The silver-spotted tiger moth, Halisidota argentata Pack., is a potentially dangerous defoliator of Douglas fir in British Columbia. Natural control factors have always prevented populations from building up to destructive proportions.

The literature contains little information on this insect. Fletcher recorded the first outbreak of what was probably H. argentata in British Columbia in 1887 (2). Moths were identified as H. sobrina Stretch, but this form is now recorded only from California so it was probably H. argentata. The outbreak, probably on southern Vancouver Island, was reported as “committing great depredations on the spruces here.” Mathers found H. argentata at Chilliwack in the Fraser River Valley in 1934, but there was no report of an outbreak (4). A few larvae were collected on southern Vancouver Island from 1936 to 1952. In 1953 a considerable number of colonies were observed, and the following year the silver-spotted tiger moth was in infestation proportions. In 1955 the outbreak increased in intensity, and spread northward to the limit of its known range. A survey in the spring of 1956 failed to find a single colony south of Lantzville, and the population in the northern portion of the range was greatly reduced.