Drywood termites are remarkably good at disappearing into the very material they destroy. Instead of building obvious nests, they can spend nearly their entire lives hidden inside beams, framing, furniture, and other dry wood, slowly carving out galleries as a colony grows.
That hidden existence makes them difficult to find and difficult to eliminate. But researchers at the University of California, Riverside identified a biological weakness that termites cannot hide from: they have to molt.
A study published in 2025 in the Journal of Economic Entomology showed that bistrifluron, an insect growth regulator that interferes with the formation of a new exoskeleton, can kill western drywood termites with remarkable efficiency. In controlled laboratory experiments, the chemical produced 95.7 percent mortality when termites had a choice between treated and untreated wood, and about 99 percent mortality when they were continuously exposed to treated wood.
Turning Termite Growth Against Them
“This chemical is more environmentally friendly than ones traditionally used for drywood termite infestations,” said Nicholas Poulos, corresponding author of the paper and a doctoral student in UCR’s Department of Entomology. “It’s specific to insects and can’t harm humans.”
That selectivity comes from the biology the treatment targets. Humans and other mammals have internal skeletons, but insects rely on a rigid outer covering called an exoskeleton. One of its most important ingredients is chitin, a durable natural material that provides structure and strength.
Chitin is common in nature. It helps form insect exoskeletons, fungal cell walls, fish scales, and structures such as the beaks of squids and octopi. For termites, it provides protective armor while also creating sturdy attachment points for muscles.
The problem for a growing termite is that this armor cannot simply stretch forever. Drywood termites molt about seven times during their lives, shedding the old exoskeleton and replacing it with a larger one.
Bistrifluron turns that unavoidable process into a vulnerability. It belongs to a group of compounds known as chitin synthesis inhibitors. Rather than acting like a conventional fast-acting poison, it disrupts the insect’s ability to manufacture enough chitin for the next exoskeleton.
“Once the termites reach a certain stage, they have to molt. They cannot avoid that,” said Dong-Hwan Choe, UCR entomology professor and senior paper author. “With a lethal dose of this chemical, they’ll try to shed their old exoskeleton but won’t have a new one ready to protect them.”
The Treatment Does Not Kill Immediately
That mechanism also explains why bistrifluron works relatively slowly. Researchers first observed decreases in activity and feeding. The termites continued toward their next molt, but eventually failed to complete it successfully and died.
The team compared three chitin synthesis inhibitors: bistrifluron, chlorfluazuron, and noviflumuron. Bistrifluron produced the fastest mortality at the concentrations tested. In one experiment in which termites had no untreated alternative, the 0.1 percent bistrifluron treatment produced about 99 percent mortality after 60 days. When termites were offered both treated and untreated wood, the same concentration produced roughly 96 percent mortality.
Those numbers are important because drywood termites are particularly challenging targets. Unlike subterranean termites, which maintain colonies connected to the soil, drywood termites can live entirely within pieces of wood.
“It’s been successfully used on subterranean termites, which are also important structural pests,” Choe said. “But native western drywood termites are also important, especially in California.”
A Few Exposed Termites Can Spread a Lethal Dose
Perhaps the most intriguing result involved what happened after only part of a group encountered bistrifluron.
Termites are social insects that routinely exchange food and other material. The researchers exposed some termites to bistrifluron and then placed them with untreated members of the same colony. Colored food was used to follow the movement of material between individuals.
Within 24 to 48 hours, material from the exposed termites had reached previously untreated nestmates. Even more strikingly, groups in which only 5 percent of the termites had initially encountered bistrifluron eventually reached 100 percent mortality by day 90. Groups that began with 50 percent exposed termites showed a broadly similar survival pattern.
That suggests a small number of termites can retain enough bistrifluron to help carry an effective dose deeper into a group.
Later observations from the UCR team have provided an unusually close look at the social behavior that may help substances move through these concealed colonies. In 2026, researchers highlighted images and video of western drywood termites performing proctodeal trophallaxis, a feeding behavior in which one termite receives material from another termite’s hindgut. The exchange is important because it transfers nutrients and gut microbes that help termites digest wood.
Normally, that intense social cooperation helps the colony survive. For pest control, however, the same behavior could become an advantage if it helps a treatment reach termites that never directly encounter treated wood.
A Possible Alternative to Whole Structure Fumigation
The slow action of bistrifluron may therefore be useful rather than simply a drawback. A chemical that kills immediately could eliminate exposed termites before they have much opportunity to interact with nestmates. A delayed treatment gives contaminated individuals time to move and exchange material.
“We believe this method of spot treatment can kill a larger colony and spread more easily than current termite control methods,” Choe said. “You don’t have to apply too much to get a very good result. The chitin synthesis inhibitors show promise as localized treatment for drywood termites.”
That could eventually offer homeowners another option when an infestation is localized and accessible.
Structural fumigation remains one of the most effective methods for eliminating drywood termite infestations throughout an entire building. But it is disruptive. Residents have to leave, food must be protected or removed, and the treatment does not leave behind lasting protection against termites that arrive later. The 2025 study also notes the cost and lack of residual protection as important disadvantages of whole structure fumigation.
