parasitic wasps introduced to save orchards from fruit flies

More than four-fifths of Kenyan mango harvests are lost to the African Fruit Fly. But a group of agricultural organisations now promise a doubling of yields on the introduction of a parasitic wasp from Hawaii that eats the flies before they mature.

The wasp, brought to Kenya by the International Centre for Plant and Physiology and Ecology (ICIPE), Agricultural Ministry and Kenya Agricultural Research Institute (KARI), is more than twice as effective as pesticides in curbing fruit fly damage, the organizations claim.

Already the parasitic wasp’s effectiveness is being tried in Ngurumani area in Rift Valley. “Per hectare 1500 wasps are enough,” said Dr Sunday Ekesi of ICIPE and the initiative’s lead scientist.

In the coming month, Dr Ekesi foresees the parasitic wasp being available for farmers to get it from ICIPE. Orchards that introduce the wasp stand to get 10 tonnes per hectare compared to orchards that use pesticides to control the fruit fly as per Dr Ekesi.

According to him, orchards that introduce the wasp deliver yields of around 10 tonnes a hectare compared with 4 tonnes a hectare when pesticides are used. Kenya has around 16000 hectares of mango plantations spread across the country.

Farmers can get the Fopius Arisanus wasps from ICIPE, and only need to introduce them once. After that they breed themselves, so long as they are not killed by pesticides. The wasp attaches itself to the eggs of the fruit fly before they hatch to larva.

On hatching the wasp attacks the larva. It can destroy other parasites that attack other fruits besides mangoes like the Mango gall fly or mango mealy bug.  Red ants that seasonally live in fruit trees also deter fruit flies from attacking the trees.

ICIPE advises farmers to maintain hygiene in orchards to stop fruit flies thriving. “Fruits that fall into the ground and left to rot, host the fruit flies,” said Dr Ekesi. Such rotting fruits Dr Ekesi advise they be removed from the orchard.

Where wasps are already introduced in orchards Dr Ekesi advises against burying the rotting fruits as that would include the parasitic wasps. He rather advises them to place the rotting mangoes in a simple shed structure built of mesh with tiny holes of 1.1mm by 1.5 mm size. The miniature mesh holes allow the wasp after it eats up the fly, to fly out through the holes.

However the fruit fly has no chance of escape from the mesh structure.  “So it dies in there,” adds Dr Ekesi. A mesh of the aforementioned holes can be sourced in farming stores in Kenya. Per hectare Dr Ekesi advises two to three such structures be present.

The fruit fly is attracted to fruits to get protein. Mechanical techniques, such as wrapping the fruits or baiting the pests can also help reduce the problem. ICIPE claims that combining the wasps, good management and even mechanical techniques can end 80 per cent of the current damage to crops, and is a cheaper set of solutions than pesticides.

ICIPE according to Dr Ekesi is going to provide the wasps for free to farmers who require them. Of all other pests that attack orchards Dr Ekesi rates the fruit fly as the most destructive hence their efforts to have it controlled.

ICIPE can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it. or by telephone on: +254 (20) 8632000

Written By James Karuga for African Laughter

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