Honey bees, which play a key role in pollinating a wide variety of food crops, are in sharp decline in the United States, due to parasites, disease and pesticides, said a federal report released on Thursday.

Genetics and poor nutrition are also hurting the species, which help farmers produce crops worth some $20 billion to $30 billion a year.

Honey bee colonies have been dying and the number of colonies has more than halved since 1947, said the report by the Environmental Protection Agency and the Agriculture Department.

The decline raises doubt about whether honey bees can fulfill their crucial role in pollinating crops that play a role in about one-third of all food and beverages sold in the United States, the report said.

“Overall losses continue to be high and pose a serious threat to meeting the pollination service demands for several commercial crops,” the report said.

Pollination demands have increased so much in recent years that California’s almond crop alone requires 60 percent of all managed colonies devoted to pollination — rather than honey or beeswax production.

The Varroa mite, a parasite first found in the United States in 1987, is the single biggest cause of colony loss in the United States and other countries, the report said.

Another main concern is the effect of pesticides on bee colonies. More research is needed to find out how much pesticide exposure bees get and their effects, the report said.

U.S. honey bees also lack genetic diversity, the result of many colonies being descended from fewer than 600 queens. That lack of diversity limits bees’ ability to develop resistance to new diseases and to develop productive worker bees.

The report also found modern weed control methods, which result in large fields with a single crop, has hurt bees by limiting the range of nutrients in their diet, compared with past decades when bees had access to a wider array of plant foods in a smaller range.

The report is the result of a conference the EPA and Agriculture Department held in October 2012. Its findings will be the basis for a revision of a federal plan to combat the decline in honey bees.

(Reuters)