Posted: March 17, 2022

Entomologist Christina Grozinger broadens her research directions and collaborations after discovering the paramount importance of climate change on pollinator health.

Christina Grozinger. Photo: Michael Houtz

Christina Grozinger. Photo: Michael Houtz

Sometimes in life, problems are bigger than they appear at the outset.

For Christina Grozinger, a series of recent scientific discoveries has revealed that the predicament of the global decline of pollinators is more complex than anyone knew.

"For more than a decade, my colleagues and I have been studying the effects of pesticides, diseases, and land-use patterns on pollinators. These are all problems that we humans have the ability to manage--to an extent," said Grozinger, who holds the Publius Vergilius Maro Professorship in Entomology. "But our most recent research has revealed that weather and climate change are much more important contributors to the decline of bees."

Grozinger and her colleagues are among the numerous scientists worldwide who are beginning to observe the impacts of climate change on the systems they study. "It feels overwhelming," she said, "because the problem exists at such a large scale and because studying weather and climate is outside of my skillset."

Fortunately, Grozinger doesn't have to go it alone.

"One of the great things about being at Penn State is the availability of collaborators who not only have a wide breadth of expertise but are also creative and interested in working together and doing new things," she said.

Evolution of a Career

As a scientist, Grozinger's modus operandi has always been to question the way the world works, an exercise that has sometimes led to answers but has almost always led to more questions. But although her questions now relate to global issues, she didn't start out studying such grandiose problems. In fact, she didn't even start out studying bees.

A graduate student at Harvard University, Grozinger began her career focused on something much smaller--histone deacetylases (HDACs), or enzymes that are involved in gene expression. "I was interested in working at the intersection of chemistry and biology," she said. "I loved working on HDACs, but these studies were really at the molecular and cellular level, and I wanted to find more organismal questions to work on for my future career."

As it happens, her brother was a backyard beekeeper. "He would tell me such amazing things about their behavior, and I began to wonder if HDACs could be involved," she said. "I did a lot of reading and searching, and eventually joined the lab of Gene Robinson at the University of Illinois to study the genetic and molecular bases of these behaviors. While I was a Beckman Institute Fellow in his lab, he led the sequencing of the honey bee genome, and that opened a lot of doors for me, and all of us who work on bees."

In 2006, bees began making headlines as the mysterious "colony collapse disorder"--in which the majority of worker honey bees in a colony disappear, leaving behind the queen and a few nurse bees to care for the babies--was first defined. While no cause has been proved, scientists believe certain stressors--such as the pathogens transmitted by Varroa mites, pesticides like neonicotinoids, malnutrition, genetic factors, and loss of habitat--may be contributing factors.

At the time, Grozinger was two years into her job as an assistant professor at North Carolina State University. Naturally, the scope of her questioning grew to encompass the stressors affecting bees, and she began to study the molecular mechanisms underpinning bees' responses to these stressors. She was particularly interested in investigating pathogens, parasites, and pesticides, as well as bee nutrition, which is a function of the diversity of flowering plants in the landscape.

Over the course of her career, Christina Grozinger has endeavored to understand the complexity of bees--from their genetics to their responses to climate change. Photo courtesy Christina Grozinger

In 2008, she joined the faculty of the Department of Entomology at Penn State, where she is now the director of the Center for Pollinator Research and the Insect Biodiversity Center. Here, she began to develop relationships with local beekeepers and came to realize that some of the challenges they faced were a result of the broader landscape in which their colonies were housed. "What these beekeepers needed were tools to help understand how various landscape factors affected their bees," she said.

So, in 2019, she and her colleagues developed Beescape, a software program that enables beekeepers and others to understand the specific stressors to which the bees in their managed hives, home gardens, or farms are exposed. The researchers are currently parameterizing the Beescape model with data provided by beekeepers from agricultural, rural, and urban landscapes across multiple states. This could allow beekeepers to determine if they should provide the bees with supplementary food, for example, or growers to decide if they should add pollinator nesting habitat near their crops.

"Beescape allows people to see the world from the perspective of a bee," said Grozinger. "This can help them to make management decisions, such as where to place their colonies and where to plant pollinator gardens, to make the landscape more bee friendly."

Talk about the Weather

Over the years, Grozinger and her colleagues, including Heather Hines, associate professor of biology and entomology, continued to study landscape-level questions. For example, in 2020, they published a study conducted in Pennsylvania demonstrating that the health of bumble bees, in terms of having lower pathogen loads, is related to the abundance of floral resources in the surrounding landscape.

