Sceliphron fistularium
Creators: name: Buys, Sandor Christiano
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Sphecidae
Sceliphron
Sceliphron fistularium

description: Sceliphron fistularium (Dahlbom, 1843)
Last instar larva
(Figures 3–19)
Head capsule. Height 2.6 mm; width 2.8 mm. Parietal bands pigmented; 600 µm long, about 8 µm wide. Antennal orbits pigmented; oval; 105 µm long, 115 µm wide. Coronal concavity not distinct; frontal and antennal concavities developed, not pigmented; clypeal concavities shallower, light brown. Coronal area strongly rugose; with 10 punctures (7–8 µm in diameter) and about five setae (15–20 µm long). Frontal area with eight punctures (about 7 µm in diameter) and 13 setae (12–17 µm long). Genal areas with 25 / 36 punctures (about 6 µm in diameter) and 7 / 6 setae (9–20 µm long). Epistomal suture ill defined. Clypeal area with 14 punctures and 25 setae (13–63 µm long); basal portion strongly papillose. Anterior tentorial arms, pleurostoma and hypostoma light brown.
Mouthparts. Labrum strongly bilobed, 370 µm in height and 540 µm wide; with about 50 punctures (7 µm in diameter) and 30 setae (7–28 µm long, about 2 µm in diameter); margin with 8 sensorial cones, 12 µm long and about 13 µm wide. Epipharynx covered with spines (up to 10 µm long, mostly shorter than 7 µm); spines on lateral portion, a few overlapped, oriented toward margin; spines on marginal portion oriented toward midline; spines on central portion denser, oriented toward base; sensory area with two basiconic sensilla on brown cones. Mandible dark brown, 660 µm long; second mandibular teeth larger and apical; basal portion with 10 punctures (6–7 µm in diameter). Maxilla with brown apical annulets; lateral and ventral portions with about 15 setae (10–30 µm long and about 2 µm wide); small spines on the dorsal portion; maxillary palpus 103 µm long and 85 µm wide; galea 125 µm long and 80 µm wide; lacinial area with spines (2–7 µm long). Labium brown in superior margin and lateral portion; 540 µm wide; dorsal and marginal portions papillose; ventral portion with setae (up to 14 µm long); labial palpi 70 µm long and 70 µm wide; labial projection 1.2 mm wide.
Body. Intense yellow. Dorsoventrally flattened; curved. Length 16 mm. Prothorax with two unpigmented callosities. Intersegmental lines distinct. Dorsal annulets developed on thorax; few distinct on abdomen. Pleural lobes indistinct on thorax, rounded and isolated, not forming continuous band on abdomen, continuous with pleural lobes. Integument partially covered by small spines; prothoracic callosities without spine, with setae (up to 38 µm long). Spiracles brown; 160 µm in diameter; spiracular depression absent.
Remarkable features visible only with scanning electron micrographs
Clypeus apically rugose (Figure 15). Labrum with two kinds of small sensillae (Figures 13, 14). Epipharynx with sensillae at base (Figure 17). Labium strongly rugose on apical and frontal portions (Figures 8, 10 and 11), smooth basally (Figure 11); median furrow on dorsal portion (Figure 10); lips of spinnerets with rows of papillae on the external faces (Figure 11) and along apical margins (Figure 12); internal faces with rows of shorter papillae (Figure 12).
Comparison among Sceliphron species based on larvae and a review
of larval characters in Sceliphrinae
The larvae of Sceliphron herein described are in general similar to those of other species of the genus (see Evans & Li 1956; Grandi 1961; Iida 1969; Asís et al. 1989); larval features that sharply distinguish species of Sceliphron were not clearly defined to date. The larvae of Sceliphron are also in general similar to those of the related genus Chalybion, as described by Evans and Lin (1956) and Tormos et al. (2006), even though the specimen of C. femoratum (Fabricius, 1781) described by the latter authors is quite distinct in several features from other described larvae of Sceliphrinae. Indeed, the paper by Tormos et al. (2006) gives rise to important doubts on generic definition of Chalybion based on larvae. Some characters that could be useful to the systematic of Sceliphron are reviewed below. A summary on morphometric features of larval Sceliphrinae is provided in Tables 1–4, in order to encourage future authors to include detailed measurements on descriptions of larval sphecids.
