Honey Bee Parasites Feed on Fatty Organs, Not Blood

Phys.org University of Maryland January 14, 2019

In this electron micrograph, a parasitic mite,  Varroa destructor , is wedged between the abdominal plates of a honey bee's exoskeleton. Credit: UMD/USDA/PNAS

In this electron micrograph, a parasitic mite, Varroa destructor, is wedged between the abdominal plates of a honey bee's exoskeleton. Credit: UMD/USDA/PNAS

Honey bee colonies around the world are at risk from a variety of threats, including pesticides, diseases, poor nutrition and habitat loss. Recent research suggests that one threat stands well above the others: a parasitic mite, Varroa destructor, which specializes in attacking honey bees.

For decades, researchers have assumed that varroa mites feed on blood, like many of their mite and tick cousins. But new University of Maryland-led research suggests that varroa mites instead have a voracious appetite for a honey bee organ called the fat body, which serves many of the same vital functions carried out by the human liver, while also storing food and contributing to bees' immune systems.

The research, published in the Proceedings of the National Academy of Sciences on January 14, 2019, could transform researchers' understanding of the primary threats to honey bees while pointing the way toward more effective mite treatments in the future.

"Bee researchers often refer to three Ps: parasites, pesticides and poor nutrition. Many studies have shown that varroa is the biggest issue. But when compromised by varroa, colonies are also more susceptible to the other two," said UMD alumnus Samuel Ramsey (Ph.D. '18, entomology), the lead author of the paper. "Now that we know that the fat body is varroa's target, this connection is now much more obvious. Losing fat body tissue impairs a bee's ability to detoxify pesticides and robs them of vital food stores. The fat body is absolutely essential to honey bee survival."

In addition to breaking down toxins and storing nutrients, honey bee fat bodies produce antioxidants and help to manage the immune system. The fatty organs also play an important role in the process of metamorphosis, regulating the timing and activity of key hormones. Fat bodies also produce the wax that covers parts of bees' exoskeletons, keeping water in and diseases out.

According to Ramsey, the assumption that varroa mites consume honey bee blood (more accurately called hemolymph in insects) has persisted since the first paper on the topic was published in the 1960s. Because this paper was written in Russian, Ramsey said, many researchers opted to cite the first English-language papers that cited the original study.

In this cross-section of a honey bee's abdomen, a parasitic varroa mite (orange) can be seen lodged between the bee's abdominal plates, where the mite feeds on honey bee fat body tissue. Credit: UMD/USDA/PNAS

In this cross-section of a honey bee's abdomen, a parasitic varroa mite (orange) can be seen lodged between the bee's abdominal plates, where the mite feeds on honey bee fat body tissue. Credit: UMD/USDA/PNAS

"The initial work was only sufficient to show the total volume of a meal consumed by a mite," Ramsey added. "It can be a lot easier to cite a recent summary instead of the original work. Had the first paper been read more widely, many folks might have questioned these assumptions sooner."

Ramsey noted several observations that led him to question whether varroa mites were feeding on something other than hemolymph. First, insect hemolymph is very low in nutrients. To grow and reproduce at the rates they do, varroa mites would need to consume far more hemolymph than they would be able to acquire from a single bee.

Second, varroa mites' excrement is very dry—contrary to what one would expect from an entirely liquid blood diet. Lastly, varroa mites' mouthparts appear to be adapted for digesting soft tissues with enzymes then consuming the resulting mush. By contrast, blood-feeding mites have very different mouthparts, specifically adapted for piercing membranes and sucking fluid.

The first and most straightforward experiment Ramsey and his collaborators performed was to observe where on the bees' bodies the varroa mites tended to attach themselves for feeding. If the mites grabbed on to random locations, Ramsey reasoned, that would suggest that they were in fact feeding on hemolymph, which is distributed evenly throughout the body. On the other hand, if they had a preferred site on the body, that could provide an important clue to their preferred meal.

"When they feed on immature bees, mites will eat anywhere. But in adult bees, we found a very strong preference for the underside of the bees' abdomen," Ramsey said. "More than 90 percent of mites we found on adults fed there. As it happens, fat body tissue is spread throughout the bodies of immature bees. As the bees mature, the tissue migrates to the underside of the abdomen. The connection was hard to ignore, but we needed more evidence."

