What’s the buzz? How the climate crisis affects insects’ bodies

As you wander through dazzling carpets of flowers on a sunny day, there comes a gentle buzz from afar. A fuzzy honey bee lands on a blossoming flower and indulges in its sweet nectar, hoping to nourish the colony. By the cabbage patches, white butterflies flutter, their bright wings glimmering in the sunlight.

With the climate crisis, however, insects are facing significant challenges. Rising temperatures can have broad effects on insects’ bodies, leading to physiological and ecological disruptions with long-term effects on the human population according to UBC entomologists.

Bees in heat

The Pacific Northwest heatwave of 2021 saw the highest Canadian temperature on record at 49.6°C and devastated several insect species, notably honey bees.

In a normal hive, honey bees rely on a healthy queen bee, the only female in a colony that can reproduce. The queen bee mates with many male bees — drones — to produce fertilized eggs, which become workers or young queen bees that maintain the population.

“Even in more northern latitudes, like [BC], the temperatures can get hot enough to pass into [the] danger zone, beyond which we expect the bees’ fertility to suffer,” said Dr. Alison McAfee, a postdoctoral fellow at UBC’s Michael Smith Laboratories whose research focuses on honey bees’ reproductive health.

Through a series of experiments, she found that half of the drones would die from heat stress after six hours in 42°C — a lower temperature than what was recorded during the 2021 heatwave.

The details are grim: when a drone dies from overheating, it convulses, forcefully ejaculating its endophallus (bee penis) out of its body.

Rising temperatures also decrease sperm viability. As queens mate early in their lives, they store the sperm for years in a specialized organ called the spermatheca. A lack of sperm viability means that queens are less productive, leading to smaller colonies.

After experimenting with the impact of heat on sperm viability, McAfee estimated that the viability of the stored sperm starts to decrease at around 38°C.

The drones’ and queens’ ability to tolerate heat also differ considerably. While half of the drones died after six hours of exposure to 42°C, almost none of the queens died.

“It [is] harder to study how the high temperatures are affecting [drones’] sperm, because it’s difficult to separate if the sperm are dying because the individual is dying, or if the sperm are dying because those specific cells are reaching their heat threshold,” said McAfee.

When being warmer doesn’t mean expanding

While matter usually expands with heat (like a balloon), rising temperatures have been shown to have the opposite effect on insects’ bodies.

Dr. Michelle Tseng, a UBC assistant zoology professor, is concerned about warmer temperatures reducing the size of certain insects.

“Let’s say your house is warmer than my house, and you take a bunch of baby beetles and I take a bunch,” said Tseng. “[The] ones that grow up in your house and turn into adult beetles are going to be smaller as adults than the ones that I grew up in my house. [That’s] a pattern that we know exists across most insects.”

This decrease in size impacts an insect’s ability to find food. For example, bigger mosquitoes can collect more blood and bigger bumblebees can travel further to access more types of flowers, so smaller insects are at a disadvantage when compared to their larger counterparts.

Tseng’s research also focuses on changes in phenology — the timing of when insects emerge in spring or summer after hibernation.

The cabbage white butterfly is usually seen flying around cabbage plants in the summer. Previous studies have shown that cabbage white butterflies are emerging in spring, much earlier than usual, due to warmer temperatures.

Although early emergence can be advantageous for some butterflies, giving them more time to search for food at warmer temperatures, Tseng is unsure whether these temperature-induced changes will be beneficial in the long run.

“There’s a limit to the temperatures that insects can withstand, and different insects have different coping mechanisms for hot weather. If we have these extreme heat events, are we going to have the same set of winners and losers? I don’t think we know that answer yet,” Tseng said.

Building a more robust future

Researchers are taking action to improve the well-being of insects amid global warming.

One example is Tseng’s Campus Trees, Microbes and Insects project, which assesses how insect diversity is related to the species of trees planted around campus.

The researchers provide valuable information on the suitable selection of urban trees to support insects and cities during climate change.

Around the world, scientists and beekeepers from different climates are collaborating to protect insect populations. Beekeepers in hotter climates, such as southern California or Australia, wrap beehives in insulation and install shade nets to protect the bees from excessive heat.

Many beekeepers also are crossbreeding heat-tolerant bees with species vulnerable to hotter climates to strengthen protection during heatwaves.

However, creating more heat-tolerant insects is not the ultimate solution for addressing the effects of climate change since there are always trade-offs. McAfee noted bees more adapted to hot climates tend to produce less honey, which may reduce the desired output for farmers. Moving forward, farmers will have to balance maximizing crop growth with the bees’ ability to cope with climate change.

Even so, McAfee emphasized the need for more climate change resistant insects.

“Honey bees that most beekeepers are keeping are like dairy cows, but we need something more like a goat ... robust and [less] vulnerable to [these] factors.”