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March/April 2007 Cover


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Villains in Vacationland

Illustration by Carrie Graham


Villains in Vacationland
UMaine entomologists study the effect of invading European fire ants on local ecosystems

About the Illustration: Multiple queens make it possible for individual nests to grow into full-blown  infestations rather rapidly. The highly mobile colonies also make the insect an excellent candidate for human-aided dispersal.
 

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A Wolf in Ladybug's Clothing
Lady beetles, commonly referred to as ladybugs, and their grub-like larvae are one of the primary predators of aphids, gorging themselves on the largely immobile herbivores and thereby helping to control aphid populations.
 

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Remember those B-movie horror flicks in which heroic scientists threw themselves in the paths of seemingly unstoppable monsters while terrified innocents ran screaming into the night?

It's kind of like that.

This true, hair-raising story that reads like the script of a '50s sci-fi thriller is about a monster on the loose in coastal Maine. The villain isn't an atomic robot or a giant alien from an experiment gone wrong, but Myrmica rubra, the European fire ant.

"I first discovered them by the vegetable garden, and now they have taken over the entire back lawn," says Polly Camp, whose yard and garden in Orono, Maine, have been overrun by the stinging pests. "I had to give up gardening last year, and I worry about my grandson going out to play. They're nasty, aggressive things, and their sting is just terrible."

Polly Camp's story is all too common. From Eastport to Kittery, the ebb and flow of Maine's natural communities are being interrupted, along with backyard barbecues, woodland walks and even elementary school recesses, by the scrappy tenacity of the fire ant. All but immune to traditional methods of control, the invasive fire ant has reached a kind of renaissance in Maine in recent years, rapidly expanding its range and increasing the size of its populations. Fire ants are slowly stinging their way up the food chain, and their success has citizens and scientists alike scrambling for answers.

"These ants are a different species from the fire ants that are causing problems in the southern part of the United States," says University of Maine entomologist Ellie Groden. "These originate from somewhere in northern Europe, whereas the southern fire ants originate from South America. The natural distribution of the European fire ants extends up into the Arctic Circle in northern Europe, so unlike the southern species, we know that these ants are well adapted to our cold climate."

These ants have been in Maine for more than half a century, Groden says, but "over the last few years, a lot of people who never noticed the ants before are saying that fire ants have taken over their lawns. There are a lot of things that could be happening, but I think that the ant's success in recent years is probably due to a combination of environmental factors and genotype."

Groden suspects that the species slowly adapted to its new home, remaining relatively inconspicuous as it tweaked its behaviors and biology to meet the challenges of its new environment. It may have recently reached a sort of threshold for success, both behaviorally and genetically, that has allowed it to rapidly expand its population.

Whatever the reason, the fire ant is definitely on the march in Maine.

A colony can make its home almost anywhere, creating cryptic nests under fallen branches, dead leaves, piles of construction materials almost any natural or manmade debris. Multiple queens make it possible for individual nests to grow into full-blown infestations rather rapidly, and the highly mobile colonies make the insect an excellent candidate for human-aided dispersal.

"Colonies move around all the time according to the abundance of food and the colony's needs, and multiple queens can 'bud' off the main group to form new nests," says Groden. "Last summer we filmed an entire colony as it moved from a stone wall into a pot that had a rhododendron in it, ready for planting. It made it easy to see how colonies can get moved around by people."


The first documented sighting of the European fire ant in the United States was in 1908 at Harvard University's Arnold Arboretum outside Boston, but the infestations that dot the Maine coast are probably the product of multiple introductions. In the past 100 years, importers and U.S. customs officials have regularly encountered the tiny, eighth-inch opportunists in plant materials from Europe. From bags of sphagnum moss from Ireland to potted dahlias from Germany, plants and garden supplies have harbored the hitchhikers, delivering the pest to urban neighborhoods in cities like Bangor and Portland, and to quiet country landscapes in areas as remote as Monhegan Island.

Groden estimates that Maine's fire ant populations started to become a real problem in the mid-1990s, but it wasn't until an infestation was discovered in Acadia National Park that the pest began to draw widespread attention. With financial support from the National Park Service, fire ants now are being monitored by UMaine researchers at more than a dozen sites on Mount Desert Island.

Groden and her team have spent more than four years studying fire ants on the island to determine the extent of the infestation, its environmental impact and potential methods for control. Recent U.S. Department of Agriculture funding has allowed the research to expand to other areas in Maine.

With established populations of the fire ant scattered across coastal Maine, the insect's potential to disrupt local ecosystems is a real concern. Ongoing UMaine research projects are assessing how fire ant colonies affect other organisms in their range.

Naturally aggressive and surprisingly efficient, the invading fire ants physically overpower and out-forage native ant species with their hunting and scavenging skills on the ground and in the trees. With the invader's potent sting and its blitzkrieg approach to foraging, native ants simply can't keep up.

