Scientists have rushed to southern Texas to thwart the nation's first invasion of "killer" bees across the Mexican border.

Officials on Wednesday slapped a quarantine on all bees in the area to keep the fierce Africanized "killer" bees from wiping out much of the domestically raised variety, which produces more honey and pollinates valuable crops.A swarm of the Africanized bees was trapped Monday near the border city of Hidalgo in the Lower Rio Grande Valley, said Anita Collins, head researcher with the U.S. Department of Agriculture's Honey Bee Research Lab in Weslaco.

The swarm was later confirmed to be killer bees, she said. To the unaided eye, they look like other honeybees; they must be identified under the microscope.

Scientists headed to the area to check for Africanized bees in all managed hives and to look for any other wild swarms, said John G. Thomas, extension entomologist with the Texas Agricultural Extension Service at College Station.

Africanized bees, hybrids descended from docile European bees and a vigorous African species, earned the "killer" nickname because of their highly defensive behavior.