Spud Web: Species Interactions and Biodiversity in Potatoes

Agroecologists often see greater biodiversity as the key to reducing pest problems on farms. Others have suggested, however, that increasing species number only increases the risk of negative interactions among species, such as predation of one predator by another, which could disrupt biological control. Such multi-species interactions have long been a topic of interest among entomologists working in potato crops, and here we review the basic ecological knowledge that has come from work in this important model cropping system. We examine the effects of increasing biodiversity on potato-insect species interactions at multiple trophic levels: among plants, herbivores, and natural enemies. Increasing plant diversity at both local and landscape scales can help build predator populations and increase suppression of potato pests. However, planting flowering plants near potato crops sometimes provides supplemental food for pests, making pest problems worse. Effects of herbivore diversity are equally complex. Feeding by early-season herbivores sometimes makes plants resistant to late-arriving herbivores, thus harming those pests most active later in the growing season. On the other hand, multiple herbivore species can “distract” predators from feeding on particular target pests, providing less-preferred herbivore species with protection from predation. Predator diversity likewise exerts varying effects. In most cases predator species appear to complement one another by foraging in different locations in the crop or by attacking different pest stages, thus improving biological control. In some cases, however, predator species feed on one another, disrupting biological control. In summary, although increasing biodiversity within potato crops sometimes worsens pest problems, it most often makes pest outbreaks less likely. Thus, work in potatoes largely supports the view of early agroecologists that increasing biodiversity restores natural balance among plants, herbivores, and natural enemies.