Donald,
Have to disagree with your comments regarding evolution!
A mite or anything else that undergoes any change in its genetic base,
causing a change in metabolic pathways - has moved along the path of
evolution, even though it may not show external changes

"Resistance" is a possible measure of fitness of the organism to the
environment it finds its self.
This may result in an advantage, resulting in stability in its niche.
If the same change puts the organism at a disadvantage, then it suffers
and the property would not usually be termed "resistance".

Peter