Many factors at play in bee decline

Many factors at play in bee decline

THE U.S. Department of Agriculture and the Environmental Protection Agency have released a comprehensive scientific report on honeybee health.

According to the report, which was released May 2, there are multiple factors playing a role in honeybee colony declines, including parasites and disease, genetics, poor nutrition and pesticide exposure.

In October 2012, a National Stakeholders Conference on Honey Bee Health, led by federal researchers and managers, along with Pennsylvania State University, was convened to review the current knowledge regarding managed bee health.

"There is an important link between the health of American agriculture and the health of our honeybees for our country's long-term agricultural productivity," deputy agriculture secretary Kathleen Merrigan said.

"The forces impacting honeybee health are complex, and USDA, our research partners and key stakeholders will be engaged in addressing this challenge," she noted.

Acting EPA Administrator Bob Perciasepe added, "The decline in honeybee health is a complex problem caused by a combination of stressors, and at EPA, we are committed to continuing our work with USDA, researchers, beekeepers, growers and the public to address this challenge."

The USDA/EPA consensus report is available at www.usda.gov/documents/ReportHoneyBeeHealth.pdf.

Key findings of the report include:

* The parasitic varroa mite is recognized as the major factor underlying colony loss in the U.S. and other countries. There is widespread resistance to the chemicals beekeepers use to control mites within the hive. New virus species have been found in the U.S., and several of these have been associated with colony collapse disorder (CCD).

* U.S. honeybee colonies need increased genetic diversity. Genetic variation improves bees thermoregulation (the ability to keep body temperature steady even if the surrounding environment is different), disease resistance and worker productivity.

* Honeybee breeding should emphasize traits such as hygienic behavior that confer improved resistance to varroa mites and diseases (such as American foulbrood).

* Nutrition has a major effect on individual bee and colony longevity. A nutrient-poor diet can make bees more susceptible to harm from disease and parasites. Bees need better forage and a variety of plants to support colony health.

* Federal and state partners should consider actions affecting land management to maximize available nutritional forage to promote and enhance good bee health and to protect bees by keeping them away from pesticide-treated fields.

* The most pressing pesticide research questions relate to determining actual pesticide exposures, the effects of pesticides on bees in the field and the potential for impacts on bee health and productivity of whole honeybee colonies.

An estimated one-third of all foods and beverages are made possible by pollination, mainly by honeybees. In the U.S., pollination contributes to $20 billion to $30 billion worth of agricultural production annually.

 

Nutrition

New research conducted at the University of Illinois indicates that diet influences honeybees' ability to withstand at least some of the assaults blamed for the development of CCD.

University of Illinois professor of entomology May Berenbaum, who led the study, said many organisms use a group of enzymes called cytochrome P450 monooxygenases to break down foreign substances such as pesticides and phytochemical compounds that are naturally found in plants.

"Bees feed on hundreds of different types of nectar and pollen and are potentially exposed to thousands of different types of phytochemicals, yet they only have one-third to one-half the inventory of enzymes that break down these toxins compared to other species," Berenbaum said.

Determining which of the 46 different P450 genes in the honeybee genome are used to metabolize constituents of the bees' natural diet and which are used to metabolize synthetic pesticides became a "tantalizing scientific question" to the research team, Berenbaum said.

"Every frame of honey (in the honeybee hive) is phytochemically different from the next frame of honey because different nectars went in to make the honey," she explained. "If you don't know what your next meal is going to be, how does your detoxification system know which enzymes to upregulate?"

Previous research had shown that eating honey turns on detoxification genes that metabolize the chemicals in honey, but the researchers wanted to identify the specific components responsible for this activity.

To do this, they fed bees a mixture of sucrose and powdered sugar, called bee candy, and added different chemical components in extracts of honey. They identified p-coumaric acid as the strongest inducer of the detoxification genes.

Berenbaum's team showed that p-coumaric acid turns on not only P450 genes but representatives of every other type of detoxification gene in the genome. This signal can also turn on honeybee immunity genes that code for antimicrobial proteins.

Many commercial beekeepers feed their colonies honey substitutes, such as high-fructose corn syrup or sugar water. Berenbaum believes the new research shows that honey is "a rich source of biologically active materials that truly matter to a bee."

She hopes that future testing and development will yield honey substitutes that contain p-coumaric acid so beekeepers can enhance their bees' ability to withstand pathogens and pesticides.

Berenbaum's findings appear in Proceedings of the National Academy of Sciences.

Volume:85 Issue:18

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