The estimates of the net brood production should be treated with some caution since they are based on a limited number of parameters and, most likely, simplified relationships. It is, for example, likely that the calculated net production in small trees is slightly overestimated since we used a linear regression to represent the relationship between DBH and number of emerged beetles per m2. In reality the net production probably drops sharply when the phloem is too thin for the beetle to survive. This has, however, only a minor influence on the stand-level net production estimate.