Greetings,
Here is an example of what happens to me if I don't treat for mites:

15 good strong colonies were purchased in May from a reputable beekeeper. These were treated in 2000 with Apistan. In 2001 they received no chemicals. Half were put on screened bottoms, half were not.

In August I did ether rolls. The numbers ranged from 2 to 27 (per 250 bees) but most were below 10.  Supers were weighed. Spring honey crop was decent.  No apparent correlation with screened bottoms.

By September, only *four* hives were still normal strength. The rest were weak or very weak and most exhibited signs of advanced mite disease.

The weak ones were all dead within a month and *not one* was strong enough to winter over. The whole apiary was folded.

Moral: I would breed from the best, but they were all dead.

pb