"Widespread laying, hatching and band formation are in progress in the spring breeding areas south of the Atlas Mountains in Morocco and Algeria," said Keith Cressman, FAO Locust Information Officer.

"This is the most serious locust situation in the region for ten years," he added.

The citrus crops grown in Morocco and exported to Europe and North America, with an estimated value of $400 million, could be at risk in the coming months.

"There are also large locust populations in northern Mauritania and some in Niger as well," Cressman said.

"It is very difficult to find and treat all of the desert locust infestations because many of them are scattered in remote areas," Cressman said. "This is further compounded by insufficient resources being available in Mauritania and Niger, and a rapid drying up of funds in other countries."

So far in April, nearly 200 000 hectares of locust infestations have been treated in Morocco. In Algeria, locust control operations are under way against swarms that laid eggs in a broad swath of the country from its borders with Morocco in the west and with Tunisia in the east.

Swarms move across Northwest Africa

In early April, some swarms moved from Morocco across Algeria into western Libya, where around 3 700 hectares have been treated. Similar infestations may be present in southern Tunisia, FAO said.

In Mauritania, new swarms are forming in the north where date palms, sorghum and oat crops have been damaged. Control operations are hampered by limited resources; only 10 800 hectares have been treated so far this month.

The situation is now less serious in northern Sudan and on the Red Sea Coast in Saudi Arabia, following extensive control operations between December and March, when about 200 000 hectares of infestations were treated.

More than $17 million have been spent since October 2003 on locust control operations that have treated nearly 1.4 million hectares. Most of this money was provided from national budgets within the affected countries.

FAO has contributed an emergency project to Mauritania and Morocco to the value of $800 000.

FAO Director-General Dr Jacques Diouf has recently decided to more than double FAO's contribution, providing assistance additionally to Algeria, Chad, Mali, Niger and Sudan.

Donors such as the European Commission, Italy, Norway, Spain and the United States have contributed more than $5 million so far.

Morocco and Algeria have assisted Mali, Mauritania and Niger with pesticides, vehicles, equipment and experts, and Saudi Arabia has provided substantial support to Sudan.

$17 million needed

An additional $17 million is needed to continue the current campaign during the spring and extend it to breeding areas in the Sahel in West Africa during the summer, FAO said.

The last desert locust plague, in 1987-1989, took several years and more than $300 million before it was brought to an end.

Crop damage has been reported on pasture, date palm, cereal and vegetation crops in most of the countries, affecting local farmers and nomads.

A locust upsurge of such a dimension can only be controlled by using insecticides, the UN agency said. FAO is applying best practice methods to reduce risks to health and the environment.

At the same time, FAO is promoting increased use of environmentally friendly biological control.