We have to worry about West Nile disease carried by mosquitoes, but I don't worry about the dang bugs breeding in my mulch. With temps in the high 90s to low 100s for months at a time in an arid climate (during the summer), the surface of the mulch seems to dry out very quickly and does not seem to be a breeding ground.
I do have to check other sources of standing water, like the bird bath, cat watering bowl, etc., but I have never worried about the mulch because the surface moisture evaporates so quickly. Even in non-drought years, I need it to maintain an even soil temperature around the plants and to maintain moisture in the soil.
Smiles,
Lyn
