Immature Stages of Agriotypidae
Immature stages of Agriotypidae were discussed in detail by Clausen (1940), as follows:
The egg of Agriotypus gracilis Waterston measures 0. 9 mm. in length and 0. 18 mm. in greatest width and is slightly larger than that of A. armatus. It is slightly convex dorsally and broadest at the anterior end, and the posterior end is smoothly rounded. The chorion is exceedingly thick and tough. At the anterior end is a heavy pedicel of variable length, ranging up to 0.25 mm., the distal extremity of which is irregularly expanded. This "button" is embedded in the integument of the host and anchors the egg firmly in position. Both pedicel and button become black and shriveled after deposition. It is noteworthy that the pedicel mentioned is not represented by any modification in the ovarian egg, which is elongated and oval in form and has the anterior end smoothly rounded. This, and the fact that the pedicel darkens and shrivels quickly after formation, would indicate that it may be formed from secretions of the accessory glands or from material that appears to envelop the anterior end of the ovarian egg, though this aspect has not been studied. It may be emphasized, also, that the pedicel is situated at the anterior end of the egg, whereas in other pedicellate ichneumonoid eggs the pedicel and its "anchor" are represented by definite structures on the ovarian egg and are situated at the posterior end. As the embryo develops, the paired caudal processes can be seen lying along the mid‑ventral line and extending forward to the posterior margin of the head.
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The first‑instar larvae (Fig. 41A, B) of the two species present no apparent points of distinction. The body comprises 13 segments, exclusive of the head, and measures 1.2 mm. in length to the base of the caudal processes. The head is heavily sclerotized, slightly broader than long, and bears dorsally a pair of horn‑like structures markedly similar to those of the planidia of the Perilampidae. There are four pairs of minute setae dorsally and three pairs ventrally. The mandibles are simple. Each body segment except the last bears a median transverse row of heavy spines dorsally, and these diminish in length caudad. On the first five segments, the rows are continuous across the dorsum, but on those following the rows are interrupted medially. The first segment bears two pairs of lateral setae, and the following segments bear one pair. The venter of each of the first eight segments bears a broad band of minute setae, and on each of the following four segments the band is interrupted medially. The caudal segment is bifurcate, and the two tapering, heavily sclerotized prongs are 0. 9 mm. in length, diverge at an angle of about 80 deg., and are directed somewhat ventrad. The lobes at the base of the prongs bear numerous robust setae dorsolaterally. The anal opening is ventral on the last segment. There are no spiracles and no visible internal tracheal system.
Henriksen describes the supposed first‑instar larva of A. armatus (Fig. 42) which he states was found internally in Silo and Goera. Aside from its occurrence internally, it differs markedly in form from the actual first‑instar larva described by Fisher. The body is 1.4 mm. in length, cylindrical, with the caudal end bluntly rounded and lacking the bifurcate process. Certain characters, however, seem to link it with the Agriotypidae, these being the "horn‑like" structures on the head and the transverse rows of spines on the dorsum of the body. It seems Improbable that this larva can be of Agriotypus, but if this proves to be the case it must be the second instar rather than the first.
The second‑instar larva of A. armatus (Fig. 41D) described by Fisher differs from the first in lacking the heavy integumentary spines, and the long bifurcate caudal process is replaced by a pair of shorter, heavy, opposed hooks. The mandibles are conspicuously toothed. An internal tracheal system is present though there are no spiracles, and the transverse commissures, also, are apparently lacking.
The third and last larval instar is similar to the second, though the caudal hooks are relatively much smaller. The head is quadrate in form, and the mandibles are coarsely dentate. In A. armatus, there are thought to be no spiracles, whereas nine pairs occur in A. gracilis. In view of the conditions under which the mature larva passes the last portion of the stage, in which it is surrounded by air rather than water, open spiracles would seem to be essential (Clausen 1940