Pesticides might just be a bee's worst enemy. They harm their brains, hinder their reproduction, and even kill their buzz. Now it seems they play havoc with their social lives and reduce their ability to care for their young.
While previous studies have shown that commonly used neonicotinoid pesticides make bees sick and affect how they forage and navigate, a new study gives more of an idea of how these chemicals affect the internal workings of a colony. Studying these effects has proved difficult, so the team employed a new technique. They stuck tiny QR codes to the backs of bumblebees and tracked their movements using a robotic camera.
The researchers looked at 12 colonies housed in a lab, giving some the same level of imidacloprid – the world's most commonly used pesticide – that they’d be exposed to in the wild while keeping others pesticide-free as controls. They checked on them for a few minutes 12 times a day. The findings are published in the journal Science.
Unfortunately, the researchers found a number of notable differences between the bees exposed to the pesticide and the controls. The bees given neonicotinoids spent less time interacting with other bees and more time resting. This lull in activity tended to happen more at night, but the researchers aren’t sure why.
"Bees actually have a very strong circadian rhythm," lead author James Crall explained in a statement. "So what we found was that, during the day, there was no statistically observable effect, but at night, we could see that they were crashing. We don't know yet whether (the pesticides) are disrupting circadian gene regulation or if this is just some, maybe physiological feedback... but it suggests that, just from a practical perspective, if we want to understand or study these compounds, looking at effects overnight matters a lot."
A drop in activity is problematic as active bees help maintain the temperature of the nest by fanning their wings and vibrating their body muscles – something that’s key to the development of healthy larvae.
What’s more, the control bees built a “wax cap” to insulate the colony, but the bees exposed to the pesticide failed to do this. The bees also tended to stay further from the center of the nest (where their brood was), suggesting that they were spending less time caring for the colony’s offspring.
There are thousands of species of bee, and both solitary bees and those that live in small colonies like bumblebees are probably more vulnerable to the pesticides than honeybees, which live in vast hives.
The new findings are worrying as bees are important pollinators, both of wild plants and the crops we rely on for food. Luckily, governments are waking up to the issue of neonicotinoids, with the EU currently banning three types. Just recently, France introduced the world’s toughest ban on the chemicals. Let’s hope other nations follow suit.