Ants are ranked the No. 1 urban pest by the structural pest industry, with an estimated $1.7 billion generated annually for pest management professionals in the United States (Curl 2005). An exotic species, the Argentine ant, Linepithema humile (Mayr), is an invasive pest with worldwide distribution and major economic and ecological impacts on urban, agricultural and natural environments (Vega & Rust 2001). They create problems in urban settings by tending homopteran pests and displacing native ant species. Pest management strategies for Argentine ants date back to the late 1800s when they were first introduced into the United States in the Port of New Orleans, probably off-loaded with cargo from Brazilian coffee ships (Newell & Barber 1913).
Controlling Argentine ants in and around homes is one of the major pest problems in California. In a survey of pest control companies in California, the Argentine ant was the most commonly encountered ant pest by pest management professionals and the most difficult to control (Knight & Rust 1990). In the greater San Diego area, they made up 85 percent of the collections by pest management professionals (Field et al. 2007). In addition to professional pest control services, many homeowners attempt their own ant control. For example, more than 50 percent of residents surveyed in California had attempted to control ants by applying insecticides (Flint 2003).
PCOS VS. HOMEOWNERS. While consulting as an expert witness on a class action construction defect case, in 2006, the senior author (Field) was able to document the treatment differences and successes for both pest management professionals and home-owners. The case involved approximately 290 homes in Southern California, with moderate to severe slab cracking, due to concrete pours that lacked proper tension support. In addition, the builder attempted to stop the cracking by cutting an expansion joint in a cross pattern through the entire slab for the purpose of relieving the stress. This attempt failed and the fissures in the foundations continued to form.
Part of the plaintiff’s lawsuit claimed the severe Argentine ant infestations that the homeowners were experiencing were a direct result of the cracks and expansion joints in the defective slabs. The senior author was retained to inspect the structures and determine how the ants were gaining access to the homes.
In performing discovery for the case, the senior author reviewed 75 CDs of depositions and noted that a set of specific questions had been prepared by counsel for the home-owner depositions. The initial review of the depositions revealed the data showed that, based upon the testimony of the homeowners, 82 percent still had ant problems after treating with various over-the-counter (OTC) pesticides, and 5 percent had achieved control.
The data further showed that when the homeowners hired a pest management professional, the degree of control was significantly improved even when the pest management professional was used without regular frequency. Pest management professionals solved the Argentine ant problem 44 percent of the time even when the pest management professional was used as a one-time treatment.
In cooperation with Dr. John Klotz at the University of California-Riverside, we prepared a survey to extract more data from the neighborhoods affected by the defective slabs. Our survey was designed to complement the data from the depositions provided by counsel. By combining the two sources of data, one can compare the results of pest control attempts by both the homeowners and pest management professionals. Nearly 90 percent of the time a pest management professional was used to control Argentine ants, the treatments resulted in either complete control or almost complete control.
HOMEOWNERS AT WORK. When home-owners treated their properties for ants, they reported 30 percent of the time they got complete control or almost complete control. However, 25 percent of homeowners reported that they had more ant problems after applying OTC products.
Ant control by homeowners can be difficult for the following reasons:
- Homeowners in California are restricted to either barrier products that are highly repellent or to toxic baits that Argentine ants find unattractive. Commercial baits that are attractive kill ants too quickly, before that bait can be dispersed through the colony (Rust et al. 2003);
- Repellent perimeter or barrier treatments are effective for some outside dwelling pests but Argentine ants generally find access to the structures by small gaps in the treatments;
- Homeowners are not trained to consider the outside environment as a dynamic ecosystem that requires the applicator to consider all entry points into the structure as potential sources of infestation.
Due to training that pest management professionals receive and the use of non-repellent products that exhibit horizontal transfer of the toxicant into the colony, the pest management professional is able to control Argentine ants effectively (Soeprono & Rust 2004a,b; Klotz et al. 2007).
Herb Field is chief operating officer, Lloyd Pest Control, San Diego. John Klotz is a cooperative extension specialist in the Department of Entomology, University of California-Riverside.
References
Curl, G 2005. A strategic analysis of the U.S. structural pest control industry-the 2005 season. A survey of PMPs in the U.S., Gary Curl Specialty Products Consultants, LLC.
Field, H.C., W.E. Evans, R. Hartley, L.D. Hansen and J.H. Klotz 2007. A survey of the structural ant pests in the southwestern U.S.A. (Hymenoptera: Formicidae). Sociobiology 49: 1-14
Flint, M.L. 2003. Residential pesticide use in California: a report of surveys taken in the Sacramento (Arcade Creek), Stockton (Five Mile Slough) and the San Francisco Bay Areas with comparisons to the San Diego Creek Watershed of Orange County, California. www.ipm.ucdavis.edu/PDF/PUBS/ncalifsurvey_1.pdf
Vega, S.J. and M.K. Rust 2001. The Argentine ant — a significant invasive species in agriculture, urban and natural environments. Sociobiol. 37: 3-25.
Newell, W. and T.C. Barber 1913. The Argentine ant. USDA Bur. Entomol. Bull 122
Klotz, J.H., M.K. Rust, L. Greenberg, H.C. Field and K. Kupfer 2007. An evaluation of several urban pest management strategies to control Argentine ants (Hymenoptera: Formicidae). Sociobiology 50: 391-398
Knight, R.L. and M.K. Rust 1990. The urban ants of California with distribution notes of imported species. Southwest Entomology 15: 167-178
Rust, M.K., D.A. Reierson and J.H. Klotz 2003. Pest management of Argentine ants (Hymenoptera: Formicide). J. Econ. Sci. 38: 159-169
Soeprono, A.M. and M.K. Rust 2004a. Effect of horizontal transfer of barrier insecticides to control Argentine ants (Hymenoptera: Formicide). J. Econ. Entomol. 97: 1675-1681
Soeprono, A.M. and M.K. Rust 2004b. Effect of delayed toxicity of chemical barriers to control Argentine ants (Hymenoptera: Formicide). J. Econ. Entomol. 97: 2021-2028.