Twenty years ago this autumn, an island off the coast of Tanzania became the first in Africa to get rid of the tsetse fly thanks to a nuclear technique. Prior to eradication, losses to livestock due to the nagana disease the flies carried used to cost farmers on Unguja Island, the largest in the Zanzibar archipelago, US$ 2 million a year.
"The removal of the tsetse fly and nagana from the Unguja island has been one of the most important achievements to enhance agriculture and improve the livelihoods of farmers in Unguja in the last 20 years," said Khalfan Saleh of the Ministry of Agriculture, who oversaw the national eradication campaign.
The nuclear based sterile insect technique (SIT) played a key role in achieving the complete eradication of the tsetse fly Glossina austeni population, and reducing the prevalence of nagana from 19% to zero. (See Scientific birth control for flies)
The 20th anniversary of the last wild tsetse fly being trapped on the Island was marked in September 2016. Since 1996, Unguja Island has been free from this large blood-sucking fly and from 1997 there has been no evidence of the presence of the parasites that cause nagana in livestock.
"The elimination of nagana has resulted in a reduction in abortion rates in cattle, calf mortality and an increase in meat and milk production as well as an increase in numbers of crossbred cows," Saleh said.
Nagana is a debilitating chronic condition in livestock that reduces fertility, weight gain, impacts meat and milk production, and makes livestock too weak to be used for ploughing or transport, which in turn affects crop production, Saleh highlighted. It is a wasting disease in cattle, caused by a parasite that is transmitted when the tsetse flies bite animals to feed on their blood.
The Tanzanian and Zanzibar governments, supported by the IAEA and the United Nations' Food and Agriculture Organization (FAO), implemented the SIT programme between 1994 and 1997.
In the initial stages of the project, the tsetse population was reduced by treating cattle with an insecticidal 'pour-on' application and using cloth targets, soaked with insecticides that attracted and killed the tsetse flies upon contact.
After the tsetse population was suppressed, weekly aerial releases of up to 100 000 sterile male tsetse flies were made to reduce the reproductive capacity of the native tsetse fly population so as to eventually bring about the elimination of both the tsetse fly population and tsetse-transmitted nagana from the Island.
To assess the impact of the SIT strategy, periodic socio-economic surveys (in 1999, 2002, 2014 and 2015) involving deployment of tsetse traps and screening of cattle nagana infections, were carried out. These confirmed the absence of both tsetse flies and nagana on the island.
Socio-economic studies in 2014 found that the total number of improved (crossbred) cattle breeds had increased by 38%.
Milk production increased following eradication of tsetse and nagana and data from the 2014 socio-economic survey found that crossbred cattle breeds were producing an average of 9.7 litres of milk per cow per day compared to 4.6 litres produced by indigenous cows.
Finding a solution over the years to the havoc created by tsetse flies to livestock has been a major challenge to the combined scientific efforts of the IAEA and the FAO, said Jorge Hendrichs, Head of the Insect Pest Control Section at the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture.
Scientific birth control for flies
SIT is a form of insect pest control that uses ionizing radiation to sterilize male tsetse flies that are mass-produced in special rearing facilities. The sterile males are released systematically from the ground or by air in tsetse-infested areas, where they mate with wild females, which do not subsequently produce offspring. As a result, this technique can eventually eradicate populations of wild flies. The SIT is among the most environmentally friendly control tactics available, and is usually applied as the final component of an integrated campaign to remove insect populations.
Source: International Atomic Energy Agency