When I was there in early April, there were actually a few mosquitos to deal with. I used bug spray one of the nights. Its still been pretty cool, but the rain has mostly gone away. Mosquitos would be localized to areas with standing water for the most part, so you won't need it the entire time.
It really depends on your bug tolerance. I have none and get eaten up pretty bad when they are around, so I always bring some. The other guy on my trip was not bothered by them.