Sterile insect technique
The sterile insect technique is a method of biological insect control, whereby overwhelming numbers of sterile insects are released into the wild. The released insects are normally male, as the females cause the damage usually by laying eggs in the crop, or, in the case of mosquitoes, taking blood from humans. The sterile males compete with wild males to mate with the females. Females that mate with a sterile male produce no offspring, thus reducing the next generation's population. Repeated release of sterile males can diminish small populations, although success with dense target populations have not been demonstrated.
The technique has successfully been used to eradicate the screw-worm fly (Cochliomyia hominivorax) in areas of North America. Many successes controlled species of fruit flies, most particularly the medfly (Ceratitis capitata) and the Mexican fruit fly (Anastrepha ludens).
Insects are mostly sterilized with radiation, which might weaken them if doses are not correctly applied, reducing their fitness. Other sterilization techniques are under development which would not affect fitness.
Raymond Bushland and Edward Knipling developed the technique to eliminate screwworms preying on warm-blooded animals, especially cattle herds. They exploited the fact that female screwworms mate only once to attack its reproduction. The larvae of these flies invade open wounds and eat into animal flesh, killing infected cattle within 10 days. In the 1950s, screwworms caused annual losses to American meat and dairy supplies that were projected at above $200 million. Screwworm maggots can also parasitize human flesh.
Bushland and Knipling began searching for an alternative to chemical pesticides began in the late 1930s when they were working at the United States Department of Agriculture Laboratory in Menard, Texas. At that time, the screwworm was decimating 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 screwworm population of Sanibel Island, Florida. The sterile insect technique worked; near eradication was achieved using X-ray sterilized flies.
In 1954, the technique was used to eradicate screwworms from the 176-square-mile (460 km2) island of Curaçao, off the coast of Venezuela. Screwworms were eliminated in a span of only seven weeks, saving the domestic goat herds that were a source of meat and milk.
During the 1960s and 1970s, SIT was used to control the screwworm population in the United States. In the 1980s Mexico and Belize eliminated their screwworm problems with SIT. Eradication programs progressed across Central America, with a biological barrier in Panama to prevent reinfestation from the south.
In 1991, Knipling and Bushland's technique halted a serious outbreak in northern Africa. Programs against the Mediterranean fruit fly in Mexico and California use the same principles. 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 non-target 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."
Sleeping sickness or African trypanosomiasis is a parasitic disease in humans. Caused by protozoa of genus Trypanosoma and transmitted by the Tsetse fly, the disease is endemic in regions of Sub-Saharan Africa, covering about 36 countries and 60 million people. It is estimated that 50,000 - 70,000 people are infected and about 40,000 die every year. The three most recent epidemics occurred in 1896-1906, 1920 and 1970.
Studies of the tsetse fly show that females generally mate only once (occasionally twice).
Studies found this process to be effective in preventing the scourge.
- Screwworm fly (Cochliomyia hominivorax) eradicated from the United States, Mexico, and Libya.
- Mexican fruit fly (Anastrepha ludens, Loew) eradicated from most of northern Mexico.
- Tsetse fly eradicated from Zanzibar.
- Medfly (Ceratitis capitata, Wiedemann) eradicated from northern part of Chile and southern part of Peru and southern part of Mexico.
- Melon fly (Bactrocera cucurbitae, Coquillett) eradicated from Okinawa, Japan.
- Anopheles mosquito - Malaria vector, example Anopheles arabiensis.
- Tsetse fly (Glossina spp) - sleeping sickness vector.
- Painted Apple Moth (Lepidoptera: Lymantriidae) in Auckland, New Zealand.
- Codling moth (Cydia pomonella) (Lepidoptera: Tortricidae) in British Columbia, Canada .
- Aedes mosquitoes, vectors for filariasis, dengue and yellow fever.
