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Teratocytes of Cotesia plutellae Inhibit Larval Development and Pupal Metamorphosis of Plutella xylostella by Secreting Protein Factors
An endoparasitoid wasp, Cotesia plutellae, parasitizes young larvae of the diamondback moth, Plutella xylostella, with its parasitic factors of polydnavirus, venom, ovarian proteins, and teratocytes (TC). TCs are originated from embryonic serosal membrane at hatch of C. plutellae eggs. TCs, after released in hemocoel of parasitized larvae, increased their average cell size from 20.6 μm to 77 μm during whole developmental period of the parasitoid larvae, but did not increase their cell number by maintaining about 150 cells per larvae. TCs of C. plutellae, are considered to be involved to extend the host larval development period and to arrest larval-pupal metamorphosis, were cultured in an insect cell culture medium for 21 days. Like TCs in parasitized larvae, in vitro cultured TCs showed increase in cell size, but did not show increase of cell number. Microinjection of in vitro cultured TCs significantly inhibited larva-to-pupa metamorphosis of nonparasitized P. xylostella, in which pupated host also showed extended larval period. Larvae injected with TCs exhibited alteration in expression of ecdysone receptor (EcR) and insulin receptor (InR) as well as in parasitized larvae. Teratocyte-secretory factors in culture medium showed this antimetamorphic effect on P. xylostella, while heat treated TC culture medium lost the effect. However, a successful parasitization of C. plutellae required both TCs and polydnavirus to alter host physiology.
