The Signs of Mite Damage - How to Identify Progressed Varroosis?

Bee Informed Partnership    September 26, 2018

BIP Tech Transfer Team Member, University of Minnesota, Written by Garett Slater, posted by Anne Marie Fauvel

Varroa infested colonies entered the United States in ~1987, and changed beekeeping forever. Beekeeping has always been time consuming, difficult and experience oriented; however, beekeeping became even more challenging when beekeepers were called to eradicate a bug on another bug. Since its introduction in the US, beekeepers have reported high annual colony losses due to mites. In fact, some beekeepers report 60% losses due to this troublesome pest. While beekeepers have faced devastating challenges before, including American Foulbrood, Varroa mites has presented damages never before seen.

Varroa have become more difficult to manage since their introduction. The mites are seemingly embedded within the honey bee industry reality as nearly, if not all, colonies have Varroa. Like many beekeepers say: ” all my colonies have mites, I just cannot see them”. Even if alcohol washes do not reveal mites, Varroa is present in the brood or will be present soon due to infestation from surrounding colonies. As mites have become more widespread, they became a vector for a variety of viruses. In fact, researchers are finding more and more variants of Deformed Wing Virus (DWV), a virus that affects the honey bee’s essential flight capabilities. Research has shown that DWV-B (Deformed Wing Virus variant B) can be responsible for high over-winter losses.

The point here is that Varroa devastates colonies.  It would also seem that Varroa are transmitting more virulent strains of viruses with each passing year. Because of this, I recommend to keep mite levels below 1 mite/ 100 bees in the spring and below 3 mites/100 bees in the fall. With Varroa loads any higher, beekeepers risk high colony losses.

Monitor, Monitor, Monitor

Beekeepers must consistently monitor mites if they expect to have strong and healthy colonies. Beekeepers can monitor their mites in various ways, but I recommend both of these two methods: perform an alcohol wash (or other monitoring method) and observe the overt signs of mite damage. It is ideal to perform monitoring methods once a month, but we realize this is not always possible. Because of this, combining both monitoring and observation methods are recommended. Ideally, mites should be monitored at least 4 times a year.  As seen in Figure 1: population increase, population peak, population decrease, and fall dormant; it is essential to understand the seasonal changes. For example, brood density varies throughout the year, so certain treatments can be less effective at different times. By understanding seasonal cycles, beekeepers can better manage their mites. I understand Figure 1 does not reflect the reality of every region but it gives a good overall general idea.  Some regions have multiple population peaks due to large honey flows, so you will need to understand the honey bee seasonal phases in your region. But essentially, as the bee and brood population increase, so do the mites.

Figure 1: Honey bee seasonal phases – Beekeepers should monitor mites once a month, but if this is not possible, mites should be monitored at least 4 times a year: during the late winter-early spring dormant, population increase, population peak, population decrease, and fall dormant phases. I recommend alcohol washes (or another monitoring method) during these periods. Photo courtesy of the Honey Bee Health Coalition.

Mite Monitoring Techniques

I attached a chart outlining the 3 major mite monitoring techniques I recommend. Perform one of these techniques 4 times a year: Early spring, late spring, late summer and early fall. Each beekeeper has their preference, so use the method you feel the most comfortable with. I use alcohol washes, but I feel comfortable with sugar rolls or CO2 as well. As long as you monitor, there is not a wrong method!


Advantages 

Disadvantages 

Sugar Rolls

Known research on accuracy

Common method

May not kill bees

Messy

Hard to do on windy, rainy or humid days

More time consuming

Less accurate

Alcohol Wash

Well documented

Quicker than sugar rolls

Can be more accurate than sugar roll

Can be messy

Kills bees

CO2

Quickest method

Easy to do with multiple colonies

Kills the bees (most likely)

