If it becomes a nuisance.

In biological pest control the pests are killed with a living organism whilst in chemical cultural pest control a chemical is used.

the scientists and or agriculturists can add all of the chemicals that they need to get rid of the organism so that it won't build up a tolerance and come back

biological pest control is when a new organism is introduced into a new community and causes a problem so a new foreign organism is introduced. This has been integrated into management because they help to increase crop growth and production as well as it helps solve problems

In agriculture, as well as in may other contexts, a pest is an organism that eats the agricultural product or plant. Aphids, weevils, and a variety of worms fall into this category.