California Red Scale

Aonidiella aurantii

1. Identification

• Common name: California red scale
• Scientific name: Aonidiella aurantii Maskell
• Order: Hemiptera
• Family: Diaspididae

2. Pest description

• Females with a circular waxy scale, yellow‑orange to reddish in colour.
• Males with a more elongated scale and a winged adult stage.
• Mobile nymphs (“crawlers”), yellow, responsible for the initial dispersal.

3. Main hosts

• Citrus (these are the main hosts).
• It also occurs on stone fruits, pear tree, grapevine and various ornamentals.
• Polyphagous species, but with greater economic impact on citrus.

4. Symptoms and damage

• Circular scales attached to branches, leaves and fruits.
• Yellow or reddish spots on the fruits, with severe commercial devaluation.
• Weakening of the plant due to sap sucking.
• Drying of branches and decline in severe infestations.

5. Biological cycle

• Winter spent as an adult female or nymph on protected branches.
• 2 to 4 generations per year, depending on the climate.
• Mobile nymphs appear in several peaks throughout spring and summer.
• Rapid fixation and formation of the waxy scale.

6. Monitoring

• Visual inspection of branches, leaves and fruits to detect circular scales.
• Observation of 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 – Aonidiella aurantii.
• CABI Invasive Species Compendium – Aonidiella aurantii.
• Grafton‑Cardwell, E. E., et al. (2006). Biology and management of California red scale. University of California Agriculture and Natural Resources.
• Smith, D., Beattie, G. A. C., & Broadley, R. (1997). Citrus pests and their natural enemies. Queensland DPI.