none The endoparasitic parasitoid Cotesia plutellae (Kurdjumov) develops in the hemocoele of larval stages of the diamondback moth Plutella xylostella (Linnaeus). Teratocytes were released from the serosal membrane during hatching of the first instar parasitoid at 33-36 h after oviposition when held at (25[plus or minus]1)[degree]C; An average of 192 cells were released per embryo the cells increased in diameter from about (15.31[plus or minus] 3.06)[mu]m to (63.25[plus or minus] 12.65)[mu]m, but some of the teratocytes attained a size of the biggest 118. 75 [mu]m. The number of teratocytes,however, declined during the course of parasitoid development. Scanning electron microscope (SEM) revealed that the surface of the teratocytes was covered with microvilli, which on the 4th day was much denser and longer than on the 1st day. This implied that they were actively involved in functions of absorption and secretion. Transmission electron microscope (TEM) revealed that mature teratocyte nucleus developed extensive dentritic ramification, and was endowed with the extensive endoplasmic reticulum, abundant mitochondria and increasing number of lysosome, also observed were the accumulation of glycogen granules and lipid droplets, especially, in older teratocytes, thus providing circumstantial evidence for the occurrence of protein synthesis and secretion. Reproduction Cotesia plutellae (Braconidae); Egg; Teratocytes; Development & ultrastructure