The preimaginal stages of T. peregrina are described. The egg displays a sculptured chorion, which is found only on those deposited externally. The immature larvae are characterized by their peculiarities in (a) a setose ring on the thoracic and abdominal segments, (b) an anal notch and (c) size and the sensory structures of the head capsule. The final instar is described and illustrated. Morphological structures of diagnostic value are discussed. The most salient character shown by the mature larva of this species lies in the epistoma, which is complete.
The family Pteromalidae includes 3506 species in 588 genera (Noyes 2003). The life-history of this family is extremely varied, including solitary and gregarious species, ectoparasitoids and endoparasitoids, koinobionts and idiobionts, primary and secondary parasitoids, and even predators. The genus Trichomalopsis Crawford, 1913, with 54 species (Noyes 2003) attacks Diptera, Hymenoptera, and Lepidoptera, and its species are either primary parasitoids of larvae or pupae, or hyperparasitoids. This study addresses the preimaginal stages of a species of this genus, Trichomalopsis peregrina (Graham, 1969). Trichomalopsis peregrina attacks Hymenoptera and Lepidoptera, and is a primary ectoparasitoid or hyperparasitoid. Within Trichomalopsis the main studies of mature larvae have been carried out by Proper (1931), who described the preimaginal stages of Trichomalopsis hemiptera (Walker, 1836), and Best & Simpson (1975), who reported on Trichomalopsis americana (Gahan, 1933). Clausen (1972) and Finlayson (1987) published compendia in which work on immature parasitoids was detailed.
Materials and Methods
Preimaginal instars of T. peregrina were obtained from Euproctis chrysorrhoea (L., 1758) (Lymantriidae) larvae in winter tents made on Crataegus sp. at the Spanish locality of Jarafuel (Zacaé) (Valencia province). The tents were collected and transported to the laboratory on 20 Jan 2004 and held for the emergence of imagos in order to identify the parasitoids.
Nine mature larvae, 2 immature larvae and 1 egg of T. peregrina were fixed and preserved in 70% ethyl alcohol (ETOH) for subsequent study and description. The methodology used in their preparation was similar to that employed by Tormos et al. (2004). The ensuing descriptions essentially employ the terminology and organization used by Finlaysson (1987) and Tormos et al. (2004). Voucher specimens are deposited at the Fundación Entomológica “Torres-Sala” (València, Spain).
Description of Preimaginal Stages
Trichomalopsis peregrina (Graham, 1969) (Figs. 1-8)
Mature Larva (Figs. 1-5)
Body (Fig. 1) (l = 1.5-2.9 mm (x̄ = 2.5), maximum w = 0.5-1.4 mm (x̄ = 1.9, n = 9) hymenopteriform, slightly broader in mid region, with a reduced head, with distinct segmentation, with 3 thoracic and 10 abdominal segments. Color whitish or yellowish. Weakly sclerotized. Pleural lobes not developed. Tegument with 3 pairs of setae (Figs. 2, 3b) (l = 8-10 μm) distributed around all 3 thoracic and the first 9 abdominal segments (setose ring). Anal segment (Fig. 3a, Fig. 3b) notched transversely, a dorsal lobe and another ventral one being differentiated, each with 2 pairs of setae (l = 8-12 μm). Spiracles (Fig. 4a, Fig. 4b) on mesothorax, metathorax and on first 7 abdominal segments; atrium (l = 74 μm, d maximum = 37 μm) with peritreme and asperities well differentiated, funnel-shaped, with approximately 5 chambers; closing apparatus (l = 55 μm; w = 7 μm) adjacent to atrium.
Cranium (Fig. 5a, Fig. 5b) (w = 145 μm, h (from apex of cranium to base of mandibles = 200 μm), higher than wide, narrower than the first thoracic segment, very weakly indented dorsally along its middle line (Fig. 5c), very weakly sclerotized, with 6 pairs of setae (l = 2-3 μm) and 4 pairs of sensilla (d = 1-2 μm). Antennae markedly papilliform (Fig. 5d). Mandibles sclerotized, triangular in form, each with sharp, toothless blade. Maxillae and labium indistinguishable. Epistoma complete. Labrum emarginate (Fig. 5b), with 4 sensilla (d = 1-2 μm). Pleurostoma and superior and inferior mandibular processes present. Tentorium more or less visible.
