Spray it around your home and you’re bug free for a year, how?
In: Chemistry
They use a persistent insecticide poison.
Many chemical compounds are long-term stable, even outdoors. Unless the area is thoroughly washed they will persist and keep killing insects for a long time.
Depends on the pesticides, you’d have to read how that particular pesticide works. But in general, pesticides that claim they only need one application every few months have a long residual.
The chemical remains on the surface, and either acts as a repellent, or makes the chemical will stick to the bug as it walks over it and it will die.
Think of it as acid being thrown at you every time you try enter a restricted area. This but at a bug scale