Antimetamorphosis by parasitization in Plutella xylostella is induced by inhibition of broad gene expression due to a polydnavirus infection

An endoparasitoid wasp, Cotesia plutellae, parasitizes larvae of the diamondback moth, Plutella xylostella. The parasitized larvae undergo various physiological alterations including failure to pupal metamorphosis. Prothoracic gland (PTG) showed marked reduction in size in the parasitized larvae compared to that of Nonparasitized larvae. Expression of ecdysteroid receptor gene was highly suppressed in parasitized larvae especially during last instar. The parasitoid wasp possesses its specific symbiotic polydnavirus, C.plutellae bracovirus (CpBV). Injection of CpBV alone inhibited pupal metamorphosis of P.xylostella in a dose-dependent manner. CpBV infection also suppressed PTG growth in a dose-dependent manner. A pupal determinant Broad gene was cloned. Its RNA interference by a specific double strand RNA inhibited pupal metamorphosis in P.xylostella. CpBV treatment inhibited expression of Broad gene. There results suggest that inability of parasitized larvae to pupal development is due to inhibition of Broad gene expression by CpBV infection.