Ramsey and his team then directly imaged the wound sites where varroa mites gnawed on the bees' abdomens. Using a technique called freeze fracturing, the researchers used liquid nitrogen to freeze the mites and their bee hosts, essentially taking a physical "snapshot" of the mites' feeding habits in action. Using powerful scanning electron microscopes to visualize the wound sites, Ramsey saw clear evidence that the mites were feeding on fat body tissue.

This microscopic image shows a varroa mite that has consumed honey bee fat body tissue tagged with Nile red, a fat-soluble fluorescent dye. Observing this red fluorescence in the mites' digestive systems helped researchers determine that varroa mites feed on honey bee fat body tissue--not blood, as previously assumed. Credit: UMD/USDA/ PNAS

This microscopic image shows a varroa mite that has consumed honey bee fat body tissue tagged with Nile red, a fat-soluble fluorescent dye. Observing this red fluorescence in the mites' digestive systems helped researchers determine that varroa mites feed on honey bee fat body tissue--not blood, as previously assumed. Credit: UMD/USDA/PNAS

"The images gave us an excellent view into the wound sites and what the mites' mouthparts were doing," Ramsey said. "We could see digested pieces of fat body cells. The mites were turning the bees into 'cream of honey bee soup.' An organism the size of a bee's face is climbing on and eating an organ. It's scary stuff. But we couldn't yet verify that blood wasn't also being consumed."

To further shore up their case, Ramsey and his colleagues fed bees with one of two fluorescent dyes: uranine, a water-soluble dye that glows yellow, and Nile red, a fat-soluble dye that glows red. If the mites were consuming hemolymph, Ramsey expected to see a bright yellow glow in the mites' bellies after feeding. If they were feeding on fat bodies, on the other hand, Ramsey predicted a telltale red glow.

"When we saw the first mite's gut, it was glowing bright red like the sun. This was proof positive that the fat body was being consumed," Ramsey said. "We've been talking about these mites like they're vampires, but they're not. They're more like werewolves. We've been trying to drive a stake through them, but turns out we needed a silver bullet."

To drive the proverbial final nail into the coffin of the idea that mites feed on hemolymph, Ramsey performed one last experiment. First, he painstakingly perfected the ability to raise varroa mites on an artificial dietary regimen—hardly an easy task for a parasite that prefers meals from a live host. Then, he fed them diets composed of hemolymph or fat body tissue, with a few mixtures of the two for good measure.

The results were striking: mites fed a diet of pure hemolymph starved, while those fed fat body tissue thrived and even produced eggs.

"These results have the potential to revolutionize our understanding of the damage done to bees by mites," said Dennis vanEngelsdorp, a professor of entomology at UMD and a co-author of the study, who also served as Ramsey's advisor. "Fat bodies serve so many crucial functions for bees. It makes so much more sense now to see how the harm to individual bees plays out in the ways that we already know varroa does damage to honey bee colonies. Importantly, it also opens up so many new opportunities for more effective treatments and targeted approaches to control mites."

Read more at: https://phys.org/news/2019-01-honey-bee-parasites-fatty-blood.html#jCp

More information: Samuel D. Ramsey el al., "Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1818371116 

Journal reference: Proceedings of the National Academy of Sciences 

Provided by: University of Maryland

Scientists Say Agriculture is Good for Honey Bees

Phys.org    By Ginger Rowsey    May 2, 2017

In a recent study, researchers with the University of Tennessee Institute of Agriculture found the overall health of honey bees improved in the presence of agricultural production, despite the increased exposure to agricultural pesticides. Credit: Scott Stewart While recent media reports have condemned a commonly used agricultural pesticide as detrimental to honey bee health, scientists with the University of Tennessee Institute of Agriculture have found that the overall health of honey bee hives actually improves in the presence of agricultural production.

The study, "Agricultural Landscape and Pesticide Effects on Honey Bee Biological Traits" which was published in a recent issue of the Journal of Economic Entomology, evaluated the impacts of row-crop agriculture, including the traditional use of pesticides, on honey bee health. Results indicated that hive health was positively correlated to the presence of agriculture. According to the study, colonies in a non-agricultural area struggled to find adequate food resources and produced fewer offspring.

"We're not saying that pesticides are not a factor in honeybee health. There were a few events during the season where insecticide applications caused the death of some foraging bees," says Mohamed Alburaki, lead author and post-doctoral fellow with the University of Tennessee Department of Entomology and Plant Pathology (EPP). "However, our study suggests that the benefits of better nutrition sources and nectar yields found in agricultural areas outweigh the risks of exposure to agricultural pesticides."

