- Author: Dong Hwan Choe
- Author: Chow-Yang Lee
- Author: Michael K Rust
Ants are one of the major seasonal pests around structures in California's urban environments. Pest management companies throughout the state report that ants are responsible for a significant proportion of their pest control services. In urban residential areas of California, the Argentine ant, Linepithema humile, is the most common nuisance ant species treated by pest management professionals (PMPs) as well as the public themselves (Figure 1).
While contact insecticides are frequently used to control Argentine ants, they also contribute to environmental contamination via drift and runoff. However, insecticide applications following California's recent regulatory changes and label updates may fail to control target pest ants consistently potentially resulting in repeated insecticide applications (Choe et al. 2021).
Baiting for ant control
Baiting (Figure 2) can reduce the need for insecticide spray applications. Active incorporation of baits in a management program may help to lower the risk of environmental contamination caused by insecticide drift and run-off. For Argentine ants, which often form large colonies with multiple nest sites and reproducing queens, the initial application of perimeter spray would still be needed to provide a quick knockdown of foraging ant populations during peak season (June or July). However, baits are particularly useful for subsequent maintenance visits (monthly or bimonthly). In fact, baiting has been demonstrated to be an effective tool for maintenance services for Argentine ants (see References).
Many bait products are available for professional use, and when strategically used, they can be effective at keeping ant numbers low (at acceptable levels) following the initial spray treatment. Gel / liquid / granular bait products containing boric acid, indoxacarb, and thiamethoxam are effective for Argentine ant control.
Importance of bait placement
If PMPs choose to incorporate baits as a main tool for maintenance visits, there is an important question to be answered: Where to place the bait? Unless bait stations are already installed in specific locations and periodically serviced (e.g., cleaning and refilling), PMPs must determine where the baits need to be applied during their visit.
Unlike insecticide sprays, the ants must consume the bait to be effective. Baits placed in just any location cannot be expected to work. Strategic placement of baits is critical to maximize the bait consumption by foraging ants and control of the pest ant populations. In fact, baits start losing their palatability (attractiveness as food) from the moment they are applied in the environment.
Since all ant foragers are liquid feeders, keeping the bait hydrated (minimal water loss) is vital to maximize bait consumption. Contamination and degradation might also impact bait palatability over time. Placing baits in the areas where the ants are currently traveling or foraging will ensure maximum bait consumption. Baits are typically more expensive than insecticide sprays (based on the product cost to treat a unit area), so strategic placement of baits is also crucial from an economic standpoint.
Label information on bait products usually includes specific tips regarding bait placement. For example, one commercial ant bait product label states, “place bait on, into, or adjacent to structures where ants are observed, adjacent to ant trails and to areas suspected of ant activity.” Another product's label instruction states, “locate areas around the building where ants are seen trailing. Apply [the bait] in areas inaccessible to children and pets. For a perimeter defense system, place bait stations near the foundation or where ant trails are found.” In essence, these instructions require knowledge of the locations where the ants are currently active or likely will be within a day or two.
Finding ant trails might be easy if customers have already observed or reported the ant infestation. However, finding active ant trails could be time-consuming, and time for careful inspection to discover active ant trails around the structure during a service visit is often limited.
Ant trail location study
Is there a quick and reliable way to identify the most likely places where Argentine ants would trail and forage in residential outdoor settings? Knowing this would make it possible to quickly determine the best sites for bait placement without looking for ant trails. Argentine ants are known to rely on chemical signals (trail pheromone) as well as structural features (structural guidelines) when maneuvering in the environment (Klotz et al. 1997). Many residential settings share some common structural features such as concrete, lawn, mulch, plant, and soil. If common features can be used to reliably locate the foraging ant trails, that could reduce the time needed to look for ant trails during bait applications.
