Legal Question in Landlord & Tenant Law in Illinois

Do you have a written lease? It would have to allow an inspection, this kind of maintenance, and if you have to be evacuated for any period of time, to cover that issue. And it should be "reasonable". If it gives the landlord this kind of latitude or some of it, you might have to let him and if you don't then technically the landlord is required to give you an official notice and then proceed with formal eviction.

If you're able to communicate with him, you could ask him to point out in the lease where it says so. If you live in an apartment building the only way to effectively deal with vermin is to do a complete job -- if your apartment isn't included vermin are pretty smart and could simply "escape" to your place until the fumes dissipate..... If you do not have a written lease, you need to see if you live in a community where there is a landlord-tenant ordinance that may provide some rights. But the bottom line is that today most landlords are required to act "reasonably" and that would include exposing you to no undue harm.

Today most exterminators are not allowed to use the kind of "poisons" you seem to be concerned about. If you expressed your concern to your landlord fine, if not you should do so and explain you just want to make sure what is happening. Once you know what will be applied, you could even call a poison hotline, or check with your community's agencies to verify whether the application is acceptable and what precautions you also need to take. I assume you don't want to live in an apartment with vermin, and the landlord may in fact be under some kind of official order to exterminate (although that too is something he should have shared with you if it is the case).

As to arrested, that's over the top and sounds more like someone who is not sophisticated, or frustrated because he needs to bomb out the building, or maybe even a bully. Even if your lease allowed an inspection, a simple breach of lease is generally not a criminal matter in most places (but that may not stop the landlord from attempting to call the police).