Parasitization by Cotesia plutellae inhibits pupal metamorphosis of diamondback moth, Plutella xylostella. Two questions are raised : (1) which parasitic factor(s) is responsible for the antimetamorphosis and (2) how the parasitized larvae are altered in endocrine signals. This study addressed both questions. When C. plutellae bracovirus (CpBV), a parasitic factor of the wasp, alone was injected to nonparasitized P. xylostella larvae, it significantly inhibited pupal metamorphosis in a dosedependent manner. Corpora allata (CA) and prothoracic gland (PTG) were compared in both nonparasitized and parasitized P. xylostella. In both groups, size and shape of CA were not different. However, PTG was detected on prothoracic tracheal trunk in nonparasitized larvae, but not detected in parasitized. CpBV injection to nonparasitized larvae inhibited the growth of PTG. Transcriptional factor, broad complex, was partially cloned and expressed in nonparasitized P. xylotella. In parasitized or CpBV-injected larvae, broad complex gene was not expressed during late larval stage.