Diets are highly species specific, but mosquitos are generally less than 3% of the diet for most birds and bats. Too small, don't fly around at the correct time of day/night, and pretty agile, so they aren't supper important for most birds and bats.

Also, usually they hatch in the billions all at once and die within a few weeks so there's a very limited amount of time that they even can be preyed on as food. Their strategy (many of them, not all species) is to overwhelm any predators with numbers.

Statistics on bug food????? For birds and plants??? Do you want the whole thing dumped here in the comments? Or do you mean "do birds eat insects"? Yes. A lot.