It's difficult to say really, I suppose the peak midge season is late June to the end of August, depending on the weather. I don't take much notice of midges because they rarely bother me.
The best repellant is my husband, whilst they are making a meal out of him, they leave me alone.
Otherwise, Skin So Soft by Avon, is far better than any of the citronella based products and less unpleasant smelling.
As far as any of the other beasties go, you just can't tell beforehand how you will react. For instance I had about 10 cleg bites this summer, I reacted really badly to two, hardly at all to the others, Clegs seem to be at their worst from mid July for about a month.
I took a couple of ticks off my dog in February this year, I'd consider them an almost all year round problem. The best advice for ticks is to wear your trousers tucked into your socks, or wear gaiters, especially if you are going to walk through heather or bracken, and check yourself at the end of the day.
If you do find a tick has bitten, remove it with tweezers, or better still a tick removal hook, which you can get from a Vets. Do NOT use any of the patent remedies such as covering it with vaseline, alcohol or a lit ciggie, all that does is make the tick vomit it's contents into whatever it is biting, so if it is carrying Lyme disease, there's probably more of the disease then going to get into you.
My Mother swears by TCP ointment, dabbed on to any insect bite, as soon as possible after the bite. I can't stand the smell of the stuff, but use a sting relief cream, when I remember to carry it.