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beet armyworm
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Lepidoptera Family: Noctuidae Genus: Spodoptera Species: S. exigua
Binomial name
Spodoptera exigua (Hübner, 1808)

The beet armyworm (Spodoptera exigua) is one of the most well-known agricultural pest insects. It is also known as the asparagus fern caterpillar, and the adult moth is known in the UK (where it is an immigrant and not known to breed) as the small mottled willow. It is native to Asia, but has been introduced worldwide and is now found almost anywhere its many host crops are grown. The voracious larvae are the main culprits. They are greenish-brown cutworms, soft and bulging caterpillars with dark longitudinal stripes. The adult is a drab brown or gray moth 2 to 3 cm in wingspan.

The larvae feed on the foliage of plants, and can completely defoliate small ones. Smaller larvae devour the parenchyma of leaves, so that all that remains is the thin epidermis and veins. Larger larvae tend to burrow holes through thick areas of plants. For example, they will burrow straight into a head of lettuce rather than neatly removing tissue from one particular leaf. This renders the produce unmarketable. They attack buds and new growth on plants, preventing flowers from opening, new leaves from sprouting, and vegetables from developing. As the smaller larvae move about they leave strands of silk behind, netting the leaves with a silvery film.

The wide host range of the beet armyworm includes asparagus, beans and peas, sugar and table beets, celery, cole crops, lettuce, potato, tomato, cotton, cereals, oilseeds, tobacco, many flowers, and a multitude of weed species. The beet armyworm does not tolerate cold. It can overwinter in warm areas, such as Florida and Hawaii, but in colder areas it dies off during the winter and the region is reinvaded by the adult moth as the weather warms and crop plants sprout.