What Wood Termites Prefer

Subterranean termite worker (Patty McKeithan Alder, NCSU)

Each year, termites cause an estimated $40 billion in damage globally and damage more than 600,000 homes in the U.S. alone. The amount of wood a single termite colony can damage depends on the species of termite, the type and condition of wood present, and what has been done (if anything) to treat the wood.

Scientists with the U.S. Department of Agriculture (USDA) recently investigated the preference of Formosan termites to 10 different species of wood. Agricultural Research Service (ARS) research entomologists Mary L. Cornelius and Weste L. Osbrink knew the heartwood of some trees contains allelochemicals, which can act as repellents and toxicants to insects including termites. The question was whether boards of lumber contain enough of these chemicals to have a real impact against 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. This research was part of the ARS Formosan termite research project in New Orleans, which has now been completed.

The researchers fed the termites a diet from one of ten commercial lumbers: redwood, birch, spruce, southern yellow pine, red oak, Brazilian jatoba, Peruvian walnut, Honduran mahogany, teak, and Alaskan yellow cedar.

After six weeks, redwood, Brazilian jatoba, Peruvian walnut, Honduran mahogany, and teak showed some level of natural resistance and led to an average of more than 74% termite mortality. Southern yellow pine and teak were the least palatable to the termites.

Termites that weren't fed at all (the starvation control) had a significantly lower survival rate on a diet of teak, indicating that there is something in the teak that may actively killed the termites.

The study also provided the first evidence that termites will eat, damage, and survive to some extent on Peruvian walnut. While Peruvian walnut caused high termite mortality - only 16.4% of termites survived after feeding on Peruvian walnut for 6 weeks - the wood also sustained a high rate of feeding damage. In the rest of the wood species, termite survivability went hand-in-hand with low consumption rates.

The researchers concluded that their ranking could be a guideline when choosing lumber in areas of high termite infestation. If the specific compounds in the resistant wood are identified, these compounds may eventually offer the possibility of a natural treatment for wood to protect against termites.

Read more about this research in the November issue of AgResearch HERE.