Where have all the bees gone?

That's the question a lot of people have been asking lately, and with good reason -- researchers say up to one-third of all the honeybees in the United States have vanished. And no one knows why exactly.

Scientists are scrambling to explain the sudden, mysterious die-off of honeybee hives -- something they've named "Colony Collapse Disorder" -- before it gets worse.

Before you roll your eyes and say to yourselves, "Ok, another science story," think about this: experts say honeybees are responsible for one-third of all the food we eat; and according to the U.S. Dept. of Agriculture, they add $15 billion to the bottom line of the agriculture industry.

These bees are like tiny workhorses. Without them flying around, pollinating millions of flowers each spring, we wouldn't have a very interesting or a very balanced diet. No apples, peaches, blueberries, cucumbers or almonds -- just some of the 90 crops dependent on honeybees for pollination, according to entomologists we spoke to. Also, beef and dairy cattle require alfalfa in their diet. Guess who is responsible for that? Yep. The honeybee. Chew on that the next time you sit down for a steak dinner.

For tonight's program, Randi Kaye and I traveled to Lewisburg, Pennsylvania, to meet the man who first sounded the alarm about the mystery and pressured the government to investigate. In the course of two months, he says he lost some 80 million bees -- 2,000 of his hives. And he's not alone. Beekeepers in more than 25 states and Canadian provinces are reporting major losses, too.

We'll take you inside the USDA Bee Laboratory in Beltsville, Maryland, and Penn State University to follow scientists who are using forensics -- just like homicide detectives -- to get to the bottom of these billions of deaths. They are performing bee autopsies and DNA work.

Think of it as CSI: Honeybee.

So then, what is killing the honeybees? Despite some pretty far-fetched theories (cell phone radiation, a bee "rapture," an Osama bin Laden plot), researchers are looking at a combination of a relatively new insecticide along with an increase in bee viruses. It's a one-two punch that weakens the bees' immune systems and leaves them susceptible to pathogens. They expect to announce preliminary findings in the next few weeks.

And while some of the affected hives seem to be improving, experts at the USDA say that is because there is more food available for the bees during the warm spring. They warn it's still too early to tell whether America's honeybees can overcome this mysterious disorder.