An 8 kilometre swarm of desert locusts laying eggs in provinces north and east of the Mauritanian capital Nouakchott has raised fears of a major locust invasion at the height of the growing season, but the United Nations said on Wednesday the situation is under control.

Just a small swarm of locusts can eat as much food in a day as 2,500 people.

The locusts were first spotted in Inchiri, a remote province 250km northwest of Nouakchott last week. On Wednesday, the UN's Food and Agriculture Organisation (FAO) said the fast-moving swarm had moved south and east and was around 150km northeast of the capital.

According to the National Locust Centre of Mauritania, the locusts are currently in the mating stage and have been laying eggs, with hatchings expected to occur in the next 10 days.

“These first stages seem to indicate that these are locusts similar to those observed since the beginning of the year in different areas. We believe that they are a native species,” Mohamed Abdalahi Ould Babah, director at the centre, said.

There is concern in Mauritania that this new batch of locusts will continue to spread. Vegetation is flourishing as the normally desert-country bristles with maize and sorghum crops at the end of a strong growing season. The affected zone has high levels of humidity which encourages locust breeding, experts said.

The FAO said in a statement on Wednesday that the infestations come from undetected breeding that occurred during the past two months in either Mauritania or northwest Mali.

Three units of ground treatment and nine canvassing teams have been deployed, including five to the affected region, which is considered an area of prime grazing land for cattle breeders. So far, more than 200 hectares of infested land have been treated.

“A military plane has also been mobilised but at the moment the area requiring treatment is not large enough to warrant its use,” said Ould Babah.

The Food and Agricultural Organisation (FAO) is sending a helicopter to help survey larger areas that are difficult to reach by land.

“Adjacent countries have been alerted,” said Wen Mullier of FAO in West Africa. Survey teams will be monitoring Senegal, Mali, Niger, and the southern parts of Morocco and Algeria, which all could potentially be affected.

The FAO said it will use the situation to do field trials of a bio-pesticide called Green Muscle, and it expects current resources to be sufficient to control the infestations.

A major outbreak of locusts in West Africa in 2004 stripped agricultural land throughout the desperately poor region at the height of the harvest season, leaving many of the region’s subsistence farmers with nothing to eat for the year ahead.

Since January 2005, few locusts have been sighted in Mauritania and only a few hundred hectares of land have been treated.