A common mosquito
Dichlorodiphenyltrichloroethane, more commonly known as DDT, is an insecticide developed in the 1870s in order to reduce malaria and typhus outbreaks by killing the mosquitoes and other insects that carried these viruses. It became one of the most popular insecticides after WW II and was used in the U.S. for almost 100 years. DDT was eventually banned in the U.S. due to its harmful effects on humans and small animals.
Mosquitoes and Disease
Mosquitoes are the primary insect species that transmit malaria. A microscopic family of parasites called Plasmodium use mosquitoes as incubators during their early development. These parasites are then transmitted to humans through the saliva of mosquito bites. The parasite invades red blood cells in order to reproduce, causing the symptoms of malaria. When a female mosquito bites an infected individual, it feeds on this blood and starts the cycle all over again.
Effects on Mosquitoes
DDT is a powerful neurotoxin for insect species. When a mosquito comes in contact with DDT, the toxin travels to its brain and into its neurons, the cells that are responsible for transmitting information to the rest of the body. DDT then blocks the sodium-ion channels that are responsible for this transmission and causes the neurons to misfire. These misfires cause the mosquito to spasm and die.
Resistance
Over time, some mosquitoes, and other insects, have built up a resistance to DDT. Insecticide resistance is a common problem in pest control, and even the most effective pesticides become less effective over time. Scientists argue that the overuse of DDT by spraying entire farm fields allowed mosquitoes to evolve resistances to the chemical through natural selection. Mosquitoes that were resistant to DDT were able to reproduce and pass on these resistances to growing populations of DDT-resistant offspring.
Controversy
In the 1970s, DDT became controversial in light of evidence that it was harmful to both humans and wildlife. Although the DDT does not work like a neurotoxin in mammals, it builds up in their bodies and can cause cancers and birth defects. The issue was popularized by Rachel Carson's book, "Silent Spring," in which she documented DDT's effects on birds. As a result of this information, combined with the increased resistance in mosquitoes, DDT began to be replaced with other pesticides and was eventually banned in the U.S.
Current Use
Today, DDT is still used in countries that cannot afford more expensive pesticides. It is especially prominent in Africa, where malaria and African sleeping sickness are still widespread problems. However, insects continue to build up resistance to DDT and so its ability to destroy mosquito populations has been steadily decreasing. Until safer, more affordable insecticides are developed, DDT will continue to be a widely used neurotoxin for killing malaria-ridden mosquitoes.
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