Here is What’s Happening to US Honey Bees

Back in the winter of 2006, beekeepers in the United States began reporting startling losses of up to 90% of their hives. “As many as 50% of all affected colonies demonstrated symptoms inconsistent with any known causes of honey bee death,” notes the U.S. Department of Agriculture,

For years, “colony collapse disorder” and the loss of honey bees (Apis mellifera) made regular headlines—and with good reason. More than 30% of the food we eat in the United States comes from crops pollinated by honey bees. Remove honey bees from the pollination equation and things start to decline rapidly.

While the media attention to the problem has waned, the problem itself has not disappeared. In a 2020 study, researchers found that between April 2019 and April 2020, there was a 43% colony loss in honey bees across the United States. Scientists have been unable to find one specific cause—according to a new study led by Penn State, the drivers of this pervasive phenomenon “are still an open matter of investigation.”

But now, after a comprehensive analysis of data from the last five years, the Penn State study offers insight into what is killing the bees. Using novel statistical methods, the study is the first to concurrently look at a mix of honey bee stressors at a national scale. 

Honey Bee Loss Has Multiple Causes

“Honey bees are vital pollinators for more than 100 species of crops in the United States, and the widespread loss of honey bee colonies is increasingly concerning,” said Luca Insolia, first author of the Penn State study, “Some previous studies have explored several potential stressors related to colony loss in a detailed way but are limited to narrow, regional areas. The one study that we know of at the national level in the United States explored only a single potential stressor. For this study, we integrated many large datasets at different spatial and temporal resolutions and used new, sophisticated statistical methods to assess several potential stressors associated with colony collapse across the U.S.”

The findings show that “honey bee colony loss in the U.S. over the last five years is primarily related to the presence of parasitic mites, extreme weather events, nearby pesticides, as well as challenges with overwintering,” writes Gail McCormick in a press statement for the study. 

Behind the research was a dynamic combination of scientists which included statisticians, geographers, and entomologists. They looked at publicly available data collected between 2015 and 2021 on honey bee colonies, land use, weather, and other potential stressors. “Because these data came from a variety of sources, they varied in resolution over both space and time,” notes McCormick. 

“In order to analyze the data all together, we had to come up with a technique to match the resolution of the various data sources,” said Martina Calovi, corresponding author of the study and currently associate professor of geography at the Norwegian University of Science and Technology. “We could have just taken an average of all the weather measurements we had within a state, but that boils all the information we have into one number and loses a lot of information, especially about any extreme values. In addition to averaging weather data, we used an ‘upscaling’ technique to summarize the data in several different ways, which allowed us to retain more information, including about the frequency of extreme temperature and precipitation events.”

With sophisticated statistical modeling techniques, they were able to assess a large number of potential stressors at the same time.

They found that more than one stressor affected honey bee colony loss across the country, including the presence of pesticides—no surprise, given that the goal of pesticides is to kill insects—frequent extreme weather events, and weather instability. Additionally, not surprising given previous evidence and research, bees were also impacted by the presence of the Harry Potteresque parasitic mites, Varroa destructor. At just 1.1 millimeters long, Varoa is one of the most troublesome pests of the honey bee and is causing concern to beekeepers throughout the world. 

The study also points out that in some states, but not all, losses happened between January and March, which can be a challenging time for overwintering animals. For bees, not surviving the winter can be a sign of poor colony health.

“Our results largely reinforce what regional studies have observed and confirm that regional patterns around these stressors are actually more widespread,” said Insolia, who led the study as a visiting graduate Penn State statistics student and who is currently a postdoctoral researcher at the University of Geneva in Switzerland. A beekeeper himself, Insolia adds, “These results also inform actions that beekeepers could take to help circumvent these stressors and protect their colonies, including treatments for the Varroa mite‚ especially in areas of weather instability. Beekeepers could also consider strategies to move their colonies to areas with high food availability or away from nearby pesticides or to provide supplementary food during certain seasons or months with frequent extreme weather events.”

When colony collapse disorder first came to rise, we all anticipated a single smoking gun. But the modern world is a complicated place and human folly is taxing the animal and plant worlds in unprecedented ways. And now, the onus is on beekeepers to protect bees from anthropogenic threats such as climate change and pesticide use.

“A changing climate and high-profile extreme weather events like Hurricane Ian—which threatened about 15% of the nation’s bees that were in its path as well as their food sources—are important reminders that we urgently need to better understand the stressors that are driving honey bee colony collapse and to develop strategies to mitigate them,” said Francesca Chiaromonte, a senior member of the research team.

“Our results highlight the role of parasitic mites, pesticide exposure, extreme weather events, and overwintering in bee colony collapse. We hope that they will help inform improved beekeeping practices and direct future data collection efforts that allow us to understand the problem at finer and finer resolutions.”

The study was published online in the journal Scientific Reports.