Population trends and feeding preferences of flea beetles (Phyllotreta cruciferae Goeze) in collard-wild mustard mixtures

Population densities of flea beetles (Phyllotreta cruciferae Goeze) were lower per unit collard plant in polycultures composed either of non-host plants (field bean, vetch and barley) or of additional host plants (wild mustard) than in collard monocultures. Flea beetles exhibited decreased movement patterns in the non-host polycultures, but similar movement activity in the monoculture and collard-wild mustard polyculture. Differences in flea beetle abundance between collard monoculture and collard-wild mustard polycultures disappeared when flowers were artificially removed from wild mustard. Significantly fewer flea beetles occurred in collard rows immediately adjacent to wild mustard borders, but their numbers tended to increase further away from the border. Collard plants sprayed with wild mustard extracts, and especially with allylisothiocyanate emulsions, proved to be more attractive to flea beetles than collard plants sprayed with water. Flower extracts seemed to exert greater attraction than leaf extracts. Understanding of these spatial and temporal interactions (apparently chemically mediated) could lead to development of effective trap cropping systems for flea beetle control in crucifer crops.