- Author: Mike Hsu
During summer swarming season, homeowners urged to check for signs of Formosan subterranean termite
In the lottery of troublesome termite infestations, “Roger,” a Rancho Santa Fe homeowner, hit the jackpot (a pseudonym is used to protect his privacy). In 2021, his house in San Diego County was identified as home to only the fourth documented colony of the Formosan subterranean termite (Coptotermes formosanus) in California.
“FST is one of the most destructive urban pests in the world,” said University of California, Riverside entomologist Chow-Yang Lee, affiliated with UC Agriculture and Natural Resources through the campus' Agricultural Experiment Station. “It's also the only termite species listed in the ‘100 of the World's Worst Invasive Alien Species.'”
Endemic to East Asia, this termite is now established in many tropical and subtropical regions, including across the American South. Annually, its infestation costs more than $4 billion in control measures and damage repairs of structures in the U.S.
FST was first discovered in California in La Mesa (San Diego County) in 1992, and it was rediscovered in that city in 2018. Another infestation was reported in Canyon Lake (Riverside County) in 2020. And then, the following year, Roger received his surprise.
“Imagine being in your kitchen looking at your drywall and it's totally normal and then the next day there's a four-inch hole there and you're like ‘What the heck is that? Who put their elbow into the drywall?'” he recalled.
FST colonies can reach millions of individuals
Roger hired a pest control company, Green Flash Pest Control, which sprayed a powerful liquid termiticide in the soil around the house. But the termites – workers, soldiers and winged “alates” – continued to appear. The company tried a second application of soil treatment. But, again, the termites kept popping up.
“We were deeply concerned about the potential damage these termites could cause to the home since these invasive termites are extremely destructive,” said Eric Veronick, director of operations at Green Flash. “Unfortunately, there isn't a whole lot of information available on the behavior and management of this termite in California.”
The company called upon Siavash Taravati, a UC Cooperative Extension urban Integrated Pest Management (IPM) advisor based in Riverside.
“Some colonies are aerial, meaning that they are formed above the ground with limited or no connection to the soil – in such cases, soil treatment using contact insecticides may not be very effective in managing these termites,” Taravati said. “Furthermore, contact insecticides usually kill a much smaller portion of the colony when compared to termite baits.”
To make matters worse, once FST is established in an area, there have been no records of successful eradication anywhere in the world, according to Taravati. He added that a major reason why the Formosan subterranean termite is so destructive is the enormous size of their colonies.
“Their colonies can reach millions of individuals, versus most native subterranean species that reach a few hundred thousand individual termites per colony,” Taravati explained.
This termite, through its sheer numbers, can turn the wood in a structure into a “spongy kind of cake,” in Taravati's words. More than 10 pounds of wood in a house can be eaten by a mature colony each month. The financial hit for a homeowner can be substantial, up to tens of thousands of dollars – not to mention the increased risks to safety.
“Anything from studs to rafters to door frames and window frames – everything is going to be compromised, if the termites are left unchecked. And then, as soon as we have a major stress on the building, let's say there's a big storm or an earthquake – there's a high risk of at least part of the building collapsing,” said Taravati, who also noted that, unlike California native subterranean termite species, FST can attack and kill live trees and plants.
“These termites can be a nightmare,” he said.
Summer is ‘swarming season' for FST
Since the Rancho Santa Fe case in 2021, four more colonies have been documented, in La Mesa again and also in Highland Park, Hollywood Hills and La Verne (the latter three in Los Angeles County). Taravati said it's possible that FST has been spreading via structural lumber or potted plants and soil.
And even if a colony appears to be eliminated at a certain locale, Taravati noted, there is always the chance that part of the colony survives or more colonies of termites already have been established in nearby locations, as a result of swarming termites from the originally infested property.
Although nominally “subterranean,” certain members of an FST colony grow wings and fly to nearby locations to establish new colonies. These winged alates are also called swarmers because of their behavior during the “swarming” season, when termites mate and reproduce.
For the Formosan subterranean termite, that swarming season in California is late May through early August, so now is the time for homeowners and building managers in southern and central California to keep an eye out for those winged termites.
“If you experience a termite swarm in your house, contact a pest management professional and keep some termite samples in a Ziploc bag in the event you need to send the samples to UC Riverside for morphological and DNA-based identifications,” said Lee, who added that it's a good idea to periodically check your structure for signs of infestation, such as wood damage or shelter tubes (mud tubes).
Lee said FST swarmers have a lighter colored body compared to the dark color of native subterranean termites and the orange-brown body of drywood termite swarmers (see this flyer for additional identification information).
Following an especially wet winter, there's a chance California could see more FST infestations, as this termite generally requires moist environments to thrive, Lee added. He recommends that concerned community members seek professional advice.
“Do not attempt to control an FST infestation by yourself,” Lee said. “This is not your typical native Californian subterranean termite species; they are highly destructive, and you want to intercept the problem with the right strategy before it's too late.”
Homeowner: ‘I owe them my house'
In Roger's case, Taravati enlisted the help of Lee and his UC colleague, Greg Kund. They made multiple visits to inspect the home and analyze the situation – going “above and beyond,” according to Roger.
At Lee's suggestion, they used a caulk gun to insert a gel-like experimental bait into the wall where the termites were coming out. Once spread and passed on to the other nestmates, the product – which contains a chitin synthesis inhibitor (a type of insect growth regulator) – interrupts the termites' development so they are unable to properly molt and replace the short-lived “workforce” of foragers and soldiers. The colony eventually collapses and is eliminated.