“Low-impact strategies like this one will become an attractive option in many cases. Furthermore, the chemical may stay active in the wood for some time, potentially providing protection from future infestations,” Choe said.
The laboratory results do not yet mean that treating a house with bistrifluron will automatically produce the same mortality rates. The experiments used small groups of termites under controlled conditions, and the researchers described the findings as support for developing bistrifluron further as a localized treatment or possible bait ingredient.
Another Strategy Lures Termites Toward Poison
Bistrifluron is only one part of UCR’s effort to make targeted termite treatment more effective.
The same laboratory has investigated pinene, a fragrant chemical naturally released by many trees. To a western drywood termite living inside wood, that scent can act like a signal pointing toward a potentially attractive part of its environment.
Researchers tested whether pinene could lure termites away from the places where they were clustered and toward localized insecticide deposits. Earlier experiments found that the approach improved the performance of an aqueous fipronil treatment.
“We saw significant differences in the death rates using insecticide alone versus the insecticide plus pinene,” said Choe. “Without pinene, we got about 70% mortality. When we added it in, it was over 95%.”
The idea has since moved another step toward potential practical use. A University of California patent application filed in April 2025 and published in October 2025 describes adding alpha pinene or beta pinene to localized insecticide injections for western drywood termites. The application proposes that attracting termites toward treated areas could potentially allow technicians to space treatment holes farther apart while reducing labor and possibly the amount of insecticide needed. Those possibilities remain part of the proposed application rather than proof that the approach has already replaced existing treatment methods.
Researchers Still Need a Better Delivery Method
Bistrifluron also faces a practical obstacle before a treatment based on the experiments could be easily translated into homes.
In the laboratory study, researchers dissolved the chemical in acetone and applied it to pieces of wood. The solvent was allowed to evaporate before termites were introduced. Acetone is useful in an experiment, but its flammability and strong odor make it poorly suited to routine household treatment.
“We are working to make it more feasible for practical application in real-life scenarios,” Poulos said.
Developing a practical formulation could make a major difference because successfully controlling drywood termites requires more than simply having an insecticide that kills them. Technicians also have to determine whether termites are still present and where inside a structure the active colony is located.
Termite Droppings May Reveal Whether a Colony Is Active
That detection problem has now become another focus of the UCR researchers.
Drywood termites eject tiny, hard fecal pellets from their wooden galleries. Those piles can alert homeowners to an infestation, but there is a catch: old pellets can remain long after termites have disappeared. Simply finding droppings therefore does not necessarily prove that termites are currently active.
Research published after the bistrifluron study found that the microbes inside those pellets may provide a kind of biological clock.
Poulos and his colleagues examined fresh western drywood termite pellets along with samples aged for three months, six months, and one year. They found that bacterial DNA declined dramatically as the pellets aged. In pellets produced from termites feeding on natural hardwood, the estimated amount fell as much as 190-fold between fresh samples and those aged for a year. A similarly large decline occurred in pellets from termites fed Douglas fir, a wood commonly used for house framing.
The types of bacteria changed as well. Some bacterial groups associated with fresh pellets disappeared as the samples aged. Researchers identified five bacterial families that were consistently found in fresh Douglas fir-derived pellets but absent after certain periods of aging.
The team hopes those microbial signatures could eventually form the basis of a simple diagnostic tool that helps pest professionals determine whether termite evidence is recent enough to justify treatment.
That could complement approaches such as bistrifluron. One strategy aims to tell technicians where an infestation is still active, while another attempts to eliminate the termites with a more localized treatment.
A Pest That Travels Inside Wood
Better detection and more targeted treatments could become increasingly valuable because western drywood termites are not confined to one small region.
The species is native to parts of the southwestern United States and northwestern Mexico and is particularly important as a structural pest in California. Human movement of lumber, furniture, and other wood products has also transported it far beyond its original range. Researchers have documented introduced populations in places including Hawaii, New York, Florida, Canada, China, Japan, Korea, and Australia.
Their lifestyle makes that spread particularly difficult to control. A colony can remain concealed inside a piece of wood, with winged reproductive termites representing one of the few life stages that routinely venture outside.
Climate conditions also help determine whether transported termites can establish themselves after arriving somewhere new. As suitable conditions shift, researchers are concerned that the insects could become a problem in additional regions.
“As we move lumber around the world, the termites are constantly transported to new locations. If they find the climate there acceptable, the problem will spread,” Choe said. “In areas where these termites are common, it’s just a matter of time before homes are infested, so this study is a good initial step toward alternative strategies for controlling them.”
Taken together, the work points toward a different style of termite control. Instead of relying only on treating an entire structure, researchers are trying to exploit the insects’ own biology, social behavior, feeding habits, and even their microbial traces.
For termites that spend almost their entire lives hidden from view, those biological clues may ultimately make them much harder to hide.
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