The United States Department of Agriculture is looking for a better way to build structures with resistance to termites.
Agriculture Research Service entomologist already knew that the heartwood of some trees contain “allelochemicals”, which can act as repellents and toxicants to insects. What they wanted to know is if boards of lumber had enough of these chemicals to have a real impact against termites.
In this study, researchers used commercial lumber from ten different species of wood. Those types tested were redwood, birch, spruce, southern yellow pine, red oak, Brazilian jatoba, Peruvian walnut, Honduran mahogany, teak and Alaskan yellow cedar.
During the tests, Formosan termites were given no choice but to consume just one variety of wood for six weeks.
Redwood, Brazilian jatoba, Peruvian walnut, Honduran mahogany, teak and Alaskan cedar showed some level of natural resistance and caused an average of better than 75 percent termite mortality. Southern yellow pine and spruce were the most palatable.
Teak was found to be the least palatable. In fact, termites had a significantly lower survival rate on a teak diet than compared to a group that was not fed at all (they call this starvation control). This is an indication there is something in teak that actively kills termites.
Results from the study also provided the first evidence that termites will eat, damage, and survive to some extent on Peruvian walnut. The amount of damage to Peruvian walnut was similar to the amount of damage found in birch and red oak.
“Our ranking could be a guideline when it comes to a choice of lumber in major termite-ridden areas,” said Mary Cornelius of the Agriculture Research Service. “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.”
