Pescription of the Larva of Oxelytrum Erythrurum (Blancha.Rd, 1849) (Coleoptera: Silphidae)
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... et ~·aiH.eurs I ... en van an~ere streken Bulletin S.R.B.E.IK.B.V.E., /40 (2004): 14/-/44 pescription of the larva of Oxelytrum erythrurum (Blancha.rd, 1849) (Coleoptera: Silphidae) A. OLIVA Laboratorio de Entomologia forense, Museo argentino de Ciencias naturales, Av. A. Gallardo 470, C1405DJR, Buenos Aires, Argentina (e-rnail: [email protected]). Abstract The larva of Oxelytrum erythrurom is described and figured. This. larva dif~ers ~om those of described species ofNeartic genera in the distribution of setae ~n the maxillary palptger, tn ~he shape of the ventral shields on the abdominal segments, in the length ratio between the second and thrrd antenna! segment and of the first and second urogomphial segments and in ~e shape of the lateral processes of the dorsal plates. No larvae ofNeotropical Silphidae had been descnbed up to date. Keywords: Forensic entomology, Neotropical fauna. Introduction conditions (OLN A, 2001 ). Field experiments in the province of Buenos Aires (CENTENO et al., The small but widespread family Silphidae 2002) showed appearance of adults as early as (Coleoptera: Staphyliniformia) includes many the first two days on dead pigs exposed in a species associated with carrion; hence the roofed cage and from day 11th onward on pigs in English trivial name "carrion beetles". The an unroofed cage. The early arriving adults may position of the family in the Order Coleoptera is feed on the carcass, but n1ost certainly they prey discussed by NEWTON & THA YER (1992) and by on the blowflies that come to lay their eggs, as HANSEN {1997). DORSEY (1940) describes and well as on the eggs themselves and newborn figures the larvae of six Neartic species of Silpha larvae (V. Trigo, unpublished data). The larvae (Silphidae: Silphinae). PETERSON (1960) takes of Neartic Silphidae Silphinae do not attack fly up DORSEY's data for two of the six species but larvae, but feed on cadaveric tissues and on does not, as far as I could ascertain, add any new occasion show cannibalism; there is no parental information. Later authors restricted the name care (DORSEY, 1940). PAYNE & KING (1970) Silpha to Old World species, and the six (working with pigs as bait) observed adults of American species treated by DORSEY were several species feeding on maggots. Lmvae of assigned to five genera (PECK & ANDERSON, Silphidae appeared after most dipterous larvae 1985). had left the remeins; however, they did not Two genera of Silphidae are known to occur in actually observe them feeding on carrion. Argentina, Nicropharus (Silphidae Nicropho On human bodies, adults have been gathered rinae) and Oxelytrum (Silphidae Silphinae). The by officials at the scene 8-12 days after death; later alone has relevance in forensic entomology. adults together with young larvae are found No larvae of Neotropical species of Silphidae around 12-18 days after death, and the larger have been described before (PECK & ANDERSON, larvae 18-30 days after death. There appears to 1985). be little doubt that the larvae of Oxelytrum are Only Oxelytrum erythrurom (Blanchard, 1840) necrophagous. They might feed on corpse has been found in the province of Buenos Aires exudates rather than on tissues, since they are (including Buenos Aires city itself) in forens~c found under the body, in areas with liquefaction cases and in field experiments to study cadavenc fauna! succession, always in rural or semirural 141 (ff: I 6 ~ 8 Fig. 1: Oxelytron erythrurum, mature larva in dorsal view, 10 x. Fig. 2. Detail of posterolateral angle ofmesothoracic tergite, 50 x. Fig. 3: idem of first abdominal tergite. Fig. 4: detail of ninth abdominal segment with urogomphi and tenth segment, 50 x. Fig. 5: left side of cephalic capsule, showing antennae, 50 x. Fig. 6: mandibles, 50 x. Fig. 7: left maxilla with maxillary palpus and left side oflabium, 50 x. Fig. 8: third and fourth abdominal segments in ventral view, showing subquadrangular ventral plates and annular spiracles with circular openings, 20 x. Scalebars =I mm. of tissues, where the underlying soil shows angles, those of abdominal segments with evidence of percolation of fluids (Oliva, pers. posterior angles acute; legs gradually increasing obs.). in length from first to third, spinose; coxa Generic characters for Silpha {DORSEY, 1940) grooved, trochanter small, femur about equal in may be applied to the whole subfamily Silphinae, length to coxa, tibia slightly shorter than femur, as far as present information goes. They include, tarsungulus long, strong, with two small lateral among others: body campodeiform; head broader spines. These characters are based on the six than long; mandible with broad base tapering to species described by DORSEY (1940), which, as it incisor lobe with two acute teeth; clypeofrontal was said before, belong to five different genera suture distinct only at lateral marging; {PECK & ANDERSON, 1985). clypeolabral suture distinct; labrum bilobed; The species treated by DORSEY are: dorsal ocelli