Honey Bees May Fight Off Viruses With Help From Fungi

Honey Bees May Fight Off Viruses With Help From Fungi
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Western honey bees (Apis mellifera) are crucial to global agriculture but are facing significant losses due to viruses and pests such as the Varroa mite. (Credit: G. Tarlach)

Western honey bees (Apis mellifera) are crucial to global agriculture but are facing significant declines due to viruses and pests such as the Varroa mite. (Credit: G. Tarlach)

It’s not easy being a bee these days. Apis mellifera, the Western honey bee, is crucial to agriculture worldwide but faces a growing number of pests and pathogens against which beekeepers have few weapons.

But the bees themselves may be showing us the way forward: New research suggests the foraging insects may obtain protection against some viruses by consuming fungi, then returning to the hive to spread its medicinal value.

Honey bees contribute more than $15 billion annually to U.S. agriculture, and hobbyist beekeepers raise millions more bees in their backyards (full disclosure: I have three hives in a community garden).

While the science and economics of saving honey bees can be controversial, no one can deny that the insects are facing a host of threats not historically seen in the U.S., which have led to a dramatic increase in colony losses. Over the past decade, annual colony deaths have averaged more than 30 percent.

Much of the blame falls on the aptly-named parasitic mite Varroa destructor, which arrived in force in the 1980s and has since been associated with the spread of at least ten viruses that affect honey bees.

One of those pathogens, deformed wing virus (DWV), causes shriveled wings and shortened life spans in individual worker bees, and can reduce an entire colony’s health. Another, Lake Sinai virus (LSV), was identified only in 2010 but has since established itself throughout the U.S.

There are no treatments for these viruses; beekeepers instead try to control the Varroa populations within each colony. (Most colonies have some degree of Varroa present; it’s when levels exceed a certain threshold that viral infection and a decline in colony health become more likely.)

The tools at beekeepers’ disposal range from chemical-free Integrated Pest Management practices (such as disrupting the mites’ reproductive cycle by manipulating where and when the parasites can breed within a hive) to a variety of miticides. Many of the miticides cause significant bee death if misapplied, and the wily Varroa has developed resistance to some of the chemicals. Robust control of the virus-carrying parasites continues to elude beekeepers.

A nurse bee attends to drones (male bees) hatching out of their cell...but at far left, a reddish, oval Varroa mite indicates the destr

A nurse bee attends to two drones (male bees) hatching out of their cell…but at far left, a reddish, oval Varroa mite indicates the destructive parasites are present in the hive. The mites weaken individual bees, introduce viruses and eventually, if left unchecked, compromise the health of the entire colony. (Credit: G. Tarlach)

What a Fungi

Foraging honey bees, however, have been observed consuming mycelium, the thread-like filaments found on many mushrooms. Like other fungi, mushrooms can produce chemicals with natural antimicrobial properties, including antibacterial and even antiviral compounds. Researchers wondered whether forager bees eating the mycelium and then returning to the hive to share it with other bees might provide some antiviral protection for the entire colony.

To find out, a team cultivated several fungi species known to produce antiviral compounds and fed extracts of their mycelium to honey bees, initially in a lab environment. Several species appeared to reduce the amount of pathogens present; the researchers chose the two most promising fungi, amadou (Fomes fomentarius) and red reishi (Ganoderma resinaceum), for field trials.

Paul Stamets with cultivated fruitbodies of red Reishi, Ganoderma resinaceum, and wearing a hat made of Amadou, Fomes fomentarius. Extracts from the cultures of these two polypore mushroom species reduced viruses afflicting bees. Credit: Paul Taylor

Cultivated red reishi, or Ganoderma resinaceum, towers over Paul Stamets, one of the authors behind today’s research and a tireless crusader for all things fungi. Stamets sports a hat made from a second type of mushroom: amadou, or Fomes fomentarius. His team’s research found that extracts from both species appear to protect honeybees from devastating viruses. (Credit: Paul Taylor)

The results of the trials were impressive: the extracts, fed to bees in sugar syrup, significantly reduced the viral load of the colonies. How significant? Colonies that were fed the extracts saw a 79-fold reduction in DWV and a 45,000-fold LSV reduction (not a typo) compared with control colonies.

The findings are potentially game-changing in the ongoing fight against bee viruses, but more work needs to be done. The researchers noted, for example, that they found some antiviral activity in the birchwood used to cultivate the mushrooms. It’s possible the tree’s phytochemicals work in concert with mycelium compounds to provide protection against viruses for the bees.

The study appears today in Scientific Reports and is open access. You can also read Discover‘s profile of one of the study’s authors, myco-evangelist Paul Stamets, who champions the many benefits of mushrooms and other fungi, from controlling blood sugar to cleaning up oil spills.

As eusocial insects, the world of the honey bee revolves around keeping the queen (larger bee in center of image) healthy and productive. (Credit: G. Tarlach)

As eusocial insects, the world of the honey bee revolves around keeping the queen (larger bee in center of image) healthy and productive. Worker bees weakened by viruses can cause an entire colony to collapse. (Credit: G. Tarlach)

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Author: Admin