In field tests, researchers at Pennsylvania State University found a class of herbicides called dicamba regularly drift onto plants in neighboring fields, affecting both the plants and pollinators.

Pesticides don't work forever. Insects and weeds adapt. And when they do, commercial farmers escalate the fight -- often spraying heavier loads of chemicals and opting for even stronger concentrations. Along the way, innocent bystanders -- or vital components of the natural cycles -- pay a price.

Genetically modified plants encourage escalation by designing plants to withstand a stronger and stronger barrage of herbicides.

"The expected high rate of adoption of the new transgenic crops will increase dicamba and 2,4-D use by four to eight times," John Tooker, an associate professor of entomology at Penn State, explained in a press release. "Our results suggest that widespread non-target damage from these herbicides may adversely affect pollinator communities."

When Tooker and his colleagues watched what happened to alfalfa (Medicago sativa) and common boneset (Eupatorium perfoliatum) when subjected to sub-lethal levels of dicamba, they found a number of negative consequences.

Both plants exhibited delayed flowering and put out fewer flowers, producing lesser quality pollen. As a result, fewer pollinators were observed visiting the two species' flowers.

"We found that both plant species are susceptible to very low rates of dicamba -- just 0.1 to 1 percent of the expected field application rate can negatively influence flowering," said Tooker. "By extension, we expect that other broadleaf plant species are similarly susceptible to this sort of damage from drift-level doses."

As transgenic crops become increasingly common in the corn belt, researchers expect farmers to spray their fields later and later in the season, when more nearby plants will be fully mature and more susceptible to herbicide drift.

"This will lead to higher levels of non-target damage to susceptible crop plants and native, wild vegetation," said David Mortensen, a professor of weed and applied plant ecology at Penn State. "For susceptible crop varieties, this sort of damage could reduce yield. For non-crop plant species, this drift-induced damage could significantly decrease the pollinator and natural enemy communities that these plants can support."