Using diverse and simple trap crop plantings to protect broccoli from the crucifer flea beetle (Phyllotreta cruciferae)

The crucifer flea beetle, Phyllotreta cruciferae Goeze (Coleoptera: Chrysomelidae: Alticinae) is an oligophagous pest of Brassica crops. In the Pacific Northwest, many growers rely on Brassica crops as a major component of mixed-vegetable production, and flea beetle (P. cruciferae) damage lowers marketable yields of these crops. In plots both west (Mt. Vernon, WA) and east (Moscow, ID) of the Cascade Mountains, we have been evaluating species identity and composition of trap crop plantings to draw flea beetles out of broccoli (Brassica oleracae var. italica ) crops. Five plant species were chosen as putative trap crops based on literature and grower recommendations: Barbarea vulgaris, Brassica napus, Brassica juncea, Brassica oleracea var. acephala and Brassica rapa subsp. pekinensis. Using a substitutive design, we compared trap crop monocultures to polycultures of 5 trap crop species in their ability to attract flea beetles and protect adjacent broccoli. Flea beetle populations in trap crops were tracked using D-vac suction, while visual observations were used to monitor flea beetle populations and damage in broccoli. Results from the D-vac samples showed a significantly lower number of flea beetles collected from polycultures containing B.vulgaris than those without. Results of these experiments will add to the knowledge of trap crops as an option for managing the crucifer flea beetle in mixed vegetable farms.