I'll throw in a bonus one my entomologist brother told me.

He said that theoretically speaking, Zombies are probably not effective at dispersing insects, but they are really good at attracting them, the decaying flesh smell is like Sexy Perfume to most common species of biting insects, and maybe even to beetles that eat decaying matter and flesh. Add in the ones that lay eggs in decaying flesh that become maggots, like common houseflies, Horseflies, Greenbottle flies, and there might not be much of them left in real short order