Many adult hymenopterous parasitoids feed on floral nectar, and occasionally pollen. However, flowers differ in both accessibility and attractiveness to these insects. Malaise traps, a type of “passive/interception” trap, were baited with potted flowering plants, Lobularia maritima L. (Brassicaceae) or Spermacoce verticillata L. (Rubiaceae), or left unbaited as controls. These plants have different floral structures, but both have been previously used as food-plants for biological control agents. In general, L. maritima captured more Braconidae, particularly Opiinae, than either alternative. Species of this subfamily attack Diptera and certain species are important natural enemies of pest Tephritidae. The roles of plant attractiveness (volatiles) and architecture (trap access) are discussed, as is the possibility of employing L. maritima and/or its products in monitoring or maintaining fruit fly parasitoids.