Kenya has released imported wasps to fight the invader fruit fly paving the way for the lifting of a ban that was imposed on avocado exports three years ago.

Scientists have been conducting research on the predator insects that were imported from the US in 2006, and last week, the country finally embarked on a concerted war against the pest that has cost  more than Ksh3 billion ($33.4 million) in export earnings since South Africa shut its doors on avocado imports in 2008.

The all-out war  was waged  with the release of the two wasps, scientifically known as B. invadens from Hawaii - Fopius arisanus which attacks eggs and Diachasmimorpha longicaudata which attacks larvae.

The wasps were let loose with government permission by scientists from the International Centre for Insect Physiology and Ecology (ICIPE) in the coast region, the first in a series of such releases in key fruit growing regions.

According to head of horticulture at ICIPE Dr Sunday Ekesi, who doubles as the principal scientist and programme leader of the African Fruitfly Programme based in Nairobi, the historical event signifies the first importation of the parasitoids in Africa, whose success will see the programme replicated all over the continent.

The wasps that are natural enemies help in controlling infestation by laying their eggs in the body of the target insect, which is then used as food for the developing larvae, eventually destroying it.

After successful experiment on eco-safety in Magadi, the researchers have done mass laboratory production and rearing of these parasitoids that were released in Kilifi at a well attended ceremony witnessed by scientists from ICIPE, agriculture ministry, farmers and other interested parties.

Considering that the natural enemies have a capacity to eliminate parasitism by 40 per cent, other methods that were also unveiled will be employed in tandem.

These include a cocktail of special traps, biological pesticides and sanitation to achieve an acceptable level of control of the pest Bactocera dorsalis, that is reported to have been introduced on the continent from Sri Lanka in 2003, spreading with reckless abandon due to lack of a natural predator.

Scientists in insect science – called entomologists — have been studying the lifecycle of the fruit fly in order to understand how to control it with methods suitable to the African environment. Research indicates that the mature female lays eggs on the fruit after piercing the skin. The eggs hatch into maggots and start feeding on the fruit, which rots and falls off. Once on the ground, the maggots develop cocoons and hibernate in the soil, hatch and attack mangoes, bananas, oranges and the cycle continues.

Alternative method

To beef up the imported natural predators, scientists are now recommending that farmers use poisoned protein baits as the best method. Females need proteins to lay eggs that hatch and are easily attracted to it from a distance and killed by the insecticide. The baits are placed at a spot on the canopy or set on the tree trunk of each tree in the orchard. The traps can be made locally from yellow plastic cans, that are poked and the bait such as Mazofern is spread. The trap is replenished weekly. Insects are naturally attracted to colour yellow.

Developed alongside the female magnet is a male version. A local firm, Farm Consult has developed wicks that only attract the males. The wicks are laced with  methyl euginol mixed with an insecticide called Malathion and works the same way. Elimination of males leads to the laying of infertile eggs drastically reducing the pest population.

 “For best results apply both methods to kill male and female insects,” said Dr Ekesi.