Insect rearing and sampling
Pieris napi eggs were collected from wild plants in Skåne county Sweden (Kullaberg; 56°18′N, 12°27′E and Vejbystrand; 56°18′N, 12°46′E), then reared using a split brood design in the laboratory following previously described methods (Lehmann et al., 2018; Lehmann et al., 2016; Pruisscher et al., 2022). To induce divergent developmental pathways, each cohort of larvae was placed in L:D 10 h:14 h at 20°C to induce diapause or L:D 22 h:2 h at 20°C to induce direct development. Upon pupation, individuals remained in their respective treatments for the first ten days, after which temperatures for the diapausing individuals were reduced to 10°C, and then to 2°C in total darkness after day 17 of pupation. Diapausing pupae remained in 2°C 24 h darkness until day 144, where temperatures were increased to 10°C, and then to 20°C on day 151. Direct developing pupae were sampled on the first day of pupation (day 0), day 3, and day 6 for head tissue. Diapausing pupae were sampled on 0, 3, 6, 24, 114, 144, and 155 after pupation (n = 3-4 individuals per time point for each treatment). When sampled, individuals were flash frozen by being submerged in liquid nitrogen. Only females were sampled to avoid the effect of sex on expression patterns, and all individuals were sampled around the same time of day (~12:00) to avoid any circadian effects.