[Ant Control Issue] To Bait or Not to Bait? That is the Question.

When treating for ants, pest management professionals (PMPs) generally have two options: baits and sprays. I was curious to know which option PMPs typically chose and asked PCT magazine to run an online poll that would shed some light on the issue. The poll appeared in the fall of 2011, and the question was: “How do you treat for ants?” The poll received 38 responses, with the following results: bait only (6 votes, 16%), spray only (5 votes, 13%), bait and spray (27 votes, 71%).

While the sample size is rather small, it is clear that most PMPs use a combination treatment when treating for ants. But why? Is the combination treatment really superior to either baiting or spraying alone? Is it perceived to be more effective based on the idea that more is better? Is it viewed as insurance against a potential failure to achieve desired control? Is it standard operating procedure, or does it depend on the situation or the ant species? Is it what the customers want? Is the combination treatment really worth the extra time and expense?
 

Key Differences. Baits and sprays may be used in a variety of combinations, but a typical treatment involves spraying outside and baiting inside. This is especially true when treating for opportunistic ants that prefer to nest outdoors, but may occasionally enter buildings in the search for resources.

Baits and sprays differ in the way they are formulated and applied, and they exhibit a number of other important differences as well. One major difference is longevity, with spray treatments lasting much longer than baits. Depending on the active ingredient and the environmental conditions, a typical outdoor spray application lasts four to 12 weeks. In contrast, a bait application may only last a few days before the bait is completely consumed, degraded by environmental conditions (e.g., washed off by rain or dried out by sunlight) or consumed by non-targets such as rodents, birds and, occasionally, pets.

Another difference is the effective range. Sprays are generally non-selective and are, therefore, effective on a wide range of ant species and other peridomestic pests such as cockroaches, termites, pillbugs, spiders, earwigs, beetles and crickets. In contrast, baits have a much narrower window of activity because they are specifically formulated for ants, are consumed mostly by ants and, as a result, kill only ants. In fact, competition for the bait among different ant species may prevent some species from consuming the bait and limit mortality to the dominant species.

Baits and sprays also differ in their efficacy relative to the level of sanitation. Sprays are not negatively affected by the lack of sanitation, such as competing food sources. In fact, the efficacy of sprays may be enhanced by the lack of sanitation, such as applications made in areas where ants are actively foraging for food (e.g., around garbage cans or landscape plants harboring honeydew-producing insects). Baits are strongly affected by a lack of sanitation, and the presence of competing food resources from honeydew-producing insects or human food may severely limit bait intake and efficacy.

Another important difference is the amount of experience necessary to use the product. Sprays are applied according to standard pesticide labels, generally require less experience and less knowledge of pest biology and are more forgiving when misapplied. Baits are far less forgiving and may require more experienced technicians who can identify the ant species, understand the feeding and foraging habits of the different species and pinpoint the exact nesting locations.

Finally, a major difference is cost. Relative to sprays, active ingredients cost much more when incorporated into baits. The active ingredient in one popular ant control product costs $1.50 per gram when formulated into a liquid spray formulation. The same active ingredient costs $557 per gram when incorporated into a gel bait. The active ingredient in another commonly used ant product costs $1.20 per gram when formulated as a spray and $26,667 per gram when formulated as a gel bait. (In comparison, the price of gold recently reached a new historical high of $55 per gram.)

In summary, spray formulations show a number of attributes that make them highly attractive and highly suitable for effective pest management.
 

Field Studies. Two field studies were conducted to compare the efficacy of spray, bait and combination treatments of indoxacarb (DuPont Crop Protection) against urban pest ants. The first study involved odorous house ants nesting around structures. Each of the three treatments was applied outside only (five structures per treatment) and the efficacy of the treatments was monitored using visual inspections. The results showed that the spray treatment (0.05% indoxacarb) was highly effective and resulted in 100 percent mortality in all colonies within a 24-hour period. The bait treatment (0.05% indoxacarb) was substantially less effective. Little mortality was observed during the first 24 hours, but mortality gradually increased and reached 82 percent eight days after the treatment. The combination treatment was highly effective and eliminated all colonies within 24 hours.

