Bugs Without Borders

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











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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