Natural Enemy Diversity and Biological Control

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Exotic pests are spread throughout the world either inadvertently or intentionally by humans. This proposal evaluates two inter-related questions: (1) does the ability of these pests to invade depend on the biodiversity of the new ecosystems they encounter, and (2) are biologically impoverished ecosystems more susceptible to invasion? The proposed research will address these questions in agricultural systems that have been subjected to numerous types of exotic pest. A dramatically successful pest, the soybean aphid, Aphis glycines, was first identified in North America in 2000. In the Upper Midwest, this invader reached outbreak levels, becoming the only serious insect pest in the otherwise insect-poor community found in soybean fields. In contrast, in alfalfa crops the pea aphid, Acyrthosiphon pisum, is a potential pest, but it never reaches outbreak levels. Unlike the low biodiversity of soybean fields, alfalfa has a high diversity of invertebrates, both herbivores and predators. My research will test whether the low diversity of the soybean community relative to the alfalfa community facilitates the invasion and outbreak of the soybean aphid, whereas predators continuously control pea aphids. Experiments will be performed to switch the invertebrate communities between soybean and alfalfa crops, thereby forcing soybean aphids to face the community of species found in alfalfa, and conversely making pea aphids face the species-poor community from soybeans. If low biodiversity of soybean crops is essential for the successful invasion of the soybean aphid, then when placed in the highly diverse community of alfalfa crops, the soybean aphid should be suppressed.