@Lavender2 I use a 4:1 water to sugar ratio all season, and I don't bother boiling it since I usually have to refill all my feeders three times a day. It is the hot temperature here that makes the syrup mold and turn to vinegar, but when it is consumed that quickly I don't have to worry about it. I have not heard of using 3:1, but they probably like it just as well. In truth I don't measure, I just eyeball the syrup when I make it.
In times of drought I feed my bees 2:1, and 1:1 in the winter (which I have to boil to get the sugar to dissolve) so I know in beekeeping the ratios are subject to change depending on your location and season, so perhaps it's the same with hummingbird syrup, too. I would think when they first arrive they could use an extra boost!
I've heard that after the baby hummingbirds hatch they switch to eating more insects. I don't know if that's to feed the young, or that it's just easier to catch your meal close to the nest when they are sitting on eggs.
As for mosquitoes, we have the world's second largest Mexican Free-tailed bat population here and they pretty much keep those under control. When we sit outside in the evening and insects are attracted to us, the Cave Myotas bats (which are very acrobatic!) swoop down, sometimes brushing our faces with their wings, to eat the mosquitoes before we get bitten. It's a great service, and eventually you get used to it!