Phileurus valgus (Olivier, 1789)

Ibarra-Polesel, Mario G., Valle, Nestor G., Neita-Moreno, Jhon C. & Damborsky, Miryam P., 2017, Description of the pupa and redescription of the third instar of Phileurus valgus (Olivier) (Coleoptera: Scarabaeidae: Dynastinae: Phileurini), Zootaxa 4290 (3), pp. 571-580 : 572-578

Phileurus valgus (Olivier, 1789)

( Figs. 1–14 )

Third instar. Dorsal body length 74.9 mm, width 10.7 mm, weight 2.9 g. Cranium ( Fig. 1 ): Width of head capsule 4.6–5.1 mm. Color yellowish brown/orange brown. Surface with wrinkles and a fine chagrin. Frons with small, shallow pits sparsely and irregularly over the anterior third. Epicraneal, frontal, and clypeofrontal suture distinct. Frons ( Fig. 1 ): Surface with 4 anterior frontal setae and 1–2 exterior frontal setae; each anterior angle with 1–2 setae and 4–6 posterior frontal setae. Remaining cranial surface with 4–6 dorsoepicranial setae on each side, 24–30 epicranial setae distributed irregularly or in row, and 3 paraocellar setae on each side. Ocellus absent. Clypeus ( Fig. 1 ): Form trapezoidal. Surface of postclypeus yellowish brown, well sclerotized, with punctures smaller than those on frons; with 2 central setae and 2 lateral setae on each side. Surface of preclypeus light brown and without punctures. Labrum ( Fig. 1 ): Slightly asymmetrical, with some discal punctures similar to those of postclypeus, with 12 posterolateral labral setae, 1 lateral seta on each side and 2 central setae. Epipharynx ( Fig. 2 ): Form transversely suboval, asymmetrical, left and right lateral margins angulate. Haptomeral process prominent and entire. Right chaetoparia with 59 setae; left chaetoparia with 51 setae; with some sensillae between the setae. Acroparia with 22 straight, long, thick setae; corypha with 8 slender, long setae; right and left acanthoparia with 6– 9 short, curved, spine-like setae. Pedium longer than wide, without setae. Dexiotorma narrow, elongate; laeotorma slightly shorter than dexiotorma. Epitorma curved on to disc of pedium, pternotorma rounded. Dexiophoba and laeophoba absents; haptolachus with 5–8 small, slender setae. Sclerotized plate of right nesium slender, acute at apex. Sense cone on left nesium represented by longitudinal, well-sclerotized plate and with some lateral sensillae. Crepis poorly defined. Left mandible ( Fig. 3 A–C): Form falcate. Scissorial region with 4 teeth, apical tooth (S1 + S2 fused), separated from S3 by scissorial notch, S4 below notch. Scrobis with 6–9 slender, long setae. Acia welldeveloped, sharp, with 3 basolateral setae. Dorsal surface with 1 stout, long setae at level to S3–S4 notch; dorsomolar area with row of 3–4 stout, slender, moderately long setae. Preartis distinct, concave. Ventral surface with elongate-oval stridulatory area formed by 54 narrowly separated, subparallel ridges. Ventral process well developed, rounded, with many asperites. Brustia with 7–10 stout, long setae. Molar area with 3 lobes, first molar lobe (M1) large. Postartis large, rounded. Right mandible ( Fig. 4 A–C): Form falcate. Scissorial area with bladelike, apical tooth (S1 + S2 fused), separated from S3 by scissorial notch, S4 below notch. Scrobis with 5–8 slender, long setae. Dorsal surface with 2 stout, long setae at level to S3 and S4; dorsomolar area with