Nun moth

Lymantria monacha

1. Identification

• Common name: Nun moth
• Scientific name: Lymantria monacha L.
• Order: Lepidoptera
• Family: Erebidae

2. Pest description

• Caterpillars of variable colour, generally greyish to brownish, with tufts of hair and dark patterns along the body.
• Adults with white forewings with a characteristic black pattern, resembling a “monastic” habit, the origin of the common name.
• Defoliating species of great forestry importance, capable of causing severe damage to conifers.
• Caterpillars feed intensively on the needles, and can cause total defoliation in young or weakened trees.
• Populations may show cyclical outbreaks, with population explosions followed by natural collapses.

3. Main hosts

• Conifers, especially Picea spp..
• Pinus spp..
• Abies spp..
• Occasionally broadleaf species in situations of high population pressure.

4. Symptoms and damage

• Partial or total defoliation of the crowns.
• Needles gnawed or completely consumed.
• Dry branches and loss of tree vigour.
• Greater susceptibility to other pests and pathogenic agents.
• Reduction of annual growth and, in severe cases, tree mortality.

5. Biological cycle

• Eggs laid in compact masses on the bark of the trees.
• Caterpillars emerge in spring and feed for several weeks.
• Pupation occurs in bark crevices or in nearby vegetation.
• Adults emerge in summer; females lay the eggs shortly after mating.
• One generation per year, typical of temperate regions.

6. Monitoring

• Direct observation of egg masses on the bark.
• Counting of caterpillars on branches and needles during spring.
• Pheromone traps to detect adults.
• Annual assessment of the defoliation level in sensitive stands.

7. Management measures

• Cultural: removal of severely weakened trees; forest management that promotes species diversity.
• Preventive: regular monitoring in conifer stands; early identification of foci.
• Biological: use of Bacillus thuringiensis at young stages; promotion of natural enemies such as insectivorous birds and parasitoids.
• Integrated protection: judicious application of authorised insecticides when intervention thresholds are reached; integration of cultural, biological and chemical measures.

Bibliographic references

• EPPO Global Database – Lymantria monacha.
• CABI – Invasive Species Compendium – Lymantria monacha.
• Carter, D. J. (1984). Pest Lepidoptera of Europe. Dr. W. Junk Publishers.
• Schwenke, W. (1978). Die Forstschädlinge Europas. Paul Parey Verlag.