[Ant Control] Big Trouble

Ants are the pinnacle group of social insects and are the most successful land animal on earth. It is no wonder they are able to utilize almost every possible niche that they can find in human dwellings. Most ant species are predators/scavengers. However, there are seed harvesters and fungi growers as well. Most ant species are not pests and go unnoticed outside the home. Those that are pests can cause problems ranging from occasional to extreme annoyance coupled with medical health risks. Discussed on the following pages are two case studies focusing on problems with a big-headed ant species, Pheidole megacephala (F.), the Argentine ant, Linepithema humile (Mayr), and methods we used to control the pest problems.

Population Issue With Big-Headed Ants

Pheidole megacephala is a cosmopolitan tramp species found in tropical and sub-tropical regions. It is notorious for invading single- and multi-family units. Populations of P. megacephala can be in the millions with interconnected colonies covering many acres.

When the population of a pest ant species is in the millions and there are multiple nests, the situation can become severe. Add a damaged foundation that produces several entry points, for example, and the result is a nightmare for the homeowner.

This was the exact situation recently for a homeowner in central Florida. The house was built beside a small lake. Unfortunately, the foundation (which was a monolithic slab) sank, producing a structural crack along the foundation and the sidewalls of the house. Big-headed ants were penetrating not only from underneath the foundation but also through any access points on the outside periphery of the house. From the intrusion points ants were following the plumbing lines and posing problems in the bathrooms and kitchen areas. Furthermore, there were satellite nests located throughout the property — some of these nests were arboreal — whereby some trees were completely infested by P. megacephala.

THE CONTROL PROCESS. When a situation arises where the pest ant population is enormous, eradication is essentially impossible in most situations because the population extends to the neighbors’ property, providing a constant viable source of ants. Such was the case in the present situation. However, this does not imply that trained professionals, applying proper chemicals via proper techniques, cannot control the situation for the homeowner. There are three basic control methods: 1) direct treatment of mounds, 2) perimeter treatments and 3) baiting.

In this situation, repeated attempts using a perimeter treatment of a liquid synthetic pyrethroid in conjunction with granules slightly reduced the population. Though numerous worker ants were killed, this did not, however, prevent intrusion into the home. Thus additional steps were required.

First, given that the ants were entering from underneath the slab, a trench and treat with a highly residual product was performed in order to ensure 100 percent coverage and contact with intruding foraging workers. Second, supplemental baiting along foraging trails on the exterior trees close to the proximity of the house was conducted. Third, an additional topical perimeter treatment with a residual contact synthetic pyrethroid was applied to prevent access to any entry points such as door and window sills. Fourth, all pest entry points, such as window sills, were treated as well.

What is important is that the four steps succeeded in killing the majority of breeding queens within the property. Furthermore, there was a variety of active ingredients used, which I feel is an important when using a variety of products. This ensures maximum control via different modes of actions.

Argentine Ants And Resource Site Fidelity

Linepithema humile is also a cosmopolitan tramp species sharing similar characteristics with P. megacephala. It has spread to more than 750 counties in the continental United States following its introduction. Populations of L. humile are characterized by many colonies interconnected in a "unicolonial" formation. Worker population can be in the multi-millions with thousands of queens.

The Argentine ant, Linepithema humile, exhibits extreme resource site fidelity; that is, they regularly revisit old areas where resources were present previously. Argentine ants expand their territory via established foraging trails. In addition, Argentine ants also exhibit trunk foraging trails that can extend for many meters into a structure (see figures at right and throughout this story). This species will also revisit old hunting grounds and commonly come in through the same point entry sites.

Visually, Argentine ants can be quite alarming to the homeowner. When working with a species that exhibits such a fervent foraging strategy, baiting can be a very useful tool. This was the exact strategy used for a homeowner’s problem in north central Georgia. The periphery of her house was a perfect breeding ground for Argentine ants — pine straw thatch used as mulch. A porch on the back side of her house provided excellent access to doors. Ants were intruding underneath the doors, moving along the baseboards to a crevice, which led to the plumbing of the kitchen sink. The plumbing in turn yielded access to the master bathroom. The homeowner was concerned about applying any liquid residual products as spot treatments on access points inside the house. Thus, we were limited in use of products and of control techniques as well.

THE CONTROL PROCESS. In this particular situation, a residual liquid treatment was applied as a barrier to the outside periphery of the house. While this is always a good strategy, the pest control technician had to make sure the applied product made good contact with the foundation. Since we were dealing with Argentine ants, it was also important to spray the length of the nesting area. In this particular case it was 4 feet.

Spot treatments were not used inside the house, since they could be accessed by children and pets. Instead, small cracks and crevices that were inaccessible to pets and children were treated with either a dust or a residual aerosol. Furthermore, containerized baits with hydramethylnon were placed in strategic places where foraging was most intense. It is to be noted that containerized baits can be the technician’s ultimate weapon, and excellent control can result when the baits are placed in proper areas were foraging is most intense.

CONCLUSION. Ants are very tricky insects to control. An almost infinite number of problem situations involving ants are possible. However, within the chaos there is law, and with proper training and experience the technician can triumph every time.