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

agricultural Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peopl ...

pest

insects Insects (from Latin ') are pancrustacean 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 j ...

. 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 there ...

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 Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word � ...

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. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, ...

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 protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from th ...

behind, netting the leaves with a silvery film.

Ecology

The wide host range of the beet armyworm includes

asparagus Asparagus, or garden asparagus, folk name sparrow grass, scientific name ''Asparagus officinalis'', is a perennial flowering plant species in the genus '' Asparagus''. Its young shoots are used as a spring vegetable. It was once classified in ...

bean A bean is the seed of several plants in the family Fabaceae, which are used as vegetables for human or animal food. They can be cooked in many different ways, including boiling, frying, and baking, and are used in many traditional dishes th ...

s and

pea The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...

s, sugar and table beets,

celery Celery (''Apium graveolens'') is a marshland plant in the family Apiaceae that has been cultivated as a vegetable since antiquity. Celery has a long fibrous stalk tapering into leaves. Depending on location and cultivar, either its stalks, ...

cole crops Cruciferous vegetables are vegetables of the family Brassicaceae (also called Cruciferae) with many genera, species, and cultivars being raised for food production such as cauliflower, cabbage, kale, garden cress, bok choy, broccoli, Brussels sp ...

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Uni ...

tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

cotton Cotton 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 cellulose, and can contain minor pe ...

cereals A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more food ...

, 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. The number of species within the genus is disputed. Three species may be recognized: '' Cannabis sativa'', '' C. indica'', and '' C. ruderalis''. Alternative ...

, 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 state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...

and

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

, 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 ''Chelonus'' is a wasp genus in the subfamily Cheloninae. Their larvae feed chiefly on larvae of moths in superfamilies Tortricoidea and Pyraloidea.Shaw, S.R. 1997. Subfamily Cheloninae. Species * '' Chelonus abditus'' * ''Chelonus abducto ...

'', ''

Cotesia marginiventris ''Cotesia marginiventris'' is a species of parasitoid wasp that develops in Noctuidae The Noctuidae, commonly known as owlet moths, cutworms or armyworms, are a family of moths. They are considered the most controversial family in the superfam ...

'', ''

Meteorus autographae ''Meteorus'' is a genus of parasitoid wasps in the family Braconidae. It comprises over 330 species worldwide. ''Meteorus'' wasps are distinguished from other braconid The Braconidae are a family of parasitoid wasps. After the closely relat ...

'', ''

Lespesia archippivora ''Lespesia archippivora'' is a species of tachinid fly, which, like all tachinids, are parasitoids of other arthropods. ''L. archippivora'' lives in the body of its host resulting in its death. This is not uncommon since it is estimated that abo ...

'' lay eggs on the caterpillars, and their larvae feed and emerge. Predators like '' Orius'' sp., ''

Geocoris ''Geocoris'' is a genus of insects in the family Geocoridae (although in the past the geocorids were subsumed as a subfamily under the family " Lygaeidae"). Commonly known as big-eyed bugs, the species in ''Geocoris'' are beneficial predators, b ...

'' sp., ''

Nabis Nabis ( grc-gre, Νάβις) was the last king of independent Sparta. He was probably a member of the Heracleidae, and he ruled from 207 BC to 192 BC, during the years of the First and Second Macedonian Wars and the eponymous " War against Nab ...

'' 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 ''Azadirachta indica'', commonly known as neem, nimtree or Indian lilac, is a tree in the mahogany family Meliaceae. It is one of two species in the genus '' Azadirachta'', and is native to the Indian subcontinent and most of the countries in Afr ...

products. Eggs can be killed by using petroleum oil concentrations. Applying cottonseed oil to leaves can eliminate both eggs and larvae.

References

External links

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''Spodoptera exigua'', a migratory plague.

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''Lepiforum e.V.''
{{clear 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

Discovery

Description

Damage

Ecology

Control

See also

References

External links