Saturday, 24 March 2012

SPODOPTERA LITURA(armyworm) AND S.EXIGUA(cutworm)----- polyphagous pests

Scientific name: Spodoptera litura Fabricius
Common name: Armyworm/ cluster caterpillar
Scientific name: Spodoptera exigua
Common name: Common cutworm/beet army worm


Cutworms and armyworms attack a number of crops and may cause significant damage depending on severity of infestation.

On hatching, clusters of young larvae feed gregariously by initially scraping the surface of the leaf. Later instars disburse and move on to other leaves and feed voraciously, producing large irregular holes and may leave only the veins. High infestation causes severe defoliation. Army worms quickly skeletonise leaves as they attack in clusters.
Egg. The eggs are laid in mass on the surface of the leaves and covered with whitish scales. The egg stage lasts for 3 days.
Larva. The larvae undergo several  colour phases from green to almost black.  The larval stage lasts for about 9-14 days and usually has six instars.
PupaPupation occurs in the soil and lasts for about 10 days.
AdultsAdults are smaller than other members of the cutworm-armyworm group, about 12 mm long with a wing spread of 25 to 40 mm. Body and wings range from silvery-grey to greyish-brown. Forewings have a lighter spot near the centre. Hindwings are paler with darker borders, with a light band at the wing edges.
Egg. The eggs are round, pearl-white, laid in mass on the ground or on the surface of the leaves and covered with yellowish brown hairs. An egg mass contains about 100 to 300 hundred eggs.  Egg hatches in 3-6 days.
Larva. The newly hatched larvae are greenish with a dark longitudinal band on each side. The larvae are pale greenish brown with dark markings and the body may have rows of dark spots or may have transverse and longitudinal grey and yellow bands. They gradually turn brownish black as they  mature. The fully grown larva  is stout and cylindrical measuring 30-50 mm in length.
Pupa. The pupae are reddish dark brown.  Their legs and appendages are not capable of free movement. Pupal stage lasts for about 12 days.
AdultThe adults are brown moths with greyish brown forewings patterned with wavy markings and the hindwings are transparent with a brown narrow band along the outer margins.
The eggs hatch after 3 days from egg deposition and take about two weeks to reach the pupal stage. The larvae prefer moist sites. The larvae hide during the day in the crevices found in the soil and plant residues and become active during dusk to dawn. Pupation takes place in the soil in an earthen cell. Pupation lasts for a week. The development of the armyworm/cutworm from egg to adult takes about 3.5 to 4 weeks. The female S. exigua lays up to 1,000 eggs while S. litura lays as many as 2,000-2,600.
Apart from sweetpotato, armyworms attack asparagus, banana, cacao, corn, citrus, garlic, jute, kenaf, mulberry, onion, passion fruit, sesame, sorghum, soybean, tobacco, rice, tomato, sugarcane, cotton, beans, peanuts, castor oil plants, taro, wheat, white potato, a number of crops under Cruciferae and Cucurbitaceae, grasses, and some broad leaf weeds.
Aside from the symptoms of damage, the plant can also be inspected for the presence of eggs and feeding larvae. 
Management Options
Biological  control
S. exigua and S. litura have several natural enemies which can be used in biological control. 
One effective control for S. exigua is the use of a solution containing the virus nuclear polyhedrosis virus (NPV).  This can be applied to plants using the common backpack sprayer. There are also predators that prey on this insect.
S. litura is preyed on by a number of predators like ants, earwigs, pentatomid bugs and predaceous beetles.  Telenomus spodopterae Dodd and Telenomus remus Nixon can parasitise the eggs and reduce its population. A species of entomogenous fungus, Nomuraea rileyi infects some larvae in the field. Caterpillars are susceptible to the biopesticide Bt which at severe infestation could be used for spot application.
Chemical  control
Azinphosethyl, carbaryl, chlorphyriphos, monocrotophous phenthoate are recommended for armyworm control.

LARVA of S.litura



S.exigua larva


Amalin, D.M. and Vasquez, E. A. 1993. A handbook on Philippine sweetpotato pests and their natural enemies. International Potato Center (CIP), Los Baños, Philippines. 82 p.

Ames, T., Smit, N.E.J.M., Braun, A.R., O’Sullivan, J.N., and Skoglund, L.G. 1996. Sweetpotato: Major pests diseases, and nutritional disorders. International Potato Center (CIP). Lima, Perú. 152 p.

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