I have not seen the question raised yet but:
Homo sapiens has added genetic insecticidal info into a variety of crops. It has been noted that lacewings (neuropterans) disappear from areas adjacent to GMO soybean acreage. It may be a longshot, but has anyone asked the question " Could we be experiencing the same thing with bees? GMO Bt is now in corn and other crops. Some dipteran species (mosquitoes, etc.) are sensitive. Might hymenopterans also have some sensitivity?
To my academic friends, don't dismiss this question unless you can provide peer review statistics, please.