Phileurus angustatus, Kolbe, 1910

Ibarra-Polesel, Mario G., Valle, Nestor G., Cave, Ronald D. & Damborsky, Miryam P., 2021, Description of the Larva of Phileurus angustatus Kolbe, 1910 (Coleoptera: Scarabaeidae: Dynastinae: Phileurini), with Notes on Natural History and a Key to the Known Larvae of New World Phileurini, The Coleopterists Bulletin 75 (2), pp. 459-471 : 461-466

PhILEURUS aNGUStatUS Kolbe, 1910

Third instar

( Figs. 1–14 )

Description. Dorsal bodY length 96.2–102.1 mm, width 14.3–14.7 mm, weight 6.6–6.9 g (preserved specimens). Cranium: Head capsule width 6.3–6.9 mm ( Fig. 1 ). Color Yellowish brown/orange brown. Surface with rugae and a fine shagreen. Frons with small, shallow pits sparselY and irregularlY over anterior third. Epicranial, frontal, and clypeofrontal sutures distinct. Small, dark area present on each side of epicranial area, close to epicranial suture and at level of posterior frontal setae. Frons: With 4–6 anterior setae, 2 exterior setae, and 4–6 posterior setae; each anterior angle with 1–2 long setae and 1–2 short setae ( Fig. 1 ). Remaining cranial surface with 2–4 anterior epicranial setae; 4–8 dorsoepicranial setae on each side, 8–11 exterior epicranial setae near each stemma and 5–9 posterior epicranial setae on each side. Non-pigmented stemmata present. Clypeus: Trapezoidal ( Fig. 1 ). PostclYpeus well-sclerotized, with 2 anterior setae and 1–2 exterior setae on each side. Punctures smaller than those on frons. PreclYpeus dark brown, lacking punctures. Labrum: SlightlY asYmmetrical, with some discal punctures similar to those on postclYpeus, with 6–14 posterior setae, 2 paramedian setae, 2 anterior setae, and 1 external seta on each side ( Fig. 1 ). Epipharynx: Transversely suboval, left lateral margin angulate ( Figs. 2A, B ). Haptomeral process prominent and entire. Right chaetoparia with 48–62 setae, left chaetoparia with 45–52 setae, with about 20 sensillae interspersed among setae, mainly on right chaetoparia. Acroparia with 16–22 straight, long, thick setae; corYpha with 5–8 long setae; right and left acanthoparia with 7–9 short, curved, spine-like setae. Pedium 1.5 times longer than width, without setae. Dexiotorma narrow, elongate; laeotorma shorter than dexiotorma; pternotorma well-developed, rounded. Dexiophoba and laeophoba absent; mesophoba between haptolachus and inner side of laeotorma, formed bY 6–11 slender setae. Sclerotized plate of right nesium well-developed, acute at apex, with 4–8 setae on base. Sense cone on left nesium represented bY longitudinal, well-sclerotized plate and with 2 lateral sensillae on each side. Crepis poorly defined. Antenna: Four antennomeres, 1–2 subequal in length. Antennomeres 1, 2, and 3 about 1.2, 1.4, and 1.1 times longer, respectively, than terminal antennomere ( Fig. 3A ). Antennomere 3 with a distal process. Dorsal surface of terminal antennomere with 2–3 dorsal sensory spots ( Fig. 3B ), ventral surface with 4–6 sensorY spots ( Fig. 3C ) and a sensorY spot at apex. Left mandible: Form falcate ( Figs. 4A–C ). Scissorial region with 4 teeth, teeth S1 and S2 forming a broad apical plate, separated from S3 by a scissorial notch. Tooth S3 separated from S4 by deep postincisor notch. S4 subconical, with acute apex. Scrobis with 6 long, stout setae and 2–4 slender, short setae. Acia well-developed, acute, with about 8 basolateral setae. Dorsal surface with 2 long, stout setae on dorsal carina at level of S3–S4 notch and tooth S4; dorsomolar area with row of 8–12 slender setae. Preartis distinct, concave. Ventral surface with elongate-oval stridulatorY area formed bY 42–48 narrowlY separated, subparallel ridges. Molar area with tuft of 8–11 ventromolar setae. Three molar lobes present, first molar lobe (M1) large, not sub- divided and below 2 acute lobes. Brustia with 14–20 stout, long setae. Postartis large, rounded. Ventral process securiform, well- developed, with manY asperites. Right mandible: Form falcate ( Figs. 5A–C ). Scissorial area with blade-like, apical tooth (S1 + S2 fused), separated from S3 by scissorial notch. S4 below notch, entire, subconical. Scrobis with 6 long, stout setae and 2–3 slender, short setae. Dorsal surface with 2 long, stout setae on carina at level of S3 and S4. Dorsomolar area with row of 10–12 slender setae. Preartis distinct, concave. Ventral surface with elongate-oval stridulatorY area formed bY 42–46 narrowlY separated, subparallel ridges. Molar area with tuft of 6–10 ventral molar setae. Calx large, molar crown with 3 large lobes. Ventral process well-developed, apicallY rounded, caudallY angled, with manY asperites. Brustia with 8–12 stout, long setae. Postartis large, rounded. Maxilla: Galea and lacinia fused, forming a mala. Galea dorsallY with 3–4 stout, long setae and 12 slender, short setae. Uncus well-developed, approximatelY 0.6 times length of apical maxillarY palpomere ( Fig. 6A ). Lacinia with 3 unci, first 2 teeth fused at their bases ( Fig. 6B ); dorsal area with approximatelY 23 spine-like setae. MaxillarY palpus with 4 palpomeres; palpomeres 1, 2, and 3 about 0.4, 0.6, and 0.5 times, respectively, length of palpomere 4. Stridulatory area formed by 7–9 blunt, truncate teeth, truncate anterior process well-developed ( Fig. 6C ). Labium: Hypopharyngeal sclerome asymmetrical, medially concave; right side with well-developed, truncate process, forming a right angle on inner side ( Fig. 7A ); left side with well-developed basal process ( Fig. 7B ). Glossa with 32–45 long setae, 16–36 short, spine-like setae, and approximatelY 12 sensillae. Left lateral lobe with 16–20 slender, moderatelY long setae; right lateral lobe with 14–18 slender setae. Left margin with row of 22–28 setae grouped in a compact line, directed toward center of sclerome and a row of approximatelY 6–10 setae near base of sclerome. Thorax: Pronotum with 16–20 sparse, long setae, sclerotized area with 1 long, stout seta on superior-posterior region, and 2 short, thin setae arranged 1 above and 1 below the long seta ( Fig. 9 ). Prothoracic spiracle 0.86– 0.78 mm long, 0.51–0.56 mm wide ( Fig. 10 ; Table 2); respiratorY plate Yellowish brown, closed C-shaped, spiracular bulla rounded, barelY elevated; distance between 2 lobes of respiratory plate much smaller than dorsoventral diameter of bulla. Plate with 38–42 microscopic pores in dorsal radius ( Fig. 14B ), 28–34 in lateral radius ( Fig. 14C ), 46–50 in basal radius ( Fig. 14D ). Pores entirelY margined, forming slightlY defined rows in internal areas of plate ( Figs. 14A–D ). Prescutum and scutum of meso- and metathorax with setae; mesoscutellum without seta, metascutellum with short seta (see Table 2). Legs: Tarsal claws falcate, with 1 basoexternal seta and 1 internal, preapical seta ( Fig. 11 ). All tarsal claws of similar size (0.54–0.61 mm). Legs graduallY increasing in length from 1 st to 3 rd pair ( Fig. 12 ). Coxa, trochanter, femur, and tibia of all legs with manY long, stout setae.

