Weaver ant shows promise in bio-control of fruit flies

A tropical ant commonly found in Africa, Asia and Australia could save Africa up to 60 percent of its high value crops such as fruits and nuts that are otherwise consistently ravaged by fruit flies. Africa’s small-holder fruit producers evade fruit fly infestation by harvesting fruit before it matures, but they still incur significant losses from fruit fly damage, newly published research reveals.

Use of the weaver ant, Oecophylla longinoda, to control fruit fly infestations is expected to challenge and radically redefine classical methods of biological control of pests. Classical pest bio-control has traditionally focused on the use of parasitic insects – parasitoids - which reside in very specific crop pests attacking only particular life stages of their hosts, according to Dr. Paul Van Mele, a specialist at the Africa Rice Centre, Benin.

“The role of predatory ants in sustaining agricultural systems is an under-explored research area yet small-scale farmers in countries such as Vietnam, India and Cuba have generated considerable knowledge on natural pest control that may be applicable to the African context,” Van Mele says. “These ants are a gift of nature.”

While the weaver ants exist in abundance in Africa, their use is still at the experimental stage in many countries. Scientists say the ants have proven effective for fruit fly control, and they can be used for controlling pests in most perennial crops except coffee. In Ghana, the ants are being used together with neem tree extracts to produce organic cocoa. Tanzania uses them to improve their coconut harvests, while various African countries use them to safeguard cashew nuts and mangoes.

Weaver ants are better than various parasitoids currently in place which only attack specific species of the fruit fly, necessitating development of numerous species-specific parasitoids, each of which takes ten years or more to develop and release. The readily-available weaver ant is indiscriminate in its predation on fruit flies and is active throughout the year. Weaver ants may completely eliminate the need for pesticides - which are expensive and inaccessible to most African farmers. This will make organic fruit farming in Africa more profitable.

Fruit flies damage an estimated 40 percent of Africa’s annual two million tonnes production of mangoes – one of Africa’s most important sources of vitamin A. This led the USA to ban on mango exports from West Africa, says Van Mele. Most small-scale farmers cannot afford pesticides and are impeded in their pest control efforts by the height of mango trees. The few that implement some form of control try to evade fruit fly infestation by picking fruits before they mature, but this method does not deter fruit fly attack once the fruits are ripe.

CGIAR