For Termites, Home is Where the Molt Is

premolt termites

As Formosan subterranean termites (Coptotermes formosanus) begin to molt, their outer exoskeletal layer is shed from the body, leaving a new one behind, as can be seen in some of the termites above. Research at the University of Florida has found that termites consistently return to their central nest to molt—a behavior that can be put to use in termite management efforts. (Photo originally published in Kakkar et al., Journal of Economic Entomology, September 2017)

If, like some creatures on this Earth, you had to periodically shed your skin, would you prefer to do that out in public or in the privacy of your own home?

If you’d choose the latter, then congratulations—you have at least one thing in common with a termite.

In a study published the Journal of Economic Entomology in September, researchers at the University of Florida found that worker-caste Formosan subterranean termites (Coptotermes formosanus) have a strong urge to return to their central nest when it’s time to molt. This habit was not previously understood, according to the study’s lead author Garima Kakkar, Ph.D., given the difficulty of studying termites’ underground behavior, and it’s also an advance in understanding why baits using chitin synthesis inhibitors (CSIs) have proven successful in eliminating termite colonies.

“Because CSIs kill termites during ecdysis [molting], our finding suggests that CSI-affected termites die in the central nest near the reproductives and brood,” Kakkar says. “This would prevent termites from dying near a bait stations that may result in bait aversion.”

Kakkar and her advisor, Nan-Yao Su, Ph.D., constructed a nest habitat for a Coptotermes formosanus colony that included both a central nesting area as well as foraging sites connected to the central nest by 15 meters of coiled tubes.

termite habitat diagram

A diagram shows the habitat created for observation of a colony of Formosan subterranean termites (Coptotermes formosanus) by researchers at the University of Florida. A planar arena (60 × 60 × 0.9 centimeters in thickness) was filled with moistened sand and extended 15 meters in one direction through Tygon tubes. Three small planar arenas (24 × 24 × 0.6 centimeters in thickness) filled with moistened sand were attached at every 5 meters along the linear foraging distance. (Image originally published in Kakkar et al., Journal of Economic Entomology, September 2017)

After the colony had a full week to settle in to its habitat, the researchers collected and marked the location of 30 molting and 30 non-molting workers. While non-molting workers were found both in the central nest and in the foraging sites, all molting workers were found in the central nest. Specifically, they were near the colony’s eggs, no more than 5 centimeters away. And newly molted workers (within 36 hours post-molt) tended to stay in the central nest area, too.

Researchers in Su’s lab have been refining CSI baits since their inception about 20 years ago, and speeding up their efficacy is one goal. CSIs specifically work by killing the termites during their molting process; so, as long as CSI-baited termites still obey their compulsion to molt in the central nest, any formulations that would accelerate that process should remain effective.

“We hypothesize that molting workers in a colony would still exhibit the molt-site fidelity when baited with CSI. In a follow-up study, we have tested if workers would die in central nest when attempting to molt under the effect of CSI. That publication is in the pipeline,” Kakkar says.

In the current study, a large portion of non-molting workers were found in the nest area, as many of them are tasked with nest maintenance, grooming eggs, and feeding larvae. Previous research, meanwhile, has shown that an average of 1.7 percent of termite workers in a colony molt each day. The discovery that foraging workers return to the nest to molt suggests that they might trade roles with workers in the nest, Kakkar and colleagues write. They also speculate that the reasons for returning to the nest to molt could include simply seeking safety during a vulnerable time to feeding the queen the workers’ shedded layers (exuviae), which contain much-needed nitrogen.

“We are also currently testing a couple hypotheses to examine its biological significance—i.e., why do they have to go back to central nest to molt?” Kakkar says.

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