Immature Stages of Heloridae
Immature stages of Heloridae were discussed in detail by Clausen (1940), as follows:
The early stages of Heloridae were known only in the case of Helorus paradixus, and consequently no general description can be given for the family. It is noteworthy, however, that the instars here described bear a striking similarity to those of Phaenoserphus and Paracodrus of the Proctotrupidae and of Collyria of the Braconidae.
The newly laid egg of H. paradoxus (Fig. 122A) is white, oblong in form, and slightly wider at the anterior end and bears a minute conical micropyle.
The first‑instar larva (Fig. 122C) is elongated and polypodeiform, with 13 body segments, of which the posterior ones are indistinctly indicated. The head is heavily sclerotized and bears a peculiar oral "sac," which is structureless and transparent. Within this sac are the mandibles, which are large and heavily sclerotized. Each abdominal segment except the last bears a pair of large fleshy processes ventrally. Those of the caudal segments are of decreasing size. The last segment is drawn out into a short, ventrally curved tail. The respiratory system is vestigial and consists only of two short lateral trunks with a small number of simple branches but no commissures.
The second‑instar larva (Fig. 122D) is unlike the preceding one; for it lacks the heavily sclerotized head capsule and the fleshy paired ventral processes, and the tail is greatly reduced. The mandibles appear to be entirely lacking. There are no cuticular spines or setae. The respiratory system comprises well‑developed lateral trunks extending the length of the body, with spiracular spurs in many segments and extensive dorsal and ventral branches, but no commissures or spiracles.
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The mature third‑instar larva (Fig. 122E) is robust in form and is distinguished principally by the markings of the head. There is a peculiar dark‑brown melanized band (Fig. 122H) encircling the lateral posterior margins, which appears gradually and is apparently oxidative in nature. The mandibles are widely spaced and vestigial. Eight pairs of spiracles are present, these being situated near the anterior margins of the second and third thoracic and the first six abdominal segments. Blind spiracular stalks occur in the seventh and eighth abdominal segments. The posterior commissure is still absent in this instar.
In the second and third instars, there is a peculiar modification in the mid‑gut, apparently not noted heretofore in parasitic larvae, consisting of a series of five membranous sacs, each within the next largest one, and connected by a definite cellular neck to the juncture of the fore- and mid-gut (Fig. 123). They are termed "peritrophic sacs" by Clancy and they increase greatly in size as larval development progresses. It has been determined that these sacs serve as a form of filter to extract the excess moisture from the meconial mass, and the solid materials are then retained in the body until the emergence of the adult (Clausen 1940).