Extreme heat affects blueberry pollen nutrition, bee health, and plant reproduction.

Extreme heat events are increasingly common, and if these align with pollen development, they can alter pollen nutrient composition. However, no studies have examined how the timing of heat relative to bud development affects the role of pollen in plant pollination and bee health. To explore this, we exposed highbush blueberry plants to extreme heat (37.5 °C) or normal (25 °C) conditions for 4 h across several floral bud stages. Pollen was analyzed for protein, carbohydrate, and amino acid content. We found that blueberry floral buds vary in their sensitivity to heat, with bud swell being the most heat-sensitive developmental stage with significant reductions in pollen protein, total and several individual amino acids. When pollen from blueberry plants exposed to the same conditions was fed to Osmia lignaria larvae, we found that individuals fed heat-stressed pollen were 7 times more likely to die compared to those fed non-stressed pollen. Blueberry flowers exposed to the same conditions were used for a hand pollination study, where we observed a 39% reduction in fruit set following heat stress at bud swell. This study reveals how extreme heat can disrupt both plant pollination and bee survival through changes in pollen nutritional composition.