Image: Scientist checks cactus for deadly moth
Phil Coale  /  AP
Ken Bloem, a Florida A&M professor and U. S. Department of Agriculture scientist, cuts open a cactus plant to check for an infestation of the cactus moth in St. Marks, Fla.
updated 1/5/2004 1:35:57 PM ET 2004-01-05T18:35:57

State agriculture inspector Laura Ooms knew at first glance something was seriously wrong with a couple of prickly pear cactus plants she found in a store’s garden section.

“They were quite ridden with worm holes,” Ooms recalled. “It wasn’t one little worm hole. There were several holes in them. They were oozing.”

She cut one cactus open and inside saw red-orange caterpillars with black spots, the larvae of Cactoblastis cactorum, commonly known as the cactus moth.

Native to South America, the gray-brown moth is a minor pest in the Southeast, dining on ornamentals and a few native species.

But it could cause economic and environmental havoc in the American Southwest and in Mexico, which is where it is headed. And infestations discovered across the Florida Panhandle show that it is gaining speed.

14 years in making
The invasion began 14 years ago in the Florida Keys. Since then, the moth has eaten its way up the eastern seaboard to Charleston, S.C., and along the Gulf Coast to within four miles of the Florida-Alabama state line, said Ken Bloem, a U.S. Department of Agriculture scientist in Tallahassee.

It had been advancing about 30 to 50 miles per year through the 1990s, but the latest statistics show it has been moving about 100 miles annually since 2000. Bloem now expects the moth to reach the Texas border by 2007 unless something is done to stop it.

The moth’s rapid advance is particularly worrisome in Mexico, where prickly pear cactus is a cultural icon — its image is on the Mexican flag and coins — and an economic mainstay.

Alien invaders“We eat cacti, we produce pharmaceuticals with cacti, we export cacti,” said Jorge Soberon, executive secretary of CONABIO, the Mexican National Commission on Biodiversity. “It is used as cattle fodder mainly during the dry years.”

Cactus is a $50 million to $100 million a year industry in Mexico, which has 56 prickly pear species. Many people also rely on it for subsistence, Soberon said. Prickly pear fruit can be made into jam and syrup while the plant itself is commonly boiled or pickled.

Preliminary estimates by the USDA show it has a trade, nursery, landscape, crop and forage value of up to $70 million a year in this country, mainly in the Southwest.

Environmentally, cacti prevent erosion and are a habitat and food source for animals.

“The Mexican government has already issued alerts in the (Mexican) states that thing will probably invade,” Soberon said. “I don’t think your Department of Agriculture is really interested in the problem, and understandably because cacti are not a major crop in the U.S.”

Bloem, co-director of the Center for Biological Control set up by the Department of Agriculture and Florida A&M University, defended the U.S. response to the cactus moth.

“I think the U.S. is taking it fairly seriously,” Bloem said, but he acknowledged: “At this point in time, nothing is actively being done to stop them.”

Cactus killer
The cactus moth is a proven killer. Prickly pear planted in Australia as a natural cattle fence grew out of control and took over 16 million acres, but it was virtually wiped out after the moth was imported in 1925.

The female lays sticks of eggs that look like cactus spikes. When they hatch, the caterpillars bore holes and begin eating the cactus from the inside out.

The moth also has been used as a biological control in Hawaii, India, South Africa and the Caribbean, unintentionally spreading from there to the Florida Keys in 1989.

Image: Adult cactus moth
Lyle Buss  /  University of Florida via AP
An adult cactus moth sits on a cactus leaf.
In the Keys, the moth quickly killed one of only a dozen adult semaphore cactus plants then known to exist, all in a Nature Conservancy refuge. Cages were put around surviving plants to keep the moths out.

Fearing the screening would cause more harm than good if battered by a storm, it was removed as Hurricane Georges took aim at the Keys in 1998, said Doria Gordon, a senior scientist with the Nature Conservancy in Gainesville.

The organization now uses volunteers to inspect the semaphores, including several hundred plants later discovered at a second site. The volunteers pluck egg sticks and remove infested pads without killing the cacti.

Mexico plans a similar low-tech approach if the moths get there as expected, Soberon said.

Ooms found the infested Gulf Breeze cacti, which had been shipped from South Florida, in June 2000. She saw no other damaged plants, and officials assumed it was an isolated infestation.

Until then, the nearest known natural infestation was 200 miles east of this Pensacola suburb in the St. Marks Wildlife Refuge near Tallahassee. It had advanced another 50 miles by 2002, but Bloem was stunned to find cactus moths at Pensacola Beach in September, a 150-mile leap in just one year. In October, it turned up at Perdido Key near the state line and other sites in the Panhandle.

Scientists at an early December meeting of cactus moth experts in Miami reported that releasing sterile males, a technique successfully used to control some other insect pests, reduced cactus larvae by 80 percent in caged tests. A full-scale control program would cost millions, but scientists say they need only $100,000 for the next step.

That would be to test the technique in the wild at the edge of the infestation, which could slow the moth’s advance and buy time, but so far nobody has come up with the funding, Gordon said.

“The situation is urgent,” she said. “This is a drop in the bucket.”

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