The fall armyworm is ahighly polyphagous migratory lepidopteron pest species. It can colonize over 80different plant species including many grasses, and crops such as alfalfa,soybean, sorghum(Brooks et al., 2007). Althoughthe fall armyworm is highly polyphagous with a host range of more than 80 plantspecies it prefers to feed on gramineous plants in particular on economicallyimportant 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 sporadicpest 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 areunpredictable 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 thearea fall army worm invades.
The first common name on record given to it bySmith and Abbot is “corn-bud-worm-moth”. Other names are” fall army worm,” ” grass caterpillar,” ” southernarmy worm,” ” southern grass worm,” ” the army worm,”” Daggy’s corn worm.” and “wheat cutworm.”(Luginbill, 1928).
1. LITERATURE REVIEW1.1. Origin and DistributionThe fall army wormundoubtedly is tropical in origin, since it does not pass the winter in any ofits stages in the United States, except in southern Florida and southern Texas,or in that regionof 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 Australregion included in the Austral life zone, and also over part of that regionincluded in the upper Austral life zone. The insect usually may be taken eachyear in these regions, and local outbreaks, especially in bottom lands, are notuncommon. During a season of general outbreak, such as occurred in 1899 andagain in 1912, the insect not only covers the whole area mentioned but alsoinvades the transitional zone of the Austral region(Luginbill, 1928). Outbreaks, when general and severe, apparentlyoriginate in Mexico and the West Indies.
During the months from December, 1911,to February, 1912, the species was abundant in Cuba and other tropicalcountries. The general outbreak which occurred in a large part of the easternUnited States during 1912 evidently originated in these countries(Luginbill, 1928). 1.2. Economic ImportanceThe fall army worm is apest of the first order, particularly in the Southern States, as it occursevery 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 otherinsects or other causes. When not exceptionally abundant the larvae may feed onthe 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 liststhis species as injurious to sugar cane in Porto Rico. 1.3. Causes Conducive to an Outbreak The probability of a general invasion of the fall army worm in the UnitedStates depends to a large extent upon the prevailing weather conditions duringthe winter months in the region wherethe insect is a permanent resident. This insect thrives best during periods ofcool weather, with an abundance of rainfall. Such conditions are favorable notonly for a luxurious growth of grasses and other closely allied plants, but areknown to check the multiplication of natural enemies, thus permitting the pestto propagate unhampered in enormous numbers.
By the time conditions become favorable forthe multiplication of natural enemies the insect has gotten beyond biologicalcontrol. If humid weather conditions prevail great damage to various crops may result.During seasons when no general invasion occurs local outbreaks of the insectoccur 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 severedrought. Later, when rains began, the insect pests became very active, but theparasites, having suffered the greatest setback, were unable to hold the insectin check, and the severe outbreak as described by Bodkin resulted. 1.
4. Nature of Injury to CornThe moths oviposit onyoung corn plants from 1 to 2 feet tall, in preference to all other plants. Thecaterpillars usually are found feeding on the corn leaves, especially those onthe young plants before the tassels appear. The large caterpillars commonlyremain in the “throat” of the plant, and feed during the day as wellas at night.
Owing to this method of feeding, the insect is commonly known inthe South as the “bud worm.” Holes are eaten through the folded leafwhich, after it grows out, appears as a row of three or four small-to-largeholes across the leaf. If the caterpillars are numerous the leaves are badlyfrayed. This injury is similar to the injury done to young corn by the larvaeof the corn-ear worm HeliotMs obsoleta (Fab.). By examining the injuredplant it is possible, however, to determine which species is responsible forthe damage, as the holes cut in the corn leaves by the larvae of Laphygma havenearly smooth edges, whereas the holes cut by the larvae of Heliothis haveragged edges. The caterpillars also feed on older corn plants, entering theears and feeding on the grain, and causing damage similar to that done by thecorn-ear worm. Sometimes the larvae are numerous enough to destroy the cornplants, which may be entirely stripped of their leaves; even the stalks ofyoung plants(Vickery, 1929).
The fall armyworm is a chronic pest and cancause severe damage to grass and forage crops. Damage varies in appearance andseverity according to the type of grass and management practices. They are mostnumerous in late summer or early fall. The size and timing of the initial mothflights are two factors that influence the outbreak potential of this pest (——–). Droughty conditions are favorablefor the fall armyworm. Fall armyworms can be found up until the first killingfrost in an area.
However, the risk of damage declines as it gets coolerbecause the pest develops more slowly in cooler temperatures (——-). Behavior Patterns the fall armywormis in the same insect family (Noctuidae) as cutworms and other armyworms. Fallarmyworm caterpillars damage grass by chewing plant tissue. Fall armyworms aretypically most active early in the morning, late in the afternoon, or in earlyevening, but on taller, unmowed grass, they can be observed feeding on foliagethroughout the day.
