Nopales, Known as Prickly Pear, Under Attack From an Argentinean Invader

In this Feb. 16, 2011 photo, a cactus moth larva crawls across the tip of a machete that was used to cut open a prickly pear cactus on the bank of Cactus Canal in Jefferson Parish, La. The moth's larvae infest prickly pear cacti, and officials are trying to prevent them from spreading further west to Texas, where the infestation could explode. (AP Photo/Patrick Semansky)

Recently, federal agricultural workers carrying blow torches moved slowly down the bank of an old oil canal, burning every prickly pear they came across. They were hoping to kill off a pest that's been on a tear across the Gulf Coast and is moving West.

Cactoblastis cactorum, a tan-colored moth from Argentina, has been moving steadily across the Gulf Coast for the past decade. The moth lays its eggs in prickly pear cacti, which its larvae then infest. They'll eat through the pads of the fruit-bearing plant worth hundreds of millions of dollars because of its use in Mexican cooking.

Cactus Canal now marks the western boundary of the moth's new habitat, and federal workers hope to stop it before it gets to Texas and the abundant food supply causes the population to explode.

"This is our line in the sand, so to speak," says Joe Bravata, an invasive species specialist with the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, or APHIS.

The cactus burning on the remote canal dug more than a half century ago by oilmen in the far-flung Louisiana marsh has support from the U.S. and Mexico. Both countries are contributing about $500,000 a year to kill the moths and save the prickly pear. The cactus is so important in Mexico, it's on the middle of the national flag under the eagle. Known as nopales, prickly pear is farmed on about 205,000 acres in Mexico with a harvest worth about $160 million.

California's harvest, the biggest in the U.S., is worth $24 million a year.

The cactus also has ecological significance. Quails and snakes find cover in prickly pear, as do fungi, reptiles and birds that eat the plant. A good portion of a white-tail deer's diet depends on the cactus, and coyotes and foxes, in bad times, will eat it too.

The moth is seen as a major threat. It arrived at the tip of Florida in the 1980s from the Caribbean and traveled up to the Florida Panhandle and across Alabama and Mississippi. In 2009, it was spotted in Louisiana.

"If nothing's done, we don't think it will take long for it to get to Texas and then into Mexico," said Rebeca Gutierrez, the cactus moth program manager with Senasica, a pest-control agency that's part of the Mexican government. "This pest has shown that it is spreading really fast."

There's concern the moth could wreak havoc on Mexico's prickly pear farms and wild plant populations. The country has launched a public education campaign, with flyers and highway billboards warning about the danger.

"Every state in Mexico is covered in opuntia (prickly pear) species," Gutierrez said. "If it gets to the country, and we can't find it in time, we don't know what the exact damage it could cause will be."

To stop the spread, the USDA has been running crews and scientists out to patches of infested marsh in Louisiana for about a year to scorch prickly pear down to the roots. There aren't a lot of the cacti in Louisiana, but scientists say it's just enough to allow the moth to hopscotch to Texas unless it's stopped.

The recent work in the canal in Jefferson Parish, about 25 miles south of New Orleans, was timed to get the pest before the adult moths take flight in search of new nesting spots in spring. A female lays up to 120 eggs at the base of prickly pears, and the larvae then drill a hole into the pad and begin munching.

Bravata used a machete to chop at underbrush as he clambered over fallen trees and clumps of marsh and berry bushes. Crossing the canal, he spotted a cactus with brownish ooze on the pads. It's the tell-tale sign: larva excrement.

"You see how they have hollowed this cactus out," he said, holding a sliced-open pad in his hand. "If you look in there, there is no meat left."

In the middle of such a vast wilderness, killing the cactus — and thereby the moth — is hard work.

"Very labor intensive, very time consuming," Bravata said. "We'll have to come back many times to catch the little pads that are sprouting."

But it's important in stopping the pest's advance. Mexico beat back the moth when it was found off the coast of Cancun in 2007. The hope is the same will happen here.

Barron Rector, a range ecologist at Texas A&M University, is part of a team setting traps for the moth. It hasn't been found anywhere west of Cactus Canal, he said, and for now the blockade seems to be working.

"It's marched through Florida, through the Panhandle, and now we're going to stop it here," Bravata declared. "We're moving east. That's the whole point of the program."

Based on reporting by The Associated Press.

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