29 , 31 )

Material examined. ARGENTINA: Buenos Aires City: “Golf Club Lagos de Palermo”, 3 breeding adults collected on 02.xi.2006 by B. Byttebier. Buenos Aires City: Ecological Reserve “Costanera Sur”; 6 breeding adults collected on 02.xi.2006 by B. Byttebier (10 egg cases, 17 instar I, 5 instar II and 7 instar III larvae, 3 pupae, 5 emerged adults).

Diagnosis. Larvae. Coronal sulcus short (instar I) or very short (instar III); left mandible with one inner tooth; AN10 and AN11 subapically on the second antennomere; stipes with MX 4–6 distally on outer margin, located on a longitudinal row; PA26 closer to PA27 than to PA17; sterna III–VII with a pair of prolegs, each one bearing a group of cuticular spine strongly curved as hooks.

Egg case ( Fig. 2 ). Total length = 4.34–6.75 mm, width = 1.91–2.36 mm; length without mast = 2.48–3.47; mast length = 1.86–4.09 mm.

Eggs, laid out without specific order pattern inside the egg case. (length = 0.52–0.67 mm, width = 0.27–0.35 mm). Number of eggs variable in each egg case, between 14 and 17 (N = 6).

First-instar larva ( Figs. 7–10 , 18 ). Morphometric measures detailed in Table 2 .

Color. Head capsule dark brown. Antenna, mandible and labium light brown. Maxilla light brown with maxillary palpomere darker in some specimens. Thoracic tergites dark brown, thoracic appendages light brown; membranous areas of the thorax grayish brown. Abdominal sclerites, urogomphi and lateral appendages of abdominal segment VIII dark brown; membranous areas of the abdomen grayish brown.

Head capsule ( Figs. 7–10 ). Coronal sulcus short. Mandible. Left mandible with one inner tooth.

Thorax. Prosternum composed by one undivided plate with a basal notch.

Abdomen. Sterna III–VII with a pair of prolegs, each proleg bearing a group of cuticular spine strongly curved as hooks ( Fig. 31 ).

Chaetotaxy ( Figs. 7–10 , 18 ). Head capsule ( Figs. 7–10 ). Ventral surface ( Fig. 10 ) of each parietale, with sensilla PA26–PA28 located on a longitudinal row, very close to each other (PA26 closer to PA27 than to PA17). Antenna ( Fig. 18 ). AN10 and AN11 situated subapically on outer margin of second antennomere.

Maxilla. Stipes with MX 4–6 located distally on outer margin, on a longitudinal row. Labium. LA2 located on the membranous area between submentum and mentum ( Fig. 10 ); LA6 very long (1/3 longer than in E. variegatus ). Legs. Ligula without apical processes. Chaetotaxy of legs summarized in Table 3.

Second-instar larva. Similar to first-instar larva except for the following features.

Morphometric measures detailed in Table 2 .

Chaetotaxy. Head capsule. Parietale with 10–12 secondary sensilla: 3 setae and 1 pore close to PA8–PA9; 4–5 setae on the lateral margin; a row of 2–3 setae between PA6 and PA7. Mandible. With 5–7 secondary sensilla. Labium. Ligula without minute process apically ( Fig. 24 ). Legs. Chaetotaxy summarized in Table 3.

Third-instar larva ( Figs. 19–21 , 24–25 , 28–29 , 31 )

Similar to second-instar larva except for the following features.

Morphometric measures detailed in Table 2 .

Head capsule ( Fig. 21 ). Coronal sulcus short or very short, in general difficult to distinguish.

Thorax. Prosternum composed by one subdivided plate with an incomplete sagittal line on more than the basal third.

Chaetotaxy ( Figs. 19–21 , 24–25 , 28–29 ). Head capsule. Each parietale with 9–11 secondary sensilla: 3 setae and 1 pore close to PA8–PA9; 4–5 setae on the lateral margin; a row of 1–3 setae between PA6 and PA7. Mandible ( Figs. 19–20 ). With 7–8 secondary sensilla. Labium ( Figs. 24–25 ). Each lateral margin of mentum with 4 stout secondary setae. Legs ( Figs. 28–29 ). Chaetotaxy summarized in Table 3.

Pupa. Body. TL (excluding pronotal styli and cerci) = 3.25–4.40 mm; MW = 1.14–1.59 mm.

Head. Maxillary palpi extending to first abdominal segment.

Abdomen. Segment I with 2 pairs of styli situated on a transversal row.

Figures

FIGURES 1 – 2. Egg cases of Enochrus: 1, E. variegatus; 2, E. vulgaris. Scale bar = 1.0 mm.

FIGURES 7 – 10. Enochrus vulgaris, first-instar larva: 7, head capsule, lateral view; 8, head capsule, dorsal view; 9, frontoclypeus, dorsal view; 10, head capsule, ventral view. Scale bars: Figs. 7 – 8 = 0.1 mm, Fig. 9 = 0.05 mm, Fig. 10 = 0.1 mm.

FIGURES 18 – 21. Enochrus vulgaris, first-instar larva: 18, right antenna, dorsal view. Enochrus vulgaris, third-instar larva: 19, left mandible, dorsal view; 20, right mandible, dorsal view; 21, head capsule, dorsal view. Scale bars: Figs. 18 – 20 = 0.05 mm, Fig. 21 = 0.1 mm.

FIGURES 22 – 25. Enochrus variegatus, third-instar larva: 22, labium, dorsal view; 23, labium, ventral view. Enochrus vulgaris, third-instar larva: 24, labium, dorsal view; 25, labium, ventral view. Scale bars = 0.05 mm.

FIGURES 26 – 29. Enochrus variegatus, legs of first-instar larva: 26, prothoracic leg, anterior view; 27, prothoracic leg, posterior view. Enochrus vulgaris, legs of third-instar larva: 28, metathoracic leg, anterior view; 29, metathoracic leg, posterior view. Scale bars = 0.05 mm.

FIGURES 30 – 31. Enochrus variegatus, prolegs of third-instar larva: 30, proleg bearing a group of cuticular spines. Enochrus vulgaris, prolegs of third-instar larva: 31, proleg bearing a group of hooks. Scale bar = 0.05 mm.