Palm Pests and Diseases
Spodoptera spp.
Armyworm
Detected in Southeast Asian Countries
Armyworms primarily feed on leaves but may also feed on the seed stem under specific conditions, leading to head loss. Armyworms are named for their habit of moving across fields in a military-like formation. As the larvae eat up the available food sources, they move to new host plants in a group. The larvae of armyworms can be different colors, ranging from dark greenish-brown to black, and they have long, pale white, orange, and dark brown stripes running along the length of their abdomen on each side.
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Several species of armyworms have been identified in Southeast Asian countries:
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Beet Armyworm (Spodoptera exigua)
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Paddy/Oriental Armyworm (Mythimna separata)
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Lawn Armyworm Moth (Spodoptera mauritia)
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​Bermuda Grass Armyworm/Black armyworm (Spodoptera exempta)
Source: Agriculture Victoria
Beet Armyworm (Spodoptera exigua)
Spodoptera exigua, also known as the beet armyworm, is a small, nondescript moth that hides during the day and is active only at night. Originally native to Southeast Asia, it has been identified in regions such as Africa, Southern Europe, Japan, Australia, and North America. Nevertheless, because of its dispersal abilities, S. exigua will regularly invade temperate areas and cause damage during the growing season.
Source: IRAC and Koppert
Life Cycle and Identification
Source: University of Florida | IFAS and Koppert
Egg: The beet armyworm (Spodoptera exigua) lays its eggs in clusters, sometimes in several layers, on top of a mass of white, cottony hairs and scales from the moth's body. Each cluster contains 50 to 150 eggs, with an average of 300 to 600 eggs laid by a female. The individual eggs are circular when viewed from above, but when examined from the side, they are slightly peaked, tapering to a point. The eggs are usually grey but can sometimes be greenish or pinkish. They are laid at night, preferably on the underside of leaves and low in the crop.
​Pupa: The pupation occurs in the soil, although it can also occur within the crop. The Pupae are light brown and 15 to 20 mm long, similar to the Noctuid family. After five or ten days, the adult moth emerges from the pupa.
Larva: The caterpillars usually go through five development instars, but there are reports of additional instars sometimes. The color and pattern of the caterpillars can vary widely and depend on factors such as the host plant, the stage of development, and the climate. As the larvae grow, they undergo several color changes. In the first and second instars, the larvae are pale green or yellow but develop pale stripes during the third instar. In the fourth instar, the larvae become darker on their backs, with a dark stripe running along their sides. A fully-grown beet armyworm (Spodoptera exigua) caterpillar can reach 25 to 38 mm. It has dark, wrinkled stripes on its back and a yellow band running the length of its body on each side, with a black dot on each segment above the band.​
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Mature larva of beet armyworm, Spodoptera exigua (Hübner). Photograph by John Capinera, University of Florida
Adult: The moths are of moderate size. The head and thorax are brown, and the abdomen is grey-brown. The wingspan measures 25 to 30 mm. The hind wings are a more uniform gray or white color and are trimmed with a dark line at the margin. The forewings have a yellowish, and generally with an irregular banding pattern and a light-colored bean/kidney -shaped spot.
Adult beet armyworm, Spodoptera exigua (Hübner). Photograph by Lyle J. Buss, University of Florida
Damage and Symptoms
The larvae feed on both foliage and fruit. As they grow older, the caterpillars move to the top of the plant, where they mainly feed on the growing tips. This results in large holes in the leaves, sometimes completely stripping them down to the mid-rib. Additionally, they burrow into the crown or center of the head of lettuce and the buds of cole crops. This extensive damage significantly impacts the crop's growth.
Paddy Armyworm (Mythimna separata)
Source: CABI Plantwise Plus
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Mythimna separata, or the paddy armyworm or oriental armyworm, is an invasive species and a significant pest of corn (cereals), pasture, and forage crops. It is widely distributed in Asia and Australia and in countries such as Afghanistan, China, Japan, Western Australia, New Zealand, Pakistan, and Western Samoa. It has also been reported in Southeast Asian countries, including Indonesia, Malaysia, Vietnam, the Philippines, Myanmar, and Laos.
