I have the same problem. And when we had a heat wave the mosquitos really went nuts. I mix lotion with mint oil and lavender oil (and citronella now as well) and use that to minimize the bites.
For 36 chickens, you're very low on ventilation as far as I can see, especially if windows aren't being left open. Ideally you'd want at least 1 sq ft of ventilation per chicken, mostly up high, but not sure how difficult it would be to hit that mark.
Against bears, electric is your best bet -...