Asynchrony between emergence and flower availability reduces flower visitation rates and may affect reproductive success in the solitary bee Osmia cornifrons

Asynchronous phenological shifts between solitary bees and their host plants in response to climate change can have negative consequences for bee reproductive success. However, the mechanisms underlying bee responses to phenological asynchrony remain unknown. Our objective was to investigate whether phenological asynchrony indirectly affects reproduction in solitary bees by influencing the length of a female’s nesting period and/or visitation to flowers. We manipulated phenological asynchrony by preventing emerged female Osmia cornifrons from accessing nectar and pollen for between 0 to 16 days. Females were then placed in flight cages where we recorded female lifespan inside cages, flower visitation rates, and reproductive output. We found that female lifespan inside cages was not affected by phenological asynchrony, but that flower visitation rates and offspring weight decreased as a function of asynchrony (days). Due to low numbers of total offspring and a lack of female offspring across treatments, we were unable to assess total offspring produced or sex ratio. Findings suggest that starvation after emergence in solitary bees may affect flower visitation rates, which in turn could affect offspring size by influencing provision quantities. In solitary bees, body size influences wintering survival, fecundity, and mating success. Thus, phenological asynchrony may have fitness consequences for solitary bees that result from reduced interaction rates with flowers, and these consequences may increase with the magnitude of asynchrony. Because reproduction in many wild flowering plants and crops rely on pollination services provided by bees, reduced interaction rates between pollinators and plants would also likely affect plant reproduction.