Data on the Egg and Immature Larvae
Egg (l = 230 μm, maximum w = 73 μm) oval, more or less cylindrical, with a granulate surface.
Immature Larvae (Fig. 7, Fig. 8)
Two small larvae (a and b) were obtained: a (l = 0.3 mm, maximum w = 0.1 mm), b (l = 0.6 mm, maximum w = 0.2 mm), whose morphology was similar to that of the mature larva, although different in presenting a large head capsule in comparison with the body; in not having the setose ring well differentiated, and with the anal notch poorly differentiated. Larva a (Fig. 7) only had 2 pairs of cephalic sensilla whereas larva b (Fig. 8) displays 4 pairs.
Discussion
The mature larva of T. peregrina share the following characters with other Chalcidoidea: (a) hymenopteriform, with a reduced head, 3 thoracic and 10 abdominal segments, and 9 pairs of spiracles; (b) cephalic structures very reduced, although mandibles are well developed, sclerotized, triangular, with a short blade without teeth: (b1) maxillae and labium completely fused, and (b2) salivary orifice absent.
Trichomalopsis peregrina shares the presence of a pleurostome and superior and inferior mandibular processes with the mature larvae of the pteromalid species Psychophagus omnivorus (Walker, 1835), Tritneptis diprionis Gahan, 1938 and T. klugii (Ratzeburg, 1844). However, the presence of a completely differentiated epistoma separates this larva from other known larvae of the family. It is different from those already described in the genus in the absence of tubercules upon the body segments, which are present, although attenuated, in T. hemiptera (Proper 1931), together with the number of sensilla of the labrum (6 pairs in T. hemiptera). The description of T. americana by Best & Simpson (1975) is extremely succinct and cannot be used for comparative purposes.
As in the case of eggs that are deposited externally, the chorion is sculptured.
The immature larvae are very similar to the mature larva, mainly differing in the size of the head capsule with respect to the body, in the number of sensory structures on the head, in the presence of setae on the tegument, and in the differentiation of the notch of the last body segment.
According to Graham (1969) the mature larva of T. hemiptera, described by Proper (1931), would correspond to that of T. peregrina, since a misidentification of this latter species was made. If this were the case, the differences mentioned above between the two preimaginal instars would have to be considered as being due to the variability of the species.
Acknowledgments
We thank Michael W. Gates (National Museum of Natural History, USA) for his observations and critical reading of the manuscript. The laboratories of the Fundación Entomológica “Torres-Sala” were used to carry out this study. The research conducted was possible thanks to contributions from the “Ministerio de Educación y Ciencia de España” (project I+D BOS2002-03820 with an associate 4-year grant FPI). Financial additional support for this paper was provided by the Junta de Castilla y León project SA012A05.
References Cited
Fig. 2, 3b, 4b, 5b. Mature larva of Trichomalopsis peregrina (Graham): (2) Abdominal segments VIII-X (lateral view). Letters a-b show the distribution of the setae on segments VIII-IX. (3b) Abdominal segments IX-X (ventral view). Note distribution of lateral (a) and ventral (b) setae on segment IX and the dorsal (DL) and ventral (LV) lobes, and the setae--dorsal lobe (c), ventral (d) of the anal segment. (4b) Metathoracic spiracle (detail). (5b) Head capsule (frontal view) Note labrum with its sensilla.
Fig. 3a. Mature larva of Trichomalopsis peregrina (Graham): Anal segment (lateral view). Setae and notch are shown.
Fig. 4a. Mature larva of Trichomalopsis peregrina (Graham): Spiracle (a: atrium, a1-a5: chambers of atrium, as: asperities, b: closing apparatus of spiracle, c: spiracular trachea).
Fig. 5a. Mature larva of Trichomalopsis peregrina (Graham): Cranium (lateral view) (a: epistoma, b: mandible).
Fig. 5.
Mature larva of Trichomalopsis peregrina (Graham): (c) Head capsule (posterior view). Note the slightly emarginate vertex. (d) Head capsule (lateral view). Note papilliform antennae (a). Fig. 6 deleted in proof.
