Now that spring is here, it’s time for many changes. Days become longer, flowers bloom…and ants become very active again. There are nearly 1,000 species of ants that call North America home. The good news is that only a small number of our ant species are considered to be pests of structures, lawns and landscapes. Of that small number, fewer still are native to North America in the first place. Our most important ant species (economically and ecologically speaking) are actually native to the South American continent. For example, ant species such as red imported fire ants (Solenopsis invicta), Argentine ants (Linepithema humile) and now tawny crazy ants (Nylanderia fulva), are known to be extraordinarily destructive to the ecosystems they invade, and as PMPs who live and work in the southern United States are aware, these ants can be quite expensive to manage.
RIFAs. Red imported fire ants (hereafter, fire ants) have been intensively studied for decades as their invasive range has expanded across the United States and elsewhere. As a result, we have a fantastic level of understanding of how to properly manage them. I often advocate for the use of insecticidal baits for the management of any pest insect if baits exist in the marketplace that are known to be effective on whichever insect species you are attempting to manage. There are MANY granular fire ant baits and a wide variety of active ingredients (hydramethylnon, indoxacarb, S-methoprene and fipronil to name a few) that work very well when applied to kill fire ant colonies. All baits take time to work as the active ingredient disperses through the colony, but some fire ant baits are known to work faster than others. The trade-off is usually found in the higher cost of fast-acting baits, and I’ll not attempt to offer guidance on making such financial decisions for your company.
Fire ants are extraordinarily competitive with other ant species for food resources in their invasive ranges, and when we attempt to manage them with fire ant baits, we exploit what would otherwise be a competitive advantage. When fire ants are present, they are typically the first ants to discover, recruit nestmates to and dominate fire ant baits after application. This fact, coupled with the understanding that fire ant baits contain very low active ingredient concentrations and are applied at very low rates, allows us to confidently apply them with minimal concerns for non-target effects.
There are also a number of granular contact insecticides that can be incorporated into an effective fire ant IPM program. These can be applied directly to individual fire ant mounds, but they also can be used as a means of preventing new infestations. When broadcast over a landscape, contact insecticides provide residual protection from the establishment of new colonies by killing newly mated fire ant queens should they select the soil in the treated area as their nesting sites.
TAWNY CRAZY ANTS. Tawny crazy ants (hereafter, TCA) are a much more recent addition to the list of pest ants that PMPs in the United States are being called on to manage. Like fire ants, TCA are native to South America. Their discovery in Texas occurred in 2002, and they have been confirmed in Louisiana, Mississippi, Alabama, Georgia and Florida. Multiple peer- reviewed publications have documented the negative impacts that this new invader has had on the diversity and abundance of arthropods in the systems they invade. They also have been observed to raid honeybee colonies, causing them to abscond, cause damage to electrical and mechanical devices such as HVAC systems, and they tend honeydew-producing insects such as pests of lawn and ornamental plants (aphids and scale insects).
TCA meet the criteria to be considered “supercolony” ants. As a result of the genetic bottleneck this species experienced during their invasion of the United States, the population of TCA in the U.S. is much less genetically diverse than the native South American population. This results in low aggression among workers, merging of colonies and sharing of resources. Local populations of invasive TCA can reach extraordinary densities in a single field season. So dense, in fact, that they are often able to outcompete populations of fire ants for resources, which can lead to local extinction of fire ants.
TEXAS RESEARCH. Our research group has been involved in many laboratory and field experiments designed to understand the most effective and efficient means of managing TCA. We’ve trialed granular and liquid/gel baits, granular contact insecticides and many liquid contact insecticides. The good news is that TCA are not very tough, and individual ants are susceptible to almost every treatment we’ve trialed. The bad news is that baits, while effective, provide no residual protection from TCA reinvasion. In granular and gel bait field trials, we have been able to decrease densities of TCA significantly (as compared to untreated controls). Unfortunately, within a couple of weeks TCA from the area surrounding the treated property typically reinvade and reach densities equal to or greater than the densities prior to baits being applied. So for now, there is not a bait that we are aware of that can be used effectively as a standalone treatment for TCA.
The best results we have experienced in field trials involved the application of liquid contact insecticides. In one study, we examined two liquid contact insecticides containing different active ingredients (fipronil and dinotefuran) and three different application strategies for keeping TCA off and out of 1,800-2,200 square foot homes on approximately 1.4 acre lots in Texas City, Texas. The strategies included: 1) treatment of exterior home perimeters with a product that contained fipronil as the active ingredient, 2) exterior treatment with the same fipronil product followed by the application of a second contact insecticide that contained dinotefuran across adjoining turf and landscape, and 3) a final strategy that included exterior perimeter and lawn treatment with the dinotefuran product only. The strategy that included fipronil on the house and dinotefuran across the adjoining turf and landscape prevented the return of foraging TCA on the house for three months. Colleagues at other universities have demonstrated similar success with these and other contact insecticides. So, baits can effectively kill lots of TCA but tend to lack long-term impacts, and contact insecticides can prevent TCA return to structures between quarterly service.
FINAL THOUGHTS. So far, no species of invasive ant that has become established in the United States has ever been successfully eradicated, and we know that fire ants and TCA are going to be an important part of the pest management industry for the foreseeable future. For that reason, my colleague Dr. Ed Vargo (professor and endowed chair of Urban Entomology, Texas A&M University) and I will continue to work with our manufacturer partners to search for the most effective products and efficient management strategies for these and other pest insects. Feel free to reach out to us should have any questions about the studies I mentioned, or our work at the Rollins Urban and Structural Entomology Facility at Texas A&M University. Be safe and have a great year!