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Fire Ants-- Applying Nature's Controls

by Ed Vargo, Ph.D.
Research Scientist, Dept.Zoology, U.Texas
Reprinted from TBGS newsletter issued December 1994- updated April 1996, and is to be progressively updated as research continues.

[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" controls.

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.]

Fire Ants
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 family.

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 78712

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 Steinberg, Editor

Further Reference by Ed Vargo