However, the magnitude of change in these factors was always much smaller than the magnitude of change in population density. Thus, the greater is the population density, the faster it grows. Bark beetles succeed in attacking a healthy tree only when the number of beetles is large. Adults of the sawyer beetle, Monochamus urussovi , feed on small branches of Siberian fir. When the density of adults is high, then they cause considerable damage and the tree looses its resistance to developing larvae of this species.
Locusts change their behavior at high population density, and their reproduction rate increases.
Population of spider mites grow very fast at high temperature. They live on plant leaves where local temperature is lower than the ambient temperature. During the draught, plant transpiration is reduced, and thus, the temperature of leaves increases causing rapid reproduction of spider mites. Draught may cause reactivation of a large proportion of diapausing sawflies. This effect is combined with subsequent escape from natural enemies.