Pulvinaria regalis
Pulvinaria regalis, commonly known as the horse chestnut scale, is a scale insect in the family Coccidae. It feeds mainly on sap from trees and shrubs, especially horse chestnut, but also on sycamore, maple, lime, elm, magnolia, bay and dogwood, among about 65 plant species.
Origin and spread: It is thought to come from Asia. It was first seen in Europe in the 1960s, reaching Paris by 1968 and Germany by 1989, and has since spread to many cities.
Appearance and life cycle: The females are wingless and stay on the bark. They reproduce mostly without males (parthenogenesis). In early summer, a mature female lays white, circular egg masses under her brown scale. The eggs hatch into crawler nymphs that crawl to the leaves to feed. In autumn the nymphs return to the trunk and large branches and overwinter as flat scales about 1 mm long. They resume feeding in spring and are fully grown by early summer. There is one generation per year, and the adults die after laying eggs.
Impact: This insect is a pest of urban trees. It sucks sap, reducing the tree’s vigor, and produces honeydew that promotes sooty mold, making trees look dirty.
Dispersal: Adults cannot fly, so spread happens mainly through movement of infested plant material like prunings or nursery stock. Crawlers can be moved by wind, and eggs or nymphs may hitch a ride on birds.
Adaptations: The insect has several types of wax. Some wax is water-repellent to keep its breathing openings clear, while long white wax filaments help form the egg sac. To avoid contamination by its own honeydew, it has a six-bristled mechanism near the rear to flick away waste.
This page was last edited on 3 February 2026, at 14:42 (CET).