Using citizen science data to compare flight phenology of two oligolectic bees (Hymenoptera: Andrenidae) with the flowering of their host plants

Understanding the relationship between solitary bee flight and flowering phenology is globally relevant for environmental management and habitat restoration. Using Swedish citizen science data over an 11 -year period, the fl ight behaviours of two oligolectic solitary bees (Andrena hattorfiana and Andrena marginata) were compared to the flowering phenology of their hosts (Knautia arvensis and Succisa pratensis) in southern Sweden. There were 2,327 and 4,566 records of fl ight and fl owering, respectively. While associative studies cannot resolve the degree of oligolecty, a strong temporal association of Andrena hattorfiana with Knautia arvensis and Andrena marginata with Succisa pratensis was indicated. Three conclusions emerged when comparing annual data: first, the flight period of both bee species studied overlapped with the flowering period of their corresponding host plants. Second, earlier fl owering of Knautia arvensis corresponded with the earlier fl ight of Andrena hattorfiana. Third, the fl ight period duration was unaffected by the flowering period duration. For Andrena hattorfiana/Knautia arvensis, climate change may shift the start of fl ight and fl owering periods to earlier dates in the year. A similar response would be expected for Andrena marginata/Knautia arvensis, but not for Andrena marginata/Succisa pratensis where there instead might be an increasing mismatch between the fl ight and fl owering periods.