Hi Ed,
 
Some feeders have the internal level of nectar that come very close to
the feeding holes, making it possible for bees and wasps to reach the
liquid. Maybe you should look for the models where the feeding opening
is the highest in relation to the opening of the bottle that holds the
nectar when the feeder is mounted. Hope this makes sense to you.
Or else you could try to install short pieces of plastic tubing over the
feeding holes so that the insects tongue can not reach the nectar.
 
Philippe
Carillon, PQ.