When monitoring for mites, beekeepers should review mite thresholds. I outline my recommended thresholds for each monitoring method below. If your colony is above threshold, I recommend taking actions. Mite thresholds are not an exact science, even if you have levels below the threshold, it is no assurance that your colonies will be healthy and successful. For example, I have sampled many commercial beekeepers with mite levels <0.5 mites /100 bees in the spring, and they eventually had huge losses. I typically see mite levels spike in the late summer because: A) summer treatment with honey supers are limited, B) Mites are often lurking in the brood, and C) Mites from other beekeepers nearby can (re)infest colonies. Because of this, always monitor and monitor again. Once mite levels do spike, they may be difficult to bring down. Too often, when you notice, the mite damage is already done. I should note that I recommend alcohol washes, powdered sugar rolls or CO2 over a sticky board. Sticky boards are not nearly as accurate, because they do not quantify the level of infestation. If a sticky board is your only option, you can attest that you have some mites or more mites, but you are not able to assess the level of infestation (1, 2, 3 mites/100 bees). Use other monitoring method options for more accurate results and an infestation level to compare with suggested thresholds. *These thresholds may vary per US regions. These are the threshold I recommend in the Midwest (MN & ND)

Monitoring Method

# of mites in early-spring

# of mites in mid-spring

# of mites in late-spring

# of mites in early-fall

# of mites in late-fall

Alcohol Wash

 

1 mite/100 bees

1 mite/100 bees

1 mite/100 bees

3 mite/100 bees

3 mite/100 bees

Powdered sugar roll

1 mite/100 bees

1 mite/100 bees

1 mite/100 bees

3 mite/100 bees

3 mite/100 bees

CO2

1 mite/100 bees

1 mite/100 bees

1 mite/100 bees

3 mite/100 bees

3 mite/100 bees

Sticky Board

9 mites/24 hours

9 mites/24 hours

9 mites/24 hours

12 mites/24 hours

12 mites/24 hours

Mite related Disease Progression 

I inspect and observe hundreds of colonies annually. When I enter a colony, I often immediately know whether it has (or did) have high mite levels simply by observing progressed signs of mite damage. Just observing progressed mite damage does not suffice, but it is a good start. By noting visual signs of Varroa, you will know just how important your mite levels are and the need for action. Monitoring is best but if you can recognize some of the visual signs, you will better understand the extend of the mite damage to your colony.

I outlined the 5 stages of mite damage, which I relay to my beekeepers. In the spring during population increase, I want to see colonies within the Stage 1- 2. While I hate to see mites in the spring, this is not always a bad sign. Even if I observe mites, the colony may be below the recommended threshold, so just continue to monitor that colony. During the late spring, summer and fall, I like to see colonies within Stage 1-3. Even if Chewed Down brood (CDB) (outlined below) and phoretic mites are seen, it does not mean that beekeepers have high levels. However, a combination of phoretic mites and CDB can signal worse mite issues. If these signs are seen, continue to monitor these colonies. As for Stage 4-5, I never want to see these stages, regardless of temporal period. Deformed Wing Virus (DWV) and Varroa Mite Syndrome (formerly Parasitic Mite Syndrome or PMS) can signify high mite levels.  Specifically for Varroa Mite Syndrome, it signifies very progressed mite damage, which often results in colony deterioration and eventual colony death. If colonies are in stage 4 or stage 5, monitor immediately to determine extent of damage. Action is often required, but may be too late.

 Stage

Visual Signs

Notes

Stage 1

Zero signs of mites, brood diseases or viruses


Stage 2

Visual signs of phoretic mites on either workers or drones.

 

This does not necessarily mean a mite issue exists, but if mites are seen, monitor to determine extent of varroosis.

 

Stage 3

Chewed Down Brood and/or phoretic mites

 

 

Stage 4

Deformed Wing Virus (DWV) and/or Chewed Down Brood and/or signs of phoretic mites.

Visual signs of Deformed Wing Virus (DWV) can mean larger varroa issues. Obviously, this depends upon the number of bees with DWV and the number of phoretic mites seen, but mite monitoring is recommended to determined extent of varroosis. These signs signal a more progressed form of varroosis.

Stage 5

Varroa Mite Syndrome (VMS) and/or Deformed Wing Virus (DWV) and/or Chewed Down Brood and/or Phoretic mites

Visual signs of Varroa Mite Syndrome usually signal extreme issues with varroasis. If Varroa Mite Syndrome is seen, then mite levels are often a significant issue and has advanced to the most progressed stage of varroosis.

