Immature Stages of Nemestrinidae
The eggs of two species of Nemestrinidae, Hiromoneura obscura Meig. and H. articulata, were described by 1940 (Clausen 1940). That of the first‑named species is 1.5 mm. long, very slender, and slightly curved. The color is at first white, changing during incubation to yellowish‑gray. The egg of H. articulata is somewhat larger, measuring 2.0 by 0.25 mm., is curved, and has both ends smoothly rounded. The white color at deposition changes to bluish after a few days.
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The first‑instar larva of H. obscura (Fig. 166), is cylindrical in form and 1.5 mm. in length and has 11 body segments following the head. A distinguishing feature of this larva is the occurrence of a pair of long hooked spines upon the "pseudopods" of the first eight abdominal segments; the ninth segment has two pairs of smaller size. The hooked points of all of these except the two pairs on the last segment are directed caudad. They are thought to aid in locomotion in a looping manner. The last segment also bears four pairs of rather fleshy spines that nearly equal the segment in length. The respiratory system comprises a pair of longitudinal tracheal trunks terminating in small simple spiracles situated dorsolaterally on the last abdominal segment. Anterior spiracles are lacking.
The first‑instar larva of H. articulata is described and figured by Stuardo, and is identical in all principal characters with that described above.
The second‑instar larva of H. obscura, as described and figured by Brauer, is elongate‑cylindrical, with the posterior end of the body broadly rounded. The integumentary armature of the first instar is lacking. The tracheal system is unchanged, though the posterior spiracles now have a large central button with a large number of short linear slits radiating outward in a complete circle.
What is presumably the second instar of T. ostracea was observed by Fuller and is apparently quite similar to that of H. obscura. Anterior spiracles are lacking, and the posterior spiracles (Fig. 167A) are circular in form with 9-10 elongated-oval slits radiating from the central button.
Potgieter's brief description of the supposed second‑instar larva of Symmictus costatus reveals a form entirely different from that of Hirmoneura. This larva possesses a tail approximately twice the length of the body, and is comparable to that of rat-tailed Syrphidae; this organ is said to serve as a means of attachment to the integument of the host and presumably functions in respiration. This adaptation is so markedly at variance with the known larval forms of this and all closely related families that a more thorough study would be highly desirable. If a respiratory connection is made by means of an opening in the integument, it would be expected that an integument funnel, or respiratory sheath would be formed. So far as is known at present this is found only in the Tachinidae and a few Sarcophagidae, with some indication of its occasional appearance in the Cyrtidae.
The mature third‑instar larva of H. obscura, as described by Handlirsch, is 22 mm. in length and measures 5.0 mm. at its widest point. The segmentation is distinct, and the abdominal segments bear various ridges, welts, and folds. The caudal segment is more heavily sclerotized than those preceding it and bears fleshy transverse dorsal and ventral lobes or ridges. The posterior spiracles are situated on the inner side of the upper lobe. The respiratory system has only this one pair of spiracles, which is in marked contrast to the number found in related families. The paired mouth hooks are short but stout, and the three pharyngeal plates are long and slender.
The third instar of T. ostracea is pale-yellow in color, 9 to 17 mm. long, and much the widest in the posterior abdominal region. Each body segment bears one or two rows of fleshy processes dorsally and ventrally. The posterior spiracles (Fig. 167C) are circular, with 20 linear slits radiating outward from the central button. Functional anterior spiracles are lacking, but vestigial ones are present on the first thoracic to the seventh abdominal segments.
The pupae are similar to those of related families in the head armature and the hooks and spines borne on the abdomen. In H. obscura, there are two long, slender, curved prongs at the anterior ventral margin of the head, and above them is a pair of conical processes. The first three abdominal segments bear a ring of forwardly directed hairs, which occur ventrally on the following segments, also; these latter segments bear dorsally a transverse row of heavy curved spines, or hooks, which are likewise directed cephalad. Distinctly raised spiracles occur on the prothorax and the first 7 abdominal segments. The last abdominal segment terminates in a pair of large, laterally directed prongs, of anchor-like form.