The second study involved black carpenter ants nesting within trees. The results were similar to those observed for odorous house ants. The spray treatment was highly effective and gave 100 percent mortality in all colonies within 24 hours. The rate and the level of mortality with the bait treatment were substantially slower, but mortality gradually increased and reached 71 percent on day eight. The combination treatment was initially slower than the spray treatment, but eventually resulted in 100 percent mortality.

These studies highlight two main points. First, the bait treatment is significantly slower and less effective than the spray treatment. Second, there is no benefit to using the combination treatment as the spray treatment is already highly effective. Post-treatment inspections of colony nesting sites revealed that the bait treatment often reduced ant counts, but rarely killed the colonies — the ants were still present, but stopped feeding or relocated nests to nearby locations.

In contrast, the spray treatment completely eliminated the colonies. This suggests that baits are better suited for ant management (partial and temporary reduction of colonies), whereas sprays are better suited for ant control (complete and permanent elimination of colonies).

In summary, the spray treatment should be the preferred method for controlling urban pest ants due to faster control, greater efficacy, lower cost and less environmental impact.
 

To Bait or Not To Bait? The efficacy of pest management depends on many factors including proper inspection, a thorough understanding of pest biology and a wide range of other factors. Selecting the management tool (bait or spray) is only one factor, and not at all the most important one. While this article highlights the benefits of sprays, baits are still a great tool for managing ant infestations. Indeed, the 16 percent of PMPs who use baits alone may very well have excellent results depending on the specific nature of the infestations they are targeting.

Baits are best suited for dealing with relatively small, single-queen colonies (e.g. big-headed ants), larger colonies that are highly discrete and thus easier to treat (e.g. mound-building species such as fire ants or field ants), or in situations where nests may be difficult to reach with sprays (e.g., pharaoh ants inside buildings). In contrast, sprays are better suited for general ant control, especially when dealing with infestations of large colonies consisting of multiple queens and nesting locations (e.g., Argentine ants, odorous house ants or white-footed ants). Also, baits are typically preferred for indoor treatments to reduce any potential hazards and avoid other issues such as staining.

In contrast, sprays are typically preferred outdoors. Regarding combination treatments, they might make sense under some circumstances. A good example of a combination treatment might be spraying for odorous house ants around the perimeter of a structure and baiting for pharaoh ants inside the structure.

In conclusion, the decision to use specific ant management tools will depend heavily on the unique circumstances of each case. Thus, information presented in this article is not intended to serve as standard operating procedure for ant treatments, but is meant to stimulate discussion regarding current practices in ant control.
 

Future Directions. Based on the above field studies, the initial conclusion is that there is no real benefit to using baits in conjunction with sprays when treating for ants. Furthermore, it appears that sprays are generally faster and more effective than baits.

However, this conclusion is based on a single active ingredient and a limited set of studies. Future work should focus on evaluating additional spray and bait formulations and active ingredients across a more diverse set of ant species. Further, the costs and benefits of baits vs. sprays should be evaluated for other urban pests that are typically targeted with both tools, such as cockroaches. The benefits of such studies would be numerous including cost savings for the industry, improved efficacy of pest management and possible environmental benefits.

The author is with the Department of Entomology, Purdue University, West Lafayette, Ind. To contact Dr. Buczkowski, write gbuczkowski@giemedia.com.

Acknowledgements
Thanks to PCT magazine for running the online poll and all PMPs who participated, DuPont Crop Protection for sponsoring the field studies and donating Arilon and Advion insecticides, M. VanWeelden and M. Nour for help with the field studies and the Industrial Affiliates Program at Purdue University for partial financial support.

Want to Learn More?
To learn more about Urban Entomology at Purdue University visit: http://www.entm.purdue.edu/entomology/urban/home.html. To learn more about Dr. Buczkowski’s research program visit: http://www.entm.purdue.edu/ants