row of 3–6 setae. Preartis distinct, concave. Ventral surface with elongate-oval stridulatory area formed by 52 narrowly separated, subparallel ridges. Molar area with a tuft of 8–11 ventral molar setae. Ventral process well developed, broadly rounded, with many asperites. Brustia with 8–12 stout, long setae. Calx large, molar crown with 3 large lobes. Postartis large, rounded. Maxilla ( Fig. 5 A): Galea and lacinia fused, forming mala. Galea with 6–9 stout setae and 1 well developed uncus at apex, about 0.6 times as long as last segment of maxillary palp. Lacinia with many stout setae and 3 unci fused at their bases ( Fig. 5 B). Maxillary palpus with 4 palpomeres, palpomere 4 twice as long as palpomere 3. Stridulatory area formed by 4–7 blunt, truncate teeth and a wide, truncate anterior process ( Fig. 5 C). Cardo subrectangular. Labium ( Fig. 6 ): Hypopharyngeal sclerome asymmetrical, concave medially; right side with well-developed, apical, truncate process; left side with well-developed posterior process. Glossa with 26–30 long and 28–30 short setae. Left lateral lobe with 14–16 slender, moderately long setae; right lateral lobe with 8–12 slender, moderately long setae. Left margin with row of 22–28 stout, moderately long setae directed toward center of sclerome and 8 setae near base of sclerome. Antennae: With 4 antennomeres, antennomeres 1–2 and 3–4 subequal in length, antennomere 3 extended into an obtuse process at distal end; terminal antennomere about 0.85 times as long as antennomere 2. Terminal antennomere on dorsal surface with 2–4 sensory spots ( Fig. 7 A–C), ventral surface with 3–5 sensory spots ( Fig. 7 D). Thorax: Pronotum wide, irregularly and weakly sclerotized, with 22 slender, long setae and 9 short, spine-like setae ( Table 1). Prothoracic spiracle 0.55 mm long, 0.38 mm wide ( Fig. 8 A), slightly larger than abdominal spiracle I ( Fig. 8 B); respiratory plate yellowish brown, regularly shaped as a closed “C”, spiracular bulla rounded, slightly prominent; lobes of respiratory plate slightly separated; plate with 30–35 holes across diameter at middle, holes with regular edges ( Fig. 8 B). Mesonotum and metanotum with variable number of setae ( Table 1). Legs: Tarsal claws with enlarged apical process, 1 basoexternal seta, and 1 internal, preapical seta ( Fig. 9 A–C). All tarsal claws similar in size ( Fig. 9 D–F). Coxa, trochanter, femur, and tibiotarsus of all legs with many long, stout setae. Abdomen ( Fig. 10 ): Abdominal spiracle I 0.54 mm long and 0.34 mm wide ( Fig. 8 B), shorter than spiracles II–VII. Spiracles on segments II and IV subequal in size (0.58 mm long and 0.40 mm wide), slightly longer and less wide than spiracles on segments V–VII (0.55 mm long and 0.42 mm wide). Spiracle VIII shorter than spiracle on segments II–VII (0.51 mm long and 0.39 mm wide). Abdominal segments I–VII each with 7–31 setae on prescutum; 2–5 setae on subscutum; 24–37 setae on scutum; 14–32 setae on scutellum; 4–8 setae on spiracular area, and 8–12 setae on pleural lobe (Table I). Abdominal segments VIII–X with sparse, minute setae. Raster ( Fig. 11 ): Surface without palidia; campus with 2–4 slender, long setae; teges with 24–26 short setae that project toward superior anal lobe; barbula with 22 long, slender setae. Anal slit transverse.

