The soybean aphid (Aphis glycines) is a new pest to soybeans in Iowa and the United States. First observed in Wisconsin in the fall of 2000, the soybean aphid has spread to most north-central U.S. soybean fields over the last three years. The soybean aphid is unique in that it is the only aphid that reproduces on soybeans. The soybean aphid caused economic losses to soybeans in northeast Iowa in 2001 and caused only isolated problems in 2002. But in August of 2003, the aphid spread rapidly and colonized soybean fields in the upper one-half of Iowa counties, causing widespread yield and economic losses.