Gypsy Moth

Lymantria dispar

1. Identification

• Common name: Gypsy moth
• Scientific name: Lymantria dispar L.
• Order: Lepidoptera
• Family: Erebidae

2. Pest description

• Adults: Marked sexual dimorphism; males with a 35–40 mm wingspan, yellowish-brown and very active; females larger (50–70 mm), whitish, with dark spots and limited or absent flight.
• Larvae: Hairy caterpillars, with pairs of blue dorsal tubercles (5 pairs) followed by red ones (6 pairs), a distinctive feature; very voracious.
• Pupae: Formed in silken cocoons attached to the bark, branches or nearby structures.
• Eggs: Laid in oval masses covered with yellowish-brown hairs from the female.

3. Main hosts

• Cork oak and various other oaks (Quercus robur, Q. ilex, Q. pyrenaica, Q. faginea).
• Other broadleaves: chestnut, alder, birch, willow, apple, pear, among many others.
• Highly polyphagous species, with more than 300 recorded hosts.

4. Symptoms and damage

• Intense defoliation, often total, especially on deciduous broadleaves.
• Young caterpillars feed on the tender leaves; larger caterpillars consume the entire leaf blade.
• Secondary flushing after severe attacks, with loss of vigour.
• In cork oak, reduced growth, greater susceptibility to secondary agents and impact on cork production.
• Under repeated attacks, progressive decline and mortality of weakened trees.

5. Biological cycle

• A single generation per year.
• Eggs overwinter; hatching in spring, synchronised with bud burst.
• Caterpillars develop over 6–8 weeks, passing through 5–6 instars.
• Pupation in summer; adults emerge after 10–14 days.
• Females lay egg masses on trunks, branches and artificial structures.
• Development favoured by hot, dry springs.

6. Monitoring

• Observation of egg masses on trunks and nearby structures.
• Detection of young caterpillars in the canopy during bud burst.
• Assessment of the degree of defoliation throughout spring.
• Pheromone traps for detecting males and forecasting population peaks.

7. Management measures

• Cultural: Manual removal of egg masses on isolated trees; destruction of accessible cocoons and nests; promotion of tree vigour through appropriate management; reduction of water stress.
• 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 young caterpillars and the formation of egg masses.

Bibliographic references

• EPPO Global Database – Lymantria dispar
• CABI Invasive Species Compendium – Lymantria dispar
• Liebhold, A. et al. (1995). The Gypsy Moth: A Handbook of the Biology, Spread, and Management of the Gypsy Moth in North America. USDA Forest Service.
• Montgomery, M. E. & Wallner, W. E. (1988). The gypsy moth: a review of the European literature. USDA Forest Service.
• Pogue, M. G. & Schaefer, P. W. (2007). A review of selected species of Lymantria. USDA Forest Service.