This chapter was published on “Inuitech – Intuitech Technologies for Sustainability” on February 13, 2012.
Here are some facts about insects: Over 1 million species of insects inhabit the world, more than the total number of species of all other animals and plants combined. Fortunately, for humankind the vast majority of these insects are either beneficial or harmless. The relatively few species, 15 000 or less, that are detrimental result in losses of 15-20 percent of the world’s agricultural (plant and animal) production. Ironically, these figures represent the 1980s and according to a recent estimates, published by, the International Atomic Energy Agency (IAEA), puts losses of food production in the range of 25-35 percent, even with use of pesticides. These losses are from direct damage to plants and animals, as well as from diseases of plants and animals transmitted by insects. Additionally, insects caused losses that are more significant during storage of agricultural products. Other important losses occur from human diseases, such as malaria, yellow fever, dengue, and onchocerciasis that are transmitted by insects.The reality is that insect pests are another serious threat to productivity as well as humanity and losses of food caused by insects creates a profound challenge for the world, which is faced with the food insecurity for the existing global population that is expected to grow to eight billions in 2020. When animals or plants are produced in concentrated areas (monocultures) they provide a culinary feast for insects and result in a great increase in insect pest numbers. Food must be produced in this manner to feed the number of people in the world; thus agricultural products, both during production and storage, must be protected from insect attack (along with other pests, such as diseases, weeds, nematodes, rats, and birds).
Modern insecticides were rapidly developed after World War II and provided plant and animal producers with an extremely powerful tool for use against insects. Insecticides provide the primary method of insect control; however, they are not completely satisfactory. Moreover, there are concerns that reliance on pesticides to maintain yields not only has negative impacts on the environment, but may also lead to the insects developing resistance to the pesticides themselves. However, Sterile Insect Techniques (SIT) offer alternative means of suppressing and, in some cases, even eradicating insects, such as fruit flies, tsetse flies, moths and malaria carrying mosquitoes.
Through its Insect and Pest Control programme, the IAEA is using nuclear science to develop environmentally friendly alternatives for pest control. One of the most successful techniques developed to date is the SIT.
The discovery that X-rays or gamma radiation could cause sufficient genetic damage to insect reproductive systems to induce sterility resulted from work conducted by H.J. Muller starting in the 1920s. Muller won a Nobel Prize for his work on the genetic effects of irradiation in insects. The sterilizing effect of radiation was noted by scientists of the US Department of Agriculture who had been seeking a method to sterilize insects for many years. These scientists had theorized that if large numbers of the target insect species were reared, sterilized, and released into the field, the sterile insects would mate with the wild insects. These mating would result in no offspring and thus a decline in the population would be obtained. They calculated that if sufficient numbers of sterile insects were released, the reproductive rate for the wild population would rapidly decline and reach zero. In simple language, birth control of insects. Radiation sterilization was the answer.
The first demonstration of this nuclear technology was the eradication of the screwworm from the Dutch island of Curacao in 1954. The programme was conducted by scientists of the US Department of Agriculture in cooperation with the Dutch Government. Thus, the initial SIT project was international, and to a large extent, operational SIT projects since then have remained international in scope.The SIT has been successfully used to eradicate several insect pests of agricultural significance. One of the most significant is the Mediterranean fruit fly (Medfly), a serious threat to more than 250 species of fruit and vegetables. Thanks to successful implementation of SIT, the Medfly has now been eradicated from Mexico and Chile, and from parts of Guatemala and the United States. The programme is now being expanded into Argentina, Southern Peru, and the Middle East.
The tsetse fly, which spreads the parasite trypanosome that causes African sleeping sickness and the cattle disease Nagana, has turned several fertile African landscapes into uninhabited green areas. Because of the risks of the tsetse, a large fraction of Africa’s best land — particularly in river valleys and moist areas where the potential for mixed farming is good — lies uncultivated. Affecting as many as 500 000 people, the tsetse fly is responsible for economic losses estimated at more than $4 billion per year. As a result of the successful combination of SIT with conventional pest control methods, Zanzibar was declared tsetse-free in 1997. Building on this success, in 2001, the Organization of African Unity established the Pan African Tsetse and Trypanosomosis Eradication Campaign (PATTEC) to combat the tsetse in the 37-Sub-Saharan African countries with support from the World Health Organization, the Food and Agriculture Organization of the United States (FAO), and the IAEA.
The use of the SIT continues to rely on the application of ionizing radiation as a means to effectively sterilize insects without affecting the ability of the males to function in the field and successfully mate with wild female insects. Ionizing radiation is the sole technology that can be used to achieve these twin goals of sterility induction coupled with effective field performance. This method is integrated with a whole suite of complementary measures that ensure success in reducing or eliminating insect pest populations. This complementarity is achieved through collaboration with other specialized organizations and, where necessary, using in-house R&D.