Visual signs

Phoretic Mite

Phoretic mites are Varroa mites seen on the abdomen of worker (or drone bees). Most phoretic mites, however, are found underneath the bee, more precisely tucked between the abdomen’s sclerites where they latch on and feed. Because of this, I typically inspect the ventral abdomen of several worker bees during inspections. This is why beekeepers “never see mites”, even if these beekeepers have higher mite levels. Visually inspect phoretic mites just on the workers, not the drones. If phoretic mites are seen on worker bees, then this represents a more progressed infestation of mites. Signs of phoretic mites indicate the colony is in Stage 2-5. Visually inspect other signs to further pinpoint extent of damage.

Phoretic mite on the thorax of a worker bee. Photo by Rob Snyde Chewed Down Brood (CDB)

Bees can sense mites in the brood. If sensed, bees will uncap and cannibalize the pupae. If CDB is seen, then mites may be at a high level, especially within the brood. CDB can indicate progressed mite damage, so continue to monitor and assess colony health.

Deformed Wing Virus (DWV)

Deformed Wing Virus (DWV) represents the next stage of varroosis progression. Bees with DWV are kicked out of the colony so if bees with DWV are seen than Varroa has become an issue. DWV does not signify un-manageable mite levels for the colony, but it is a more progressed sign of mite damage.

The bottom right corner contains a cell with chewed down brood (CDB). Bees begin chewing brood when they sense mites within the cell, so this can indicate larger mite issues. Photo by Rob Snyder

This bee has deformed wing virus, a debilitating virus than can easily deplete a colony. Oftentimes, bees with the virus are removed from the colony. So if bees with Deformed Wing Virus are seen, than this can indicate larger issues. Photo by Rob Snyder

Symptoms

Spotty brood and Varroa present on adult

Mites may be present on brood

Mites seen on open brood cells

Small population size

No odor present, just sunken brood

Varroa Mite Syndrome (VMS) is the most progressed sign of mite damage. If VMS mite is seen, than the damage is done. These colonies will likely collapse, and there is nothing a beekeeper can really do. At this stage, the colony has already dwindled and deteriorated. Photo by Rob Snyder

Varroa Mite Syndrome (VMS)

A pathogen has not been identified for this diseased, however mites are always present when this disease is seen. This brood symptom looks similar to other brood diseases except the larvae do not rope like foulbrood. Larvae do appear sunken to the side of the cell. If Varroa Mite Syndrome is observed, then colony has likely dwindled and deteriorated. Varroa Mite Syndrome is the most progressed sign of mite damage, and truly at a stage of no return. Even if low phoretic mites are seen, Varroa mite syndrome often means an end to your colony, even if treatment is applied.



Summary

All beekeepers should consistently monitor mites throughout the year. Even if mite levels are low at one point, it does not mean they will stay low. Mite levels can easily spike, so always be aware and monitor and re-monitor. Beekeepers should learn how to monitor and visually inspect for mites. By doing so, varroa mites can effectively be managed. Varroa mites are the most challenging issue beekeepers face, so make sure you know where your colonies stand. If you don’t, then you risk losing your colonies.

https://beeinformed.org/2018/09/26/the-signs-of-mite-damage-how-to-identify-progressed-varroosis/

(Note: Thank you to Jaime E. Garza, Apiary/Agricultural Standards Inspector, Department of Agriculture, Weights & Measures, County of San Diego for the link and his quote, “With the lack of floral resources this year, Varroa mites may put more stress on your colonies. Hopefully the information will help give you a better idea of how to look for signs of Varroa mite infestations and encourage you to monitor and control them if you are currently not doing so.”)

Varroa Mites - Bees' Archenemies - Have Genetic Holes in Their Armor

Michigan State University Environment + Science & Technology     August 14, 2017

Contact(s): Layne Cameron, Zachary Huang

National Honeybee Day is celebrated Aug. 19, but MSU scientists work year-round to protect these important pollinators. Varroa mites have decimated honeybee populations and are a primary cause of colony collapse disorder. Researchers have now found genetic holes in the seemingly indestructible pest's armor that could potentially reduce or eliminate the marauding invaders.

Varroa mites attached to honeybees. Photo by Zachary Huang

The team’s results, published in the current issue of the Journal of Insect Science, have identified four genes critical for survival and two that directly affect reproduction.

“The Varroa mite is the worst threat to honeybee health worldwide,” said Zachary Huang, MSU entomologist. “They have developed resistance to many pesticides, so it’s urgent that we explore and target these genes to develop better control methods.”

