Sphecidae, Latreille, 1802

Buys, Sandor Christiano, 2020, A study on taxonomy and phylogeny of immature stages of Sphecidae (Hymenoptera: Apoidea), Zootaxa 4869 (1), pp. 78-90 : 83-88

Description of Sphecidae based on the last instar larva

( Figs 2–25 )

Diagnosis. Besides the apomorphic features, the last instar larvae of Sphecidae are distinct from those of other families of Aculeate Hymenoptera for the following combination of features: integument of the body with small isolated setae and, at least partially, with small spines; antennal orbits with three basiconic sensilla; antennal papillae absent; labrum bilobed; epipharynx with acute spines on the lateral, basal, and median portions; mandibles usually with pores at the base, almost always with four teeth, rarely with three teeth; spinnerets formed by a transversal slit with a labial projection more or less uniform in width; anus terminal.

Head. Coronal suture distinct. Parietal bands well developed and almost always brown ( Fig. 6 ). Antennal orbits usually light brown; circular or oval in shape; with three small basiconic sensilla ( Figs 8 , 21 ). Cephalic rugosity sometimes present, stronger in Sceliphron and Chalybion ( Fig. 6 ). Punctures and spines, in general, abundant on genal areas and almost always present in the clypeal, coronal and frontal areas. Apparently, there is no symmetric pattern of distribution of the setae or punctures on the head. Pairs of antennal and clypeal concavities usually present; integument on the bottom of the concavities usually brown; more rarely a coronal concavity also distinct. Epistomal suture indistinct or poorly developed; margin of the clypeus usually straight, but sometimes tending to be bilobed or with the corners somewhat expanded ( Fig. 21 ). Posterior thickness of the cephalic capsule not pigmented; anterior tentorial arms, pleurostoma and hypostoma usually brown.

Mouthparts. Labrum strongly bilobed; with punctures and setae ( Figs 3, 7 ); basiconic sensilla in the margin ( Figs 15, 17 ); Sceliphrinae and Chloriontinae with sensorial cones in margin ( Figs 3, 7 , 15, 17 ). Epipharynx with spines on the lateral, marginal and median portions; the lateral spines facing the apex and gradually facing the midline in direction to the marginal portion, in the median portion the spines are directed to the base ( Fig. 23 ); one pair of sensorial areas often partially pigmented, with basiconic sensillae ( Figs 11 , 22, 23 ); Sphecinae and Ammophilinae with a brown marginal band bearing basiconic sensilla ( Fig. 11 ). Mandibles brown, darker in the apical half and in the internal and external mandibular articulations ( Fig. 12 ); usually with four teeth ( Figs 5 , 12 ), Podalonia spp. and Prionyx fervens with three mandibular teeth; mandible with small denticles on the external surface in Ammophilinae ( Fig. 12 ); basal area laterally with punctures and rarely with small setae ( Fig. 4 ). Maxillae usually with setae in the basal external portion; inner basal portion with papillae serrated in the margin ( Fig. 18 ); a brown band near to the apex; lacinial area usually densely covered with usually curved spines facing the mouth ( Fig. 16 ); maxillary palpus brownish and approximately conical, apex rounded with two sensillae ( Fig. 10 ); galea brownish, approximately conical, longer than maxillary palpus, apical portion rounded, with two sensillae ( Fig. 10 ). Labium usually with brown areas laterally and in the superior margin; dorsal portion smooth or with papillae; labial palpus brownish, approximately conical, usually little longer than wide, with two sub-apical sensilla ( Figs 2 , 9 ); spinnerets formed by a transversal slit, protected by a labial projection approximately uniform in width, rarely brownish, with rows of digitiform or spiniform papillae in the margin ( Figs 15, 19, 20 ).

Body. White, sometimes greyish or yellowish, also intense yellow or green, but always the colour of the larvae is due to the internal structures; the green colour is more evident in the early instars of Ammophilinae and of some Sphecinae , which also can be lightly reddish or somewhat pink; reddish parts, especially in the thorax, are present in Prionyx . Integument rarely with brownish areas in stronger sclerotized portions. Without prolegs. Dorsoventrally compressed, somewhat rounded dorsally and flattened ventrally; more rarely cylindrical; more or less gradually tapered toward the extremities and usually broader in the fifth or in the sixth abdominal segment. Pleural lobes almost always indistinct in the thorax, well developed in the abdominal segments I to IX, absent in the abdominal segment X; isolated or laterally joined, forming a distinct continuous band. Integument covered with minute spines, at least sometimes there are folds in the integument where the spines are found; spines widely distributed on the body or restricted to some portions, sometimes isolated and scarce. Sub-integumentary granules of uric acid usually indistinct in the thorax, but visible in the abdominal segments I to X, usually less abundant in the abdominal segment X. Sceliphrinae and Chlriontinae with one to three pairs of callosities dorsal or dorsal-laterally on the prothorax. Anus a transversal slit, terminal or sub-terminal. Spiracles on thoracic segments II and III and abdominal segments I to VIII; atrium brownish; globose; peritremes not pigmented, sometimes with ornamentations (visible with S.E.M.) ( Figs 13 , 24 ); Sceliphrinae with all the spiracles about the same diameter; Sphecinae and Ammophilinae with spiracles of segments TII–TIII, and sometimes those of the segment AI, with smaller diameter than the other spiracles; opening of the atrium to the sub-atrium with branched spines of variable shapes ( Figs 13, 14 , 24, 25 ); walls of the atrium internally with ridges forming polygonal reticulation or concentric rings.

Figures

FIGURES 2–8. Larval morphology of species of Sceliphrini. 2, Penepodium luteipenne: part of the labium; 3–5, Podium denticulatum: 3, labrum, frontal view; 4, mandible, basal portion; 5, mandible, apical portion; 6–8, Sceliphron fistularium: 6, head, frontal view; 7, margin of the labrum; 8, antennal orbit. (AO = antennal orbit, LP = labial palpus, P = puncture, PA = parietal band, PB = parietal band, Po = pore, S = seta, SC = sensorial cone, SM = serrated margin of the third mandibular tooth, Sp = spines)

FIGURES 9–12. Larval morphology of species of Sphecini and Ammophilini. 9, Prionyx thomae: part of the labium; 10, Prionyx fervens: apex of the maxilla; 11–12, Ammophila sp. 1: 11, epipharynx; 12, mandible, frontal view. (MA = internal mandibular articulation, BS = basiconic sensilla, De = area with denticles, G = galea, LP = labial palpus, (MP = maxillary palpus, S = setae SA = basiconic sensilla in sensorial area, SB = basiconic sensilla in marginal band)

FIGURES 13–20. Larval morphology of Podium denticulatum (S.E.M). 13, ornamented peritreme of the spiracle; 14, flattened spines in the spiracle atrium; 15, oral portion of the head; 16, lacinial area; 17, detail of the apex of the labrum; 18, maxilla, internal basal view; 19, detail of the labium, ventral view; 20, papillae of the apex of the spinnerets. (BS = basiconic sensilla of the labrum, MS = spinulose margin of the spinneret, SC = sensorial cone)

FIGURES 21–25. Larval morphology of Sphecini (S.E.M.). Prionyx thomae: 21, part of the head, showing specially the clypeus; 22, sensorial area of the epipharynx; 23, median portion of the epipharinx; Sphex dorsalis: 24, peritreme and pore of the spiracle; 25, detail of the spines of the spiracle atrium. (AO = antennal orbit, BS = basiconic sensilla, SA = basiconic sensilla of the sensorial area, SS = basiconic sensilla of the superior portion of the epipharynx, TP = anterior tentorial pit)