Differential expression profiles across the blood but not the sucrose feeding conditions. The most significant differences were observed between the early blood and early sucrose transcriptomes, where 5,712 genes, 35% of the total number shared, were differentially expressed. In contrast, fewer differences were seen between the late blood and late sucrose transcriptomes. The comparison of the LB, LS and teneral transcriptomes showed only 68 differentially expressed genes, which implies that 36 h after feeding on either diet, a large part of the expression profile is returning to a condition similar to that seen in non-feeding midges. The genes with differential expression profiles identified during the course of both the blood and sucrose meals were categorized according to GO classifications to depict global differences between blood and sucrose feeding. The physiological response to blood feeding was strikingly different from the teneral state, while sucrose feeding showed fewer differences in response; this stark contrast between the two diet sources was evident in both in the diversity of categories and the number of genes differentially expressed in those feeding conditions. Genes with differential expression profiles in response to blood feeding were further classified into functional categories in order to observe trends in molecular function. In comparison to the teneral midges, the early blood fed midges showed the strongest genetic response through transcript abundance changes in genes classified within anatomical structure development, cellular differentiation, reproduction, signal transduction, response to stress, transport, embryo development, lipid and ion binding, and carbohydrate metabolism. Table S4 in File S1 is a list of the top 100 genes with at least a 2-fold increase or decrease in transcript abundance as a result of an early blood meal. Intriguingly, 36 of the top 100 induced genes had no homology to other organisms, revealing new targets for functional classification. Not surprisingly, many genes that were differentially expressed in early blood feeding are associated with blood digestion, hematophagy, and vitellogenesis. At 36 h post blood feeding, we observed a general decrease in the number of genes with differential expression profiles, suggesting that many major metabolic and biological events unfold within 12 h post blood meal and the expression of these early response genes subsides within the window of 36 h. Comparison of the early and late blood-fed midge transcriptomes revealed 7,334 differentially expressed genes categorized within anatomical structure and cell differentiation, transport, ion binding, oxidoreductase, signal transduction, embryo development, response to stress, and peptidase activity, were more significantly upregulated in comparison to the measurement at early blood feeding, while categories such as reproduction, DNA binding, and cell cycle were downregulated.