How to control fruit flies using pheromone traps

Farmers who attended the farmers show in Jinja last week got a chance to learn how they can fight fruit flies on their farms.

"Fruit flies must not continue attacking and destroying fruits because we have the means to handle them," says Judith Tukamushaba, from Gold Seed International, who exhibited the Pheromeno traps that are used to attract and kill the flies. 

A pheromone is a chemical an animal produces which changes the behaviour of another animal of the same species (animals include insects). Some describe pheromones as behaviour-altering agents.

Like many insects, male and female fruit flies find each other using smell. The female produces a pheromone when she wants to mate and lay eggs. Some plants mimic this smell by producing chemicals called parapheromones.

People cannot smell these chemicals, but male fruit flies are attracted to the smell and will fly towards it.

What are fruit flies?

Oriental fruit fly originates from Asia and has invaded various parts of Africa including Uganda and other tropical countries. According to farmers, this fly is a menacingly aggressive invader. According to scientists, the fly attacks several fruits.

These include mangoes, oranges, paw-paws, lemons, grapefruit, bananas, watermelon, plantain, tomato, guava, pepper, avocado, cucumber, pumpkins and many others. 

They attack all fruit keeping districts of the country, including Soroti, West-nile and Kasese.

If not tackled, an entire fruit harvest can be destroyed. For example, if a farmer has one acre with 300 mango trees, he would expect to harvest at least 100 bags of mangoes each of 100kg.

Each sack, during the peak season goes for around sh50,000, which means that a farm loses sh5m per acre. 

How damage is caused to fruits

Female flies lay eggs on flowers and fruits. Then eggs hatch into larvae that feeds on pulp of the fruit and then the larvae emits the bacteria that cause rotting of fruits. Infested fruits spoil quickly and often fall to the ground prior to ripening. 

Such is the damage caused by the flies to fruits are so big that none of the fruits can be taken to the market. In many cases, losses are 100%.

How the trap works

The trap uses sex attraction of male flies to attract them into a bottle. This may be an element/juice/oil squeezed out of crops like raspberry or ginger. This element is mixed with insecticide and applied to a suitable medium that may be cotton or sponge to allow for slow release of the hormones that selectively attract and kill the male flies.  

Steps for making the traps

• Cotton or sponge strips are treated with an element that attracts the flies. Treatment is done in a vacuum and cotton treated strips covered in air tight containers for 24 hours. You can use mineral water bottles, a bucket or a jerrycan that is clean. Two small holes opposite each other are made on the container.

• Using a nail, holes are made on bottom of container to allow water to drain out of the container when it rains. The treated strip is picked and suspended in a container using a copper wire or string. Suspension of the strip is above the openings to avoid wind blowing the strip. The trap is suspended on a tree branch. One acre of around 400 trees will require 15 traps.