What are the measures to control plant pests?

There is a wide variety of insects. Many of them are capable of destroying a plant or spoiling a person’s harvest. This often led to hunger, especially in ancient times when biology was not much studied. But now in developed countries this is impossible, since biologists create various poisons against insects. They can be both chemical and created using plants, fungi and others. Sometimes, in order to destroy insect pests, the number of some animals is maintained, which are natural enemies of pests.