Site types | Surface/characteristics |
---|---|
L | Lawn |
C | Concrete |
D | Dumpster/trashcan |
T | Tree |
V | Vegetation/bush |
LC | Lawn – concrete interface |
SC | Soil – concrete interface |
MC | Mulch – concrete interface |
BS | Building (vertical surface) – soil interface |
BC | Building (vertical surface) – concrete interface |
A simple field experiment was designed to identify the best sites for bait placement. The study was conducted in October on the University of California, Riverside campus. Several site types were identified based on structural characteristics. Five of these site types were characterized by the presence of a single surface type or a single characteristic item—lawn (L), concrete (C), dumpster or trashcan (D), tree (T), vegetation/bush (short plant without trunk, V). Five other site types were characterized by the presence of two surface types and the interface between them – lawn and concrete (LC), soil and concrete (SC), mulch and concrete (MC), building and soil (BS), and building and concrete (BC). The list of site types is provided in Table 1.
The experiment was replicated 5-13 times for each of the site types. Small squares of cotton (monitoring squares) soaked in 25% (wt:wt) sucrose solution were placed in these sites. The monitoring squares were collected after one hour, and Argentine ants on the cotton squares were counted. The number of ants on the monitoring square was used as the quantitative indicator for ant foraging activity.
The overall data suggest the interface between lawn and concrete (LC) was the location with the highest level of Argentine ant foraging activity (Figure 3). The interface between lawn and concrete (LC) had a much higher number of ants than its single-surface counterparts (L, lawn only or C, concrete only). Bases of the tree (T) and dumpster site (D) also had a good amount of ant activity, but there can be significant amounts of variation in ant activity, especially for dumpster sites (i.e., hit-or-miss). Open concrete surface (C) had the lowest level of foraging activity. Lawn (L), vegetation/bush (V), and four other interface types (SC, MC, BS, and BC) showed intermediate levels of ant activity.
Certain structural and landscape features can be used to quickly determine the best locations for inspection and bait (liquid or gel) placement against Argentine ants. Interfaces between lawns and concrete are among the most common structural features of residential outdoor settings. For example, they are found between lawns and various concrete surfaces, such as driveways, sidewalks, patios, and landscape curbing (Figure 4).
There are possible reasons why the Argentine ants prefer to trail along the interface between lawn and concrete. Preferred microclimate conditions (moisture, temperature) may exist in that location. The absence of heavy vegetation along the lawn and concrete interface (ease of travel), but still with some level of protection (partially shaded), may also be preferred by trailing ants. Environmental factors such as relatively high humidity and partial protection from direct sunlight would also be advantageous in keeping the liquid or gel bait palatable for extended periods.
Take-home message
It is vital to effectively manage pest ants in urban environments with minimal impacts on human health and the environment. To help reduce our reliance on repeated application of insecticide spray products, baiting should be considered for maintenance service visits for pest ants. To maximize the impact of baiting, the baits should be placed along lawn and concrete surfaces. Of course, a control program should not rely only on baiting but also be supplemented with non-chemical techniques such as exclusion, sanitation, removal of honeydew sources, and water management.
It is important to note that the information and data discussed in this article are focused on Argentine ants and sugar-based bait products targeting this species. Thus, the information may or may not directly apply to other ant species with different feeding habits, foraging strategies, or population structures.
For more information about ant management, see the UC IPM Ant page https://ipm.ucanr.edu/PMG/invertebrates/links.ants.html.
References cited
Choe D-H, Paysen, E, Greenberg L, Campbell K, Rust MK. 2019. A closer look: Argentine ant control. Pest Control Technology. GIE Media, Inc. p. 130-135. Vol. 47. No. 10.
Choe D-H, Tay J-W, Campbell K, Park H, Greenberg L, Rust MK. 2021. Development and demonstration of low-impact IPM strategy to control Argentine ants (Hymenoptera: Formicidae) in urban residential settings. J. Econ. Entomol. 114: 1752–1757.
Klotz JH, Greenberg L, Shorey HH, Williams DF. 1997. Alternative control strategies for ants around homes. J. Agric. Entomol. 14: 249-257.
[Originally featured in the Spring 2024 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
/h2>/h2>/caption>/h2>/h2>/h2>
- Author: Ben Faber
Argentine Ant Management in Citrus (July 8, 2020)
What Are the UC Ag Experts Talking About?
What is involved in the webinars?
