Ants employed to defend African mangoes

[LILONGWE] African farmers could effectively control fruit fly damage to citrus fruit, cashew and cocoa crops by using the weaver ant as a method of biological control, according to researchers.

Paul Van Mele and colleagues published their work in the June edition of the Journal of Economic Entomology.

The weaver ant, Oecophylla longinoda — commonly found in Africa, Asia and Australia — preys on fruit flies and is already used in several Asian countries and Australia to protect citrus and other fruits from fruit fly damage.

Fruit fly damage has a large economic impact on African farmers. As pesticides are often too expensive, they harvest fruit before it matures to prevent damage, but an estimated 40 per cent is still lost. The European Union and the United States have banned imports of West African mangoes due to fruit fly damage.

Van Mele and colleagues conducted a study in Benin to assess whether mango plantations containing weaver ants had less fruit fly infestation than those with few or no ants.

They found that where weaver ants were abundant, infestation of fruit flies of several species was significantly reduced and the plantations produced fruit of significantly better quality.

In 2006 Van Mele introduced weaver ant use in Benin and Guinea to help cashew and mango farmers grow tree crops without pesticides as part of efforts by the Inland Valley Consortium hosted by the Africa Rice Center to protect the human and environmental health in African inland valley ecosystems.

Van Mele says they intend to take the research to other African countries, including East Africa.

Ana Varela of International Centre for Insect Physiology and Ecology in Kenya, says there are still challenges associated with using weaver ants.

For example, because of the ants’ aggressive nature, farmers are not generally aware of their value, she says.

There are also other ant species that kill and displace weaver ants and do not themselves protect trees against pests, so the trees often suffer serious damage by pests.

These other ant species need to be managed in such a way that they do not disturb weaver ants, says Varela.

In Africa, weaver ants are also known to control the coreid bug, a coconut pest, and ants of the Myrmicaria species that prey on cashew trees, according to Zuberi Seguni of the Tanzania-based Mikocheni Agricultural Research Institute.

Link to abstract in the Journal of Economic Entomology

Reference: Journal of Economic Entomology 100, 695 (2007)