The genus Diadegma is a well known parasitoid group and some are known to have symbiotic virus. A novel IV was discovered from the calyx of D. fenestrale female. This virus was named as D. fenestrale Ichnovirus (DfIV) and its genome contains 62 circular DNA segments with an aggregate size of approx. 240kb. We examined its gene expression patterns depending on the hosts (hymenopteran host, D. fenestrale and lepidopteran host, Plutella xylostella) and stages of P. xylostella based on RNAseq. Among 62 genome segments, only two segments such C15 and D14 were highly expressed in ovary of D. fenestrale. On the other hands, five segments were differently expressed depending on the developmental stages (3 rd and 4 th instar larvae). Additionally we confirmed integration of DfIV genome segments into the chromosome from the Plutella xylostella via genome sequencing of the lepidopteran host.