- Fruit fly species, including Medfly, Caribbean and Mexican fruit fly (Nth, Sth and Central America), Queensland fruit fly in Australia (Bactrocera tryoni) and several other Bactrocera sp. across Australia, Asia and Oceania. The IAEA lists 41 different SIT facilities (DIR-SIT) across the globe, aiding the retrieval of information on mass production and on radiation doses (IDIDAS). It includes data on both the radiation dose required for the disinfestation of generic commodity groups, and the radiation dose used to induce sterility for pest control through the sterile insect technique.
- Repeated treatment is sometimes required to suppress population before the use of sterile insects.
- Sex separation can be difficult, though this can be easily performed on Medfly and screwworm.
- Radiation treatment can reduce male mating fitness.
- The technique is species specific. For instance, the technique must be implemented separately for each of the 22 Tsetse fly species.
- Mass rearing and irradiation require precision processes. Failures have occurred when unexpectedly fertile breeding males were released.
- Migration of wild insects from outside the control area could recreate the problem.
- The cost of producing sufficient sterile insects can be prohibitive in some locations.
Using recombinant DNA technology to create genetically modified insects called RIDL ("release of insects carrying a dominant lethal") is under development by UK company Oxford Insect Technologies (Oxitec). They introduce a repressible "dominant lethal" gene into the insects. This gene kills the insects but can be inhibited by an external additive (tetracycline) that allows the insects to be cultivated in bulk. This external additive can be administered orally via insect food. The insects can be given marker genes, such as DsRED fluorescence, that enable monitoring of the eradication progress under field conditions.
Among several approaches to RIDL, the more advanced forms employ a female-specific dominant lethal gene. This avoids the need for a separate sex separation step, as the inhibitor can be withdrawn from the final stage of rearing, leaving only males.
Males are then released into the target region. The released males are not sterile, but female offspring express the dominant lethal gene, reducing survival rates to some 5%.
Since the males are not sterilized by radiation before release, they have equivalent fitness to wild males. Progress towards applying this technique to mosquitoes has been made by researchers at Imperial College London, who created the world's first transgenic malaria mosquito.
A similar technique is the daughterless carp, a genetically modified organism produced in Australia by CSIRO in the hope of eradicating introduced carp from the Murray River system. As of 2005[update], it was undergoing safety tests.
Conclusion and perspectives
Biotechnological approaches based on genetically modified organism (transgenic organisms) are still under development. However, since no legal framework exists to authorize the release of such organisms in the nature, sterilization by irradiation remains the most used technique. A meeting was held at FAO headquarters in Rome, 8 to 12 April 2002 on "Status and Risk Assessment of the Use of Transgenic Arthropods in Plant Protection". The resulting proceedings of the meeting have been used by the North American Plant Protection Organization (NAPPO) to develop NAPPO Regional Standard No. 27 on "Guidelines for Importation and Confined Field release of Transgenic Arthropods", which might provide the basis for the rational development of the use of transgenic arthropods.
Economic benefits have been demonstrated. The direct benefits of screwworm eradication to the North and Central American livestock industries are estimated to be over $1.5 billion/ year, compared with an investment over half a century of approximately $1 billion. Mexico protects a fruit and vegetable export market of over $3 billion/year through an annual investment of ca. $25 million. Medfly-free status has been estimated to have opened markets for Chile’s fruit exports of up to $ 500 million. Eradication of tsetse has resulted in major socio-economic benefits for Zanzibar. When implemented on an area-wide basis and a scaled rearing process, SIT is cost competitive with conventional control, in addition to its environmental benefits.
- Genetically modified insect
- Inherited sterility in insects
- The Screwfly Solution by James Tiptree, Jr.— a classic science fiction horror story based on the Sterile Insect Technique
Notes and references
- Dyck, V.A.; Hendrichs, J.; Robinson, A.S., eds. (2005). Sterile Insect Technique: Principles and Practice in Area-Wide Integrated Pest Management. Dordrecht, The Netherlands: Springer. ISBN 1-4020-4050-4.
