As the article explains fairly well, this technique targets a gene that, if it mutates, causes that mosquito to be sterile. So when it happens de novo, you have

As the article explains fairly well, this technique targets a gene that, if it mutates, causes that mosquito to be sterile. So when it happens de novo, you have a sterile mosquito that is simply not going to pass its genes along. Since this technique leaves the male mosquitos alone, it will spread as they mate with unaffected females (spread as in being transmitted to offspring — it’s not a virus, etc).