The future of bees may depend on understanding their past. Bees are in trouble. Honeybee colonies in the United States have suffered devastating losses in recent years. But colony collapse disorder, as it’s called, affects only the species kept in beehives, the European honeybee, Apis mellifera. There are almost 20,000 species of wild bees, and they aren’t faring well, either.

Nearly a third of bumblebee species in the United States are declining. In the Netherlands, more than half of the country’s 357 species of wild bees are endangered. Many species of plants, including crops, depend on wild bees to spread their pollen. When they lose their pollinators, they may suffer, too.

“It’s essential to know what is causing those declines,” said Jeroen Scheper, a graduate student at Alterra, a research institution at Wageningen University in the Netherlands.

But it is not enough to consider the many challenges, from pesticides to parasites that wild bees face right now. “We need to go back in time,” said Mr. Scheper.

As it turned out, the fate of the bees often was tied to that of the plants they depended on. The growing intensity of farming in the Netherlands since the 1950s hit many wild plant species hard. “There were a lot more flowers in the landscape before,” said Mr. Scheper.

Dutch farmers cleared more land, used more toxic herbicides, and blanketed their farms with fertilizers.

Some wild plants were able to survive these challenges, but others became scarce. Mr. Scheper and his colleagues found that the bees that preferred declining plants also declined.

This link held true even for bees that collect pollen from dozens of plant species. The results suggest that without the preferred kind of pollen, the bee larvae suffered.

Mr. Scheper and his colleagues also found that big bees were at greater risk than small ones. He suspects that is because big bees need to eat more. If the plants they depend on get harder to find, they are more likely to suffer than smaller bees.