> I have been strongly suggesting to my contacts at EPA, 
> as well as to beekeeping leadership, that we shift our 
> focus with insecticide adverse effects away from honey 
> bees (managed livestock) to "pollinators" in general.

I don't think we (as an industry) have enough hands-on experience to be able
to judge the "success" of a solitary bee population, at least not East of
the Rockies.

TL;DR: It is difficult to keep even moderate populations of solitary bees
viable for more than a few years at a go.  What part of "solitary" is
unclear?  :)

It is difficult to successfully keep and manage a statistically significant
population of solitary bees over several generations.
We simply do not have enough husbandry technology or expertise to maintain
breeding populations of solitary bees for more than 3 or 4 years at a
stretch.
Also, the highly localized nature of solitary bee forage means that even
something simple like a lack of a reliable water source within the few acres
a solitary bee might explore can prove fatal.
We can provide water (and mud for mason bees) and we can otherwise provide
an "optimal environment", and STILL see populations collapse.
There is not a single location that I know of where introduced and "managed"
solitary bees have thrived without periodic reintroduction of cocoons from
elsewhere to essentially replace a collapsed population.

While west-of-the-Rockies solitary bees seem to have less frequent
collapses, be aware that east of the Rockies, even populations of 100 tubes
in a coffee can is simply "too dense" a congregation of bees to be a
sustainable community over multiple seasons.  What I've learned the hard way
is that no more than 11 7mm tubes in a 2.5-inch PVC tube with a test cap on
the back is about as "dense" a population as one can expect to avoid the
sweeping fungi that wipe out populations even if one changes paper liners
religiously, protects tubes from parasitic wasps with screen  mesh from in
mid-summer onward, and individually candles each cocoon to cull any infested
cocoons prior to spring deployment.

A dozen or so tubes is a fine pollinator for a small garden, but my dream of
driving nothing but a Volvo wagon full of coolers full of nothing heavier
than tubes of Osmia to pollinate apples never came to fruition.  Every time
I got up to about 1000 tubes, the population would collapse from one or
another still-undefined malady.  An effective pollination force for an apple
orchard simply cannot result from mounting a dozen tubes in each tree,
because you'd never finish deploying before the king bloom was done.  But
"coffee-can loads" of tubes are simply too dense a population unit, and
anything less than about 2 dozen tubes per set of 5 or 6 apple trees does
not get the work done.

But what can one expect from a field where the best guide to practical
husbandry is still the writings of Henri Fabre from 1914?

I find bumblebees to be MUCH easier to keep alive and happy, but bumbles
start over from zero each spring, so you can't even know if the current
queen is the progeny of the bees that occupied a nest box in the prior
season.  And bumbles don't like apple trees so much, so they are my "just
for fun" bees, I've never tried to put them to work.

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