Beet Armyworm

Spodoptera exigua

1. Identification

• Common name: Beet armyworm
• Scientific name: Spodoptera exigua Hübner
• Order: Lepidoptera
• Family: Noctuidae

2. Pest description

• Adults: Moths with a 25–30 mm wingspan, greyish-brown forewings with light spots; whitish hindwings.
• Larvae: Greenish-brown to greyish caterpillars, with light longitudinal lines and a dark head; very mobile and voracious.
• Pupae: Formed in the soil, in earthen chambers.
• Eggs: Laid in masses covered with scales, generally on the underside of the leaves.

3. Main hosts

• Beet, spinach and other chenopods.
• Various vegetables: tomato, pepper, lettuce, cabbages, onion.
• Industrial and extensive crops: maize, cotton, tobacco.
• Polyphagous, with more than 80 recorded hosts.

4. Symptoms and damage

• Intense defoliation, especially on young leaves.
• Irregular perforations in the leaf blade.
• Damage to shoots, flower buds and young fruits.
• In beet, consumption of the central whorl and destruction of central leaves.
• In severe attacks, significant reduction in vigour and productivity.

5. Biological cycle

• Several generations per year, with greater intensity in spring and summer.
• Adults active during much of the year in mild climates.
• Eggs laid in masses; caterpillars develop over 2–4 weeks.
• Pupation in the soil; adults emerge and restart the cycle.
• Development favoured by high temperatures and high availability of hosts.

6. Monitoring

• Observation of egg masses on the underside of the leaves.
• Detection of young caterpillars on shoots and tender leaves.
• Assessment of the degree of defoliation and damage to reproductive organs.
• Light traps and pheromones for detecting adults.

7. Management measures

• Cultural: Removal of infested plants; surface tillage of the soil to expose pupae; elimination of host weeds; crop rotation with less susceptible species.
• Biological: Use of authorised entomopathogenic microorganisms; application of microbial bioinsecticides; conservation of natural enemies through appropriate cultural practices.
• Integrated protection: Regular monitoring; intervention only when necessary; practices that reduce the survival of pupae in the soil and the availability of food for young caterpillars.

Bibliographic references

• EPPO Global Database – Spodoptera exigua
• CABI Invasive Species Compendium – Spodoptera exigua
• Capinera, J. L. (2001). Handbook of Vegetable Pests. Academic Press.
• Hill, D. S. (1987). Agricultural Insect Pests of Temperate Regions and Their Control. Cambridge University Press.
• Smits, P. H. (1996). Biological control of Spodoptera exigua. Biocontrol Science and Technology, 6: 3–10.
• Pogue, M. G. (2002). A world revision of the genus Spodoptera. American Entomological Society.