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Sterile Insect Technique


Summary: Sterile insect techniques introduces millions of sterile male insects into an environment to reduce the reproductive rate of harmful insects. It has been an effective method to eradicate the Screw fly in several parts of the world.

Wouldn't it be nice if we could control insect populations without the use of pesticides? Guess what? In some instances we can. The sterile insect technique is a method of biological control that uses sterile male insects to reduce the reproductive rate of a species of target insect.

Sterile insect technique is effective in many insect species because the female only mates once during her lifetime. She carries her mate's genetic material with her for the rest of her life and may lay several batches of eggs, but in many cases, she only receives genetic material from a male a single time during her life. If the genetic material she receives from the male fails to produce offspring, then the female will be unable to lay eggs that hatch into young insects.

Sterile insect technique works great with Screw flies, as an example. The Screw fly lays its eggs into the open wound of a large animal like a cow, goat, or sometimes even a human. When the eggs hatch the larvae feed on the flesh of the host animal. The Screw fly larvae are parasites that can kill their host in as little as ten days. This used to be a huge problem for the cattle industry in North America. They would lose about $200 million worth of cattle annually.

In the 1930s American entomologists Raymond Bushland and Edward Knipling started researching ways that they could reduce pest populations without the use of chemicals. Their research was interrupted by World War II, but in the 1950s they renewed their work. This lead to their pioneering the use of sterile insect technology to reduce Screw flies populations in North America. They bred Screw flies and used radiation to sterilize the males. The sterile males would be introduced into the wild population in large numbers outnumbering the fertile, wild Screw flies by at least ten to one.

This sterile insect technique was used successfully with Screw flies in North America, South America, and Africa. In some areas the Screw fly was completely eradicated. This was a major breakthrough because it provided pest control without the use of chemical pesticides that might harm people or the environment. This technology has also been used on the Tsetse fly that causes sleeping sickness in parts of Africa, and to control the Mediterranean fruit fly, which can be a pest of citrus crops.

Recently, sterile insect technology has had another breakthrough. Mosquitoes were previously thought to be untreatable by this method because when they lay their eggs the eggs harden too quickly to apply a sterilization treatment. The breakthrough occurred when European scientists were able to delay the hardening of the eggs and to alter the genetic material of the mosquitoes. This variation of sterile insect technology does not use radiation to sterilize insects, but genetic modification. This is also known as recombinant DNA technology. It works by adding a Dominant Lethal gene to the mosquitoes DNA that can be suppressed in mosquitoes that are bred in the lab, but becomes active in mosquitoes in the wild. The gene, if not suppressed in the lab, causes any mosquito that carries it to die before they are able to reproduce, or to be unable to be a host to the malaria parasite. This is an exciting new technology that might be used to drastically reduce the number of yearly malaria infections.

Insect sterilization technology does have its drawbacks. Repeated treatments are often required for the method to be affective. It is more expensive than ordinary pesticides and many insects must be bred in factories and released into the wild. It can sometimes be difficult to separate the insect sexes for sterilization. Also, the technology is species specific, so while there are twenty two species of Tsetse fly living in Africa, sterile males would have to be produced for each different species. Furthermore, when radiation is used it can affect the health of the male insect, causing it to be less likely to mate. This reduces the effectiveness of the effort. Any insects that are eliminated in an area are likely to eventually return when insects from outside of the control area migrate to the areas with reduced populations.

Despite the drawbacks, sterile insect technology is an effective tool to fight insect infestations and insect spread diseases around the world. It has the benefit of not using chemicals that affect the environment or any species other than the target species. It has also saved many grateful cows from Screw flies that people and bovines would rather not have around.



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