Here’s what you need to know about the plight of bee colonies across the globe.

If you think bees are only good for making honey, think again. They are essential for maintaining global food supplies, and these creatures are facing a number of threats.

In the U.S. alone, the pollination activity from bees is worth about $20 billion a year. Most of the crops that bees pollinate are vegetables, fruits, and nuts—all staples of a healthy diet. In fact, honeybees pollinate plants that produce about a quarter of the food Americans consume.

One threat to bees that many people are aware of is Colony Collapse Disorder (CCD). Parasites, pesticides, pathogens, poor nutrition, habitat fragmentation, agricultural practices, and poor bee management are all linked to the disorder, but there is no official known cause of CCD, according to the United States Department of Agriculture’s Agricultural Research Service (ARS).

According to a recent ARS survey of people who manage about 600,000 U.S. honey bee colonies, there was an average total colony loss of 22 percent between October 2011 and April 2012, down from 33 percent reported during the same time in 2010-2011. During the 2012-2013 winter season, about 31 percent of colonies were lost.

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Knowing about CCD is one thing, but there are other factors leading to dwindling colonies.

One reason for the decline could be the tobacco ringspot virus, which usually infects plants but has recently been found in bees. The virus, also known as TRSV, was also found in varroa mites, a type of parasite that spreads viruses among bees while feeding on their blood.

“The increasing prevalence of TRSV, in conjunction with other bee viruses, is associated with a gradual decline of host population and supports the view that viral infections have a significant negative impact on colony survival,” the Chinese researchers said.

The scientists studied bee colonies that were both strong and weak, and found that the virus was more common in the weak colonies. Colonies with high levels of multiple viral infections started failing in late autumn and died before February, but hives with fewer infections made it through the colder months.

About 5 percent of known plant viruses can be transmitted via pollen. These “toxic viral cocktails” seem to correlate with honeybee CCD, the researchers said. Many scientists in the field believe that a combination of factors is contributing to lower bee populations.

“The results of our study provide the first evidence that honey bees exposed to virus-contaminated pollen can also be infected and that the infection becomes widespread in their bodies,” said Ji Lian Li of the Chinese Academy of Agricultural Science in Beijing, who was the lead author of the TRSV study.

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Not only are colonies declining, but a study from the Royal Holloway University of London found that agricultural pesticides are causing worker bumblebees—a relative of the honeybee—to hatch at a smaller size than usual. These bees are also an essential part of the food chain.

The research showed that exposure to a pyrethroid pesticide, which is used to prevent insect damage to flowering crops, decreases the size of individual bees by 16 percent on average.

“We know that smaller bees are less efficient foragers, but we don’t know whether that translates into them being less efficient pollinators—research is definitely needed to answer that question,” said Mark Brown, Ph.D., a professor at the School of Biological Sciences at Royal Holloway.

“We know we have to protect plants from insect damage, but we need to find a balance and ensure we are not harming our bees in the process,” he added.

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Concern about bees is apparent across the globe. Researchers in Australia have attached tiny sensors to honeybees as part of a two-month study to explain bee colony declines.

The U.S. Environmental Protection Agency (EPA) recently granted about $460,000 to Louisiana State University, Penn State University, and the University of Vermont to come up with practices to reduce the use of potentially harmful pesticides. The EPA has said that protecting bees is a top priority.

Carl Chesick, director of the Center for Honeybee Research in North Carolina, said that bees are one of only a few creatures that live their lives to benefit the greater good.

“If human beings change the conditions of our planet so that bees can’t exist, we are foolish to think we can escape the consequences of our own choices,” Chesick said.

A bee is at least 100,000 times smaller than a human being and is exponentially more sensitive to substances in the environment, he explained. As such, they can’t adapt as quickly to new technology—including pesticides—as we might think.

Gene Robinson, Ph.D., an entomologist and director of the Institute for Genomic Biology at the University of Illinois at Urbana-Champaign, said that people can do more to help bees on a local level.

“Citizens can help by minimizing uses of highly toxic pesticides in their gardens and backyards and, where possible, creating habitats for wild bees to nest,” Robinson said.