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Out of the Lyme-Light
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ARS tick-control efforts
are targeting the female
blacklegged tick, Ixodes
scapularis, which can lay
up to 3,000 eggs in her
lifetime. Her young offspring
are key links in the
transmission of Lyme disease,
a flulike illness in humans
that can become chronic and
progressive if not treated.
(K9407-1)
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Ticks aren't insects; they're
acarines, closer kin to spiders. Unlike an insect's, a tick's head and body are
one unit, resting entirely on eight legs. Even with so many legs, they can't
get far without help from their hosts. It's a fact that ticks live where their
hosts live.
White-tailed deer are the keystone host for maintaining populations of the tick
Ixodes scapularis. In the Northeast, this tick was initially described
as the deer tick because it was first found on deer. Since then, scientists
have shown that the deer tick is actually the blacklegged tick.
In the Northeast, these ticks are notorious for transmitting the agent that
causes human Lyme disease: Borrelia burgdorferi. They also transmit
lesser known human diseases like ehrlichiosis and babesiosis—microbial
infections characterized by flulike symptoms but much shorter-lived than Lyme
disease.
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Technician Kenneth Young
applies acaricide to paint
rollers on the ARS-developed
four-poster device. The
acaricide rubs off on deer
as they feed on corn bait
dispensed by the device.
(K9405-1)
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Populations of blacklegged ticks are
spreading to new locations each year. More than 10,000 human cases of Lyme
disease are reported annually in the United States, according to the Centers
for Disease Control and Prevention, in Atlanta, Georgia.
Lyme disease occurs mainly in suburban areas with an overabundance of deer.
That's why USDA implemented a 5-year tick-control project in the Northeast in
1997. The project uses a device developed and patented by
ARS scientists in Kerrville, Texas. The
device, named the "four-poster," is being tested in four areas where
the incidence of Lyme disease was among the highest in the country when the
project started—Old Lyme, Connecticut; Bedford, New York; Colts Neck, New
Jersey; and Narragansett, Rhode Island—and also at the Beltsville
Agricultural Research Center (BARC) in Maryland. With a goal of reducing 90
percent of the nymphs, the researchers set out 25 four-posters at each of the
five 1,280-acre treatment sites. |
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An adult female blacklegged tick,
engorged after a blood meal, rests
on a leaf.
(K9411-2)
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Safety First
"People and deer will be able to live together without fear of Lyme
disease," says ARS entomologist J. Mathews Pound. Pound is optimistic
because he, ARS agricultural engineer J. Allen Miller, and ARS biological
technician Craig LeMeilleur at the Knipling-Bushland U.S. Livestock Insects
Research Laboratory in Kerrville invented the four-poster as an alternative to
eliminating deer populations or applying chemical sprays to the environment.
The four-poster consists of a bin filled with whole-kernel corn. "On the
four corners of the bin are paint rollers, which hold one of the safest
acaricides we could find—amitraz," says Pound. The corn lures deer to
the feeding station, where they brush up against the paint rollers. The
acaricide rubs off and kills ticks on the animal's head and neck, where 90
percent of adult ticks are found. As the animal grooms itself, the acaricide is
spread to other areas of the body. |
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In the Northeast, the white-tailed
deer is the primary host for adult
blacklegged ticks.
(K5437-3)
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Amitraz targets ticks and mites
without harming beneficial insects. It is currently approved for use on
livestock, so the U.S. Environmental Protection Agency (EPA) granted the
researchers special permission to use it on white-tailed deer during the 5-year
project.
"Choosing amitraz helped us gain public acceptance of the project. Even
during hunting season—from October through December, which also coincides
with the time most adult blacklegged ticks feed on deer—amitraz is
considered safe.
"Currently, no pesticide is approved for use on white-tailed deer. But
this situation may soon change. The technology and its implementation are
reminiscent of the chicken-or-the-egg story. No one was willing to try to get a
pesticide approved for white-tailed deer until there was an application device.
Vice versa, no one can make good use of the applicator without an approved
pesticide," says Pound. |
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At a heavily used four-poster
in a Maryland suburb,
entomologist John Carroll (left)
and Kenneth Young examine
acaricide-impregnated paint
rollers for signs of wear.
(K9403-2)
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Knowing a Good Thing When You See
It
"When I found out about the four-poster, I immediately started the
licensing process," says David Weld, executive director of the American
Lyme Disease Foundation, which is forming a subsidiary company to market the
four-posters. Concurrently, Y-Tex Corporation, an animal health company in
Cody, Wyoming, began seeking EPA approval to register one of its products
containing the insecticide permethrin for use on white-tailed deer. The Y-Tex
product, Brute, is made and sold commercially for killing ticks on cattle and
swine.
