Black cutworm moth: An adult black cutworm, Agrotis ipsilon. (Photo Marlin E. Rice)
Yellow striped armyworm: An adult yellowstriped armyworm, Spodoptera ornithogalli. (Photo Marlin E. Rice)
The black cutworm migrates north to Iowa each year (producing 2-3 generations per year) as summer winds assist long-distance flights from the southern US where it has continuous generations (Showers 2003). A theory has been proposed to explain the stimulus for summer migration that is based on exposure of pupae to specific range of temperatures (Showers 2003). Development of this caterpillar is determined beginning with the detection of the first flight. Using a base developmental threshold of 500F initial cutting is estimated at 300 degree days (DD) with pupation at approximately 641 DD.
The most common armyworms in Iowa soybean are the fall and yellowstriped armyworms,Spodoptera ornithogalli. The fall armyworm migrates into Iowa from the southern US each year to produce a single generation. The yellowstriped armyworm overwinters as a pupa and produces three generations a year. This insect can develop from egg to adult in 23-25 days on warm summer days and usually has 3 generations in Iowa and rarely reaches an economically important population abundance.