Relative Frequencies of Visits to Selected Insectary Plants by Predatory Hoverflies (Diptera: Syrphidae), Other Beneficial Insects, and Herbivores

Abstract

The use of insectary plants in agroecosystems to provide floral resources for enhancing natural enemy activity is an increasingly used practice, but candidate flowering plant species are not always screened for their attractiveness to key arthropods in the system being studied. In the work presented here, the relative attractiveness of four species of insectary plants to beneficial and pest insect species was assessed by observing the relative frequencies of flower visits to replicated blocks of the insectary flowers in two Oregon broccoli fields. The four plant species tested were alyssum (Lobularia maritima L. Desv.), coriander (Coriandrum sativa L.), buckwheat (Fagopyrum esculentum Moench), and phacelia (Phacelia tanacetifolia Benth.). Predatory hoverflies (Syrphidae) were identified to species, where possible, because of their previously observed importance as aphid predators in broccoli fields in the study area. The other beneficial insect groups observed were in the families Apidae, Coccinellidae, Tachinidae, and Vespidae, and the three main pest species were western tarnished plant bug (Lygus hesperus Knight), western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata Mannerheim), and imported cabbageworm (Pieris rapae L.). The Syrphidae visited mostly coriander, but this “preference” was probably influenced by competition from other foragers. Bumblebees and the three pest species visited mostly phacelia, and other species groups were less consistent in their flower choices. The different insect preferences for flowers are discussed in terms of the key influencing factors that should be considered when assessing the relative attractiveness of insectary plants in the field.