Immature Stages of Cynipoidea
Immature stages of Cynipoidea were discussed in detail by Clausen (1940), as follows:
The Egg.‑‑The eggs of the parasitic members of the superfamily are uniformly of the stalked type, with the stalk, which is situated at the anterior end, ranging in length from less than that of the main body, as in Charips sp. (Fig. 126A), to several times its length. That of Figites anthomyiarum (Fig. 128A) is elongated and somewhat constricted in the middle and has a stalk of about equal length. In Eucoila keilini, the stalk is twice the length of the egg body, and in Ibalia leucospoides it is about four times as long. The chorion is thin and transparent and without surface ornamentation.
First‑instar Larva.‑‑The known first‑instar larvae of the superfamily are of several distinct types. The "polypodeiform" larva of I. leucospoides (Fig. 127A) is unusually elongated, with a relatively large head, which is somewhat flattened dorsoventrally and is provided with falcate mandibles. Of the 13 body segments, all except the last bear a pair of fleshy, finger‑like processes ventrally, which are of uniform length. There are no integumentary spines or setae. The last abdominal segment is prolonged into a dorsally curved tail equal in length to the four preceding segments.
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The first‑instar larvae of the several genera of Eucoilinae that have been described are distinctive and readily recognized and have been designated as "eucoiliform." The essential characters of this larval type that distinguish it from the polypodeiform are the long, paired, fleshy ventral processes on the thoracic segments only and an exceptionally long tapering tail. In Eucoila keilini (Fig. 127B), the head is large and somewhat conical, and the body segmentation is indistinct. The fleshy thoracic processes are about half the length of the body and taper to a blunt point. The posterior segments of the abdomen are very much narrowed, being only very slightly wider than the base of the tail, and the tail itself is appreciably longer than the thoracic processes, is curved ventrally, and terminates in a sharp point. The segment immediately preceding the tail bears a fleshy conical lobe on the median ventral line. The integument of the posterior abdominal segments bears numerous short sclerotized spicules.
The larva of Cothonaspis rapae described by James and Malchanova is similar to that of Eucoila. There are at least seven distinct abdominal segments in addition to the two or more that make up the tail, and the latter organ is nearly as long as the entire body. There are a few setae upon the thoracic processes, and the distal third of the tail bears numerous spines.
The eucoiliform larva of Kleidotoma marshalli figured and described by James has 12 apparent body segments, and the body is much more slender than that of Eucoila or of Cothonaspis. The head is large, with the mouth opening distinctly ventral. The fleshy thoracic processes are much shorter, being equal only to one segment in length, and they bear no setae. Stout setae are present on the distal portion of the tail. The anal opening is indicated on the dorsum of the eighth abdominal segment.
The first‑instar larva of Figites anthomyiarum (Fig. 128B) is modified eucoiliform the thoracic processes being even more reduced than in Kleidotoma with the prothoracic pair only as long as wide, and the tail is short, almost cylindrical, and bluntly rounded rather than pointed at the tip. The segmentation is distinct, and the 12 body segments preceding the tail bear fleshy spines on the dorsum, these being largest in the mid‑abdominal region.
In the Charipinae, the only first‑instar larva that was described by 1940 was that of Charips sp. (Fig. 126B) by Haviland. This larva has few characters in common with other members of the family and must be considered as a modified caudate form. The head is large, equaling the thoracic segments in width, and is produced anterioventrally into a conical "proboscis." There are three pairs of sclerotized "nodules" ventrally and one pair dorsally, which presumably are sensory organs. The mandibles are long and slender. There are 13 body segments, of which the first 12 diminish gradually in length and width caudad. The last abdominal segment is broad at its base, tapers sharply, and terminates in a cylindrical, ventrally directed tail. This last segment is equal in length to the 9 abdominal segments preceding it. The anal opening is large, situated dorsally at the base of the last segment, and encircled by a sclerotized ring. The head, and the body segments except the last, are heavily sclerotized, and each of the body segments telescopes into the one preceding it.
None of the first‑instar larvae of the family that has been studied possesses any indication of a tracheal system, and respiration is consequently by diffusion only.
Second‑instar Larvae. --The second‑instar larvae of the Cynipoidea reveal differences that are almost as great as those in the first instar. In Ibalia, the paired ventral processes have disappeared, and the tail is somewhat reduced. The second‑instar larva of Cothonaspis rapae retains the eucoiliform characters of the first instar, but the segmentation is more distinct, whereas in Kleidotoma marshalli there is a change to the polypodeiform. The head of the latter is very large, exceeding the body segments in width and length, and the segmentation is exceptionally distinct. The minute paired processes occur ventrally on the first 10 body segments. The larva of Figites anthomyiarum (Fig. 128C) is similar to Kleidotoma in all essential respects though the head is small, the segmentation indistinct, and the tail situated ventrally and at right angles to the axis of the body. An internal tracheal system is present, but there are no spiracles. The second‑instar larva of Charips sp. (Fig. 126C) is still of the caudate form, though the heavy sclerotization of the integument is lacking. Each of the thoracic segments bears a pair of small processes ventrally, and a pair of large conical structures is present at the posterior ventral margin of the head.
James studied the early instars of cynipoid larvae and came to the conclusion that the eucoiliform first‑instar larvae of Eucoila and Cothonaspis are derived from eggs which hatch in the middle of the protopod stage of embryonic development, whereas the polypodeiform larvae correspond, as the name implies, to the polypod phase. The form of the Figites larva, with its reduced appendages and distinct segmentation, indicates hatching in a later embryonic stage than does any of the other species discussed. The Charips larva, being devoid of appendages, is regarded as preceding or as being a very early form of the protopod stage. This view of the stage of development at the time of hatching is borne out by the occurrence of polypodeiform second‑instar larvae following the eucoiliform first instar in Figites and Kleidotoma.
Only three instars have been distinguished in the species studied, with the exception of Ibalia leucospoides, which has four. The third‑instar larva of Ibalia is cylindrical in form with the tail still further reduced and may be readily recognized by the presence of spiracles on the second and third thoracic segments.
Mature Larvae.--The mature larvae of the various species differ in only relatively minor characters. That of Ibalia has the integument smooth and shining except in the pleural areas of the second to eleventh body segments, which bear rounded "bases" studded with minute spines. The mandibles are tridentate, whereas they ere bidentate in Figites and Charips. There is a somewhat surprising variation in the number and position of the spiracles. Ibalia has 10 pairs, situated on the second and third thoracic and the first eight abdominal segments; Eucoila keilini and Figites anthomyiarum have nine pairs, on the last two thoracic and the first seven abdominal segments; Cothonaspis rapae eight pairs, on the third thoracic and the first seven abdominal segments; and Charips sp. has only six pairs, on the second and third thoracic and the first, second, fourth, and sixth abdominal segments.