Host Preference and Performance of the Aphid Brevicoryne brassicae Are Not Associated With Olfactory Orientation Towards Kale and Mustard

Host plant selection by insect herbivores involves successive steps of orientation, exploration, acceptance, and colonization, and behavioral responses at one stage do not necessarily predict those at subsequent stages. This distinction is relevant for selecting attractive plants, either for trap‐cropping strategies or as the pull component of push–pull systems. In this study, we evaluated behavioral and ecological traits relevant to the potential use of curly mustard Brassica juncea (L.) Czern., as a candidate trap plant for the management of the cabbage aphid Brevicoryne brassicae (L.) (Hemiptera: Aphididae) in kale crops ( Brassica oleracea L. var. acephala DC.). We tested whether aphid preference and biological performance were associated with olfactory attractiveness. In dual‐choice cage assays, winged aphids preferred to settle on mustard plants, which concentrated 70% of the individuals. In performance assays, aphid populations reached significantly higher numbers of adults and total individuals on mustard than on kale. In a four‐arm olfactometer, winged aphids were attracted to volatiles from both plant species when tested individually against clean air; however, when exposed to odors from both plant species simultaneously, they preferred kale. Volatile profiles differed between plant species: α‐thujene and β‐phellandrene were detected in higher abundance in kale, whereas ocimene was more abundant in mustard. Allyl isothiocyanate was detected exclusively in mustard, although at a low amount. The results reveal a dissociation among different steps of host selection, indicating that olfactory attractiveness alone does not determine the colonization and settlement of B. brassicae on kale or mustard plants. These findings demonstrate that candidate trap plant selection should not rely exclusively on olfactory attractiveness, but should also integrate retention and population growth, providing more robust criteria for integrated pest management.