In the present study, expression of a newly identified Glyptapanteles indiensis polydnavirus (GiPDV) gene encoding a putative protein tyrosine phosphatase (PDVPTP) was monitored in vivo in the parasitized host, L. dispar, using one step RT-PCR. Expression levels of the PDVPTP transcript were also evaluated in various host tissues at different times post parasitization (pp) using RT quantitative competitive PCR (RT-qcPCR). Expression levels varied, with the most abundant transcript detected in host haemolymph 2 h pp. The high expression level in host haemolymph at an early stage of parasitization suggested a potential role for viral PDVPTP in disruption of the host immune system and protection of the endoparasitoid egg from encapsulation. Additionally, the PDVPTP gene or its homolog(s) mapped to more than one GiPDV genomic DNA segment, which may account for its increased level of expression in the absence of virus replication. Associations; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Diseases and disorders; Microbial diseases; Immunology and repair mechanisms Lymantria dispar (Lymantriidae); Hymenopteran parasites; Glyptapanteles indiensis; Viral diseases; Glyptapanteles indiensis polydnavirus; Viral protein tyrosine phosphatase gene expression in relation to hymenopteran parasite infection; Immune like reactions Glyptapanteles indiensis (Braconidae); Associations; Polydnavirus (virus); Expression of viral protein tyrosine phosphatase gene in parasitized lepidopteran hosts; Lepidopteran hosts; Lymantria dispar none