The yellow precession is not indicating teeth. However that is not to say insects are not involved because they are a major vector for bacteria and viruses to enter a plant. However, once bitten, the plant become infected and the sequence of stopping the insect and then curing the plant of either a bacteria or virus becomes a problem. It could be fungal for all I can tell. A bug bite would explain the starting spots, but not the yellow ring ahead of the dead border which is obviously inside the cells of the leaf and appear to be causing cellular collapse. There are many similiar looking possibilities.
I would think using scissor sterilized between cuts with clorox water could be used to remove infected parts to the garbage. A few tablespoons of sulfur in a gallon of water as a spray or a spray of chlorothalonil or serenade would help if it is fungal. Actinovate or Mycostop maybe be best if it is bacterial.
Having said all that, most plants will swap leaves sometime if not annually. They hit the end of their particular cycle and go away. I sure wish I knew its name.
