Bees Get 'Blinded' by Polluted Scents: New Insights into Colony Collapse Disorder

Photo: Innotata

Last winter, roughly a third of commercial bee colonies in the United States died off—a staggering percentage in the already unsustainable population decline first observed in 2006. The rapid global disappearance of bee colonies known as colony collapse disorder (CCD) has serious repercussions for food production worldwide.

“One in three mouthfuls of our food depends on bee pollination,” said Dr. John Bryden, the lead author of a new study funded by the Insect Pollination Initiative. “By understanding the way colonies fail and die, we've made a crucial step in being able to link bee declines to pesticides and other factors, such as habitat loss and disease which can all contribute to colony failure.”

Bryden's research team at Royal Holloway University discovered that exposure to low levels of neonicotinoid pesticides subtly affects the behavior of bees. The pesticide is not directly lethal, but because it's a neuroactive chemical, it has an obvious effect on the mental state of individuals. The bees become stressed out by the presence of the pesticide, dramatically impeding their ability to properly maintain their hives.

“Exposing bees to pesticides is a bit like adding more and more weight on someone's shoulders,” explains Bryden. “A person can keep walking normally under a bit of weight, but when it gets too much—they collapse. Similarly, bee colonies can keep growing when bees aren't too stressed, but if stress levels get too high the colony will eventually fail.”

A healthy commercial hive. Photo: Björn Appel

Pesticides are just one of many threats to healthy bee populations. Earlier this week, a team at the University of Southampton published a study in Scientific Reports about the effect of diesel fumes on bee behavior. Led by Dr. Tracey Newman and Professor Guy Poppy, the team discovered that diesel exhaust can alter the profile of floral odors, which confuses honey bees and reduces their foraging efficiency.

The Southampton team combined eight chemicals found in the rapeseed flower—a popular plant among honey bees—with both clean air and air polluted with NOx gases found in diesel exhaust. The odor was unaffected by clean air, but the polluted air radically altered the profile: two chemicals were completely overpowered within a minute, while the other six were reduced in volume. When honey bees were exposed to the contaminated odor profile, they could not recognize it as rapeseed.

"Honeybees have a sensitive sense of smell and an exceptional ability to learn and memorize new odors,” Dr. Newman said. “NOx gases represent some of the most reactive gases produced from diesel combustion and other fossil fuels, but the emissions limits for nitrogen dioxide are regularly exceeded, especially in urban areas.This could have serious detrimental effects on the number of honeybee colonies and pollination activity.”

“Honeybee pollination can significantly increase the yield of crops and they are vital to the world's economy—£430 million a year to the UK alone,” added Professor Poppy. “However to forage effectively they need to be able to learn and recognize the plants.”

A honey bee pupa infected with Varroa destructor mites. Photo: Agricultural Research Service

Though neonicotinoids are regarded as the most damaging culprit of CCD, disease, pollution, loss of habitat, poor nutrition, and the aptly named Varroa destructor mite are all contributing factors.

But despite the staggering losses, scientists remain hopeful about restoring healthy bee populations. “Our research will provide important evidence for policymakers,” said Dr. Nigel Raine of Royal Holloway. “The way we test pesticides, the way we assess their impact on bees, and the way we manage pesticides can all be improved.”