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Life Cycle and Identification
Source: CABI Plantwise Plus and ICAR
Egg: The female moth lays between 500 and 900 eggs, with a maximum of 1943 recorded. The egg stage lasts for 2 to 7 days. The eggs are shiny milky white in color and are laid in rows or masses of 20 to 76, between overlapping leaf-sheaths and attached to the leaf using a sticky secretion. When dry, this secretion appears white and flaky. Each moth may lay 1 to 4 egg masses.
Larvae: The head is grayish brown with dark reticulation. The general body color varies among different individuals, with some being a dirty pale brown, while others appear very dark and, in some cases, almost velvety black. A dark brown median dorsal line is interrupted by narrow white dashes and interfused with pale lines on the margin. Laterally, a dark brown stripe is followed by a white stripe just above the spiracle line. Below the line of spiracles is a yellowish stripe with a pinkish tint, contrasting with the dark brown line above and the dusky brown area beneath. The body is sparsely covered with fine hairs placed on minute black tubercles. Larval development is completed in 14-22 days.
Hairless, brownish caterpillar of Paddy armyworm with a narrow, white dorsal line (NBAIR)
Pupae: The pupae are initially cream-colored and then change to dark brown before pupating in an earthen cell in the soil or inside the leaf sheath of the plant. The pupal period lasts for 8-9 days.
Adult: The moth is pale brown with dark specks and blotches. The fore-wing has slight traces of kidney-shaped stigmata: a minute white speck about the middle, a black speck inside, and an indistinct oblique streak. The hind wing is pale with a reddish tinge, and the underside sometimes has faint spots in the middle and a series of specks post-medially. The male moths are smaller and lighter in color than the female moths.
Adult of Paddy armyworm moth (Source: epitree via Flickr)
Symptoms and damage
During the vegetative stage of rice, M. separata causes significant damage by consuming leaves and developing grains and anthers. The larvae also sever panicles during grain-filling, resulting in yield loss. Research indicates that a population of 15 larvae per hill can lead to yield reductions of 38% and 93% at the booting and panicle stages, respectively. Moreover, for each additional larva per hill, the number of grains per panicle decreases by 4 and 9 during each growth stage. In severe infestations, damage could exceed 60% (Dale, 1994). However, the prevalence of M. separata has decreased in the past 30-40 years due to the expansion of irrigated rice cultivation.
Prevention
Source: CABI Plantwise Plus
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Mix rice with vegetables like other cereal crops, which are essential hosts for paddy armyworms.
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​Manage grassy weeds in the rice field as they serve as alternative hosts.
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Minimize pesticide application and plant flowering plants along the borders to protect natural predators like Cotesia or Trichogramma wasps and Carabid ground beetles.
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Use nitrogen fertilizer at the recommended dosage (100 kg N/ha) to prevent excessive growth, which can lead to increased armyworm infestation.
Paddy Swarming Catepillar (Spodoptera mauritia)
The rice-swarming caterpillar, also known as the armyworm Spodoptera Mauritia (Noctuidae: Lepidoptera), is a sporadic pest that can cause significant crop losses. This insect is known to infest various grassy crops and weeds. It has been reported in countries such as Afghanistan, Australia, and Southeast Asia, including Indonesia, Laos, Papua New Guinea, the Philippines, Malaysia, Myanmar, Thailand, and Vietnam.
Source: ICAR-NICPM, India
Life cycle and Identification
Source: ICAR-NICPM, India
​Egg: A single female generally lays 5-6 oblong egg masses, each containing 150-200 eggs at the tips of upright leaves. Eggs are covered with gray hairs/setae from the anal tuft of the female. An egg is spherical and creamy in colour when laid and acquires a brown tinge as development proceeds.
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Larva: The newly hatched or young larvae are light green with yellowish-white lateral and dorsal stripes, and they measure about 2 mm long, making them difficult to notice on the foliage.
Mature larvae reach a length of 3.8-4 cm and can be green, grey, or brown, with dark, dull dorsal and sub-dorsal longitudinal stripes. Two rows of C-shaped black spots are visible along their backs.