Abdomen: Abdominal spiracles on segments I–VIII of subequal size. Spiracle I 0.75 mm long and 0.51 mm wide ( Fig. 10 , Table 2), narrower than spiracle VIII (0.73 mm long and 0.61 mm wide) and smaller than spiracles II–VII. Spiracles on segments II–VII of subequal length (0.80–0.82 mm) and pro- gressivelY wider (II: 0.55 mm; VII: 0.69 mm). Long setae present on scutum of abdominal segments I– VIII, prescutum of segments I and VIII, and scutellum of segment VIII ( Fig. 8 ; Table 2). Segments IX and X with numerous short setae and sparse, widelY separated, long setae. Raster: Surface without palidia; campus with 6–12 slender, long setae; barbula with 10–16 long, widelY separated setae on each side ( Fig. 13 ). Teges with 36–56 setae projecting towards anal slit; ventral anal lip with 36–44 hamate setae; anal margin with 10–18 long, cYlindrical setae. Dorsal anal lip (apical margin of segment X) with 78–96 short, flattened setae curved mediallY and 10–18 long, cylindrical setae. Anal slit transverse.

Natural History. In Argentina, adults of P. angustatus are frequentlY captured with light traps in riparian forests ( Figs. 15, 16 ), but theY have also been collected among stands of Copernicia alba Morong ( Arecaceae ) and in forests of quebracho [ Schinopsis sp. ( Anacardiaceae )] ( Figs. 17, 18 ). Larvae of P. valgus are also found in rotten palm trunks of C. alba ( Ibarra-Polesel et al. 2017) , which suggests that, in this environment, adults and larvae of P. angustatus and P. valgus could be sharing the same resource. In northeastern Argentina, adults have been collected during September, October, November, December, JanuarY, and March. Immatures and adults have been observed together during December.

