The Buzz Around Hydration

ARS Researchers find that hydration is key to bee survival in hot and humid environments. 

We humans are always reminded to hydrate, hydrate, hydrate. Among other benefits, proper hydration helps make sure our organs function properly, helps improve our brain function, helps regulate our temperature, and helps with digestion. We are not the only species, however, that depends on proper hydration for healthy living. It turns out bumble bees need to stay hydrated as well. 

“For insect pollinators like bumble bees to survive and reproduce, they need to maintain an adequate hydration level,” said Karl Roeder, Research Entomologist at the North Central Agricultural Research Lab in Brookings, SD. “Erratic weather patterns have the potential to increase the rate at which insects lose water. This increased desiccation stress may lower survival rates, but more work is needed to link individual physiology to the dynamics of wild and managed bee populations.” 

ARS postdoc Jamieson Botsch used samples of the common eastern bumble bee to measure how they resist and tolerate water loss across a range of temperature and humidity conditions.

Because of their small size, terrestrial insects like bumble bees can struggle to maintain proper water levels. As the air becomes drier, as predicted for some parts of the country, they may become more susceptible to dehydration – what Roeder called “desiccation stress”. Many insects have adaptations that help them slow water loss or tolerate higher levels of dehydration. However, little is known how temperature and humidity combined may affect a bumble bee’s water balance. 

“Warming temperature and drying humidity increase the likelihood that individual bees experience desiccation stress,” said Jamieson Botsch, an ORISE postdoc at the Lab. “In environments where floral resources are scarce, this physiological stress may be exacerbated because bees will be less able to replenish the water that they lose.”

Hydrating Eastern Bumble Bee

Understanding their physiological capacity to survive and prevent water loss in hot and dry conditions provides an important first step in developing management practices that support and enhance native and managed pollination in agricultural systems. 

“We are only beginning to understand the sensitivity of bees to desiccation and the interactive effect of warming and drying conditions,” Botsch said. “This study begins to address this gap using one species of bumble bees as a model system.”

Roeder and his research colleagues in Brookings measured the ability of the common eastern bumble bee (Bombus impatiens) to resist and tolerate water loss across a range of temperature and humidity conditions. This species was chosen for the study because it is both found unmanaged in the wild and is sold commercially for pollination services. Researchers placed 540 individual bumble bee workers in small chambers that either had low (<5% relative humidity, RH), moderate (50% RH), or high humidity (>90% RH). Inside these chambers, bees did not have access to nectar. The bees were checked every 2-4 hours and researchers measured the rate at which the bees lost water and total water content. 

The results concluded that the bees were indeed sensitive to temperature and humidity. Bumble bees survived three times as long in the coolest temperatures as they did in the warmest temperatures, with no effect of humidity on survival time. However, they lost water much faster in warmer and drier environments. These results highlight the importance of bees’ access to nectar, their primary water source, and nesting environments that allow them to avoid stressful conditions. 

“Nesting environments are incredibly important for bees,” Roeder said. “In addition to selecting favorable nesting sites, there is evidence that social bees like bumble bees and honey bees are able to partially regulate the environment within their nests through their behavior. The extent to which nests can mitigate environmental conditions is a very important area of ongoing research.” 

From these results, researchers are evaluating the sensitivity of three other economically important bee species (honey bees, alfalfa leafcutter bees, and blue orchard mason bees) to humidity. They are also studying how these managed bee species compare to native bee species in their ability to prevent water loss. 

“Insect pollinators provide an important ecosystem service for growers,” Roeder said. “Understanding their sensitivity to different stressors will allow us to develop management schemes that promote their health.” – By Todd Silver, ARS’s Office of Communications 

For more information, check out the research paper.

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