- 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: Andrew M Sutherland
Baits Eliminate and Prevent Subterranean Termite Colonies
Subterranean termites (Family Rhinotermitidae) are considered the most serious wood-destroying pests in the world, causing an estimated $32 billion in global economic impact each year. California is home to both native and introduced subterranean termite species (Figure 1). Infestations of wooden structures are widespread and common. Pest control operators (PCOs) have conventionally applied liquid termiticides to control these pests, usually as soil drenches or injections around structures. These treatments may not always be effective, however, especially if good underground coverage is not achieved, if local termite pressure is very high, or if dealing with the invasive Formosan subterranean termite in Southern California. Furthermore, the active ingredients in most liquid termiticides are increasingly monitored by the State as environmental contaminants and may be subject to legal restrictions in the future.
Bait systems for subterranean termites (Figure 2), which employ slow-acting insecticides that kill worker termites by preventing successful molting, may represent effective alternatives to liquid treatments. Baits, deployed within stations installed in the ground or in line with aboveground shelter tubes, have gained popularity during recent decades and are now considered the primary subterranean termite control tactics in many parts of the world. Adoption of bait systems in California has lagged most other regions, however. Reasons PCOs in California have reported being reluctant to use bait systems include 1) time required to achieve control is too long, 2) little efficacy data in California, and 3) the regular monitoring of bait systems is too labor intensive or otherwise does not fit established business models.
Recently, the third “adoption barrier” may have become less important: new product label guidelines allow PCOs to extend inspection intervals up to 12 months and allow for baiting without the previously required monitoring phase (provided the target pest is confirmed at the site). Considering the regular revenue streams created by “controlled service agreements”, where PCOs contract with property owners to prevent and control pests over a long term, these newer labels should drive more widespread use.
Some observations and case studies indicate that, indeed, bait system adoption is now slowly increasing in California. To address the other two reported barriers (speed of control and efficacy), we secured funds from the state's Structural Pest Control Board to evaluate and demonstrate three different in-ground bait systems in the San Francisco Bay Area and the greater Los Angeles area.
Bait Efficacy
Our first objective was to evaluate efficacy at single-family homes. To do this, we collaborated with five different PCO companies who expressed interest in the new business models made possible by the newer bait product labeling guidelines. Some of these companies had experience with baits, while some gained their first experiences through this project. Companies received research stipends to subsidize their participation. Fifteen single-family homes were eventually selected, based on several experimental criteria: 1) documented activity of subterranean termites within 1 meter of the structure, 2) no liquid termiticide application within the previous 5 years, and 3) no significant structural infestations detected during the initial inspection. Participating homes were in Alameda, Contra Costa, Los Angeles, Orange, and Santa Clara counties. Bait stations, baits, service equipment, and, in some cases, training, were provided by manufacturers.
The UC research team and the PCOs installed bait systems according to product labels, usually with one bait station for every 10–20 linear feet of the structural perimeter. Since all 15 sites had confirmed termite activity at the perimeter, all stations installed contained active bait, rather than monitors. The UC research team installed monitoring stations with wooden blocks immediately adjacent to each bait station. The UC team then visited each participating home every 3 months for 2 years, checking termite activity within monitoring stations and collecting termites whenever possible. The PCOs and the UC team visited each participating home every 6 months to check termite activity within bait stations, replenish baits (as per product label), and to collect termites. Collected termite specimens were sent to a collaborating lab for DNA analysis, where each sample was assigned a “Colony ID” based on its genetic signature, distinguishing it from all other colonies. At the end of the 2-year period, a final structural inspection was conducted at each home.
Findings
Most importantly, despite significant termite pressure, none of the 15 homes became infested during the study period. Foraging termites were observed and collected during initial inspections, from wood blocks during quarterly inspections, and from bait matrices during bi-annual inspections with PCOs. In some cases, termites were observed and collected from bait stations only 6 months after installation. 132 separate samples of western subterranean termites (Reticulitermes hesperus species complex) were collected. DNA analysis revealed that many of our research sites included between 3 and 5 unique colonies; 1 property included 15 unique colonies! Bait was consumed at all sites, to varying degrees. No termite colony recovered from bait stations was ever detected again.
These observations strongly suggest that all three studied bait systems were effective at eliminating termite colonies and at preventing structural infestations over a 2-year period. Furthermore, post-project surveys conducted with property owners and PCOs indicated that all parties were satisfied with the services provided and control achieved; several companies new to baiting have now embraced the program we demonstrated as a new service offering for their customers.
