Photo: Pixabay/designerpoint

Insects worldwide are facing several grave challenges with bees being among the most at risk. Habitat loss, pesticide use and climate change comprise the most severe risks to bee populations.

Heat waves, it turns out, also take their toll on the insects, scientists have found, even as these extreme weather events become ever more common in North America and Europe.

An international team of researchers have realised this after examining how extreme heat waves affect the host-pathogen relationship between two species of solitary bees (Osmia cornifrons and Osmia lignaria) and a protozoan pathogen (Crithidia mellificae).

Once infected, the studied insects were less likely to forage for food during periods of extreme heat and if bees don’t look for food they also don’t pollinate crops and other plants. That is a problem as bees perform important functions as pollinators both for the natural environment and agriculture.

Solitary bees are deemed to be the “workhorses of the pollinator world,” the experts note, as a result of their high foraging capacity, but during their lifetime they pollinate for less than a month so heat waves can deprive them of precious time in which to do their work.

“We are now experiencing the highest temperatures in recorded history,” says Mitzy Porras, a postdoctoral researcher in Penn  State University’s College of Agricultural Sciences and who was the lead author of a study. “These heat waves are lasting three, or even four days, which is a long period of heat tolerance for bees. Then, when you combine that with prior infection from a pathogen, we’re looking at two factors that can severely negatively impact pollinator populations.”

The researchers placed bees in a tunnel with a chamber warmed to the temperatures of a summer heat wave on one side and a meal of sugar water and pollen on the other. Bees infected with a protozoan pathogen proved far less tolerant of the heat and much less likely to endure it to reach the food.

It seems that this common form of infection greatly reduces infected bees’ heat tolerance. “When we looked at the host and pathogen in tandem, we found that infection greatly reduces heat tolerance in the host: a finding we wouldn’t have discovered if we had only been studying bees,” Porras notes.

The findings are troubling as climate change may have many unexpected consequences for insects, including bees, according to the scientists.

“We’re not going to see a simple, linear change as the climate warms. Every organism will respond differently and the relationships between organisms will be fundamentally altered,” explains Ed Rajotte, professor emeritus of entomology at Penn State.

“If we’re going to try to predict the impacts of climate change, relationships matter. There are real consequences to changes in our ecosystems and we must understand the subtleties if we are going to prepare ourselves for the reality of a changing climate,” the scientist adds.

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