1) If you believe you can show, such as with the testimony and/or reports of an exterminator(s) you hire, that your neighbor's actions caused your infestation, you could sue him for any costs or damaged/destroyed goods you thereby suffered. Suing may be a disincentive to doing this again.2) If you think he is violating any city health or building codes in how he keeps his property, in how he exterminates it, etc., you could contact the relevant municipal department (e.g. of health; of buildings) to file a complaint.