Too much sugar in nectar 'slows down bees'

Too much sugar in nectar slows down bees, a study has found.

Bumblebees offload the nectar they drink from flowers by vomiting, but the more sugar nectar contains, the thicker and stickier it becomes - meaning it takes more time and energy for the bees to regurgitate it.

A report, published in the Journal of the Royal Society Interface, looked at both stages - drinking and vomiting - in one of the most common bumblebees in the UK, the Bombus terrestris (or the buff-tailed bumblebee).

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As part of the study, they were allowed to forage on three different concentrations of sugar solutions - with researchers timing how long it took the bees to vomit up the nectar they had collected.

Dr Jonathan Patrick said: "For low strength nectar, bees had a quick vomit that only lasted a few seconds, then were back out and foraging again.

"But for really thick nectar they took ages, sometimes straining for nearly a minute."

Usually, bees regurgitate the drink faster than they consume it.

"It's hard to drink a thick, sticky liquid, but imagine trying to spit it out again through a straw - that would be even harder.

"At a certain sugar concentration, the energy gain - versus energy loss - is optimised for nectar feeders.

"Bumblebees must strike a balance between choosing a nectar that is energy-rich, but isn't too time-consuming to drink and offload.

"Nectar sugar concentration affects the speed of the bees' foraging trips, so it influences their foraging decisions."

The scientists hope their study can help other researchers make better predictions as to which types of nectar bumblebees and other pollinators would prefer - and therefore the kinds of flowers they are more likely to visit.

That, in turn, could help crop breeders produce the most appealing plants, and therefore lead to higher yields.