Bugs Without Borders

Minnesota state epidemiologist Art Mason tracks the new global migrants
Michael Dvorak

If you have a bug story to tell Art Mason, he'd appreciate it if you'd bring the carcass. Recently, he says, his neighbor told him about seeing a tarantula on her rear-view mirror a day after a grocery run: "It probably had gotten in on bananas in her groceries. She called me, frantic, and I asked her, 'Where's the specimen?' She said, 'There's nothing left for you on this one. It's smashed on the road somewhere.'"

Mason is Minnesota's state entomologist--the man in charge of monitoring flying and crawling threats to the state. Bespectacled and professorial, he clearly relishes his job--a position for which, he notes, he began training at an early age: During his childhood in Maine, his family put him to work picking up plant-munching Japanese beetles in the garden. "You know how little children can watch ants for a long time?" he grins. "I never outgrew that. When I go grocery shopping, I'm looking for insects."

But Mason's brow furrows as he rattles off the list of creatures that have been showing up in Minnesota in recent years. The Japanese beetle he used to chase out East has made its way here in nursery stock. Shoppers not infrequently discover black-widow spiders on grapes in local produce departments; shipments of fresh flowers covered with foreign thrips are routinely turned back at the airport. "In all of the 37 years that I've been working in entomology, I've never been more concerned with all the species threatening this country," Mason says.

Earlier this year those concerns were echoed in Washington, when President Clinton signed an executive order appointing an inter-agency council to create an "invasive species management plan." The executive order noted that "the total economic impact of invasive species on the U.S. economy is estimated to be about $123 billion annually." Clinton's budget for fiscal year 2000 proposes an increase of almost $30 million in the budgets of various agencies to combat invasive species.

Minnesota legislators have also jumped onto the bug-fighting bandwagon: This spring lawmakers appropriated $276,000 in new funds for Mason's office, a 40 percent increase over the current budget of $700,000. But even that, says Mason, is only a drop in the bucket when you're dealing with something like the Asian long-horned beetle.

So far, no one in Minnesota has seen the two-inch long, black-and-white spotted beetle with the whiplike antennae and the voracious appetite for wood. But the insect has caused the destruction of more than 2,000 trees in New York City, where it is thought to have arrived in the wood of pallets from China in late 1996. A similar infestation now plagues Chicago, where 500 infested trees have been removed since the beetle showed up last July. The Asian long-horn doesn't fly far, but it will hitch rides when it can; at one point, Chicago bug hunters suspected that it might be riding the El train from one location to another.

What bothers entomologists about this particular beetle, says Mason, is that they seem to be powerless against it. "We have no chemicals to control it, no biological control, no pheromone that attracts it. We don't even have methods for looking for it." The only way to stanch invasion seems to be to establish strict quarantine areas, cut down all the trees in them, and burn the wood. Asian long-horns have been found in shipping yards and warehouses across the nation; in the Twin Cities, staffers from the state and federal Departments of Agriculture have combed warehouses where pallets made of Chinese wood might be stacked. Thus far they haven't found anything. But it's only a matter of time, says Mason--and, perhaps, of coincidence: In Chicago the beetle was first discovered by a man who'd bought a load of firewood and found the creature in the bed of his truck.

Recently, while vacationing in northern Minnesota, Mason wandered into a sporting-goods store for a quick browse and noticed something that made his heart sink: "There was a stack of the crating material that barbells had come in. There were huge holes in it, probably made by the Asian long-horned beetle, probably back in China, but we can never know that for sure." Mason quizzed the shop owner and found out that the crates were the last from a large shipment, and that the rest had already gone to a landfill. "We have our work cut out for us," he concludes wryly.

The arrival of the Asian long-horn is a reminder, Mason and other bug-fighters say, that national boundaries mean nothing to insects. The USDA has more than 1,300 inspectors stationed at 90 ports and border crossings; in some of those places, including the Minneapolis-St. Paul airport, they are accompanied by dogs trained to sniff out vegetables, plants, and fruit. But there's no way those inspectors could disassemble every crate or rummage through every suitcase, says Scott Tincher, senior officer for the Animal Plant Health Inspection Service (APHIS) office at the Minneapolis-St. Paul airport.  

In Minnesota, says Tincher, "most of the insects we find are on passengers. A lot of people want to bring back fruit from where they've been traveling. They don't realize that they can bring back a harmful insect along with their gift. We can look at that perfectly healthy mango, and if it came from India, the Philippines, or Nigeria, we know that it probably has a mango weevil lurking inside."

