I work on a crop- cranberries, which requires honey bees for pollination.
One problem we have is that farmers have to spray for fireworm when the bees
are still being used. Most farmers wait until the bees are gone until they
spray, others spray at night. By the next day their  doesn't usally appear
to be too much effect on the bees. I am evaluating the merits of various
insecticides that are labelled on cranberries for their abiltiy to kill
fireworm yet have no effect on the bees.  One of the big problems are that
the insecticides are usally put out throught the irrigation system - ie high
volume 500-1000gpa.  This tends to reduce efficacy.
 
My questions are these -
 
Does anyone have data/experience that sublethal doses of an insecticide like
guthion will dramatically reduce pollen collection by bee for long periods
following spraying?
 
Does anyone have experience with trying to reduce bee poisoning by
irrigating the spray off in  the morning, following an evening spray?
 
Does anyone have experience with sevin XLR - it is suppose to be fairly safe
if it can dry on the leaf surface. What about if it gets rewetted after
spraying by irrigation? Is it now more toxic than before?