Alburaki and fellow researchers established experimental apiaries in multiple locations in western Tennessee ranging from non-agricultural to intense agricultural production. Over the course of a year, colonies were monitored for performance and productivity by measuring colony weight, brood production and colony thermoregulation. Colony thermoregulation, or the ability to maintain an optimal temperature within a hive, is an important factor in brood development and the health of the resulting adult bees.

According to the study, hives located in areas with high to moderate agricultural vegetation grew faster and larger than those in low or non-agricultural areas. Researchers suggest the greater population sizes enabled better colony thermoregulation in these hives, as well.

Meanwhile, bees located in a non-agricultural environment were challenged to find food. Although fewer pesticide contaminants were reported in these areas, the landscape did not provide sustainable forage. In fact, during the observations, two colonies in the non-agricultural areas collapsed due to starvation.

Disruptions and fluctuations in brood rearing were also more notable in a non-agricultural environment. Interestingly, brood production was highest in the location that exhibited a more evenly distributed mix of agricultural production, forests and urban activity.

"One possible explanation for this finding could be the elevated urban activity in this location," says Alburaki. "Ornamental plantings around homes or businesses, or backyard gardens are examples of urban activity that increase the diversity of pollen in an area. Greater pollen diversity has been credited with enhancing colony development."

Researchers also evaluated trapped pollen from each colony for pesticide residues. Low concentrations of fungicides, herbicides and insecticides were identified, but at levels well below the lethal dose for honey bees. Imidacloprid was the only neonicotinoid detected, also at sub-lethal levels.

Agricultural pesticides, particularly neonicotinoids, are considered by some to be a key factor in declining honeybee populations. The UTIA study found that higher exposure to pesticides in agricultural environments did not result in measurable impacts on colony productivity.

"We train agricultural producers on careful selection and conscientious application of pesticides to reduce bee exposure," says Scott Stewart, Integrated Pest Management Specialist with UT Extension, "but it's becoming more clear that the influences of varroa mite and food availability are more important factors in honey bee health than agricultural pesticides."

 Journal reference: Journal of Economic Entomology

https://phys.org/news/2017-05-scientists-agriculture-good-honey-bees.html

When Varroa Mites Hitch a Ride

Bug Squad    By Kathy Keatley Garvey   March 1, 2016

Varroa mite on a honey bee (drone) pupa. (Photo by Kathy Keatley Garvey)Those blood-sucking varroa mites (Varroa destructor) are considered the No. 1 enemy of beekeepers. In powerful numbers and weakened colonies, they can overwhelm and collapse a hive.
 

We remember seeing a varroa mite attached to a foraging honey bee one warm summer day in our pollinator garden. The mite was feeding off the bee and the bee was feeding on the nectar of a lavender blossom.

Didn't seem fair.

We've never seen a varroa mite on bumble bees or carpenter bees, but Davis photographer Allan Jones has--and he's photographed them. (See below)

When varroa mites tumble off a honey bee and into a blossom, they can hitch a ride on other insects, such as bumble bees and carpenter bees.

"Varroa have been recorded hitching rides on bumble bees and yellowjackets," observed native pollinator specialist Robbin Thorp, distinguished emeritus professor of entomology at UC Davis. "Varroa have been reported as feeding on larvae of these and other critters--but not successfully reproducing on them.  Also bumble bees and yellowjackets typically overwinter as hibernating queens not as perennial colonies like honey bees.  Thus they are not suitable hosts for Varroa."

Extension apiculturist emeritus Eric Mussen says that bees other than honey bees aren't reproductive hosts for the varroa mite.

"As far as I know, Varroa destructor may be able to find soft areas of the exoskeleton of insects other than honey bees and feed on them," he says. "I have no idea whether or not the substitute hemolymph would sustain the mites for very long.  The mites have practically no digestive capabilities.  They simply utilize the previously-synthesized bee blood, to which they seem to be perfectly adapted."

 "Since the mites reproduce on honey bee pupae, there are a number of considerations about potential other reproductive hosts," Mussen said, citing:

  1.  Are the nutrients of the substitute host close enough to those of honey bees to support immature mite development? 
  2. Can immature mites that develop properly at honey bee cell environmental conditions (temperature and relative humidity) find a similar environment in the nests of other insects? 
  3. Do other insects tolerate the presence of mites on their bodies or in their brood nests?

