Nowadays, when we combine the word ‘agriculture’ and ‘pollinators’ together, the association tends to be negative.  

After what we’ve seen and heard lately in the global media, the two don’t seem to match. Due to agriculture, among many other things, populations of pollinators have gone down largely and quickly worldwide.  

Well, we might be proven wrong. According to a new study led by Penn State, one bee species, namely the squash bee (Eucera pruinosa), has in fact thrived and expanded its population because of agriculture. 

However, squash bees grow because of cultivated plants in the squash family such as pumpkins, zucchinis, and well, other squashes.  

Cultivation of those crops has increased across North America over the last 1000 years; the bees feel like they should adapt to the change, and they’ve so far succeeded. 

The study, published in “Proceedings of the National Academy of Sciences”, found how the bee species has evolved in response to the ever-increasing intense squash agriculture, particularly in the genus Curcubita. 

Examining the squash bee phenomenon 

According to the study, this is the first research to demonstrate the role of agriculture as an evolutionary force that acts on a wild insect pollinator, which may have implications for food security. 

Researcher Margarita López-Uribe said, “When we think of insects benefiting from and adapting to widespread agriculture, we tend to think of pests such as certain kinds of moths, flies and beetles.” 

While we certainly know the negative effects of intensive agriculture on the environment and native insects, its impact on the evolution of beneficial pollinators has been lacking.  

“We found that agriculture facilitated increases in population size of this squash bee, and this may be the case for other insect pollinators, as well,” López-Uribe said. 

The study suggests that human agriculture in North America hasn’t been always moving towards something bad. It has, contrarily, had an impact on the evolutionary history of an insect that is an essential pollinator of squash crops. 

“This research highlights how domesticating plants can have important indirect effects on the organisms that pollinate those plants,” said Sam Scheiner, program director at the U.S. National Science Foundation, which partially funded the work. 

 

 

The bee’s journey through the millennia 

Before the massive agriculture, the squash bee’s primary source of pollen was the wild buffalo gourd (Curcurbita foetidissima). This small squash grew in the deserts of Mexico and the southwestern United States.  

Like corn and beans, squash was an important crop of Indigenous Peoples in the Americas. Then, around 3000 years ago, Indigenous Peoples began cultivating pumpkins, squash, and gourds—which was intensified around 1,000 years ago with the introduction of maize to the agricultural systems of North America. 

López-Uribe said, “By planting squash all over North America, humans created habitat for the squash bee, and that allowed its population to explode. Today, the squash bee occurs throughout the United States and southeastern Canada—far beyond the range of its original food source.” 

To understand exactly how the E. pruinosa bee has evolved in response to the intensification of Curcurbita agriculture, the team sequenced the bee’s genome. 

They wanted to find out its genetic structure, the amount and distribution of genetic diversity within and among the bee’s various populations, basically tried to spot where or when there was adaptation. 

When there were decreases in genetic diversity, it would mean that the bee has undergone beneficial mutations, increased the mutations’ frequency, and the mutations eventually have become fixed—also known as selective sweeps. 

The team then developed a model to estimate the bee’s migration and effective population size across populations.  

It turns out that the bee, thanks to the selective sweeps, has transitioned from its preferred wild host plants in deserts to temperate agricultural habitats. It resulted in reductions in genetic diversity in some parts of the genome, at nearly 20 percent. 

What could be the cause? According to López-Uribe, cultivated Curcurbita plants produce floral blends that are simpler than those of the wild Curcurbita plant. 

“It is likely that E. pruinosa adapted to a new sensory environment in agricultural habitats, which enabled it to expand its range and significantly increase its population size,” López-Uribe said. 

But what does this mean? 

While this study gives the vibe of “See? Intensive agriculture isn’t that bad,” we must remember that the observed bee is only one species.  

And it’s still unknown if the selective sweeps will be beneficial in the future (like resistance against environmental changes, for instance) or not. Moreover, it’s also not clear about the native plants: if the bee likes cultivated plants more, what will become of the wild counterparts?  

Although, this finding could be a start of understanding pollinators better, so that researchers in the future could make other pollinators more adaptable. 

After all, “pollination is such an important process that impacts so much of the food we eat. Understanding how humans have and continue to impact that process and pollinators—through agriculture, urbanization and in other ways—is key to ensuring we maintain food security,” as Scheiner said. 

This isn’t to say that we should be complacent about important, native insects as well. We should also remember that the health of pollinators such as wild bees has been declining due to many factors—one of which is agriculture. 

Just as a reminder, in 2020, York University researchers found that climate change and disturbed habitats from expanding development and agriculture were likely responsible for a 94% loss of native plant-pollinator networks.  

The researchers examined plant-pollinator networks from 125 years ago through present day. They found that around 30% of such networks were completely lost, meaning that either the bees or the plants (or both) have disappeared. 

Meanwhile, 64% of the network loss, the wild bees (like miner bees) or native plants (like willow) were not totally lost. However, the bees didn’t want to pollinate or visit the plants any longer. Only 6% were stable or thriving.  

 

 

Many contributors to the bees’ decline 

Disrupting habitats for agriculture is a driving factor to the network loss, but the researchers were inclined more to climate change. Over the last 100 years, annual temperatures have changed by two and a half degrees. Although it looks minute, it’s enough to alter the time when certain native plants bloom. 

Corresponding author Professor Sandra Rehan said, “For a bee that’s out for months on end or is a generalist pollinator, this isn’t such a critical mismatch, but for a bee that’s only out for two weeks of the year and only has a few floral hosts, this could be devastating.” 

According to the researchers, the other main reason for the network loss is an increase of non-native species of bees and invasive species of plants. As we know, both have displaced or replaced some of the native species—some from industrial byproduct, some from household stuff like imported plants. 

Rehan said, “We are getting a lot of invasive species and new records of invasive species every year. This is usually accidentally through trade and through ornamental plants.” 

If we want to make a change to restore the native plant-pollinator network loss, the researchers suggested to increase habitat restoration and native flowering plants in agricultural landscapes, as those may significantly improve wild bee biodiversity as well as food security. 

Looking back at the Penn State research, a question asks, “So, should we keep cultivating plants/crops that the bees have adapted to? Should we make them get used to the native plants again? Should we plant both?” 

Well, we still don’t completely know it yet.  

But the 2020 York University research and the 2023 Penn State study are in accord with one theme: we still need to understand the species and the connection better. 

“There is an urgent need to gain a deeper understanding of the environmental circumstances affecting these wild pollinator populations and their specialised, evolutionary relationships with plant communities. Plant pollinator webs are dependent on changes in the landscape, so knowing how these networks are shaped is important for all regional habitats,” Rehan said. 

 

Sources

https://www.sciencedaily.com/releases/2023/04/230403162405.htm   

https://www.sciencedaily.com/releases/2020/07/200716144740.htm