insects in or not PT

Do you guys let insects into your pollytunnel ? the worst one for me last year was the cabbage whites as they laid eggs on all my greens that was going to the allotment we need some insects to help pollination dont we ?

SK

Yes you need insects and you need to cover the brassica seedlings with netting, same as you would outside 

Why are they in the p/t anyway, when they don't like the heat?

i have always started the seeds off in the pt  i now have a plan to build a netted over frame 
thankyou

SK

I don't let insects into the greenhouse or polytunnel and have fine mesh netting over vents and doorways.  I rarely see pollinating insects enter, and all I seem to get is an infestation of crop munching bugs  and a billion flies buzzing along the PT ceiling (I use sticky yellow & blue pads now  )

Most of my fruiting crops in the PT/greenhouse are easily pollinated by hand and as I usually need to make at least one if not 2 visits a day for watering and care, it gets done then.  It's also a good way to make sure there is no cross pollination and seed, especially from heirloom varieties, can therefore be saved.