There were two reasons why larger trees generally produced more beetles than the small trees: (i) the relationship between tree diameter and percent beetle-caused tree mortality tended to follow a sigmoid distribution with larger trees being attacked more frequently (Fig. 1); and (ii) among attacked trees the larger ones generally had a higher net production of beetles. The higher net production was due to larger trees having a higher maximum height of attack, i.e., they were attacked over a much larger surface area than smaller diameter trees, they produced more beetles per m2 of bark at DBH, and other general factors that are summarized in Safranyik (1988).