Are polythene tunnels a danger to bumble bees?

I have a 50 foot walk-in polythene tunnel with doors at each end. I grow strawberries in this tunnel. Bees of all sorts are to be encouraged and they more than oblige in pollinating the strawberries. But I have noticed a number of dead bumble bees recently. Notwithstanding the news of a sickness that is killing bees I wonder, in this case, is there a contributing reason for bees dying in polythene tunnels, or at least in my tunnel?

I wonder is heat stress a factor?  I note that the bees freely fly in through the open doors and do their good work among the strawberry plants. But when it is time to leave a problem seems to arise. The bees fly towards the roof of the tunnel expecting to make their way out into the light by that means. Endlessly they push against the polythene here looking for a way out. At the height of summer the heat in a tunnel can be surprisingly high which must add to their distress. This constant searching for a way back out of the tunnel in most cases leads the bees to bump along the roof to eventually find themselves trapped against the vertical one to two feet of polythene above either of the doors. If they would only drop down that two feet they would find their way out the door again.

I have found several dead or dying bumble bees in the tunnel and wonder would this be from their exhaustive efforts in trying to escape from the tunnel? (Honey bees don’t seem to have a difficulty and fly out through the doors without problems.) If this is indeed the case tunnel design that allows an open flap above each door that could be buttoned up in winter might be helpful.

Have any others observed this to be a problem? I would welcome your views.

Polythene tunnel designers might wish to consider this.



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