Reducing “time-to-attack”
Our second objective in this research project was to investigate factors influencing bait interception time (also called “time-to-attack”). One explanation for lengthy bait interception times in California may be the interaction of climate (hot summers with little to no rain) and soil texture (high proportions of clay). Termite foraging at or near the soil surface may be limited or even nonexistent during summer months, especially when areas are not irrigated. Some research supports this idea: western subterranean termites have been observed to forage near the surface mostly during winter months in Southern California. This suggests that baits installed in summer may sit uninvestigated for 6 months or more. To test this hypothesis, we established five research plots at the UC Berkeley Richmond Field Station directly on top of areas where naturally occurring Reticulitermes termites had been observed or collected. Around these areas, we established 3 concentric rings of bait stations at 3 distances from the center, installing 1 station from each of 3 registered systems (Table 1) along each of the 3 distance rings at the beginning of each season over 1 year, for a total of 36 bait stations per plot. We didn't want to kill the termites in these plots because that would significantly confound our data, so we used cellulose bait matrices from manufacturers that did not contain the active ingredients. We also installed monitoring stations containing wood blocks at the center of each plot and along each of the three distance rings. We then checked each station every 2 months for 2 years, recording bait consumption and termite incidence.
Of the 180 bait stations and 20 monitoring stations installed, 78 bait stations and 9 monitoring stations had been hit by the end of the 2-year project period, representing an overall hit rate of 44%. Three stations were attacked within 60 days after installation, and 10 stations were attacked within 120 days. Overall, however, the average bait interception time was 367 days, supporting the general claims of California's pest control operators that baiting may take too long for most remedial termite control jobs. There were no significant differences between the three bait systems or the three distance rings.
Bait System, Manufacturer |
Bait Information |
Installation Specifications (for in-ground use) |
Service Specifications |
---|---|---|---|
Sentricon Always Active, Corteva Agriscience |
Recruit HD Termite Bait (EPA# 62719-608): cellulose tube, 0.5% noviflumuron |
≤ 20 feet intervals; buildings, fences, decking, utility poles, trees |
Inspections at least once annually; replace bait if damaged or ≥ 1/3 consumed |
Advance Termite Bait System (ATBS), BASF |
Trelona Compressed Termite Bait (EPA# 499-557): cellulose wafers in plastic housing, 0.5% novaluron |
≤ 20 feet intervals; buildings, trees, wood piles, landscape elements, railroads |
Inspections at least once annually; replace bait if damaged or ≥ ½ consumed |
Exterra Termite Baiting System, Ensystex |
Isopthor Termite Bait (EPA# 68850-2): cellulose wafers within burlap sachet, 0.25% diflubenzuron |
≤ 20 feet intervals; buildings and other structures |
Inspections every 45 – 120 d, up to six months allowed; replace bait “after sufficient consumption” |
Our study's main question was whether installation season significantly impacts “time-to-attack” due to seasonal differences in termite foraging in California. To answer this, we pooled data from all five sites and all three bait systems and then considered just the first year of observations. The result was clear: baits installed at the beginning of winter (December 16) were intercepted ~100 days faster than baits installed at the beginning of summer (June 24)!
Conclusions
Bait stations systems may be very useful pest control tactics for use against subterranean termites in California, especially when dealing with very large colonies of native western subterranean termites, multiple colonies, sensitive sites, or sites where liquid treatments have failed. According to the labels of the three products evaluated, systems can be installed with active ingredients present on Day 1, provided a licensed Field Representative has detected and identified the target species at the site. Licensed Applicators may, according to label language and California's Structural Pest Control Act, then service bait stations, replenishing bait that has been consumed or damaged. Two of the systems evaluated allow for annual inspections, while one allows for bi-annual (every 6 months) inspections. Operators in California may decrease the bait interception time, and therefore the perceived early efficacy, by targeting initial installations for the beginning of the wet season.
[Originally featured in the Fall 2023 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
- Author: Saoimanu Sope
Sugar-feeding ants protect pests that infect trees and damage the fruit they bear. Insecticides are often a go-to solution, but may kill beneficial insects in the process, too. Thankfully, Mark Hoddle, University of California Cooperative Extension entomologist and biological control specialist at UC Riverside, together with UCR colleagues in chemical engineering, developed a biodegradable hydrogel baiting system that targets ant populations, which protect sap-sucking pests from their natural enemies. Control of ants allows beneficial parasitoids and predators to greatly reduce pest populations.
Deciding to expand Hoddle's research was a “no-brainer” according to David Haviland, UC Cooperative Extension farm advisor in Kern County.
Haviland is investigating active ingredients that can be effectively used in hydrogel baiting systems. His research builds on Hoddle's use of alginate gels, also known as water beads, soaked in sugar water to control Argentine ants.
“What we're doing in California can benefit places like Florida, Texas, Mexico and beyond,” Haviland said.