A series of 1-hour webinars, designed for growers and pest management professionals, highlighting various pest management and horticultural topics for citrus, avocados, and other subtropical crops. Master Gardeners can benefit from participating, but the pest management methods presented, especially the pesticides, are not to be followed without a clear understanding of their legal use by homeowners.
During each session, a UC Expert on the subject makes a presentation and entertains write-in questions via chat during and/or after the presentation. As we develop this program, we may expand to other crops. Both DPR CE units are available, as are CDFA-CCA units- Author: Karey Windbiel-Rojas
As written in my blog post from 2 days ago, I found carpenter ants in my house recently and decided to call a pest control company to help manage them.
Yesterday, the field representative from the pest control company (both of whom will remain unnamed) showed up as scheduled, the day after I submitted a service request. Prompt service, which I appreciated! I had collected some of the perpetrators for him, and had both dead and live specimens on hand for his expert ID and advice.
The job of the licensed structural field rep is to identify the pest. I already knew what I had, having some prior knowledge of ants and having used the UC IPM Key to Common Household Ants to identify the invaders. The field rep eyeballed the captive specimens without opening the plastic container or using a hand lens and declared them to be Argentine ants. I said "No, I'm pretty certain these are not Argentine ants." He assured me they were and Argentine ants can be large and they are commonly found in homes, etc.
So I fessed up: I work at UC IPM (which he had not surprisingly never heard of) and I know some stuff. I showed him where else I was seeing the ants and elaborated on the damage we are experiencing in our home. After describing more and showing him the other signs, he looked at the ants again (more closely) and agreed they were carpenter ants.
I was fairly dismayed at the super quick "identification" but glad that once I showed him more signs and gave more information he changed his diagnosis. Just like giving a doctor all the facts about bodily ailments and symptoms, it's also important to give a pest control professional all the signs, damage, and other info you've noticed when you think you have a pest issue.
Up next: the recommended treatment plan and what happened.
- Author: Dong-Hwan Choe
Our postdoctoral scholar, Dr. Jia-Wei Tay, has successfully completed her postoctoral research, and will be leaving the Choe laboratory. Dr. Tay has been working on a novel baiting system (i.e., biodegradable hydrogel bait) for Argentine ant, one of the most important invasive pest ant species in California. She will be taking a new position in University of Hawaii soon, working on urban / structural insects. For more about her research, visit http://www.jiaweitay.com/.
The lab members had the farewell lunch with Dr. Tay on Dec 4, 2018.
Good luck and all the best for your new endeavor, Dr. Tay!
- Author: Siavash Taravati
[From the Fall 2018 issue of UC IPM's Green Bulletin newsletter]
The dark rover ant (Brachymyrmex patagonicus) is an invasive species which is increasingly being noticed in Southern California. It is a nuisance species that invades structures as both workers and winged (alate) individuals.
This article aims to introduce structural and landscape pest management professionals (PMPs) to the dark rover ant and includes several important references for readers to learn what is currently known about its biology, behavior, and control.
Identification
Dark rover ant (DRA) workers are usually 1–2 mm long and are typically reddish-brown to blackish-brown (Figure 1). They have one node on the waist hidden under the gaster (abdomen), with long erect hairs mixed with sparse fine pubescence on the gaster (Figure 2), and nine-segmented antennae (Figure 3). The only other rover ant species reported from California is B. depilis which is rarely seen in the field (1) and can be distinguished from DRA by their yellow to yellowish-brown color (2).
Where are dark rover ants found?
The dark rover ant is native to South America and is found in several countries including Argentina, Paraguay, Brazil, and Venezuela(3).It was first discovered in the United States in 1978 in Louisiana (4).
This ant was found in California for the first time in 2010 in Orange and Riverside Counties (5). The author found this species in Los Angeles County in Pacoima and Sylmar as well as Citrus Community Park (Riverside, CA) and Andulka Park (Corona, CA). Pat Copps of Rollins Inc., reported DRA presence in Bakersfield. This species may already be widely distributed in Southern California and could be dispersing to newer areas.
Biology
DRA nests both indoors and outdoors (6). They forage without making trails but trailing has been observed in the laboratory between the sub-units of a colony (7). High levels of aggression toward individuals of other colonies has been observed, which may prevent the establishment of multiple colonies in a small area (8).
