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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