[Ant Control Issue] A Powerful Combination

Solenopsis invicta, the red imported fire ant, is a nasty critter. Since its introduction to the United States from South America, it has spread throughout the Southeast and isolated areas in the Southwest. The venom of its sting causes welts, possible anaphylactic shock and is just down right painful. Fire ants occasionally intrude inside homes but are usually an outdoor pest.
Control methods for this species are numerous — broadcast baits are typically the standard method of control for single and multiple mounds. Though there are other products that work well in different ways, particle baits always will have a place in the pest management industry’s toolbox. Particle baits are even used by termite technicians to control ants that have infested termite baiting stations. Unfortunately, 99 percent of formulated baits currently available are manufactured for broad-spectrum uses and are not customized for specific ant species. Customizing baits would help incorporate Integrated Pest Management (IPM) strategies into a baiting program.
IPM involves the use of a variety of techniques (i.e., cultural, mechanical and chemical, to name a few) to reduce the pest population below a defined tolerable “threshold” for a specific “system” (i.e., corn, cotton, citrus, households, etc.). Long-term goals of IPM are to maintain profits for the pest management firm, to maintain environmental quality and to sustain management practices.
For many years, Iowa State’s Dr. Larry Pedigo has been a national leader in IPM, and his approach to establishing Economic Injury Levels (EIL) has been the primary method used in the United States. While the foundation of IPM theory has been incorporated into urban pest management, application of the “threshold” level in urban settings is practically non-existent — not many people, for example, will wait six to eight weeks for parasitic wasps to reduce a roach population in their home. Even so, some aspects of IPM have been applied. As an example, efforts are commonly made to educate the customer about the efficacy of cutting back tree limbs (mechanical/cultural strategy) to prevent carpenter ant intrusions.
For the pest management professional, it is imperative to understand that it is the incorporation of a multitude of techniques that facilitate the reduction of chemical use. Please note that IPM is not purposely trying to reduce the use of chemicals. The majority of times the pest management professional solely uses chemicals to achieve proper control. What is important here is the application technique itself, which can help reduce chemical use.
Application technique is an aspect of IPM. In many situations, customized application techniques can result in efficient control with reduced chemical use. This is important in reference to baits, because bait particle size, in addition to the timing of application, can influence the efficacy of particle baits.

UNIVERSITY RESEARCH. As a University of Georgia graduate student, I wanted to “test the waters” with IPM baiting strategies. I had the resources that gave me the ability to play with several ideas and bring them to fruition. The objective of one of the studies I conducted as a graduate student was to determine whether particle bait applied at the lowest spreader setting, with the tiniest particles eliminated, would achieve significant reduction in red imported fire ant population levels.
A single research plot in Clarke County, Athens, Ga., measuring 120 by 40 meters, was used as the study site. The single plot was divided into 12 individual subplots measuring 10 by 40 meters. A different subplot was baited every two hours to measure forager abundance (see the blue line in the figure on page 66). Petri dishes baited with 1 gram of canned tuna fish in oil were used to measure forager abundance. Bait dishes were placed at 1-meter intervals along the lengthwise diameter of each rectangular subplot. These dishes remained uncovered for 45 minutes, after which they were covered, sealed, and placed on ice for transport to the lab, where the ants were counted and stored in 75 percent ethanol alcohol. Three days after initial petri dish baiting, particle bait was applied by using a hand-held spreader (Scotts, Marysville, Ohio). To incorporate IPM, particle bait was sieved through a size 20 sieve mesh (Fisher Scientific, Pittsburgh, Pa.) to eliminate the smaller particles (sieve size 20 and smaller). Particle bait then was applied using half the recommended amount specified on the label. The smallest particles were removed because S. invicta was found to prefer larger particles in lab studies (unpublished data). Particle bait was applied at 11:00 a.m., because the first sampling date indicated high fire ant foraging activity at this time. Sampling dates were in August and September. Differences in ant forager numbers before and after application of bait were then determined.
All ants collected were S. invicta. A total of 18,073 ants were collected before the application of particle bait and a total of 540 afterwards (September). Clearly, the sample dates exhibit significant differences. The figure at right shows the number of foragers collected during the 24-hour baiting period for both sampling dates. Note the difference! The blue line indicates numbers of foraging workers exhibited by S. invicta before particle bait application. I use this as an indication for optimal times to bait, the theory being that if one applies bait during peak foraging times (high points of the blue line in the figure at right), one will achieve maximum control. What I find most interesting is the pink line, showing numbers of foragers a month after particle bait application, at the same time of the day as that when numbers of foragers were measured before particle bait application. Look at the large reduction and how it correlates with the blue line in the figure. Even when the population decimated in the plots, S. invicta still exhibits the same foraging time line.
One might ask the question whether differences were associated with temperature. The answer is no. According to the Georgia Automated Environmental Monitoring Network, temperature ranges during both sampling periods were theoretically within limits that would allow maximum foraging activity. In regards to year-round foraging, Porter and Tschinkel (1987, J. Econ. Entomol. 16: 802-808) postulated that year-round 24 hour foraging should occur in south Florida and south Texas. Year-round 24 hour foraging will not occur in central Georgia, but 24 hour foraging should occur there from mid-March through October. Thus, I am confident that the difference in numbers of foragers collected was not associated with temperature.

MEANING FOR PCOs. The main point is that visual observations verified bait retrieval, and significant results occurred with minimal product used. Would the same control occur if bait particles were not sieved and sorted? Probably so, but one should keep in mind the issue of level of chemical use.
Pest management professionals should focus on chemical use and efficacy. Few particle baits are manufactured in the specific sizes that would narrow their use niche but make them more efficacious for particular ant species. This type of formulation is what pest management professionals need — baits that are manufactured for species with specific head capsule widths. Research has noted that the size of the bait particle selected and carried by a worker ant is positively correlated with the head capsule width of the ant.
Furthermore, Hooper (1998 Ph.D. dissertation, University of California, Riverside) postulated that matching particle size with a specific pest ant species could increase the amount of toxicant brought into the colony, thereby increasing the measure of control with a bait. Perhaps the use of bait formulated for a specific species, such as the red imported fire ant, will help reduce the impact on native ant species that compete against it. Is this IPM or what?
The pest control industry is still in its early stages regarding the incorporation of Integrated Pest Management strategies. Again, the down side is that there is no “threshold” when dealing with homeowners or commercial customers. Even so, there are ways to control pest populations by tweaking methods in such a way to reduce chemical use and fine tune the targeting of the “target pest.” The task requires diligence and an understanding of the species, but the results can be remarkable.

The author is a regional technical director with HomeTeam Pest Defense. He can be reached at ripser@giemedia.com.