But bug invasions didn't begin with global air travel: One of the most damaging additions to the U.S. insect population arrived back in the 1880s, when a French entrepreneur tried to hybridize silkworms with the European gypsy moth. A century later, according to a 1993 report from the U.S. Office of Technology Assessment, the moth "exacts the greatest measurable losses and expenditures for research, control, and eradication [of any nonindigenous species]." The U.S. Forest Service alone spends $20 million each year to fight the creature.

Gypsy-moth larvae defoliate trees--literally: In the worst-hit areas of the East, there won't be a leaf in sight for miles, says Peter Dziuk, the gypsy-moth program coordinator at the state Department of Agriculture. "And the caterpillars can cover the trees, everything around. There's the sound of a gentle rain, but it's the pitter-pat of caterpillar feces. If a caterpillar fell off a tree onto you, you'd have a huge, smarting rash. They have erdicating hairs--tough, stinging hairs with chemicals in them." (Gypsy-moth caterpillars are not to be confused with the forest tent caterpillars, also called army worms, that have been plopping into northwoods tourists' hair this summer: Those, says Dziuk, are a long-established local species that happens to be at the peak of a typical ten-year cycle.

The one good thing about the European gypsy moth, says Dziuk, is that the female can't fly very far. "She has nice wings," he notes, pointing out the argyle pattern in a mounted sample on the shelf in his office. "But look at that body." The insect's thorax looks pumped up, grossly out of proportion to the wings. "Her life isn't very exciting," Dziuk explains. "She can't get off the ground. She emerges [from the pupa], mates, and she's dying as she's laying her eggs. Often the egg mass and pupa case are found right next to each other."

But what the moth lacks in flying ability, it makes up in persistence: Over the past century it has slowly, but inexorably crept west, typically hitching rides in the wheel wells of cars, trucks, and campers. Egg masses and pupal cases were first recorded in Minnesota in 1969, and Dziuk's program was established not long after that.

Dziuk's staffers hunt the moth using the lure of sex: Each summer, they swarm out across southern Minnesota distributing cardboard boxes baited with the scent of the female gypsy moth. Males looking for a date fly into the boxes and are trapped by the sticky substance that lines their walls. As recently as 1992, Dziuk says, the workers rarely encountered the insect in the field. "Now, all of our trappers will see moths." Between 1997 and '98, the number of moths captured this way increased 265 percent.

Dziuk and his colleague know they've already lost the battle to keep Minnesota gypsy-moth-free; now they're searching for ways to keep the pest population to a tolerable level through biological controls. "Right now, gypsy moths have no predators here," Dziuk explains. "In heavily infested areas, birds--who were initially turned off by those stinging hairs--learn how to grab a hold of larvae and knock them against the tree to get rid of that hair. But birds will never make a big enough difference. Other insects and diseases are the biggest things that affect bugs." Dziuk's program and its counterpart at the U.S. Department of Agriculture have been releasing parasites known to kill other moths in infested areas, hoping that the microbes will develop a taste for the gypsy.

But finding just the right predator takes time--and time is short when you're dealing with creatures that go through three generations in the period it takes to appoint a task force. In a vial on his desk at the state Department of Agriculture, Art Mason has a jar containing four or five black beetles, smaller than ladybugs: These, he explains, are Minnesota's newest pest, discovered on April 13 in a bee honeycomb near Glenville. Investigators contacted the Smithsonian Institution, which maintains a massive bug collection, and learned that it was the small hive beetle, Aethina tumida, an African native that feeds on bees and honey. They also discovered that the beetle has a weakness for moldy fruit, and finally trapped it using fermented cantaloupes as bait.  

For now, that's the end of the story--or at least of one episode in one chapter of a multivolume saga. "The thing about insects that's both frightening and compelling is that they're very adaptable, more so than we are," Mason muses. "They reproduce so prolifically, they can generate resistant strains, and--like the hive beetle--they adapt to such specific habitats. There are insects found only in beaver houses. The loon has its own black fly; ducks have their own parasites. If you go outside right now and dig up one square foot of dirt,"--he leans forward and maps out a box with his hands--"in just one square foot, you'll find any number of insects that have never even been described." He leans back in his chair and smiles: "I have to admit--it's so fascinating to me."

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