“Generally speaking, IGRs are much more effective, but they require more patience,” Taravati explained. “You're not going to see the results the next day, or two-three days. You're going to see the results in a few weeks – but when you see the results, it's massive.”
And that's exactly what Roger and Green Flash Pest Control saw.
“Soon after their bait application, the termites stopped emerging from the walls and that gave us and the homeowner a big sigh of relief,” Veronick said. “I appreciate their expertise and dedication in helping us get rid of this destructive pest."
Roger said he is immensely grateful to the UC team.
“They were fantastic; I owe them my house,” he said. “They were super gracious and helpful and responsive and – ultimately, the thing I care most about – they were effective; they fixed the problem. Here we are two years later and – knock on wood, or maybe I should knock on something else! – everything is good.”
Lee also credited Taravati for bringing his knowledge and “can-do” attitude to communities across Southern California.
“He is highly knowledgeable and always able to come up with feasible solutions,” Lee said. “We need good Cooperative Extension urban IPM advisors like Siavash who could provide good advice and bring solutions to the stakeholders, be they homeowners or pest management professionals.”
Taravati said community members need to maintain their vigilance and urges them to download and share the FST flyer that includes identification tips and contact information. He said they are always free to e-mail him with their concerns and photos of suspected FST – not only to help stop the spread of the pest but to expand scientific understanding.
“This termite is so new to California – even for us, as researchers. Despite being in La Mesa since the 1990s, it wasn't until 2020 when these termites were detected in other places, including Riverside and Los Angeles counties,” Taravati explained. “All of us need to learn more about this pest and closely monitor the behavior of this pest.”
- Author: Kathy Keatley Garvey
Sutherland, UC Riverside professor and urban entomologist Chow-Yang Lee, and USDA forest entomologist Lori Nelson want to compare the spring swarming populations of Reticulitermes hesperus with the fall swarming populations.
“A major taxonomic question surrounding western subterranean termites remains unsolved,” said Sutherland, the Urban IPM Advisor for the San Francisco Bay Area. “Most termite species simultaneously swarm over a relatively short period during one season, facilitating genetic exchange during mating. Individuals thought to represent Reticulitermes hesperus, however, have been observed swarming during both autumn (usually on a sunny day after the first autumn rain event) and spring (sunny days when soil is moist) suggesting that there are at least two cryptic species considered within the western subterranean termite complex or that speciation is underway (individuals swarming at different times of the year cannot mate with one another).”
In fact, says Sutherland, USDA Forest Service research by Michael Haverty and Lori Nelson indicates that spring and autumn swarming populations can actually be distinguished by different cuticular hydrocarbons (waxes on exoskeleton).
In the collaborative UC IPM, UC Riverside, and USDA Forest Service research project, “we seek to resolve this question once and for all by comparing DNA microsatellite data and cuticular hydrocarbon data from alates (winged termite swarmers) collected during these different seasons,” Sutherland said.
Residents of California, Oregon, Washington, Idaho, western Nevada, southern British Columbia, and northern Baja California can help by collecting at least 25 individuals of swarming Reticulitermes and freezing them in a hard-walled container, such as a pill bottle, film canister or a food storage plastic container. Contributors will receive a Common Cockroaches of California poster or another special gift. Contributing pest management professionals will receive a free training opportunity with ‘IPM' continuing education units for California's Structural Pest Control Board licenses.
Sutherland's program will fund the shipping of the specimens. He may be reached at amsutherland@ucanr.edu for further information, such as if the termite specimens qualify.
About Termites and Sutherland's Work
Termites, like cockroaches, are members of the order Blattodea and evolved some 120 million years ago. Structural infestations of subterranean termites are usually not visible, but the annual flights of winged termites (alates) are. This research will help pest control providers and residents understand the most likely swarming periods in their specific region, improving monitoring and control for these important structural pests.
Sutherland, who began researching termites in 2014, says the western subterranean termite, “is the most damaging wood destroying insect in northern California and most other parts of the Pacific Northwest, causing billions of dollars of damage to homes and other structures each year. Conventional treatments use soil drenches or injections of liquid termiticides to create protective barriers around wooden structures.”
One of his research projects seeks to evaluate an alternative management tactic for subterranean termites: bait station systems that use insect growth regulator insecticides to eliminate entire termite colonies. “Bait systems represent reduced environmental contamination as compared to liquid treatments, but adoption of their use in California and other Western states has been slow to progress,” he said, adding that he hopes his research will demonstrate the relative efficacy of baits and increase both demand for and provision of bait services.
Sutherland, who holds advanced degrees in entomology and horticulture from UC Davis and the University of Florida—including a doctorate in entomology from UC Davis in 2009-- is a Board-Certified Entomologist (Entomological Society of America certification program). He focuses his research on developing new IPM strategies or adapting and implementing current IPM strategies, in cooperation with other researchers, pest control operators, pest management professionals, public agencies, schools, parks, public housing, and regulatory agencies involved with household, structural, and industrial IPM.
His work includes education about IPM principles, development of IPM programs for clientele, reduction in unnecessary pesticide applications, and mitigation of surface water contamination due to urban pesticide applications.
See more information on termites on the UC Statewide Integrated Pest Management (UC IPM) site, Subterranean and Other Termites.