In a separate study from 1996 to 1998, NASA researcher Vickie Solberg reported
using several four-posters in a secured area at the Goddard Space Flight Center
in Greenbelt, Maryland. Her control site was the Patuxent Wildlife Research
Center in Laurel, Maryland. By the second year, she says, "we saw 98
percent control of nymphs and 100 percent control of adult ticks using the
four-posters with permethrin. So we know the chemical works." Permethrin
is already known by many consumers as an ingredient in head lice shampoos for
children. |
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Kenneth Young examines leaf
litter for blacklegged tick
nymphs.
(K9414-1)
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Previous ARS trials with the
four-poster proved its ability to kill and reduce populations of another tick,
the lone star tick, Amblyomma americanum, in Texas. But when the
researchers in the Northeast used the same methods, they found some surprising
differences between Texas deer and northeastern deer. "Deer in the
Northeast are more numerous, are larger, and have bigger appetites and thicker
haircoats. So the first reality check was that we had to use lots more corn and
more pesticide," says Pound.
"Deer are as attracted to whole-kernel corn as children are to chocolate
candy," says Pound. But, the researchers at four of the Northeast
treatment sites—to varying degrees and in different yearsencountered
competition from the number of acorns dropping from trees in the fall.
"The deer ate the acorns instead of the corn in our feeders. It was
certainly something we hadn't expected," he explains. |
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A nymph-stage blacklegged tick
on a leaf. Infected nymphs transmit
most cases of Lyme disease.
(K9409-1)
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Life Cycles
In the Northeast, I. scapularis has a 2-year life cycle. Larvae become
infected during their first summer, when they feed on white-footed mice and
other small mammals and birds, which are reservoirs for the spirochete B.
burgdorferi. Nymphs—the stage after larvae—survive winter and
spread B. burgdorferi the following spring and summer. By their second
fall, nymphs have turned into adult ticks, and the females begin seeking a host
that offers a large blood meal, most often the large population of white-tailed
deer.
"If there are fewer adult ticks to reproduce, we can expect fewer larvae
in the spring. Infected nymphs, smaller than a pinhead, transmit the most cases
of Lyme disease because their presence can go unnoticed until the infection is
established and because they are biting in the summer when people are outside
in shorts and T-shirts," says Pound.
Ticked Off in Maryland
The spring of 1998 was a busy time for ARS entomologist John F. Carroll,
technicians Kenneth W. Young and Eliseo N. Miramontes, and others at BARC.
That's when they set out four-posters at BARC and at two other locations in the
Baltimore-Washington area—Loch Raven and Gibson Island, Maryland. The
devices were placed along trails and in areas where deer congregate.
On fall and spring days, and on winter days when the temperature stays above 45
°F, the researchers spend their time stocking the feeders with corn and
applying acaricide to the rollers. "That's when adult blacklegged ticks
look for a blood meal," explains Carroll, "and nearly all female
ticks feed on deer."
Carroll says they are targeting female adults to prevent them from laying eggs.
"A female tick can lay up to 3,000 eggs in her lifetime," says
Carroll.
In the third year of treatment in Maryland, Carroll says, "it looks like
we're having an effect—but not yet at the level we had anticipated."
At the Loch Raven site, numbers of blacklegged tick nymphs were 71 percent
lower in treated areas in 2000 than in 1998. Reductions were nearly as good at
BARC—68 percent. And they were promising on Gibson Island—59
percent—the last site to go into operation.
Reductions of lone star tick nymphs were similar. The Maryland and New Jersey
sites are the only project sites to have deer that play host to the lone star
tick, which transmits a bacterium that causes human monocytic ehrlichiosis.
"If during 2 or 3 years, you can reduce nymph numbers by half, after 4
years you can reasonably expect to reduce them by 75 percent or more,"
says Carroll. To calculate the level of control, he uses a mathematical formula
that accounts for the natural rise and fall of tick populations in any given
season, depending on weather and other factors.
Thanks to the American Lyme Disease Foundation, Lyme disease has become a
household word. Although there is currently one Lyme disease vaccine on the
market, its effectiveness hasn't been established for total disease prevention.
For more information about Lyme disease, see the Foundation's web site at
http://www.aldf.com.
"In terms of having an impact on Lyme disease risk over a community-based
area, the four-poster is the only current technology I know of that can do the
job," says Pound. "I believe we are having an impact on tick
populations in the Northeast, and there's still time to reach our
goal."—By Linda McGraw,
and Judy
McBride, Agricultural Research Service Information Staff.
This research is part of Arthropod Pests of Animals and Humans, an ARS
National Program (#104) described on the World Wide Web at
http://www.nps.ars.usda.gov.
To reach scientists mentioned in this article, contact
Linda McGraw, phone (309) 681-6530, or
Judy McBride, phone (301) 504-1628.
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"Out of the Lyme-Light" was published in
the May 2001
issue of Agricultural Research magazine.
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