[Ant Control Issue] Big Question

In most recent surveys, ants are ranked as the most important pest that pest management professionals face in structural pest control. While treatments of existing ant infestations usually require determination of nests and elimination of indoor ant populations, occasional invading ants are often controlled with perimeter applications of liquid residual insecticides.
With the advent of new non-pyrethroid chemistry appearing on the market, a perception has arisen that pyrethroid insecticides are repellent to ants and that perimeter treatments with pyrethroids can exacerbate ant problems by trapping foraging ants inside the home. This article summarizes laboratory, field research and observations with dried surface deposits of a microencapsulated pyrethroid to evaluate these perceptions. Microencapsulation involves the creation of a polymer or other capsule around the active ingredient. This encapsulation can change the release rate, adhesion, and resistance to environmental conditions vs. an “unprotected” active in other types of formulations (WP, EC, SC, etc.).

EXPLAINING REPELLENCY. “Repellency” is a term used to describe negative chemotactic responses in insects that causes orientated directional movement away from the chemical stimulus. If insects are repelled away from a treated surface (deterrence) before picking up a lethal dose of insecticide, the effectiveness of the treatment may be compromised.
A stage of pyrethroid poisoning is hyperactivity or irritancy of the exposed insect. This response, not to be confused with deterrence with regard to treated surfaces, involves rapid, random movements. This response accounts for the flushing effects of pyrethroids on cockroaches, and results in the subsequent death of the insect with more potent pyrethroids. This effect will vary with the insect species, the type and formulation of pyrethroid and the rate of application.
The phenomenon of ants becoming trapped by pyrethroid treatments is poorly documented, and generally seems primarily based on general assertions and incidental observations. It is also inappropriate to generalize such phenomena within a class of chemistry. An insect’s response to a compound can vary according to how that compound is formulated (Wege, et al. 1999). 

RIFA TESTS. Fire ant (Solenopsis invicta) workers were placed in an arena containing unglazed ceramic tiles (model porous surface) treated with either a microencapsulated pyrethroid formulation of lambda-cyhalothrin (Demand CS Insecticide with iCAP technology) or water. The arena construction ensured that ants foraged in contact with a tile at all times. Ants were free to move between tiles. The time spent on the treated tile or untreated tile was recorded for a period of five minutes. (See chart at left.)
The results showed that there were no significant differences between times spent by the foraging fire ant workers on a tile treated with Demand CS with iCAP technology compared to a tile treated with water. (Daly, 2000).

PHARAOH ANT TESTS. Subsequent work (Bywater, 2002) determined if residual insecticide deposits were repellent to workers of the Pharaoh ant, Monomorium pharaonis.
Single whole colonies containing workers, queens and larvae were placed in test arenas with a water source. In each arena, ants were presented with two food sources located equidistant from the colony.
One of the food sources was surrounded by a residual treatment of water and the other by the test substances. The test substances evaluated included a microencapsulated pyrethroid (Demand CS) and a non-encapsulated formulation of a second insecticide both applied at 0.06 percent, and a known ant repellent (Farnesol Repellent, 3,7,11-trimethyl-2,6,10-dodecatrien-1-ol). Water was used as a control.
Assessments of worker ants were made every 20 minutes to calculate the relative proportions of foraging ants in each arena that chose to cross the dried test chemical deposits or the water-treated area to reach food. The test was repeated six times for every treatment combination. Results were averaged and divided into three time groups, 0 to 40 minutes, 41 to 80 minutes or 81 to 120 minutes.
In the initial forage and recruitment phase of the test (0 to 40 minutes), there was little difference in the proportion of ants choosing to cross either a residual deposit of Demand CS or water to reach food, with 49.3 percent of the foraging ants crossing the Demand CS treatment, compared with 50.7 percent crossing the water treatment.
This was almost identical to that in the water vs. water test, where ants split 46.5 percent vs. 53.5 percent between the two food sources.
The trial with the non-encapsulated formulation revealed 31 percent of ants crossing the chemical treatment vs. 69 percent crossing the water barrier.
DISCUSSION. Soeprono and Rust (2004) found in tests of treated surfaces with Argentine ants that some pyrethroids did not reduce foraging significantly less than controls, although other pyrethroids did cause a significant reduction in foraging, suggesting that active and formulation may be relevant in this response. Speed of kill may be important in affecting behavior and movement after exposure. The former authors did not test encapsulated formulations of lambda-cyhalothrin.
Behavioral tests with ants are difficult, and many current techniques can be criticized as influencing behavior or otherwise introducing bias. Direct measurements of electrical stimulation of an ant’s antenna when exposed to various chemicals are possible and such work may be more definitive with regard to studies of deterrence (Dan Suiter, personal communication).
Microencapsulated pyrethroid formulations have been confirmed as efficacious perimeter treatments for ants under field conditions with no indications of repellent behavior compromising the effectiveness of the treatment (e.g., Morris, 1998; Suiter & Ratliff, 1999).
Where unsatisfactory control has been achieved from an application of pyrethroid insecticides, the first factors that should be investigated include location and frequency of irrigation, exposure to direct sunlight and high temperature, whether or not ground cover may be breaching the treatment and other factors (Rust, et al. 1996).
Microencapsulated formulations appear less vulnerable to some of these environmental parameters as compared with other pyrethroid products, offering superior results in difficult conditions.

Authors’ notes: Thank you to Dr. Dan Suiter of the University of Georgia for helpful comments and suggestions concerning a draft of this article.

Farnesol Repellent is a registered trademark of Technology Science Group, Goodyear, Ariz. Demand CS with iCAP technology is a registered trademark of a Syngenta group company.

The authors are public health research scientist, Syngenta Research Laboratories, Stein, Switzerland and former senior technical representative, Syngenta Professional Products, respectively. They can be reached at abywater@giemedia.com and dkaukeinen@giemedia.com, respectively.

References
Bywater, A. (2002) in Syngenta Internal Report IPP02/004B
Daly, G (2000) The response of the red imported fire ant Solenopsis invicta to residual deposits of synthetic pyrethroids. MSc. Thesis, Imperial College of Science, Technology & Medicine, Ascot, UK.
Morris K D (1997) in Syngenta Internal Report TMPH 97E034/B
Rust M K, Haagsma K, and Reierson, D A. (1996) Barrier sprays to control Argentine Ants. J. Econ. Ent 89 (1) p134-137.
Soeprono, A M and Rust M K (2004) Effect of Delayed Toxicity of Chemical Barriers to Control Argentine Ants (Hymenoptera: Formicidae). J. Econ. Ent. 97(6): 2021-2028.
Suiter D R and Ratlif C R (1999) in Syngenta Internal Report TMPH 99E012/B
Wege, P J; Hoppe, M A; Bywater, A F; Weeks, S D & Gallo, T S (1999) Proceedings of the 3rd International Conference on Urban Pests. Eds. W. H. Robinson, F. Rettich and GW Rambo. Pp301-310
Wege, P J; Bywater, A F; Le Patourel, G N J & Hoppe, M A (2002) Proceedings of the 4th International Conference on Urban Pests. Eds. S.C Jones, Zhai, J and W.H. Robinson. Pp135-147.