The SIT technology has been traditionally associated with programmes aimed at the eradication, i.e., the complete elimination of all individuals of pest populations; indeed it is one of the strengths of the nuclear technology that it is able to do this. However, sterile insects can also be deployed in AW-IPM programmes in other control strategies. Sterile insects can be released in a containment strategy to prevent an established pest invading a nearby area still free of the pest. An example of this is the release of sterile screwworms as a barrier in Panama to avoid re-invasion of Central America from where this pest has been eradicated. The majority of sterile flies, which are continuously being released as part of this programme, come from the El Pino facility in Guatemala, where the genetic sexing strain (allowing male-only production) developed by the IAEA is being mass-reared. A fourth deployment strategy, which is considerably gaining in importance and encouraging the involvement of the private sector, is to use sterile insects as a “biological insecticide” to continuously suppress a pest population below a level which causes economic damage without any intention of eradication of the pest population.
AW-IPM programmes are logistically complex and management intensive; their implementation requires flexible procedures and non-bureaucratic management structures. In general, the scientists who have been closely involved with developing the technology should not be responsible for programme implementation, as other skills are needed. Also research activities should not be part of an operational programme; instead, a separate unit (but associated with the programme) is needed for problem-solving and continuous improvement of procedures; technology can always be improved. The basic components in the use of the SIT — mass-rearing and release of sterile insects — are hardly likely to change. However, as new technologies come on line and new scientific discoveries are made, R&D will continue to play a major role in improving the overall effectiveness and efficiency of the technique. The topics highlighted below could be some exciting new R&D components of future SIT programmes.
The continued expansion of the technique will also be facilitated if commercial companies can become involved and governments may decide to subcontract private companies to operate a whole programme or just individual components of a programme. The diversification described above in the use of sterile insects will help to develop commercialization. However, commercialization of the SIT has been a difficult concept to promote and establish, despite the fact that there is currently no shortage of customers who would purchase sterile insects if they were available. The use of sterile insects only for eradication of pest populations was not an attractive proposition for commercialization, but the widespread use of sterile insects for suppression, containment, and prevention programmes provides some continuity in the need for sterile insects. Commercialization will require a regulatory framework to facilitate the production, trade, shipment, and release of sterile insects.
Nevertheless, more use of the SIT will result from increased efficacy and improvement in economics. This continues to show that when applied against an appropriate insect or insects, the technique is more cost efficient than other technologies. Additional factors favouring its use include the growing problem of insect populations that become resistant to insecticides, and concerns about environmental damage caused by continuous annual use of insecticides to control the same insect species.
Sterile insects are mass-reared, in this case in Guatemala, which has the largest sterile insect production facility in the world. Some 3 000 sterile males are needed per hectare to suppress these pests in heavily farmed areas, such as coffee plantations. As a comparison, for IAEA field work in Croatia, in locations where there are fewer fruit and vegetable types grown, only some 500 to 1 000 sterile flies are needed on average per hectare.
“If you want to export, and also avoid the application of costly post-harvest treatments that can reduce produce quality, you have to get rid of both the Mediterranean and native fruit flies,” says Jesus Reyes Flores, an entomologist of the FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. “Sterile insect technology consists of rearing massive quantities of the same pest, sterilizing it by irradiation through a simple radiation device that otherwise causes no harm to the insect. The male insects are fed and later systematically freed in the fields, where they then mate with the pest insects present in the field, producing no progeny so that after the continuous release over several years the pest disappears.”
The IAEA, in collaboration with the FAO, helped deploy SIT, a nuclear application, to assist in curbing Guatemala’s fruit fly population, thereby providing a host of new jobs and at least doubling, over four years, export earnings from non-traditional agricultural export crops of tomatoes, bell peppers and papaya.
While prices slumped over the past decade for Guatemala’s traditional exports of coffee, banana and sugar cane, sales of tomatoes quadrupled to $10 million in 2010 from $2.5 million in 2007, with export income from bell peppers roughly tripling to $3.2 million in 2010, and papaya doubling, also to $3.2 million. These increases vaulted Guatemala into first place as the largest Central American supplier to its nearest major international market, the USA, and created hundreds of rural jobs, typically for men in field pest control and for women in the packing and transportation services industries.
Finally, in addition to SIT, there are nuclear applications which deploy isotopes and radiation in order to control insects. Isotopes are used as tags or markers, for instance, of chemical molecules, insects, or plants. For example, with these tags one can follow the fate of insecticides within insects and the environment; the incorporation of nutrients into the insect; and the movements of insects under field conditions. They also can mark plants on which insects feed so that the quantity of consumed food can be measured and directly correlated with plant resistance. They can be used as well to follow parasites and predators of insects — for example, their movements, numbers, and ability to help control insect pests.
In a SIT operation, radiation is used to sexually sterilize insects. The SIT is the largest part of the programme of the Insect and Pest Control Section of the Joint FAO/IAEA Division. Radiation is also used in insect studies including genetics, genetic engineering, microbial control, quarantine treatments of agricultural commodities, and induction of mutants in plants to breed resistant varieties.
- Insects, Isotopes, and Radiation;
- Improving Productivity in Agriculture;
- Sterile Insect Technology – Research and Development;
- Battling Bugs; and