Pteromalidae Dalman, 1820

Gómez, Jose F. & Nieves-Aldrey, Jose Luis, 2012, Notes on the larval morphology of Pteromalidae (Hymenoptera: Chalcidoidea) species parasitoids of gall wasps (Hymenoptera: Cynipidae) in Europe, Zootaxa 3189, pp. 39-55 : 41-42

Pteromalidae Dalman, 1820

General larval morphology of Pteromalidae associated with cynipid galls. The terminal instar larvae of all studied species are morphologically very similar and share several features with other chalcidoid larvae (especially Eulophidae ) as described below.

Body segmentation ( Fig. 1 ). As for all Chalcidoidea larvae, the body consists of the head plus 13 post-cephalic segments. Three segments form the thorax (THS1–THS3) and the remaining ten segments form the abdomen including the anal segment (ABS1–ABS9, ANS).

Spiracles ( Fig. 2 ). The tracheal system is composed externally of nine pairs of lateral spiracles (epc) opening on segments THS2 to ABS7.

General morphology in lateral view ( Fig. 2 ). Following Gómez et al. (2008), we divided the body segments in lateral view into three areas: the pleural area, which includes the spiracles, and the areas situated ventrally and dorsally of the pleural area. The three regions are denoted as the pleural (P), ventral (V) and dorsal (D) areas. In all areas setation is inconspicuous. In general, terminal instar larvae of species of Pteromalidae associated with cynipid galls have only a few inconspicuous body setae compared with other chalcidoid species (except Eulophidae ) present in the gall assemblages.

General morphology in ventral view ( Fig. 1 ). We divided the body into a ventro-medial (vmr) and a ventro-lateral (vlr) region. In both regions setation is inconspicuous.

Head ( Figs 3A , 6 ). Head usually rounded, slightly broader than high. Upper margin of vertex regularly convex, with its medial area incised. Antennae (an) always visible on frons (fr), situated slightly below vertex area (vr), usually short and button-like; basal region or antennal foramina (af) distinct, resulting in a remarkable outward antennal region (anr). Head with 6 pairs of inconspicuous setae: (i) pair of antero-medial setae on frontal area (amf); (ii) pair of antero-lateral setae on vertex (val); (iii) pair of antero-medial setae on antennal area (am); (iv) pair of genal setae (gn) on genae (gr); (v) pair of clypeal setae (cs) on clypeus (cl) and (vi) pair of lateral clypeal setae (lcs) situated in lower frontal area. Clypeus (cl) a more or less triangular region with a variably shaped ventral margin anterodorsal to mouth region. Labrum (lb) a single structure above the underlip complex (mpu), usually semicircular and bearing a pair of dorso-labral setae (dls) above and a pair of labral setae (lbs) below ( Fig. 3 B).

Mouth parts ( Figs 3 B, 7). The mouthparts comprise the mandibles (see below) and the underlip complex (Mpu), which is formed by the hypopharynx (hardly discernible), the maxillae (mx) and the labium (lbi). As for other chalcid families, the maxillae and labium are not clearly separated in pteromalid terminal instar. The maxillary palps are inconspicuous and seldom visible. Below the maxillae ventrally is the labium, an area that is usually convex. The maxillae and labium bear two pairs of short setae, often hardly visible: a pair of antero-medial labial setae (ul) and a pair of maxillary setae (ms) on one of the two maxillary palps.

Mandibles ( Fig. 8 ). Larval mandibles, especially the blades, are not clearly visible in the pteromalid species studied except for Stinoplus lapsanae . Both are usually symmetrical and single-toothed. They are often small and differences between the species are relatively inconspicuous. Generally the larval mandible is considered an important character in systematics and taxonomy and has been described for all studied species. As far as is known pteromalid larvae have mandibles with one or rarely more than one tooth.

Figures

FIGURE 1. Pteromalus hieracii (Thomson), body in ventral view illustrating terminology used for general description (see text). Abbreviations: ABS 1 – ABS 9, abdominal segments; ANS, anal segment; THS 1 – THS 3, thoracic segments; vlr, ventrolateral region; vmr, ventromedial region.

FIGURE 2. Cecidostiba geganius (Walker), body in lateral view. Abbreviations: ABS 1 – ABS 9, abdominal segments; ANS, anal segment; D, dorsal area of body; epc, spiracles; P, pleural area of body; THS 1 – THS 3, thoracic segments;. V, ventral area of body.

FIGURE 6. Anterior view of the head of terminal instar pteromalid larvae (A = agamic generation; S = sexual generation for host). A. Arthrolytus glandium ex Callirhytis rufescens (A). B. Cecidostiba fungosa ex Andricus quercusradicis (S). C. Cecidostiba geganius ex Andricus quercusradicis (A). D. Pteromalus bedeguaris ex Diplolepis rosae. E. Pteromalus hieracii ex Aulacidea follioti. F. Pteromalus isarchus ex Xestophanes potentillae. G. Rivasia fumariae ex Neaylax versicolor. H. Stinoplus lapsanae ex Timaspis lapsanae.

FIGURE 8. Anterior view of left mandible of terminal-instar pteromalid larvae (A = agamic generation for host). A. Arthrolytus glandium ex Callirhytis rufescens (A). B. Cecidostiba geganius ex Andricus quercusradicis (A). C. Pteromalus bedeguaris ex Diplolepis rosae; and anterior view of the left mandible. D. Stinoplus lapsanae ex Timaspis lapsanae. E. Rivasia fumariae ex Neaylax versicolor.

FIGURE 3. A. Pteromalus hieracii (Thomson), anterior view of head illustrating terminology used for general description (see text). Abbreviations: af, antennal foramina; am, antero-medial setae of antennal region; an, antenna; anr, antennal area; cl, clypeus; cs, clypeal setae; dls, dorso-labral setae; fr, frons; gn, genal setae; gr, genal region; hr, hypostomal region; lb, labrum; lbi, labium; mx, maxillae; vr, vertex region. B. Rivasia fumariae Askew & Nieves-Aldrey, anterior view of mouthparts (Mpu). Abbreviations: dls, dorso-labral setae; lb, labrum; lbs, labral setae; lbi, labium; ms, maxillary setae; mx, maxillae; ul, anteromedial labial setae.