COTTON ARMYWORM | ASEAN FAW ACTION

Palm Pests and Diseases

Spodoptera littoralis

Egyptian Cotton Leafworm

Spodoptera littoralis, also known as the Egyptian Cotton Leafworm, is a highly destructive agricultural pest that can cause serious damage to a wide range of economically important crops belonging to more than 40 families. Host plants include wheat, maize, rice, sugarcane, soybeans, fruits, vegetables, ornamentals, and cotton. It is native to Africa and is widely distributed across the Middle East and Southern Europe. There are reports of this insect being identified in India. It is important to remain vigilant for this serious pest in Southeast Asia.
For example, see India Zoological Annual Report 2022-2023.

Life Cycle and Appearance

Eggs are laid in groups of up to 350 eggs per batch
Spherical, somewhat flattened
Width x height is approximately 0.45 mm x 0.35 mm
Whitish-yellow in colour (changing to black just before hatching)
They are usually laid in one layer and are typically covered with hairs.

Eggs. Source: Photo M. vd Straten © NPPO, The Netherlands.

Spodoptera littoralis 1st (right) and early 2nd instar (left). Source: Photo M. vd Straten © NPPO, The Netherlands.

Note that the larvae of S. littoralis and S. litura cannot be distinguished from each other for most of the stages.
Larvae grow to 40-45 mm and are hairless
Variable in colour (blackish-grey to dark green, becoming reddish-brown or whitish-yellow)
The sides of the body have dark and light longitudinal bands
Both S. littoralis and S. litura can be recognized by the increasing size of the dark spot on the first abdominal segment which turns black in the early L2 stage and becomes more prominent during development into the third larval stage (OEPP/EPPO, 2015)
Spots on the first and eighth abdominal segments are larger than the others.

Fully grown larva. Source: E. Roditakis (Plant Protection Institute Heraklion, GR).

The 4th instar of Spodoptera littoralis. Source: Photo M. vd Straten © NPPO, The Netherlands.

47-Pupa-of-Spodoptera-littoralis-dorsal-

Pupae turn dark reddish-brown after a few hours.
Shape is cylindrical.
Pupation usually occurs 3–5 cm in the soil.

Pupae. ©NPPO, The Netherlands

The adult moth. Source: GEORG GOERGEN/IITA INSECT MUSEUM, COTONOU, BENIN

Adult moths have a greyish-brown body
Body Length: 15-20 mm
Wingspan: 30-38 mm
Forewings: grey to reddish brown with paler lines along the veins
Hindwings: greyish white
Live 5-10 days

Other points:

S. littoralis can have from two to seven generations per year and does not undergo diapause.
As the insect develops, it completes six instars. Early instars remain on the underside of leaves and feed throughout the day. The third and fourth instars remain on a plant but prefer feeding at night. Later instars migrate off the plant, rest in the soil during the day and return to the plant at night.
Adults fly at night, mostly between 8 pm and midnight and around half of females lay their eggs before sunrise the same night of mating.
Many populations of S. littoralis are extremely resistant to pesticides, and if they become well-established, can be exceptionally difficult to control (USDA, 1982).
Both the eggs and larvae can move in international trade on planting material, cut flowers, or vegetables. This species has been trapped outside of its normal range, likely due to the movement on imported commodities (EPPO, 1997). Let's keep a watch in Southeast Asia!

Damage Symptoms

On most crops, damage occurs due to extensive feeding by larvae, which can result in complete stripping of the plants. On cotton, leaves are heavily attacked, and bolls have large holes with yellowish-green to dark-green larval excrement protruding. Maize stems are often mined, and young grains in the ear may be injured.

The damage caused by S. littoralis infestation
Source: Koppert

Spodoptera littoralis, Spodoptera frugiperda, Spodoptera litura

S. littoralis, S. litura, and S. frugiperda (FAW) are important pest species known for their highly polyphagous and destructive nature. The focus of the ASEAN FAW Action Plan is on Fall Armyworm, however, it's also important to keep a watch out for S.littoralis and proactively work to prevent its establishment or spread. Spodoptera litura is often confused with S. littoralis, since the larvae and adult stages of the two species are nearly identical.

Distribution

Refer to the EPPO Global Database. (https://gd.eppo.int/)

Spodoptera littoralis

Spodoptera frugiperda

Spodoptera litura

The current distribution of these three species is shown in the maps above. Currently, S.littoralis is not established in Southeast Asia. However, studies that have modelled the potential distribution of this pest show current areas with highly suitable habitats (including Indonesia and Thailand), as well as other regions at risk of invasion by S. littoralis in the future. It is important to monitor for this pest and to ensure that strong quarantine measures are in place, particularly in importing countries that do not currently have this pest.

ElShahed, S.M., Mostafa, Z.K., Radwan, M.H. et al. Modeling the potential global distribution of the Egyptian cotton leafworm, Spodoptera littoralis under climate change. Sci Rep 13, 17314 (2023). https://doi.org/10.1038/s41598-023-44441-8

Identification

It is best to conduct morphological identification at late larval and adult stages. Identification at early larval stages is not recommended. Molecular methods are strongly recommended for accurate species-level identification.

Here are some resources for assisting with morphological identification: