it's like the bees can't find their way back home. >> reporter: it's a mystery that has puzzled people. like a bee pocalypse. scientists say another big loss this year could devastate the american food supply. fewer bees means fewer pollen nators for plants to produce their fruit. that could mean fewer broccoli, celery, even avocadoes. >> all the fruits, nuts, vegetables that enrich our diet, those are the things that are at risk. >> reporter: jeff pettis is the government's researcher. >> how good is this colony? >> it's good, but not great. >> reporter: he's found plenty of clues from viruses and disease but no smoking gun. >> what can each of us do to be more bee friendly and help this