Farmers using weaver ants to control fruit flies in Southern Tanzania have recorded increased yields and income.
Weaver ants are tiny ants that belong to a group of beneficial insects on the farm that can be called ‘Friends of the Farmer’. Since time immemorial, nature has created a balance between all living organisms. This balance ensured that harmful pests and diseases were controlled naturally by beneficial insects which acted as predators of the harmful pests (for instance the fruit flies), reducing their multiplication and damage to crops and the environment.
Weaver ants are social insects, which live in colonies on selected trees. They prefer to live in cashew nut, mango and cotton plantations. When their numbers increase, they often divide themselves and inhabit new trees on the farm; this is one reason why they are useful to the farmer.
Weaver ants live in nests in trees. They built them using broad leaves, which they pull, and glue together using a sticky substance obtained from their bodies. Like colonies of bees and other insects, each weaver ant colony has one or more queens whose duty is to lay eggs and produce more ants. Weaver ants in the colony are divided and given different roles; there are worker ants, food gatherers, and even soldiers who provide security to the colony. The main food for weaver ants are other insects such as fruit flies that live in the same trees, or honeydew, produced by other insects in the trees they inhabit.
Good bio-control agents
Weaver ants are small in size, but they are very tough fighters and can ward off any intruders or harmful insects that attack their colony. They are hardworking and will be seen moving from up and down trees carrying loads of food, some bigger that their own size, to feed the colony. The ants usually communicate through a unique scent (or pheromones), which elicits an immediate reaction from all ants in the entire colony to offer defense or undertake a particular task.
They help reduce pest levels
Weaver ants consume a large amount of food, and workers continuously kill a variety of insects for this purpose. Because weaver ants prey on harmful plant pests, any plant inhabited by weaver ants has low pest levels. Weaver ants have proved to be effective bio-control agents against agricultural pests especially in horticultural crops such as mango and cashew nut plantations. Fruit trees harbouring weaver ants produce higher quality fruits, they have less leave damage – making it unnecessary to use expensive and harmful chemical pesticides.
To encourage weaver ants to do their work, farmers tie ropes between mango trees and orchards to facilitate the movements of ants to unoccupied trees. In some countries in South East Asia, weaver ants are provided with food to promote their fast growth and to discourage them from moving away.
Organic mangoes and cashew nuts
In Tanzania, cashew nut farmers using weaver ants to control fruit flies have managed to increase their cashew nut production by up to 75 per cent. Since the farmers do not use chemicals, the cashew nuts they produce are sold as organic, which fetches a higher price in the international markets compared to conventionally produced cashew nut that use chemicals to control fruit flies and other pests.
More income for farmers
For example, 1 kg of cashew nut that is grown organically is selling at Ksh 97 while the ones grown using chemicals to control fruit flies are sold at Ksh 83 per kg. From this it is easier to see the benefits organic producers stand to gain from using a less costly and an environmentally friendly production method.
Access to credit for farmers
In Tanzania farmers groups that have embraced organic methods in cashew nut production can benefit from credit schemes funded by the Swiss Development Corporation (SDC). The project is being implemented in Masasi region in Mtwara province, Tanzania. In order to protect the weaver ants and other beneficial insects in cashew nut plantations, farmers are advised to stick to the following guidelines:
• No chemical are used in their plantations.
• Crop residue is recycled and not burnt.
• Farmers are encouraged to facilitate the movement of weaver ants from one tree to the next using bridge ropes.
• Barriers are placed at the base of the cashew nut trees to stop predators from attacking weaver ant nests.
• Since weaver ants can only prevent fruit flies in cashew nut and coconut trees, farmers are advised to survey their plantation regularly to ensure they able to identify diseases and other pests and to use plant extracts and other bio-pesticides to control these diseases and pests.
This article is a translation of a text published in our sister magazine, Mkulima Mbunifu, which is distributed in Tanzania.