Are we managing the Soybean aphid (Hemiptera: Aphididae) in enemy free space?

insecticide when soybean aphid (Aphis glycines Matsumura, Hemiptera: Aphididae) populations exceed 250 aphids per plant on more than 80% of the plants from the onset of flowering to early pod development. This is an economic threshold (ET) for an economic injury level (EIL, 674 aphids per plant) that was calculated from crop values and management costs typical for soybean growers in the Midwest United States. This ET is based on the population growth rate of the aphid and allows growers 7 days to apply an insecticide before populations reach the EIL. The soybean aphid suffers mortality from several insect predators that are commonly found in soybean fields. When predators are absent, the population growth rate of the aphid increases. Recently two lines of research has suggested that agricultural practices common to the North Central region may negatively affect the abundance and diversity of aphidophagous predators in soybean fields (i.e. increases production of corn and the use of seed applied insecticide). We will report trends in the abundance of soybean aphids and their associated natural enemies from farm fields in central Iowa during a period when corn production increased by 17%. We will also review an experiment that measured the population growth rate of aphids between the ET and EIL in absence of predators. We will discuss if soybean aphid management should be altered if the impact of predators declines.