Not sure what's happening here, normally bumbles are great pollinators, when honey bees are at home due to cool weather, bumbles can still fly.

Check this out..

Here is a link that might be useful: Bumbles pollinating blueberry

You can tell if a bumblebee is doing it's job, when you see it shaking the blueberry flower.

Interesting video Konrad! I wish the bumble bees by me were as helpful as those in the video.

Pretty sure it's a female carpenter bee not a bumble bee.
I'm also pretty sure she knows her job.

myk1 nailed it - carpenter bee.
Found this on a page about blueberry pollenation

"Carpenter Bee (family Xylocopidae) often resemble large bumble bees. These insects use their strong mandibles to excavate nesting holes in wood. They are often seen flying around old packing sheds or other wooden structures. Carpenter bees visit blueberry flowers, but they cut a hole near the base of the corolla and "steal" nectar. Since they never make contact with the stigma, pollination is less likely to occur. Honey bees quickly learn to use these holes and also become "nectar robbers". The southeastern blueberry bee and other native bumble bees have not been seen using the robber holes. They continue to pollinate flowers that have been damaged by carpenter bees.

A carpenter bee can be distinguished from a true bumble bee by looking carefully at its abdomen. Bumble bees always have a dense coat of hair over the entire abdomen, giving them a very fuzzy appearance. Carpenter bees, in contrast, have little or no hair on their big black bottoms!"

See Scott's comment on the topic Watching the Pollen Dancers. He and I get great blueberry pollination at sites separated by 2 states, even if they do slit the flowers and appear to be the only ones tending the blueberries.

Every spring the bumblebees come out and pollinate our blueberry shrubs. Most years, they are the only bees I see out that early. I have never seen a bumblebee cut a hole at the base of the flower, so the photo above must be a carpenter bee. Sure looks like a bumblebee, though.

"Sure looks like a bumblebee, though."

Black not so fuzzy butt = carpenter. Black face on carpenter = female.

I have not seen any bees at my blueberry. I think he wind will do the job. I hope.

A couple of points if I may.
Bumble bee bottoms or abdomens always have bands of yellow/black colors.
Wind cannot pollinate blueberries due to the flower shape.