Still Crazy After All These Years

The tawny crazy ant, Nylanderia fulva (Mayr), may be old news to some of you by now. PMPs in the Southeast have been struggling with this ant for more than a decade, some before 2002. It has been called the brown crazy ant, the Caribbean crazy ant, the Rasberry crazy ant, and finally, the tawny crazy ant, which is the Entomological Society of America’s formal common name. Why so many names? Partly taxonomic confusion, partly difficulty in identification if only a few worker ants are submitted. (Males are the caste needed for identification.)

However, you know you are dealing with the tawny crazy ant if:

• Yougo to an account and the ground seems to be moving.
• Clients think they have fire ants, but the ants crawl on them and do not sting.
• You’ve tried every perimeter spray treatment and you are ready to give the customer their money back (Figure 1).
• Your best recommendation is to pray for cold to knock the ants back.

Tawny crazy ants have been responsible for failed real estate transactions and electrical shorts; they even have outcompeted fire ants and pushed them out of a territory during the initial stages of invasion. We know these ants are faster to a food source, have significantly larger colonies than any other invasive ant, more queens (hundreds), and workers that can move colony fragments faster than you can bring your hose around a property to perform a perimeter treatment.

Face it: Eradication of tawny ant populations is not realistic when the ground appears to be moving because of large numbers. Do not make that promise to your customers. But, is there some relief? Yes!

In 2010, Bayer and the University of Florida partnered in search of solutions to manage these ants using an IPM approach. In June 2010, when populations were likely at their highest, we monitored ant activity at a site in Jacksonville. The site included a large concrete structure that was partitioned into 100-foot sections, each containing an area treated at the label rate with Suspend SC, 1 pound of Maxforce Complete in a secured container and an untreated control at the concrete structure. The purpose of placing the Maxforce Complete in a secured container was to prevent access by non-target organisms and to protect the bait from the harsh Florida summer rains. We also included a second untreated control site in a separate section of the property in anticipation of treatments confounding the first set of controls.

We monitored ant populations before and after treatment using Vienna sausage slices. The average ant count before treatment was 65 out of 100. Two days post-treatment, the ant counts in the Suspend SC treatment dropped to zero, but quickly rebounded to the original pre-treatment levels within two weeks. On the other hand, areas where Maxforce Complete bait was installed also dropped to an average of four ants, and remained low (about 19 of 100) over the same time period. Untreated controls placed away from the treated area continued to increase to about 79 of 100.

TAKE HOME #1. Sprays can provide immediate relief and can have a place as spot treatments, but should not be relied upon as the sole method of control for this ant. Granular baits can suppress populations over time, but ants can still be present at levels for customer concern.

After the ants around the Suspend SC treatment returned to pre-treatment levels, we installed additional secured monitors with Maxforce Complete bait around the concrete structure and continued to monitor almost weekly through the beginning of November 2010. We learned that 4 ounces of bait was sufficient and that changing the bait every three weeks instead of four weeks probably aided population suppression. We also included one dose of Maxforce Quantum dilute to see if the ants would consume the bait as a test for the next year’s trial.

The ants indeed consumed the Maxforce Quantum diluted in a 25 percent sucrose solution. We performed some laboratory tests and observed that both the undiluted and diluted Maxforce Quantum resulted in 100 percent control of small numbers of worker ants. We also observed that the workers tended to feed to repletion in a very short time on the Quantum dilute, then quickly shared the bait via trophallaxis; whereas ants also consumed the undiluted bait, but seemed to have a more difficult time manipulating and consuming the bait. Many ants did not appear to feed to repletion.

In 2011, we set our goal to suppress populations so that a service call would be once or twice a month instead of every one or two days. We began to monitor in February and performed our first treatment in April. We applied Maxforce Complete as a broadcast application according to the label along about 418 feet of fence line that separated a wooded area from a more manicured part of the property. Three days post-treatment, populations were reduced by about 72 percent, but within a week, the ants were creeping back in. We experimented with two times the label rate and got suppression for about 10 days, but the more interesting observation was that other ant species were beginning to move back in.

