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June 25, 2007

Researchers study how fire ants spread during mating flights

Scientists have calculated flight distances and are measuring weather conditions that occur during aerial swarms of the red imported fire ant in a step toward better predicting the insectís spread in California.

   UC Riverside entomologist Michael Rust prepares sticky traps and a balloon for his research project with red imported fire ants.
  

UC Riverside entomologist Michael Rust prepares sticky traps and a balloon for his research project with red imported fire ants.
Photo by Les Greenberg

In the southeastern United States, massive fire ant colonies destroy crops, damage farm and electrical equipment, and hasten soil erosion. Humans and livestock are particularly vulnerable to the insect's stinging attacks.

Although the red imported fire ant is common in 12 southern states, it is new to California and now infests numerous residential and commercial areas in Orange, Riverside, Los Angeles, and to a lesser extent, San Bernardino and San Diego counties. The ant has also been found in almond orchards in the Central Valley. The spread of these ants has largely been a result of the introduction of infested plants and honeybee hives infested with fire ants from other states.

During the three-year project, University of California Riverside entomologists Michael Rust and Les Greenberg learned how to tether the ants to flight mills and measure their flight duration and speed. “Once tethered to the arm of the flight mill, the ants fly in circles around a pivot point,” explains Rust. “We can record how long they fly and how long it takes them to move 360 degrees. Using the arm of the flight mill, we calculate the circumference of the circle it traces. From this, we learn the ant’s flight distance.”

Armed with this new information about fire ant flight distance, Rust and Greenberg then set out to determine weather conditions that occur during aerial swarms of the insect.

“Normally, in the southeastern United States, fire ant flights are triggered by warm weather, rainfall, and subsequent high humidity,” says Rust.  “Under California conditions, we have seen flight activity associated with irrigation. For example, in the Coachella Valley on almost any summer day, flight activity occurs at some locations after sprinklers turn off at large, infested golf courses or city parks. Mating swarms may be found near these large irrigated areas. Walking through these areas, we can see whether females are surfacing and preparing for flight.”

“Rain is a precursor to fire ant flights. However, the queens wait for sun and blue sky before they’ll fly,” says Greenberg. “Also, they don’t fly if it's windy.  So, it’s unlikely that fire ants will fly during or shortly after thunderstorms.”

During the last year, researchers have perfected and extensively tested the device they need to study flight in fire ants. Rust and Greenberg recently took their equipment to Alabama for field trials with urban entomologist Art Appel and extension entomologist Fudd Graham from Auburn University. Auburn is in an area heavily infested with fire ants where rain stimulates flights. Researchers want to know how the ant flights there differ from southern California where rainfall and humidity are severely limited.

Scientists used a 10-foot helium balloon packed with weather instruments to record temperature, humidity, and wind speed. They used a ground weather station to compare with the instruments on a tether. Large sticky traps were lifted with the balloon at 50-foot intervals along the tether. These triangular traps are about 2 feet long, and their inner surfaces are coated with a sticky material that traps the insects.

“This spring in Alabama we trapped our first flying fire ant in these traps. This is significant because right now there aren’t any monitoring traps for fire ants,” says Rust. With this experience, the researchers are designing improvements in the equipment for future trials in California.

With the balloon and weather equipment, Rust and Greenberg logged wind speed, temperature, humidity, and barometric pressure at the swarm, as well as conditions measured at various altitudes.

“These discoveries will help regulatory agencies to search for new infestations in particular areas based on weather conditions and the influence it has on fire ant swarming, rather than randomly searching for new infestations,” says Rust. “The ability to trap flying ants could also lead to the development of attractants that could be put into traps as a monitoring tool.”

The UC Exotic/Invasive Pests and Diseases Research Program, a collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research, sponsored this project. U.S. Department of Agriculture, Cooperative State Research, Education and Extension Service, funds the program.

To learn how to identify the red imported fire ant, visit www.ipm.ucdavis.edu.

California currently does not have a program aimed at eradicating the red imported fire ant within the state. In Orange County and the Coachella Valley, homeowners should contact their local Vector Control agency for advice on control measures. In Los Angeles and San Diego counties, the local agricultural commissioner can be contacted for advice. In other locations, any suspected infestation should be reported using the statewide toll free number that has been set up by the California Department of Food and Agriculture for this purpose (1-888-4fireant). There is also an informative web site, http://www.fireant.ca.gov. Once contacted, state personnel will determine if the ants are red imported fire ants, and if so, will apply approved treatments free of cost or recommend a course of action.

Resources

High-resolution image (140KB) "UC Riverside entomologist Michael Rust prepares sticky traps and a balloon for his research project with red imported fire ants." Photo credit: Courtesy of UC Statewide IPM Program, by Les Greenberg.

High-resolution image (668KB) "Red imported fire ant." Photo credit: Courtesy of UC Statewide IPM Program, by Jack Kelly Clark.

High-resolution image (260KB) "UC Riverside entomologist Michael Rust prepares sticky traps for his mating study of red imported fire ants." Photo credit: Courtesy of UC Statewide IPM Program, by Les Greenberg. Photos are for use with this release only. All other uses see Legal Notices.

Red Imported Fire Ant Pest Note

Contacts

Stephanie Klunk, Communications Specialist
UC Statewide IPM Program
(530) 754-6724

Les Greenberg
Department of Entomology
University of California
Riverside, CA 92521
(951) 827-3217

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