The mite sucks the blood of honeybees and transmits deadly viruses. Its lifecycle consists of two phases: one where they feed on adult bees, called the phoretic phase, and a reproductive phase that takes place within a sealed honeycomb cell, where the mites lay eggs on a developing bee larva.

Varroa mites' lifecycle consists of two phases: one where they feed on adult bees, called the phoretic phase, and a reproductive phase that takes place within a sealed honeycomb cell, where the mites lay eggs on a developing bee larva. Photo by Zachary HuangHaving the double-whammy of eating bees and spreading disease makes Varroa mites the number-one suspect of honeybee population declines worldwide.

Controlling pests like Varroa mites succeeds by either eliminating them or reducing their ability to reproduce. The team used RNA interference to identify the key genes, which could achieve these outcomes. They injected the mites with double-stranded RNA, or dsRNA.

Interfering reduces transcription of a specific gene, the first step of making a gene, a piece of DNA, into a protein. This process, also known as “gene knockdown,” has been successful in reducing the mating success and the number of eggs produced by cattle ticks, which threaten cows and other livestock around the world.


This bee is suffering from deformed wing virus, which is transmitted by Varroa mites. Photo by Zachary Huang

Using this approach, the team identified two genes that caused high mortality in Varroa mites – Da and Pros26S. In fact, Da killed more than 96 percent of mites. They also identified four genes – RpL8, RpL11, RpP0 and RpS13 – that control reproduction.

Earlier researchhas shown that a combination of dsRNAs can be fed to bees at the colony level. Varroa mites absorb the “genetic cocktail” via bee blood and their population was reduced. Future research will explore whether a single-gene approach can be scaled up and achieve the same effect at a colony-wide setting. Using a single gene with a known mechanism will be more cost effective and safe to the honeybees.

The results may have applications beyond honeybees, too.

“It’s worth noting that Da reduced reproduction in species of mosquitoes and Drosophila,” Huang said. “Future research could help not only protect honeybees, but also reduce disease-carrying mosquitoes or crop-damaging pests.”

Seemingly indestructible Varroa mites. Photo by Zachary Huang

Additional MSU researchers contributing to this study include Guowu Bian and Zhiyong Xi. Xianbing Xie, with Nanchang University (China), also was part of this paper.

This study was supported by the Almond Board of California, the Foundation for the Preservation of Honey Bees, the National Honey Board, MSU’s Project GREEEN, Michigan Beekeepers Association, National Natural Science Foundation of China, General Project of Jiangxi Provincial Department of Education and a fellowship from the China Scholarship Council.

http://msutoday.msu.edu/news/2017/varroa-mites-bees-archenemies-have-genetic-holes-in-their-armor/

Deformed Wing Virus Affecting Florida Bees

NPR WUFT FM   By Ashlyn Pinter    March 1, 2016

A global epidemic is hitting Florida honeybees, and it could affect your kitchen table.

The virus, called deformed wing virus, or DWV, is man-made and driven by European populations of the honeybee, according to a recent study.

DWV is a virus that infects honeybees, bumblebees and other pollinators. It is not harmful to honeybees on its own, but in combination with Varroa mites (ectoparasites that feed on bees’ blood) it can kill honeybee colonies, said Lena Wilfert, senior lecturer in molecular evolution at the University of Exeter in England and an author of the study.

As for human involvement, Wilfert said beekeepers who move colonies around for pollination services has led to the emergence of the Varroa mite and its rapid global spread. This follows the same spreading pattern as the virus.

Once the bees are infected with the virus and the mite they can lose their ability to fly, causing them to die prematurely. Bees may develop malformed wings, depending on when it is infected. The younger the bee is infected, the worse the malformation, said William Kern, University of Florida associate professor at the Fort Lauderdale Research and Education Center.

Both DWV and Varroa are widespread in Florida. DWV has been in Florida since honeybees were brought from Europe more than 300 years ago. Varroa, however, was not found in Florida until 1987, he said.

The University of Florida Honey Bee Research Lab in the Entomology and Nematology Department of IFAS has been working constantly on developing methods of Varroa and disease control,” Kern said in an email. The USDA Agricultural Research Service labs, which are located around the U.S., have been working on controlling the pests of both honeybees and native solitary bees. At this time, however, there is no treatment for DWV.

