In a science first, a study from the University of Guelph and the Royal Holloway University of London has determined that a widely-used group of pesticides harms the reproductive cycles of four different species of bumblebees.
Insects like bumblebees are important pollinators for both crops and wild plants, but bee populations around the world have been declining significantly over the past decade. A recent report from the Center for Biological Diversity in the United States found that of the more than 4,000 native bee species in North America and Hawaii, more than half are in decline, with almost one in four species at increasing risk of extinction.
Habitat loss, monocultural farming practices, climate change and parasites have all been identified as potential contributors to the problem, as has the use of neonicotinoid pesticides, which studies show can negatively impact bumblebees both at an individual and colony level and interfere with their ability to pollinate.
But the effects of neonics on queen bees and queen reproduction have so far been less studied. Published in the journal Proceedings of the Royal Society B, the new research looks at how exposure to thiamethoxam, a commonly used neonic, impacts reproduction for four different species of bumblebees.
Researchers took 506 queen bees caught in the spring of 2014 in Surrey, UK, and allocated them to three different treatment groups: one which received a 1 part per billion dose of thiamethoxam, one which received 4 ppb and the third which served as a control. Both dosages of thiamethoxam are known to be within the range of pesticide residues typically found in the wild and in the stored pollen and nectar of wild foraging bumblebee colonies.
The bees were observed for two weeks at the given dosage and then frozen and dissected. Researchers found that across all four species, the queen bees given the higher doses of the pesticide had smaller, less-developed eggs than the queens not exposed to the pesticide. “This study provides the first evidence that field-relevant doses of thiamethoxam can have sublethal impacts on ovary development of queen bumblebees from multiple wild bumblebee species,” say the study’s authors.
The researchers also found that queen bees from two of the bumblebee species ate less nectar after being exposed to the chemical, a result which speaks to the variation in the effects of pesticides across different bee species.
“Most of the work to determine levels of toxic exposure to pesticide has used honeybees as a model pollinator,” says Nigel Raine, Rebanks Family Chair in Pollinator Conservation at the University of Guelph, in a press release. “But our findings show that bee species vary in their level of sensitivity to pesticides, which is important information that should be factored into regulatory decisions on these chemicals.”
Raine contends that the metabolic stress on the bee’s system as a result of detoxifying from pesticide exposure is a probable cause of the reproductive disruption. “Queen bees will only lay eggs when the eggs are fully developed,” says Raine. “[Detoxification] will likely translate into slower egg-laying rates, which will then impede colony development and growth.”