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This page was updated on
June 12, 2008

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, so Aspen scale is a natural fit for a common name, at least in CO. Identification as Diaspidiotus gigas was confirmed by

Trees that are under stress seem to be most susceptible to attack. The most highly affected trees in Aspen, CO are the street side trees. Nearby trees in homeowners yards are not as severely impacted.
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 Aspen.

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.
Scale Cluster
 Close up dorsal view of Aspen scale. When in high populations, the scale can completely cover the bark.
Scale Cluster Underside Ventral view of scale. The small orange dots are crawlers photographed in February 2008 in Aspen CO.
Crawler (Male) Scale Male Aspen scale?? These were collected in April 2007.
Male Aspen Scale View .wmv video clips of male Aspen scale. 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 dominant overwintering form found under scale. This picture was taken in February 2007.
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.