How are they naturally controlled?
Healthy trees defend against beetle invasion by producing resin. Resin, or pitch, flushes the adult beetles out of the tree. This is effective when only a few beetles attack a tree, but if many insects attack, or if the tree is stressed, resin flow is reduced. Temperature is also an important factor in determining beetle survival. Mountain pine beetle larvae must develop to a certain stage to tolerate cold winter weather (-40 C inside the bark). Late spring frosts and cool summers may delay beetle flight and subsequently slow brood development and increase overwintering mortality. The previous two outbreaks in Alberta, in 1984 and 1985, were ended by unseasonably cold temperatures (-30 C) in October and November. Depletion of pine hosts also controls beetle populations. Once the beetles kill all the old, large pines in an area, they must fly to find more hosts. While flying, the beetles are susceptible to dehydration, predation and the possibility of not finding a suitable tree. Wildfi
