Immature Stages of Eulophidae
Immature stages of Eulophidae were discussed in detail by Clausen (1940), as follows:
The eggs of the great majority of Eulophidae are simple; they are oblong or ovatc to elongate, are often slightly arched, and have both poles smoothly rounded. The chorion is usually delicate and unsculptured, though in Microplectron fuscipennis it shows, under high magnification, minute, conical projections. In a number of species, the micropyle is distinguishable as a small thickened area at the anterior end.
The eggs of several genera of Elachertinae differ from those of the majority of the members of the family. Those of Euplectrus and Elachertus have been stated by several authors to have a pedicel at the middle of the mid‑ventral curve; this serves as an anchor in the skin of the host in the same manner as with the pedicellate eggs of other groups. Observations regarding its form and origin are incomplete. In the figure given by Silvestri for Euplectrus bicolor (Fig. 63A), the pedicel appears to be a definite adaptive modification possibly comparable to that of the tryphonine Ichneumonidae, and Tothill stated that it is "continuous with the egg shell" in Elachertus sp. It may prove, however, to be similar in origin to those of Euxanthellusand the male eggs of some Coccophagus, in which a fold of the unmodified chorion is knotted or twisted at the time of deposition and is inserted into the puncture in the host skin. An examination of the ovarian egg would probably clarify this point
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The pronounced darkening of the chorion of the egg during incubation, which occurs in Euplectrus plathypenae (Fig. 63B) and E. comrstocki, has not been observed in other species of the family.
Records of the number of larval instars of the different species show little consistency. Only three have been detected in Eulophus viridulus and Melittobia acasta, four in Pleurotropis parvulus, Tetrastichus ovivorax, and Euplectrus bicolor, and five in Microplectron fuscipennis.
The first‑instar larvae are hymenopteriform and somewhat cylindrical, with 13 distinct body segments, and they have no
characters to distinguish them readily from larvae of related families. Occasional species bear fleshy protuberances or tubercles on the body. In Diaulinus sp. (Solenotus sp.) figured by Parker (1924), the sensory setae are borne upon distinct tubercles. The larvae of Dimmockia javana possess distinct intersegmental protuberances, which function as pseudopodia, on the mid ventral line from the second to the ninth body segments. Each segment bears a transverse row of minute setae on the dorsum and sides near the posterior margin. The last abdominal segment is bifurcate in Tetrastichus sp. (Berry, 1938); this species has been confused with T. xanthomelaenae from the same host, but the latter does not possess this character. Melittobia acasta has a row of minute spines at the anterior margin of each segment, and T. taylori has a double row in the same position. In T. avivorax (Fig. 64A), this row of spines occurs only dorsally on each segment except the first and in the Tetrastichus sp. mentioned above they encircle the segments. According to Silvestri (1910c), the row of spines occurs at the posterior margin of the segments in T xanthomelaenae. P. parvulus apparently lacks the sensory setae and cuticular spines.
The integument of a number of species bears a distinct sculpturing. That of T. ovivorax has a pebbled appearance, whereas in T. xanthomelaenae it is imbricated. Hyperteles intermedia Thoms. (Parker and Thompson, 1928) has irregular areas of minute tubercles on all body segments except the last two. There are three pairs of sensory tubercles on each thoracic segment and four pairs on each abdominal segment except the last, which has only one.
The majority of species that have been studied have an open tracheal system, with spiracles on the mesothorax and the first three abdominal segments. Euplectrus bicolor is said to have five pairs, the additional one being on the metathorax. Several species of endophagous habit lack the open tracheal system, among them being P. parvulus, Tetrastichus taylori, Anellaria conomeli, and Thripoctnus bruni.
The distinguishing characters of the first instar, particularly the cuticular spines and ornamentation, usually do not persist after the first molt, and the intermediate larval instars of the different species are consequently quite similar. In Diaulinus, however, the tubercles and setae are retained to the final instar, and this is true, also, of the two pairs of "papillae" on the last abdominal segment of Eulophus viridulus. In most species, the full complement of nine pairs of spiracles, situated on the last two thoracic and the first seven abdominal segments, appears in the second instar. They are stated to be on the mesothorax and the first eight abdominal segments of Melittooia acasta.
The mature larvae are usually of simple form, with very few integumentary spines or setae, and are usually without surface sculpturing. Tetrastichus eriophyes bears transverse striations, whereas T. ovivorax has the minute tubercles, mentioned for the first instar, ventrally. The larva of H. intermedia (Fig. 64B) bears numerous small integumentary tubercles in transverse rows both ventrally and dorsally on all body segments except the last. In Thripoctenus brui, the mature larva differs considerably from that of other genera in being cylindrical and about three times longer than wide, with both ends broadly rounded and no visible segmentation; it bears a transverse ring of about 12 short but stout spines at the middle of the body. The mandibles of Tetrastichus ovivorax bidentate, in contrast to the simple form of other species of the family.
The larvae of the gregarious species, such as Euplectrus (Fig. 63C) upon free living hosts, are pear‑shaped and are very broad in the mid‑abdominal region; the last four or five segments are much narrowed.
Nine pairs of spiracles are usually present, these being on the last two thoracic and the following seven abdominal segments. Pleurotropis benefica, P. parvulus, and Chrysocharis laricinellae Ratz. larvae only seven, those on the third thoracic and on the first abdominal segments being missing. In P. parvulus the number is said to be variable, usually smaller than the full complement mentioned, and it may differ on the two sides of the same individual. Thripoctenus brui and Anellaria conomeli lack the spiracles even in the mature larva, and Silvestri did not mention or figure them in Tetrastichus ovivorax.
The pupae of a considerable number of species, particularly of the Eulophinae, have an exceptionally heavy integument which m&y be jet black or dark‑brown in color. In a species of Elachertus found attacking Altona by Tothill, the pupa bears a pair of fleshy processes at the lateroventral margins of the seventh and eighth abdominal segments, each of which bears a spiracle at its tip.