How to control mango fruit flies

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In East Africa, damage from fruit flies has been reported to range between 40 - 80 % since the invasion by one of the most destructive mango pests – Bactrocera dorsalis. This fruit fly species is the dominant pest in lowland areas such as Keiyo South in Elgeyo Marakwet.

The pest is also known to attack over 40 unrelated fruits which include oranges, tomatoes, bananas, guava, custard apple and avocadoes.

Other fruit fly species of economic importance are the Ceratitis Cosyra, C. rosa, Ceratitis anonae, C. and C. fasciverantris - these pests also attack other cultivated and wild fruits. The female fruit fly lays its eggs under the skin of the mango fruit. The eggs hatch into whitish maggots that feed on the decaying fruit, which cause rotting and great damage to the fruits, resulting in great losses to farmers. Farmers can control fruit flies through the following Integrated Pest Management (IPM) methods:

Food baits: The food bait attracts the fruit flies from a distance to the spot of application where the flies feed on the food bait which contains a “soft” pesticide. They die when they eat the bait, killing them before they infest the fruits. The bait is applied to a localized 1 m² spot on the fruit tree canopy using CP 15 knapsack sprayer when the mango fruits are about golf ball size (about 4cm in diameter). This application should be continued until fruit harvesting is completed.

Fruitfly trap, with bait inside the trap

Commercial baits in the market include NuLure®, Buminal, GF-120®, Solbait, Biolure®, Torula yeast®, Hymlure® - these can be mixed with biopesticides such as spinosad and applied as explained above. GF120® is already mixed with spinosad.

Traps baited with such food baits capture both females and males of several species of fruit flies. Apart from Biolure, which is replaced every four weeks, all the other food attractants are renewed every 7 days. However, because these baits are expensive and not readily available, ICIPE is in collaboration with a private partner in Kenya to fast-track the production of local bait (Dudulure®) as an alternative source that is equally effective and can replace the more expensive products in the markets. This food bait will be made easily accessible to all farmers at much lower and reasonable prizes for the local farmers.

Soil inoculation: Research at ICIPE has identified a potent fungal isolate (Metarhizium anisopliae) that is effective against adult or the pupa and larval stages of major fruit fly species that are of native and of exotic origin. During the developmental cycle of fruit fly, the mature larvae leave the fruit and drop to the ground where they burrow into the soil and form resting stage called puparia. An important part of fruit fly suppression includes soil treatment with these fungal pathogen to kill the maggots and puparia in the soil. The fungus is formulated into granules, which can be dispersed by hand and then raked into the soil while oil-based formulation is applied using a knapsack sprayer. Both formulations are effective and only one application is required on the ground below the mango canopy. Application is usually done at the onset of fruiting and can persist in the soil for over a year.

Orchard sanitation: Orchard sanitation involves the collection and destruction of all fruit fly infested mangoes found on the trees and fallen ones on the ground to significantly reduce fruit fly populations in the orchard. This should be done at least twice a week for the entire mango fruiting season. In this regard, the collected fruits should be destroyed or composted by dumping them in an Augmentorium rather than burning or burying deep in the soil or putting them into plastic bags to kill the fruit fly maggots.

The Augmentorium is a tent-like screen structure that is designed to retain fruit flies (while allowing their parasitoids to leave or enter the structure).

Augmentoria can be easily constructed by farmers. It serves the double purpose of field sanitation and conservation of natural enemies of fruit flies. The tent is designed in such a way that it is able to confine all the fruit flies that emerge from the fallen rotten fruits that are collected from the field and deposited in the structure, while at the same time conserving their natural enemies by allowing the parasitoids to escape from the tent through a fine mesh at the top of the tent.

Biological control is the use of beneficial insects like parasitoids whose immature life stages develop within the fruit fly host (pest), ultimately killing the fruit fly before they emerge. They are also referred to as “farmers’ friends” and help to reduce the damage caused by fruit flies. One of the most outstanding successes against fruit flies is attributed to the use of the egg parasitoid, Fopius arisanus against Bactrocera dorsalis. It attacks the eggs of the fruit fly in the fruits and develops through the larval stages of the fruit fly and emerges as an adult parasitoid in the pupa of the fruit flies. This parasitoid is presently being released for free in major mango growing zones in Kenya and Africa at large.

Another important parasitoid that is being released alongside with F. arisanus in Kenya and other African countries is a solitary larval-pupal parasitoid called Diachasmimorpha longicaudata. Both parasitoids are now established in most areas of Kenya or other countries where they have been introduced.

Male annihilation technique

(MAT): This involves the use fruit fly traps particularly Lynfield traps consisting of a male attractant (methyl eugenol) combined with an insecticide, which are distributed at regular intervals over a wide area in the mango orchard to reduce the male fruit fly populations to low levels that mating does not occur or reduced to low levels. MAT is currently being promoted by ICIPE as a component of the IPM Strategy for fruit flies. Male attractants such as methyl eugenol, cuelure, vertlure and terpinyl acetate can be used with appropriate toxicant such as Mimbecidine® spinosad and deployed in the orchards. The traps should be serviced after every 6 – 8 weeks.

Fruit protection: Fruit protection involves wrapping, bagging or sleeving of individual fruits or bunches of fruits with plastic or paper bags to prevent adult fruit flies from laying eggs on the fruits. The fruits must be wrapped well before fruit fly attack at least one month before harvest. The method is effective especially if used to protect fruits meant for export or home use.

>>Tell us how useful this information is to your farming enterprise. Share your experience by email to admin@theorganicfarmer.org,  leave a comment below this article.

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