Check that out close, Nicky. I have never heard of it, but that doesn't mean anything.

What Dr. Bliss talks about is the life cycle of the lice. The biting lice and then the eggs that hatch 14 days later. There have been many false claims oncontrolling lice. Cydectin had a claim that it would last for 6 months. It was a false claim and the government made them strike that. It was a good marketing tool, but untrue. I had a friend that was selling it to ranchers, when the claim was pulled, she lost her job.
IGR is for flies. Didn't know it was for lice as well, but lice are easy to kill. I'm going to check into this, simply because I am curious.
Did an online search as I couldn't reach our veterinarian.
Interesting:
http://feedlotmagazine.com/bayer-launches-new-pour-on-insecticide-for-lice-control/
However, Valley Vet description says nothing about it as a one-time treatment.
https://www.valleyvet.com/ct_detail.html?pgguid=e18cad5c-2319-404c-8608-ed104c730889
It seems to cost $1/hd which isn't bad if it truly does take only one application. If not, it is pretty spendy. I don't think the IGR has anything to do with lice; if not, using it in winter would be somewhat of a waste if you are paying for fly control. Just my two cents. I'm going to keep trying our vet and see what he has to say.
Very interesting. Glad you brought this up. I enjoy learning new things.