In addition, previous
defoliations of Scots pine by pine sawflies and pine looper
are known to make trees more susceptible to secondary attack
by the pine shoot beetles (Cedervind et al., 2003; La°ngstro¨m
et al., 2001). In general moderate stress seems to increase the
susceptibility of trees to bark beetles (Larsson, 1989). Our
study seems to support this view, since thinning reduces the
intra-specific competition