The beet armyworm or small mottled willow moth (''Spodoptera exigua'') is one of the best-known

agricultural Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...

pest

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

. It is also known as the asparagus fern caterpillar. 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. In the British Isles, where it is an

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...

and not known to breed, the adult moth is known as the small mottled willow moth.

Discovery

Thought to have originated in south-east Asian countries, it was first discovered in North America about 1876, when it was found in Oregon, and it reached Florida in 1924.

Description

The adult is a drab brown or grey moth with a wingspan of . Forewing is greyish ochreous in color, washed with dull yellow and sprinkled with black scales. Inner and outer lines are double, indistinct, filled in with pale yellowish color. A dark waved median shade visible before lower half of outer line. Cell is dark brown. Orbicular stigma is pale or bright yellow, and round, whereas reniform has a curved brown lunule in centre. The submarginal line is pale grey. There is the darker shade preceding it with dark streaks between the veins. Terminal spots are black. Hindwings semihyaline are white, with the veins dark brown. All three margins are shaded with fuscous color. Larvae are pinkish brown, clotted with black. Spiracular line pale ochreous, with dark upper edge. They are greenish-brown cutworms, soft and bulging caterpillars with dark longitudinal stripes.

Damage

The larvae feed on the foliage and fruits of plants, and can completely defoliate small ones. Smaller larvae devour the

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

of leaves, so 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 Lettuce (''Lactuca sativa'') is an annual plant of the family Asteraceae mostly grown as a leaf vegetable. The leaves are most often used raw in Green salad, green salads, although lettuce is also seen in other kinds of food, such as sandwiche ...

rather than neatly removing tissue from one particular leaf, rendering the produce unmarketable. Larvae also 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 Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is most commonly produced by certain insect larvae to form cocoon (silk), c ...

behind, netting the leaves with a silvery film.

Ecology

The wide host range of the beet armyworm includes

asparagus Asparagus (''Asparagus officinalis'') is a perennial flowering plant species in the genus ''Asparagus (genus), Asparagus'' native to Eurasia. Widely cultivated as a vegetable crop, its young shoots are used as a spring vegetable. Description ...

bean A bean is the seed of some plants in the legume family (Fabaceae) used as a vegetable for human consumption or animal feed. The seeds are often preserved through drying (a ''pulse''), but fresh beans are also sold. Dried beans are traditi ...

s and peas, sugar and table beets,

celery Celery (''Apium graveolens'' Dulce Group or ''Apium graveolens'' var. ''dulce'') is a cultivated plant belonging to the species ''Apium graveolens'' in the family Apiaceae that has been used as a vegetable since ancient times. The original wild ...

, cole crops,

potato The potato () is a starchy tuberous vegetable native to the Americas that is consumed as a staple food in many parts of the world. Potatoes are underground stem tubers of the plant ''Solanum tuberosum'', a perennial in the nightshade famil ...

tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...

cotton Cotton (), first recorded in ancient India, is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure ...

, cereals, oilseeds,

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...

, many flowers, and a multitude of weed species. The beet armyworm does not tolerate cold. It can overwinter in warm areas, such as

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

and

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

, 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.

Control

Pheromone traps and mechanical hand picking of adults and caterpillars are extensively used.

Parasitoid In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...

s such as '' Chelonus insularis'', '' Cotesia marginiventris'', '' Meteorus autographae'', '' Lespesia archippivora'' lay eggs on the caterpillars, and their larvae feed and emerge. Predators like '' Orius'' sp., '' Geocoris'' sp., '' Nabis'' sp., '' Podisus maculiventris'' are also effective controlling measures. Pupal stages can be eliminated by introducing '' Solenopsis invicta'' to the field. Apart from biological control, many chemical pesticides are extensively used. Larvae are susceptible to neem products. Eggs can be killed by using petroleum oil concentrations. Applying cottonseed oil to leaves can eliminate both eggs and larvae.

References

External links

"73.087 BF2385 Small Mottled Willow ''Spodoptera exigua'' (Hübner, [1808])"
''UKMoths''. Retrieved January 13, 2019. * Taxonomy
''Fauna Europaea''beet armyworm video
''Spodoptera exigua'', a migratory plague.

on the UF / IFAS Featured Creatures Web site
''Lepiforum e.V.''
{{Authority control Spodoptera Moths described in 1808 Agricultural pest insects Owlet moths of Africa Moths of North America Moths of Cape Verde Moths of Europe Moths of Japan Moths of the Middle East Moths of Réunion Moths of Asia Taxa named by Jacob Hübner Insect pests of millets