College of Agriculture & Natural Resources Department of Entomology

A recent study led by a recent MSU Entomology graduate, Jenna Walters, PhD., has found that extreme heat can negatively impact plant pollination and bee survival by altering the nutritional composition of the pollen.

"Extreme heat affects blueberry pollen nutrition, bee health, and plant reproduction" (Walters et al. 2025) examined how exposure to extreme temperatures at different floral developmental stages affects the nutritional composition of pollen in highbush blueberry plants, as well as the resulting impacts on bee health and plant reproduction. 

This research highlights a critical link between climate change and crop production, as pollinators like bees are essential for the reproduction of many crops, including blueberries. If extreme heat alters pollen nutrition in a way that harms the health of bees and their ability to pollinate effectively, it could lead to lower crop yields and diminished biodiversity, which directly harms food production.

To test this, they exposed highbush blueberry plants at various stages of flower development to extreme heat—99.5 degrees Fahrenheit (37.5 Celsius)—for four hours. They then analyzed the pollen’s protein, carbohydrate and amino acid content, as well as the plant’s percent fruit set, or the percentage of pollinated flowers that developed into marketable fruit, and compared the results to plants grown under historically normal conditions of 77 degrees (25 Celsius). Additionally, this pollen was fed to orchard mason bee larvae (Osmia lignaria) to observe their survival rate as a follow-up to a 2024 study in which they observed the effects of indirect heat stress on native bee behavior, development and survival.  

The effects of extreme heat varied across the different growth stages of the blueberry floral buds, with bud swell (visible swelling of flower buds, the first sign of growth in the spring) being the most heavily affected, with significant reductions in pollen protein and several amino acids. As a result, it was found that bee larvae that were fed the heat-treated pollen were seven times more likely to die than those who were fed normal pollen. 57% of the bee larvae that were fed the heat-altered pollen died before pupation, and none of the male offspring that were raised on this pollen survived to adulthood. 

Pollen is a primary diet source for bees, so when the nutrient composition of their pollen is altered, their development, fertility, resilience to stress and overall survival is disrupted. 

These findings have serious implications for the stability of pollinator populations. The dramatic increase in bee larval mortality linked to heat-altered pollen suggests that rising global temperatures could severely impact bee reproduction and the overall health of their colonies.

Additionally, it was observed that there was a 39% reduction in fruit development among blueberry plants that were heat-treated during the bud swell stage. This could suggest that plants are more susceptible to damage during the early spring, when the bud swell stage typically occurs.

As Walters noted in a previous study published in Proceedings of the Royal Society B, “Combatting the effects of climate change-induced heat extremes will require creative solutions on both short- and long-term scales. To effectively address the implications of heat stress on bees and their interactions, we must broaden our understanding from direct, isolated stressors to indirect and interactive stressors.” This call for creative and comprehensive solutions remains highly relevant to the current research, which expands upon the previous work. 

Overall, this study suggests that climate change impacts on pollinators may be more complex than they first appear. By focusing on indirect stressors that emerge later in the ecological chain, the research shows how heat can disrupt the plant-pollinator relationship by altering something as small as pollen grains. This is especially important when considering crop production. If extreme temperatures cause pollen to be less nutritious, bee populations will decrease, which in turn will cause crop yields to decline. The impacts of this would go even further, potentially driving up crop prices or even directly harming food security.