How droughts could starve bees and crops

By the end of this century, drought conditions could leave bees with nectar that’s nearly empty of calories – up to a 95% loss. That’s not just bad news for bees. It’s also bad for plants, crops, and the people who grow and rely on them.

In a more moderate future, where rainfall drops by 30 percent, nectar calories could still fall by about a third. That kind of change ripples through entire ecosystems and straight into agriculture.

The findings come from scientists at São Paulo State University (UNESP), based on research supported by FAPESP.

“In terms of calories potentially lost in the nectar, this is equivalent to more than a ton of sugar per hectare, from 1,325 to 71 kilos. Without nectar to consume, the bees leave, the plants don’t reproduce, and the farmers lose production,” said study co-author Professor Elza Guimarães.

Rainfall, drought, and food for bees

The research team found that more rain can actually help nectar production. Under increased rainfall, nectar calories jumped by 74 percent. But that doesn’t mean “more rain” is always good.

“A high frequency and intensity of rainfall can have devastating consequences for plants, flower visitors such as birds and insects, and the maintenance of interactions between plants and pollinators,” said Maria Luisa Frigero, the study’s first author, who conducted the research during her master’s program at UNESP.

Rainfall affects everything from how easily bees can fly, to how much energy they need to stay warm and forage, to how nutrients move through soil. Heavy rains can wash away vital nutrients, erode topsoil, and suppress pollinator activity.

“The most recent IPCC report, AR6, presents evidence that extreme events, such as intense rainfall and droughts, are becoming increasingly frequent and severe in different regions worldwide,” wrote the researchers.

“On one hand, the direct effects of an excessive increase in rainfall on crop production include soil erosion and damages to crop, jeopardizing food production; on the other hand, extended periods of drought can lead to land degradation, resulting in a decrease of crop productivity.”

Inside the greenhouse

The team conducted controlled experiments using zucchini plants, growing them in greenhouses where light, temperature, and nutrients were kept consistent. The only variable was the amount of water each group received.

The researchers tested four different watering scenarios: one group received normal rainfall, serving as the control; another group received 30% less water; a third group got 57% more; and the final group experienced a simulated drought followed by extreme rainfall.

Each group had 30 plants. In total, 120 plants were observed for 60 days. No pollinators were allowed in, ensuring precise measurement of nectar and sugar production per flower and per plant.

Even though this work focused on one species under greenhouse conditions, the researchers believe the results are representative of what could happen to other crops in natural environments.

The impact of drought on bees

“We’re now exploring the effects of climate change on native and cultivated plant species by testing the impact of heat waves and other extreme events,” said study co-author Priscila Tunes.

“Another development of this study is the investigation of how bees react to the changes that occur in flowers in this context, by means of behavioral analyses.”

Tunes and the team are pushing the research forward, not just by measuring what plants produce, but by watching how pollinators respond.

From nectar to our plates

This study draws a direct line from climate change to nectar, pollinators, and food production. It shows how changes in rain patterns – something as simple as more or less water – can ripple outward into big, visible consequences.

And it raises real questions for the future: What happens if flowers stop feeding bees? Who will pollinate the plants? And what will we do when the crops don’t come?

“Animal pollination is responsible for most plant species’ reproduction including several crops that rely especially on bees for fruit and seed production,” wrote the researchers.

“Thus, extreme climate events can cause disruptions in pollination mutualism and lead to a decrease in the production of many crops worldwide.”

The full study was published in the journal Scientific Reports.

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