Gymnetis holosericea ( Voet, 1779 )

Orozco, Jesus & Pardo-Locarno, Luis Carlos, 2004, Description of immature stages of three species of American Cetoniinae (Coleoptera: Scarabaeidae: Cetoniinae), Zootaxa 769, pp. 1-14 : 3-6

Gymnetis holosericea ( Voet, 1779)

Gymnetis is a Neotropical genus in the tribe Gymnetini. The species are not easily distinguished since very few diagnostic characters have been found in the adults (Ratcliffe personal communication.). Recently Antoine (2000) has suggested nomenclatural changes to some species, but generally a review is urgently needed. Five larvae in this genus have been described: Gymnetis flavomarginata sallei , G.(Paragymnetis) chalcipes , G. hebraica difficilis , Gymnetis holosericea (this work) and G. pantherina (this work).

Gymnetis holosericea is an easy species to rear. The female deposits the eggs singly within the substrate, the whole cycle takes about 7 months (LII about four weeks, LIII about 12–13 weeks, and pupa from 4–6 weeks). As with other cetoniines, the third instar larvae form a pupal chamber (21–29 mm high 15–19 mm wide) with soil and some feces, and the larval exuvium is maintained at the ventral side of the pupa just in front of the abdominal sternites. The adults are long­lived with the reared ones dying 6–8 weeks after the offspring emerge. Mutilation of adults is common in nature and in the laboratory, but its origin is unknown. Feeding habits of larvae and adults in nature are not well understood.

The studied population corresponds to a medium size form (17.5–20 mm). The males usually have a very fine yellow stripe along the extension of the elytra without insertions and the coloration of the abdomen is matte or opaque, while the females have slight yellow insertions at the posterior middle of the elytra and the ventral area of the abdomen is glossy ( Fig. 1 a–d). This species is very similar to two other populations found in western Colombia, differing mainly in the size and in the yellow stripe pattern on the elytra. For practical purposes we refer to one of them (the larger one, 21.8–22.9 mm) with the yellow stripe without insertions in both sexes as “magnifica” ( Fig. 1 f–h) and to another with two strong yellow insertions without defined margins (16.5 mm) as “chevrolat” ( Fig. 1 e). It is not clear if these populations correspond to different species or not, but we hope that larval descriptions will help to define the taxonomic boundaries between species in this group.

THIRD INSTAR LARVA. This description is based on 50 larvae reared from adults collected in a disturbed tropical dry forest near a city. Locality data: COLOMBIA: Santander, Bucaramanga, Vía Chimitá; 12­XI­02, 730m; Orozco, J. Leg. The vegetation of the zone is mainly composed by Pithecellobium dulce (Roxb.)(Mimosaceae) , Erythrina sp. ( Fabaceae ), Bambusa vulgaris Schrad. (Poaceae) , Cecropia sp. ( Cecropiaceae ), Ricinus communis L. ( Euphorbiaceae ), Psidium guajava L. ( Myrtaceae ), and Mangifera indica L. ( Anacardiaceae ). This is the first record of this species from Santander.

