Scale insects

Scale insects (superfamily Coccoidea)

1. Identification

• Common name: Scale insects
• Scientific name: Various species within the superfamily Coccoidea (see point 3)
• Main families: Diaspididae, Pseudococcidae, Coccidae, Eriococcidae (see point 3)
• Order: Hemiptera

2. General description

• Small sucking insects, generally immobile in the adult stages (females).
• Body covered with waxes, scales or protective secretions.
• Mobile nymphs (“crawlers”) responsible for dispersal.
• Males, when present, are winged and short‑lived.
• Great morphological diversity among families.

3. Main hosts

• Aonidiella aurantii Maskell – Citrus, stone fruits, pear tree, grapevine, ornamentals.
• Aonidiella citrina Coquillett – Citrus, ornamentals.
• Quadraspidiotus perniciosus Comstock – Pome fruits, stone fruits, small fruits, ornamentals.
• Lepidosaphes beckii Newman – Citrus, ornamentals.
• Parlatoria ziziphi Lucas – Citrus, ornamentals.
• Aspidiotus nerii Bouché – Oleander, citrus, ornamentals.
• Planococcus citri Risso – Citrus, grapevine, fig tree, ornamentals, tropical plants.
• Planococcus ficus Signoret – Grapevine, fig tree, ornamentals.
• Pseudococcus viburni Signoret – Pome fruits, stone fruits, grapevine, ornamentals.
• Pseudococcus longispinus Targioni‑Tozzetti – Citrus, grapevine, ornamentals, tropical plants.
• Pseudococcus comstocki Kuwana – Citrus, pome fruits, grapevine, ornamentals.
• Saissetia oleae Olivier – Olive tree, citrus, ornamentals.
• Coccus hesperidum L. – Citrus, ornamentals, tropical plants.
• Ceroplastes sinensis Del Guercio – Citrus, ornamentals.
• Acanthococcus araucariae Maskell – Araucaria.

4. Symptoms and damage

• Presence of scales, waxy masses or bodies attached to leaves, branches and fruits.
• Production of honeydew (Pseudococcidae and Coccidae), favouring sooty mould.
• Weakening of the plant due to sap sucking.
• Leaf fall, drying of branches and reduction of vigour.
• Commercial devaluation of fruits due to spots, deformations or waxy residues.
• In Diaspididae, direct damage to the fruits and necrosis in the tissues.

5. Biological cycle

• Winter spent as a nymph or adult female, depending on the species.
• 2 to several generations per year, favoured by warm and dry climate.
• Mobile nymphs appear in seasonal peaks, being the main moment for intervention.
• Dispersal facilitated by ants, wind, birds and movement of plant material.

6. Monitoring

• Regular visual inspection of leaves, branches and fruits.
• Observation of honeydew and sooty mould as indirect signs.
• Identification of mobile nymphs with a magnifying glass.
• Sticky traps for males in some species.
• Reinforced monitoring in orchards with a history of the pest.

7. Management measures

• Cultural: They include practices that reduce the conditions favourable to the development of scale insects and limit their establishment. Pruning improves air circulation and light penetration, reducing favourable microclimates. The removal of heavily infested branches decreases population pressure. Excess nitrogen, which promotes tender and susceptible shoots, should be avoided. The use of certified plant material and the inspection of plants before planting help to prevent introductions. The control of ants is essential, as they protect the scale insects and facilitate their dispersal.
• Biological: They are based on the action of natural enemies that naturally regulate the populations. Parasitoids such as Aphytis melinus, Coccophagus lycimnia and Leptomastix dactylopii are effective on various species. Predators such as ladybirds (Cryptolaemus montrouzieri, Chilocorus bipustulatus) and lacewings contribute to the reduction of the populations. In specific situations, the release of Cryptolaemus montrouzieri can be carried out in greenhouses or orchards with mealybugs. The preservation of these auxiliaries requires avoiding broad‑spectrum insecticides and maintaining conditions favourable to their activity.
• Integrated protection: They are based on regular monitoring of the populations and on intervention only when the levels justify action. Treatments should be targeted at the mobile nymphs, the most susceptible stage. Selective substances compatible with the auxiliary fauna are preferable. Mineral or paraffinic oils can be applied in winter and early spring to reduce initial populations. The rotation of active substances helps to prevent resistance. The control of ants, the integration of cultural practices and the conservation of auxiliaries complete an effective and sustainable strategy.

Bibliographic references

• EPPO Global Database – Coccoidea (various species).
• CABI Invasive Species Compendium – Diaspididae, Pseudococcidae, Coccidae.
• Franco, J. C., Silva, E. B., & Branco, M. (2009). Cochonilhas‑farinhentas em Portugal. ISA Press.
• Daane, K. M., et al. (2012). Integrated management of mealybugs in perennial crops. Annual Review of Entomology.
• Smith, D., Beattie, G. A. C., & Broadley, R. (1997). Citrus pests and their natural enemies. Queensland DPI.