If it's a copy of the same thing then any measure that works against one would work against all. Other ways of reproduction add randomness and mutations which make it difficult
Modulo any environmental or self-mutation factors, I suppose? Might be that a tick which sucks blood from deer with XYZ picks up a parasite or bacteria which protects it against your measure. Or one crawls through some chemical goop / radioactive slop / gets hit by a cosmic ray etc. and gets a mutation which helps.
(Both fairly unlikely, I'll grant, but when you're dealing with millions or billions of ticks, unlikely is likely to happen a lot.)