Imported fire ants are a major pest problem throughout the Southeast. No methods have been developed to successfully eradicate fire ants, but research may ultimately provide a method to eliminate this pest.
Two species of imported fire ants were accidentally introduced into the southern United States from South America in the early 1900s. The red imported fire ant, Solenopsis invicta, and the black imported fire ant, Solenopsis richteri, interbred and produced sexually active hybrid ants.
Imported fire ants have two colony types: the single queen (monogyne type) and the multiple queen (polygyne type).
Workers in ant colonies with a single egg-laying queen are territorial and will fight with fire ants from other colonies.
Worker ants in colonies with two or more egg-laying queens do not have this territorial behavior. Therefore, these polygyne fire ants occur in much higher densities because the mounds they build can be closer together. More mounds and ants mean more problems in areas infested with the polygyne colonies.
The single-queen colony is predominant throughout most of the southern United States, while the multiple queen colony is predominant throughout the eastern two-thirds of Texas.
In 2003, the U.S. Department of Agriculture estimated that the annual cost of problems caused by imported fire ants in agriculture was $750 million, with $38 million in losses to livestock.
When land needs a fire ant treatment, the two-step method is most suitable. It relies on the broadcast application of a bait-formulated product once or twice per year.
Baits can be broadcast using handheld seeders or spreaders. They must be calibrated to apply the amount of product per acre as directed on the product label. Rotating or vibrating agitator mechanisms are preferable because they do not grind the bait particles, which can result in clogging.
The hopper opening should be adjusted as small as possible to allow bait to drop onto a spreader fan. Calibrate by applying bait to an area of known size. For larger areas, use a vehicle-mounted, electric-powered applicator specifically manufactured to broadcast bait products.
Fire ant workers forage for food only during favorable conditions. This occurs when air temperatures range from 65 to 90 degrees Fahrenheit. In the heat of the summer, foraging occurs mostly at night, so baits should be applied in the late afternoon or early evening. During winter months and times when colonies are not actively producing brood, attractiveness to baits may be reduced.
At certain times, some colonies may be more attracted to other food sources and will ignore the bait. When in doubt about product freshness or presence of foraging behavior, place a potato chip or a small pile of bait near a fire ant mound. If ants are carrying off bait particles or the potato chip within 30 minutes of placement, the time is right and the bait is attractive.
Faster-acting mound treatments - which are more expensive and labor-intensive - are used to treat only nuisance ant mounds that may develop between broadcast bait applications. This approach can provide about 90 percent control that can be maintained at a relatively low cost.
Acephate products, such as Orthene, are dust formulations, and they can be used straight from the container by sprinkling powder on top of the mound. Alternatively, a contact insecticide, such as fipronil granules, or a pyrethroid liquid or granular formulation, such as permethrin and bifenthrin, can be applied to the surface of the entire lawn as directed.
Fire ant problems in sensitive areas such as compost piles and gardens may be prevented by treating around the perimeter with a bait or granular insecticide. If it is necessary to control fire ants in vegetable gardens, use only products registered for this use.
For more information on fire ant management in Texas, visit the Web site fireant.tamu.edu.
• Eric Zimmerman is a Texas Cooperative Extension agent in Brazos County.