The problem with DE (diataenous earth) is that it is inert; that is, if the
larva manage to get by the DE, or if you miss a spot, your treatment has
failed. What I think might be a better idea is a treatment that actively
searches for and destroys the SHB pupa, and for that bio-control, or
beneficial nematodes might fit the bill.
    The nematodes are voracious parasites of soil-dwelling insects, and
especially target those in their larval and pupal stages. The nematodes have
not yet been scientifically tested against the SHB, but they have proven
deadly to nearly all other agricultural beetle pests that live the pupal or
larval stages of their lives in the soil. They are sold commercially in
Europe and the North America. The nematodes probably aren't going to be a
threat to your bees unless you spray them in the hives on the brood.
Good choices that I am considering include:
    Heterorhabitis heliothdis, a nematode that works in the top 6 inches of
soil (SHB pupae inhabit the top 4 inches), can be purchased from a company
called Hydro Gardens in Colorado Springs, CO under the commercial name Lawn
Patrol. This one can penetrate soft tissue directly, and doesn't need a body
opening to infect its victims.
    Heterorhabditis megidis, a nematode that releases a symbiotic bacteria in
the gut of infected larva, is available from Bunting Biologicals in England
(commercial names Nemasys-H, Bio Nem HI)
    Neoaplectana carposcapsae, a cold-resistant strain of nematode that can
survive temperatures of -20F. Available from a company called Biologic in
Chambersburg, PA under the commercial names Scanmask, or Ecomask. First
collected near the Arctic Circle in Sweden.
    Another good source, I am told, for beneficial nematodes is a company
called M&R Durango in Bayfield, CO.
    I was appalled to read of beekeepers using insecticidal soil drenches in
Florida in the recent ABJ. Isn't Coumaphous enough? Lacking a surefire magic
bullet that will take out the SHB once and for all, a good IPM strategy
should include organic and biological controls too, where possible.