Beet armyworm

Scientific name

Spodoptera exigua (Lepidoptera: Noctuidae)

Other common names

small mottled willow moth, common cutworm

Similar species

Larvae of the beet armyworm can be confused with the southern armyworm, Spodoptera eridania. Larvae of beet armyworm and southern armyworm are distinguishable by the presence of a large black spot laterally on the first abdominal segment of the southern armyworm.

Distribution

United States: Widespread almost everywhere host plants are grown; overwinters in Arizona, California, Colorado, Florida, Hawaii, Kansas, New Mexico, and Oregon.

Worldwide: Everywhere host plants are grown, most notably Australia, Africa, Southeast Asia, southern England, and Wales.

Native to Southeast Asia.

Diagnostic characteristics

Adults

• Wing span 25 - 30 mm (1 -1.2 in.).
• Forewings mottled gray brown with irregular banding pattern.
• Hindwings are usually a uniform white or gray color with a dark line at the margin and a fringe-like border.
• Soft, scaled wings held around the body when at rest.

Pupae

• Light brown.
• 15 - 20mm (0.6 - 0.8 in.) in length.
• Pupation chamber is composed of sand and soil that is held together with oral secretions.

Larvae

• 5 larval instars.
• Early instars are gregariousgregarious:
  exhibiting the behavior of moving or feeding in a group of individuals of the same species; early instars of many insects feed in groups
  and later instars are solitarysolitary:
  insects that feed or move about individually, not in groups
  .
• Pale green or yellow in color during 1st and 2nd instarinstar:
  immature stages (larva or nymph) of insects in between molts
  .
• Develop stripes in 3rd instarinstar:
  immature stages (larva or nymph) of insects in between molts
  .
• During 4th instarinstar:
  immature stages (larva or nymph) of insects in between molts
  , stripes get darker.
• 5th instarinstar:
  immature stages (larva or nymph) of insects in between molts
  is variable, dark dorsally and light ventrally with a white stripe laterally.
• A series of dark spots or dashes presents dorsally.
• 25 - 30 mm (1 - 1.2 in.) in the last larval instarinstar:
  immature stages (larva or nymph) of insects in between molts
  .

Eggs

• Appear circular from above, but from the side, eggs taper slightly at the top.
• Fine, longitudinal lines.
• Greenish to white in color.
• 50 - 150 eggs per mass.
• Egg masses can be several layers deep.
• Covered with a layer of whitish scales that give the egg mass a fuzzy appearance.

Hosts

Citrus hosts

• sweet orange, Citrus sinensis

Non-citrus hosts

Broad host rangehost range:
the range of species that a particular organism can feed on to achieve successful growth and reproduction
, including weeds as well as vegetable, field, and flower crops. A partial list includes:

• all cruciferous vegetables, Brassica spp.
• alfalfa, Medicago sativa
• asparagus, Asparagus officinalis
• bean, Phaseolus vulgaris
• celery, Apium graveolens
• chickpea, Cicer arietinum
• corn, Zea mays
• cowpea, Vigna unguiculata
• cotton, Gossypium spp.
• eggplant, Solanum melongena
• lambsquarters, Chenopodium album
• lettuce, Lactuca sativa
• melon, Cucumis spp.
• mullein, Verbascum spp.
• onion, Allium cepa
• parthenium, Parthenium spp.
• pea, Pisum sativum
• peanut, Arachis hypogaea
• pepper, Capsicum annuum
• pigweed, Amaranthus spp.
• potato, Solanum tuberosum
• purslane, Portulaca spp.
• radish, Raphanus sativus
• Russian thistle, Salsola kali
• safflower, Carthamus tinctorius
• sorghum, Sorghum spp.
• soybean, Glycine max
• spinach, Spinacea oleracea
• strawberry, Fragaria spp.
• sugar beet, Beta vulgaris
• Ssweet potato, Ipomoea batatas
• tidestromia, Tidestromia spp.
• tobacco, Nicotiana tabacum
• tomato, Solanum lycopersicum

Host damage

Fruits

• Chew holes and bore into fruit in the later instars.

Leaves

• Larvae will produce marginal damage on leaves as smaller instars.
• Can be skeletonized, leaving only the veins.
• Stems are rarely eaten.

Biology

The life cycle consists of 5 instars and can be completed in 24 days. Mating occurs soon after emergenceemergence:
used to describe the completion pupation that culminates in the appearance of the adult form of an insect
. Ovipositionoviposition:
the act of depositing eggs
occurs within 2 - 3 days of mating and lasts a week. Adults die within 9 - 10 days of emergenceemergence:
used to describe the completion pupation that culminates in the appearance of the adult form of an insect
. A female lays 300 - 600 eggs in her lifetime. Eggs are deposited on the lower surface of the leaf, near blossoms, or on the tip of a branch. Eggs hatch in 2 - 5 days in warm weather. Larvae are initially gregariousgregarious:
exhibiting the behavior of moving or feeding in a group of individuals of the same species; early instars of many insects feed in groups
, eating in groups, but become more solitarysolitary:
insects that feed or move about individually, not in groups
as they mature. Larvae can leave silksilk:
a natural fiber produced by some insects that can be utilized to construct shelters, leave a trail, build a cocoon, etc.
trails behind them while foraging. Pupation occurs underground.

Overwintering is usually limited to places where frost will not kill the host planthost plant:
the plant the provides sustenance for an insect
, including the warmer climates of the states in the southeastern and southwestern U.S.

Comments

Considered a minor pest of citrus, rarely causing economic damage.

References

Atkins, J.R. and E. Laurence. 1960. The beet armyworm, Spodoptera exigua: an economic pest of citrus in California. J. Econ. Entomol. 53(4): 616-619.

Capinera, J.L. 2006. Featured creatures fact sheet: Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Publication EENY-105. University of Florida. (http://entnemdept.ufl.edu/creatures/veg/leaf/beet_armyworm.htm).

University of California, IPM Online. 2008. UC IPM Pest Management Guidelines: Citrus. (http://www.ipm.ucdavis.edu/PMG/r107302111.html).

Authors

Weeks, J.A., K.W. Martin, A.C. Hodges, and N.C. Leppla