Insect immune responses play important roles in host defense against pathogens and parasitoids. In this study, we propose that the regulation of host immune responses may determine the succesful parasitization of Campoletis sonorensis in the host. To investigate the regulation of innate immune responses by parasitization, a microarray approach and quantitative real time PCR experiments will be carried out. From cDNA libraries derived from Heliothis virescens hemocytes and fat body tissues, we obtained 44,844 ESTs that were assembled into putatively different transcripts. All putative transcripts were used to construct a custom microarray. As expected, we detected differential expression of some immune genes after immune challenges in our microarray and quantitative Real Time PCR studies. By using quantitative Real Time PCRs, we also found that parasitization caused the differential expression of the H. virescens genes involved in innate immune responses. The findings of this study will provide insights into lepidopteran innate immune responses.