- Author: Ben A Faber
Update on Novel Ant Control Method in Citrus (MyAgLife in Citrus, Episode 828)
Recently, the Citrus Research Boards, IPM Entomologist, Ivan Milosavljevi?, Ph.D., was a guest on Episode 828 of MyAgLife in Citrus, where he provided an update on on a novel method of ant control in citrus. This method utilizes hydrogel beads filled with trace pesticide amounts.
To listen to the episode, please click below.
Episode 828 | April 30, 2024 | MyAgLife in Citrus – MyAgLife Daily News Report
- 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.]
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Synergizing IPM of Argentine ant and biocontrol of sap sucking pests with biodegradable hydrogels, infra-red sensors, and cover crops in commercial citrus orchards
Ivan Milosavljevi?, Department of Entomology, University of California, Riverside, CA
Nicola A. Irvin, Department of Entomology, University of California, Riverside, CA
Kelsey A. McCalla, Department of Environmental Science, Policy, and Management University of California, Berkeley, CA
Mark S. Hoddle, Department of Entomology, University of California, Riverside, CA
Argentine Ant control critical for IPM in citrus groves
The invasive Argentine ant (AA) (Linepithema humile) is a serious impediment to the biological control of sap sucking pests (SSPs) in citrus orchards (Hoddle et al. 2022). SSPs include mealybugs, scales, aphids, and Asian citrus psyllid (ACP), the vector of a bacterium that causes HLB, a lethal citrus. AA protect >85% of SSPs and >55% of ACP colonies from their natural enemies which exacerbates pest infestations. In return for protection from natural enemies, ants are rewarded for this service by SSP's through the provision of a sugary waste product, honeydew, which ants harvest and return to nests to feed brood and queens. Contact sprays for AA and SSP control applied to soil, trunks, and foliage kill natural enemies, cause secondary pest outbreaks, and increase the likelihood of insecticide resistance developing. IPM of AA and SSPs requires an accurate method of assessing pest densities so that appropriate treatment decisions can be made, precision delivery of insecticides to kill foraging AA is necessary if natural enemies are to be preserved, and enhancement of natural enemies through conservation biocontrol can increase the efficacy of free pest control services provided by natural enemies in citrus orchards.
Enhancing and automating Argentine ant monitoring using infra-red sensors and the internet of things
Efficient and accurate pest monitoring is a key component of IPM programs. There are currently no standardized monitoring programs for assessing AA infestation levels. Visual ant counts are time consuming, tedious, and become inaccurate when counting fatigue sets in. To remedy this problem, we developed and field-tested infrared sensors (IRS) that clamp to irrigation lines to automate ant counts . AA use irrigation lines as super-highways to rapidly move across the orchard floor to reach pest infested citrus trees. Statistical analyses indicated that it is possible to predict with about 85% accuracy the average number of ants ascending tree trunks based on the average number of ants running on irrigation lines. Thus, ant counts made by IRS on lines can be used to accurately predict the average number of ants ascending tree trunks in citrus orchards. Ant counts made by IRS are relayed wirelessly to the cloud where average AA densities are reviewed on an App that is loaded onto a smart device. IRS's eliminate the need for humans to monitor ant densities, they provide block specific estimates of AA activity, and they can potentially operate 24/7/365! We are currently determining the minimum number of IRS needed per acre to estimate ant densities with fixed levels of precision (e.g., 85, 90, 95% accuracy).
Based on accurate ant density estimates treatment decisions can be made, and importantly, just the areas of the orchard exceeding acceptable ant densities can be identified and treated (Schall et al. 2018). Focused applications reduces insecticide use, saves money, and minimizes adverse effects of insecticide use on beneficial non-target species, like natural enemies (McCalla et al. 2020). As part of an AA IPM programs, treatment decisions require action thresholds and when AA densities exceed the action threshold, treatments can be initiated. At this time, there are currently no established action thresholds for AA in citrus. This is an important problem we are currently working on.
(A) Infra-red sensor (IRS) clamped onto an irrigation line in a commercial citrus orchard. (B) Argentine ants use polyethylene irrigation lines that sit on the soils surface as “super-highways” to move from underground nests to tree canopies where they collect honeydew. (C) Close-up of IRS counting Argentine ants running on irrigation lines. (Photos by Mike Lewis and Mark Hoddle, UC Riverside).
