A friend lived in an apartment for 14 months. The apartment was a room in someone's residence, and it was one of four rooms. There was no printed/signed lease, only a verbal agreement. Over the course of the stay, it became apparent that bedbugs had been a problem before he moved in, and persisted till he moved out. The landlord lives in the house too, so it was to his credit that he tried to remediate this problem three times during my friend's stay, and paid for the treatments. My friend brought no furniture into the apartment. The landlord actually replaced the bed prior to him moving in.

However, during that time, there was significant damage to my friends possessions due to the infestation. Bedbugs were found in storage containers under the bed and their contents were destroyed. Also, part of the Landlord's remediation process included discarding infested property.

I understand that the landlord is responsible for remediation, and though ineffective, he did make the effort. But who is responsible for the damage to personal possessions?

This is a Small Claims court case. A lot will depend on the resistance of the landlord, who will have some leverage since there was no written agreement or lease. Some will depend on your friend's proof of the value of the items lost, how long it's been, and why they were lost, and so on. Small Claims cases are quick and sometimes arbitrarily decided by the judge. The judge might wonder why he didn't move out after the first treatment didn't work, or even as soon as the bugs were evident to him.

Your friend might want to start by sending a bill to the landlord who could possibly see if his HO insurance covers it, and take it from there.