Stop and smell the flowers: an approach to attract syrphids into apple orchards

Woolly apple aphid, Eriosoma lanigerum Hausmann, has become a pest of increasing importance in Washington apple orchards for the past few years. The increase in aphid outbreaks seem to be associated with the changes in pesticide programs where broader spectrum pesticides that used keep this pest in check are being substituted by more specific pesticides. The problem is especially critical in organic orchards, where few approved pesticides are available. However, there is a good potential for biological control of this pest, both in conventional and organic orchards. A preliminary survey of predators has indicated that syrphids (Diptera: Syrphidae) are one of the most common predators found in woolly apple aphid colonies. One approach to enhance biological control is the conservation of natural enemies, which may be achieved by altering crop systems to provide necessary resources for beneficial insects. Syrphids are predacious as larvae, whereas the adults are nectar and pollen feeders. Engineering the orchard ecosystem to include plants that attract and sustain adult syrphids should therefore enhance biological control. In the current study, we investigated the attractiveness of six flowering plant species to adult syrphids. The plant species tested were sweet alyssum, Lobularia maritime; buckwheat Fagopyrum esculentum; mustard Brassica juncea; cosmos Cosmos sulphureus; zinnia Zinnia hybrida; and marigold Calendula officinalis. Sweet alyssum attracted significantly more adult syrphids than all the other plant species tested.