Hydrogel baits provided targeted and highly effective Argentine ant control in citrus orchards
Chlorpyrifos, the industry standard insecticide for AA control, was recently banned in California because it poses significant risks to human health. In response to this ban, we developed biodegradable hydrogel beads (HGBs) as an alternative highly specific treatment that targets AA. HGBs contain a 25% sucrose solution, and an ultra-low dose of insecticide (0.0001%). HGB's are applied to the ground under citrus trees and spread out so foraging AA can rapidly find them. Ants imbibe sugar water laced with insecticide, return it to the nest to feed brood and queens which kills them. Consequently, HGB's may provide a superior alternative to plastic liquid bait stations for delivering toxins to AA as bait stations are cost-prohibitive for mass use in orchards. Our lab has demonstrated that both thiamethoxam and an organically approved spinosad formulation are highly efficacious when delivered to AA using HGBs infused with sugar water that is laced with insecticide. Within 2-3 days of HGB applications, AA colonies collapse, and AA densities are reduced by >95% in comparison to untreated plots. Rapid (< 5 days) long term (> 3 months) control of AA results from repeated HGB applications (~3-4 applications ~3 weeks apart over summer). Once AA are controlled long-term reductions in densities of SSPs in citrus results because natural enemies are able to more effectively control SSP's in the absence of AA. We are currently determining the minimum amounts of HGBs, and frequency of applications needed to optimize AA control at the lowest costs to growers.
Using flowering plants to enhance natural enemies of ACP and SSPs in citrus orchards
Our previous work has shown that natural enemies, especially hover flies (syrphids), respond strongly to flowering alyssum (Lobularia maritima) and buckwheat (Fagopyrum esculentum). Field work has also shown that ACP in citrus plots with flowering plants suffer significantly greater levels of natural enemy attack, especially by predatory hover fly larvae, when compared to plots lacking flowering plants. Hover fly larvae are dominant predators attacking ACP nymphs and other SSPs in citrus (Kistner et al. 2016, 2017). Tamarixia radiata, a tiny parasitic wasp has been imported into California from the Punjab of Pakistan to attack ACP nymphs also feed from buckwheat flowers. We have also found that hoverflies in southern California are most active in spring and fall and this is when flowering plants are most beneficial to them. This finding is important as ACP (and SSP) populations are greatest in spring and over fall also. Sowing flowering plants late-February and re-sowing in early-September would synchronize hoverfly activity with ACP population increases. We are currently assessing the efficacy of flowering plants in multiple commercial citrus orchards to the magnitude of reductions in populations of ACP and SSP densities when cover crops are present and absent.
Take home messages
IPM of AA and SSP's in citrus, include ACP, requires new and innovative approaches if long-term sustainable management is to be achieved. To achieve this, we are working on developing a package that combines three tools, HGBs, IRS, and flowering plants that enhance monitoring of AA (IRS), provides targeted highly specific control of AA (HGBs) that in turn relieves natural enemies from pressure of foraging ants which permits them to increase the free pest management service that they provide in citrus orchards. These agroecosystem services provided by natural enemies can be further enhanced through resource provision, cover crops, which provide pollen and nectar to natural enemies. This combination of tools, IRS, HGBs and cover crops, synergizes IPM of AA and biocontrol of sap sucking pests infesting California-grown citrus.
- Author: Dong-Hwan Choe
Benning Le, a MS student from the Choe laboratory successfully defended his MS thesis today (March 9, 2022). Benning's thesis research was on the development and laboratory / field testing of boric acid hydrogel bait targeting Argentine ant populations in agricultural settings. Benning is one of the students who went through our department's new graduate program, the combined BS+MS (4+1) program.
Congrats, Benning!
For more information regarding the UCR Entomology's combined BS+MS program, please click here.
/span>- Author: Dong Hwan Choe
Our research on Argentine ant IPM was published in August 2021 issue of Journal of Economic Entomology (JEE).
Choe, D.-H., J.-W. Tay, K. Campbell, H. Park, L. Greenberg, and M. K. Rust. 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.
In addition, the photo showing a pair of Argentine ant workers feeding on a biodegradable hydrogel bait (made form alginate compound) was selected as the cover page for August 2021 issue of JEE. The biodegradable hydrogel bait with boric acid as the active ingredient was incorporated as the maintenance treatment option for the study.
To find more about the research, please visit here to access the full research article.
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