I always do any of my spraying just after nightfall. This assures me that the bees are all safely in their hives.
I know that there are a ton of beneficial insects in the evenings, and they too would be at risk of spraying, but nothing as devastating as losing our bee population.
What is it you are spraying? What is the insect problem that is hitting your trees?
I use red ball traps for bugs rather than spray. Seems to work fine, and a lot easier on my back than hauling around a sprayer full of liquid. And then I spray dormant oil twice after the leaves die back in winter--lots of those type of bugs overwinter in the tree bark or buds, so spraying dormant oil in winter smothers them to death.