In June 2011, we began baiting with Maxforce Quantum dilute along the entire fence line and with Maxforce Complete in secure stations along the concrete structure about 56 feet away from the Quantum dilute stations. Both treatments ran parallel to each other, decreasing populations at the fence line by 48 percent. This was the first time that we had been able to significantly reduce populations and keep them suppressed. Of course, if you have millions of ants, decreasing the population by half still leaves millions of ants, but over time, it may have the effect of changing the odds against the tawny crazy ant.

TAKE HOME #2. The timing of your application is as important as the product. Baiting early in the season is important. Knowing when to use a granular and a liquid also can contribute to your success.

In May 2012, we applied Maxforce Complete and Quantum dilute in secured stations and proposed to add Suspend PolyZone as a treatment along the concrete structure perimeter when ant populations appeared. However, we noticed other species of ants (fire ants, pyramid ants, rover ants) moving back into the area in June. Our control site eventually lost all tawny crazy ant activity which effectively ended our experiment. We would like to say that the treatments caused the decrease and eventual disappearance of tawny crazy ants at our site, but we cannot draw that conclusion from this demonstration project. However, the fact that other species were moving back into an area meant that something changed so that the tawny crazy ant had less of a competitive advantage.

The area of Jacksonville where we did our testing struggled with the tawny crazy ant for more than 10 years. Columbian researchers who worked on controlling this ant in the 1960s and 1970s observed that around 10 years after the initial infestation, these ants began to “naturally” decline in population. The cause for the decline is still not known; however, many researchers are investigating potential causes for the eventual restoration of other ant species to areas previously completely dominated by the tawny crazy ant.

In 2015, a publication titled “Evidence of Niche Shift and Global Invasion Potential of the Tawny Crazy Ant, Nylanderia fulva” predicted areas of suitable habitats that ranged as far north as southern Missouri, Illinois and Indiana with preferred habitats in the southern states that already suffer from this invasive ant. Globally, eastern Mexico, the Caribbean islands and Central America are predicted to be “highly suitable” areas, in addition to Colombia, parts of Brazil, Ecuador, Peru, Bolivia, Paraguay, Uruguay and Argentina.

Some hypotheses of why this ant is successful when it moves into a new territory include an absence of natural enemies, its ability to exploit niches that may be empty, which allows colonies to grow to tremendous size, giving it a competitive advantage against other species — not just ants. Given its potential to spread globally, the most effective way to control the tawny cray ant is through monitoring and surveillance as a way to prevent its spread.

PMP TIPS. What follows are some tips for PMP to help manage tawny crazy ants:

1. Think about lines of defense. Use baits. Baits are transferred via trophallaxis, an ant behavior that shares food through the colony. Let the ants do the work for you.
2. Know what ants are consuming, then use that bait. Granular? Liquid? Both?
3. Start early in the season. Consider a granular bait that can be broadcast according to the label. Or put 2 to 4 ounces into secured containers, which will protect the bait from weather or irrigation to minimize reapplications. Secured rodent stations can work well. Note: Not all baits will hold up for three to four weeks in secured stations.
4. Bait at the edge of the property to slow the onslaught. Bait inside the property. Use sprays as spot-treatments, sparingly. Do not spray where you baited.
5. Inspect trees. If honeydew-producing insects are present (Fig. 2), treat with a systemic insecticide.
6. Previous research also indicates that colonies can harbor around trees as fall approaches (Fig. 3). Consider treating around the base of trees that harbor tawny crazy ants in the fall with a liquid insecticide. It may help you control these pests the following spring.
7. If you are called to an account where ant populations are getting into the structure, you may have to use a contact insecticide, but be mindful of the pyrethroid label language changes and pollinator protection language. Contact insecticides can be highly effective, but may lead to ants dying inside the structure which can sometimes trigger a callback from the homeowner. Discuss this option with customers to set realistic expectations.

Faith Oi is an associate extension scientist, University of Florida, Entomology and Nematology Dept., Gainesville, Fla. John Paige III is with Bayer Environmental Science, Research and Development.