Associational resistance occurs when host plants experience reduced attack when in the presence of other plant species (Atsatt & O'Dowd 1976, Tahvanainen & Root 1972). The issue is most studied in agriculture and forestry because of the potential benefits to pest control (Andow 1991, Brown & Ewel 1987, Tahvanainen & Root 1972), but recent research indicates that associational resistance may be relatively common in natural systems as well (Hjältén et al. 1993, Karban 2007, Vehviläinen et al. 2007, Wise et al. 2009; but see Östergård & Ehrlén 2005, White & Whitham 2000), especially against specialist herbivores (Hambäck et al. 2000, 2003; Stenberg et al. 2007).
