The Sterile Insect Technique

The Sterile Insect Technique (SIT) is the first insect pest control method that uses genetics. It is most simply described as a form of insect birth control that is carried out on an area-wide basis.

The SIT involves mass breeding huge quantities of target insects in a "factory" and sterilizing the males by exposing them to low doses of radiation. These sterile male flies are then released by air over infested areas, where they mate with wild females. If the sterile males vastly outnumber the fertile wild males, the wild fly population quickly dies out. The proportion of infertile males to fertile wild males must be at least 10:1. In Zanzibar the proportion was as high as 50:1.

Cattle in Mexico, which is now free of New World Screwworm, thanks to the Sterile Insect Technique

The SIT was previously applied to eradicate the New World Screwworm (NWS) from North Africa in the early 1990s. Before 1988, the NWS was confined to the tropical and subtropical Americas. Its discovery in the Libyan Arab Jamahiriya posed a threat to the rest of Africa, Asia, the Near East and southern Europe. During a year-long eradication campaign - headed by FAO - cardboard boxes of sterile male NWS were dropped from aircraft over an area of 40 000 square kilometres.

At the peak of the North African operation, 40 million flies were being released every week. These flies were transported by air in specially commissioned aircraft from the only available source in Mexico. The number of confirmed cases of screwworm in Libya had reached almost 3 000 in September 1990. By March 1991, there were no new cases.

The SIT was applied over a period of 20 years to eradicate NWS from North America and Mexico, and efforts to eradicate it from all of Central America are now under way.

FAO and the IAEA (International Atomic Energy Agency) also helped Chile and Mexico to eradicate the Meditteranean fruit fly using the SIT, thereby overcoming barriers to the export of fruit to profitable markets in the United States and Japan. The UN agencies are currently assisting national plant protection authorities in Argentina, Guatemala and several countries in the Near East to eradicate this pest or establish pest-free zones.

Details of these and other integrated pest management programmes that use the SIT for area-wide control of insect pests will be presented at an international conference being organized by FAO and the IAEA in Malaysia from 28 May to 2 June 1998.

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