Don't confuse western bean cutworm with other moths

Western bean cutworm adults have not yet started to fly in Iowa, but there may be some confusion over misidentification of other moths that are now flying. Several species are now being collected in Ames, and if you are unfamiliar with the western bean cutworm, then these moths may present challenges for proper identification. The most commonly collected moths during the second week of June were armyworm, yellowstriped armyworm, and spotted cutworm. A brief description of these three species and the western bean cutworm follow:


Forewing pale buff; a small white spot, often with small dark markings on either side on back half of wing. Larvae feed on grasses, small grains, and corn. This insect gets its name of armyworm because at times the larvae migrate in "armies" from small grains in tremendous numbers. There are three generations a year.

Armyworm, Pseudaletia unipuncta or Mythimna unipuncta. (Marlin E. Rice)Armyworm, Pseudaletia unipuncta or Mythimna unipuncta. (Marlin E. Rice)

Spotted cutworm

Forewing purplish brown; a prominent, pinkish, triangular marking along middle section of wing edge. Larvae feed on vegetables, deciduous trees, small fruits, and cereal crops. There are two generations a year.

Spotted cutworm, Xestia dolosa. (Marlin E. Rice)Spotted cutworm, Xestia dolosa. (Marlin E. Rice)

Yellowstriped armyworm

Forewing a riotous mixture of buff, tan, brown, black, and white; short, white, broken bar near tip of wing; long, teardrop-shaped spot near base of wing. Larvae are general feeders and hosts include alfalfa, clover, corn, and grass. There are two or three generations a year.

Yellowstriped armyworm, Spodoptera ornithogalli. (Marlin E. Rice)Yellowstriped armyworm, Spodoptera ornithogalli. (Marlin E. Rice)

Western bean cutworm

Forewing a mixture of buff, tan, and gray with a cream-colored bar extending four-fifths the length of the wing along the front edge; two spots in the shape of a "full moon" and a "boomerang" touching the cream-colored bar near the mid-length of the wing. Larvae are pests of corn and dry beans. There is one generation a year.

Based on historical trap captures, western bean cutworms would not be expected in either pheromone or light traps until the last week of June in Iowa. Table 1 shows the first, peak, and last captures of adult western bean cutworms during the previous five years.

Adult western bean cutworm (Striacosta albicosta, formerly Richia albicosta). (Marlin E. Rice)Adult western bean cutworm (Striacosta albicosta, formerly Richia albicosta). (Marlin E. Rice)

Table 1. Five-year blacklight captures of western bean cutworm adults from Woodbury Co., Iowa, 2002-2006.

Western Bean Cutworm Adults
Year First Capture Peak Capture Last Capture Total
2002 June 28 July 13 August 11 12,739
2003 July 10 August 1 August 17 244
2004 July 5 July 23 August 10 531
2005 June 28 July 13 August 10 1,328
2006 June 24 July 15 August 14 1,183

This article originally appeared on page 173 of the IC-498(14) -- June 11, 2007 issue.

Updated 06/15/2007 - 12:22pm