Dryinus tarraconensis Marshall , 1868

Guglielmino, Adalgisa, Parise, Gianluca & Bückle, Christoph, 2015, Description of larval instars of Dryinus tarraconensis Marshall, 1868 and Gonatopus baeticus (Ceballos, 1927) (Hymenoptera: Chrysidoidea: Dryinidae), parasitoids of the genus Dictyophara Germar (Hemiptera: Auchenorrhyncha: Dictyopharidae), Zootaxa 4032 (1), pp. 42-54 : 44-48

1. Dryinus tarraconensis Marshall, 1868

( Figs 2–5 )

A. Last immature larval instar ( Fig. 2 ). Maximal width: ca. 1.6 mm.

Brown in colour. Cephalic region with two sickle-shaped vesicles quite distant from each other ( Fig. 2 ); posterior region of the body bent ventrally. Segmentation of the body indistinct, respiratory system peripneustic with nine pairs of lateral spiracles (one thoracic + eight abdominal). Ventral process absent.

Body partially covered by the discarded exuviae of the previous larval instars, immersed into the host's haemocoel with its anterior part, the posterior part protruding outside ( Fig. 2 ). The position of the exuviae shows that for each moult the cuticle breaks along a preformed mediodorsal line.

In the Dictyophara nymphs the dryinid larva protrudes between the host’s metathorax and abdomen below the metathoracic wingpad (as in Fig. 1 ). In the rather rare case we found parasitized adults it was inserted in the abdomen and protected below the wings.

B. Mature larva ( Figs 3–5 ). Length: ca. 4.6–6.5 mm; width of head 0.72–0.80 mm.

Larva apodous, white yellowish, subcylindrical ( Fig. 3 A). Head yellowish, well sclerotized, with barely visible medial ecdysial line posteriorly ( Fig. 4 A). Antennal orbit circular with two sensilla ( Figs 4 A, 5E). Head capsule with three pairs of long sensory bristles located in proximity of anterior margin and on each side one pair of sensory pits between antenna and anterior margin, a single small indistinct sensory pit more laterally and one pair of sensory pits in anterolateral position ( Fig. 4 A, arrow). Frontoclypeal suture distinct. Anterior margin of clypeus straight ( Fig. 3 B). Labrum large, wider than clypeus, anterior angles rounded, dorsal surface with two sensory pits and numerous long bristles irregularly distributed until the anterior margin and the distal region of epipharynx ( Figs 3 B, 4B). Epipharynx with basal large triangular lobe; lobe covered by scaly microsculpture as on surrounding posterior part of epipharynx, and with dorsad directed sagittal fold, visible ventrally as distinct groove; medioanterior region of epipharynx with pubescence of long robust bristles gradually decreasing in length basad and laterad and within medioposterior part of pubescence with about four cone-shaped sensilla; posterior part of epipharynx covered by scaly microsculpture, scales of lobe anteriorly pectinate forming slightly curved transverse rows of spinules ( Fig. 5 A). Mandible strongly sclerotized, stout, securiform with broad base and apical portion divided in an internal simple and an external bidentate lobe ( Figs 4 C, 5B). Each mandible with one long sub-basal sensory bristle. Maxilla weakly sclerotized, with maxillary palp and five long sensory bristles ( Figs 4 D, 5D). Maxillary palp unsegmented, subcylindric, with distinct lateral sensory depression and with subapical sensory bristle ( Figs 4 D, 5C), apically with four sensilla of different size and structure: two uni-articulated, small and coneshaped and two bi-articulated consisting of a long cylindrical basal and a small cone-shaped apical article. Labium sclerotized, distally with spinneret and subapically with labial palps ( Figs 4 D, 5F). Three sensory bristles in proximity of each palp, two in basal and one in lateral position. Labial palp ( Figs 4 D, 5F) unsegmented, with small circular sensory depression on midlength and with four distal sensilla structurally similar to those of maxillary palp. Spinneret with two sensory pits on each side ( Figs 4 D, 5G, arrows), apically opening by transverse slit.

Thorax and abdomen with indistinct segmentation ( Fig. 3 A). Numerous and very small sensory bristles (ca. 10–15 µm) arranged in transverse rows around each thoracic and abdominal segment. Tracheal system with one pair of large thoracic spiracles (pro-mesothoracic) ( Figs 3 C, 5H–N) and eight pairs of smaller abdominal ones located on the first eight abdominal segments. Atrium of thoracic spiracles formed by about 20 cells ( Figs 5 H, 5L), with exterior margin consisting of about 12 cells ( Fig. 5 I, 5N). All spiracles simple, without bristles, hairs or other particular protection structures.

Figures

FIGURE 1. Nymph of Dictyophara pannonica (Germar) parasitized by immature larva of Dryinidae.

FIGURE 2. Dryinus tarraconensis Marshall, immature larva. A. Lateral view. B. Frontal view. C. Anterior region with cephalic vesicles, frontal view. D. Anterior region with cephalic vesicles, lateral view.

FIGURE 3. Dryinus tarraconensis Marshall. A – D. Mature larva. A. Dorsal view. B. Head, frontal view. C. Anterior region, dorsal view. D. Anterior region, ventral view. E, F. Cocoon on Rubus.

FIGURE 4. Dryinus tarraconensis Marshall, mature larva. A. Head capsule without clypeus, dorsal view. B. Labrum. C. Left mandible, dorsal view. D. Right maxilla and labium, ventral view.

FIGURE 5. Dryinus tarraconensis Marshall, mature larva. A. Epipharynx. B. Mandibles, dorsal view. C. Right maxillary palp, dorsal view. D. Maxillae and labium, dorsal view. E. Antenna. F. Labium, ventral view. G. Apex of spinneret. H. Thoracic spiracle, from inside. I. Exterior margin of thoracic spiracle, from outside. L. Atrium of thoracic spiracle, from outside. M. Thoracic spiracle and part of trachea, lateral view. N. Exterior margin of thoracic spiracle, lateral view.