Also in that year, together with Maggie Douglas, a former Penn State graduate student and now a professor at Dickinson College, Grozinger published a paper showing that during the past 20 years, insecticides applied to U.S. agricultural landscapes have become significantly more toxic to bees. "We found that increased use of neonicotinoid seed treatments in corn and soy are the primary drivers of this change," she said. "This study was the first to characterize the geographic patterns of insecticide toxicity to bees and reveal specific areas of the country where mitigation and conservation efforts could be focused."

In 2021, however, the results of two studies left Grozinger not only surprised but also hurrying to shift her research program in a new direction.

In one of the studies, she and her colleagues worked with the Pennsylvania State Beekeepers Association to collect data on the winter survival of bees. For each participating apiary, the team compiled data on landscape variables that influence the availability of floral resources and insecticide exposure risk. Because Grozinger's collaborator, Sarah Goslee from the USDA Agricultural Research Service based at the Penn State University Park campus, has expertise in assessing weather and climate effects on plant species distributions, they decided to add weather, including temperature and moisture conditions, to the mix. "We were trying to include all the environmental factors that we thought might be relevant to the bees," she said.

The team found that although the local landscape variables they looked at were important, the weather was much more important to honey bee winter survival. In fact, they learned that winter survival was most strongly influenced by summer temperatures and precipitation in the prior year. "It could be that the weather is influencing plants and their ability to flower and produce nectar and pollen, or it could be that the weather affects the abilities of the bees to collect the nectar and pollen," says Grozinger. "It definitely suggests that honey bees have a 'goldilocks' preferred range of summer conditions outside of which their probability of surviving the winter falls."

According to Grozinger, the effects of weather on honey bee survival are already being felt. Honey bees suffered estimated overwintering mortality rates of more than 53 percent from 2016 to 2019 in the United States, she said, thus greatly reducing the economic and ecosystem contributions of these pollinators. That's a problem because the economic impact of insect pollinators is quite high--$34 billion in 2012, which is much higher than previously thought, according to another of Grozinger's recent studies, which was in collaboration with Vikas Khanna, associate professor of civil and environmental engineering at the University of Pittsburgh.

"Pollinators play an extremely important role in agriculture," she said. "It's important for us to consider all environmental factors, including weather, when modeling and predicting their survival, and that requires large data sets that span multiple types of habitats, microclimates, and years."

Not Just Honey Bees

Next, the team set out to study how wild bees are affected by land use and climate factors in a study led by former Penn State graduate student Melanie Kammerer, and involving Grozinger, Goslee, and Penn State professor of entomology John Tooker. Specifically, they analyzed a 14-year U.S. Geological Survey (USGS) data set of wild bee occurrences from more than 1,000 locations in Maryland, Delaware, and Washington, D.C. This data set had been generated through the efforts of Sam Droege, the lead researcher at the USGS's Bee Monitoring Lab. Using land cover maps and spatial models, the researchers described the landscape surrounding each of the sampling locations, including the habitat size and available floral and nesting resources. Finally, they compiled a large suite of climate variables and used machine learning models to identify the most important variables and quantify their effects on wild bees.

They found that wild bees are more affected by climate change than by disturbances to their habitats. "Our results indicate that temperature and precipitation patterns are more important than suitable habitat or floral and nesting resources in controlling wild bee abundance and species diversity," said Grozinger. "These findings suggest that addressing land-use issues alone will not be sufficient to protect these important pollinators."

As weather changes are likely to worsen in the coming years, with warm winters and long, hot summers predicted to occur more frequently, both wild bees and managed honey bees will likely continue to be at risk. "We are just beginning to understand the many ways that climate influences bees," said Grozinger. "But in order to conserve these essential pollinators, we need to figure out when, where, and how changing climate disrupts bee life cycles, and we need to move from considering single stressors to quantifying multiple, potentially interacting pressures on wild bee communities."

The associate director of research programs for the Penn State Institute for Sustainable Agricultural, Food, and Environmental Science (SAFES), Grozinger is part of a growing group of scientists who are tackling complex problems related to vulnerabilities in ecosystems, resilience, and economic sustainability. To that end, she and her colleagues are undertaking several new studies to better understand how bees are responding to their changing environments and what can be done to protect them.

Future Work

With recent funding from USDA-NIFA's Data Science for Food and Agriculture Systems program, Grozinger, Goslee, Khanna, and collaborators Anthony Robinson, associate professor of geography at Penn State; Patrick Dudas, data visualization research and development engineer for the Penn State Institute for Computational and Data Sciences; and Eric Lonsdorf, lead scientist in the Institute on the Environment at the University of Minnesota, have developed a Coordinated Innovation Network to create "Beescape NexGen." The goals of this project include integrating data from diverse government data sets and information and perspectives gleaned from beekeepers, growers, and conservationists to build a new version of Beescape. Beescape NexGen will include detailed information on landscape quality and economic value of pollination services spanning spatio-temporal scales, all in a format designed to support the decision-making processes of these different groups of stakeholders.

