> Of the leaf cutters that "go native", what are the chances that they
survive in the orchard areas,  presuming that such areas are subjected to
spraying regimes after the removal of dedicated  pollinators?

I do not raise leaf  cutters but mason bees. I do not know if escaped
Alfalfa leaf cutter bees would survive in a area of seed Alfalfa being
sprayed or even if they would nest elsewhere.

I doubt the mason bee  would survive. Even hives of bees suffer and
sometimes die when close to the typical commercial orchard. I do not use
pesticides in my small orchard and there are no large orchards for miles so
my *go native* mason bees  seem to be doing great.

>
> Have populations of Osmia L. increased in the area?

I have always seen Osima L. in our area. Their numbers have  really
increased according to the numbers I have seen last spring in my orchard . I
have got a bee yard about 10 miles away with a abandoned one acre apple
orchard (all young trees). I have seen Osmia L. on the blossoms ever since I
have had the yard. The Osima L. work the blossoms along with honey bees but
fly earlier and even in light rain. Osmia L. (mason bee) uses its whole body
to polinate like the bumble bee. Researchers say one orchard mason bee can
do the same polination of 100 honey bees (USDA , Utah).

Bob