Horse Chestnut Scale Insect - Pulvinaria regalis

P. regalis is most conspicuous in May and June when the scale-like adult females produce large, white, waxy ovisacs in which they lay about 2000 eggs. The adult females die after oviposistion but often remain attached to the trees with their ovisacs throughout the summer (as shown in the images below). The eggs hatch in June and July and the first instars, commonly known as 'crawlers', migrate to the undersides of leaves to begin to feed. The first instars are the main dispersal stage and can be carried long distances in air currents, by other animals or in plant trade. The immatures migrate back on to the branches in Autumn before leaf fall. They mature in the following May, mate and migrate to a suitable oviposition site.

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P. regalis is broadly polyphagous being recorded on approximately 100 species of woody plants. In Britain, it is most commonly found on limes (Tilia spp.), sycamore (Acer pseudoplatanus), maples (Acer spp.), elms (Ulmus sp.), sweet bay (Laurus nobilis), horse chestnut (Aesculus hippocastanum), magnolia (Magnolia spp.), Skimmia spp. and Cornus spp. Adult female P. regalis may leave their host plant before producing the ovisac and this has resulted in incorrect host plants being recorded. Adult females and ovisacs have been found on brick walls, iron railings, in leaf litter and on herbaceous plants near infested trees!

May to August.  

Heavy infestations of P. regalis can kill apical twigs and cause premature leaf drop. However, the damage caused by the pest to a mature healthy tree is usually minimal despite large populations. Young and stressed plants are most at risk. An indirect effect is the contamination of foliage with the copious quantities of excreted honeydew, which serves as a medium for the growth of black sooty moulds. This may lower the value of amenity trees. The population levels vary significantly from year to year and in some years they can completely cover the trunks and main branches with ovisacs. These large populations are controlled by parasitoid wasps, ladybirds and birds.

Pulvinaria regalis was first recorded in Britain in about 1964 in Kew, London and has since become widespread throughout Britain. It is the most abundant soft scale insect in urban areas and is also common in many rural areas in Britain. It has also spread throughout north-west Europe. It is not known how it was introduced into Europe or where it originates from although it almost certainly native to Asia. The heaviest infestations are found on urban trees and it has been suggested that this is due to the trees being more susceptible resulting from stress by pollution, water shortage and cramping by pavements and buildings.

Status in Leicestershire and Rutland not known.