16 The Role of Insect Herbivores in Exotic Plant Invasions: Insights Using a Combination of Methods to Enhance or Reduce Herbivory

Exotic plant invasions are threatening biodiversity and altering fundamental ecosystem properties and processes worldwide. Escape from native insect herbivores is believed to be one of the primary causes contributing to the successful invasion of many introduced plants. With biotic homogenization increasing globally, studies that examine the effects of herbivores on both native and introduced species are essential for understanding the influence of exotic species invasions on community dynamics and ecosystem function. While collecting field observations and life history characteristics of an exotic plant can be useful, it is experimental manipulations that will most clearly reveal the mechanisms responsible for the dominance of an aggressive invasive species. Employing a variety of methodological approaches that both increase and decrease insect herbivory will best elucidate the population ecology and ecosystem impact of an exotic plant invader. There is a pressing need to develop effective management strategies to lessen the effects of exotic invaders on a variety of threatened species and imperiled ecosystems. Such experiments will not only increase basic ecological knowledge, but also provide useful insights to land managers pressed with addressing a large and growing problem with tremendous societal, economic and environmental costs.