The fall armyworm is a
highly polyphagous migratory lepidopteron pest species. It can colonize over 80
different plant species including many grasses, and crops such as alfalfa,
soybean, sorghum(Brooks et al., 2007). Although
the fall armyworm is highly polyphagous with a host range of more than 80 plant
species it prefers to feed on gramineous plants in particular on economically
important crops such as maize, millet, sorghum, rice, wheat, and sugar cane(Tindo et al., 2016).
The fall army worm, spodoptera frugiperda has been classified a sporadic
pest due to its migratory behavior. This species dose not inters diapause,
because it can migrate from unsuitable to suitable places(Luginbill, 1928). An outbreak and its subsequent damage of fall army worm are
unpredictable hence when outbreak do occur the severity of the problem is compounded
(Hardke, Iii and Leonard, 2017).
Laphygma frugiperda is known under a variety of common names throughout the
area fall army worm invades. The first common name on record given to it by
Smith and Abbot is “corn-bud-worm-moth”. Other names are
” fall army worm,” ” grass caterpillar,” ” southern
army worm,” ” southern grass worm,” ” the army worm,”
” Daggy’s corn worm.” and “wheat cutworm.”(Luginbill, 1928).
1. LITERATURE REVIEW
Origin and Distribution
The fall army worm
undoubtedly is tropical in origin, since it does not pass the winter in any of
its stages in the United States, except in southern Florida and southern Texas,
or in that region
of the United States included in the Tropical lite zone (Hinds and Dew). The species redistributes itself every year,
through the migration of the moths, over most of that part of the Austral
region included in the Austral life zone, and also over part of that region
included in the upper Austral life zone. The insect usually may be taken each
year in these regions, and local outbreaks, especially in bottom lands, are not
uncommon. During a season of general outbreak, such as occurred in 1899 and
again in 1912, the insect not only covers the whole area mentioned but also
invades the transitional zone of the Austral region(Luginbill, 1928). Outbreaks, when general and severe, apparently
originate in Mexico and the West Indies. During the months from December, 1911,
to February, 1912, the species was abundant in Cuba and other tropical
countries. The general outbreak which occurred in a large part of the eastern
United States during 1912 evidently originated in these countries(Luginbill, 1928).
The fall army worm is a
pest of the first order, particularly in the Southern States, as it occurs
every year in some part of that region and often does serious damage to crops,
especially those of the lowlands. Sometimes this damage is attributed to other
insects or other causes. When not exceptionally abundant the larvae may feed on
the corn earworms, in the buds of plants, and later, on the grain of the ears,
and so may be mistakenly thought to belong to the latter species. Van Dine lists
this species as injurious to sugar cane in Porto Rico.
Causes Conducive to an Outbreak
The probability of a general invasion of the fall army worm in the United
States depends to a large extent upon the prevailing weather conditions during
the winter months in the region where
the insect is a permanent resident. This insect thrives best during periods of
cool weather, with an abundance of rainfall. Such conditions are favorable not
only for a luxurious growth of grasses and other closely allied plants, but are
known to check the multiplication of natural enemies, thus permitting the pest
to propagate unhampered in enormous numbers.
By the time conditions become favorable for
the multiplication of natural enemies the insect has gotten beyond biological
control. If humid weather conditions prevail great damage to various crops may result.
During seasons when no general invasion occurs local outbreaks of the insect
occur following a period of heavy rainfall and humid weather. (Bodkin) as follows:
Insect life was checked early in the year due to a prolonged and severe
drought. Later, when rains began, the insect pests became very active, but the
parasites, having suffered the greatest setback, were unable to hold the insect
in check, and the severe outbreak as described by Bodkin resulted.
Nature of Injury to Corn
The moths oviposit on
young corn plants from 1 to 2 feet tall, in preference to all other plants. The
caterpillars usually are found feeding on the corn leaves, especially those on
the young plants before the tassels appear. The large caterpillars commonly
remain in the “throat” of the plant, and feed during the day as well
as at night. Owing to this method of feeding, the insect is commonly known in
the South as the “bud worm.” Holes are eaten through the folded leaf
which, after it grows out, appears as a row of three or four small-to-large
holes across the leaf. If the caterpillars are numerous the leaves are badly
frayed. This injury is similar to the injury done to young corn by the larvae
of the corn-ear worm HeliotMs obsoleta (Fab.). By examining the injured
plant it is possible, however, to determine which species is responsible for
the damage, as the holes cut in the corn leaves by the larvae of Laphygma have
nearly smooth edges, whereas the holes cut by the larvae of Heliothis have
ragged edges. The caterpillars also feed on older corn plants, entering the
ears and feeding on the grain, and causing damage similar to that done by the
corn-ear worm. Sometimes the larvae are numerous enough to destroy the corn
plants, which may be entirely stripped of their leaves; even the stalks of
young plants(Vickery, 1929).
The fall armyworm is a chronic pest and can
cause severe damage to grass and forage crops. Damage varies in appearance and
severity according to the type of grass and management practices. They are most
numerous in late summer or early fall. The size and timing of the initial moth
flights are two factors that influence the outbreak potential of this pest (——–).
Droughty conditions are favorable
for the fall armyworm. Fall armyworms can be found up until the first killing
frost in an area. However, the risk of damage declines as it gets cooler
because the pest develops more slowly in cooler temperatures (——-).
Behavior Patterns the fall armyworm
is in the same insect family (Noctuidae) as cutworms and other armyworms. Fall
armyworm caterpillars damage grass by chewing plant tissue. Fall armyworms are
typically most active early in the morning, late in the afternoon, or in early
evening, but on taller, unmowed grass, they can be observed feeding on foliage
throughout the day. On closely grazed or recently mowed hayfields, fall
armyworm larvae spend the warmer hours of the day deep in the sod (——-).
