̽��ֱ�� of Cambridge - Hamish Symington

Getting maximum calories in shortest time is the priority for bumblebees

jg533 — Tue, 24 Oct 2023 15:05:06 +0000

A new study investigating nectar drinking in one of the most common bumblebees in the UK, Bombus terrestris, has found that when foraging they maximise the amount of nectar sugar they take back to the colony each minute.

To make their choices, the bumblebees trade off the time they spend collecting nectar with the energy content of that nectar. This means they will forage to collect nectar that’s hard to access – but only if the sugar content of that nectar makes it worth doing so.

This big-and-fast approach contrasts with honeybee foraging: honeybees make their decisions by optimising their individual energy expenditure for any nectar they collect. This more measured approach should prolong the honeybee’s working life.

“As they forage, bumblebees are making decisions about which nectar sources will give the greatest immediate energetic return, rather than optimising the energy efficiency of their foraging,” said Dr Jonathan Pattrick, joint first author of the report, who started the research while in the ̽��ֱ�� of Cambridge’s Department of Plant Sciences.

Pattrick, now based at the ̽��ֱ�� of Oxford, added: “Our results allow us to make predictions about the sorts of flowers the bumblebees are likely to visit, which could inform the choice of which flowers to plant in field margins to support these important pollinators. It’s also relevant to crop breeders who want to make varieties that are ‘better’ for bumblebees.”

̽��ֱ��results are published today in the journal iScience.

Over six months the researchers made 60,000 behavioural observations of the bumblebees, allowing them to precisely estimate bumblebee foraging energetics. It was painstaking work: each bumblebee in the study was watched for up to eight hours a day without a break.

̽��ֱ��team used vertically and horizontally oriented artificial flowers, with surfaces that were slippery and difficult for the bumblebees to grip.

A custom computer program allowed the team to measure the split-second timing as the bumblebees flew between the artificial flowers and foraged from them. This meant the team could track how much energy the bumblebees spent flying as well as how much they collected when drinking, and identify how the bumblebees decided whether to spend extra time and energy collecting high-sugar nectar from slippery flowers, or take the easier option of collecting lower-sugar nectar from flowers they could land on.

“It’s amazing that even with a brain smaller than a sesame seed, bumblebees can make such complex decisions,” said Dr Hamish Symington in the ̽��ֱ�� of Cambridge’s Department of Plant Sciences and joint first author of the report.

He added: “It’s clear that bumblebee foraging isn’t based on a simple idea that ‘the more sugar there is in nectar, the better’ – it’s much more subtle than that. And it highlights that there’s still so much to learn about insect behaviour.”

Individual bumblebees were given one of three tests. In the first test, the nectar on both vertical and horizontal artificial flowers had the same amount of sugar, and the bumblebees made the obvious choice to forage from the horizontal flowers, rather than spend extra time and energy hovering at the vertical ones. In the second test, the nectar on the vertical flowers was much more sugary than the nectar on the horizontal flowers, and the bumblebees chose to drink almost exclusively from the vertical flowers.

In the third test, the vertical flowers offered nectar which was only slightly more sugary than the horizontal flowers. This created a situation in which the bumblebees had to make a trade-off between the time and energy they spent foraging and the energy in the nectar they were drinking – and they switched to feeding from the horizontal flowers.

̽��ֱ��results show that bumblebees can choose to spend additional time and energy foraging from hard-to-access nectar sources – but only if the reward is worth it.

Bumblebees drink nectar from flowers, then offload it in their nest – by regurgitation – for use by other bumblebees in the nest. Unlike honeybees, bumblebees only store a small amount of nectar in the nest, so they need to make the most of every opportunity to forage.

This research was funded by BBSRC.

Reference

Pattrick, J G et al: ‘Bumblebees negotiate a trade-off between nectar quality and floral biomechanics.’ iScience, Oct 23. DOI: 10.1016/j.isci.2023.108071

Research has found that bumblebees make foraging choices to collect the most sugar from flowers in the shortest time – even if that means using more energy in the process – to provide an immediate energy boost for the colony.

It’s amazing that even with a brain smaller than a sesame seed, bumblebees can make such complex decisions.

Hamish Symington

Bumblebee foraging for nectar

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Vomiting bumblebees show that sweeter is not necessarily better

jg533 — Wed, 22 Jan 2020 00:01:00 +0000

Bumblebees drink nectar from flowers, then offload it in their nest – by vomiting – for use by other bees in the colony. ̽��ֱ��sugar within nectar makes it appealing, and the more sugar within the nectar, the more energy it contains. But nectar also gets more thick and sticky as the sugar content rises, and this makes it more difficult for bees to drink and regurgitate – requiring more time and energy.