Shape of the head
One must be cautious to analyse the shape of the head of larval apoid wasps based on published illustration, because different methodologies used to study the specimens by the distinct authors can influence the illustrations and the measurements. Anyway, Buys (2004) studied several larvae of Podium, Penepodium, Ammophila, Sphex and Prionyx using an uniform technique of preparation and observation and found that genal areas of larval Sceliphron, especially of S. fistularium, tend to be more prominent that those of larvae of other genera (see Figure 1), a feature that is numerically reflected by the relation between the head width and labrum width (Table 1). The head of the examined larvae of Sceliphron are similar to those of the most of the Sceliphrinae in being a few wider than longer (compares Tables 1 and 2). On the other hand, Podium rufipes (Evans and Lin, 1956) and especially Chalybion femoratum (Tormos et al. 2006) are exceptions in having the larval head higher than wide (Table 1).
Rugosity on the top and sides of the head
The larvae of S. asiaticum and S. fistularium have the top and sides of the head roughened, similarly to the larvae of other species of the genus (see Evans & Lin 1956; Iida 1969; Asís et al. 1989, fig. 2). Among sphecid larvae, similar rugosity on the head has been found only in the larvae of the Sceliphrinae (e.g. Evans & Lin 1956; Buys 2001), apparently more intensely in larvae of Chalybion californicum (Saussure, 1867) (Evans and Lin 1956). Therefore, rugosity in the top of the head capsule could be used as a distinctive feature of the larvae of Sceliphrinae, although Tormos et al. (2006) have found that larvae of C. femoratum have the convexities on the top and sides of the cephalic capsule almost indiscernible.
Shape of the mandibles
The mandibles of Sceliphron are apparently similar to those of Chalybion illustrated by Evans and Lin (1956) and Tormos et al. (2006), but are quite distinct to those of Podium (Buys et al. 2004) and Penepodium (Buys 2001, 2006) and from other sphecids (e.g. Evans & Lin 1956). They seem to be relatively shorter and stouter, apparently in most part because of the development and apical position of the second mandibular tooth. In the mandibles of other Sceliphrinae, as well of other sphecids in general, the first mandibular tooth is larger and apical (Evans & Lin 1956; Buys 2001; Buys et al. 2004).
Papillae on spinnerets
Papillae on the spinnerets have rarely been included in morphological descriptions of sphecid larvae, but possibly may be a widespread feature among Apoidea. All the larval apoid wasps and bees that I have examined to date have rows of papillae in the spinnerets. The papillae are always organized in parallel rows, but the structure and density of the papillae is very different between species; for example, Centris (Hemisiella) tarsata Smith, 1874 (Apidae) has apically rounded papillae on the spinnerets (Buys 2005) and Ampulex compressa (Fabricius, 1781) (Ampulicidae) has spatulated papillae (Buys 2007).
Size of setae on the head
The setae on the head of larval Sceliphron are not distinctly longer than those of other Sceliphrinae (Tables 3 and 4). Evans and Lin (1956, p. 139) remarked that larvae of Podium differ from those of Sceliphron and Chalybion in having the apical part of the labrum with long setae protruding from it. However, this feature apparently is more related to the distribution of the setae than to its length.
Length of the labial palpi and galeae
The labial palpi tend to be as long as wide in the majority of the Sceliphrinae larvae (Table 2). On the other hand, the maxillary palpi and the galeae are longer than wide in all known larvae of Sceliphrinae (Table 2).
Body colour
Among Sphecidae, an intense yellow body, as observed in both of the examined Sceliphron species, was observed only in the genus Prionyx (Sphecinae) by Buys (2011). This author observed intense yellow colour in larvae of the two species of Prionyx he examined, but larvae of this genus are promptly distinguished in also having reddish coloration in parts of the body. Buys (2011) discussed the necessity of observing living or freshly killed larvae to accurately describe the colour. Alive, the larva of Penepodium luteipenne is pale yellowish (Buys 2001, 2004).
Comments on scanning electronic micrographs of S. fistularium
Some characters visible only with scanning electron microscopy seem to be useful to the systematic of Sceliphrinae, for example: (1) rows of papillae on spinnerets; (2) median furrow dorsally on labium; (3) distinct types of apical sensillae on labial palpi; and (4) galeae. However, the scarce use of this microscopy technique in Sphecidae to date does not allow a widely comparative discussion.
description: Published as part of Buys, Sandor Christiano, 2013, Morphology of the last instar larvae of Sceliphron asiaticum (Linnaeus, 1758) and S. fistularium (Dahlbom, 1843), with a review on larval characters in Sceliphrinae (Hymenoptera: Sphecidae), pp. 375-386 in Journal of Natural History 48 (7 - 8) on pages 378-385, DOI: 10.1080/00222933.2013.802385, http://zenodo.org/record/4632161