The pollen samples represented up to 30 plant families and contained residues from pesticides spanning nine chemical classes. The highest concentrations of pesticides in bee pollen, however, were pyrethroids, which are typically used to control mosquitoes and other nuisance pests. "Although crop pollen was only a minor part of what they collected, bees in our study were exposed to a far wider range of chemicals than we expected," said Krupke. "The sheer numbers of pesticides we found in pollen samples were astonishing. Agricultural chemicals are only part of the problem. Homeowners and urban landscapes are big contributors, even when hives are directly adjacent to crop fields." The samples showed that honeybees collect the overwhelming majority of their pollen from uncultivated plants, particularly the plant family that includes clover and alfalfa. The researchers found 29 pesticides in pollen from the meadow site, 29 pesticides in pollen from the treated cornfield and 31 pesticides in pollen from the untreated cornfield.