The indirect consequences of extreme heat on Osmia lignaria behavior, development, and health

Extreme heat events pose a major threat to plant-pollinator interactions, but the full effects are not well understood. Native solitary bee pollinators are especially vulnerable to the effects of heat stress. Adult bees and their offspring may be affected indirectly when host plants endure heat stress during floral development, as the quantity and quality of nutritional resources may be reduced. To better understand the effect of heat stress on bees, we conducted a no-choice field cage study with Osmia lignaria females who were provided blooming blueberry, phacelia, and clover plants that had been recently exposed to either extreme heat (37.5°C for 4 h) or normal temperatures (25°C for 4 h). Females that were provided only heat exposed plants produced significantly fewer offspring than females provided non-stressed plants. Of the offspring produced in cages with heat-stressed plants, larval survival was significantly lower compared to those that visited flowers of plants exposed to normal temperatures. Subsequent studies are exploring the role of maternal effects on larval development and survival using in-vitro techniques. We are also testing the effects of feeding bee larvae with pollen from heat stressed plants to determine how that influences growth and development. Results from this research highlight how extreme heat can influence both sides of plant-pollinator interactions, with compounding influence on pollination.