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Partners

  • International Institute of Tropical Agriculture (IITA, Benin)
  • Northern Territory University (Australia)
  • Cheikh Anta Diop University (Senegal)
  • University of Aarhus (Danemark)
  • University of Abomey Calavi (Benin)

For further information

Vayssières J.-F., Sinzogan A.A.C., Adandonon A., Van Mele P., Korie S., 2013. Ovipositional behaviour of two mango fruit fly species (Diptera, Tephritidae) in relation to Oecophylla cues (Hymenoptera, Formicidae) as compared to natural conditions without ant cues. International Journal of Biological and Chemical Sciences, 7: 447-456. Doi: 10.4314/ijbcs.v7i2.3

Adandonon A., Vayssières J.-F., Sinzogan A., Van Mele P., 2009. Density of pheromone sources of the weaver ant Oecophylla longinoda affects oviposition behaviour and damage by mango fruit flies (Diptera, Tephritidae). International Journal of Pest Management, 55: 285-292. Doi: 10.1080/09670870902878418

Van Mele P., Vayssières J.-F., Adandonon A., Sinzogan A., 2009. Ant cues affect the oviposition behaviour of fruit flies (Diptera, Tephritidae) in Africa. Physiological Entomology, 34: 256-261. Doi: 10.1111/j.1365-3032.2009.00685.x

Van Mele P., Camara K., Vayssières J.-F., 2009. Thieves, bats and fruit flies: local ecological knowledge on the weaver ant Oecophylla longinoda in relation to three “invisible” intruders in orchards in Guinea. International Journal of Pest Management, 55: 57-61. Doi: 10.1080/09670870802450276

Vayssières J.-F., Adandonon A., Sinzogan A., Van Mele P., 2009. Allies in nature. IITA-R4D Review, 3: 31-33. http://r4dreview.org/2009/10/allies-in-nature/

Sinzogan A., Van Mele P., Vayssières J.-F., 2008. Implications of on-farm research for local knowledge related to fruit flies and the weaver ant Oecophylla longinoda in mango production. International Journal of Pest Management, 54: 241-246. Doi: 10.1080/09670870802014940

Van Mele P., Vayssières J.-F., Van Tellingen E., Vrolijks J., 2007. Effects of the African weaver ant Oecophylla longinoda in controlling mango fruit flies (Diptera Tephritidae). Journal of Economic Entomology, 100: 695-701. Doi: 10.1603/0022-0493(2007)100

Contact

Jean-François Vayssières
Cotonou, Benin
Agroecological Functioning and Performances of Horticultural Cropping Systems

Whatever would mango producers do without weaver ants?!

10/2013

Fruit flies cause considerable damage in West African orchards, making mangoes, citrus fruits and cashew nuts unfit for consumption. In recent years, researchers from CIRAD and the IITA have developed a range of biological control techniques against these primary and quarantine pests. In particular, they have looked at the weaver ant, a fruit fly predator, which not only eats their larvae but also emits chemical signals that serve to repel female flies.

Fruit production in West Africa is a victim of a group of Diptera, Tephritidae that go under the name of fruit flies. These insects lay their eggs inside the fruits and their larvae, which feed on them, destroy them.

An invasive species from Sri Lanka, Bactrocera invadens, is one of the most dangerous. It was detected in 2004 in Benin, Senegal and Togo. It has since spread throughout West Africa, and mango growers, who had few control methods at their disposal at the start of the invasion, have become discouraged.

CIRAD and the IITA launched a regional project in 2008 to control fruit flies, WAFFI (West African Fruit Fly Initiative). It centres on mango, and set out to provide producers with integrated control techniques that would allow them to grow healthy fruit. It was within the framework of this project that researchers decided to study weaver ants, a biological control method against fruit flies and other pests in the forests of West Africa.

Complex, well organized societies

African weaver ants, Œcophylla longinoda, are found in tropical forests, where they form complex colonies. They often colonize mango, citrus and cashew nut plantings, and less frequently cocoa and oil palm plots. They are unusual in that they build nests in trees, by "weaving" the leaves of the trees together with the silk threads produced by their larvae. They are also fierce defenders of their territory, prepared to fight any intruders.

Within a colony, the ants recognize each other and communicate via the various pheromones they emit. The African species produces at least six types which, combined with specific behaviour patterns, enable them to attract their peers, explore new territories, warn of intruders, attack enemies, obtain food and call for help.

Each colony comprises many nests. In the mango orchards of Borgou, in Benin, researchers have counted between 800 and 1300 per hectare, corresponding to 20 to 30 colonies. Each colony has a queen, males and two castes of workers that differ in terms of their size and function: the smallest workers, "minors", stay in the nests to take care of the young, while the largest, "majors", are constantly on the lookout for prey within the colony's territory.

Predation and repulsion: the two assets of weaver ants

It is for this capacity to eliminate intruders that weaver ants are of interest to researchers. They have, in fact, developed effective strategies for hunting in groups on the leaves of the trees, but also on the soil at the foot of the tree in which they nest, and capturing any insects they find. Right at the start of this study, the researchers observed that the fruits of mango trees with numerous nests were much less severely damaged by fruit flies than others.

More in-depth studies confirmed their impact on the structure and composition of and fluctuations in neighbouring insect communities, particularly those of plant-eating insects, and showed that they prey mainly on larvae, as they leave infested fruits, and rarely on adults.

However, this is not their only mode of action. The scientists discovered that they have a repellent effect on fruit flies: after ants have been on mangoes, fruit flies turn away from them and lay much fewer eggs. This phenomenon of repulsion, which was confirmed in the laboratory and in the field, is due to the physical signals (micro-spots) and chemical signals (pheromones) left by the ants.

Protected orchards and better quality fruits

Weaver ants have many other advantages. They protect fruit trees against certain hemipteran pests, by preventing the terrestrial ants that carry them from reaching the foliage.

They also have a repellent effect on fruit bats, which feed on fruits, and maybe also on dangerous tree snakes, such as green mambas, and could even serve to dissuade fruit thieves.

Lastly, they play an undeniable role in improving fruit quality, particularly mangoes. Their presence in a tree increases fruit sugar concentration, reduces acidity and improves microbiological quality.

Prophylaxis, biopesticides and biological control: agro-ecological pest management

This research is now being backed up by training courses for fruit tree farmers throughout the region. Weaver ants, which at the start of the project were seen by growers as pests due to their bites, are now more widely accepted. They are protected, fed and sometimes even introduced into orchards, and are now becoming valuable auxiliaries in Benin, and also in Togo, Ghana, Guinea and Senegal.

In weaver ants, mango producers now have a comprehensive arsenal of weapons against pests in their orchards and are able to produce healthy fruits while preserving the environment.

The methods developed under the project West African Fruit Fly Initiative enable agro-ecological pest control, be it preventive, by removing infested mangoes, treating the foliage with biopesticides or biological control using parasitoids and weaver ants.