The mites and the virus weaken the bee colonies and, under stress, decreased pollination can kill the colonies. In turn, the inadequately-pollinated fruits tend to be misshapen. For instance, there are not enough bees to pollinate the California almond crop, said Kern. 

Florida is one of three main hubs where honeybees are shipped out to other places for pollination. Roughly 27 states are using Florida as a nursery due to the warmer weather in winter. In February, honeybees are shipped from Florida to pollinate the California almonds.

Between 2005 and 2007, pollination raised prices from $70 a hive to $145 a hive.  By 2013 the price was up to $185 a hive and as of 2015 it was up to about $225 a hive due to this problem, he said. This makes the price of honey raise too. 

Dave Westervelt, chief of aviary inspection at the Bureau of Plant and Apiary inspection said, “It’s (the virus) reducing the life expectancy of the honeybee so we don’t have the number of bees we have to pollinate the 1/3 of our fruits and vegetables that are pollinated by European honeybees.”

Beekeepers are now losing 30 to 40 percent of bees because of this virus, Westervelt said. “Almost every bee keeper that has bees has an issue with the ongoing virus.”

Since people rely on pollination for a third of their food, DWV and Varroa could hinder the pollination of foods like honey, almonds, fruits and vegetables globally and we would lose roughly a third of those foods. For instance, in Florida, bees pollinate blueberries and squash. If bees meant to pollinate these foods are dying due to virus, the consequences could be severe, Westervelt said.

“We need honeybees and wild pollinators for maintaining food security, as much of our vegetables and fruit rely on pollination,” Wilfert said. “They maintain biodiversity of flowering plants, which we need to maintain resilience in ecosystem services.”

http://www.wuft.org/news/2016/03/01/deformed-wing-virus-affecting-florida-bees/

Researchers Find Link Between Honey Bee Virus and Colony Trafficing

The Daily Californian    By Alexander Barreira and Young Min Kim    February 15, 2016

The global spread of a virus that leads to stubby wings and early mortality for honey bees has been linked to beekeeping practices, suggests a recent study by campus scientists in tandem with other institutions.

Mike Boots of UC Berkeley, in collaboration with scientists at the University of Exeter, led the team in analyzing the genomes of various viruses in order to trace the origins of Deformed Wing Virus to human-managed honey bee colonies in Europe. Their study, published in Science Magazine on Feb. 5, adds to growing concerns on the health of global honey bee populations.

According to Lena Bayer-Wilfert of the University of Exeter, the study’s lead author, beekeepers often trade queen bees among different colonies to maximize honey production or to breed other desirable traits. This practice, while producing better quality honey, can lead to the spread of infectious viruses such as DWV.

According to Robbin Thorp, a UC Davis emeritus professor and member of UC Davis’ Honey Bee Research Facility, large agricultural operations such as almond farms rely on imported honey bee colonies to make production of pollinated fruits and vegetables possible. Although honey bees are not the most efficient pollinators, they are ideal for transportation, Thorp added.

Thorp noted that the disease can spread easily in such operations because hives from different parts of the country may be housed in close proximity on the same orchard.

The disease, originally found in Asian honey bees, has spread to European honey bees and across the globe over the last 80 years. Thorp described rules governing colony movement as a “real problem” for beekeepers trying to stop the spread of the virus.

According to the study, the disease is transmitted through parasitic Varroa mites that feed on bees’ blood. The combination of mites and disease hurt honey bee colonies’ ability to survive cold winters and adds to existing difficulties faced by honey bee colonies, such as disorientation from pesticide use and colony collapse disorder, in which the majority of worker bees abandon a hive.

The study urged for tighter controls on the movement of bee colonies. Wilfert added in an email that beekeepers need to follow existing legislations regarding transportation of colonies, which include screenings for disease.

Healthy bees and other wild pollinators are vital for human food security and are just as important for maintaining biodiverse communities and resilience in ecosystems, according to Wilfert.

“They provide much of the fruit and vegetables that make our food tasty and healthy,” Wilfert said in an email. She added that the preservation of honey bees is especially important to solving the problem of long-term food supply.

“Any damage that might be done has been done,” Thorp said. “We’re just beginning to realize that some of these things are going on.”

http://www.dailycal.org/2016/02/15/researchers-find-link-between-honeybee-virus-and-colony-trafficking/

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