Figure 4. Schematic of expected expression differences after the host switch, when compared to differences between control lines using the example switch Urtica to Ribes. Here, we use the differences between Host 1 control lines (UdUd ) and either the Host 2 control lines (RuRu ) on the X axis or the switch from Host 1 to Host 2 (UdRu ) on the y-axis to identify 5 different categories of expression change: (1) Differences in the gene expression after the host switch correspond to differences found between the controls, indicating an adjustment to the new host (green). (2) No differences in gene expression after the switch despite differences between the controls, corresponding to the gene expression profiles on Host 1 (yellow). (3) Differences in gene expression after the switch but no differences between the controls (blue). (4) differences in gene expression after the switch that are opposite to differences between controls (orange) were considered as “mismatches”. (5) Genes that were not significantly differentially expressed are not shown here. We predict that 2 hours after a switch the majority of transcriptional differences will match categories 2 and 3. After 17 hours, larvae should predominantly show adjustments to the new host (category 1). Expression changes of category 4 are not expected, and if seen may indicate transcriptional dysregulation upon switch to the novel host.Ud =Urtica dioica , Ru =Ribes uva-crispa.