Reliable testing of the suitability of various flower species for natural enemies is an important step in developing a conservation biological control programme. Laboratory tests showed that the suitability of nine candidate flower species for the parasitoid wasp Aphidius ervi varied tremendously. However, it did not matter whether the flowers were presented as either excised flower shoots in water or flowers that remained attached to a rooted plant. Nonetheless, the effect of flower presentation method should not be discounted in future studies involving other flower species or different insect species.