Swarms of locusts in north Africa could be on the verge of threatening crops further south, the UN has warned.
Swarms can devour fields of crops in a few minutes
Winds could sweep breeding locusts in Morocco, Algeria, Libya and Tunisia southwards to countries in the Sahel.
Chad, Mali, Mauritania, Niger and Senegal would then risk losing some of their harvests, according to the Food and Agriculture Organization (FAO).
"If there are good rains we could be in a plague condition by the end of the year," FAO's Clive Elliott said.
The Rome-based organisation urged the countries at risk to prepare against possible locust invasion.
It appealed for the funds needed to buy the sprayers, vehicles, pesticides and training needed to contain the outbreak.
Race against time
"If you don't deal with locusts early, the problem gets worse. The last plague cost donors $300 million dollars," Mr Elliott told BBC News Online.
FAO says it has received less than $4m of the $17m needed.
The current desert locust outbreak began last October.
Already two million hectares of land have been treated against the insect.
But small swarms have started forming in northern Mauritania, damaging millet, sorghum, date palms and vegetable crops.
If a plague were to break out, the impact would be much graver with a total of $2bn dollars worth of maize, sorghum, millet and wheat at risk of being destroyed.
The locusts could start breeding in as little as two weeks' time, the FAO says.
"Control teams are doing their best, but it is a race against time," Mr Elliott said.
Normally solitary insects, desert locusts can rapidly increase in number when climatic conditions are favourable.
When they group, the young, wingless locusts - known as hoppers - march together in search of food.
As adult, winged insects they form swarms that can travel in tens of millions and cover great distances, crossing international borders in search of food.
A major locust plague in 1987 to 1989 originated in western Sudan and spread as far as India.