Johannesburg and Durban, South Africa – Several initiatives to control insect pests using nuclear techniques in South Africa are entering the advanced research stage – offering a new possibility to eventually contribute to the control of malaria as well as a major pest attacking sugarcane. By joining forces, researchers hope to accelerate development of the technology in coming years.
These projects come on the heels of the successful suppression of the false codling moth, a major pest of oranges and other citrus, with support from the IAEA, in collaboration with the Food and Agriculture Organization of the United Nations (FAO).
"We have seen the tremendous effects of the sterile insect technique on the citrus industry and we are working to develop a similar solution against Eldana," said Des Conlong, senior entomologist at the South African Sugarcane Research Institute (SASRI), and manager of the project. The Eldana moth, whose larvae penetrate and feed on the soft tissue inside sugarcane, destroying the crop, has been decimating sugarcane in South Africa since the 1970s. The current damage is estimated at 750 million rand (US$ 48 million) in lost output per year. This represents close to 10% of the total income of the canegrowing sector, which comprises close to 22 000 farmers, from smallholders to large commercial plantations. The sugarcane industry is an important source of employment, particularly in rural areas in the northeast of the country.
The sterile insect technique (SIT) is a form of pest control that uses ionizing radiation to sterilize pests that are mass-produced in special rearing facilities. The sterile insects are released in infested areas, where they mate with wild populations, but do not produce offspring. As a result, the technique can suppress and in some cases eventually eradicate populations of insect pests. It is among the most environmentally friendly control tactics available, and is usually applied on an area-wide basis as part of an integrated campaign to control insect populations. The Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture spearheads global SIT research.
SASRI has introduced several methods to control Eldana over the last few decades, and while they have all helped, none of them have led to the desired results. Although resistant varieties of sugarcane have been developed, they are sometimes not used, with farmers preferring less resistant but more productive varieties, which do not contribute to the control of the pest. Insecticides are used on large plantations, but are too expensive for small farmers. The introduction of parasitoids to attack life stages of the moth in sugarcane has not worked, because the parasitoids did not recognize sugarcane as a habitat for the moth and themselves, and so do not attack them, Conlong explained.
Conlong and his team have shown that Eldana moths can be sterilised using gamma radiation without compromising their ability to mate in the wild. "All our research indicates that SIT is a suitable option," Conlong said. They have developed a rearing facility and feeding system, and have optimized the production of sexually competitive insects. As the next step, they are looking to carry out a pilot trial on an isolated, five-hectare Eldana-infested plantation in KwaZulu-Natal province. Some 8 million rand (US$ 500 000) is required to buy an irradiator and install it. "The last few years have been tough for the sugar industry due to the prolonged drought, so funding for the project has been postponed," he said. The South African government, however, is ready to fund part of costs to buy an irradiator for the program, he added.
SASRI is now looking to join forces with the National Institute for Communicable Diseases (NICD), whose researchers are looking to use SIT to further suppress the last pockets of malaria-carrying mosquitoes in the north-eastern part of the country. Around 10% of South Africans live in the malaria zone.
Thanks to other malaria control measures, the number of cases is down to around 9000 per year from over 60 000 in 2000, but it has proven hard to bring the insect population – and infection rates – down any further using the traditional method of indoor residual spraying, said Lizette Koekemoer, who runs the project at NICD. The problem is that the Anopheles mosquito, which carries and spreads the disease to humans, rests both indoors and outdoors. As a result, even if all mosquitoes were eradicated indoors, those resting outside would still survive and spread malaria.
NICD has been researching the application of SIT for the control of Anopheles, with support from the IAEA and the FAO for five years. The IAEA has provided mass rearing equipment and, in cooperation with the FAO, trained NICD researchers in its laboratories in Austria in insect feeding, rearing and sterilization, Koekemoer said. Participating in a network of SIT researchers in other countries has enabling the NICD team to learn from other initiatives in customizing SIT. "This has helped us move through the phases of the research much more rapidly than if we had to do this by ourselves from scratch," she said.
NICD has been able to determine the amount of radiation required to sterilize the mosquitoes without killing them or compromising their sexual competitiveness, said Senior Researcher Givemore Munhenga. They are currently working on sterile male quality control, as well as on finding a suitable technique to separate male from female insects. This separation is crucial in the case of mosquitoes: it is the females that spread the disease and mass releasing only males eliminates any risk of increasing the number of mosquitoes that carry the malaria parasite, thereby inadvertently spreading the disease. Therefore, in order to avoid this risk, female mosquitoes must be removed before release.
NICD, through collaboration with the country's Nuclear Technologies in Medicine and the Biosciences Initiative (NTeMBI), has secured funding to build a mass rearing facility on its campus near Johannesburg to produce sterile mosquitoes for a pilot project in a small village in northern KwaZulu-Natal Province. The weekly production of a large number of mosquitoes and the eventual rollout of the programme would require irradiation close to malaria hotspots in the northeast, which is also the heartland of sugar cane country (see map). Additional funding has been raised for the mass rearing effort from the South African Industrial Development Corporation.
"By joining forces with SASRI we could hit two insect pests with one stone," Koekemoer said.
The IAEA is supporting the joint project and is looking at how it may be able to facilitate the set-up of the irradiation facility, said Michel Warnau, Section Head at the IAEA's Technical Cooperation Division for Africa. "South Africa has been very successful in using SIT against various pests, and the IAEA stands ready to further support the national initiative through its technical cooperation programme."