Secondary Repellency: What It Is and How to Avoid It

In the rush to eliminate a termite colony, PMPs and their customers might be tempted to take a “more is better” approach by using liquid termiticides in addition to in-ground bait stations. But a recent study published by the University of Florida confirms what researchers have observed for some time: The combination of liquid termiticides and chitin synthesis inhibitor (CSI) baits, such as the Sentricon system, is unlikely to result in colony elimination and may leave the colony viable and able to cause ongoing damage to structures.

The problem? Secondary repellency, also known as the “death zone.”

“The current products used for liquid termiticides…kill termites relatively quickly,” said Thomas Chouvenc, Ph.D., associate professor, urban entomology, Ft. Lauderdale Research and Education Center, University of Florida. “The problem is, because they’re…dying within proximity of the treatment, it creates what we’re now calling the ‘death zone.’”

How do liquid termiticides impact bait station efficacy?

This “death zone” forms when powerful, fast-acting liquid termiticides create what is effectively a barrier of dead termites. Active foragers then avoid the area, preventing further transfer of the termiticide. In his paper, “Death Zone Minimizes the Impact of Fipronil-Treated Soils on Subterranean Termite Colonies by Negating Transfer Effects,” Chouvenc noted: “The emergence of a ‘death zone’ triggers behavioral avoidance and closure of foraging tunnels within 3-5 meters from the treatment, which ultimately prevents further toxicant exposure to the broader…foraging population.”

While some PMPs may be tempted to compensate by installing bait stations in addition to liquid termiticide treatments, Chouvenc’s research suggests this approach will likely not deliver the desired result, especially if both treatments are used in close proximity

“Unfortunately, the current study implies that there is a high risk for bait stations to not be readily found by foraging termites if placed in the death zone,” he said. “It therefore raises questions about the practicality and the cost-effectiveness of the combined use of both products.”

In everyday terms? Positioning both liquid termiticide applications and bait stations for optimal protection of the structure will likely put the bait stations inside the “death zone,” potentially minimizing or neutralizing the effects of the bait while allowing the colony to rebuild.

“So using both simultaneously may be counterintuitive because the synergistic activity between the two products is unlikely,” Chouvenc said. “They have a negative effect on each other; the liquid termiticide may prevent in-ground baits within direct proximity from being discovered.”

Can foraging spread liquid termiticides?

Chouvenc’s study also challenges the assumption that the active ingredient from a liquid treatment will be spread throughout the colony through foraging activity.

The study “…suggests that once the initial mortality is expressed…any subsequent mortality of a few foragers from the recurrent exposure to the death zone is largely compensated by the inherently high reproductive rate of the colony.”

“The liquid termiticide may well protect the structure. However, because of [the] ‘death zone’ and the limited transfer of active ingredients…the termite colony can continue to grow around this treatment to increase their density and, therefore, maintain their potential for damage over time,” he said.

The bottom line? While liquid termiticides have their place, their ability to eliminate a subterranean termite colony is limited, and the protection offered by liquid treatments is likely temporary.

However, in-ground and above-ground CSI baits, such as the Sentricon system, have repeatedly proven their ability to protect homes and other structures by eliminating termite colonies, not just forcing them to move to another location on the property.

Chouvenc’s study concludes “…when diligently applied, liquid termiticide products can effectively protect a structure from termite infestation but may have minimal impact on surrounding termite populations. Commercial CSI bait products now offer simple and effective alternatives, from colony elimination efficacy, practicality and environmental perspectives.”

Always read and follow label directions.