I generally agree with Wright, but it also depends.

Flooding can wash away insects, particularly when they are in an active, vulnerable stage. When you see stream sections where the rocks have been scoured clean, you can bet that many of the clinger mayflies, cased caddis, etc. have been scoured away as well. These insects will be down in numbers for a while, but the flood doesn't get them all so they bounce back. In fact, flooding may clear out silt and create more insect habitat in the longer run. I think a lot of this depends on when the flooding occurs relative to the insect life cycle.

My impression is burrowing type flies -- some mayflies, crane flies, midges -- are generally less effected by flooding.

Also depending on where you're at and the time of year, flooding can wash high levels of farm chemicals or manure into the streams which can be toxic for insects as well.