​S. mauritia larva; first pale green, later brown with dark dorsal and lateral stripes, up to 38mm long. MERLE SHEPARD
​Pupae: The mature larvae burrow into the soil to find a suitable place for pupation. Pupation occurs in an earthen cell slightly below ground level. The pupa is dark brown in color, measures 13-17 mm in length, and has two slender apical spines. The pupal period lasts for 7-10 days.
Adult: The moth is stoutly built and dark brown, measuring about 15-20 mm long and with a wing expanse of 30-40 mm. The forewings of female moths are greyish brown with wavy lines and a dark spot in the middle. Male moths have immense tufts of hairs on their forelegs, and their wings are more greyish. The hind wings are brownish-white with thin black margins.
Adult Lawn armyworm, Spodoptera mauritia Photograph by Victor W Fazio III on I NautalistAU
Symptoms and Damage
The swarming caterpillars damage paddy crops by cutting off leaf tips, leaf margins, leaves, and even the plants at the base, more severely on the seedlings in nursery and direct seeded crops and early tillering stage in transplanted rice. The swarming caterpillar occasionally caused yield loss of up to 20% (Dale, 1994). Attacked plants are recorded to be damaged from 10-100% depending upon the density of the pest larvae. Under severe infestation, complete plant damage has been reported, which warrants re-sowing or replanting the crop.
Black armyworm (Spodoptera exempta)
Source: CABI
Spodoptera exempta, also known as the black or African armyworm, is a destructive pest that targets pastures and cereal crops in various regions, including Africa, Asia, Australia, the Pacific, and Arabia. These migratory pests can cause severe damage to crop yields during plague years. The life cycle of the African armyworm is particularly destructive, as it grows and reproduces rapidly within ten days between hatching and pupation. In Southeast Asia, it is most frequently recorded in the Indonesian islands, such as Kalimantan, Sulawesi, and the Philippines.
Life Cycle and Identification
Source: CABI
Eggs: The eggs of Spodoptera exempta are initially pale yellow, but they darken as they develop. They are approximately 0.5 mm long and conical, with a slightly rounded apex and a densely sculpted surface. The eggs are laid in batches of 10-600 and are covered by black scale hairs from the tip of the female's abdomen. A single female can lay between 400 and 1300 eggs over her lifetime. Moths typically lay their eggs on the underside of leaves and cover them with protective scales rubbed off from their abdomen to protect them from predators, dehydration, and natural enemies. The moth lays eggs on both crops and pastures.
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Larvae: The larvae come in two primary forms: the gregarious form, found in high-density populations, and the solitarious form, found in low larval densities. There are also intermediate forms known as "transients." Gregarious larvae have a velvety-black upper surface with pale lateral lines, a green or yellow underside, and no body hairs. The prothoracic segment has three parallel lines on the dorsal surface, and there is always a paler stripe running down the mid-dorsal surface of the body. The head is shiny-black. Solitarious larvae are cryptically colored in shades of green-brown or pink, appear fat, and are extremely slow.
Larva of Spodoptera exempta. Source: CABI
Pupae: After 10-14 days, the fully grown caterpillar will burrow into soft, damp soil at the base of plants or sandy banks to pupate. The pupae are mahogany-brown, 10-14 mm long, and have a smooth, shiny surface.
Adult: Adult S. exempta are stout-bodied with a typical noctuid look, measuring 14-18 mm in length and 29-32 mm in wingspan. The abdomen is mainly covered in pale grey-brown scales, except for the female's tip, which features black hair scales unique to this species. Their forewings are dark brown with distinct grey-black markings.
Adult male S. exempta (museum set specimen). ©Georg Goergen/IITA Insect Museum, Cotonou, Benin
Damage and Symptoms
Source: CABI
The signs of an S. exempta infestation include extensive damage to plant foliage, growing points, and young stems, which can lead to complete defoliation or the destruction of the plant. These infestations can cause significant losses in local, national, and regional agricultural production. In maize, the reduction in yield due to defoliation is directly related to the percentage of leaf area available to the larvae at the time of the attack. Reported losses range from 9% in plants attacked at the early whorl stage to 100% in those damaged at the pre-tassel stage. Severe damage occurs when the apical meristem is affected, but if it remains underground until near the pre-tassel stage, it may escape damage. However, severe damage can rapidly develop once the larvae reach the IV instar.
Further Resourches