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Winged Invader

A moth that devastates prickly pear cactus may be headed our way

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David Wrench reaches into a palo verde tree and loosens a cardboard trap wired to its lower branches. He does this quite gingerly, because directly below the trap spreads a prickly pear cactus, Opuntia wilcoxii to be exact, and its thorns look truly unforgiving.

The proximity of plant to trap is not a coincidence. Rather, the very future of this cactus may depend upon the work by Wrench and other volunteer docents here at the Arizona-Sonora Desert Museum.

A couple of times each month, these folks fan out to "hot zones" across Tucson, namely nurseries that import prickly pear from eastern states. They check the plants and traps for winged hitchhikers called Cactoblastis cactorum, a wee but voracious South American moth whose larvae devastates this particular cactus. Signs of the winged invader include small "egg sticks" which mimic cactus thorns, and oozing from the pads, which reveals the presence of hungry larvae inside.

It's a mundane chore, but one that's critical to the Southwestern habitat, according to Joel Floyd, an entomologist with the U.S. Department of Agriculture. Just consider animals such as javelina, he says. "Around 80 percent of their diet is prickly pear. Deer use it, along with birds and pollinators. It's a major part of the ecosystem, and also holds the soil with its roots."

There's a proposed regulation that would restrict the import of prickly pear cactus from Florida, says Floyd, and it can't come too soon. "All of these years have gone by, and it was allowed. Probably the biggest worry would be a big-box store, where they place an order with a distributor for a whole bunch of different types of plants. Prickly pear might be one of them that they order, and it's provided by a grower in Florida. So there's a pathway there that we're worried about."

If it ever reaches Arizona, the moth will certainly have taken the long way. Its journey began in the 19th century, when Australian cattlemen imported prickly pear to use as natural fencing. Their strategy backfired, however, when this prolific cactus began choking the range. They followed one bad attempt at engineering nature with another, importing the South American moth to keep the cactus in check. The moth attacked with a vengeance, and the cattlemen were pleased. By 1957, the insect had also been introduced to the West Indies.

From there, it was a relatively short jump to the Florida Keys and then up the Gulf Coast to Alabama and Mississippi. Now scientists and agriculture officials are fighting to keep it from reaching Texas; if that border is breached, the moth may quickly arrive in Arizona.

The USDA's Animal and Plant Health Inspection Service (APHIS) has been most active in monitoring the cactus moth and developing ways to check its progress. With assistance from the U.S. Department of the Interior, nonprofit groups such as The Nature Conservancy, and the government of Mexico—a country where the prickly pear is a cash crop—the USDA is currently fine-tuning irradiation techniques to render moths sterile.

Even as the clock ticks, the department still doesn't have congressional funding directly dedicated to fighting the cactus moth. To change that, The Nature Conservancy is lobbying to have a separate, $3 million line item in the USDA budget explicitly for moth control. "So far, though, we can't claim to have any champions in Congress," says Faith Campbell, a senior policy representative for The Nature Conservancy. "I'm afraid it's hard getting people to have warm, fuzzy thoughts about protecting cacti."

But the public does have deep affection for its public lands, where a moth infestation could devastate entire ecosystems and lay landscapes to waste. That potential weighs on Kevin Dahl, Arizona program manager for the National Parks Conservation Association. He says Congress should exercise a little foresight by squeezing moth-control funding into its stimulus spending. "It's one of those things where we ask for a little bit of money now, and prevent devastation and the huge job of cleaning up the mess if the moth arrives here."

Of course, as go our public lands, so goes Tucson's outdoor-tourism industry. That point is driven hard by Mike Wallace, survey and detection manager for the Arizona Department of Agriculture. "I've had the opportunity to speak to various groups about the cactus moth," he says, "including the Tucson Metropolitan Chamber of Commerce, where I talked about the impact it could have economically should it be introduced. It was something new for them to look at the potential introduction of a pest, and what it could do."

A 2007 study by the Environment Arizona Research and Policy Center showed that Arizona's national forests—such as the Coronado, which flanks Tucson—generate about $2.2 billion annually in tourist revenue. And a recent study by the Metropolitan Tucson Convention and Visitors Bureau pegged tourism as bringing more than $2.3 into this area each year, and directly or indirectly employing about 40,000 people.

So you could say that the Arizona-Sonora Desert Museum is in the worst possible spot should the moth invade, since the venerable institution is both an important research outpost and reliant on visitor revenues. The museum now provides information on its Web site regarding the moth, and oversees the 10-volunteer crew that will be checking traps.

As the museum's curator of botany, George Montgomery knows full well the havoc this moth could wreak. So do the volunteers he dispatches to local nurseries. "The USDA says that the moths are only active in the warm months, April through October," he says. "So the traps just went out two weeks ago." Now it's a waiting game. But so far, fingers crossed, the moths have yet to be detected anywhere in Texas or Arizona.

Montgomery watches as David Wrench pulls apart the museum's own small, white trap. Constructed like a tiny tent, it has a stubborn adhesive substance on the bottom to catch unlucky insects. On the top is an eraser-size rubber piece containing a cactus moth-attracting pheromone.

The sticky part will be shipped off to Department of Agriculture offices in Phoenix. "Then they send these to one of the Mississippi universities, where there's an expert," says Montgomery. "And that team analyzes everything that's on here, especially looking for the Cactoblastis."

So far, the moths assembled here are just innocent victims to science. "They gave their lives willingly," says Montgomery, joking around. Then he and Wrench fall silent. Ultimately, there's not much humor to be wrung from waiting for the dreaded cactus moth.

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