Nitro-Nosh: Why Termites’ Molted Exoskeletons Never Go to Waste
By Ed Ricciuti
Scientists have linked a behavioral trait of two destructive subterranean termite (Coptotermes) species to their remarkable survival as working colonies on boats for long periods, helping them spread widely from their native southern Asia. The colony carries and recycles its own nitrogen, essential for growth and reproduction, by eating exuviae, the exoskeletons shed when termites molt.
Nitrogen is present in all arthropod exoskeletons. It is scarce in the wood diet of subterranean termites, but they remedy this deficiency by consuming millions of exuviae produced by fellow colony members and, occasionally, eating dead mates. Meanwhile, not long ago it was discovered that termite workers return from foraging to the nest when ready to molt. They molt in the central part of the nest where the queen, king, and their progeny are sited.
In a research study published in February in the journal Environmental Entomology, researchers report that manipulating the availability and consumption of nitrogen-rich exuviae impacts the queen’s production of young and thus overall colony growth. In a second study, published in February in the Journal of Insect Science, they describe using biomarkers to trace movement of nitrogen through the food chain to the queen. In the latter experiment, says lead author Reina Tong, Ph.D., the “marker level in the queen was not significantly different than the workers. However, the queen does not feed herself, so the fact that the queen had the same amount of marker as the workers that directly fed on the marked exuviae suggests that numerous transfers occurred from workers to the queen.” This suggests that the conservation of nitrogen from eating shed exoskeletons is targeted at the queen and her ability to reproduce.
Tong led the team conducting the studies while working as a research graduate assistant at the University of Florida and now a postdoctoral researcher at the University of Hawaii. The experiments focused on the Asian subterranean termite (Coptotermes gestroi), which, along with its cousin the Formosan subterranean termite (C. formosanus), has a foothold in southern United States but seems restricted by cold from moving north. Coptotermes gestroi has shown up in Florida and Hawaii while C. formosanus appears in Hawaii and almost a dozen southern states on the U.S. mainland.
Describing the significance of their work, Tong and colleagues write that “the success of Coptotermes colonies as invaders could partially be attributed the centralization of nitrogen recycling through exuviae consumption at the central part of the nest, where the recycling process is most efficient.”
Proof of the role played by exuviae consumption was that, after 6.5 months, colonies reared in nitrogen-poor environments “gained significantly more biomass when exuviae were added than colonies with no added exuviae.” On the other hand, adding shed exoskeletons had no effect on growth of colonies reared in nitrogen-rich environments. Moreover, queens with less exuviae available laid fewer eggs than those in colonies in which exuviae had not been reduced.
The second study describes how the transfer of nitrogen through colony members was followed by tagging exuviae with a biomarker, rabbit immunoglobulin, often used with arthropods. Tracing the path of nitrogen in exuviae experimentally fed to workers—which, in turn, regurgitate food to the young and queen through the food chain—showed that molting in the nest is indeed a mechanism for recycling and distributing nitrogen thorough the colony.
“Returning to the central nest to molt brings a nitrogen-rich resource—exuviae—close to the queen and larvae, both of which have high nitrogen demands,” says Tong. “This study demonstrates nitrogen conservation within a colony and exemplifies the idea that nitrogen may be allocated in a way that prioritizes increased reproduction.”
Journal of Insect Science
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.