A growth blocker killed about 99% of drywood termites in lab tests by stopping their molt

A chemical that stops termites from building a new exoskeleton killed about 99 percent of western drywood termites in laboratory tests at the University of California, Riverside. The compound, bistrifluron, worked by catching the insects in the middle of a molt they could not finish. When termites had a choice between treated and untreated wood, mortality was still 95.7 percent.

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The result points toward a spot treatment for a pest that homeowners usually fight with whole-house fumigation.

How bistrifluron stops the molt

Bistrifluron belongs to a class called chitin synthesis inhibitors, which interfere with the material insects use to build their outer shells. Termites must molt as they grow, and a termite that tries to shed its old exoskeleton without a new one ready to protect it dies. Dong-Hwan Choe, the UC Riverside entomology professor who is senior author, put it directly in the ScienceDaily account of the work: once the termites reach a certain stage, they have to molt, and they cannot avoid that.

The effect is slow by design. Termites that eat treated wood slow their feeding, fail to molt and die, and a full colony collapse takes about two months, according to the UC Riverside Department of Entomology summary. Because the compound acts slowly, exposed termites live long enough to pass it on to nestmates, which is what lets a small dose spread through a colony hidden inside a wall or rafter.

Lab mortality across three inhibitors

The study in the Journal of Economic Entomology tested three chitin synthesis inhibitors, bistrifluron, chlorfluazuron and noviflumuron, on the western drywood termite, Incisitermes minor. In the no-choice test, where treated wood was the only food, bistrifluron reached 99 percent mortality over 60 days at a concentration of 0.1 percent. In the choice test at the same concentration, mortality was about 96 percent. Chlorfluazuron was the least effective in the choice test, which the authors suggest may reflect ineffective concentrations, though they have not confirmed that. Bistrifluron was also the fastest of the three at the concentrations used, although all three acted more slowly than conventional fast-acting poisons.

A transfer experiment gave the strongest sign that the chemical moves through a group. Termites fed bistrifluron passed it to unexposed nestmates within 24 to 48 hours, and when only 5 percent of a group had been exposed the whole group was dead by day 90. The authors write that lethal doses were retained and transferred even when few termites had ingested the compound.

Why fumigation is the benchmark

The journal paper frames the work against current practice. Fumigation with sulfuryl fluoride is costly, requires people to leave the building and leaves no lasting protection, while spot treatments are variable and rarely eliminate whole colonies. Chitin synthesis inhibitors were already used in baits for subterranean termites but had not been tested against drywood species.

Nicholas Poulos, the doctoral student who is corresponding author, said the chemical is specific to insects and cannot harm humans, a claim the ScienceDaily account does not back with a human safety study. In the original UC Riverside announcement, the researchers said it is more environmentally friendly than treatments traditionally used for drywood infestations, and Choe said spot treatment might reach larger colonies and remain active in wood to help prevent new infestations.

Drywood termites are a particular problem because they live entirely inside the wood they eat. Native to North America, they feed on dead wood above ground and cannot tell dead trees from lumber in a house, which puts homes at risk in California, Florida and parts of Canada and Mexico, as the same research group has described. A colony that never touches the soil cannot be reached by the soil barriers and ground baits that work on subterranean species, leaving fumigation or localized injections as the standard options.

Limits before any product reaches a home

The caveats are substantial. The transfer tests used small groups of 20 termites, and the authors say larger colonies still need testing. The laboratory formulation dissolved bistrifluron in acetone, which Choe and Poulos acknowledge is flammable and smells bad, so it would not suit a house. Poulos said the team is working to make the treatment more feasible for practical use in real-life settings.

A second line of work adds a lure. A UC patent application proposes pairing localized injections with alpha or beta pinene, the pine scent that attracts drywood termites from a distance. In an earlier UC Riverside study, Choe’s group found that adding pinene to the insecticide fipronil raised mortality from about 70 percent to over 95 percent. The team also reported that bacterial DNA in termite droppings fell as much as 190-fold after one year in a related pellet analysis, which may eventually help identify which colonies are still active. For bistrifluron, the pinene pairing remains a proposal rather than a demonstrated treatment, and no product date has been announced. For a homeowner weighing a tent against a needle, the lab result is a promising early signal rather than a purchasable option.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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