9.1. Introduction. Main ProblemsSome populations have considerable oscillations in their numbers. There are well-known cycles in rodent populations. Many insect pests have regular or irregular outbreaks, e.g., larch budmoth in Switzerland, spruce budworm in Canada, gypsy moth in Europe and in USA.
Example: Gypsy moth population dynamics in Yugoslavia:
Gypsy moth numbers increased by several orders of magnitude. Pest outbreaks resulted in forest defoliation in large areas.