Second instar. Head capsule 2.6–2.9 mm, chaetotaxy similar as larvae of third instar, anterior frontal setae present. Terminal antennomere with 6–9 sensory spots. Prothoracic spiracles 0.25 mm long, 0.14 mm wide. Abdominal spiracles progressively more rounded (0.23– 0.18 mm long, 0.14–0.18 mm wide). Approximate dorsal body length 36.4 mm.

Segment Tergum Long, slender setae Short, spine-like setae Pronotum 22 9

Mesonotum Prescutum 3 2

Scutum 17 6

Scutellum 0 0

Metanotum Prescutum 4 2

Scutum 18 6

Scutellum 0 0

Abdominal segment I Prescutum 1 6 Scutum 20 4 Subscutum 1 1 Scutellum 0 14 Spiracular area 5 0 Pleural lobe 8 0 Abdominal segment II Prescutum 0 22 Scutum 7 25 Subscutum 1 1 Scutellum 0 24 Spiracular area 5 0 Pleural lobe 11 0 Abdominal segment III Prescutum 0 18 Scutum 6 26 Subscutum 2 2 Scutellum 0 21 Spiracular area 2 4 Pleural lobe 10 2 Abdominal segment IV Prescutum 0 19 Scutum 6 23 Subscutum 1 3 Scutellum 0 24 Spiracular area 1 3 Pleural lobe 0 9 Abdominal segment V Prescutum 0 24 Scutum 6 31 Subscutum 1 4 Scutellum 0 32 Spiracular area 4 2 Pleural lobe 10 0 Abdominal segment VI Prescutum 0 31 Scutum 7 22 Subscutum 2 1 Scutellum 3 16 Spiracular area 6 2 Pleural lobe 10 0 Abdominal segment VII (Two row) 5 30 Spiracular area 7 0 Pleural lobe 8 0 Abdominal segment VIII (Two row) 6 31 Spiracular area 7 0 Pleural lobe 8 0 Abdominal segment IX 22 37 Abdominal segment X 13 42 First instar. Similar to second and third instars. Head capsule 1.8 mm, dorsal body length 15.4 mm. Terminal antennomere shorter than antennomeres 1–2, and subequal to antennomere 3. Eclosion spine on each side of metanotum conical, with acute apex, small (0.08 mm). Thoracic and abdominal spiracles kidney shaped, similar in size: 0.11–0.09 long, 0.08– 0.07 mm wide, without definite bulla.

Male pupa ( Figs. 12 A–C). Length 23.8– 22.6 mm; greatest width 11.2– 9.7 mm. Adecticous, exarate, body elongate, oval, stout. Color yellowish brown. Head: Surface glabrous, mouthparts directed ventrally; antenna, labrum, mandibles, maxillae and palps discernible; antennal tecae expanded, stout, with apices rounded. Compound eyes sunken, partially covered by the anterior edges the pronotum, with 2 tubercles between eyes. Thorax: Pronotal surface glabrous. Form transverse, with wide, anteromedial, round apex. A narrow, median and longitudinal sulcus extending from apex to base. Mesonotum and Mesonotum well differentiated. Elytral and posterior wing tecae appressed, curved ventrally around body; elytral tecae extending to middle of abdominal segment II–III; posterior wing tecae extending to the end of abdominal segment III–IV. Legs: Protibia with 3 distinct teeth on external edge and with tubercle-like apical spurs. Mesotibiae and metatibiae with inner and external spines well developed at apices. Mesotibiae and metatibiae each with inner well developed; apex of metatibia with 2 visible teeth. Metafemur and metatibia covered by elytra and wings. Tarsomeres and pretarsus not distinct. Abdomen: Segments III–X (ventral view) well defined, sternite III and IV are the widest, intersegment VII–VIII, VIII–IX, and IX–X poorly defined. Segment X with genital ampulla (male). In dorsal view, segments I– IX well defined, dioneiform organs between segments I–II, II–III, III–IV, IV–V, V–VI, and VI–VII, the first strongly sclerotized. Pleural lobes rounded. Spiracle I elongate, with fine peritreme, partially covered by wing tecae; spiracles II–IV ovate, prominent, each with strongly sclerotized peritreme; spiracles V–VIII closed. Abdominal apex rounded, with fine, short setae. Genital ampulla sub-trapezoidal, at basal area a sclerotized structure in “U” shape, with basal notch ( Fig. 13 ).

Female pupa. Length 25.2– 19.7 mm; greatest width 12.1– 10.3 mm. Same characteristics as in male, but apical area of tergite 9 slightly shorter than in male. Sternite IX anteriorly convex in males, in females with subtrapezoidal shape and 2 small lateral lobes in basal area. Genital pore a “W” shape. Genital ampulla with base slightly sclerotized ( Fig. 14 ).

