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Biological
Control Sends
Scurrying Scourge Scrambling
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Technician John Davis measures
a black imported fire ant mound
while entomologist James Vogt
records data. Mound area
affects visibility in aerial
images.
(K10387-1) |
Like the industrious
ant in one of Aesop's fables, the imported fire ant thrives because it's
diligent. The fictional ant in the famous story worked hard to prepare for the
onset of winter while the grasshopper played. But a modern retelling of the old
tale might have ARS scientists working
equally as hard to gain the upper hand over troublesome fire ants.
Although the red imported fire ant, Solenopsis invicta,
is more well-known to most Americans because it infests a larger area, the
black imported fire ant, S. richteri, actually arrived here first, back
in 1918. They are currently found only in Mississippi, Alabama, and
Tennessee.
A hybrid fire anta cross between a red and a
blackwas first identified in 1985 by ARS scientists at the Imported Fire
Ant and Household Insects Research Unit at Gainesville, Florida. No one is
entirely sure why different species of fire ants predominate in certain
regions.
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Black imported fire ant
(S. richteri)
traveling on a plastic strip
that hangs down from a
lifter cup that is part of
a system designed to make
the fire ants susceptible to
phorid fly attack.
(K10391-1) |
The abundance of
black imported fire ants in the Mid South provides James "J.T." Vogt,
an entomologist at the Biological Control of Pests Research Unit in Stoneville,
Mississippi, with the opportunity to evaluate control agents against them as
well as the red ones. One agent under study is Thelohania solenopsae, a
single-celled protozoan parasite first isolated by ARS scientists at
Gainesville. (See "Update: Hot on
the Trail of Fire Ants," Agricultural Research, February 2003,
p. 20.) Infected colonies die out in 9 to 18 months. Another biocontrol tool
they're investigating is the fire ant-decapitating phorid fly, which uses the
ant's head as a protective home for its developing maggot young.
The Stoneville program is relatively new, established in 2000.
Vogt and his research leader, entomologist Doug Streett, began a 5-year project
in 2001 to assess the impact of biological control agents used along with
chemical bait toxicants in keeping imported fire ants at manageable levels.
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Phorid fly, Pseudacteon curvatus,
about 1/32-inch long.
(K10386-1) |
"The ants are
more than a simple annoyance," Vogt says. "If disturbed, they sting.
They're called fire ants because their sting causes an intense
burning sensation. Some people are hypersensitive and react strongly, and some
even die." Fire ants also reduce populations of native ants, other
insects, and ground-nesting wildlife.
In cooperation with the Mississippi Agricultural and Forestry
Experiment Station, Stoneville researchers established four demonstration sites
in the state to explore the feasibility of a biological control program.
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Entomologist James Vogt
examines a lifter cup in a
phorid fly rearing system.
The cups alternate up and
down inside trays containing
worker ants and their young
and cause the ants to trail
back and forth in seeking
shelter from attacking phorid
flies. Being frequently on
the move, the ants are unable
to group together to defend
against the flies.
(K10390-1) |
Two of the four
sites contain T. solenopsae and phorid flies in combination with bait
toxicants, and two sites contain baits alone as a control group, for
comparison. This helps researchers learn whether the biological control agents
slow reinfestation by the ants. The baits are highly effective and achieve 90
to 95 percent control with a single application, but baits aren't enough if
used alone because ants reinfest areas after treatments. T. solenopsae
and the flies, on the other hand, are sustainable solutions.
ARS researchers are working with Alabama A&M, Auburn
University, and Tennessee State University (TSU) to study phorid fly
effectiveness. Cooperators at these institutions released flies in 2002 in an
effort to reduce fire ant problems over large, low-value areas such as
pastures, where baits are not practical. Cattle producers find it too expensive
to treat with baits every year and are interested in self-sustaining
alternatives, such as phorid flies. Long-term projects are under way to assess
the flies' impact as they're introduced and established.
Mass-rearing technology ensures a steady supply of flies for
research, release, and establishment in the United States. Vogt established a
rearing facility at the Biological Control and Mass Rearing Research Unit in
Starkville, Mississippi, for one biotype of a specific species of phorid fly
called Pseudacteon curvatus that especially favors black imported fire
ants and hybrids.
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Technician John Davis uses
a GPS unit to record the
exact position of a fire
ant mound. Mound position
data are overlaid onto
aerial digital images of
the study site to determine
mound visibility. Knowing
the exact location of a
mound also allows researchers
to place parasitized ants
back into their original
colonies.
(K10389-2) |
"The facility can produce
3,000 to 5,000 flies a day," Vogt says. "To establish flies in an
area, ants are collected from the field, exposed to the flies in large
attack boxes in the laboratory and then released back into their
source colonies."
High-Tech Solutions
The researchers are using a geographic information system to track phorid
fly establishment with geographically referenced coordinates. Using the global
positioning system to calculate their positions, they can relocate ant mounds
where they released flies with an accuracy of less than 1 meter. Otherwise, it
can be difficult to navigate rough terrain and return to an exact point. They
use hand-held personal computers to display coordinates in a map overlay to
monitor their spread and measure the progress of their attempts to establish
the flies.
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Technician Debbie Smith weighs
groups of fire ants for use
in the phorid fly rearing
system.
(K10388-1) |
Vogt and cooperators developed
techniques to secure imagery of fire ant mounds from airplanes and quantify
infestations over large areas. They use passive remote sensing instruments to
detect sunlight reflected by mounds and mark areas infested by imported fire
ants.
The plane-mounted camera system uses four separate sensors to obtain
true-color and false-color infrared, multispectral images of fire ant mounds.
Vogt says the mounds typically have a ring of thriving vegetation surrounding
them at certain times of the year. The digital images display a dark spot where
the mound is located, surrounded by a bright red ring, which indicates healthy
vegetation in the false-color infrared images.
Also, because mounds heat up in morning hours more quickly than the
surrounding soil does, the researchers are using thermal cameras to measure
infrared emission (heat) and locate fire ant mounds, which appear as bright
spots in images taken from the air.
The Stoneville researchers will use their remote sensing techniques in the
spring of 2003 when they partner with Jason Oliver of TSU to help nurseries in
Warren County, Tennessee, hold off quarantine status of the ball and burlap
tree and plant industry. Counties to the south of Warren are under partial
quarantine to help slow the spread of imported fire ants to other areas of the
state. This means they have to treat their stock and soil with the few, costly
insecticide treatments approved by USDA's Animal and Plant Health Inspection
Service. The Stoneville researchers plan on using remote sensing imagery to
help the Tennessee Department of Agriculture identify high-priority areas in
those quarantined counties as part of an areawide program to manage imported
fire ants.By Jim
Core, 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
www.nps.ars.usda.gov.
Douglas A. Streett and
James T. Vogt are with the USDA-ARS
Biological
Control of Pests Research Unit, 141 Experiment Station Road, Stoneville, MS
38776; phone (662) 686-5229 [Street], (662) 686-3065 [Vogt], fax (662)
686-5281.
"Biological Control Sends Scurrying Scourge Scrambling" was
published in the May
2003 issue of Agricultural Research magazine.
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Last Modified: 02/15/2009
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