Generally it is the landlord’s responsibility to take care of any pest problem in a rental unit. However, if it’s clear that the problem was caused due to the tenant’s neglect, such as not removing garbage, it would not be unreasonable to ask them to pay for the cost of the extermination or at least splitting the costs with you.
Generally landlords are responsible to take care of any pest problem in a rental unit and it seems that you have done so in this case. However, the law does not state specifically whether you are responsible for anything else. It would be up to the Board to decide if the tenant is entitled to any further compensation. If the tenant has deducted amounts from the rent you can serve them with a notice of non-payment of rent for the amounts that you stated, in this case you will have to use the Form N4.