Movin' on up the Map

For years, the red imported fire ant has been a source of fear and pain for the 40 million Americans who live in infested areas. Fire ants are highly aggressive, spilling forth when their mounds are disturbed, inflicting painful stings that result in burning, itching, blisters and in rare cases, death. While the threat of fire ants has become a way of life for many Southerners, their northern and western neighbors are now on the lookout for the first signs of these unwanted newcomers.

MIGRATION UPDATE. Fire ants have been migrating across North America since their introduction in the 1930s in Mobile, Ala. Since their arrival in the United States, fire ants have moved throughout the Southeast and north along the East Coast. The western fire ant expansion has reached across Arizona and New Mexico into California. Fire ant migration has been exacerbated in part by the human relocation of fire ant-infested soil, nursery stock and sod. Traditionally believed to be limited by arid conditions, fire ants may have been introduced to western states by development in areas where water is plentiful. With few natural predators, a fast reproductive capacity and an aggressive nature, fire ants have flourished. Today, they occupy about 330 million acres of lawns, public parks, schoolyards, pastures and commercial landscapes. (Source: 2005 Federal Imported Fire Ant Quarantine information from the Code of Federal Regulations USDA-Aphis)

No other ant has been studied more than the fire ant, and several scientists have created predictive models to determine the range of fire ant migration. It was always thought that fire ants could only move into an area with mild winters, since they do not hibernate and need to keep up with colony maintenance and foraging activities. Most of the research used to predict the northern expansion of fire ants is based upon their “cold tolerance.” Probably the most comprehensive model used to predict the expansion of fire ants in the United States was developed by Korzuukhin et al. (2001). This model predicts the fire ant range under natural conditions, and to date, has correctly forecasted fire ant migration into southern Delaware, throughout Tennessee and Oklahoma, and across the Southwest to California. The model also suggests that fire ants could reach as far north on the West Coast as Washington.

Are fire ants evolving or adapting the ability to live in cooler climates? To date, there is no evidence to suggest that fire ants are developing any physiological adaptation to cold tolerance or arid conditions. What we do know is that when environmental conditions change, fire ants rely on the structure and placement of their mounds to help thermo-regulate the colony, which ultimately helps it survive unexpected conditions. For example, the dome at the top of a fire ant mound helps direct heat to the colony. Therefore, when establishing a colony in colder climates, fire ants may build their mounds against brick retaining walls, homes or fence posts to absorb extra heat.

BAITING TECHNIQUES. For effective results with baits, pest management professionals should start with a broadcast treatment when fire ants are actively foraging. In the spring, foraging occurs throughout the day. On hot summer days, baits are most effective when applied late in the day when the ground starts to cool off and fire ants prepare for overnight foraging. Broadcast treatments typically take less time than inspecting for individual mounds and also will control small colonies that are just developing that easily could be missed during an inspection. It’s also important to keep the weather forecast in mind; do not apply bait when rain is predicted to occur in the next 12 hours. Finally, always remember that using fresh bait improves the overall treatment.

Reference
Korzukhin, M.D., S. D. Porter, L.C. Thompson, and S. Wiley. 2001. Modeling temperature-dependent range limits for the red imported fire ant (Hymenoptera: Formicidae: Solenopsis invicta) in the United States. Environmental Entomology 30:645-655.

The author is a research scientist for Bayer Environmental Science. He can be reached at tmacom@giemedia.com.

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As fire ants enter new territory, pest management professionals should learn to detect their mounds, identify the species correctly and treat infestations quickly. Allowing fire ants to establish colonies only allows them to expand their range more quickly. Choosing the right control method is of utmost importance. A pest management professional’s best bet is to consider a variety of approaches that can offer quick knockdown and long-term control of an infestation.

Mound treatments are ideal in cases of a single mound. Broadcast treatments, on the other hand, are the best choice when faced with several mounds in a specific area. Depending on the location, population density and type of infestation, PCOs should consider the merits of either a “passive” bait treatment or an “active” broadcast direct-contact treatment.

A granular treatment such as Bayer Environmental Science’s TopChoice offers year-long control and prevents the formation of new colonies with a single broadcast application. The treatment remains active all the time, as its unique chemistry binds to the soil, which is helped along by rainfall. Fire ants unknowingly contact the active ingredient, fipronil, and bring it back to contaminate the rest of the colony through the “Domino Effect.” TopChoice is ideal for treating large areas, lawns, sports fields and parkland.

For faster control and control of protected colonies hidden under sidewalks, driveways and slabs, a bait such as the new Maxforce FC Fire Ant Bait may be the best choice. Specifically formulated to please the fire ant’s palate, it’s the only fire ant bait that features the active ingredient fipronil, which kills by both contact and ingestion, and the benefits of the Domino Effect.™ It can be used as a broadcast or mound treatment.

Maxforce FC Fire Ant Bait also can be used in combination with a TopChoice application. For example, a pest management professional might use TopChoice to treat high-traffic areas like a school athletic field and use the bait to treat around protected areas below bleachers and along sidewalks.
For more information about fire ant control methods from Bayer, call 800/331-2867. — Tom Macom