This is the Centaurea cyanus from the Asteraceae famly.

This deciduous annual plant can reach up to 75cm in height. It has narrow lanceolate leaves and flowers late spring to summer. It varies in colour from purples to blues to pinks ect, however the most common Centaurea cyanus is a deep blue.

This plant gets its common name 'cornflower' from farmers, as it used to be considered a weed in corn fields which lead to its decline in population but now it is used as an ornamental plant and its population is slowly raising again. The bees love this flower!

As you can see this bee, which I believe to be a female Bombus cullumanus has rather large and full pollen baskets!