Humidity cycles steer insect behavior

In a novel experiment at the University of Cincinnati, researchers isolated kissing bugs, fruit flies, mosquitoes and spider beetles in a climate- and light-controlled environment and found that they responded predictably to cycles of humidity in the same way they do temperature and daylight. After the humidity cue was removed, the insects continued to respond to the cyclical fluctuations of humidity and dryness established in the experiment.

“They take humidity cues as a biological clock,” UC Professor Joshua Benoit said.

The study was published in the Nature journal Biological Timing and Sleep. It was supported with grants from the National Institute of Allergy and Infectious Diseases.

Circadian rhythms can affect everything from body temperature to hormones. But few studies have examined circadian rhythms for humidity, said lead author Shyh-Chi Chen, a former researcher in Benoit’s lab.

“Light and temperature are well-known environmental factors that can entrain the circadian clocks,” said Chen, now an assistant professor at Georgia College & State University. “Humidity, like light and temperature, fluctuates daily.”

For people, extremely high or low humidity is a mere annoyance. But for insects, it can mean life or death, Chen said.

“This could be critical for terrestrial organisms, as their survival depends on staying hydrated or avoiding dehydration,” Chen said.

So it’s useful for creatures to anticipate when conditions will be optimal to forage or otherwise expend energy, he said.

While the results were statistically significant, insects are less connected to humidity than daylight and temperature, researchers said. And mosquitoes showed the least behavioral connection to humidity.

Many animals respond to predictable cycles, such as the lunar calendar which also governs the tides, or the solar calendar, which governs the hours of daylight. UC researchers discovered that monarch butterflies rely on daylight as a sun compass to navigate on their epic continental migration.

Could mammals like us also take our cues from cycles of humidity?

Researchers said it’s possible, but the effects are probably far too miniscule to notice.

“While our current study focuses on animal models, it opens a fascinating door to human biology,” Chen said. “Although mammalian circadian biology is heavily dominated by the light-dark cycle, the potential for subtle, multisensory integration — including humidity — cannot be ruled out.”

Researchers carried out the experiment in the 16-story Crosley Tower, which is now being demolished. The lab space on UC’s Uptown campus was isolated within a larger lab on the top floor of the concrete building to provide a secluded, quiet place where the experiments could be carried out under strict controls, Benoit said.

“It was extraordinarily difficult, but we finally got consistent stable conditions we needed for the experiment,” he said.

Researchers recorded the movement and sleep of the insects to observe any correlation between their behavior and humidity levels.

“It is a unique new aspect of circadian rhythms,” Benoit said. “In the grand scheme of rhythm biology, it’s going to have a comparatively smaller effect.”

Featured image at top: UC researchers found that some insects have a connection to humidity much like they do for daylight. Photo/Studio-OMG/iStockPhoto