On closely grazed or recently mowed hayfields, fallarmyworm larvae spend the warmer hours of the day deep in the sod (——-). Fall armyworm damage often seems to appearovernight. Young armyworms don’t eat much. Almost all the damage is caused bythe oldest caterpillars, which in four days of feeding; eat more than all the otherages put together. Therefore, an infestation may have been present but notdetected because of the small size of the caterpillars. Another reason for thesudden appearance of this insect is that the larger fall armyworms willsometimes march into (quickly invade) an un-infested area in search of food oncean adjacent field has been defoliated.
Large armyworms frequently disappearalmost as suddenly as they appeared, either burrowing into the ground to pupateor moving on in search of food. Fall armyworms marching from right to leftacross a pasture completely defoliating the foliage as they move. Fall armywormdamage on closely mowed grass.
In closely grazed fields, the grass may seem tothin out and develop brown spots similar to those sometimes seen on golfcourses; these spots look burned or browned out. This appearance is the resultof grass plants rapidly dehydrating after fall armyworm larvae have chewed offthe tender foliage. For this reason, fall armyworm damage often resemblesdrought damage. In hayfields or in pastures, virtually all tender greenmaterial may be removed, leaving only tough stems. Caterpillars have eaten the tender, greenportions of the grass, leaving jagged leaf edges and tough leaf bases(Vickery, 1929).1.5.
Insect Biology The fall army worm has several generations& it consists a life cycle of egg, 6-7 larval instar, pupa and adult. In asuitable condition, more than six generation will be occurring per year(Luginbill, 1928). Four weeks in favorable condition and twelve weeks in lowtemperate condition is needed to complete one life cycle(Vickery, 1929).
The best location for oviposition is on leave directly from themain stem and lowers to medium portion of the plant canopy (Ali, 1989). Uponeclosion neonates consume the egg mass from which they hatched; but larvae candisperse 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 apre-pupal state for two to four days(Meagher et al., 2004). Depths of the pupa buried depend on many factors such as soiltexture, soil moisture and soil temperature (Sparks, 1979). As moths emergefrom the soil it can mate locally or migrate up to 300 miles before mating andovipositting(Ashley.
T.R, 1979).1.6. Oviposition The moths fly at nightand hide during the day on the food plant of the larvae.
On corn theyfrequently 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 notcertain that they do not oviposit to some extent during the day. They lay theireggs in masses, usually on the upper surface of the leaf of corn, butoccasionally on other parts of the plant. The female covers the egg mass with agray down from her body(Vickery, 1929).1.7. Description of life stageEgg: it is oblate spheroidal shapedwith 0.
39mm height and 0.47mm in diameter. Eggs are greenish gray immediatelyafter oviposited, become darker after wards and become nearly black just priorto larval eclosion (Luginbill, 1928).Larva: it is difficult to decide thecolor of larvae in the first instar but it can lied between white and yellowand it bears black spots from which primary setae protrude. The proceeding twolarval instars are similar in color from L1at the early stage of molting andthey 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.egenerally 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 havewhite or light gray spots near the tips. The back wings are white with anarrow, 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).. 1.8.
Behavior and host strainThere are two morphologically identicalfall army worm strains; namely R-strain and C-strain (rice strain and cornstrain respectively), and they are only distinguished by their hosts. Geneticmarkers 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 variationto several life history characteristics. Differences in larval development onhost plants, mating behavior, use of food resources, resistance to insecticidesvariation in susceptibility to plants expressing Bascillus thuringiensis(Bt) can influence management tactics (Veenstra, 1994).Inter strain mating can occur, butvariability exists in mating preference. R-strain females prefer to acceptC-strain males, resulting mixed population; but C-strain females and R-strainmales appears to be reproductively incompatible (Whithford, 1988).1.
9. Identification Half-grown or fully grown caterpillars are theeasiest to identify. Fall armyworm caterpillars have a characteristic patternof 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 darkspots forming a square on the second to last segment (red circle). Each of theother body segmentsalso has four spots, but they do not from a square pattern (yellow circle). Thehead is dark and shows a characteristic upside down Y-shaped pale marking onthe front (CABI,2017).1.
10. Fall Armyworm in EthiopiaFallarmyworm is new in Ethiopia and even in east Africa; it was happen whenmillions 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. Generallyfall armyworm was first detected in Africa since 2016. But in Ethiopia it wasdetected at the last weeks of February 2017 on irrigated maize field.
But untilMay 30, 2017 the fall armyworm covers 52,962 hectares 144 districts in three ofmajor maize growing regional state (Gambela, Oromia &SNNP). Withthe collaboration of FAO and other development partners the government ofEthiopia has intensified efforts to protect major maize growing areas from theravage of the fall armyworm. Hence the government allocated around two million USDto tackle this problem(FA O, 2017).