Insects Keep Warm In Winter By Maintaining Salt Balance, Researchers Say

When winter temperatures plummet humans stay warm by layering up with hats, mittens and wool socks, but how do insects protect themselves from a frosty fate? In a new study, researchers from York University revealed some insects are able to survive the cold weather by simply maintaining salt balance.

"Insects lose the ability to maintain proper salt and water balance in the cold. When they are chilled, sodium and water move from the insect's blood into their gut," Heath MacMillan, study leader from the Department of Biology and York University, explained in a news release. "This is bad news for the insect because it concentrates potassium in the hemolympha [blood] where it remains."

Unlike humans who generate and retain heat, insects are ectothermic, which means their body temperature is dependent on the surrounding air. Some species have evolved with adaptations to make it through winter, but others lack the ability and die off when the weather gets too cold. One such adaptation includes the ability to keep blood potassium levels low.

"Like us, insects always work to keep levels of potassium outside of their cells low because high levels can completely disrupt nerve signaling and the ability of muscles to contract. If potassium levels get high enough in the cold, they can even cause permanent tissue damage and death," MacMillan added in the university's release.

To better understand this adaptation, tesearchers turned their focus to Malpighian tubules, organs that help species remove salt and water from the blood as needed. For their study, five different fruit fly species exposed to various climates around the world were analyzed in order to get a better idea of cold weather impacts one's salt and water balance.

"The species of flies from high latitudes, where winters are colder, were much better at maintaining ion and water balance at low temperatures," MacMillan explained, adding that this ability to survive in the cold seems to be specifically associated with the Malpighian tubules. "The tubules of the cold tolerant insects helped to keep sodium and potassium at normal levels in the blood during cold exposure, while those of insects that are easily killed by low temperature lost their ability to properly regulate salt balance in the cold."

Their study, recently published in the journal Scientific Reports, improves our understanding of insect stress tolerance and has significant implications for creating new methods of pest control.

"The Malpighian tubules are regulated by some hormones that are only found in insects, so there is great potential for safely and precisely altering the ability of agricultural pests or insects that transmit disease to regulate salt and water balance under times of stress," co-author Shireen Davies of Glasgow University concluded. "By doing so, we may find new and safe ways of controlling how well these species survive winter in temperate and polar climates."

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