Fire Ants-- Applying Nature's Controls
by Ed Vargo, Ph.D.
Reprinted from TBGS newsletter issued December 1994- updated
April 1996, and is to be progressively updated as research
Research Scientist, Dept.Zoology, U.Texas
[Dr. Vargo summarizes current management efforts, spearheaded at
U.T. under the direction of Prof. Gilbert; rather than employing
pesticides that have been ineffectual in preventing their spread,
their efforts are directed to the use of "nature's own"
There are currently present in this state four species of fire
ants, three of which are considered "native". Solenopsis
geminata, S. xyloni, and S. aurea belong to us, while S. invicta
- the import - is the one that causes so much distress.
The burning stings and the postules that follow - often forming
scars - are bad enough. But repeated stings coupled with the
extremely toxic venom of S.invicta can make for serious medical
reactions. In some, it results in secondary infections. Others,
following previous bites, may have become profoundly sensitized
to the toxic proteins, histamines, etc., in the venom, and even
wind up with anaphylactic shock. Ed.]
They infest gardens, parks, yards, playgrounds, and
pastures throughout the southeastern and southcentral U.S. These
pests arrived accidently as part of a shipment from their native
Argentina or Brazil some 60 years ago. From the point of their
introduction, Mobile, Alabama, they spread quickly, and now
occupy about 250 million acres in the U.S., including about 60
million acres in Texas.
Pesticides- they may create difficulties
Recognized as a serious pest as early as 1949, the imported fire
ant has been the target of numerous control efforts undertaken by
federal, state, and local agencies. Many of these programs
involved aerial application of various highly toxic
organochlorines and Mirex, all of which are now banned for use in
the U. S.
Despite spending more than $200 million on these control
programs, the fire ant now occupies more territory than ever. The
problem with this chemical approach to control is that it ignores
the ecological complex in which fire ants live.
The use of broad spectrum pesticides may kill fire ants but
it also poisons other insects, including native ants, that can
repel and compete with fire ants. After the successful poisoning
[clearing out] of an area, fire ants, so very good at colonizing
suitable habitats, will reinvade. If the resistance from native
ants is absent, fire ants can become even more numerous after
such a treatment than they were before pesticide application.
Current Research Strategies
The approach of the fire ant lab at the University of Texas
has been to identify and develop species-specific control
measures that will affect only the imported fire ant - specific
management agents. Our lab, directed by Prof. Larry Gilbert,
Chairman of the Zoology Dept., is following two lines of research
in this respect:
First - Pheromones
My own work is aimed at developing birth control for fire ants.
Like the queens of most ants, fire ant queens emit chemical
signals, pheromones, that serve to control reproduction in the
nest. Worker ants, reacting to these signals, kill young larvae
that otherwise could develop into new queens; in some cases, they
may even induce workers to kill the adult queens in the nest.
We have located the gland that produces the pheromone and are
working on isolating and identifying the precise chemical
structures that trigger the killer instinct in workers.
If successful, this could lead to a species-specific
bio-pesticide that would both eliminate existing colonies, and
prevent the establishment of new colonies without affecting the
populations of native ants.
Second - Natural Balances
Introduced to the U.S. without any of its natural enemies,
the imported fire ant thrives much more vigorously here than it
does in its native South America. One reason is that South
American fire ants are parasitized by a small fly of the phorid
So, the avenue we also are pursuing concerns this tiny fly
parasite of S. invicta fire ants. These flies lay their eggs
inside the heads of worker ants. The developing larva feeds on
the tissues in the host-ant's head and brain. After about three
weeks, the ant's head falls off, and the adult fly emerges from
it a few weeks later.
Although only a small percentage of worker ants from a colony may
be parasitized, the flies can have a dramatic effect on the
behavior of the entire colony. Working in Brazil, Matt Orr, a
researcher in our lab, has seen phorid flies chase fire ants away
from a food source. Normally, fire ants dominate a food source
near their mound, fending off any other ant species that
intrudes. But when the phorid parasites are active, fire ants
will run for cover, abandoning food, and leaving it free for
other species to plunder.
By interfering with the ability to collect food, the flies weaken
the fire ant colonies. Then, faced with such weakened fire ants,
other ants are in a better position to compete. (Concerning the
other ants, it should be noted that many of them are also
victimized by their own species-specific phorids.)
We currently have a permit to import the flies from Brazil
to our Austin lab, and a permit to release the phorid flies
in Texas. Some experimental, small scale releases are underway. .
We are now seeking funds to build a rearing facility. Given a
playing field made a little more level, our native ants should be
able to hold their own, reducing the imported pest to just
another member of the ant community.
After several decades of failed chemical control, the above
more ecologically sound means of controlling fire ants are being
studied. If successful, they will help reduce the fire ant
problem, not by killing these pests with toxic substances, but by
bringing them into balance with the native ecosystem.
Inquiries are invited: Edward l. Vargo, Ph. D.
Research Scientist, Zoology, University Of Texas, Austin, TX
Notes From The Editor
Even before the invasion of S.invicta, our three native fire
ants had been around long enough to have been controlled here by
their own predators, some of them by other species of phorid flies. The fact
that S.invicta is not "that serious a problem" in S.America led
to the search there for its own natural enemies.
Phoridae number in excess of 1,000 species. They are all very
small flies, and deposit larvae not only in the heads of ants,
but also nests of termites, bees, and even spider eggs. Many of
the flies are species-specific in their predaceous acts.
Pheromones are a means of chemical communication, not only
among insects, but for many mammals as well. They are often used
in courtship, sometimes released by males, while for other
species, it's the female that attracts via scents. Some moths can
detect infinitely tiny amounts of pheromones- the equivalent of
one or two molecules, and at surprisingly large distances.
But specific chemicals are also used to serve other purposes, as
by ants to lay down a chemical path for other workers to follow,
or to signal the colony that dangers abound and flee, or call for
belligerent or defensive behavior.
Readily detectable within its own species, the same chemicals may
help the predators get the same messages and act upon them.
The double-barrelled approach ongoing at U.T. is becoming
increasingly important in view of the inroads by S. invicta. The
colonies contain upwards of 100,000 to 500,000 workers, with as
many as several hundred with wings, and many with multiple
queens, some of which can live five or more years. They attack
and destroy other insects, some "good," and many "bad," which
tends to alter the balance that previously existed.
Today's practices of applied chemicals are only a temporary
measure, because they must be reapplied periodically. They also
kill the native insects, some "bad," and some "good."
Pheromones that can make them flee, or pheromones that can
make them kill queens, or small flies that can fight them on
their own turf, within their own colonies, these measures taken
individually or together with others will resolve many problems
here in Texas, and throughout the south.
As an occasional victim, may we wish them "GOOD LUCK." Sol
Reference by Ed Vargo