The Aspen Scale, AKA The Willow Scale, Poplar Scale
Diaspidiotus gigas, AKA Quadraspidiotus gigas

The Aspen scale is an exotic armored scale that is attacking and severely impacting aspen and narrow leaf cottonwoods in several mountain towns in Colorado and Idaho. The Aspen scale is also known as willow scale or poplar scale in some publications. In Colorado, it is rare on willow, while common on aspen, especially in the town of Aspen and several other mostly west slope towns. Aspen scale is a natural fit for a common name, at least in CO.
Scale on Aspen Tree These trees in Aspen, CO are heavily infested with Aspen Scale. These street trees are in a stressful environment and are typical of heavily infested trees in downtown Aspen. Many streetside trees are infested while trees in nearby yards are not. In other landscape situations, seemingly random infested trees are scattered with non-infested trees.

Colony of Scale on Apen Tree

Aspen scale are light colored, very similar to the color of aspen bark. This pictured infestation is relatively light. Heavier infestations cover the entire bark. They can be found on the primary trunk and smaller diameter branches. Scale can be found from ground level to high in the crown of the tree.
Scale Cluster
Close up dorsal view of Aspen scale. When in high populations, the scale can completely cover the bark. Scale covers are roundish in shape witha raised central "nipple" They cannot be confused with oyster shell scale which is also common on aspen trees. Oyster shell scale is linear is shape.
Scale Cluster Underside Ventral view of scale. The small orange dots are crawlers photographed in February 2008 in Aspen CO. There are also early instar sacle nymphs and adult female sclae in the picture
Male aspen scale are present in the springtime. This male was photographed on 16 June 2008 in Aspen. The wingspan is slightly less than 2 mm.
Crawler (Male) Scale Scale sampling is confused by these small tailed insects that we misidentified as male scale . They were identified as early instar Phylloxerina aphids. These wooly aphids are common coinhabitants of aspen trees.
Male Aspen Scale View .wmv video clips of these immature Phylloxerina. These specimens were collected from Aspen, CO on April 29, 2008.
Male Aspen Scale Close Up video
Female Scale Mature female scale. This is the one of, and the most common overwintering form found under scale cover. This picture was taken in February 2007. Mature females are present at any time of the year. They are apparently long lived.
D. gigas crawlers are tiny orange spots in this picture. They are no longer than 0.1 mm in length. The crawlers needed viewing under a compound microscope to determine that they were actually insects.
D. gigas is often confused with oystershell scale, Lepidosaphes ulmi. Oyestershell is pictured on the left and can be distinguished by its linear shape. D. gigas is circular in shape. Oystershell scale overwinters as eggs under the mature cover, while Aspen scale overwinters as a mature female.

This page was updated on April 26, 2014