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In Malawi, the battle to save mangoes

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DRIVING THE POINT HOME—A research assistant explains the approach used to trap the flies

Malawi, like other African fruit producers, is drawing on local and global resources to combat a pest which threatens vital fruit exports. CHARLES MKOKA followed this participatory research and now writes.

Mango farmers in Malawi, who have always considered the fruit to be a source of revenue when food is scarce, have declared war on the Bactrocera dorsalis fly which threatens their crops and livelihood.

The mango is one of the most important fruits in Malawi, and is a source of income and nutrition for many smallholders—vulnerable farmers holding small plots of land used to produce an export commodity as a main source of income. Women and youth are among the main beneficiaries as they are involved in the harvesting, and sale, of fresh mangoes from their homes, by the roadsides and at small markets, thereby improving household income.

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However, in recent years, many farmers have seen an increase in rotten mangoes and lost revenue due to what scientifically is called Bactrocera dorsalis, more commonly known as the fruit fly. According to the Centre for Agriculture Biosciences International (CABI), this is a highly invasive species native to Asia that is now found in at least sixty-five countries, including parts of America and Oceania, and most sub-Saharan African countries.

The potential risk of their introduction to a new area is caused by increasing international tourism and trade, and is influenced by changes in climate and land use.

In a bid to address the threat posed by fruit flies, researchers in Malawi, Mozambique, Zambia, and Zimbabwe are implementing the Alien invasive fruit flies in southern Africa project which calls for the implementation of a sustainable Integrated Pest Management (IPM) program to combat their spread.

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The project has received funding of C$ 2.8 ($2.2) million from the Canadian International Development Research Centre and the Australian International Food Security Research Centre, for the wide scale adoption of IPM interventions including combating fruit fly infestations.

The project kicked off in 2019 and will wrap up in September 2022.

Source of income, nutrition and export

In addition to the presence of wild mangoes that are managed by Malawian subsistence farmers, the demand for both fresh and dried mangoes in global markets helped create the right market conditions for the establishment of the first commercial mango farming company—Malawi Mangoes— in 2009. This is Malawi’s largest mango farming company and is based in the Lakeshore district of Salima about 110 kilometers east from the capital Lilongwe.

The company has set up the first large scale fruit processing facility in Malawi. Its proximity to Lake Malawi, Africa’s third largest lake, has helped the company to grow preferred grafted species of mangoes using technologies such as drip irrigation as part of the Green Belt Initiative, a government project to boost self-sustenance in food security.

Charles Leaper, Malawi Mangoes Chief Executive Officer, told The Cairo Review by phone that they now have 230 hectares of land using drip irrigation technology—an approach which conserves water and minimizes water waste. So far, they are exporting 100 tonnes of fresh mangoes and 240 tonnes of dried mangoes to the United Kingdom and the European Union.

“We have close to 5,000 farmers who are on contract farming with us. Our plan is to increase our area under cultivation to 350 hectares of land. As such, the combined harvests of our farmers who sell to us plus our own harvest will lead to us producing close to 800 tonnes of finished dried mangoes product for export,” Leaper said.

With such tonnage, his company hopes to export to India and Singapore, as well as to penetrate new markets in North America and Canada. Leaper said they are aware of the prevalence of fruit flies as a major threat to the mango business. However, with a fully-fledged agronomy unit, a branch of agriculture that grows crops, they have put stringent controls, such as nets, to trap the flies.

In a bid to address the widespread mango losses as a result of fruit flies, Malawi’s Department of Agriculture Research Services at Bvumbwe Station based in the southern district of Thyolo—with support from the International Centre of Insect Physiology and Ecology (ICIPE) a regional think tank on entomology research based in Nairobi, Kenya, — is working with farmers in Ntcheu and Lilongwe districts to contain the devastating effects of these pests.

The two districts are where wild mango trees are produced in large quantities. This is being done in hopes that extension staff can replicate these IPM interventions in other districts throughout the country.

The package includes various components of interventions such as baiting techniques, male annihilation, biopesticide application, orchard sanitation, and biological control using wasps called parasitoids, which attack fruit fly eggs and maggots.

Researchers have also extended a regional approach to the fruit fly Integrated Pest Management package, which has been adapted and promoted in the project’s target countries of Mozambique, Zambia and Zimbabwe which are close neighbours of Malawi.

Experts hope the proximity of these countries which share common borders and were once under a single federation (in the case of Malawi, Zimbabwe and Zambia) will help address the fruit fly challenge from a regional perspective.

They are also of the view that tackling the challenge in one country alone will only make the problem a challenge in another country as fruit flies do not respect international borders and territories.

Pheromones, known as Host Marking Pheromones (HMP), are used by insects to mark ‘hosts’ (usually a fruit), where they have already laid their eggs. These were evaluated in Kenya for their application and efficacy in deterring fruit flies of the same or different species from laying their eggs on host fruits, such as mango and guava.

The results, which are applicable to the target countries, indicate a seven to nine fold decrease in fruit infestation by three types of indigenous fruit flies in plots treated with HMP compared to controls. This information not only contributes to knowledge on the chemical ecology of fruit flies but indicates the potential for these pheromones to be incorporated within IPM fruit sprays. HMP thus widens the options for fruit fly management through integrated pest management.

Mass rearing of parasitoids

Colonies of two parasitoid species have been boosted by the ICIPE based in Nairobi, Kenya—the third largest exporter of mangoes in Africa. The laboratory has a capacity to produce approximately 25,000 wasps per month— sufficient to supply all target countries. However, Zambia has yet to upgrade its national laboratories in order to rear and multiply the wasp species and still needs to obtain an import permit to receive the parasitoid shipments from ICIPE. Malawi and Mozambique have upgraded their facilities in readiness of receiving the parasitoids and are now awaiting processing of the import permits and required phytosanitary certificates. Parasitoids have already been shipped to Zimbabwe where project staff have started rearing insects at a small scale but aim to be able to supply farmers with 1,500 wasps per hectare.

Male annihilation

One other technique is male annihilation. This is the mass killing of male fruit flies in an area. The males are killed in mass by setting traps containing a parapheromone which attracts the fruit flies but also contains a killing agent which exterminates them when trapped. The technique works in a way that when many male fruit flies are killed in the environment, many females lay eggs which are not fertile and consequently the population of the pests reduces over time.

Since mango is important in these countries and fruit flies are constraining its production and utilization, the combined use of all these techniques as part of fruit fly management will enhance the incomes and nutrition of farmers, entrepreneurs and commercial growers through increased production and consumption.

What comes next

When asked about the possibility for extension after 2022, ICIPE postdoctoral fellow Shepard Ndlela explained that, like any other donor-funded project, the Alien invasive fruit flies project in southern Africa will come to an end next September. The governments of Malawi, Zambia, Zimbabwe, Mozambique are expected to extend activities beyond the project implementation phase.

Hundreds of extension officers have been trained in fruit fly IPM, model farmers have also trained to be a source of information including Masters and PhD students. Thousands of women also trained through gender transformative actions, he added.

“We are building the capacity of these countries so that extension officers can incorporate what has been learned into their day to day activities with farmers,” Ndlela told The Cairo Review from Nairobi.

“We have made great strides in the other countries where thousands are now using the fruit fly IPM package.”

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