Published today in the Journal of the Royal Society Interface, the study looked at the mechanics of both nectar drinking and regurgitation in one of the most common bumblebees in the UK, Bombus terrestris. It found that the best concentration of nectar for bumblebees in terms of overall energy gain is lower than might be expected. Nectar that is low in sugar is easy for bees to drink and very easy to vomit back up. As nectar gets more sugary, it gradually takes bees longer to drink, but swiftly becomes much more difficult to vomit.

“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,” said Dr Jonathan Pattrick, first author of this study, formerly a PhD student based jointly in the ̽��ֱ�� of Cambridge’s departments of Plant Sciences and Zoology and now a post-doctoral researcher in the ̽��ֱ�� of Oxford’s Department of Zoology.

While it has long been known that nectar with a higher sugar concentration takes bees longer to drink, its effect on nectar regurgitation has not previously received much attention. This new information will help scientists make better predictions about which types of nectar bumblebees and other pollinators should like best, and consequently the kinds of flowers and plants they are most likely to visit. This will inform crop breeders in producing the most appealing flowers for better crop pollination and higher yields.

To conduct the research, bees were allowed to forage on sugar solutions of three different concentrations in the Department of Plant Science’s Bee Lab. While doing this, the bees were also timed and weighed. When the bees returned to their ‘nest’, the researchers watched them through a Perspex lid, timing how long it took for the bees to vomit up the nectar they had collected.

“For low strength nectar, bees had a quick vomit that only lasted a few seconds, then were back out and foraging again,” said Pattrick, “but for really thick nectar they took ages to vomit, sometimes straining for nearly a minute.”

For any given nectar concentration, bees regurgitate the nectar quicker than they initially drink it. But as nectar sugar concentration – and therefore stickiness – goes up, the rate of regurgitation decreases faster than the rate of drinking. “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,” said Pattrick. “At a certain sugar concentration, the energy gain versus energy loss is optimised for nectar feeders.”

̽��ֱ��perfect nectar sugar concentration for the highest energy intake depends on the species drinking it, because different species feed in different ways. Bumblebees and honeybees feed by dipping their tongue repeatedly into the nectar, but regurgitate by forcing the nectar back up through a tube – just like when humans are sick. Other species such as Orchid Bees suck nectar up instead of lapping it, so struggle even more when nectar is highly concentrated. This influences nectar preference and the plants visited by different species.

Current crop breeding is focused on enhancing traits like yield and disease resistance, rather than considering pollinator preference. ̽��ֱ��new results improve predictions of the perfect nectar concentration for making the most efficient use of pollinating bumblebees.

Nectar is produced by flowers to attract pollinators, and a source of food for many species of insect, bird and mammal. ̽��ֱ��levels of the sugars sucrose, glucose and fructose within the nectar vary depending on the plant producing it.

“Studies have shown that numbers of some pollinators are going down, but there are more and more people in the world to feed. We need to make better use of the pollinators we have,” said Professor Beverley Glover in Cambridge’s Department of Plant Sciences and Director of Cambridge ̽��ֱ�� Botanic Garden, who led the study. “This research will help us understand the types of flowers and plants the bees are most likely to visit, which will inform crop breeding to make the best use of the available pollinators.”

This research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

Reference
Pattrick, J.G. et al. ‘ ̽��ֱ��mechanics of nectar offloading in the bumblebee Bombus terrestris and implications for optimal concentrations during nectar foraging.’ Interface, Jan 2020. DOI: 10.1098/rsif.2019.0632

Animal pollinators support the production of three-quarters of the world’s food crops, and many flowers produce nectar to reward the pollinators. A new study using bumblebees has found that the sweetest nectar is not necessarily the best: too much sugar slows down the bees. ̽��ֱ��results will inform breeding efforts to make crops more attractive to pollinators, boosting yields to feed our growing global population.

With really thick nectar the bees took ages to vomit, sometimes straining for nearly a minute

Jonathan Pattrick

Yani Dubin on Flickr

Bumblebee, Bombus terrestris

Improving flowers to help feed the world

A rising world population means we’ll need more food in the coming years. But much of our food relies on insect pollination, and insects are in decline around the world. Can we make flowers better at being pollinated, to help solve this problem?

This film was funded by EIT Food, as part of the #AnnualFoodAgenda project.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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