- Vreysen, M. J. B., Robinson, A. S., and Hendrichs, J. (2007). "Area-wide Control of Insect Pests, From Research to Field Implementation." pp. 789 Springer, Dordrecht, The Netherlands
- (French) Luigi D'Andrea, "Des insectes transgéniques contre la dengue. Sous quel contrôle et avec quels dangers ?", Stop OGM infos, no. 52, 2013.
- Collins S. R. , Weldon C. W., Banos C., Taylor P. W. 2008. "Effects of irradiation dose rate on quality and sterility of Queensland fruit flies, Bactrocera tryoni (Froggatt)". Journal of Applied Entomology 132 (5): 398–405. doi:10.1111/j.1439-0418.2008.01284.x
- Kumano Norikuni; Kawamura Futoshi; Haraguchi Dai; Kohama Tsuguo 2008. "Irradiation does not affect field dispersal ability in the West Indian sweetpotato weevil, Euscepes postfasciatus". Entomologia Experimentalis et Applicata 130 (1): 63–72. doi:10.1111/j.1570-7458.2008.00795.x
- Kumano Norikuni; Haraguchi Dai; Kohama Tsuguo 2008. "Effect of irradiation on mating performance and mating ability in the West Indian sweetpotato weevil, Euscepes postfasciatus". Entomologia Experimentalis et Applicata 127 (3): 229–236(8). doi:10.1111/j.1570-7458.2008.00706.x
- The Area-Wide Sterile Insect Technique for Screwworm (Diptera: Calliphoridae) Eradication
- The Sterile Insect Technique: Example of Application to Melon Fly Bactrocera cucurbitae. (accessed October 13, 2009)
- Benedict Mark Q, Alan S Robinson and Bart GJ Knols (edts.) 2009. Development of the sterile insect technique for African malaria vectors. Malaria Journal Volume 8 Suppl 2"
- A Genetically Engineered Swat
- World-Wide Directory of SIT Facilities
- International Database on Insect Disinfestation and Sterilization
- FAO/IAEA/USDA-2003-Manual for Product Quality Control and Shipping Procedures for Sterile Mass-Reared Tephritid Fruit Flies, Version 5.0. International Atomic Energy Agency, Vienna, Austria. 85pp.
- FAO/IAEA. 2006. FAO/IAEA Standard Operating Procedures for Mass-Rearing Tsetse Flies, Version 1.0. International Atomic Energy Agency, Vienna, Austria. 239pp.
- Oxitec Ltd How the self-limiting gene works Retrieved 14 February 2016
- Hogenboom, Melissa (13 August 2014) Genetically modified flies 'could save crops' BBC News, Science & Environment, Retrieved 15 August 2014
- Leftwich, Philip; et al. (2014). "Genetic elimination of field-cage populations of Mediterranean fruit flies". Proceedings of the Royal Society (Royal Society Publishing) 281 (1792). doi:10.1098/rspb.2014.1372.
- Webb, Jonathan (10 June 2014) GM lab mosquitoes may aid malaria fight BBC News, Science and Environment, Retrieved 11 June 2014
- citation needed
- Knols BG and Louis C. 2005. Bridging laboratory and fields research for genetic control of disease vectors. In proceedings of the joint WHO/TDR, NIAID, IAEA and Frontis workshop on bridging laboratory and field research for genetic control of disease vectors, Nairobi, Kenya 14–16 July 2004 Wageningen. Frontis
- Scott TW, Takken W, Knols BG, Boete C. 2002. The ecology of genetically modified mosquitoes. Science. 298: 117-119
- Eradication of tsetse
- Hendrichs, Jorge, and Alan Robinson. 2009. Sterile Insect Technique. In Encyclopedia of Insects, ed. Vincent H. Resh and Ring T. Carde. pp.953-957. Second Edition. London, Oxford, Boston, New York and San Diego: Academic Press, Elsevier Science Publisher.
- Mosquito birth control
- BBC Online article
- Plan to Eradicate the Tsetse Fly
- IPC-SIT webpage
- Improving Sterile Male Performance in Fruit Fly SIT programmes
- BBC article
- SIT Book Review
- A General-Purpose Species-Eradication Method