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Description and Life Cycle
Seasonal activity varies considerably according to climate. In
warm locations such as Florida, all stages can be found throughout
the year, although development rate and overall abundance are reduced
during the winter months (Tingle and Mitchell 1977). The life cycle
can be completed in as few as 24 days, and six generations have
been reared during five months of summer weather in Florida ( Wilson
1934).
Egg: Eggs are laid in clusters of 50 to 150 eggs
per mass. Normal egg production is about 300 to 600 per female.
Eggs are usually deposited on the lower surface of the leaf, and
often near blossoms and the tip of the branch. The individual eggs
are circular when viewed from above, but when examined from the
side the egg is slightly peaked, tapering to a point. The eggs
are greenish to white in color, and covered with a layer of whitish
scales that gives the egg mass a fuzzy or cottony appearance. Eggs
hatch in two to three days during warm weather.
Larva: The larvae are pale green or yellow in
color during the first and second instars, but acquire pale stripes
during the third instar. During the fourth instar, larvae are darker
dorsally, and possess a dark lateral stripe. Larvae during the
fifth instar are quite variable in appearance, tending to be green
dorsally with pink or yellow color ventrally and a white stripe
laterally. A series of dark spots or dashes is often present dorsally
and dorsolaterally. Sometimes larvae are very dark in color. The
spiracles are white with a narrow black border. The body is practically
devoid of hairs and spines. In the southern states, the larva of
beet armyworm is easily confused with southern armyworm, Spodoptera
eridania (Cramer), but southern armyworm can be distinguished
by the presence of a large dark spot laterally on the first abdominal
segment that disrupts the lateral stripe. Beet armyworm occasionally
bears a spot laterally, but if present it occurs on the mesothorax,
not on the first abdominal segment.
Pupa: Pupation occurs in the soil. The chamber
is constructed from sand and soil particles held together with
an oral secretion that hardens when it dries. The pupa is light
brown in color and measures about 15 to 20 mm in length. Duration
of the pupal stage is six to seven days during warm weather.
Adult: The moths are moderately sized, the wing
span measuring 25 to 30 mm. The forewings are mottled gray and
brown, and normally with an irregular banding pattern and a light
colored bean-shaped spot. The hind wings are a more uniform gray
or white color, and trimmed with a dark line at the margin. Mating
occurs soon after emergence of the moths, and oviposition begins
within two to three days.
The beet armyworm has a wide host range, occurring as a serious
pest of vegetable, field, and flower crops. Among susceptible vegetable
crops are asparagus, bean, beet, broccoli, cabbage, cauliflower,
celery, chickpea, corn, cowpea, eggplant, lettuce, onion, pea,
pepper, potato, radish, spinach, sweet potato, tomato, and turnip.
Field crops damaged include alfalfa, corn, cotton, peanut, safflower,
sorghum, soybean, sugarbeet, and tobacco. Weeds also are suitable
for larval development, including such common plants as lambsquarters, Chenopodium
album; mullein, Verbascum sp.; pigweed, Amaranthus spp.;
purslane, Portulaca spp.; Russian thistle, Salsola
kali; parthenium, Parthenium sp.; and tidestromia, Tidestromia sp.
In the Southeast and Southwest, the relatively high abundance
of beet armyworm has stimulated frequent application of insecticides
to foliage. Insecticide resistance is a major problem in management
of this insect, possibly because it attacks crops such as flowers,
cotton, and vegetables - crops that are treated frequently with
insecticides.
Beet armyworm larvae are susceptible to neem products (Prabhaker et
al. 1986). Eggs can be killed with petroleum oil , and both
eggs and young larvae can be controlled with foliar applications
of 5% cottonseed oil, but this concentration is damaging to some
plants (Butler and Henneberry 1990).
For selected insecticides approved for use on insects attacking
lettuce go to: http://edis.ifas.ufl.edu/IG161
For selected insecticides approved for use on insects attacking
endive and escarole go to: http://edis.ifas.ufl.edu/pdffiles/CV/CV12600.pdf
For selected insecticides approved for use on insects attacking
tomato and bell pepper go to: http://edis.ifas.ufl.edu/IN169
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