We visit the Fort almost every October, and have never had a problem with bugs.
In fact, I can't recall any visit, any time of year, when there has been a problem with bugs.
I think they do a lot of pest control around the Fort.
We live in Florida, and have been to some places where the mosquitoes literally attack you. I remember one trip, in particular, where I must have had twenty mosquitoes on me within the first sixty seconds of getting out of the car (and that was in September at Rainbow River State Park) But, we don't even bother with bug spray at WDW.
TCD