Different authors have reported that this species can coexist with other ant species, most notably Argentine ant (Linepithema humile) and red imported fire ant (Solenopsis invicta), and has even nested alongside the latter (4, 5). In Los Angeles and Riverside counties, the author has seen DRA workers walking near trails of red imported fire ants and Argentine ants without alarming the workers of these other two species.
DRA have been observed feeding on plant nectar in the field. In the lab, a 30% honey solution along with a liquid tuna mixture and caterpillars has been observed to support reproducing colonies (7).
DRA as a Nuisance Pest
Foragers and alates of DRA invade structures and can become nuisances. In Orange County, there were more incidences of DRA infestations in 2018 as compared to 2017. In June and July of 2018, customer calls were made regarding reproductives when clients saw them at bright lights inside. David Taylor from The Bugman Pest and Termite Control reported that clients were often unaware that workers were also present.
According to Pat Copps, in southern California, DRA infestations have been more common in Orange County but are still relatively rare as compared to the pervasive Argentine ant, which accounts for about 90% of customer calls for ant infestations. He also says DRA foragers are usually seen in kitchens, bathrooms, and laundry rooms inside and around grade/wall junctures, stone borders, patios, and tree roots.
How to Manage DRA
Pest management professionals have reported difficulty in managing dark rover ants in other parts of the United States (4). This is believed to be due to the existence of long-lived satellite colonies, which can survive for around three months when separated from the main colony (8). Consequently, a structure treated for DRA may soon be re-invaded by ant individuals from adjacent satellite colonies.
In California, similar difficulties have been reported in controlling this pest. These difficulties have been overcome by some PMPs by using combinations of baits, dusts, and liquid sprays as interior and exterior treatments. Copps reported that very limited success has been achieved when attempting to control this pest outdoors.
Research by Miguelena and Baker (6) on the efficacy of selected pesticides against DRA showed higher ant mortality when using Arilon (indoxacarb, Syngenta) and Demand CS (lambda-cyhalothrin, Syngenta) liquids as well as Maxforce Quantum ant bait (imidacloprid, Bayer CropScience) when compared to other insecticides used in the study (Figure 4).
Since DRA control failure is very common, it is important for PMPs to consider using products which have been scientifically proven to be effective in controlling DRA. Other products may eventually prove to be effective against DRA, but at this time there has been limited published research on the management of this pest.
References
- Ward, P.S., A synoptic review of the ants of California (Hymenoptera: Formicidae). Zootaxa, 2005. 936(1): p. 1-68.
- McGown, J.A. Ants of the Southeastern United States. 2003.
- Quirán, E.M., J.J. Martínez, and A.O. Bachmann, The neotropical genus Brachymyrmex Mayr, 1868 (Hymenoptera: Formicidae) in Argentina: Redescription of the type species, B. patagonicus Mayr, 1868; B. bruchi Foel, 1912 and B. oculatus Santschi, 1919. Acta zoológica mexicana, 2004. 20(1): p. 273-285.
- MacGown, J.A., J.G. Hill, and M.A. Deyrup, Brachymyrmex patagonicus (Hymenoptera: Formicidae), an emerging pest species in the southeastern United States. Florida Entomologist, 2007. 90(3): p. 457-464.
- Martinez, M.J., et al., New records for the exotic ants Brachymyrmex patagonicus Mayr and Pheidole moerens Wheeler (Hymenoptera: Formicidae) in California. The Pan-Pacific Entomologist, 2011. 87(1): p. 47-50.
- Miguelena, J.G. and P.B. Baker, Evaluation of liquid and bait insecticides against the dark rover ant (Brachymyrmex patagonicus). Insects, 2014. 5(4): p. 832-848.
- Tamayo, D. Dark Rover Ant: Brachymyrmex patagonicus Mayr. 2011.
- Miguelena, J. and P. Baker, Why are rover ants (Brachymyrmex patagonicus) so difficult to control? Graduate Student Poster Session, Entomological Society of America Annual Meeting, San Diego, California, 2010.