Yes, you can depend on the yeatsies on the skin of the pears to start your fermentation. But it could be a low-alc tolerance yeast strain, or one that produces off-flavours. Also maybe the yeast is not strong enough to compete with other micro organisms on the pears and the entire batch may be lost. Still, many people have succesfully used wild yeast and produced fine perry or cider.
I would personally always add a yeast strain suitable for perry or cider. Wine yeasts are no worse than wild yeast and you will not drink any of the yeast anyway. If you do, something has gone wrong in your procedure. Bottling only takes place when your wine is clear as a bell, so there's no yeast in it anymore. If there were, you'd also run the risk of exploding bottles as you could have a restart of fermentation in the bottle.
I know from experience:
http://plot101.wordpress.com/2008/01/14 ... -accident/
Also for about 35 euro's you can purchase a 'sterile' filter which wil remove any stray yeast cells before bottling. So no need to ingest any yeast at all.
Hope this helps.
Jandra
