Weaver ants clear crops of pests in minutes
By Farmbiz | Fri 17 Aug, 2012

weaver-ants-killing-fruit-flies-kenya.jpTanzanian farmers are teaching Kenyan counterparts how to domesticate weaver ants that ward off the voracious fruit flies responsible for huge horticultural crop losses and serial export bans on Kenyan goods, in a 'taming of nature' that is delivering near-instant 75 per cent yield increases. The Tanzanian farmers from Mtwara Province have borrowed from traditional knowledge that ensured that farmers relied on nature to create a balance between all living organisms.

This balance ensured that harmful pests and diseases were controlled naturally by beneficial insects, commonly referred to as 'friends of the farmer', which acted as predators of the harmful pests, reducing their multiplication and damage to crops and the environment. Weaver ants are generalist predators and fearless foragers, scouting trees in search of palatable pests, including beetles and fruit-piercing bugs, caterpillars, mites and thrips.

Furthermore, their continual patrolling disturbs fruit flies during egg-laying, with adults often caught in the act and eaten. With their insatiable appetites and constant patrolling of crops, the ants can wipe out a swath of fruit flies in minutes with a study in Benin in 2007 hailing the ants as a "gift of nature" after researchers found that weaver ants were an effective biological control tool, reducing fruit fly attacks and significantly improving fruit quality in commercial mango plantations. There is also evidence that their painful bite deters rats, snakes and possibly fruit bats.

Fruit flies have been African farmers' biggest headache for years, damaging crops and depriving the economy of millions as a result of export bans. Fruit flies destroy some 750,000 tonnes - about 40 per cent - of Africa's mangoes every year. They deprive communities of an important source of vitamin A, and are also quarantine pests, with the US banning imports of West African mangoes, the most affected by the fruit flies. Kenya only recently resolved a three year avocado ban with South Africa, which banned avocado imports from Kenya on the grounds that they were carrying fruit fly that was causing the fruit to rot.

The ban cost the country close to Sh1 billion. Many smallholders try to deter infestations by picking fruits before they are ripe or applying pesticides, but these are expensive and often ineffective. But scientists argue that if weaver ants can eliminate the need for pesticides, farmers will be able to access lucrative international markets with high-quality tree crops. According to the Benin research, weaver ants are the perfect protection for trees like citrus, cashew, mango, coconut, oil palm, cocoa and lychee. Because weaver ants prey on harmful plant pests, any plant inhabited by weaver ants has low pest levels. The ants usually communicate through a unique scent that elicits an immediate reaction from all ants in the entire colony to offer defense or undertake a particular task.

They consume a large amount of food, and workers continuously kill a variety of insects for this purpose. Under a farmers exchange programme, farmers from Witeithie area of Thika District had visited their counterparts in Tanzania to learn more about the weaver ants. “We would want to use the weaver ants on our mango trees and we plan to start with a demonstration plot. But the revolutionary way of controlling pests without using synthetic pesticides that have become prohibitively expensive and dangerous to our farms, and the success of yields in Tanzanian farms, has definitely drawn us to this pest control method,” said Nathaniel Kiuma, one of the farmers who went on the exchange programme.

One important lesson they learnt was that the ants move in groups from one tree to another and to encourage weaver ants to do their work, the farmers tie ropes between mango trees and orchards to facilitate the movements of ants to unoccupied trees. The Tanzanian farmers, predominantly growing cashew nuts, have managed to increase their cashew nut production by up to 75 per cent by relying on the ants in an area seasonally affected by fruit flies. Since the farmers do not use chemicals, the cashew nuts they produce are sold as organic, which fetch a higher price in the international markets than conventionally produced cashewnut that use chemicals to control fruit flies and other pests.

For example, 1 kg of cashew nut grown organically is selling at Sh97 while those grown using chemicals to control fruit flies are sold at Sh83 per kg. Tanzania is among the top global producers of cashew nuts. Scientists argue that the fact that the weaver ants are readily available in Africa, are environmental friendly and can clear large number of pests within minutes, makes them the best intervention for Africa.

Written by Bob Koigi for African Laughter

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