From tomatoes to pumpkins, most fruit and vegetable crops rely on pollination by bees and other insect species, though, in the Northern Hemisphere at least, the future of these species is far from certain.

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Researchers from North Carolina State University claim to have developed a set of guidelines for assessing the performance of pollinator species, in an effort to determine which species perform most pollination. Although the guidelines will be a welcome aid to understanding pollination, a key 'ecosystem service', the researchers' plans to use their pollinator assessments to prioritise certain species for protection over others will prove controversial.

Dr. Hannah Burrack, an associate professor of entomology at NC State, who worked on developing the guidelines, said, "Widespread concerns over the fate of honey bees and other pollinators have led to increased efforts to understand which species are the most effective pollinators, since this has huge ramifications for the agriculture industry."

She explained her desire for a set of all-encompassing guidelines for assessing insect pollination, adding, "various research efforts have taken a wide variety of approaches, making it difficult to compare results in a meaningful way. We've developed a set of metrics that we think offers a comprehensive overview of pollination efficiency, which would allow researchers to compare data from different crops and regions."

The new approach looks at four specific metrics. First is single-visit efficiency, which measures the number of seeds produced when one bee visits one flower. Second is abundance, which measures the number of each type of bee observed in a study area. Third is inclement weather behaviour, which tracks how active a bee species is during cool, cloudy and/or windy weather. Fourth is visitation rate, or the number of flowers that a bee visits while foraging, and the amount of time it spends at each flower.

The researchers tested their guidelines on various bee species visiting economically important highbush blueberry crops in North Carolina. They found that small native bees had extremely high single-visit efficiency rates and were active during inclement weather. However, small native bees did not have high abundance nor appear to have high visitation rates.

"This highlights the importance of incorporating multiple metrics," said Dr. David Tarpy, another NC State professor, "Because researchers looking only at visitation rates or abundance may think the small native species are unimportant, when they actually appear to be important pollinators for blueberry growers."

The researchers concluded that, as their "results show that bee groups contribute to pollination in different ways," factoring in their differences between species may lead to better ways to support populations, both for the benefit of bee species and increasing the "stability of pollination services to agricultural systems."

"The perfect bee would produce a lot of seeds and visit a lot of flowers, even in poor weather – and there would be a lot of them," Burrack said. She admitted, "But as far as we know, the perfect bee doesn't exist."