On specimens in good shape, the forewing is tan to reddish-brown with a small white mark in the center. The armyworm is a moderately sized moth with a wingspan of approximately 1½ inches. Note the tan color, diagonal line of dark spots and white dot on the forewing. To avoid confusion with other species that have armyworm as part of their approved common name or are regionally known as “armyworms,” Mythimna unipuncta is often referred to as “true armyworm.” Adultįigure 1. Some Minnesotans also call the eastern forest tent caterpillars (Malacosoma americanum) that create communal webbed shelters (tents) and feed on the leaves of broadleaf trees and shrubs “armyworms.” However, these moths belong to the insect family Lasiocampidae and are not related to Mythimna unipuncta. One example is the fall armyworm ( Spodoptera frugiperda), an infrequent late-season migrant visitor to Minnesota from the tropics. Most species that include armyworm in the common name belong to the Noctuidae family. The caterpillars of several other insect species display similar group behavior. The larvae’s behavior of congregating and moving in large groups when looking for new food sources is the basis for the name armyworm. Description and life cycle What is in a name? The larvae can feed and complete their development on a wide variety of broadleaf species when large populations deplete their preferred food plants. The larvae, however, feed primarily on grasses and are an infrequent, but significant, pest of cereals including small grains, corn, rice, forage grasses, and turf grasses. Host rangeĪrmyworm adults feed on plant nectar and are not a threat to crops. In Minnesota, annual infestations are the result of adult moths migrating from wintering areas in the south. The armyworm cannot survive winters with persistent freezing winter temperatures. The highly migratory behavior of the armyworm adults allows them to exploit new geographic areas when weather is suitable. In North America, crop damaging infestations are most often observed east of the Rocky Mountains as far north as southern Canada. It is a member of the moth family Noctuidae, a large group that includes most species of cutworms. The armyworm is native to the Americas, but localized invasive populations have been observed in areas of Europe, Africa, the Mideast, and Asia. Mythimna unipuncta (Haworth, 1809), (Lepidoptera: Noctuidae) Distribution
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