Building greenhouse/polytunnel questions.

[goodmow]

I'm planning on building a greenhouse/polytunnel over the winter.
I'm planning on building a rectangular frame out of 3 x 3 inch timber,6ft high and approx 10 ft wide and 30ft long covered with polytunnel plastic.
I will fit two autovents on either ends in the roof.
My questions are that i want to encourage bees into the building for pollination but i also want to discourage butterflies and the like,is this wishfull thinking or does anyone have any good ideas?

[Shadylane]

Cover the doors in butterfly/pond netting. Should be wide enough for bees, but will the cabbage whites out.

[goodmow]

Thanks for the advice,do you think i should have the door and another area covered in netting?

[Shadylane]

I think what a lot do is have a top section of the door covered in netting and the bottom two thirds (ish)covered in plastic. I expect bees would have trouble getting in and out though, so you'd probably best having both doors open with some netting covering the opening, secured to the frame in some way. I only have a cheapo zip up poly and only grow toms in it so no need for bees and no need for the doors to be open. Hopefully a polytunnel expert will be able to give you some more expertise advice and let you know if butterflies are generally a problem if you leave the doors open.