"What we do know is that native ants, almost to a species, are being eliminated," says Groden. "In most sites in Maine, (fire ants) are very aggressive, but their impact on small vertebrates is still in question. There is some evidence that they are causing declines in the number of visits by native bees and other pollinators."


While much remains unknown about the European fire ant, what seems clear is that the species is here to stay. In Eastport, where one colony stretches for more than 2 miles along the coast, the question of control is on everyone's mind. Thankfully, Groden is on the case. A specialist in insect disease and pest management, Groden traveled abroad with colleague Frank Drummond to the fire ants' home range in search of pathogens that could provide new methods of control.

Their quest paid off. After scrutinizing thousands of fire ant nests across the English countryside, Groden and Drummond discovered not one but three fungal pathogens not found in the U.S. After a nearly catastrophic misunderstanding with customs officials, they were able to bring ants killed by fungal pathogens back to the States to begin the long process of culture and analysis.

"We were quite successful finding pathogens in England, and they have become a significant part of our research," says Groden. "We collected cadavers and found new fungi not found in the U.S., one of which may be a new genus. We have worked very hard to establish a culture and reinfect the ants to determine whether there is any potential for use as a biological control."

Reinfecting the ants in the lab proved almost as difficult as finding a single dead ant in the rolling hills of the English countryside. Ants are extremely fastidious when it comes to personal hygiene, constantly grooming themselves and each other, even applying anti-microbial compounds to nest mates. The U.S. populations also perform a unique housecleaning ritual studied by UMaine graduate student Carrie Graham.

As part of her master's research, Graham examined ant middens select locations away from the nest where workers bring the colony's refuse and, more importantly, its dead. Graham discovered that the ants carry off their cadavers to very specific sites. She examined these "ant graveyards" to determine how environmental factors influence site selection for the middens.

"Preliminary lab experiments showed that the ants tend to prefer warm areas where there is direct sunlight for disposing of cadavers. A lot of ant pathogens are UV sensitive," says Graham. "They may be baking their dead to disinfect them."


Understanding the interaction between members of neighboring colonies may be just as important as the ants' behaviors in and around an individual nest. Drummond has focused his research on the relationships between groups of ants, hoping to determine whether Myrmica rubra has formed so-called supercolonies like those of the invasive Argentinean fire ant in Europe and the southern United States.

"Usually ants are fiercely territorial. The fighting that they do among themselves helps to keep populations down," says Drummond. "In a supercolony, that competition disappears. Ants will work together, foraging and sharing the care of the young.

"In Europe, the Argentinean fire ant has established a supercolony along the Mediterranean that is more than 600 km long, which means that you could take an ant from either end of that 600 km area and put them in the same jar and they wouldn't fight. In their home range, ants from nests separated by just a couple of meters fight."

Using a variety of laboratory and field experiments, Drummond showed that ants from different nests in Maine did, indeed, fight, suggesting that Maine's invading fire ants are multicolonial, despite the high number of nests per acre in infected areas. Ants are able to recognize a nest mate based on the chemical signature of complex hydrocarbons that cover its body. By examining these compounds, along with genetic data that shows the degree of relatedness between colonies, Drummond's research is unraveling the complexities of fire ant communication and aggression.


As if their aggressive tendencies and painful stings weren't enough, the fire ants' agricultural proclivities also are proving to be a problem. Fire ants make excellent herders, patiently and ferociously tending aphids small sucking insects that feed on the juices of a variety of plants. From aphids, the ants get sugar-rich secretions.

UMaine ecology and environmental sciences graduate student Katie McPhee is studying the ants' unique farming practices to better understanding the invaders' effect on its environment.

Her research is focused on measuring the extent to which fire ant and homopteran (aphids, mealybugs and other sucking insects) populations affect one another. The big questions: Is there one homopteran species in particular that is associated with Myrmica rubra, and, if so, is that giving rubra a competitive edge over native species?

"The research also is helping to show how rubra is affecting both the insect and the plant community," she says.

The unique behaviors of fire ants may be the key to their control. From tracking ant foraging movements with fluorescent dyes to examining modes of aggression between ant species, Groden and her team are amassing data that may expose a chink in the ant's armor, paving the way for effective control.

"One of the approaches we are taking now is to examine how fire ants are able to prevent infection. If we can disrupt their behavior in ways that increase their susceptibility to pathogens, we may be able to come up with an effective strategy for control that, along with an inoculant or pesticide, may keep fire ants in check."

For homeowners like Camp, who recently began working with Groden's team to control the infestation spreading through her yard, any degree of fire ant control would be a relief.

"I can't pick my raspberries, I can't hang out my sheets to dry, I can't do anything in the yard without getting stung," says Camp. "The ants really disrupt everyday summer living, and they seem to be moving closer and closer to the house. They're menacing. They really are."

by David Munson
March-April, 2007

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