Bees help plants produce flowers faster by nibbling on their leaves

Cunning bumblebees help plants produce flowers by nibbling away on their leaves in way that speeds up blooming, according to a new report.

Bumblebees that wake up earlier in the year than normal due to climate change face a scarcity of pollen because flowers are yet to bloom, European researchers claim.

They therefore bite the leaves of flowerless plants to cause intentional damage in such a way that accelerates the production of flowers.

In experiments, this unusual behaviour was seen to have a drastic effect on plant flowering by compelling some to bloom two weeks to a full month earlier.

The researchers, who claim to be reporting on a previously unknown behaviour of bumblebees, are unsure how leaf-damaging bumblebee bites stimulate the flowers.

‘We know that some other stressors, such as drought and pathogen infection, can induce early flowering,’ co-author Dr Mark Mescher at the Department of Environmental Systems Science at ETH Zurich in Switzerland told MailOnline.  

‘In those cases, it may reflect a strategy of the plants to shift investment to short term reproduction when prospects for long term survival are threatened.

‘On a mechanistic level, the bee damage may be triggering similar physiological responses within the plant – that is something we are currently investigating.’ 

‘Damaging behaviour might benefit bees by providing earlier access to floral resources – nectar and pollen – and the plants might also benefit by responding to a cue that lets them know the bees are present and available to pollinate flowers.’  

Plants and pollinators rely on one another for survival – just as pollinators such as bumblebees depend on flowers for nutrition, plants need pollinators to reproduce.

This relationship is shown by the simultaneous emergence of hibernating insects and blossoms during the spring.

But the effects of human-induced climate change can raise average temperatures earlier and throw the fragile arrangement off balance, making them out of sync.

For instance, warming early season temperatures could cause pollinators to wake up too soon, before the springtime bloom and without a source of food.

In experiments, the researchers discovered an adaptive strategy used by food-deprived bumblebees to manipulate the timing of a plant’s flowering.

The team observed bumblebee workers that had been starved on pollen colonies use their mouthparts to cut distinctively shaped holes in the leaves of flowering plants. 

Bee damaged plants flowered about two weeks earlier than undamaged plants in one species, the mustard plant, and nearly a month earlier in another, the tomato plant.  

Although they were unable to pin down a reason why, it was likely due to the unique symbiosis between bee and plant – one that couldn’t be triggered by a human to the same extent.

The authors were not able to reproduce the effects by mimicking the damage on their own, which suggests an as yet unknown feature distinct to the bees’ approach.

‘We tested plants that we damaged mechanically, using forceps and razor blades, to try and mimic the bee damage as closely as possible,’ said Dr Mescher. 

‘That treatment caused slightly earlier flowering in both species, but not nearly as dramatic as the effect of bee damage.’

The team say their results, published in Science, reveal bumblebees as ‘powerful agents’ in influencing the local availability of floral resources.

Professor Lars Chittka, a German zoologist at Queen Mary University of London, who was not involved in our research, has authored a perspective piece about the research that appears in the same issue of Science, interpreting the possible ‘secret lives of bees as horticulturists’. 

‘An encouraging interpretation of the new findings is that behavioural adaptations of flower-visitors can provide pollination systems with more plasticity and resilience to cope with climate change than hitherto suspected,’ he said.

‘Understanding the molecular pathways by which one could accelerate flowering by a full month, as reported, would be a horticulturalist’s dream.’

Over the last few years, flowers blooming early has also recently been a sign that spring has sprung much sooner.

This suggests that flowers could have a set of coping strategies in case the reverse happens – flowers bloom before the appearance of pollinators. 

‘This is likely often the case, although effects can vary from place to place,’ Dr Mescher told MailOnline.   

‘The more general point is that environmental change may lead to less predictable conditions and may tend to disrupt the timing of interactions between plants and pollinators.

‘In such cases, the existence of interactions like this, involving direct communication between the bees and plants could tend to enhance the resilience of these interactions to climate change or other forms of environmental disturbance.’  

A report from last year revealed climate change is shifting spring forward in the UK and disrupting life cycles of ecosystems.

Aphids, moths and butterflies are now flying and birds are laying eggs much earlier than in the mid-20th century, according to the 50-year study in Global Change Biology.

Climate scientists warned that variations in how animals were shifting their behaviour means wildlife could get out of kilter with life cycles of other species. 

Habitat will not provide a ‘buffer’ to rising temperatures, it said, although the amount an ecosystem changes depends on where they are in the world and which habitat they live in.