Weaver Ants to Control Fruit Fly Damage to Tanzanian Mangoes

Project summary

This project will evaluate the potential for increasing the income of small scale mango producers in Tanzania by using weaver ants to repel the fruit flies that are responsible for the commercial loss of 40% of their crop. The system works well in Australia, for example, and could improve the size and quality of the Tanzanian harvest, with the potential to increase market volumes and prices. The research will discover the farmer’s perception of weaver ants and their interest in keeping them for biological control. Those farmers with strong interests will be invited to participate in a field study to see how many ants are needed to give sufficient protection of the mangoes and what other, practical issues are involved. The study will involve Sokoine Agricultural University and, with their help, a Field School organised by farmers will be established. Here they will be able to learn how to conduct their own studies and gather practical knowledge about weaver ants and the fruit fly problem. The Field School will be encouraged to produce an information leaflet for their communities and to develop training materials, and Sokoine and Copenhagen Universities will develop these into a computer/internet-based training resource.

Outputs

Project completion report:

This study investigated the effectiveness of weaver ants in protecting mangoes from fruit flies. The study was carried out on the local mango variety ‘Dodo’ grown by small scale farmers in Tanzania.

The farmers did not believe weaver ants had any effect on the fruit fly infestation level, and small observation studies supported the farmers’ view.

Broadly speaking fruit flies were a problem for those farmers who harvested their mangoes at a ripe stage, while those who harvested at a premature or mature stage did not lose many fruits.

When premature and mature mangoes were to be sold on bigger markerts, they were packed tightly in baskets. The heat produced by the packed, ripening mangoes increased to levels that killed the fruit fly eggs/larvae. Hence, the way the mangoes were packed helped to reduce the fruit fly infestation level. Increasing the weaver ant population in an attempt to control the fruit flies can therefore seem unnecessary.

Some of the volatile compounds collected from mangoes with weaver ants may explain why weaver ants have a deterrent effect on fruit flies, but more research is needed to answer this question.