Effect of Pieris egg-induced HR on Trichogramma parasitism and performance in a natural B. nigra population collected in three different seasons in 2010 and 2011 (generations 1 and 2). (a) Percentage (estimated mean ± s.e.) of eggs that were parasitized by Trichogramma wasps. Picture shows a parasitized egg with HR-like necrosis. (b) Percentage of parasitized eggs (estimated mean ± s.e.) from which Trichogramma wasps emerged. Numbers inside the bars represent number of plants for data of 2011 and number of eggs for data of 2010. Different plant phenotypes: hypersensitive response (HR), HR−: no necrotic zone observed, HR+: with necrotic zone. ***p < 0.001, *p < 0.05; n.s., not significant (GLM, p > 0.05). (Online version in colour.)