The Hoddle lab conducted two years of orchard research showing that when ants are controlled, the amount of citrus flush infested with Asian citrus psyllid (ACP), a mottled brown insect that vectors the pathogen causing citrus greening, decreases by 75%. Citrus flush refers to newly developed leaves.
“But benefits are not restricted to just ACP with Argentine ant control, as natural enemies destroy colonies of other sap-sucking pests too,” said Hoddle. “For example, citrus mealybug infestations on leaves were completely eliminated by natural enemies, 100% control, while densities of fruit infested by mealybugs were reduced by 50%.”
The Hoddle lab's success inspired Haviland to consider how this approach will fare in different regions of the state where there are different crops, different pests and different ant species.
Haviland has worked for many years on solid baits that are effective and affordable for ants that feed primarily on protein, like fire ants in almonds, but successful control measures for sugar-feeding ants that drink their food have been elusive.
“Therefore, we're using hydrogels to essentially turn a liquid bait into a solid, making it effective and commercially adoptable,” Haviland said. He and his team are assessing whether active ingredients that undoubtedly work against ants, like thiamethoxam, maintain their effects in a hydrogel system.
Unlike Hoddle's biodegradable alginate gels, Haviland is relying on acrylamide gels that are similar to the absorbing material you would find in a diaper. These gels are not organic, but are currently accessible on a commercial scale, and have been shown to be effective in wine grapes on the North Coast by a Cooperative Extension advisor in Napa County, Monica Cooper. Haviland's current research efforts are focused on citrus, table grapes and wine grapes in the San Joaquin Valley, and on lemons on the coast.
The primary challenge now is navigating pesticide regulations and registration.
“This is cutting-edge research,” Haviland said, and manufacturer labels for the products being used need to be updated to include hydrogels as an approved use. This process takes time. Additionally, adding new product uses needs to make economic sense for the manufacturer.
Hoddle and Haviland's research can provide data for adding these methods to the product labels.
“If we can show that this tech works against lots of pests, lots of ant species, in lots of different crops across California, hopefully we'll achieve a critical mass of benefits that motivates product manufacturers to make modifications to their labels,” said Haviland.
Haviland is hopeful about the process, and said he believes that UC ANR is in a prime position to lead innovation for an issue that requires collaboration among specialists, advisors and the industry.
- Author: Lauren Fordyce
You may not think about rodents such as rats, mice, or gophers until they become a pest around your home. Because rodents can be major pests in and around homes, gardens, landscapes, restaurants, and other buildings, each year pest control experts “celebrate” Rodent Awareness Week. Rodent Awareness Week (October 16-22) is an annual campaign created by the National Pest Management Association to educate the public about the potential harm associated with rats and mice. In addition to damaging structures and property, rodents can transmit diseases to humans and other animals. During the fall and winter months, rodents will seek food and shelter in homes and other buildings
Some general tips for keeping rodent pests out, include:
- Seal structural cracks and openings larger than 1/4 inch. Utilize weather stripping or door sweeps, and ensure doors and windows fit tightly. Wire screen can also be used.
- Keep food storage and garbage containers sealed.
- Remove or thin vegetation around structures. Rodents, especially house mice, will use climbing vegetation to scale buildings.
- Don't touch rodents with your bare hands. Dispose of dead rodents by placing them in plastic bags and putting them in the garbage.
- Avoid poison baits as the rodents can die in hidden places and they can be harmful to children and wildlife.
House Mice
Adult house mice can be 5 to 7 inches long with 3- to 4-inch-long tails. They are light brown to gray rodents with a characteristic musky odor. House mice are well adapted to living in close contact with humans. They are most active at night, but you can also see them during the day. Check behind boxes, in drawers, or around woodpiles for nests made of finely shredded materials. Control them by placing snap traps or glue boards in secluded areas along walls, behind objects, and in dark corners. Read the Pest Notes: House Mouse for more information.
Rats
The most troublesome rats are two introduced species, the roof rat and the Norway rat. Knowing which species is present is key in effective management. Norway rats arelarger than roof rats but usually have smaller ears and tails. When Norway rats invade buildings, they can commonly be found in the basement or ground level. They create burrows, holes in the ground, along buildings and beneath wood or garbage piles. Roof rats are excellent climbers so they can commonly be found in attics, walls, ceilings, and other elevated surfaces. They nest above ground in trees, shrubs, or dense vegetation. To learn more about rats, see the Pest Notes: Rats.
Of course, rats and mice aren't the only rodents you might find around your home and landscape. You may also encounter other rodent pests such as Voles (Meadow Mice),Deer Mouse, Gophers, Ground Squirrels, or Tree Squirrels.
/span>
- 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>