BREDASDORP, South Africa — A scruffy crew of scientists barreled down a dirt road, their two-car caravan kicking up dust. After searching all day for ancient beaches miles inland from the modern shoreline, they were about to give up.

Suddenly, the lead car screeched to a halt. Paul J. Hearty, a geologist from North Carolina, leapt out and seized a white object on the side of the road: a fossilized seashell. He beamed. In minutes, the team had collected dozens more.

A new method for monitoring the decline in bee populations may prove a useful tool in much-needed conservation efforts. It requires only a few hundred pan traps: bright shallow bowls partly filled with soapy water or propylene glycol.

When United Nations experts noticed that crop production was flagging in seven countries around the world, from Brazil to Nepal, they contacted Gretchen LeBuhn, an associate professor at San Francisco State University who studies bees.