Head: ( Fig. 2 a) Maximum width of head capsule 4.1–4.3 mm. Cranium: Smooth; color yellowish brown. Frons with a median longitudinal depression, a single posterior frontal seta, and a single anterior angle seta. Dorsoepicranium with one large and 4–5 small setae in a line diverging from mediobasal portion of head and, one lateral line of 3–6 short setae at each side. Tentorial pits evident. Ocelli absent. Clypeus: Shape subtrapezoidal with one posterior clypeal seta and 0–3 exterior clypeal setae. Preclypeus weakly sclerotized and without setae. Labrum: Anterior border trilobed, clithra present. Epipharynx: ( Fig. 2 b) Plegmata absent. Corypha with 4 long stout setae. Haptomeral region with cone­like process with a curved row of 12–14 heli and 6–8 stout, spine­like setae irregularly placed behind row. Acanthoparia with 6–8 short setae. Chaetoparia with 18–34 setae on each side. Dexiotorma long and pternotorma small and rounded. Laetorma short and pternotorma small and rounded. Nesia with sensorial cone. Haptolachus without sensillae below the cone. Mandibles: Right mandible ( Fig. 2 d) with one scissorial tooth anterior to scissorial notch and two weakly defined scissorial teeth posterior to notch. Stridulatory area elongate, length over three times its width. Molar area trilobed, lateral edge with seven setae, dorsal surface in apical half with two setae. Brustia formed by five setae. Left mandible ( Fig. 2 e) with one scissorial tooth anterior to scissorial notch and two well­defined scissorial teeth posterior to notch. Molar area trilobed, lateral edge with five setae, dorsal surface in apical half with one seta. Basomedian angle with brustia consisting of eight setae. Maxilla ( Fig. 2 c) Mala with large uncus at apex and one subterminal bifid uncus. Stridulatory area with row of 4–5 curved acute teeth and a distal, truncate process. Labium: ( Fig. 2 c) Hypopharyngeal scleroma asymmetrical, left side with 7–10 setae, right side more prominent, sclerotized, without setae. Antennae: First antennomere longer than the two following antennomeres together. Surface of last antennomere with two dorsal and 2–3 ventral sensory spots.

Thorax: Thoracic spiracles ( Fig. 2 g) with C­shaped respiratory plate, size 0.82 mm high and 0.65 mm wide. Dorsal area of thoracic segments with abundant setae. Legs: Tarsungulus cylindrical ( Fig. 2 f) rounded apically, possessing 10–11 setae.

Abdomen: Spiracles of abdominal segments I–VIII similar in size, distance between the two lobes of respiratory plate of spiracles much less than the dorsoventral diameter of the bulla. Dorsal surface of segment I–X with abundant long and short setae irregularly placed, longer posteriorly. Dorsum of segment VII with two annulets. Segments IX and X fused, covered with short and long setae. Spiracular area of abdominal segments I–VIII with 34–41 setae. Raster: ( Fig. 2 h) Palidia monostichous, open posteriorly and anteriorly, each palidium consisting of a row of 10–16 spiniform pali. Septula elongate, length 10 times its width. Lower anal lip with many short and medium size setae proximally to the anal aperture and many long setae distally.

PUPA

Description based in 8 pupae. Length 21.3–24.5 mm. Shape subovate, stout, exarate. Color cream­white yellowish without microtrichia in abdominal segments.

Head: Glabrous, bent downward, mouthparts separated. Frons with slight depressions. Clypeus trapezoid slightly concave.

Thorax: Pronotum glabrous, convex, sub­heptagonal in shape with two rounded protuberances at each side just in front of the pteroteca. Pteroteca free, compressed around the body, hind wing teca longer reaching the abdominal sternite IV. Meso­metasternal process large, between the pro and mesocoxa, with a stout process at the middle projected strongly to the front, apex not rounded sometimes with two ending points. Protibia with one apical spur and three protuberances vaguely defined or absent in most of the cases. Meso and metatibia with two apical spurs.

Abdomen: Tergites II–VI with tergo­lateral tubercles surrounded by fine rugae, segment VII with tubercle vague or absent. Spiracle I with sclerotized peritreme covered by the hind wing pteroteca and protected by a fleshy fold. Spiracles II–IV rounded, prominent. Spiracles V–VIII closed. Last tergite without urogomphi, genital ampulla bilobed. Female without bilobed ampulla.

Gymnetis holosericea larvae differs from other Gymnetis larvae by the following combination of characters: Tentorial pits evident, dorsoepicranium with central row of 5–6 setae, last antennomere longer that the two following segments together, surface of last antennomere with 2–3 ventral sensory spots, spiracles of abdominal segments similar in size and palidium with 10–16 spiniform pali.

Figures

FIGURE 1. Gymnetis holosericea (a – b, males; c – d, females), e. chevrolat form (male), f – h. magnifica form (f – g, males; h, female). Scale line = 1 cm.

FIGURE 2. Gymnetis holosericea, larva. a. head, b. epipharynx, c. labium­maxilla, d. right mandible, e. left mandible, f. tarsungulus, g. respiratory plate, h. raster. Scale lines = 0.5 mm, except fig. 2 a = 1 mm.