Is global warming killing bees?

Study finds 15 common bee species suffer as temps rise

A common bumblebee visits a garden in Vienna, Austria. @bberwyn photo.

Staff Report

The urban heat island effect isn’t just bad for people — it’s also harming bees, according to a new study from North Carolina State University.

“We looked at 15 of the most common bee species in southeastern cities and – through fieldwork and labwork – found that increasing temperatures in urban heat islands will have a negative effect on almost all of them,” said associate entomology professor Steve Frank.

“What’s exciting is that we were able to use a relatively easy lab test on individual bees to predict how whole populations will fare at higher temperatures in urban areas,” says Elsa Youngsteadt, a research associate at NC State and co-lead author of the paper. “This is a tool we can use for additional bee species in the future, giving us insights into how urban warming affects ecosystems.”

The researchers established threshold maximum temperatures for 15 bee species in the lab, heating the insects in test tubes until they became incapacitated.

“After measuring the CTmax values, we still didn’t know whether the way individual bees responded to temperature in the lab would correspond to how bee populations respond to higher temperatures in messy, real-world habitats,” Youngsteadt says.

To address this question, the researchers sampled bee populations 11 times over two years at 18 urban sites in Wake County, North Carolina.

The researchers found that the response of the 15 bee species studied in the lab corresponded to each species’ abundance in urban yards. In other words, the lower a species’ CTmax, the more its numbers declined with urban warming.

“This is certainly relevant for urban heat islands, but it may also help us understand potential effects of global climate change on bee species,” Youngsteadt says. “If species that have a lower CTmax are most sensitive to urban warming, they may also be most sensitive to warming in other environments.”

The  research was published in the Royal Society journal Biology Letters.

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