Bee colonies exposed to a common class of pesticides may produce fewer queens and the chemicals may lead to insects’ deaths by impairing homing abilities, according to two studies in the journal Science.
Bumblebee colonies fed doses of imidacloprid, a neonicotinoid insecticide routinely used on crops including corn and rapeseed, produced about 85 percent fewer queen bees than unexposed colonies, researchers found in a study led by Penelope Whitehorn of Scotland’s University of Stirling that was published today.
A separate study led by Mickael Henry of France’s National Institute for Agricultural Research found honeybees given a dose of thiamethoxam, another neonicotinoid, were about twice as likely as untreated bees to die away from the hives, which the researchers said suggested the chemical interfered with the insects’ ability to find their way home.
Beekeepers in countries from China to the U.S. have observed large-scale honeybee deaths in recent years that may be linked to multiple factors, including pesticides, the United Nations’ environmental agency said last year. The die-off may have wider implications as 71 of the about 100 crops that provide 90 percent of the world’s food are bee-pollinated, according to the UN’s Food and Agriculture Organization.
“Given the scale of use of neonicotinoids, we suggest they may be having a considerable negative impact on wild bumble bee populations across the developed world,” Whitehorn wrote in her study. “We suggest that there is an urgent need to develop alternatives to the widespread use of neonicotinoid pesticides on flowering crops wherever possible.”
The studies led by Whitehorn and Henry add to evidence of the pesticides’ negative effects on bees and possible links to colony collapse disorder, characterized by the sudden disappearance of worker bee populations. Corn planting using seeds coated with neonicotinoid insecticides was linked to honeybee deaths, according to a study by researchers at Italy’s University of Padova published earlier this month.
In the bumblebee study, the insects were divided into three groups, two of which were fed pollen and sugar water with amounts of imidacloprid similar to levels found in rapeseed grown from insecticide-coated seed, the researchers wrote. Bumblebees are valuable pollinators of crops and wild flowers and vital components of ecosystems, according to Whitehorn.
Imidacloprid is registered for use on more than 140 crops in more than 120 countries, and the effects of the insecticide on wild bumblebee reproduction are likely to be “widespread and significant,” the U.K. researchers wrote. Global sales of neonicotinoid-class pesticides exceed $1 billion a year, they said in a separate statement.
In the French study, researchers fed foraging honeybees a sugar solution with a non-lethal dose of thiamethoxam similar to levels found in the field. They glued a radio-identification chip to 653 treated and untreated bees for tracking and released the insects away from the hive in four experiments.
“Our study clearly demonstrates that exposure of foragers to non-lethal but commonly encountered concentrations can impact forager survival, with potential contributions to collapse risk,” Henry wrote in the study.
Computer simulations showed deaths from impaired homing combined with natural mortality could reduce bee-hive populations, according to the study.
“Our study raises important issues regarding pesticide authorization procedures,” Henry said in a statement released by Science. Rules “mostly require manufacturers to ensure that doses encountered on the field do not kill bees, but they basically ignore the consequences of doses that do not kill them but may cause behavioral difficulties.”
Other factors that may cause the collapse of colonies include new or emerging diseases such as Israeli acute paralysis virus, poor nutrition and bee management stress, according to the U.S. Environmental Protection Agency.
The research led by Whitehorn was supported by Agralan Ltd., an Ashton Keynes, England-based supplier of gardening products that provided the bumblebee colonies. The study led by Henry was funded by a European Union program for French beekeeping coordinated by the French Ministry of Agriculture.