As the planet heats up, growing pest numbers threaten Kenya's lucrative mango, avocado and other fruit crops
By Caroline Wambui
KIRWIRE VILLAGE, Kenya, April 12 (Thomson Reuters Foundation) - Gideon Gitonga inspected his avocado orchard in central Kenya with military precision, revealing that some of the fruit were tinged with a worryingly familiar yellow colour.
Yet again, it was the same culprits attacking his crop on the farm in Kirwire village in Meru County: fruit flies.
"Most of the fruits you see with a ripening colour are not ripe," he said. "(They) have been punctured by fruit flies and are in the process of rotting and eventually falling off."
As the planet's climate heats up, rising temperatures have driven a massive increase in Kenya's fruit fly population, say agricultural experts.
Farmers in fruit fly-infested areas are losing on average up to half their crops each year to the tiny pests, said Onesmus Mwaura, a research assistant at the Nairobi-based International Centre of Insect Physiology and Ecology (ICIPE).
Fruit-fly damage costs farmers an estimated 50 billion Kenyan shillings ($472 million) every year, according to the government's Horticultural Crops Directorate.
The fruit fly population in Gitonga's two-acre (0.8-hectare) orchard was "minimal" when he first started commercial avocado farming eight years ago.
It has since turned into an infestation, destroying up to three-quarters of his crop each year since 2017, he said.
Even when the affected avocados survive, their quality is so degraded it is difficult to find anyone willing to buy them.
"The damage by the fruit flies is quite devastating," Gitonga told the Thomson Reuters Foundation.
HEAT-LOVING PESTS
Paul Thiuki, an agricultural extension officer who has been working in Meru for 20 years, said the region's warming climate has turned it into a perfect breeding ground for fruit flies.
Average temperatures in Kenya have risen by 0.3 degrees Celsius (0.54 degrees Fahrenheit) per decade since 1985, according to the U.S. development agency USAID.
In 2011, when farmers in Meru first started noticing more fruit flies, the county's central ward had about 10,000 of the insects - a manageable number at the time, Thiuki said.
ICIPE researchers calculate the number of fruit flies by laying monitoring traps, counting how many are caught after two months, and then extrapolating the figure for the whole area.
Mwaura said warmer weather speeds up a fruit fly's development, giving it more time as an adult to lay eggs and produce more offspring.
"The body activity increases with the rise in temperature, hence feeding and reproduction is highly increased, leading to population build-up," Mwaura explained in an email interview.
Higher temperatures also cause fruit to ripen faster and release more of the compound that attracts fruit flies, encouraging their feeding and egg-laying, he added.
Adult flies burrow into the fruit's flesh to lay their eggs, introducing bacteria that causes the fruit to rot. When the eggs hatch, the larvae eat the fruit from the inside out.
An adult fly can lay between 100 and 500 eggs in its lifetime, Mwaura explained.
"Fruit flies (are) denying farmers a chance to generate any substantial income," he said.
Every year, the country's farmers see "a surge" in the number of fruit flies, said Johnson Nkanata Mwongera, chairman of Avocado Champions, a fruit-growers' association.
"We attribute (it) to the warming climate, as even in the tea-growing regions which were considered a bit cold and (therefore) would be free from the attack are now fruit fly-infested," he added.
EXPORT BAN
When fruit flies first started multiplying dramatically around Kenya, the insects were only attacking mango trees, said Benald Kinoti, an officer with Meru's ministry of agriculture.
Then most households grew mangoes for their own consumption and to sell locally, so the fruit was plentiful, he explained.
But when people started cutting down mango trees to meet growing demand for firewood and charcoal, the flies started looking for new soft-tissue fruits to infest, including avocados, bananas and tomatoes.
Over the past decade, non-profits working with the ICIPE have introduced measures to help farmers protect their crops.
They include releasing parasitic wasps that lay their eggs on fruit-fly eggs, thereby destroying the pests, as well as using traps and biological pesticides.
But those measures have not been enough.
In 2014, the Kenya Plant Health Inspectorate Service (KEPHIS) imposed a ban on the export of home-grown mangoes to lucrative markets such as the European Union and the United States due to the high levels of fruit flies in the shipments.
Desperate to find a solution, many small-scale farmers turned to synthetic pesticides, said extension officer Thiuki.
But, besides being potentially harmful to human health and the environment, synthetic pesticides kill the fruit flies' natural predators, such as bees, ants and parasitic wasps, allowing the fly population to skyrocket, he noted.
BAGGING AND TRAPPING
With the chemical option failing, some farmers are now experimenting with pest control methods that are cheaper, safer and more environmentally friendly.
They include covering the fruit with plastic bags to keep insects out, collecting fallen fruit promptly and treating the soil regularly with organic pesticide.
Farmers also try to pick their fruit as soon as it is ripe to shorten the time it can attract fruit flies.
Augustus Kivi, a plant health officer at KEPHIS, said the organisation is encouraging farmers to use a combination of methods, including pheromone-based fruit fly traps.
At the start of this year, Gitonga installed such traps in his avocado orchard.
He also killed the maggots in infested avocados by burying the fruit at least 2 feet (0.6 m) deep or putting them in plastic bags and leaving them in the sun for a few days.
He also disinfected the ground with organic pesticide to target maggots that might be pupating in the soil.
"At the end of January, (the traps) were full of pests, indicating the massive infestation that gave me sleepless nights," he said.
But in the past two months, he has noticed a drop in the trap levels, giving him hope that close to 90% of this season's harvest will be saved.
"Avocado is a super-fruit to me," he said.
($1 = 106.0000 Kenyan shillings)
Read more:
As fruit trees fall, a hunger threat looms in Kenya
Farmers adapt to climate change
(Reporting by Caroline Wambui; Editing by Jumana Farouky and Megan Rowling. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers the lives of people around the world who struggle to live freely or fairly. Visit http://news.trust.org)
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