Actually, Scilla is not grape hyacinth; one common name of Scilla sibirica is
"squill", and the garden variety most often seen has a few, true BLUE
lily-type flowers with separated tepals.  Grape hyacinth is in the genus
Muscari, most likely M. botryoides, and has a compact raceme of numerous,
smaller flowers with tubular/globular perianths.  The common "blue" variety
is distinctly purplish in comparison to squill flowers.
     Both of these have been blooming on Long Island for ca. 10 days.
On the question of Osmia diseases and enemies--I heard a talk at last summer's
meetings on Non-Apis pollination (at Logan, UT) by N. Sekita about the use of
O. cornifrons for apple pollination.  He dwelt on mite control; possibly his
group may have some useful information.  (Aomori Apple Expt. Station,
Kuroishi, Japan is all the address I have.)