Dechambre (1998) cited observations by M. Couturier, who mentioned Oenocarpus mapora Karsten (Arecacae) , a palm grown bY EMBRAPA (Brazilian Agricultural Research Corporation) in eastern Amazonia, as a host of P. angustatus . The larvae developed in unopened areas of the palm that were previouslY attacked bY several species of Curculionidae ( Coleoptera ) that destroyed the living tissues of the inflorescence, leaving a “breeding ground” favorable for the development of P. angustatus .

The three larvae found in the trunk of I. verna were parasitized bY endoparasitic flY larvae ( Diptera : Tachinidae ) that caused the death of the beetle larvae 7–10 days after collection. In one of the P. angustatus larvae, six maggots were found, most of which were located in the thoracic zone and the first abdominal segments. The endoparasitoids were found with the oral region facing the internal area of the beetle and the pedicel of the spiracle (apex of the abdomen) attached to the integument of the larva, leaving a sclerotized area at this junc- tion superficially visible ( Fig. 19 ).

The larval stages of several species of Scarabaeidae are known to be parasitized bY ecto- or endoparasites of numerous species of Diptera . Albertoni et al. (2014) found a species of Mystacella van der Wulp ( Diptera : Tachinidae ) parasitizing larvae of P. felscheanus Ohaus. Castelo and Capurro (2000) studied the preference of larval Mallophora ruficauda Wiedemann ( Diptera : Asilidae ) for larvae of Cyclocephala signaticollis Burmeister ( Coleoptera : Scarabaeidae : DYnastinae), which had a high probabilitY of being parasitized even when larvae of other scarab beetles were accessible to the asilid. Ramírez-Salinas et al. (2006) reported on the specificity of the endoparasitoid Cryptomeigenia sp. ( Diptera : Tachinidae ) to adults of Phyllophaga rufotestacea (Moser, 1918) ( Coleoptera : Scarabaeidae : Melolonthinae), despite 15 other scarab beetle species occurring in the area. Other studies on cYclocephaline scarab beetle larvae subjected to parasitism by flies are cited by Moore et al. (2018).

Based on previous experience, we offered balanced dry cat food (protein) to a captive adult female of P. angustatus that consumed the food repeatedlY. However, the adults of P. angustatus possiblY have predatorY habits. We also fed P. valgus adults with cat food, since theY were observed in the laboratory preying on larvae of Leucothyreus costatus chaconus Ohaus ( Coleoptera : Scarabaeidae : Rutelinae ) and adults of Stenocrates holomelanus (Germar) ( Coleoptera : Scarabaeidae : DYnastinae) ( Ibarra-Polesel et al. 2017). The predatory behavior of P. valgus was first reported bY Velázquez et al. (2006), who mentioned this species as a natural enemY of the agave weevil ( Scyphophorus acupunctatus GYllenhal ; Coleoptera : Curculionidae ). Other studies have also reported predatory behavior by other phileurine species ( McCleve 2007; Neita and Ratcliffe 2010; Ratcliffe and Morón 1997).

Figures

Figs. 1–3. Phileurus angustatus, third instar. 1) Cranium, frontal view; 2) EpipharYnx (A) and detail in apical view

Figs. 4–7. Phileurus angustatus, third instar. 4) Left mandible, dorsal view (A), lateral view (B), and ventral view (C); 5) Right mandible, ventral view (A), lateral view (B), and dorsal view (C); 6) Right maxilla, dorsal view (A), apex of mala showing unci (B), and detail of stridulatorY teeth of maxilla (C); 7) Dorsal view of labium (A) and detail of hypopharyngeal sclerome (B).

Figs. 8–13. Phileurus angustatus, third instar. 8) Habitus, lateral view; 9) Detail of sclerotized area of pronotum; 10) Thoracic spiracle (Th) and sequence of abdominal spiracles from first (Ab I) to last (Ab VIII) segment; 11) Claws, dorsal view, from pro-, meso-, and metathoracic legs; 12) Pro-, meso-, and metathoracic legs, lateral view; 13) Apical abdomi- nal segments, dorsal view.

Fig. 14. Phileurus angustatus, third instar. Thoracic spiracle (A) and detail of microscopic pores on the dorsal (B), lateral (C), and basal (D) areas of plate.

Figs. 15–20. 15) Adult Phileurus angustatus on trunk of Copernicia alba near light trap. Typical habitats of P.angustatus in northeastern Argentina: 16) Riverside forest; 17) C. alba palm grove; 18) Quebracho forest, Schinopsis sp. 19) Endoparasitic flY larva (arrow indicates spiracular pedicel) inside larva of P. angustatus; 20) Habitus of endoparasitic flY larva, ventral view (A), lateral view (B), dorsal view (C), and detail of spiracles (D).