Sterile insect technique

The technique has successfully been used to eradicate the screw-worm fly (Cochliomyia hominivorax) from North and Central America in the past. Many successes have been achieved for control of fruit fly pests, most particularly the Mediterranean fruit fly (Ceratitis capitata) and the Mexican fruit fly (Anastrepha ludens). Active research is being conducted to determine this technique's effectiveness in combatting the Queensland fruit fly (Bactrocera tryoni).

Sterilization is induced through the effects of x-ray photon irradiation on the reproductive cells of the insects. SIT does not involve the release of insects modified through transgenic (genetic engineering) processes. Moreover, SIT does not introduce non-native species into an ecosystem.

History

The use of sterile males was first described by the Russian geneticist A.S. Serebrovsky in 1940, but the English-speaking world came up with the idea independently, and applied it practically around the 1950s. Raymond Bushland and Edward Knipling developed the SIT to eliminate screw-worms preying on warm-blooded animals, especially cattle; this was effective because female screw-worms mate only once. The larvae of these flies invade open wounds and eat into animal flesh, killing infected cattle within 10 days. In the 1950s, screw-worms caused annual losses to American meat and dairy supplies that were projected at above $200 million. Screw-worm maggots can also parasitize human flesh.

Bushland and Knipling began searching for an alternative to chemical pesticides in the late 1930s when they were working at the United States Department of Agriculture Laboratory in Menard, Texas. At that time, the screw-worm was devastating livestock herds across the American South. Red meat and dairy supplies were affected across Mexico, Central America, and South America.

Knipling developed the theory of autocidal control – breaking the pest's reproductive cycle. Bushland's enthusiasm for Knipling's theory sparked the pair to search for a way to rear flies in a "factory" setting, and to find an effective way to sterilize flies.

Their work was interrupted by World War II, but they resumed their efforts in the early 1950s with successful tests on the screw-worm population of Sanibel Island, Florida. The sterile insect technique worked; near eradication was achieved using X-ray-sterilized flies.

Successes

In 1954, the technique was used to eradicate screw-worms from the 176-square-mile (460 km²) island of Curaçao, off the coast of Venezuela. Screw-worms were eliminated in seven weeks, saving the domestic goat herds that were a source of meat and milk.

During the late 1950s to the 1970s, SIT was used to control the screw-worm population in the US. In the 1980s, Mexico and Belize eliminated their screw-worm problems with SIT. Eradication programs progressed across Central America in the 1990s, followed by the establishment of a biological barrier in Panama to prevent reinfestation from the south. The map shows the current and former distribution area and the approximate seasonal spread of the screw-worm fly.

In 1991, Knipling and Bushland's technique halted a serious outbreak of New World screw-worm in northern Africa. Programs against the Mediterranean fruit fly in Mexico, Florida and California use the SIT to maintain their fly-free status. The technique was used to eradicate the melon fly from Okinawa and in the fight against the tsetse fly in Africa.

The technique has suppressed insects threatening livestock, fruit, vegetable, and fiber crops. The technique was lauded for its environmental attributes: it leaves no residues and has no (direct) negative effect on nontarget species.

The technique has been a boon in protecting the agricultural products to feed the world's human population. Both Bushland and Knipling received worldwide recognition for their leadership and scientific achievements, including the 1992 World Food Prize. The technique were hailed by former U.S. Secretary of Agriculture Orville Freeman as "the greatest entomological achievement of the 20th century."

South Australia has since 2016 been producing tens of millions of sterile fruit flies a week during peak summer months, as part of a program to control and eventually eradicate the horticultural pests.

Emergency applications

In July 2016, New World screwworm (Cochliomyia hominivorax) was detected in the Florida Keys — the first confirmed presence in the continental United States since the species had been eradicated from North and Central America through decades of SIT campaigning. The outbreak posed an acute threat to the endangered Key deer (Odocoileus virginianus clavium), a subspecies of white-tailed deer restricted to a small island range. Between October 2016 and January 2017, more than 130 Key deer were killed by screwworm or had to be euthanized as a result of infestation. Adult males were disproportionately affected due to wounds sustained during the autumn rutting season, which provided oviposition sites for screwworm flies.

SIT was implemented in the Keys on October 11, 2016, as quickly as sterile pupae could be flown in from the USDA's production facility in Panama, which immediately ramped up its production of flies to support the response. Over the course of the eradication effort, over 150 million sterile flies were released across the affected areas using ground-based release chambers.

By March 2017, the screwworm had been successfully eradicated from Florida, approximately five months after the outbreak was first confirmed. Containment was achieved before the 2017 fawning season, limiting mortality among females and preserving the reproductive capacity of the herd.

The outbreak highlighted several important considerations for SIT infrastructure and emergency preparedness. The speed of eradication depended critically on the pre-existing Panama production facility — operated jointly with the Panamanian government as part of the ongoing Darién Gap barrier programme, which continuously releases approximately 20 million sterile flies per week to prevent northward migration from South America. Without this maintained standing capacity, emergency deployment would have been significantly delayed.

The incident also illustrated an ecological consequence of long-term SIT success: the Key deer population had no exposure to screwworm for several decades and lacked any behavioural or demographic adaptations to the parasite, leaving them acutely vulnerable upon reintroduction. The case further established a precedent for SIT as a conservation tool deployed specifically to protect an endangered wildlife population, rather than livestock or crops.