Fluerne – eller mel-lus, som de hedder på dansk – spreder sig med stor hast og truer en af kontinentets vigtigste og mest klima-tolerante afgrøder, rodfugten cassava (maniok), som forskerne ellers håber vil skaffe mad på bordet for millioner.
JOHANNESBURG, 7 May 2013 (IRIN): A tiny, rapidly breeding cyanide-munching (cyankalium-fortærende) insect, dubbed a “super-fly” by scientists, is threatening the food security of millions of Africans.
The Bemisia tabaci – one of several whitefly (mel-lus) species – carries lethal (dødbringende) viruses that cause cassava brown streak disease (CBSD) and cassava mosaic disease (CMD), which have decimated the hardy cassava plant.
(NB: Cassava /maniok er stærkt giftig i rå tilstand bl.a. på grund af sit indhold af cyankalium – se https://en.wikipedia.org/wiki/Cassava)
Cassava, a tropical root crop, is the third most important source of calories in the tropics, after rice and maize.
According to the UN’s Food and Agriculture Organization (FAO), it is the staple food (grundnærings-middel) for nearly a billion people in 105 countries, where it comprises as much as a third of daily calories consumed.
The cheapest known source of starch (stivelse), cassava is grown by poor farmers – many of them women – often on for these people, the crop is vital for both food security and income generation.
The threat to cassava is particularly alarming as the plant is often called the “Rambo” root for its ability to withstand high temperatures and drought.
With climate change expected to take a major toll on maize in the coming decades, many hope cassava will offer an alternative route to food security in Africa. Cassava may also prove to be an important source of biofuel.
Experts took aim at the whitefly this week, at a conference of the Global Cassava Partnership for the 21st Century (GCP21), at the Rockefeller Foundation Bellagio Center in Italy – se http://ciat.cgiar.org/gcp21
The conference is dedicated to “declaring war on cassava viruses in Africa.”
Pandemics (store epidemier)
From the 1980s to the mid-2000s, CMD-disease ravaged more than 4 million square km in Africa’s cassava-growing heartland, stretching from Kenya and Tanzania in the East to Cameroon and the Central African Republic in the West.
But in recent years, the scientific community developed cassava varieties resistant to CMD.
James Legg, a leading cassava expert at the International Institute of Tropical Agriculture (IITA), who works out of Tanzania, told IRIN:
“The premature celebrations for this apparent victory were very soon squashed (knust), however, as sinister new reports were received of the occurrence and apparent spread of CBSD-disease in southern Uganda.”
Until then, scientists had assumed that the viruses causing CBSD could not spread at medium-to-high altitudes; the disease had previously only been reported in coastal areas of East Africa and the low-altitude areas around Lake Malawi.
“The spread recorded from Uganda instantly cast doubt of the validity of that earlier theory,” said Legg, adding:
“Worse still, the disease spread out from Uganda over following years, and into the neighbouring countries of Kenya, Tanzania, Burundi and Rwanda.”
Whiteflies have increased a hundredfold
CBSD is now a pandemic, threatening Nigeria, the world’s largest producer and consumer of cassava.
The cassava starch industry in Nigeria generates 5 billion US dollar (28,5 milliarder DKR) per year and employs millions of smallholder farmers (småbønder) and numerous small-scale processors.
Only in 2005 were scientists able to confirm that the whitefly responsible for spreading CMD was also responsible for spreading CBSD.
“With this realization, it became clear that the spread of these two disease pandemics was really only a consequence of the fact that East and Central Africa was experiencing a devastating outbreak of the whitefly that transmits both of them,” explained Legg.
He told IRIN that in the 1980s, researchers recorded an average of less than one fly per plant, but by the mid-1990s, the number of whiteflies had increased a hundredfold.
Arms race (kapløb med fluerne)
Læs videre på
http://www.irinnews.org/Report/97986/Super-fly-threatens-Rambo-cassava-food-security
Cyankalium er et hurtigt dræbende stof, som lammer åndedræts-organerne og bl.a. blev brugt i selvmordskapsler under Anden Verdenskrig.
