A polydnavirus, Cotesia plutellae bracovirus (CpBV), is symbiotic to an endoparasitoid wasp, C. plutellae, which specifically parasitizes young larvae of the diamondback moth, Plutella xylostella. Parasitization by an endoparasitoid wasp, Cotesia plutellae, delays the larval development and metamorphosis in Plutella xylostella. Nutritional deprivation by the wasp may induce these developmental alterations in growing host. This study focussed on the change of insulin signaling of the parasitized host. The parasitized larvae exhibit a significant suppression in insulin-like peptide (ILP) expression, which was induced only by the injection of the CpBV. Reduced ILP expression significantly increased the blood sugar level (trehalose) level in the parasitized host, which was mimicked by starvation. Foxo was expressed in the parasitized larvae, but localized mostly in the nucleus. Overexpression of ILP gene in the parasitized larvae induced translation of Foxo to cytoplasm and significantly decreased trehalose level in the plasma. Interestingly, the overexpression of ILP gene significantly prevented the successful parasitization and allowed the host metamorphosis.