Climate change and an increase in disturbed bee habitats from expanding agriculture and development in northeastern North America over the last 30 years are likely responsible for a 94 percent loss of plant-pollinator networks, researchers found.

The paper, “Wild bee declines linked to plant-pollinator network changes and plant species introductions,” was published in the journal Insect Conservation and Diversity.

Sandra Rehan, an associate professor in York University’s Faculty of Science, and grad student Minna Mathiasson of the University of New Hampshire, looked at plant-pollinator networks from 125 years ago through present day. The networks are comprised of wild bees and the native plants they historically rely on, although most of those have now been disrupted.

About 30 per cent of plant-pollinator networks were completely lost, which translates to a disappearance of either the bees, the plants or both. In another 64 per cent of the network loss, the wild bees, such as sweat or miner bees, or native plants, such as sumac and willow, are still present in the eco-system, but the bees no longer visit those plants; the association is gone.

The remaining six per cent of the plant-pollinator networks are stable or even thriving with pollinators such as small carpenter bees, which like broken stems for nest making.

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“There are several reasons for the losses in the networks,” Rehan explained. “Climate change is likely the biggest driver. We know that over the last 100 years or so annual temperatures have changed by two and a half degrees. This is enough to alter the time when certain native plants bloom.

“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.”