Insect material
Pieris brassicae L. (Lepidoptera: Pieridae) butterflies were obtained from a rearing of the Laboratory of Entomology, Wageningen University. Insects were kept in a greenhouse under standardized conditions (21 ± 4° C, RH: 60 – 80 %, L16: D8). Larvae were reared on Brussel sprout (Brassica oleracea var. gemmifera ) cv. Cyrus, while the adults were fed with a 10 % honey solution and allowed to oviposit on clean plants of the same genotype.