Antimetamorphic effect of teratocytes and their secretory products of Cotesia plutellae (Braconidae: Hymenoptera) on its parasitized host, Plutella xylostella

Teratocytes are originated from embryonic serosal membrane of some endoparasitoid wasps. Cotesia plutellae eggs release teratocytes in parasitized host hemocoel at hatch in about 150 cells per egg. Teratocytes of C. plutellae were cultured in an insect culture medium for at least 14 days. Teratocytes cultured in vitro showed no change in cell numbers but increased in cell size. Similarly, teratocytes in parasitized larvae did not change cell numbers, but increased their cell size. Microinjection of in vitro cultured teratocytes into third instar larvae of nonparasitized larvae of Plutella xylostella showed a dose-dependently inhibitory effect on larval development and larva-to-pupa metamorphosis, in which teratocytes prolonged larval period and reduced pupation. The sensitivity to teratocytes was different among host ages, in which young instars were more sensitive to teratocyte treatment than old larvae. Culture medium of teratocytes for 4 days contained the inhibitory effect on larva-to-pupa metamorphosis in a dose-dependent manner. The heat treatment (75^oC for 20 min) inactivated the inhibitory activity of the culture medium. Proteomic analysis of the teratocyte culture medium identified novel factors to inhibit larva-to-pupa metamorphosis. These results suggest that teratocytes play a crucial role in successful parasitization of C. plutellae by altering host developmental program.