Like honey bees, bumble bees do segregate their pupae in single cells, Mussen says, but he was unable to find any studies devoted to whether bumble bee pupal conditions support Varroa destructorreproduction.

Sounds like a good research project!

A varroa mite attached to a honey bee forager. It's the reddish brown spot near the wing. The bee is foraging on lavender. Photo: Kathy Keatley Garvey http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=20360

Deformed Wing Virus A Global Epidemic

CATCH THE BUZZ    By Alan Harmon   February 9, 2016

A new analysis of the widespread deformed wing virus (DWV) in honey bees shows that the virus has gone from an endemic to a global epidemic because of greater movement of a major vector, the Varroa mite.

The mite has spread in large part due to human trade of the bee colonies it infests.

The study published in the journal Science adds to scientists’ understanding of the globally pressing issue of pollinator health by describing the worldwide transmission routes and dynamics of DWV based on analysis of a new and large molecular data set.

Previous evidence indicates that the presence of the mite Varroa increases the spread of DWV across honey bee populations, not only by acting as a vector but also by increasing the virulence of the virus.

While scientists have a grasp on how Varroa affects DWV spread at the individual and colony level, its importance to the global spread of DWV is less well understood; some scientists think the mite became an important factor when it expanded from its native host, the Asian honey bee, to the European honey bee – then going on to cause an epidemic of DWV.

Others think DWV was native in the European honey bee but reemerged because of the mite’s increasing presence.

Here, to better understand how the Varroa mite has impacted global DWV spread, Lena Wilfert of the University of Exeter in the United Kingdom and colleagues used molecular sequencing of the virus and mites from 32 locations in 17 countries.

Wilfert worked with researchers from the University of Sheffield in the UK; ETH Zürich in Zürich, Switzerland, University of Cambridge in the UK; University of Salford in Manchester, UK; and University of California, Berkeley.

They estimated the major routes of the virus’s spread by comparing geographic and host-specific patterns.

Their results lend support to the idea that DWV is an endemic honey bee pathogen of the European honey bee that has recently re-emerged through the spread of Varroa as a vector.

The authors say that to reduce the negative effects of DWV on pollinators, tighter controls, such as mandatory health screenings and regulated movement of honey bees across borders, should be imposed.

http://goo.gl/50CTZd

Australia-wide Survey to Ascertain Health of Bees

abc.net   By Rosemary Grant     June 11, 2014

Australia's honey bee population and their hives have been booked in for a thorough health assessment.

Australia remains free of many major honey bee pests, such as the Varroa mite, that are present in other countries.

But speculation in the USA that a virus, potentially imported from Australia, may contribute to colony collapse disorder in honey bee populations across north America, has halted Australia's live bee exports to the US.

Continue reading... http://www.abc.net.au/news/2014-06-11/bee-disease-survey/5514550

USDA Focus on Honey Bee Health

CATCH THE BUZZ   By Kim Flottum   May 21, 2014

Statement of Jeff Pettis, Research Leader USDA - Agricultural Research Service

Testimony before the House Committee on Agriculture, Subcommittee on Horticulture, Research, Biotechnology and Foreign Agriculture - April 29, 2014 

Chairman Scott, Ranking Member Schrader and members of the subcommittee, I am Dr. Jeff Pettis, Research Leader of the Bee Research Laboratory in Beltsville, Maryland, a research laboratory dedicated to honey bee health and part of the USDA Agricultural Research Service. I am pleased to appear before you to discuss a serious threat to the honey bee and thus our food security in the United States.

Ultimately, if no long-term solutions are developed to slow bee decline, consumers will pay more for the food they buy. The foods that bees are responsible for pollinating tend to be the foods that add vital nutrients, flavor and diversity to our diet: the fruits, nuts and vegetables that maintain health. Bees pollinate more than 90 crops and are responsible for $15 billion in added crop value. Over half the nation’s bees are needed to pollinate almonds alone, a $3 billion crop with increasing acreage. 

One of the biggest problems facing honey bees and beekeepers today is the varroa mite. The varroa mite’s full name is Varroa destructor, and it is...

Read more... http://home.ezezine.com/1636/1636-2014.05.21.06.53.archive.html

The above brought to us by CATCH THE BUZZ: Kim Flottom,  Bee Culture, The Magazine Of American Beekeeping, published by the A.I. Root Company. Twitter.FacebookBee Culture’s Blog.

