Linking aboveground and belowground herbivory

Plants are exploited and attacked by a range of organisms both above and below the soil surface. Many of these interactions play key roles in complex food webs that link aboveground and belowground terrestrial ecosystems (Van der Putten et al., 2001; Wardle et al., 2004). Soil organisms intimately associated with plant roots have the potential to induce marked aboveground effects; these organisms include both mutualists such as mycorrhizal fungi and nitrogen-fixing bacteria, and antagonists such as root pathogens and root herbivores. Of the latter group, insect herbivores are an important component, with increasing attention being focused on how belowground herbivores interact with aboveground herbivores, and vice versa (Masters et al., 1993; Blossey and Hunt-Joshi, 2003). The number of studies investigating interactions between aboveground and belowground insect herbivores remains small. Bezemer et al. (2002) and van Dam et al. (2003), for example, listed only seven and nine studies, respectively, that involved both aboveground and belowground herbivores. Recently however, a growing number of studies (reviewed in Tables 9.1 and 9.2) suggest plant-mediated linkages between rootand foliar-feeding insects are more widespread than previously thought.