four, arranged round a small Necrophila americana (L., 1759) (sub Silpha rounded mound; ventral ocelli two, on ventral americana L.) surface of the head; maxillae with mala and Oicoeptoma rugulosum (Portevin, 1903) (sub stipes fused, galea with rounded brush-like tip; Silpha inequalis Fab.) spiracles annular, the mesothoracic spiracle about 0. noveboracensis (Forster, 1771) (sub Silpha twice the size of other spiracles; dorsal shields of noveboracensis F orst.) thoracic segments with u-shaped posterolateral Heterosilpha ramosa (Say, 1823) (sub Silpha 142 ramosa Say) strong, curved, without molar area, incisor lobe Thanatophilus lapponicus (Herbst, 1793) (sub ending in two acute teeth; asymmetrical, right Silpha lapponica Hbst) mandible without any cutting edge, left mandible Necrodes surinamensis (F., 1775) (sub Silpha with small cutting edge between the two. teeth surinamensis Fab.) (fig. 6). I did not find any traces of the setae The material of Oxyelytron erythrurum mentioned by DORSEY (1940). Maxillary examined is of the same basic type as the figured palpiger small but distinct. Maxillae as described species of Silphidae Silphinae (DORSEY, 1940; by DORSEY (1940), but with a single seta atiterior PETERSON, 1960; HANSEN, 1997). A few to base of palpus and two posterior, the first of characters have been found to differ. It remains these inserted at the very base (fig. 7). Maxillary to ascertain whether these character have a pal pi 3-segmented; first segment convex .in its generic or a specific value. anterior outline, second shorter than first, thickened towards apex, third subulate, a little Material examined longer than the precedent segment (fig. 7). Labial palpi two-segmented, not extending beyong Argentina: Buenos Aires province: Tandil, glossae; second segment minute (fig. 7). 21/XI/2003, under a dead pig set as b~it for Stemmata as described by DORSEY (1940) for the sarcosaprofagous insects at the Facultad de genus Silpha. Ciencias Veterinarias (UNC); in the collection of Dorsal shields of thoracic segments with the Laboratorio de Entomologia forense. Larva posterior angles produced into broad, blunt found along with an adult of 0. erythrurum. This processes directed outwards and backwards (fig. specimen has been used for habitus and gross 2). Dorsal shields of abdominal segments with detail drawings, as better fixated and preserved leaf-shaped processes, the apices pointing than the remaining material. Five specimens outwards and backward in an angle of form the general collection of the Museo approximately 45 degrees to the longitudinal axis argentino de Ciencias naturales {MACN), dry of the body (fig. 3). Margins of thoracic and mounted, labelled "Bs. Aires", "6327", one of abdominal dorsal processes minutely serrate, which was used for drawing mouthparts. A series each with a short seta directed outwards and from a forensic case (Buenos Aires: San lsidro backwards, in the abdominal segments placed at 30-IX-2000, P:MI estimated 45 days). the apex of the leaf-shaped process (fig. 2, 3). The drawings were made with a camera lucida Ventral shields of abdomen subquadrangular, not in a Zeiss stereomicroscope. The mouthpieces, produced backwards (fig. 8). Urogomphi (fig. 4) cephalic capsule and legs were dissected out of with two subcylindrical segments, the first long, the second specimen after treatment with hot subcylindrical, slightly concave along its inner NaOH and rinsing in water with acetic acid. face; the second one a little less than half the They were mounted afterwards in a vinyl-based length of the first. Measures on specimen medium for drawing. figured: urogomphus 1. 7 mm, basal segment 1.2 mm, apical segment 0.5 mm. Length of Description of the larva of urogomphi distinctly greater than length of tenth Oxelytron erythturum (Bianchard, 1849) abdominal segment. Spiracles as described by Length of figured specimen 17,5 mm; no DORSEY (1940) except that the mesothoracic rearing has been completed, but larvae of this spiracle is the only one to have a kidney-shaped species certainly surpass 20 mm in length. Cam opening, those. on abdominal segments having a podeiform, depressed (fig. 1). General colour circular opening. Legs as described by Dorsey light yellowish brown, darker on the more (1940) for the genus. sclerotized plates, with narrow median light The larva of Oxelytron erythrurum differs stripe along the whole body, excepting the from those of the Neartic species described by anterior half of the head. Cephalic capsule dark DORSEY (1940) as follows. From all of them, by reddish brown. Dry-preserved specimens (not the more robust mandibles (fig. 6), by the ventral unusual in old collectio~s) take on an uniform abdominal shields subquadrangular, with dark reddish brown. posterior angles not produced (fig. 8) and by the Head prognathous, rounded, somewhat second segment of the urogomphi about half the broader than long; suture apparent. Antennae 3- length of the first (fig. 4). From Heterosilpha segmented, with apical segment subulate, hardly ramosa by the antenna with the third segment shorter than the precedent one (fig.