Consequences of extreme heat for a solitary bee pollinator Osmia lignaria and its pollen nutrition

Pollen is central to the interactions between bees and flowering plants, yet heat stress can disrupt the nutritional content of pollen with compounding consequences for bees, flowering plants, and their interactions. Despite this, no studies have evaluated the effects of brief, field realistic heat stress on pollen nutrition in the context of plant functioning and bee health. To address this, we evaluated the protein, carbohydrate, and amino acid content of northern highbush blueberry pollen exposed to extreme heat (37.5°C for 4 h) or normal temperatures (25°C for 4 h). We found that pollen from heat stressed plants had negative repercussions for Osmia lignaria fecundity, development, and survival. We also used methods for analysis of small volumes of pollen to compare pollen composition between treatments. Protein and amino acid profiles were affected by heat exposure, and the largest effect was detected on starch content. These results highlight that extreme heat from climate change has the potential to disrupt bee-plant interactions through indirect effects mediated through pollen nutrition.