Effects of Grassland Habitat and Plant Nutrients on Soybean Aphid and Natural Enemy Populations

Abstract

<p>The soybean aphid <em>Aphis glycines</em> Matsumura (Hemiptera: Aphididae) is an invasive economic pest of soybean (<em>Glycine max</em>[L.] Merrill) in the United States. Research has shown the endemic natural enemy community in the United States is capable of suppressing <em>A. glycines</em> below EILs, but this biological control is inconsistent, especially in simple agricultural landscapes. In the course of a 3-yr project (2006–2008) we sought to determine the affects of landscape composition, configuration, and plant nutrients (N, P, and K) on <em>A. glycines</em> and aphidophagous natural enemy abundance. Specifically, we tested whether nearby grasslands contribute to the abundance of natural enemies and the suppression of <em>A. glycines</em>. The study site was located around the Neal Smith National Wildlife Refuge, composed of >2,000 ha of reconstructed prairie, located in Jasper County, IA. We sampled <em>A. glycines</em>, natural enemies, and plant nutrients in 100 soybean fields while characterizing the landscape surrounding each field. <em>A. glycines</em>abundance was lowest in 2006 but reached economically damaging populations in 2007 and 2008. The ratio of natural enemies to <em>A. glycines</em> decreased in each year of our study (2006 > 2007 > 2008). Variation in <em>A. glycines</em> and natural enemies was best explained by year and, to a lesser extent by plant nutrient levels and landscape variables. Results suggest grassland habitat did not significantly contribute to the biological control of <em>A. glycines</em>. Furthermore, yearly decline of natural enemy may have facilitated the colonization of <em>A. glycines</em> leading to outbreaks later in the season.</p>