Immature Stages of Conopidae
De Meijere, described and figured the eggs of several species of Conopidae. The body of the egg is quite large, ranging from 0.7 mm. to 1.4 mm. in length, with the greatest width 1/5th to 1/4th the length. It tapers gradually to a rather blunt point at the posterior end in Dalmannia punctata F. (Fig. 184B), whereas in Physocephala flavipes L. (Fig. 184C) the maximum width is near the posterior end and the tip is drawn out to a sharp point. The distinguishing feature among the eggs of the different species of the family is the form and size of the anterior stalk and the micropylar structure. In D. punctata, the stalk is small and button‑like, with a series of small flanges radiating from the distal end. This egg is quite similar to that of Adapsilia in the family Pyrgotidae. In P. rufipes, the short stalk bears distally about 20 long, slender tubular processes, each 3 microns in width. Physocephala rufipes, P. vittatus F., and Zodion notatum Meig. have similar modifications with a variation in the length of the stalk and in the number of the filamentous processes. The eggs of Myopa buccata L. (Fig. 184A) and Sicus ferrugineus are essentially similar to that of D. punctata, though with the stalk considerably longer and heavier and terminating in four heavy hook‑like flanges. The micropyle is borne at the end of the stalk. The purpose of these flanged micropylar structures is not clear, but they would appear to be admirably suited to fixing the stalk in the oviposition puncture in the intersegmental membrane or to an abdominal air sac of the host, by which means an air supply for the developing embryo would be ensured. The egg of S. ferrugineus is found free in the abdominal cavity of the host, alongside a trachea.
The first‑instar larva has been observed and described for P. rufipes (Fig. 185A) and S. ferrugineus. The body is distinctly pear‑shaped with the greatest width in the mid‑abdominal region. The thoracic segments are indistinct, narrow, and elongated whereas the seven abdominal segments are distinct. The broad caudal segment bears two patches of dark spines. Anterior spiracles are lacking, and the posterior pair that are markedly dorsal in position; are small and simple, represented by a dorsally directed hook, set upon a sclerotized plate, with the opening occurring near the tip. The pharyngeal skeleton is not well‑developed.
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The second‑instar larva is likewise pear‑shaped, somewhat flattened dorsoventrally. with the thoracic segments long and narrowed. The caudal segment bears a transverse band of spines or warts interrupted on the median line in some species, beneath the spiracles. P. rufipes, P. vittatus, and Zodion sp. lack the anterior spiracles, whereas in S. ferrugineus they occur as minute black dots, comprising about 12 papillae; but are rudimentary and nonfunctional and connect with the tracheal stalk by a solid thread only. In P. rufipes, the posterior spiracles (Fig. 185D) are large, oval in form, and pointed dorsally and have about 126 papillae arranged in irregular rows. A large stigmatic scar occurs near the inner margin. Those of P. vittatus are oblong, are not pointed dorsally, and have about 75 papillae. Slightly in front of each spiracle is found a dark sclerotized tubercle or process which is surmounted by 5 blunt spines. In S. ferrugineus (Fig. 185C), the spiracles are elongate oviform pointed at the dorsolateral margin and have only 6-8 papillae, arranged in an arc. A pair of small oval eversible anal "vesicles" is present. The larva of Zodion sp. also bears the sclerotized processes immediately in front of the posterior spiracles.
The third‑instar larva has the same general body form as the preceding instars, with the thoracic segments even more attenuated, and the body as a whole is somewhat broader than thick and is yellowish‑white in color. The body is almost covered with minute tubercles or setae, most numerous in the dorsal and caudal regions, and those on the thoracic segments are mostly at the anterior margins and arranged in transverse rows. The anterior spiracles are lacking in P. rufipes, P. sagittaria Say, P. vittatus, and Zodion sp., whereas they are present on the posterior margin of the prothorax in S. ferrugineus and are fan‑shaped, with about 35 openings. The posterior spiracles are very large, convex, ranging from kidney‑shaped to almost hemispherical, brown to dark reddish‑brown in color, and quite closely set together. The principal variation among species is in the number and arrangement of the spiracular openings. In P. rufipes, these are found in circular groups of 5-10, the groups themselves numbering about 70. The stigmatic scar is large and situated near the inner margin. The spiracles of P. vittatus are somewhat narrower, with about 40 groups of openings, each group comprising 10-15, whereas in S. ferrugineus they do not occur in circular groups but are arranged in irregular rows or patches and number ca. 400. In P. sagittaria (Townsend, 1935) (Fig. 185F) and Zodion sp., the groups of openings are situated upon pronounced raised areas. The third‑instar larvae of Zodion (Fig. 185B) and S. ferrugineus are also distinguished from those of other species by the presence of a pair of rather large, laterally directed anal vesicles which contain tracheal branches. In all species studied by De Meijere, the small sclerotized process surmounted by blunt spines, is found dorsally immediately in front of each posterior spiracle. In P. sagittaria, it is spine‑like in form. The larva in perforating the air sacs of the host so that the spiracles can be applied to the punctures and an air supply thus secured may possibly utilize these structures.
A particularly interesting feature in the morphology of the larvae of the Conopidae is the occurrence, in the 2nd and 3rd instars of S. ferrugineus and Zodion sp., of the paired anal vesicles, which are retractile. Another parasitic group of Diptera known to have a somewhat similar structure is the genus Cryptochaetum, of the family Agromyzidae, in which they are also paired. They differ in origin, however, for those of Cryptochaetum are apparently lobes of the body wall. The vesicles of the Conopidae consequently are more nearly homologous with those of various Hymenoptera.
The puparia (Fig. 185G) are rather robust in form, not more than 2X as long as wide, and somewhat flattened, with the segmentation indistinct and the surface smooth or transversely wrinkled. In P. rufipes, the venter is more convex than the dorsum. The anterior end is narrower than the posterior, whereas in certain other species, such as C. coronatus Rond., the opposite is true. In color, the puparia are brown to dark reddish‑brown, though those of Z. cinereum F. are delicate and glossy and have a yellowish‑brown or reddish tint. The prothoracic cornicles of the pupa do not protrude through the puparial wall. In P. rufipes and S. ferrugineus, the prothoracic spiracles are not elevated and comprise up to 115 papillae arranged in radiating rows. Those of P. vittatus are similar but have a smaller number of papillae. The large posterior spiracles are more prominent and project more than in the 3rd instar larva. De Meijere called attention to the occurrence of a delicate transparent lining of the puparial wall, which may possibly represent a prepupal exuviae such as has been observed in certain other cyclorrhaphous Diptera.