 What is a pest? You're annoying neighbor or sibling? No. A pest is an organism that eats or damages crop plants that are grown in agriculture. For example, slugs eating lettuce in my garden. Pests can be controlled using pesticides or by introducing other species also known as biological control. Pesticides are natural or synthetic chemicals that are sprayed on crops. They include insecticides that control insects, fungicides that control fungi and herbicides that control weeds other plants that are not supposed to grow with the crop. Pesticides can be sprayed all over a field using industrial machinery like tractors or planes or in specific areas by humans. Why do you think this person is wearing so much protection while spraying crops with pesticides? Pesticides can be toxic to other organisms, not just the organisms they aim to control. One example of this is DDT. DDT was used as an insecticide in the mid 20th century to control mosquitoes which spread malaria, a potentially fatal disease amongst humans. However, DDT was found to accumulate in food chains, also known as bioaccumulation. The molecules of DDT did not break down, but instead were stored in the bodies of organisms and passed on when those organisms were eaten. The DDT became more concentrated in the higher levels of the food chain. The effect on birds of prey was catastrophic. It caused them to lay eggs with thin shells that broke easily when the birds incubated them. This led to a fall in the birthrate of birds of prey and a massive decrease in their populations. The use of DDT was eventually banned as a result. Through the process of evolution and natural selection, some pests become resistant to pesticides. They survive and reproduce. The overuse of pesticides has led to an increasing number of those organisms, which means that some pesticides are now useless. Apart from using pesticides, which is also known as chemical control, farmers can use biological control mechanisms. Can you think what that could be? Biological control is the use of a natural predator of the organism you wish to control. For example, aphids or green flies are herbivores that feed on many human crops. Aphids are eaten by lady birds. Lady birds could be added to an environment to control the number of aphid pests. Sometimes this method of control works well. However, the introduction of a new species to an environment can have unexpected effects. One example of this, the Hawaiian cane toad. It was introduced in Australia to control the population of the cane beetle, a pest that damaged sugar cane crops. However, the Hawaiian cane toad had little effect on the cane beetle population. Instead, cane toads reproduced rapidly and spread across Australia as they had no natural predators. It's now considered a pest species itself and has been blamed for the extinction of some endemic species. So now you know how pests can be controlled to allow farmers to grow the maximum amount of crops possible. If you want to learn more about intensive farming methods and why they use pesticides and fertilisers, watch this video. If you like the video, give it a thumbs up and don't forget to subscribe, comment below if you have any questions. Why not check out our Fuse School app as well? Until next time.