July, in general, is the worse time for mosquitoes in the Sierras. These head nets are very good, lightweight, and inexpensive. I'm getting one this year because I'm tired of getting eaten alive.
However, it also depends on the year. If it's been a big snow year then there will more mosquitoes and there are several places which may still be snowed in. I've hiked in 5 feet of snow at 6500 feet elevation on Father's day in late June. I've had to turn the car around up near Sierra City because road access to the trail was still under 3 feet of snow on the 4th of July. I've even been unable to drive the dirt back roads as late as early August due to heavy snow coverage.
More snow = more bugs. So it's really going to depend on how much snow we get this year. I'd like to go in September when the weather is wonderful and the bugs will be less of a problem. It may still be useful to carry a bug net in September. By late September I don't need a bug net even when I sleep.
However, right around late August we go on fire restrictions which would disallow the use of wood burning stoves like the Element or Caldera Cone. So that means bringing fuel for the whole trip.
Also, I'm hearing that bear canisters are absolutely needed up there. I've seen black bears in the town of South Lake Tahoe so that makes sense.
Overall, July will be buggy, but not overwhelmingly so. If you can get 50 yards away from lakes or marshes you'll notice that it's vastly better