• Twardus, Daniel B.
  U.S. Department of Agriculture
  
• Carolin, V.M.
  Entomologist
  

Sampling egg masses of western spruce budworm (Choristoneura occidentalis Freeman) is an accepted method of estimating population density and predicting population trend (Buffam and Carolin 1966, Carolin and Coulter 1912,McKnight and others 1970). One critical aspect of the sampling is distinguishing between newly deposited (new) egg masses and those from previous years (old).

In spruce budworm (C. fumiferana [Clemens]), Morris (1955) observed that sampling error can be introduced by the mistaken inclusion of old egg masses as new; retention of egg masses on foliage from one year to the next was as high as 20 percent. Buffam and Carolin (1966) reported that many western spruce budworm egg masses are retained, especially in drier areas. This observation led to their development of population-trend prediction based on old and new egg-mass ratios.

Estimates of budworm population density should be based on sampling the current year's egg masses only and should exclude the egg masses deposited during previous years. To do this consistently, foliage collectors and examiners must be trained to follow certain precautions and guidelines.