Weaver ants to help African farms yield fruit

December 18, 2010 04:09 pm | Updated November 28, 2021 08:54 pm IST - AARHUS, Denmark

An arboreal insect known for its lethal biting power, the weaver ant has been recorded to serve as a natural biocontrol agent against agricultural pests. Photo shows weaver ants at the bio-diversity park in Visakhapatnam. Photo: K. R. Deepak

An arboreal insect known for its lethal biting power, the weaver ant has been recorded to serve as a natural biocontrol agent against agricultural pests. Photo shows weaver ants at the bio-diversity park in Visakhapatnam. Photo: K. R. Deepak

A research team at Aarhus University, Denmark, is ready to launch a weaver ant project next month in Tanzania and Benin in collaboration with local scientists and farmers to produce organic fruits, with the ants themselves possibly serving as an alternate source of protein for human beings.

An arboreal insect known for its lethal biting power, the weaver ant has been recorded to serve as a natural biocontrol agent against agricultural pests, according to ancient Chinese texts dated as early as 304 B.C. Scientists in Denmark found that the weaver ant may effectively help farmers in Africa in fruit agriculture, after researching on the ant’s interaction with pests on mango and cashew nut trees.

Fruit flies and other pests lay their eggs inside the trees’ fruits, making them go rotten. Up to about 80 percent of annual fruit crops harvested in Africa were lost in this way, estimates show.

“To kill the flies with pesticides, you have to make the mango so poisonous that it can kill the maggot,” said Mogens Gissel Nielsen, associate professor of Biology at Aarhus University, currently managing the weaver ant project. “But when it is too poisoned for the maggot to eat, it might not be good for us to eat either.” In an interview with Xinhua on Friday, Nielsen described the way the weaver ant attacks fruit flies. Since it takes a fly up to 20 minutes to lay her eggs, “when an ant comes along, the fly will give up, or she will be eaten by the ant.” The weaver ants’ killer instinct helps farmers protect their crops, and saves them a lot of pesticides, which can contain chemicals that are harmful to human beings. These chemical-free fruits can fetch good prices on organic foods markets in Europe and the United States.

With a 1.3 million euro grant from the Danish International Development Agency (DANIDA), researchers at Aarhus University will launch a program to make the ant project commercially viable for small-scale farmers in Benin and Tanzania.

Starting January, the programme will support high-level research on biological pest control measures while training local farmers to use the ants in farming organic mangoes and cashew nuts. Universities and scientists in Africa will also join the program.

Tasty side effect

The project also has an unexpected, and tasty, side benefit. Weaver ant queens, the reproductive females in an ant colony, and weaver ant larvae, which are the immature ants, have a soft, slightly sweet taste and is rich in protein. In Thailand and elsewhere Southeast Asia, the ants have been served as a traditional delicacy.

“We are actually turning pests into edible protein,” said Joachim Offenberg, a senior scientist affiliated with the National Environmental Research Institute, Denmark. He has been researching on the agricultural and nutritional applications of weaver ants in Thailand for years.

“The ants eat pests in plantations, and surplus ant larvae can be harvested sustainably without destroying the ant population and their bio-control services,” Offenberg told Xinhua in an e-mail.

He said although weaver ants and their larvae have traditionally been harvested for food in Thailand, this has not harmed ant population or colonies. “On the contrary, more worker ants — the caste that hunts pest insects — developed in harvested ant colonies.” This means that weaver ants can both increase fruit production by destroying fruit flies and other pests, and at the same time serve as a sustainable source of protein for human beings.

Offenberg also points out that the natural habitat of the weaver ant, straddling the Equator in Asia, Africa and Australia, overlaps places where most of the world’s one billion chronically undernourished people live.

“Protein is highly needed in Africa, where the average intake is very low,” he observed. “Introducing this method in Africa will provide Africans with better fruit quality, allowing export and cash earnings, and at the same time provide rural people with a protein source.”


While the nutritional side of the program is appealing, it remains to be seen how African farmers get along with this new biological tool.

The weaver ant construct nests by weaving together leaves and their colonies can be extremely large containing millions of ants spanning up to one hectare. It is an aggressive species that is known for its hard bite, making it very difficult for fruit growers to collect from the wild.

But in early 2010, a research team at Aarhus University discovered how to breed weaver ants in nurseries, giving farmers a safer means to obtain these insects.

The team hopes to build ant nurseries that farmers can buy entire colonies of ants to transplant to their fruit plantations. Over time, farmers may themselves become ant breeders to earn a second income.

But that still leaves farmers with a small problem: how to collect your fruits without getting bitten? “They are scared of water,” Nielsen said, “When you are going to pick the fruits, just spray the trees with water, and the ants will return to their nests... in about 20 minutes.”

Stable income for farmers

Nielsen realizes the project won’t be fully accepted by the African farmers unless they can find a market to sell their ant-protected organic fruit. That is why researchers are relying on the Aarhus School of Business (ASB) at Aarhus University to identify commercial opportunities for the farmers.

“The basic purpose of the project is to create better and more stable incomes for farmers in Africa”, said John Thoegersen, professor of Economic Psychology at ASB.

He and his colleagues are currently investigating the barriers that exist for exporting these organic products to Europe, including the need to comply with strict European regulations regarding the certification of organic products.

Thoegersen told Xinhua in a telephone interview that Europe presents a big opportunity for organic food producers in developing countries. Denmark, for instance, has the highest market share of organic food (7 percent) of any European Union country, while Germany has the largest market for organic goods by volume.

But he cautioned that when marketing these agricultural products in Europe, “there needs to be a fit between retailers’ demand and what the African producers can deliver.” Some retailers may want whole, packaged organic fruit like raw mangoes, or plain fried cashew nut, while others might want organic fruit pieces ready to be used in cakes, energy bars and ice-creams.

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