San José scale

Quadraspidiotus perniciosus

1. Identification

• Common name: San José scale
• Scientific name: Quadraspidiotus perniciosus Comstock
• Synonym: Diaspidiotus perniciosus Comstock
• Order: Hemiptera
• Family: Diaspididae

2. Pest description

• Females with a circular, light‑grey waxy scale, with a central yellowish exuvia.
• Males with an elongated scale and a winged form in the adult stage.
• Mobile nymphs (“crawlers”), yellow, responsible for dispersal.

3. Main hosts

• Pome fruits: apple tree, pear tree.
• Stone fruits: peach tree, plum tree, cherry tree.
• Small fruits, ornamentals and various spontaneous species.

4. Symptoms and damage

• Circular scales attached to branches, trunks, leaves and fruits.
• Red spots on the fruits (“pitting”), with severe commercial devaluation.
• General weakening of the plant due to sap sucking.
• Drying of branches and progressive decline in severe infestations.

5. Biological cycle

• Winter spent as an adult female or nymph on protected branches.
• 2 to 3 generations per year, depending on the climate.
• Mobile nymphs appear in spring and summer, promoting dispersal.
• Rapid fixation and formation of the waxy scale.

6. Monitoring

• Visual inspection of branches and fruits to detect circular scales.
• Observation of red spots on the fruits as an indirect sign.
• Reinforced monitoring in orchards with a history of the pest.

7. Management measures

• Pruning and removal of heavily infested branches.
• Treatments targeted at the emergence period of the mobile nymphs.
• Conservation of natural enemies (e.g.: Aphytis melinus).
• Avoid treatments that reduce the auxiliary fauna.

Bibliographic references

• EPPO Global Database – Quadraspidiotus perniciosus.
• CABI Invasive Species Compendium – Diaspidiotus perniciosus.
• Walker, J. T. S. (1985). Biology and control of San José scale.
• Branco, M. et al. (2010). Pests of fruit trees and ornamentals.