West African farmers prepare for ant-aid
The African weaver ant (Oecophylla longinoda) is an effective predator of fruit flies and could help African farmers suffering infestations. With their insatiable appetites and constant patrolling of crops, the ants have been praised as a "gift of nature" following a recent study* in Benin, where researchers found weaver ants to be an effective biological control, reducing fruit fly attacks and significantly improving fruit quality in commercial mango plantations.
Weaver ants are generalist predators and fearless foragers, tirelessly 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.
Weaver ants are accomplished climbers, offering protection to fruit grown in tall trees, which are notoriously difficult to keep pest-free. There is also evidence that their painful bite deters rats, snakes and possibly fruit bats. The report's authors envisage Integrated Pest Management (IPM) schemes employing weaver ants as a low-cost, low-maintenance biological control, safeguarding tree crops such as citrus, cashew, mango, coconut, oil palm, cocoa and lychee.
Scourge of the mango
Fruit flies destroy some 750,000 tonnes - about 40 per cent - of Africa's mangos every year. As well as depriving communities of an important source of vitamin A, fruit flies are quarantine pests, with the United States banning imports of West African mangos.
Many smallholders try to deter infestations by picking fruits before they are ripe or applying pesticides, but these are expensive and often ineffective. If weaver ants can eliminate the need for pesticides, farmers may be able to access lucrative international markets with high-quality tree crops. According to report co-author Dr Paul Van Mele, of the Africa Rice Center (WARDA), the benefits of weaver ant technology are that it is "free of costs, labour-saving and requires relatively little intervention, making it particularly suitable for sub-Saharan Africa."
Trail of success
Complementary use of these endemic insects has a long tradition in Asia. Farmers in the orange groves of ancient China controlled beetles, mites and stinkbugs by encouraging the Asian weaver ant (O. smaragdina) to flourish. Studies also demonstrated improvements in the quality of mandarin fruits in Vietnam when weaver ants were present. Dr Van Mele, who worked in Asia for ten years, said: "Citrus farmers in Vietnam have developed a whole range of techniques that are of direct use to African farmers. These include the introduction and management of new colonies, reducing competition from less useful ant species, providing food and shelter, avoiding fights between different ant colonies, and reducing the nuisance caused by ants during harvest."
The research from Benin shows that nearly complete control of pests is possible when weaver ants are in abundance. But a major hurdle to the acceptance of weaver ant husbandry in Africa is overcoming negative perceptions. Farmers and extension officers often regard the ants themselves as pests, a situation not helped by a powerful pesticide lobby. Raising awareness of the multiple benefits of weaver ants has become a central part of Dr Van Mele's work.
The Conservation, Food and Health Foundation is currently supporting a project in Guinea, Benin and Tanzania, assessing farmers' knowledge and perceptions of weaver ants. The results will help in developing programmes to inform farmers about the positive impact of weaver ants on tree crops, and how to optimise their use. It is hoped that emerging markets for organic and sustainably managed fruit and nuts will prompt growers to look to the humble weaver ant as a necessity, rather than a nuisance.
*Effects of an African Weaver Ant, Oecophylla longinoda, in Controlling Mango Fruit Flies (Diptera:Tephritidae) in Benin by Paul Van Mele, Jean-Francois Vayssieres, Esther van Tellingen and Jan Vrolijks.
Date published: September 2007
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