Research Funding Essential to Keep Honey Bees Abuzz

Western Farm Press    By Cary Blake   April 20, 2014
 
  • More funding is needed to support expanded research for the U.S. honey bee industry.
  • Honey bees pollinate about 140 crops - one out of every three bites of food we consume.
  • From the hive destroying varroa mite to a new honey bee pest threat found in Asia, research is critical to keep honey bees - and our food supply - safe from pests, diseases, and other threats.

What is in this article?:

One of the top ways to create a healthier U.S. honey bee industry - which in turn can lead to successful crop pollination and honey production - is additional funding for expanded apiculture (beekeeping) research.

More dollars are needed to improve the honey bee industry which can benefit agriculture as a whole.

“Beekeeping has never had the needed research dollars or inputs to study its problems as other sectors of agriculture have had,” says entomologist Dick Rogers who has 35 years in the bee business as an entomologist.

Rogers is the bee research manager at the new Bayer Bee Care Center for North America located in Research Triangle Park, N.C. which opened to the public April 15.

“Beekeeping has always worked on a shoestring (budget) basically,” the veteran bug man said. “There are new research dollars coming along which will definitely help things progress.”

Honey bees pollinate one-third of the world’s food supply – in other words, one-out-of-three bites of food the consumer eats. About 140 crops are pollinated by bees.

The largest demand for honey bee pollination is the California almond industry. This spring, 1.6 million honey bee colonies pollinated California’s 840,000 bearing acres of almonds.

Almond pollination is the largest pollination event in the world. Without honey bees, the $4.3 billion California almond industry would almost cease to exist.

Bees and the crop production engine

“Honey bees are the spark that starts the crop production engine,” Rogers said. “If you can’t start your car without a spark you won’t go very far. The same is true of honey bees.”

Rogers and other honey bee specialists discussed the U.S. honey bee business – its successes and challenges - during the Southwest Ag Summit held in Yuma, Ariz. this spring.

Other speakers included beekeepers Thomas “Rick” Smith of Yuma and Bret Adee of Bruce, S.D., plus Christi Heinz of the bee research organization Project Apis m.

Read more...
http://westernfarmpress.com/tree-nuts/research-funding-essential-keep-honey-bees-abuzz?page=1

 

Monsanto Announces Clinton Global Initiative Commitment on Honey Bee Health

The following is brought to us by CATCH THE BUZZ (Kim Flottum) Bee Culture, The Magazine of American Beekeeping, published by A.I. Root Company.    10/14/13

Ivestment Launches Coalition to Research the Challenges Facing Honey Bees

Monsanto recently announced its commitment to honey bee health at the 2013 Clinton Global Initiative Annual Meeting with support from the Keystone Center, The American Honey Producers Association, The American Beekeeping Federation, The World Wildlife Fund, and Project Apis m. (PAm), plus several commodity groups.

A significant decline in the honey bee population is posing a threat to agricultural sustainability and food security, as well as to ecosystem health and biodiversity, thus the coalition will have four priority areas of focus: 1) improving honey bee nutrition; 2) providing research investment in novel technology for varroa and virus control; 3) understanding science-based approaches to studying pesticide impacts on honey bees and increasing awareness of pesticide best management practices among growers and beekeepers; and 4) enabling economic empowerment of beekeepers.

Monsanto has been involved with bee research since 2011 when it acquired Beeologics, an organization focused on researching and testing biological products to provide targeted control of pests and diseases in order to provide safe, effective ways to protect the honey bee. Monsanto also has collaborated with PAm to assist in forage projects in order to provide more nutritious food for bees, and is doing extensive research on the varroa mite, which may be one factor in the decline of honey bee health. 

By Jerry Hayes
Beeologics


"My goal in life and work is continuous improvement. And, it has happened here since coming to Monsanto with lots of help from like-minded people who have really engaged and seen the vision of what Monsanto can offer to honey bee health.

I’m a firm believer that everything should build on the previous effort. Back in June, we were able to sponsor a first-of-its-kind Honey Bee Health Summit, hosted by Project Apis m. (PAm) and Monsanto’s Honey Bee Advisory Council. The leaders in the world of honey bee health were here and shared how we could help them reenergize this industry. The presentations are available at the site. After most meetings, workshops and conferences, everybody leaves with optimism and excitement and then nothing happens. Well, after this meeting, building to the next goal was to get honey bees positioned in front of global leaders that create and implement innovative solutions to the world’s most pressing challenges. One of the only places where you can do that and stand in front of the world is at the Clinton Global Initiative. We did it."