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Immature Stages of Scelionidae

 

Immature stages of Scelionidae were discussed in detail by Clausen (1940), as follows:

 

The eggs of the species of Scelionidae that have been described are of a uniform type, all being stalked, with the main body ovate to spindle shaped and the tapering or tubular anterior stalk ranging in length from 1/2 to 1 & 1/2 X that of the main body.  The eggs of Scelio are slender, with the line of demarcation between the stalk and main body not distinct, and that of S. pembertoni has a small pedicel at the posterior end, also.  There is an increase in size during incubation, as a result of which the stalk disappears.

 

The first‑instar larva of the family is "teleaform," so‑called from the larva of Tiphodytes (Teleas sp.) described and figured by Ganin (1869).  It is characterized by a complete lack of segmentation but with the body divided by a sharp constriction into two almost equal portions.  There is a difference of opinion as to the parts that constitute the anterior portion.  Henriksen, Bakkendorf (1934), and Pagden (1934) considered that it represents the head alone, while Noble & Kamal termed it the cephalothorax, made up of the head and the three thoracic segments.  This latter interpretation is more probably correct.  The mandibles of all species are external, widely spaced, exceedingly large, curved, and sharply pointed and may be either heavily sclerotized or fleshy and unsclerotized.  In Phanurus sp. dissected from eggs of Chrysopa in Japan, there are no other evident structures or organs on the cephalothorax, while in several other species of the family various head structures are well­ developed.  The antennal processes of Scelio fulgidus (Fig. 113E) and S. pembertoni are large and conical, are widely spaced, and arise immediately above the bases of the mandibles.  In a number of species, there is a large, fleshy lobe or process on the median ventral line of the cephalothorax, below or behind the mandibles.  This is highly developed in the genus Scelio (Fig. 113I) and has been considered the labium by several authors.

 

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                        Fig 113

 

The abdomen is almost globular in form and terminates in a caudoventral horn, or tail, which may be fleshy and of irregular form or heavily sclerotized, sickle like, and terminating in a sharp point.  In some species, there are one or two supple­mentary lobes at the base of the tail.  The fleshy type of tail is usually spined dorsally and on the distal portion and is occasionally bifurcate. at the tip.

 

In Eumicrosoma, Telenomus, Scelio, Phanurus, and Microphanurus, and probably in other genera also, there is a partial or complete transverse ring of long hairs near the anterior margin of the abdomen.  These hairs vary considerably in number and distribution.  In E. benefica (Fig.  113B), they occur upon the sides only, whereas in others the ring is complete and it is double in several species of Phanurus.  The abdominal hairs of Teleas sp.  (Fig.  113C, D) figured by Ayers (1884), Limnodytes, and Tiphodytes are in distinct tufts upon the summits of a pair of fleshy lobes situated at the lateroventral margins on the anterior portion of the abdomen.  Marchal (l900) illustrated them in that arrangement in T. gerriphagus Mnrchal, who;e Martin (1928), dealing with the same species, shows the hairs in a transverse row.

 

Chopard (1923) figured several supposed developmental phases of the first‑instar larva of Rielia manticida in the eggs of Mantidae.  The first (Fig. 113F), secured from host eggs in April, is of simple form, with the abdomen lacking the band of hairs and the tail.  Those found in May show a lateroventral tuft of short hairs, and the tip of the abdomen is produced into a broadly conical tail.  The form found in June and July (Fig. 113G) has the lateral abdominal hairs well‑developed and the tail further enlarged (Fig.  113H).  The author is inclined to consider the latter to be the second instar.  It is however, identical in general characters with the first‑instar larva of various other species.

 

The second‑instar larva had been described in only a few species as of 1940 (Clausen 1940).  That of T. gerriphagus figured by Martin is irregularly ovoid in form, with the mandibles still large and a small hook‑like caudal horn.  Immediately above the mandibles are two plate like thickenings of the integument, separated by a median depression.  The abdominal hairs are present in groups of 5-6 in a band across the dorsum and sides.  None of these characters was found in all of the specimens examined, and the true form of the second instar is thus doubtful.  That of M. basalis is very robust, with the segmentation indistinct; the mandibles are small and simple.  There are no integumentary spines or setae, and the caudal horn is lacking.  The second‑instar larvae of  T. ulyetti and Phanurus angustatus Thom. (Fig. 113J) are cylindrical and distinctly segmented, but otherwise similar to that of M. basalis..  Neither the first‑ nor second‑instar larva of any species has been found to possess a tracheal system or spiracles.

 

The third‑instar larva of T. ulyetti is similar in form to the second but may be readily distinguished by the presence of nine pairs of spiracles, situated on the last two thoracic and the first seven abdominal segments.  Kamal mentioned that only the two pairs of thoracic spiracles are functional in M. basalis, the following seven being minute and closed.  The integument of the abdomen bears numerous small tubercles at the lateroventral margins, which extend across the venter on the posterior segments.  This species and S. fulgidus are grayish‑green in color.

 

The mature larva of Cacus oecanthi Riley bears a pair of rounded protuberances Internally on each body segment except the last, and the second to seventh segments also have a pair of prominent tubercles dorsally (Parrott & Fulton 1914).

 

In n number of species, only two larval instars are mentioned, this being due presumably to the marked similarity of the second and third.  The larva of P. angustatus (described and figured as the second and last instar (Bakkendorf 1934) is probably the true second, as judged by the lack of a respiratory system.

 

References:   Please refer to  <biology.ref.htm>, [Additional references may be found at: MELVYL Library ]