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The smell of ants May 15th, 2016 by

weaver ants on bamboo 2Last week Jeff wrote a short blog story on Ants in the kitchen. It brought back memories on how nearly 20 years ago I embarked on an exciting project in Vietnam involving ants in biological pest control. Even though various ants really can control pests, it can be challenging to convince farmers that the ants are not all bad.

When in the early 1990s the American-French scientist Marco Barzman interviewed fruit farmers in southern Vietnam about managing insect pests in citrus with the red weaver ants, he came to a remarkable finding.

While many farmers went through great efforts to encourage weaver ants in their orchards, a few said they would like scientists to reproduce the smell of the ants so they could spray the trees and keep the insect pests away. This would be easier than managing ant colonies and, crucially, avoid their bites.

What seemed odd at the time has since been shown to be a sophisticated observation by farmers. Scientific research has revealed that ants leave behind chemical markers that ward off other insects, who smell danger and retreat.

1331 Lamatou harvests mangoesWomen who pick and sell mangoes for a living in Benin, West Africa, prefer picking and buying fruits from orchards that have weaver ants because they know that trees are less likely to have fruit with “white worms” inside. These are the larvae of fruit flies, which can destroy entire crops.

After decades of heavy scientific investments on fruit fly pheromones (odours that attract insects of the same or closely related species), commercial products are now available on the market that attract and kill fruit flies.

Research on how ant odours can be used in repelling fruit flies and other insect pests is still in its infancy. Revealing the exact chemical compounds involved in the complex communication system between different insect species is a daunting task and dependent on uncertain funding.

It may take decades for such products to be developed, tested and sold. But farmers do not have the luxury to wait; they want to protect their crops now.

1172 Martin Kwasi Agyeman rubbing ash against weaver ant attacksFor the time being, the best option is to support extension efforts that help orchard farmers to appreciate weaver ants. We can build on local knowledge, as across Africa and Asia fruit growers and pickers have developed various strategies to avoid being bitten by the ants. Promoting weaver ants as biological pest control also has to convince farmers that the ants are their friends.

The series of training videos that we developed for CORAF in West Africa on fruit flies, contain two videos on weaver ants. The videos help farmers understand the economic importance of these ants, present scientific information on ant ecology, and share local knowledge on reducing ant nuisance.

Scientific names: Weaver ant: Oecophylla smaragdina (Asian species), Oecophylla longinoda (African species).

Related videos

  1. Integrated approach against fruit flies
  2. Collecting fallen fruit against fruit flies
  3. Killing fruit flies with food baits
  4. Mass trapping of fruit flies
  5. Weaver ants against fruit flies
  6. Promoting weaver ants in your orchard

Further reading

Barzman, M.S., Mills, N.J. and Cuc, N.T.T. 1996. Traditional knowledge and rationale for weaver ant husbandry in the Mekong Delta of Vietnam. Agriculture and Human Values 13(4), 2-9.

Van Mele, P., Cuc, N.T.T., Seguni, Z., Camara, K. And Offenberg, J. 2009. Multiple sources of local knowledge: A global review of ways to reduce nuisance from the beneficial weaver ant Oecophylla. International Journal of Agricultural Resources, Governance and Ecology, 8, 5/6, 484-504. Read article ›

DSCN1564 weaver ants building nestsThe training manual “Ants as Friends: Improving your Tree Crops with Weaver Ants” is downloadable for free in five languages:

English (2003, 2007)
French (2008)
Khmer (2010)
Vietnamese (2005)
Bahasa Indonesia (2004)

Other publications on weaver ants are downloadable from the Agro-Insight Resources.

Related blog stories

Sugar sweet ants

Guardians of the mango

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