A Changing Landscape in Subterranean Termite Control
This is a summary of a recent presentation by Dr. Thomas Chouvenc on the importance of termite colony biology on control methods
Termites evolved from cockroaches 150 million years ago. There are now over 3,000 termite species worldwide, yet only 3 percent of the overall diversity are pests. They have extremely important roles in subtropical and tropical ecosystems, decomposing wood and other forest litter, and returning those essential nutrients and carbon stored within the dead wood back into the cycle for soil enrichment. That alone is a worthy designation. However, for all the amazing benefits termites provide in the natural environment, there is a zero-tolerance policy once they enter our homes. A mature Formosan subterranean termite colony can consume about 300 pounds of wood per year.
In Florida, we have the highest diversity of termites in the United States. There are 21 different species of termites in Florida, and two of the most damaging termite pests occur in south Florida, Formosan subterranean termites, Coptotermes formosanus, and Asian subterranean termites, Coptotermes gestroi. Within six months of an infestation, structural damage of a home can occur because of the sheer size of the colony. Subterranean termites have large underground colonies, often in the millions, with a central nest where the king and queen reproduce and brood are maintained by young termites. Termite workers go out and forage for new food sources, often very far, up to 300 feet, from the central nest, through an underground tunnel system. They need to maintain a moist environment and cannot survive without water. Subterranean termites attack wood that contacts the soil and build mud tubes or tunnels, to maintain moisture, and reach wood in structures and trees away from the soil surface. So, if a subterranean infestation is discovered in a home, it is only a small portion of the entire colony, which is why we do not fumigate for such subterranean species. Structural fumigation is used against drywood termites, which colonies often infest a single piece of wood.
What has recently been discovered, is these invasive subterranean termites are also killing living, healthy trees in the urban south Florida environment. In most cases, the termites feed on the wood or old xylum tissue deep within the tree, not on the live vascular tissue, so the tree appears to be healthy until it collapses on its own weight or when a tropical storm or hurricane passes. One of the ways to detect the early presence of invasive subterranean termites is to regularly inspect trees surrounding structures and look for termite activity, often noticeable by the presence of mud tubs on the bark or at pruning wounds. Knowing if these species are established in your area is also important, as it tells if you are in an area at risk of infestation. The current distribution map of termite pest species is accessible at https://flrec.ifas.ufl.edu/termites-in-florida/termite-distribution/.
Termites are eusocial insects, like ants and bees, that live in massive colonies with cooperative care of the young, overlapping generations, and a reproductive division of labor, meaning only a few members of the colony reproduce (king and queen). However, they differ from ants and bees, in that they are hemimetabolous, which means the immature insects looks like miniature versions of the adults and do not have go through metamorphosis. So, termite workers, which are sterile, will continue to molt throughout out their life until they die. Interestingly, they do not molt at the foraging sites due to lack of care and protection in these environments and return to the central nest to be cared for by nurse termites (young workers) during the molting process. This has become a very important aspect in understanding their biology and adapting control practices based on new technologies.
Traditional subterranean termite control involves the use of liquid termiticides and still represents a significant portion of all subterranean termite treatments in the United States. The goal of these treatments is exclusion from the home through a chemical, insecticidal barrier around the structure, killing organisms that encounter the barrier before they enter the home. These products are mostly non-repellent, meaning they are undetected by the termites, and are broad-spectrum insecticides, so they are not only going to kill termites on contact, they will kill any insects that come into contact with the treatment area. Additionally, most liquid termiticides are non-persistent and break down in the environment within a few years. In recent years, more and more pest control operators have been reporting failures with liquid termiticide treatments of Asian subterranean termites according to Dr. Thomas Chouvenc, as cumulative evidence suggests that such subterranean termites may eventually find a way to bypass the treatment through strong foraging pressures.
Newer technology involves the use of Chitin Synthesis Inhibitor (CSI) Baits placed around the structure or home. The goal with CSI baits is colony elimination. Chitin Synthesis Inhibitors work by preventing the formation of chitin which is needed to form an insect’s exoskeleton. So, the insects grow normally until it is time to molt, and the inhibitors prevent the new exoskeleton from forming properly and the insect dies, usually around 40 days after ingestion. These insecticides are targeted for consumption by termites only and a minute amount of pesticide is used in comparison to liquid termiticides. So, termite workers forage and feed on treated wood baits, return to the main nest, and share the food (carrying the active ingredient) with the brood and the rest of the colony through trophallaxis (a food exchange process common in social insects). Colony elimination is usually achieved within 90 days after the initial feeding on the bait.
A study by Dr. Nan Yao Su in 2005 looked at distance as a parameter for understanding termite control. In a laboratory experiment with about 10,000 foraging termites and 150 feet of tubing used as the foraging system, Dr. Su found termites within 10 to 15 feet of a commonly used liquid termiticide treatment died within one week. However, beyond that, the colony was not affected, and the remaining termites closed the tunnel system to separate themselves from the area with termite mortality. So, what is happening, according to Dr. Su, is secondary repellency in the treated area due to rapid death by those exposed to the liquid termiticide. Later, Dr. Chouvenc replicated the study with whole termite colonies, containing reproductive adults, brood and different aged individuals and effectively achieved colony elimination within three months with small amount of CSI bait formulation. His study confirmed what Dr. Su found, which was secondary repellency occurs with liquid termiticide treatments because the death of exposed termites occurs so rapidly, living termites can seal off the area with termite mortality and can use other means to access structures.
Dr. Thomas Chouvenc believes these recent discoveries and the more we continue to learn about termite biology, will continue to change the way we control these destructive pests moving forward. Asian subterranean termites start swarming in early March in south Florida. This is a good time to go around and inspect trees for mud tubes and other signs of termite activity to help detect a termite infestation.
Thank you to Dr. Thomas Chouvenc for his review of this article.
For more information on the studies mentioned in this article:
Subterranean Termites Feeding on CSI Baits for a Short Duration Still Results in Colony Elimination: https://academic.oup.com/jee/article/110/6/2534/4563823?login=true
Response of the Formosan Subterranean Termites (Isoptera: Rhinotermitidae) to Baits or Nonrepellent Termiticides in Extended Foraging Arenas: https://academic.oup.com/jee/article/98/6/2143/2218430