The sap feeding insect Pulvinaria regalis or Horse Chestnut Scale insect is prevalent on Lime, Sycamore, Magnolia and Horse Chestnut in the summer months.
Chestnut Scale infestations are most notable in the summer when the females are seen to deposit eggs under white cotton-wool-like waxy threads secreted from the rear edge of the shell-like scale. The shells or scales of these insects are brown in colour and measure up to 5mm long.
The females migrate to the bark of the branches and trunk during May where they can lay up to 3000 eggs. They protect their eggs with their bodies and a white wool which they secrete. The females die and eventually fall from the tree. Once the eggs hatch, the nymphs move onto the leaves to feed and then back to the twigs in winter to continue feeding until fully grown and then they overwinter as immature nymphs. They are capable of reproducing without fertilisation from males.
The main means of the spread lies in the transportation of prunings, following tree surgery or via the transportation of infested nursery trees. Furthermore, the young, non-sedentary nymphs are able to spread from tree to tree with the help of the wind. It is also possible that eggs and nymphs maybe spread by birds. Primarily, Horse Chestnut scale damages host plants through the extraction of plant juices, and also by contaminating leaves with honeydew (upon which sooty moulds develop). This results in a decrease in the rate of photosynthesis. The ornamental value of heavily infested plants is decreased considerably, and the immediate surroundings are persistently contaminated with Honey Dew and Sooty Mould.

Control of this insect is very straight forward with treatments applied in Autumn and Spring. A winter Horticultural Oil wash is also a good treatment and reduces early sumer populations.