The genus Diadegma is a well known parasitoid group and some are known to have symbiotic virus, PDV. A novel IV was discovered from the calyx of D. fenestrale female. D. fenestrale has more than two hosts, including PTM and DBM. The oviposition and survival rate results showed that D. fenestrale preferred PTM to DBM as hosts. Nevertheless, the developmental period and morphology of D. fenestrale were not significantly different between PTM and DBM. To identify these phenomena, DfIV genome expression patterens were compared between PTM and DBM under various conditions. DfIV genes were more widely expressed in PTM than in DBM after parasitized by D. fenestrale, particularly at the initial point. In addition, large numbers of DfIV genes were expressed only in PTM and they showed differential expression patterns between two lepidopteran hosts. This DfIV genome expression plasticity showed a dependency on the lepidopteran host species and parasitization time, suggesting that it may contribute to the parasitoid survival rate increase. This may be one of the key elements that determine the symbiotic relationship between PDV and parasitoid.