I have read before that elector PSP kills nits so just wondering if those eggs are dead now or if I should treat again. I just don’t want to introduce them to my existing flock if they still have lice.
Thanks so much!
I think that's a great question actually!
If that's what it says they probably are dead. They won't just disappear or fall off suddenly, in my experience they are glued on. Just because the lice are gone (presuming) doesn't mean an itch is not there. My dogs itch sometimes despite not having flees. Plus some mites (depluming and scaly leg) are microscopic and will never be seen but only their symptoms.. Point being there could be more to the story.. Not sure if PSP is effective against either of those, topical permethrin is NOT.
Treat according to directions. If it says treat again after a certain period then do it. If not, I would not worry about it... unless you are unsure if you treated correctly the first time. Then go with your gut.
Honestly, lice is the least of things to worry about when introducing birds from other flocks.

Marek's, New Castle's, Mycoplasma, Infectious Bronchitis, internal parasites, etc. You currently are treating what you can see and easily get rid of (good job BTW), not what you can't that MIGHT effect your flock forever. Some things take not less than 3 weeks or even longer before they ever show symptoms, so the previous home might not even know about it or seen it yet.
Hope this is helpful, and that everything goes well for you and your flock!
