Dynastes neptunus Quenzel

Onore, Giovanni & Morón, Miguel-Angel, 2004, Dynastes neptunus Quenzel (Coleoptera: Scarabaeidae: Dynastinae); Descriptions of the Third Instar Larva and Pupa, with Notes on Biology, The Coleopterists Bulletin 58 (1), pp. 103-110 : 106-109

Dynastes neptunus Quenzel , pupa

( Figs. 17–18 )

The description is based on 5 pupae (2 males, 3 females) reared from larvae collected at Ecuador: Cotopaxi, San Francisco de Las Pampas, 3-VII-2002, C. Tapia , inside hollow trunk of ‘‘canelo’’ tree ( Ocotea sp. Lauraceae ) 1,600 m (QCAZ; IEXA).

FEMALE ( Fig. 17 ). Body shape elongate, oval, stout, exarate. Color yellow reddish. Entire body with fine velvety-gold vestiture.

HEAD. Bent sharply beneath thorax. Clypeus tumid, bilobed, with an anterior central ‘‘Y’’ shaped depression. Frons with lateral depression at each side clearly separated. Eyes well defined but partially hidden. Antenna widened, stout, with 3–4 defined rings. Labrum semitrapezoidal, rounded, short (1.8 3 wider than long) with an anterior central, small depression. Mandibles wide and prominent. Maxilla long and stout. Maxillary palpi conical, with 4 rings. Apex of the labium cordiform with a middle depression. Labial palpí rounded with 3 rings.

THORAX. Pronotum nearly transverse; disk irregular, tumid, with an anterior central callus and the ecdysial suture clearly marked. Pronotal anterior border widely sinuated; posterior border slightly bisinuated. Pronotal anterior angles straight, stout, prominent; posterior angles widely rounded. Meso- and metanotum with ecdysial suture clearly marked. Prosternal process subtrapezoidal and much evident. Mesosternum hidden. Metasternum surface slightly irregular. Elytral tecae narrowed, closely appressed, curved ventrally around body, with some coarse striae. Protibia with 3 projections on exterior border, and recognizable subapical spur. Tarsomeres delineated.

ABDOMEN. Nine visible segments. Spiracles of segment I hidden by elevated oblique fold, ovateelongate, reddish chestnut, with narrow, sclerotized, flattened, asymmetrical peritreme. Spiracles on segments II–IV ovate-elongate (0.9 mm width, 2.0 mm length), reddish chestnut, with narrow, sclerotized, prominent, asymmetrical peritreme. Spiracles on segments V–VII occluded, rosetiform, without sclerotized peritreme, not pigmented; spicrales on segment VIII absent. Tergal area of segments II–VII with 5 pairs of deep and wide dioneiform organs. Tergal area of segment VIII with 2 kidney-shaped, deep impressions. Last segment with 2 symmetrical, fleshy ventrolateral folds covered by dense, fine, golden vestiture, longer than in other parts of the body. Sternite II short, triangle-like, hidden between metacoxae. Sternites III–VI convex, with similar length. Sternites VII and VIII fused at the middle third. Sternite IX and genital ampulla small, partially retracted under last tergum. Body length 65–72 mm.

MALE ( Fig. 18 ). Fronto-clypeal area with long, narrowed, curved upward, horn-like projection, longer than pterothorax and abdomen. Pronotum with posteromedial long, narrowed, curved downward, horn-like projection, nearly as long as the frontoclypeal projection. Antero-lateral area of pronotum with 2 spine-like, stout projections. Genital ampulla large, swollen. Otherwise similar to female. Length including horn-like projections 110–139 mm.

Biological Observations. In Ecuador, Thierry Porion recorded adults of Dynastes neptunus arriving at light traps just before dawn, whereas D. hercules arrived from the beginning to the middle of the night ( Lachaume 1985). According to the observations of G. Onore in the area of San Francisco de las Pampas, Cotopaxi, Ecuador, at 1,500 – 1,600 m of elevation, Dynastes neptunus and D. hercules are sympatric, but in the neighboring locality of Rio Negro, at 1,800 m elevation, only D. neptunus is found. As inferred by the flying sounds, the adults of D. neptunus apparently were active near the canopy at 20 m hight around 04:00 h. The larvae of D. neptunus live inside hollow trunks of ‘‘achotillo’’ ( Alchornea sp. Euphorbiaceae ), ‘‘canelo’’ or ‘‘cashiacara’’ ( Ocotea sp. Lauraceae ), and ‘‘ortiguillo’’ ( Urera sp. Urticaceae ) occupying hollows extended all along the standing trunk from the soil to the canopy. Inside each hollow trunk, G. Onore found 1– 12 larvae. Two or three was usual. They fed on reddish, rotten wood, frequently humid (nearly muddy), mixed with many fecal pellets of the same larvae. This species is abundant at Rio Negro because hollow trees with larvae were found at 100–250 m interval.

One female of D. neptunus collected at lights in San Francisco de las Pampas on 30 June 1993 was transported to Quito by G. Onore and placed in a 20 liter plastic container filled with rotten wood of Lauraceae . The wood was previously boiled, cooled, and powdered fecal pellets of larval D. neptunus were added, to promote the growth of the microflora needed by the future larvae. The female fed on fruits of banana and papaya, with scattered honey, until 21 September 1993. During this time, the female laid 19 eggs that were 5.3 mm in length and 5.0 mm in width that were placed inside cells in the rotten wood.The cells were 10 mm in length and 8 mm wide. Milky white eggs did not change color until hatching but increased their diameter to 7.5 mm just before hatching. Male and female larvae are well differentiated by the shape of the preanal white structures, known as Herold’s organs ( Menees 1957), observed beneath the transparent cuticle, with an external scar located in the anterior part of the raster.

Five third-instar larvae collected at San Francisco de Las Pampas on 3 July 2002 were reared in Quito with rotten wood of Ocotea sp. at 14–25 8 C. Pupae were obtained on 23 November 2002. Before pupation, the mature larva of the male made a large cell between the rotting wood debris and the inner walls of the hollow trunk, which was much longer and wider than the dimensions of the future adult. In captivity, complete development from egg to immature adult required 443–724 days: 41–48 days from egg to early first-instar larva, 28–70 days from first-instar larva to second-instar larva, 28– 124 days from second-instar larva to third-instar larva, and 346–482 days from thirdinstar larva to adult. Probably, in nature the life cycle requires two years.

Remarks. At present, we have morphological information on the larvae of four species of Dynastes ( Ritcher 1966; Morón 1987; present paper) that enables us to propose the following generic diagnosis and a key to separate the larvae of these species. Besides the width of the head capsule, body size, and the number of setae on the tarsal claws, the differences between larvae of each species are mainly those of chaetotaxy. Dynastes larvae may be distinguished from other Dynastinae larvae by the following combination of characters: head capsule coarsely pitted, with 2–8 dorsoepicranial setae on each side; frons with 1–4 posterior frontal setae and 1–2 exterior frontal setae on each side, without anterior frontal setae; ocelli differentiated; with 5–10 dorsal sensory spots on last antennal segment; lateral borders of labrum more or less angled; maxillary stridulatory area with 4–10 truncate teeth and 1 anterior process; abdominal spiracles with lobes of respiratory plates contiguous, the bulla rounded, weakly prominent; tarsal claws with 2 or 4 setae.

Figures

Figs. 17–18. Dynastes neptunus, lateral view of pupa inside pupal chambers formed in the rotten wood of rearing containers. 17) Female; 18) male. Photographs by G. Onore.