armyworm, larva, or caterpillar, of a moth, Pseudaletia unipuncta or Mythimna unipuncta, found in North America E of the Rocky Mts.; also known as the common, or true, armyworm. When numerous, armyworms move in hordes, traveling by night and devouring grasses, young grains, and some leguminous crops. The full-grown larva is about 2 in. (5 cm) long, dark gray with yellow and green stripes. There are usually two generations in a season, the larvae hatching from eggs in late spring and again in late summer. Pupation (see insect) is underground. The moth is grayish brown with a white spot on each fore wing. Armyworms are sometimes serious pests, especially in the second generation of the summer, which occurs when corn and wheat are maturing. Control methods include the use of poisoned bait and the digging of ditches and holes as traps. The armyworm can also be controlled by toxaphene insecticide, but this chemical is prohibited in most states. The caterpillars of several other moth species that form similar hordes and can be serious pests are also known as armyworms. The fall armyworm, Spodoptera frugiperda, of E and central North America and South America is also a serious pest in Africa, where it is typically more destructive than the African armyworm, Spodoptera exempta, in part because it can have six generations in a growing season. The armyworm species are classified in the phylum Arthropoda, class Insecta, order Lepidoptera, family Noctuidae.
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