I need a scapegoat for the weather, and you're it, sister. Sorry.
Bugs. I have lived in 10 states (including TX, LA, VA, and MD) and visited all but two states (VT and NH), and I can unequivocally state that Alaska has the worst mosquito population of any of them. That being said, I wouldn't think you'll have any issues on board, certainly not while sailing. Now, at any given port if you get off the ship, you may encounter some, though generally they aren't bad in town or city streets. Now, if you plan any excursions that take you outside city limits into more natural areas, then I'd wear repellent. Unless you enter an area likely to have swarms of them--bogs, wet zones, etc.--you should be okay. However, I suspect the actual vendors or companies running the excursions would be prepared for anything you face. If you only get off to walk around, say, Juneau, I don't think you'll have any issues. Once again, however, it wouldn't hurt to take some repellent and use a little of it.
Here are a few examples regarding my suggestions above. If I walked around Anchorage during the summer, I rarely noticed any. Same with the smaller town center of Eagle River about 10 minutes outside of Anchorage. I lived in a subdivision that was less than a five-minute drive from the Eagle River town center, but when I mowed, I made sure to wear repellent as the mosquitoes were noticeable. About three miles from my house in the other direction is the Eagle River Nature Center where you can hike among other things. Around the small lake there, the mosquitoes could be dense. By and large, I don't believe you'll have an issue as, obviously, all the ports of call are on the water, and the prevailing breezes and suburban nature of the towns will push most of those biters farther inland. As for other bugs, no. The cold weather does a number on most of them, so you won't see much else I wouldn't think. Keep in mind, that on any given day, you might also need to be long pants and a jacket, so that will help, too.
