Bumblebees exposed to common neonicotinoid pesticides may do a poorer job of pollinating crops such as apples, leading to poorer-quality fruit, a new Canadian-led study suggests.
When apple trees were pollinated by bees exposed to those pesticides, commonly called neonics, the trees produced about a third fewer seeds.
The number of seeds is generally linked to fruit quality in apples – apples with more seeds tend to be larger, firmer, tastier and more symmetric, said Nigel Raine, the University of Guelph researcher who led the study with his postdoctoral researcher Dara Stanley.
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Apples with fewer seeds are more likely to end up as lower-value products such as applesauce.
"Bumblebees are essential pollinators of many important crops other than apples, including field beans, berries, tomatoes and oilseed rape," the researchers wrote in a paper published today in the journal Nature.
"If exposure to pesticides alters pollination services to apple crops, it is likely that these other bee-pollinated crops would also be affected. Most importantly, the majority of wild plant species benefit from insect pollination services."
Raine said that means the findings might be "really important… not just in terms of economics and food production of agriculture, but also thinking about biodiversity more broadly."
Costs of pesticide use
Overall, the information suggests that using neonics has costs – to both production of other crops and wild ecosystems – that may not have previously been considered when weighing the costs against the benefits of using the pesticides.
Neonics, or neonicotinoids, are widely used to treat seeds of crops such as canola, corn and soybeans. The pesticide ends up in the entire plant as it grows, making it resistant to many insect pests.
Because bees are so important for crop production, Raine said, he and his colleagues were interested in finding out whether the effects on bees might translate into effects on crop production.
The team, which included researchers at the University of London and the University of Reading in the U.K., fed eight colonies of bumblebees sugar water that contained 2.4 parts per billion of the neonic theiamethoxam for 13 days. Eight other colonies were fed 10 parts per billion for the same amount of time.
"They're both levels of exposure that bees can encounter in the field," Raine said.
Afterward, they released the bees into enclosures containing two different apple varieties for a controlled amount of time. Apples of one variety generally need to be pollinated with pollen from a different variety in order to produce good fruit, Raine said. The enclosures, similar to aviaries, were surrounded by fine netting to keep other pollinators out.
The researchers found that bumblebee colonies exposed to the higher level of pesticide collected less pollen from the trees and visited the flowers less frequently. When the apples were harvested in the fall, the researchers found that those pollinated by the bees exposed to the higher level of pesticide produced about a third fewer seeds than those pollinated by bees exposed to the lower level or not exposed at all.
The findings suggest that the amount of exposure makes a difference.
"Reducing pesticide usage would help," Raine said.
Trying to create "refuge" areas with lower levels of pesticides, as some scientists have suggested, would also probably be a good thing, he added.
However, he acknowledged that the study is just a "first step" in looking at the impact of neonic exposure on pollination. For one thing, it only looks at the effects on bumblebees.
Neonics are also known to have more severe effects on many wild bees, called solitary bees, that live alone rather than in hives or colonies, Raine said.
For the production of crops where wild bees are important, he added, the effects may be more severe than seen in the results of this study.