Technical Abstract: Four invasive Brassicaceae are currently being studied for biological control at the CABI Centre in Switzerland. A phylogenetic approach to host testing has so far been hampered by the fact that the evolutionary relationships of taxa within the Brassicaceae were unclear. Recently, a new phylogeny of the Brassicaceae, largely based on molecular studies, has been proposed. This presented a unique opportunity to relate host range test results for some of our Brassicaceae agents to the new phylogeny. The host range of Ceutorhynchus scrobicollis Nerensheimer & Wagner, a root-crown mining weevil investigated as a potential agent for Alliaria petiolata (Bieb.) Cavara & Grande (garlic mustard) appeared to closely follow the new classification (significant linear relationship between phylogenetic distance and host range test results). However, for Ceutorhynchus cardariae Korotyaev, a gall-inducing weevil considered as biocontrol agent for Lepidium draba L. (hoary cress), phylogenetic distance of the test species to the target weed did not explain a significant amount of the variation in host preference or suitability. These results question the general applicability of the centrifugal phylogenetic method, where it is assumed that species more closely related to the target are at greater risk of attack than species more distantly related. The importance of other factors, specifically secondary metabolite profile and morphological characteristics for the host choice behaviour of C. cardariae are currently being investigated.