In a second study, with a new grant from the Human Frontier Science Program, Grozinger and her colleagues from the University of Muenster and the Swedish University of Agricultural Sciences are designing and implementing innovative computer vision methods, along with plant quantitative genetics and pollinator behavioral ecology techniques, to identify the mechanisms controlling plant-pollinator interactions on a large scale. Using multiple state-of-the-art deep-learning and analytic computer vision algorithms and other tools, they will automatically detect, identify, track, and annotate pollinator visitations from videos recorded with a consumer-grade camera. Ultimately, their goal is to link plant genes and traits to attraction of different insect species and determine how these traits contribute to plant fitness and reproduction. "By linking plant genetics, pollinator health, and quantitative behavioral data, this project will generate novel concepts and approaches to select and breed for more pollinator-attractive plants that can better support pollinator communities in agricultural, urban, and natural ecosystems," said Grozinger.

With another new grant from USDA-APHIS, Grozinger and Hines are extending the bumble bee study they conducted in Pennsylvania to North Carolina, which has different bumble bee species and a larger variety of habitat types. "We want to understand how different bumble bee species might be responding to different habitats and weather conditions, and why some of these bees are doing well and others are not," said Grozinger. "So instead of lumping everything together into one category of 'pollinators,' we are trying to understand the differences among species and how we might design systems and habitats that can support all these bees and buffer them from climate issues."

In another study, Grozinger and her collaborators are weighing beehives to document how they gain or lose weight across the season and how this is influenced by landscape and climate. "This type of nuanced information can give us a bit more understanding about the point at which weather begins to create an issue for bees," she said. "We also want to look at microclimate [the climate of a small, restricted area] effects, as that could be a strategy used by beekeepers or land managers to mitigate the larger-scale climate affects. This work can't be done without a lot of input and engagement from beekeepers to get the detailed data that we need but also to understand what results are most helpful for them."

In addition to beekeepers, Grozinger is also looking to engage with the broader public. In collaboration with Shannon Cruz, assistant professor of communication arts and sciences at Penn State, she is trying to understand people's attitudes about pollinators. Last year, the duo conducted a survey of undergraduate students, asking them what they knew about bees and pollinators, if they were scared of them, if they thought bees were beautiful, and what activities they engage in to support pollinators. They also collected information about the students' backgrounds, experiences, and leanings toward other environmental issues. They are currently expanding the study, which was funded by the Communication, Science, and Society Initiative of the Penn State Huck Institutes for the Life Sciences, to include people from across Pennsylvania.

"We can study the effects of all these environmental factors on bees, and we can make recommendations for things that can be done to support bees, but we have to understand what people are actually willing to do about it," Grozinger said. "How can we help them understand this information in a way that allows them to make more informed decisions about their personal and professional activities?"

To that end, Grozinger is involved in The Arboretum at Penn State's new Pollinator and Bird Garden, which opened to the public this summer. "The garden showcases Penn State research on pollinators and provides inspiration for people to make their own efforts to improve pollinator habitat," she said.

The Pollinator and Bird Garden at The Arboretum at Penn State opened to the public in June. The garden is designed to serve as a research and teaching tool, as well as a place to inspire and foster an appreciation for pollinators. Photo: Michael Houtz

Although Grozinger is happy that her work is having a broader applied impact, she said her research has ultimately been driven by her interest in the scientific questions themselves.

"Climate change could be disrupting bees in so many ways," she said. For example, new weather patterns can change the flowering times of plants and the length of the flowering period, and this may not align with when bees are out and in need of nutrition. Stressful weather conditions, like drought, might also reduce the quality and quantity of pollen and nectar provided by plants.

"We have to think strategically and thoughtfully about how we are going to deal with this issue of climate change," she said. "As individuals, we can do our best to create habitats in our backyards for pollinators, but the real changes need to come at the policy level."

Grozinger received the 2021 National Academy of Sciences' Prize in Food and Agriculture Sciences for her efforts to address the crisis of global declines in pollinator populations.

"I am so honored to be selected for this award and to have the importance of pollinators to our food and natural ecosystems recognized," she said. "Tackling pollinator declines requires an approach that crosses academic disciplines and engages stakeholders in a shared discovery process. The dynamic, creative, and collaborative environment at Penn State really has made this work possible, and I am so excited to see where we will take this research in the future."

-- Sara LaJeunesse