Gasteruption assectator (Linnaeus, 1758), s. str.

Bogusch, Petr, van Achterberg, Cornelis, Silhan, Karel, Astapenkova, Alena & Heneberg, Petr, 2018, Description of mature larvae and ecological notes on Gasteruption Latreille (Hymenoptera, Evanioidea, Gasteruptiidae) parasitizing hymenopterans nesting in reed galls, Journal of Hymenoptera Research 65, pp. 1-21 : 5-7

Gasteruption assectator (Linnaeus, 1758), s. str.

Figs 4A-C (whole larva), 5A-C (drawings of body parts)

Previous descriptions.

Larva of this common species is mentioned to be the only larva of this genus previously described in literature: Crosskey (1951) published very brief description and Short (1952) described in detail the head of the larva. However, the rest of the body was undescribed, and it is necessary to compile a detailed description of the whole larva.

Material examined.

Hungary bor., Tát env., 47.761468, 18.702050, reed bed surrounding water reservoir, 15.i.2016, 1 larva from nest of Pemphredon fabricii , P. Bogusch lgt .; Hungary occ., Balaton region , Fonyód env., 46.738374, 17.586305, terrestrial reed bed, 1 larva from nest of Hylaeus confusus , P. Bogusch & P. Heneberg lgt., both P. Bogusch det. & coll .

Diagnosis.

The mature larva of G. assectator is similar to other larvae of this genus. It is smaller in total length as well as the body parts (head, mandible) are smaller than in the larvae of bigger species G. phragmiticola and G. nigrescens . The body is less sclerotized, which is well-visible especially on the head and mouthparts - the yellowish-colored more pigmented mandible, apices of maxillae and labium and antennal tubercles are in contrast with the same parts brownish in the other two species. The mandible is shorter with apical tooth not projecting as much behind the other, its top is blunter than of the other species. The presently described larvae are both very similar in the morphology although they differ in size (which is normal in parasitic species) and their morphology corresponds with the description of Crosskey (1951) and figures of head of G. assectator in Short’s (1952) study.

Description.

Body: Body length 5.4 and 6.7 mm (N=2). Body vestiture without spicules consisting only of numerous slender, pale setae, tapering to fine points, arising from small but distinct alveoli; these setae conspicuous and elongate. Setae abundant on elevated dorsal surfaces of thorax and widely scattered on anterior ventral surface of thorax; some setae present on dorsal surfaces of metasomal tergites while tergites 3-7 possess less setae than T1-3 and T8-T10. Caudal annulets of abdominal segment 8, 9, and 10 are most setose; dorsal surface elsewhere with scattered short inconspicuous setae. Body form of postdefecating larva wide and dorsoventrally flattened, robust; body segments of similar width on whole length (Fig. 4A-B ). Paired body tubercles absent or very ill-developed on thorax but present and well-developed on metasomal segments except last (T10), T7-9 with less-conspicuous tubercles than previous tergites. Dorsal tubercles flat and well-developed on thoracic segments 2 and 3, and abdominal tergites while most conspicuous are on T2-T6. Body shape of predefecating larva in lateral outline with first abdominal segments having greatest diameter and outline tapering slightly forward and strongly backward from there. Abdominal segment 9 shorter and more hirsute than previous, segment 10 attached to middle of segment 9 in lateral view; anus positioned medially and transverse. Spiracles (Figure 5C ) unpigmented, subequal in diameter; atrium globular, slightly wider than deep, projecting little above body wall, with rim; atrial opening diameter vs. peritreme width ratio 1.5; atrial inner surface with rows of wrinkles concentric with primary tracheal opening; primary tracheal opening with collar; subatrium long, with about 20 or more chambers of approximately equal size except one or two next to atrium slightly larger in diameter. Sex characters unknown.

Head: Head moderately small in relation to body size; oriented in normal, hypognathous position relative to thorax. Setae long but sparse on upper part of head capsule; those of maxillary and labial apices large, straight and conspicuous. Head capsule unpigmented except at points of articulations with mandibles; labrum faintly pigmented; mandibles moderately pigmented except mandibular apices and areas of articulation with head capsule strongly pigmented; maxillary sclerites faintly pigmented; salivary lips not projecting, unpigmented; antennal papilla, maxillary and labial palpi all uniformly moderately pigmented (Figs 4C , 5A ). Spiculation apparently absent even on hypopharynx, not on maxilla. Coronal ridge present for more than half distance from postoccipital ridge toward level of antennae in frontal view; postoccipital ridge developed but badly visible, not bending forward; hypostomal ridge well developed, giving rise to pronounced dorsal ramus that extends posteriorly for short distance before ending abruptly in front of postoccipital ridge; both hypostomal ridge and ramus unpigmented; posterior part of ridge bending strongly mesad, forming deeply recessed posterior tentorial pit at junction with posterior tentorial bridge; posterior bridge absent in postdefecating larva because specimen preparing to molt; internal pleurostomal ridge obviously present but not well defined; epistomal ridge not developed. Tentorium mostly absent because of impending ecdysis. Parietal bands absent. In lateral view, clypeus not projecting beyond frons, antenna arising from well-developed prominence, and labrum not extending much beyond clypeus. Diameter of basal ring of antenna about two-thirds distance from closest point on ring to center of anterior tentorial pit; antennal papilla distinctly but not strongly pigmented, moderately large and elongate, longer than twice basal diameter, apically rounded, bearing perhaps two sensillae apically. Frontal area between antennae with two linear rows of six setae and one sensilla in middle, two additional setae laterally near highest positioned sensillae. Parietal region with several setae - five setae from pleurostomal ridge to front tentorial pit, four smaller setae under antennal orbit and one conspicuous seta just above basal clypeal margin. Clypeus wide with ill-developed basal and apical margins, two sensillae basally on sides and three small sensillae more medially on each side. Labrum shallowly emarginated apically in middle, with a group of four conspicuous and several smaller sensillae on each side apically; labral sclerite not defined and only very poorly pigmented. Epipharynx simple without any visible structures. Mandible moderately robust, darkly pigmented, tridentate with apical tooth longest and blunt, medial tooth with blunt apex, lateral tooth small; cuspal area developed, projecting, with surface irregularly uneven; outer mandibular surface without setae (Fig. 5B ). Maxillary apex strongly bent mesad in frontal view, so that maxillary palpus subapical in position; cardo distinct, posterior end directed toward posterior tentorial pit; stipes weakly sclerotized; maxillary palpi elongate, probably more than two times basal diameters, both pigmented like antennal papilla but slightly thinner than papilla. Stipes with four conspicuous setae. Labium not divided into prementum and postmentum; apex moderately narrow in frontal view; premental sclerite apparently absent as well as border between pre- and postmentum. Two setae on both sides and two smaller on ventral surface. Salivary lips round and well-visible, with inner surface bearing parallel longitudinal grooves; width of lips slightly more than double width of maxillary palpus. Labial palpus scale-like with three sensillae in middle.

Figures

Figure 4. Larvae of Gasteruption. Gasteruption assectator. A mature larva, lateral view B mature larva, dorsal view C head - mouthparts. Gasteruption nigrescens D mature larva, lateral view E mature larva, dorsal view F head - mouthparts. Gasteruption phragmiticola G mature larva, lateral view H mature larva, dorsal view I head - mouthparts.

Figure 5. Body parts of larvae of Gasteruption. Gasteruption assectator. A head, frontal view B mandible, frontal view C spiracle. Gasteruption nigrescens D head, frontal view E mandible, frontal view F spiracle. Gasteruption phragmiticola G head, frontal view H mandible, frontal view I spiracle.