Scientists also found pesticide exposure caused changes in expression of genes that are sensitive to diet and nutrition.
"Honey bees are exposed to hundreds of pesticides while they are foraging on flowers, and also when beekeepers apply chemicals to control bee pests," said Center for Pollinator Research at Penn State University director Christina Grozinger.
"Our study demonstrates that exposure to non-lethal doses of at least two of these pesticides causes large changes in the expression of genes involved in detoxification, immunity and nutrition-sensing.
"This is consistent with results from previous studies that have found that pesticide exposure compromises bees' immune systems. Furthermore, our study reveals a strong link, at the molecular level, between nutrition, diet and pesticide exposure."
Exploring this link further, the researchers found that diet significantly impacted how long bees could survive when given lethal doses of a pesticide
To determine the impact of pesticide exposure on gene expression patterns in honey bees, the scientists first fed one of two miticides - coumaphos or fluvalinate, the two most abundant and frequently detected pesticides in the hive - to bees for a period of seven days.
On the seventh day, the researchers extracted Ribonucleic acid (RNA) from the bees, attached a fluorescent marker to the RNA and examined differences in gene expression patterns between the pesticide-treated bees and the control bees.
The researchers found significant changes in the RNA among the bees that were fed either of the two miticides compared to the control group.
"This is the first time such a strong link between pesticide exposure and diet has been demonstrated at the molecular level, and the first time the effects of artificial versus natural diets have been explored in terms of resistance to pesticides," Grozinger said.
"Diet and nutrition can greatly impact the ability of bees to resist pesticides, and likely other stressors. However, agriculture and urbanization have reduced the amounts and diversity of flowering plants available to bees, which likely nutritionally stresses them and makes them more sensitive to these other stressors.
"If we can figure out which diets and which flowering plants are nutritionally optimal for honey bees, we can help bees help themselves."
Other authors on the paper include U.S. Department of Agriculture (USDA), Penn State professor emeritus James Frazier, and University of Florida postdoctoral researcher Daniel Schmehl.
The results will appear in the online issue of the Journal of Insect Physiology.
Photo: Daniel Schmehl/University of Florida, via Flickr Creative Commons