Migration of moths presenting a prickly situation.(Knight Ridder Newspapers)

MIAMI _ In Florida, where chain saws and homeowners howl in the rancorous war to control citrus canker, few people have paid much notice to a small bug with a big appetite for spiny plants.

But scientists who have watched the cactus moth munch its way north from the Florida Keys, where it was first found more than a decade ago, warn that the obscure insect now deserves immediate attention _ as in a good dose of sterilizing radiation.

Left unchecked, they fear the moth will move from merely menacing rare Florida species toward the Southwestern United States and Mexico, where cacti are as common as citrus used to be in South Florida backyards and, in some rural regions at least, a food staple of daily life.

''It appears to be spreading much more rapidly than some of the earlier estimates had been predicting,'' said James Carpenter, a researcher with the U.S. Department of Agriculture and co-author of a paper scheduled to be published this month in the scientific journal The Florida Entomologist. ``If …