Life cycle and natural history. Our results based on field and laboratory work showed that P. valgus on the Argentina northeast has a bivoltine life cycle ( Fig. 15A ). That seems to be associated with precipitation and the increase in temperature ( Fig. 15 B). Under laboratory conditions, the duration of third instars was 38–42 days (n = 21), pre-pupa 6–9 days (n = 13), pupa 11–13 days (n = 8), and the adults lived three months (n = 7). Our results were similar to those reported by Garcia et al. (2013) from Brazil. In the C. alba palm grove, however, was observed a faster development of immatures, which could be attributed to higher average temperature in field.

In the laboratory, most larvae began pupation when they reached a weight of approximately 3 g. Before pupation, larva builds a cocoon with sawdust and its own excrement, and remains within it. The larval exuvia is pushed to the rear of the pupal chamber. In the field during March, several pre-pupae and pupae were found dead in their camera, days after intense rainfall, perhaps because of the high humidity in the rotting wood.

The adults were captured with a light trap in September, January, February, and March; immatures and imagoes were observed together in November and December ( Fig. 15 ). Laboratory specimens that emerged in April lived to July. We believe that in the field, however, the adults could have a longer life span, because a wider range of microhabitats and food resources are available. The adults collected in September showed a great wear on their cuticle, which suggest that these are specimens with a considerable lifespan. Therefore, adults could be present all year long, although their activity is limited to the warmer months. Ratcliffe (2011) mentions that adults have been captured every month of the year, and Morelli (1990) collected adults of P. affinis from October to late March.

In the laboratory, adults were observed preying on larvae of Leucothyreus costatus chaconus Ohaus ( Coleoptera : Scarabaeidae : Ruteliane), and adults of Stenocrates holomelanus (Germar) ( Coleoptera : Scarabaeidae : Dynastinae ). For that reason, we offered balanced dry cat food (protein) to the adults, which they accepted and consumed throughout the adult stage. The predatory habitus of P. valgus were documented by Velázquez et al. (2006), who observed adults consume 1–3 Scyphophorus acupunctatus larvae per day. Other studies also cited predatory behavior in other Phileurini species ( Ratcliffe & Morón 1997; McCleve 2007; Neita & Ratcliffe 2009, 2010).

Figures

FIGURE 15. A, Phileurus valgus development seasonality of larval stadium (L 1 = first instar, L 2 = second instar and L 3 = third instar), pupal, and adult stages under laboratory conditions and in the natural environment (a Copernicia alba Morong (Arecaceae) palm grove) between September 2014 to August 2015 in Chaco, Argentina. B, Historical data (1968 – 2015) of average temperature and rainfall records of the study area.

FIGURES 1 – 7. Phileurus valgus, third instar. 1, Cranium, frontal view; 2, epipharynx; 3, left mandible, dorsal view (A), lateral view (B), and ventral view (C); 4, right mandible, ventral view (A), lateral view (B), and dorsal view (C); 5, left maxilla, dorsal view (A), apex of mala showing unci (B), and stridulatory teeth of maxilla (C); 6, dorsal view of labium; 7, terminal segment of antenna in dorsal view, with four (A), three (B), and two (C) sensory spots and ventral view of terminal segment (D).

FIGURES 8 – 11. Phileurus valgus, third instar. 8, Spiracles, prothoracic (A), first abdominal (B), and spiracular holes (C); 9, prothoracic (A), mesothoracic (C), and metathoracic (E) claws in dorsal view, and lateral view of protarsus (B), mesotarsus (D), and metatarsus (F); 10, third instar, entire body in lateral view; 11, terminal abdominal segment, ventral view.

FIGURES 12 – 14. Phileurus valgus, pupa. 12, Male pupa in dorsal view (A), ventral view (B), and lateral view (C); 13, male pupa, ventral view of apex with genital ampulla; 14, female pupa, ventral view of apex with genital ampulla.