Your little boy is so cute! Anyhow... this sounds like you need to "desensitize" your son to flying insects. The way to do that is as follows.
1. prepare him in advance (before you go outside, remind him that there's bugs out there and he's a lot bigger than they are... and the bugs can't hurt him.
2. go outside and look for bugs (may need to keep this very short at the beginning.)
3. when back inside, review what happened. practice relaxing, etc.

maybe if you played like cooties with him too and explained they were just bugs or found a bug app on the iphone and i had another thought... hatch butterflies... you can usually find this at a science store and get catapillers and grow butterflies... that way he can see how pretty they are and have fun taking care of them

My son went through that phase too. It was short lived. Try having him watch the movie Bugs or The Bee movie. If he can like bugs, he will stop being afraid of them. Also, try a cute stuff animal of a bug too!

My older neurotypical son had a fear of flying insects so don't feel discouraged its not really just limited to autism. Be calming and reassuring

Thank you, Jill! I will try it!