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Immature Stages of Pteromalidae: Spalangiinae


Detailed information on immature stages of Pteromalidae (Spalangiinae)  is being acquired.  However, Clausen (1940) noted that the 1st instar larva is very active and capable of extended movement over the surface of the body of the host pupa.  This is for the purpose of finding a suitable point for feeding, which varies, but usually is around the dorsum or dorsolateral areas of the abdomen.  The skin of the pupa is much thinner at these points and more easily punctured than elsewhere.  The 2nd and 3rd instar larvae have a fixed feeding position.      


The eggs of Spalangia muscidarum and S. nigra are elongate‑ovate in outline and broader at the anterior end, which bears a nipple‑like protuberance.  That of Cerocephala is of similar form except that the anterior protuberance is lacking.


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                    Fig. 58


The first‑instar larvae are hymenopteriform and elongate‑oval in outline and have a relatively large head.  In S. nigra (Parker, 1924), each body segment bears a band of minute setae at the anterior margin.  An open tracheal system is found in S. nigra with the spiracles occurring on the second thoracic segment, or on the membrane between the first and second, and on the first three abdominal segments (Fig. 58 A).  Richardson emphasized that not only does the first‑instar larva of S. muscidarum lack spiracles, but the intermediate and mature larvae are likewise apneustic.


The number of larval instars in the family is uncertain, with only three mentioned for S. muscidarum and four for S. nigra.  The second‑ (Fig.  68) and third‑instar larvae of the latter species bear nine pairs of spiracles, situated on the second and third thoracic and the first seven abdominal segments.


The mature larvae of the genus Spalangia (Fig. 58C) are distinguished by the possession of distinct conical protuberances or tubercles at each dorsolateral margin of the first eight abdominal segments.  A minute pair is found on the first thoracic segment.  These tubercles have not been noted upon larvae of other genera.  They are considered by Richardson to have neither an ambulatory nor sensory function, but appear to relate to prepupal growth.  The mature larva of C. cornigera is more elongated than that of Spalangia, and each body segment bears four pairs of setae, those of the last segment being longest.


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