Honeybees acquire pesticides as they collect pollen from non-crop plants, a new study finds.

Even honeybees that live in agricultural regions get most of their pollen from non-crop plants. Avoiding commercial crops isn't sparing bees from potentially harmful pesticides.

Researchers at Purdue University tracked the pollen sources and pesticide levels of honeybees over the course of 16 weeks. Samples taken from their hives revealed pollen foraged from 30 plant families. The samples contained residues of pesticides from nine chemical classes, including neonicotinoids -- a pesticide implicated in colony collapse disorder.

"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," Christian Krupke, professor of entomology, said in a news release. "The sheer numbers of pesticides we found in pollen samples were astonishing."

"Agricultural chemicals are only part of the problem," Krupke added. "Homeowners and urban landscapes are big contributors, even when hives are directly adjacent to crop fields."

In addition to neonicotinoids, researchers found significant traces of pyrethroids, an insecticide commonly used by homeowners to battle wasps, mosquitos and other nuisance pests.

Increasingly, studies point to a combination of disease, pesticides and habitat fragmentation as the reason for the continued decline in honeybee numbers.

The latest research, published this week in the Nature Communications, suggests pesticide exposure is a more widespread and varied problem than originally thought.

"These findings really illustrate how honeybees are chronically exposed to numerous pesticides throughout the season, making pesticides an important long-term stress factor for bees," researcher Elizabeth Long said.