Fall armyworm damage often seems to appear
overnight. Young armyworms don’t eat much. Almost all the damage is caused by
the oldest caterpillars, which in four days of feeding; eat more than all the other
ages put together. Therefore, an infestation may have been present but not
detected because of the small size of the caterpillars. Another reason for the
sudden appearance of this insect is that the larger fall armyworms will
sometimes march into (quickly invade) an un-infested area in search of food once
an adjacent field has been defoliated. Large armyworms frequently disappear
almost as suddenly as they appeared, either burrowing into the ground to pupate
or moving on in search of food. Fall armyworms marching from right to left
across a pasture completely defoliating the foliage as they move. Fall armyworm
damage on closely mowed grass. In closely grazed fields, the grass may seem to
thin out and develop brown spots similar to those sometimes seen on golf
courses; these spots look burned or browned out. This appearance is the result
of grass plants rapidly dehydrating after fall armyworm larvae have chewed off
the tender foliage. For this reason, fall armyworm damage often resembles
drought damage. In hayfields or in pastures, virtually all tender green
material may be removed, leaving only tough stems. Caterpillars have eaten the tender, green
portions of the grass, leaving jagged leaf edges and tough leaf bases(Vickery, 1929).
The fall army worm has several generations
& it consists a life cycle of egg, 6-7 larval instar, pupa and adult. In a
suitable condition, more than six generation will be occurring per year(Luginbill, 1928). Four weeks in favorable condition and twelve weeks in low
temperate condition is needed to complete one life cycle(Vickery, 1929). The best location for oviposition is on leave directly from the
main stem and lowers to medium portion of the plant canopy (Ali, 1989). Upon
eclosion neonates consume the egg mass from which they hatched; but larvae can
disperse in all directions to feed the vegetative parts of the plant(Luginbill, 1928). Larvae fall from the plant and buried in to the soil in a
pre-pupal state for two to four days(Meagher et al., 2004). Depths of the pupa buried depend on many factors such as soil
texture, soil moisture and soil temperature (Sparks, 1979). As moths emerge
from the soil it can mate locally or migrate up to 300 miles before mating and
ovipositting(Ashley. T.R, 1979).
The moths fly at night
and hide during the day on the food plant of the larvae. On corn they
frequently rest during the day among the unopened leaves of the young plants.
In the writer’s experiments the female oviposited at night, but it is not
certain that they do not oviposit to some extent during the day. They lay their
eggs in masses, usually on the upper surface of the leaf of corn, but
occasionally on other parts of the plant. The female covers the egg mass with a
gray down from her body(Vickery, 1929).
Description of life stage
Egg: it is oblate spheroidal shaped
with 0.39mm height and 0.47mm in diameter. Eggs are greenish gray immediately
after oviposited, become darker after wards and become nearly black just prior
to larval eclosion (Luginbill, 1928).
Larva: it is difficult to decide the
color of larvae in the first instar but it can lied between white and yellow
and it bears black spots from which primary setae protrude. The proceeding two
larval instars are similar in color from L1at the early stage of molting and
they will be darken to prepare for the next molting. Even factors can affect,
the final three instars are dark in color and they lack primary setae (i.e
generally smooth)(Hardke, Iii and Leonard, 2017).
Pupa: the pupa stage case has an orange
–brown appearance typically of most noctuids and turning darker as it ages(Hardke, Iii and Leonard, 2017).
Adult: Adult fall armyworm wings are mottled and have
white or light gray spots near the tips. The back wings are white with a
narrow, smoky-brown edge. Moths become active at twilight and feed on nectar.
They have an average life span of 2 to 3 weeks(CABI, 2017).
Behavior and host strain
There are two morphologically identical
fall army worm strains; namely R-strain and C-strain (rice strain and corn
strain respectively), and they are only distinguished by their hosts. Genetic
markers and allozyme variants are used to distinguish these two strains(Meagher et al., 2004). Differences between these two strains have a profound effect on crop protection strategies due to variation
to several life history characteristics. Differences in larval development on
host plants, mating behavior, use of food resources, resistance to insecticides
variation in susceptibility to plants expressing Bascillus thuringiensis
(Bt) can influence management tactics (Veenstra, 1994).
Inter strain mating can occur, but
variability exists in mating preference. R-strain females prefer to accept
C-strain males, resulting mixed population; but C-strain females and R-strain
males appears to be reproductively incompatible (Whithford, 1988).
Half-grown or fully grown caterpillars are the
easiest to identify. Fall armyworm caterpillars have a characteristic pattern
of dark pimples (spots) on their backs; each spot has a short bristle (hair).
Although the skin looks rough it is smooth to the touch. Look out for four dark
spots forming a square on the second to last segment (red circle). Each of the
other body segments
also has four spots, but they do not from a square pattern (yellow circle). The
head is dark and shows a characteristic upside down Y-shaped pale marking on
the front (CABI,
1.10. Fall Armyworm in Ethiopia
armyworm is new in Ethiopia and even in east Africa; it was happen when
millions of farmers in the region seek to recover from a devastating drought.
The pest was recently detected in Kenya and it will be from Uganda. Generally
fall armyworm was first detected in Africa since 2016. But in Ethiopia it was
detected at the last weeks of February 2017 on irrigated maize field. But until
May 30, 2017 the fall armyworm covers 52,962 hectares 144 districts in three of
major maize growing regional state (Gambela, Oromia &SNNP).
the collaboration of FAO and other development partners the government of
Ethiopia has intensified efforts to protect major maize growing areas from the
ravage of the fall armyworm. Hence the government allocated around two million USD
to tackle this problem(F
A O, 2017).