Figure 3.

Proportion (mean ± s.e.) of female Trichogramma wasps choosing OIPVs of B. nigra plants. Plants were infested with single eggs of P. rapae. Columns represent the mean proportion of choice for OIPVs of isofemale lines from Trichogramma brassicae (lab strain Y175) (light grey) and T. evanescens (native strain RU124, medium grey and native strain RU 263, dark grey) tested in a Y-tube olfactometer. Numbers in the columns represent number of responding wasps. All experiments were conducted in a two-choice situation between plants infested with eggs of different ages (24 and 72 h) and uninfested control plants. *p < 0.05; n.s., not significant (p > 0.05); one-sample t-test. The dashed line indicates 0.5 = no preference. Each treatment combination was replicated with five to seven plant pairs and 10–20 wasps of each strain per plant pair (n = 70–100 wasps per treatment/strain). Different plant phenotypes: hypersensitive response (HR), HR−: no necrotic zone observed, HR+: necrotic zone. (Online version in colour.)