When every known control measure failed to stop termites from gnawing their way through 250-year-old Fort Christiansvaern overlooking Christiansted's picturesque harbor, the U.S. National Park Service turned to a University of Florida termite expert for help.
Now, after battling the pest for more than three years, UF entomologist Nan-Yao Su and his colleagues say the old Danish fort in the Christiansted National Historic Site is termite-free.
Joel Tutein, superintendent for the park service on St. Croix, said termites have been the single most destructive force ever to hit the fort, which was built between 1739 and 1749 when the island was colonized by Denmark. The fort now is one of the island's most popular tourist sites, attracting nearly 100,000 visitors annually.
"The fort has been through hurricanes, floods, earthquakes and occupations, but nothing has been more destructive than subterranean termites," Tutein said. "If we did not solve our termite problem, we would have watched the entire structure crumble before our eyes."
He said things started to get expensive in the 1980s, when termite-infested pine and tropical hardwood had to be replaced every five or six years.
"We tried every available chemical and treatment, including tenting and drilling pesticides into the walls, but nothing seemed to work. It was really frustrating because we were spending money on the same repair projects over and over again," Tutein said.
The problem reached a crisis about three years ago when the park service wanted to start a long-overdue $750,000 restoration project.
"We could not begin a major renovation program at the fort until we found a way to stop the termites," Tutein said. "Otherwise wooden beams, floors, doors and shutters would have to be replaced every few years at enormous cost."
In 1995, the park service contacted Su, a professor of entomology with UF's Institute of Food and Agricultural Sciences, who already was working on termite control projects at other park service landmarks.
Su, based at UF's Fort Lauderdale Research and Education Center, has earned an international reputation in the pest control industry for developing a new baiting system – the first effective method for stopping all types of subterranean termites.
"Conventional pesticide treatments may keep termites out of buildings, but they don't control termite colonies in the ground," Su said. "Unlike traditional barrier control methods, our new system eliminates underground colonies, which was the key to controlling termites at the fort in Christiansted."
He said the system is effective because termites themselves spread the pesticide bait.
"The key to success is getting the termites to come back for more until the entire colony gets a lethal dose of the bait," Su said.
Zandy Hillis-Starr, chief of natural resources for the National Park Service on St. Croix, worked on the project with Su and his assistant, Paul Ban. Hillis-Starr said she believes termites at the fort are under control for the first time.
"When we first started on this project, I was not very optimistic the pest could be controlled because of all the disappointments we've had over the years," she said. "But now I feel comfortable that we will not have to deal with this problem again for at least 20 years. If we do have a problem, UF will be back to help."
During the initial phase of the project, which lasted about two years, Su, Ban and Hillis-Starr located the sources of termite infestations. Then, beginning in 1997, they installed Su's new baiting system to monitor and control the pest. The historic site now is protected by 40 monitoring stations, and no activity has been detected for more than 12 months.
"It's safe to say that all underground termite colonies around the fort are gone," Su said. "During the height of the infestation, there probably were 20 to 30 underground termite colonies with millions of termites attacking the fort, building tubes up through floors, walls and other wood structures."
The Park Service estimates the termite eradication program will save up to $700,000 in repair costs over the next 20 years. Su identified the termite as the Heterotermes species, which is common in the Caribbean, Central America and some South American countries.
Su's system uses a chemical called hexaflumuron, a growth regulator that prevents subterranean termites from molting and reduces the worker population's ability to sustain the colony. Used in very small amounts, less than one gram of active ingredient will kill an entire colony containing millions of termites. The chemical has a low toxicity to humans and the environment.
To deliver the growth regulator, Su placed a small monitoring/feeding station in the ground near buildings. When termite activity is detected, the monitoring devices are replaced with a cellulose material laced with the insect growth regulator.
He also developed an above-ground delivery system, or bait station, to help control the termite problem at the Christiansted fort.
The new system is licensed by UF to DowAgroSciences in Indianapolis and is marketed worldwide as Sentricon Termite Colony Elimination System.
