Healthy Animals 38
Controlling Imported Fire Ants
Imported fire ants, native to South America, first appeared in Mobile, Ala.,
in the 1930s and have since advanced throughout the southern United States.
These pests have a powerful sting, and their venom gives rise to the painful
burning sensation for which the ants were named. Imported fire ants are
extremely irritating to large animals, and they can be fatal for young
Fortunately, Agricultural Research Service (ARS) scientists are
collaborating to combat this painful pest.
Much of this work has occurred at the ARS
Control of Pests Research Unit in Stoneville, Miss., the ARS
for Medical, Agricultural and Veterinary Entomology (CMAVE) in Gainesville,
Fla., and the ARS
American Biological Control Laboratory (SABCL) in Hurlingham, Argentina.
The ARS scientists at Stoneville have evaluated baits for controlling
imported fire ants and have identified biological control strategies to reduce
the ants numbers. They've also conducted surveys to compare the
population sizes of native ants and imported fire ants in different regions and
under different management strategies.
In one study, entomologist
Streett is developing commercial biopesticides using insect-killing fungi.
He is currently evaluating two registered fungal products to assess their
effectiveness in controlling imported fire ants. This work can be used to
develop novel fire ant controls and improve existing tools.
In related work, entomologist
Chen developed fire ant baits with improved water resistance. Many fire ant
baits use soybean oil to attract the ants, and defatted corn grit to carry the
oil and a delayed toxicant. Unfortunately, defatted corn grit lacks water
resistance, which reduces the efficacy of many fire ant baits.
Chen developed novel methods for improving the ability of fire ant baits to
withstand water damage. These methods not only improve the sturdiness of the
baits, but also increase their ability to attract ants. Chen is now working
with pest control companies to develop commercial baits employing these
At CMAVE, scientists led by chemist
Vander Meer are also working to improve fire ant targets using pheromone
attractants specific to fire ants.
"Most baits affect both fire ants and non-target ant species, which are
important predators of new fire ant queens," Vander Meer says.
"Specifically targeting fire ants will decrease the likelihood of new
infestations because native ants will be more likely to survive and attack
newly mated fire ant queens."
Collaborative Control of Red Imported Fire Ants
Fungi aren't the only biological control agents ARS researchers are pitting
against red imported fire ants. ARS researchers are also collaborating to
assess potential biological control agents like phorid flies, microsporidia
diseases and viruses.
Spores of the microsporidian pathogen Kneallhazia
solenopsae, a potential biocontrol of fire ants.
Two pathogenic microsporidia, Kneallhazia solenopsae and
Vairimorpha invictae, are associated with population declines of red
imported fire ants in Argentina, according to CMAVE entomologist
Oi. And phorid flies parasitize fire ants with fatal results. Now, CMAVE
and SABCL scientists are investigating the possibility of using the phorid fly
as a vector for infecting the fire ant population with these pathogens.
Although preliminary data showed that V. invictae didn't successfully
transmit to phorid flies effectively, CMAVE scientists were able to infect
phorid flies with K. solenospae without harming the flies. The
scientists observed that K. solenopsae reduced the size of the fire ant
colony and the number of reproducing ants.
Understanding how fire ants behave in their native environment is crucial to
developing effective control strategies. ARS scientists at CMAVE and SABCL have
collaborated for more than 20 years to research the biology of red imported
fire ants and assess potential biological controls.
Led by director Juan Briano, the SABCL staff has conducted more than 340
field trips in Argentina, Uruguay, Brazil, Paraguay, Bolivia and Chile for
exploration and monitoring of fire ants and their natural enemies.
Despite the widespread effects of this pest, little is known about its
competitive nature or how it interacts with other ants in its homeland. SABCL
scientists have studied interactions between the red imported fire ant,
Solenopsis invicta, and other aboveground foraging ants in two habitats in
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Prior to the study, it was thought that the fire antsnow established
throughout the Americaswere not dominant in their native land, but this
study showed them to be numerically and behaviorally dominant, winning 78
percent of their encounters with other ants.
For more information about ARS research on fire ants, contact
Strickman, Leader of ARS National Program #104: Veterinary, Medical and