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COUNTRY LIFE IN BC • MARCH 2020


Bumblebees prefer low-fat, low-sugar diet Foraging habits and bee vomit provide key insights into pollinator health


Without insect pollination,


many plants, including a wide variety of crop species, simply cannot reproduce. In fact,


Research by MARGARET EVANS


animal pollinators drive the production of 75% of the world’s food crops. Now, two new studies have shown the particular nutrient preferences in the diet of bumblebees in order to maintain optimum health. And they apparently have very discerning tastes. They like their pollens not too fat and not too sweet.


"Bees obtain most of their nutrients from their main food sources, which are nectar and pollen,” said Sara Leonhardt, a professor and specialist in plant-insect interactions with the Technical University of Munich in a press release. “While nectar is mainly a source of carbohydrates, pollen contains most of the other necessary nutrients [such as] proteins, fat, minerals and vitamins. Until today, most bee researchers assumed that bees, like other herbivores, mainly consider the protein content when choosing their food.” Through observation, the


researchers learned that bees had a taste for both fat and protein. But they also learned that the threshold level of fat is critical. “We focused on fatty and amino acids which represent


the two essential pollen macro-nutrients and which are likely to be perceived and tasted by bees,” said study author Fabian Rudenauer. By adding


incrementally small amounts of fatty acids to pollen, they discovered that bumblebees could


differentiate between normal levels of fat content and increased levels. Importantly, the bees clearly showed a preference for normal levels. However, when it came to amino acid content, they made no specific distinction when those levels were altered. It became clear through


the feeding studies that the level of fatty acid was significant enough to drive the bees’ selective foraging behaviour, enough to influence reproduction and survival. “The more fat the pollen contained, the less the bumblebees consumed that pollen,” said Leonhardt. “The bees can taste what is good for them and collect their food accordingly.” Currently, the researchers


are amassing a dataset of nutritional chemistry across a wide spectrum of plant species. They are also looking at the nutritional needs of other bee species to gain a deeper understanding of a wide variety of flowering plants and their value to bees. This could lead to improvements in the biodiversity of flowering strips in the agricultural landscape. Flowering plants


FILE PHOTO


sown by farmers around their fields are deliberately chosen to attract a diversity of pollinator insects that will benefit crops. Another study, at the


University of Cambridge in the UK, explored bumblebees’ dependence on nectar and the actual level of sugars they can afford to drink. Sugars such as sucrose, glucose and fructose vary within nectar, depending on the plant producing it. If the sugar content is too high it can get thick and sticky, which is a problem for bees. It is not only more difficult to drink but more challenging and time-consuming to regurgitate in the nest where the sugar is used by other bees in the colony.


"Bumblebees must strike a


balance between choosing a nectar that is energy-rich but isn't too time-consuming to drink and offload,” said Jonathan Pattrick, who undertook doctoral studies in Cambridge’s departments of Plant Sciences and Zoology and is now a post-doctoral researcher with the University of Oxford’s Department of Zoology. The Cambridge study


looked at the mechanics of both nectar drinking and regurgitation. 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 bring back up in the nest. “For low-strength nectar,


bees had a quick vomit that only lasted a few seconds then were back out foraging again," said Pattrick. “But for really thick nectar they took ages to vomit, sometimes [they were] straining for nearly a minute.” According to the press


release, the perfect nectar sugar concentration for the highest energy intake depends on the species drinking it since species feed differently. Bumblebees and honeybees feed by dipping their tongue repeatedly into the nectar but regurgitate by forcing the nectar back up through a tube. Other species such as orchid bees suck up nectar so they struggle even more when it is highly concentrated. This influences nectar preference and the plants visited by different species. The take-away from this


research is that, by knowing the type of nectar and the level of sweetness bumblebees like best, farmers developing flowering strips can select plant species that bees are likely to visit and which, in turn, would lead to greater crop pollination opportunities and higher yields. The research from


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Technical University of Munich was published in Ecology Letters and the research from the University of Cambridge was published by the Journal of The Royal Society Interface. Margaret Evans is a


freelance writer based in Chilliwack specializing in agricultural science.


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