The host Plutella xylostella L. -parasitoid Cotesia plutellae (Kurdj.) system was used to study the effects of superparasitism, host age at the time of oviposition and host starvation after parasitism on the growth of the parasitoid larvae and their teratocytes in host larvae. The results showed that the percentage of pseudoparasitism increased and the developmental duration of parasitoid larvae was variable when the 4th instar host larvae were parasitized as compared to those when the 2nd and 3rd instar larvae parasitized. More teratocytes were present in host haemocoel with their diameters distinctly decreased after the host larvae were superparasitized as compared to those normally parasitized only once, and the growth of parasitoid larvae was obviously stunted with the increase of degree of superparasitism. After the parasitized host larvae were starved for 62 h, the number of teratocytes decreased and the activity of teratocytes was reduced in the host larvae, and the growth of parasitoid was also arrested at the same time, suggesting that there is a positive interaction relationship among the growth of host larvae, parasitoids and teratocytes. These results indicated that superparasitism, host age at the time of oviposition and host nutritional status after parasitism had obvious effects on the growth of the parasitoid larvae and their teratocytes in host larvae. Plutella xylostella (Plutellidae) : Host Cotesia plutellae (Braconidae) : Parasite Biometrics; Nutrition; Reproduction; Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Cotesia plutellae; Egg; Teratocytes in host larvae; Larval development; Lepidopteran hosts; Larval growth & teratocytes; effects of superparasitism; host age & starvation; Plutella xylostella Plutella xylostella; Age; Starvation; Hymenopteran parasites; Parasite larval growth & teratocytes; effects of superparasitism; age & starvation; Cotesia plutellae none