Drywood termites, the ones that hide in wooden structures, molt about seven times in their lives. UC Riverside researchers have found a chemical preventing them from growing new exoskeletons will also end their infestation of your home.
The chemical, bistrifluron, and its ability to kill about 95 percent of a termite colony without off-target effects on mammals, are documented in a paper published in the Journal of Economic Entomology.
"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."
Unlike humans with skeletons located inside their flesh, termites have exoskeletons on the outside that protect them from the elements. The main component of these external skeletons is chitin, which is also found in fungal cell walls, fish scales, and the beaks of squids and octopi. Chitin also provides mechanical strength for insect exoskeletons, making them suitable as armor as well as sites for muscle attachment.
As termites are getting ready to molt, something they must do in order to grow, they also produce chitin to create the new exoskeleton. Bistrifluron prevents them from doing so.
"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 researchers observed that bistrifluron initially slows the termites down, reducing their feeding activity. Eventually it prevents them from molting, and they die. This is one of the first studies, Choe said, that looks at the impact of chitin-inhibiting chemicals on drywood termites.
"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."
As the termites eat the treated wood, they also spread the chemical to other members of the colony. Full collapse happens in about two months, which is slower than other methods but carries certain advantages in addition to lower toxicity.
"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."
Traditional fumigation is not only toxic to humans and stressful ¾ it requires people to bag all of their food and move out of their home ¾ it also does not keep the termites from returning.
"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.
Previously, the Choe laboratory discovered a potent yet nontoxic way to lure western drywood termites to their doom. Pinene, a pleasant-smelling chemical released by forest trees, reminds the insects of their food. They follow the scent to wood treated with insecticide.
"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%.
Moving forward, the researchers are looking into ways to make bistrifluron easier to apply to wood. For the research described in the paper, the chemical was dissolved in acetone and applied to wood. However, in real life, this solvent isn't desirable because it is flammable and smells bad.
"We are working to make it more feasible for practical application in real life scenarios," Poulos said.
Property owners will likely welcome the innovation, as this species of termite causes a great deal of damage. They are endemic to northern Mexico and California, but as the climate warms, their range is expanding north to areas they did not previously inhabit.
"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."
