Any kind of annoying pest really, but I chose arthropods because I hate them. And someone else hates them too. Let's say he's some sort of well-intentioned but reckless mad scientist who really needs to think his plans through better. He releases a lab-engineered genophage (probably made using CRISPR) that targets and sterilizes all species of a certain pest or virulent/invasive species. No other animals are affected, but within ten years, the genophage will have spread across the globe and those species will probably all go extinct within twenty years.
What kind of fallout are we looking at here? What kind of consequences would suddenly wiping out an entire family or clade of pest species have on the environment and the rest of the global ecosystem?