none Regulation of protein synthesis was studied in Microplitis croceipes (Cresson) during oogenesis and after oviposition in its host, Heliothus zea (Boddie). Oocytes were dissected from ovaries of M. croceipes during various stages of development and from second instar host larvae at various times after egg oviposition. Uridine incorporation into RNA was highest in oocytes in the ovarian egg tube, then declined in oocytes present in the egg reservoir and calyx of the ovary. During blastoderm formation, 4-6 hr after the egg was oviposited into the host, uridine was still incorporated at low levels. At 18-24 hr after ovipositin (14-18 hr after blastoderm formation), uridine incorporate returned to the level observed in eggs in the ovarian reservoir. Protein synthesis, measured by (3H)leucine and (35S)methionine incorporation was continuous at all stages of development and was most rapid 14-20 hr after blastoderm formation when RNA synthesis was highest. Patterns of polypeptide synthesis as analyzed by one-dimensional SDS-PAG changed quantitatively but this method did not reveal any new polypeptides in oocytes in various stages of development or during early and late embryogenesis. However, when polypeptide patterns of eggs were compared on two-dimensional gels during embryogenesis, synthesis of new polypeptides was evident after cellularization of the blastoderm (4-6 hr after oviposition). These changes in synthesis after blastoderm formation may be the result of transcription and subsequent translation of embryonic mRNA.