I have had more inquiries this spring than in the past several years regarding brown and gray moths flying around lights at night or being flushed from weedy areas in fields. There are dozens of species of moths that occur in Iowa in the spring, but only a few are potential pests. The eight most common moths collected during mid-May in a light trap in Ames were armyworm, black cutworm, celery looper, spotted cutworm, and variegated cutworm. All of these moths have multiple generations in the Midwest, so it is possible to see them again in mid- or late summer.
Of these eight species, only the armyworm, black cutworm, green cloverworm, and variegated cutworm are potential threats to Iowa field crops. But even if these moths are found in your area it does not indicate that an economic infestation of that particular insect is imminent in a crop. Most moths are highly mobile and move many miles, searching for desirable hosts and laying eggs along the way. This mobility is why black cutworm problems occur in some fields but not others.
For each moth species shown, the blue arrow points toward a marking that helps identify that species.
A. Black cutworm. Forewing black but lighter colored near wing tip; a small, dagger-shaped black marking near outer edge of wing. Larvae are pests of seedling corn and rarely seedling soybean. There are three generations a year.
B. 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.
C. Variegated cutworm. Forewing grayish brown; a pale oval marking near wing edge adjacent to a darker kidney-shaped marking. Larvae are common on vegetables. They can defoliate alfalfa regrowth after a cutting and this year they were found feeding on young corn. There are three generations a year.
D. Armyworm. 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 because at times the larvae migrate from small grains in tremendous numbers. There are three generations a year.
E. Celery looper. Forewing gray mixed with rust; a silvery white, tear-shaped marking in middle of wing. Larvae feed on vegetables, grasses, and low weeds. There are two generations a year.
F. Green cloverworm. Forewing black and gray, mixed with rust in center; mouthparts projected forward from head to form a "proboscis." Larvae can be significant pests of Iowa soybean. Larvae also feed on clover, alfalfa, strawberry, garden beans, peas, and weeds. There are two or three generations a year. The moth shown here was captured on May 25. It was a migrant into Iowa, having flown in from a southerly state. Moths produced in Iowa will be darker later in the summer.
G and H. Forage looper (G, female; H, male). Forewing light brown; female with two contrasting darker bars on wing, male with bars not contrasting in color but bars outlined in a darker color. Larvae feed on clover, alfalfa, grasses, and ragweed. There are two or three generations a year.
I. Bilobed looper. Forewing gray mixed with rust; a large, two-lobed, silvery marking in middle of wing. Larvae feed on alfalfa, clover, and weeds. Moths have been common at lilac blooms this spring. There are two generations a year.
This article originally appeared on pages 98-99 of the IC-486(12) -- June 4, 2001 issue.