Sterile Insect Technique

The sterile insect technique (SIT) controls an insect pest by releasing large numbers of males made sterile, usually by radiation. These males mate with wild females, which then lay eggs that do not hatch, so the population shrinks without the use of chemical insecticides.

Edward Knipling and Raymond Bushland developed the idea in the United States in the 1930s to 1950s to fight the screwworm fly, whose larvae feed on the flesh of livestock. After a trial on the island of Curaçao in 1954, the method eliminated the screwworm from Florida and later from the entire United States, and a barrier of released flies is still kept up in Panama. The technique has also been used against the Mediterranean fruit fly and tsetse flies, which transmit sleeping sickness.

Females of many species mate only once, so a female that mates with a sterile male produces no offspring. The method works best when the pest is rare, because the ratio of sterile to wild males then becomes large, so it is often used after other measures have lowered numbers. Mass rearing, sex separation and safe release are the main technical challenges, and released males must still be competitive in mating.

Pilot projects have used sterile male Aedes mosquitoes against species that spread dengue and other arboviruses, such as Aedes albopictus. A related approach releases males infected with Wolbachia, whose bacteria make eggs of wild females fail to develop. A newer idea, the gene drive, would spread sterility genes through a population on its own, raising ecological and ethical questions.

• Gene Drive — a genetic alternative
• Wolbachia — a bacterium used in related methods
• Vector Control — the wider field