Walnut Husk Fly

Rhagoletis completa

1. Identification

• Common name: Walnut husk fly
• Scientific name: Rhagoletis completa Cresson
• Order: Diptera
• Family: Tephritidae

2. Pest description

• Adults about 4–6 mm, yellowish-brown body and wings with a typical pattern of dark bands
• White, apodous larvae, develop exclusively in the green husk of the walnut
• Brown-coloured pupae, formed in the soil
• Eggs laid in the green husk, leaving small egg-laying marks

3. Main hosts

• Walnut tree
• Other Juglans species can be attacked
• Pest specialised in walnut trees

4. Symptoms and damage

• Dark spots and softening of the green husk
• Formation of black, moist areas due to larval feeding
• Difficulty in dehusking and stains on the endocarp
• Reduction of the commercial quality of the walnut
• Significant losses in years of heavy infestation

5. Biological cycle

• One generation per year
• Adults emerge in summer, between June and August
• Egg laying in the green husk of developing walnuts
• Larvae feed for 3–5 weeks
• Pupation in the soil, where they spend the winter
• Emergence synchronised with fruit development

6. Monitoring

• Yellow chromotropic traps with specific attractants
• Weekly counting of captured adults
• Visual observation of symptoms on the green husk
• Fruit sampling to detect larvae
• Intensive monitoring between June and September

7. Management measures

• Cultural: collection and destruction of infested fruits; removal of the green husk after harvest; shallow tillage of the soil to expose pupae.
• Biological: conservation of natural parasitoids; use of entomopathogenic nematodes in the soil.
• Integrated protection: continuous monitoring; bait treatments during critical periods; application of authorised insecticides when thresholds are reached; use of mass-trapping traps; appropriate orchard management to reduce pupation sites.

Bibliographic references

• EPPO Global Database – Rhagoletis completa
• CABI Invasive Species Compendium – Rhagoletis completa
• Daniel, C. et al. (2014). Biology and control of walnut husk fly
• Yee, W. L. et al. (2012). Ecology and management of Rhagoletis species
• EPPO Standards – Guidelines for monitoring fruit flies