Immature Stages of Bombyliidae
The eggs of the Bombyliidae, in so far as they are known, present no adaptive modifications whatever (Clausen 1940). They are oblong in form, are at times slightly curved, have both ends smoothly rounded, and are 2-4 X longer than broad. They are relatively large, measuring 1.0 by 0.25 mm. in Hyperalonia morio F. and Bombylius fugax Wied. Apparently all species cover the egg with a coating of mucilaginous material to which soil particles adhere at the time of deposition.
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The first‑instar larva of H. oenomaus (Fig. 170A) (Clausen, 1928b) is vermiform, 0.9 mm. in length, and grayish‑white in color. There are 12 body segments which, with the exception of the last, are of equal width. The head capsule is heavily sclerotized, its anterior margin is serrated, and it bears a number of heavy setae. Each thoracic segment bears a long slender spine, directed laterally, at each lateroventral margin. The caudal segment bears a pair of slender spines, which are ca. 1/3rd the body length, dorsolaterally, each arising from a distinct conical protuberance. Intersegmental welts occur lateroventrally between the abdominal segments. The two pairs of spiracles are of simple form and are situated at the anterior margins of the first thoracic and the last abdominal segments, respectively.
The described first‑instar larvae of other species of the family are similar in all essential respects to the larva of H. oenomaus. That of B. pumilis Meig. described by Nielson (1903) is stated to have the lateroventral welts at the anterior margins or the 2nd to 6th abdominal segments only. The posterior spiracles of this species are elevated and occur at the posterior margin of the eighth abdominal segment, rather than on the last segment. No thoracic spiracles were detected. The larva of B. fugax Wied. (Seguy & Baudot 1922) is similar to B. pumilis in all characters mentioned. The mouth hooks of this species are thought to be paired and articulated.
The second‑instar larva has been described for H. oenomaus and B. pumilis. The body is rather maggot‑like as contrasted with the vermiform first‑instar larva. That of H. oenomaus (Fig. 170B) has 12 distinct body segments with the intersegmental constrictions very pronounced, is widest in the mid‑abdominal region, and bears no spines or setae. The color is mottled white and yellow, the latter due to the large and numerous fat bodies which are visible through the transparent integument. The two pairs of simple spiracles are situated at the posterior margin of the first thoracic and eighth abdominal segments, respectively. The larva of B. pumilis is similar except that the body segments are of nearly uniform width and the segmentation is not pronounced.
The third‑instar larva has been described for only a few species. That of H. oenomaus (Fig. 170C) has 12 body segments and is somewhat elongated, curved, and widest in the mid-abdominal region. The integument is smooth and glistening, without setae or other ornamentation. The posterior spiracles (Fig. 170D), situated somewhat dorsally on the eighth abdominal segment, are small and crescent‑shaped and have ca. 12 openings. The anterior spiracles, at the posterior margin of the first thoracic segment, are of similar form but less heavily sclerotized. The larvae of other species are of similar form. That of S. oreas O.S. is stated to have the anterior spiracles of elliptical form and situated between the 2nd and 3rd thoracic segments, while the posterior spiracles are semicircular, with 9-10 openings. In B pumilis, the latter are said to be fan-shaped. In Cyrtomorpha flaviscutellaris Rob. (Fuller 1938), the anterior spiracles are larger than the posterior pair and have 5 slits whereas the latter has only 3, located at one end of the oval plate. Both pairs of spiracles are completely concealed by folds of the integument. Each of the first 7 abdominal segments has a pair of spiracles of minute size.
The pupae of Bombyliidae are of the free type (Fig. 171) and bear a considerable resemblance to those of the Asilidae, Nemestrinidae, and related forms. One of the most conspicuous characters is the head crown which consists usually of three pairs of heavily sclerotized, pointed projections, or teeth, of which the medium pair may be bifurcate or otherwise modified. The posterior pair occurs on the proboscis sheath and are close together. In some species, such as A. anale Say (Shelford 1913), the median and anterior pairs are fused at the base to form a fan‑shaped crown. Each abdominal segment bears a transverse ring of long slender hairs, and dorsally there is a transverse row of short, curved hooks. The last abdominal segment terminates in one or two pairs of short heavy spines.
Several species lack the conspicuous head crown of spines or teeth described above, among these being Systropus conopoides (Kunckel d'Herculais 1905) which bears instead a pointed plate over the front of the head, markedly similar in form to that borne by the pupa of its eucleid host, Sibine bonaerensis Berg., and which serves the same purpose.