Honey bees and other pollinators are critically important to securing the nation’s food supply and providing ecosystem services that insure plant diversity, soil stability and species richness. Fruit and seed yields increase when many bee species are present – whether in undisturbed ecosystems or in crops such as apples or almonds where pollination by both honey bees and native bees generates greater yields and better-quality fruit. There are more than 4,000 species of bees in the United States, with many bumblebee and solitary-bee species remaining to be described and life histories understood.

The importance of pollinators is widely known but populations have been declining for more than a decade. Losses of managed honey-bee colonies are almost 40 percent annually, jeopardizing the financial solvency of our nation’s beekeeping industry. Causes for colony losses include nutritional stress from lack of pollen and nectar sources, parasitic Varroa mites and the viruses they transmit, and pesticide exposure. Many of the same stresses are also affecting other bee species such as bumblebees, where many species are experiencing decreasing colony numbers and one is now on the endangered-species list. Similar declines in populations of solitary bees might also be occurring but survey data are lacking.

Scientists work with honey-bee colonies that were shipped from cold-storage facilities in Idaho to almond orchards in California as part of a cold-storage overwintering-management study at the U.S. Department of Agriculture-Agricultural Research Service’s Carl Hayden Bee Research Center in Tucson, Arizona.

Climate change is a significant factor contributing to the decline in pollinator populations. The warming of the planet and changes in weather patterns are altering the synchrony between flowering plants and their pollinators, causing nutritional stress. Radical shifts in temperature as well as droughts and floods are disrupting native ranges for pollinators. That makes ecosystems unsuitable for the processes needed to sustain populations – such as overwinter hibernation, spring nest establishment and reproduction. In the case of honey bees the warmer temperatures in late fall and winter that are occurring with greater frequency in northern latitudes have made it increasingly difficult to reduce winter colony losses. That’s because the warmer fall and winter temperatures are extending the period when bees are foraging. That disrupts the colony age structure and resource utilization, enabling Varroa mites to migrate among colonies on foragers – spreading the parasite and the viruses it transmits throughout apiaries.

Research conducted by Agricultural Research Service scientists is focused on understanding the impact of a changing climate on bee health and survival – and finding solutions to reduce pollinator losses. In the spirit of delivering cutting-edge scientific tools and innovative solutions, scientists at the Carl Hayden Bee Research Center are developing management schemes for overwintering honey-bee hives in cold-storage facilities to reduce the impact of Varroa mites and nutritional stress, and to increase colony survival. Scientists there also are studying how environmental factors affect the nutrients in pollen and nectar, and how growing conditions can be managed to optimize the nutritional quality of those food sources.

European honey bee with a Varroa mite on its back. The mites cause death and disease in bee colonies.

The Agricultural Research Service’s Pollinating Insect-Biology, Management, Systematics Research Unit in Logan, Utah, is the home of the U.S. National Pollinating Insect Collection. Scientists there are investigating other bee species that can be managed for pollination. They’re learning how multiple species are needed for pollination of our crops and natural ecosystems. For bumblebees and managed solitary-bee species, research is defining how climate is affecting bee nutrition, development, reproduction and survival. The research will increase our understanding of how variable climate impacts different bee species. It will direct the next steps for beekeepers and managers to help their bees survive those challenges.

The overall goal of the research is to sustain our nation’s agroecosystems and natural resources – and to ensure the economic competitiveness and excellence of our agriculture.

Visit www.ars.usda.gov -- search for "insect biology" and "hayden bee" for more information.

Diana Cox-Foster is the research leader of the Agricultural Research Service’s Pollinating Insect-Biology, Management, Systematics Research Unit in Logan, Utah. Gloria DeGrandi-Hoffman is the research leader at the Agricultural Research Service’s Carl Hayden Bee Research Center in Tucson, Arizona.