What "Wood" a Termite Prefer To Eat?

Every year, termites cause about $40 billion in damage globally and destroy parts of more than 600,000 homes in the United States alone.

The amount of wood a single colony destroys principally depends on the type of termite, the type and condition of wood, and what has been done to treat the wood.

But today’s growing concerns about the environmental impact of preservative chemicals, such as chromated copper arsenate, used to treat wood against insects got Agricultural Research Service entomologists Mary L. Cornelius and Weste L. Osbrink looking for a better way to build structures with resistance to termites.

Cornelius is now with the Invasive Insect Biocontrol and Behavior Laboratory in Beltsville, Maryland, and Osbrink is with the Tick and Biting Fly Research Unit in Kerrville, Texas. Both were with the ARS Formosan termite research project in New Orleans, Louisiana, at the time the research was done.

The researchers already knew that the heartwood of some trees contains “allelochemicals,” which can act as repellents and toxicants to insects, including termites. The question was whether or not boards of lumber contain enough of these chemicals to have a real impact against termites.

“So we tested Formosan termites on a diet of commercial lumber from 10 different species of wood—redwood, birch, spruce, southern yellow pine, red oak, Brazilian jatoba, Peruvian walnut, Honduran mahogany, teak, and Alaskan yellow cedar—to see how well the termites would do,” says Cornelius.

When termites were given no choice but to consume just one variety of wood for 6 weeks, six of the woods—redwood, Brazilian jatoba, Peruvian walnut, Honduran mahogany, Alaska yellow cedar, and teak—showed some level of natural resistance and caused an average of better than 75 percent termite mortality. Termites found southern yellow pine and spruce the most palatable and teak the least palatable.

Termites had significantly lower survival on a diet of teak compared to a group not fed at all—called a starvation control. This indicated that there is something in teak that actively kills the termites.

The study also provided the first evidence that termites will eat, damage, and survive to some extent on Peruvian walnut. Average termite survival on Peruvian walnut was only 16.4 percent after the 6-week diet, but the amount of Peruvian walnut destroyed was similar to the amount of birch and red oak damaged, both of which are termite-susceptible woods. So Peruvian walnut caused high mortality, but also sustained a high rate of feeding damage; in the rest of the woods, low termite survivability went hand in hand with low consumption rates.

“Our ranking could be a guideline when it comes to a choice of lumber in major termite-ridden areas,” Cornelius adds. “If the specific compounds in the resistant woods are identified, these chemicals could eventually offer the possibility of a natural treatment for wood to protect against termites.”—By J. Kim Kaplan, Agricultural Research Service Information Staff.

“What "Wood" a Termite Prefer To Eat?” was published in the November 2015 issue of AgResearch Magazine.