I agree with you almost entirely but I would like to point out if the building has a history of infestation unrelated to a particular tenant, then the tenant shouldn't have to foot that bill. So long as they're not breeding ant colonies with a bag of sugar, then any infestation that existed prior to their lease shouldn't be their problem. I suppose it wouldn't be wrong to charge them anyways, but I think it wouldn't help to build a good relationship between the tenant and the landlord.
Legally these things fall on the responsibility of the landlord. Even if you try to play it any other way, it's going to be damn hard to have any definite proof that it's the tenants lifestyle that has caused the infestation. But if I would have a tenant like this he would be gone from the apartment in a heartbeat.
It is a wise policy to break off these things before they get worse. That said, it's nice to have a backup plan in case you get into a situation where it spiraled out of control before you ever learned of the situation. And nicer to be friends with the Terminix guy.
Sadly in many urban area things like pests and vermin are part of the package. It is the landlords responsibility to perform regular maintenance functions that will make the chance of investigation less. This includes extermination when necessary and reasonable availability of items that will decrease the chances of infestation, for example locking lids on garbage cans, regular cleaning of cans, removal of debris from the property, repair of holes in property and so on. Whether the place is empty, leased or sub-leased it is still up to the owner to keep it secured. I am not going to go into the whole hoarder debate because that is an entire different issue, as an owner there are limitations on what you can and cannot do with a tenant, If you feel like it is the renters fault you should get legal advice and if possible start eviction.
It is always the tenant who has the duty to keep the property in a tenable state. With that said, you will always find that a contract has a forfeiture clause, which means that a landlord may request the tenant to surrender his lease and thereby extinguish any other sub-lease(s) for failure to keep the contract's provisions. Simple reaons for forfeiture of a lease agreement would be; 1) for failing to pay rent. 2) for an act of malicious destruction of the property and 3) for not keeping the terms of the contract. So, there you have it. If a tenant is being nasty, simply end the lease agreement in writing, make sure you have you copy and make sure that you have evidence that you have served the notice to quit.
I don't think that subleasing the apartment is legal considering it doesn't belong to him. That should be in the contract, the lease is for someone to live there, not to sublease it and make a profit.
I do think the landlord has a responsibility to make sure that there are no pests or bugs on the property he is leasing for before a tenant comes in. The tenant on the other hand has the responsibility to maintain the original pest-free state of the place. Now, if after a period of time and the property gets infested because of the tenant's unhygienic measures then it would be his/her responsibility to get rid of those pests. A well written rules of agreement should be prepared by the landlord before accepting any tenant though. Just to make sure that everything is well documented and understood by both parties. Regarding sub-tenants, I think it's absolutely rude for a tenant to do such a thing without even informing his/her landlord. The landlord has the right to evict a tenant that way, right?
Over here, subletting is illegal unless it has the explicit permission of the landlord. But I know there are tenants doing that in a sly fashion - introducing the boarder as their relative so the landlord would not suspect anything. When it comes to hygiene, most landlords are strict on that matter. Pests like cockroaches are easy to eradicate including rats and mice. But the landlord is more concerned with the dirt especially with the dirty living room not to mention the toilets. I think those issues can be a reason for ejectment of the tenant.
