Honey Bee Viruses, the Deadly Varroa Mite Associates - eXtension
The parasitic mite Varroa destructor and the deformed wing virus (DWV) are linked deformed wing virus, mutualistic symbiosis, honeybee colony losses by combined stress from parasites, pesticides, and lack of flowers. In relation to control of varroa parasite by using four volatile plant oils, data Essentials Oils on Varroa destructor Mite of the Honey Bee. Varroa mites (Varroa destructor and V. jacobsoni) are tiny red-brown external parasites of honey bees. Although Varroa mites can feed and live on adult honey .
The cycle is repeated. The beekeeper will put a frame in the hive that is sized to encourage the queen to lay primarily drone brood. Once the brood is capped, the beekeeper removes the frame and puts it in the freezer. This kills the Varroa mites feeding on those bees. It also kills the drone brood, but most hives produce an excess of drone bees, so it is not generally considered a loss. After freezing, the frame can be returned to the hive. The nurse bees will clean out the dead brood and dead mites and the cycle continues.
Drone brood excision method is a variation applicable to top bar hives. Honey bees tend to place combs suitable for drone brood along the bottom and outer margins of the comb.
Integrated pest management Sugar shaking is an effective means of monitoring Varroa mite levels. The IPM approach has been widely adopted in other agricultural industries, and has proven to be an effective management measure for Varroa by beekeepers around the world. Adopting IPM practices includes regularly monitoring for pests and only applying chemicals when needed such as when the pest is present above a set leveland using non-chemical management options to control the pest population where appropriate.
This is much more effective than the alternative of waiting until pest numbers have reached a damaging level before applying controls, or applying the same controls year after year, regardless of pest numbers. For more information about early surveillance techniques for Varroa, which are also effectively used overseas as monitoring techniques, click here. For beekeepers, good husbandry and colony management should be the starting point for effective IPM control of Varroa mite.
Keeping a close eye on the health of your honey bees and making sure you can recognise the signs of low levels of Varroa mite infestation are particularly important. To aid in this, regular monitoring of the Varroa mite levels in hives should be conducted.
Mite levels between colonies and apiaries can vary greatly, so it is always a good idea to monitor a representative proportion of colonies in each apiary, including strong and weak hives. Sticky mats under mesh screen bottom boards are an effective means to monitor natural mite fall and mite levels. Rob Manning, DAFWA Other key husbandry and management practices that beekeepers can adopt include maintaining apiaries to minimise the effects of robbing and drifting, aiming to keep strong colonies free from other pests and diseases, as well as selecting strains that seem to show some Varroa tolerance.
For beekeepers, adopting an IPM strategy for the control of Varroa can have many benefits. Control at various points throughout the year makes it harder for the mite population to reach damaging levels, at which point colony loss would occur.
Combining the use of biotechnical and chemical management options will reduce the reliance of pesticides, as well as delay the development of mite resistance to chemicals. Reducing the use of chemicals will also benefit the bees.
The effect of in-hive Varroa chemicals on honey bees has been shown to reduce the longevity of queen bees, reduced sperm loads in and longevity of drones, brood death and reduced queen laying patterns. Many more effects are believed to exist. Since Varroa levels will vary from year to year, control options can be easily altered to reflect the changing infestation levels.
Unfortunately there is no single IPM strategy for Varroa that is suitable for all circumstances.
This is because there are enormous variations in the rates of mite invasion, climate, beekeeping practices, infestation levels and economic threshold levels. For Australia, only experience with dealing with Varroa will provide reliable information about region specific IPM programs which could be implemented.
Timing of Varroa management methods There are a number of factors that affect the effectiveness of Varroa control. If not there is a risk of Varroa mites rapidly reinfecting treated hives Various treatment programs or regimes can be used to manage Varroa and are listed below. Always remember that treatment does not specifically mean using a Varroa chemical and can include using a range of other biotechnical control methods, such as drone removal.
For the spring treatment, it ensures that the bees have emerged from winter with a very low mite infestation level, which will help the bees over their busiest time of the year spring and summer.
For the winter treatment, the colony will be reducing in size while the infestation will be continuing to increase. The aim of this treatment is to significantly reduce the mite population, thus protecting the last few brood cycles that produce the young bees needed for a successful colony over winter. If you miss or delay this treatment, the bees will carry a higher Varroa load into winter, which will mean shorter life spans, subsequent dwindling of the adult bee population and possible colony collapse.
As all hives are treated this method reduces monitoring costs but also means that there are additional chemical control costs as some hives may not have needed treatment eg if Varroa was absent or not at damaging levels. This treatment method will have advantages in the early stages of a Varroa introduction as all hives are treated even if the mite population is not high enough to be detected.
Treatment based on Varroa numbers Treatments based on Varroa numbers involve the IPM see above principles of monitoring the Varroa population and only treating the hive when the Varroa population has reached an economic threshold ie hives are only treated when economically justifiable. This treatment method has the advantage that it reduces chemical use and therefore reduces chemical costs and the build-up of Varroa resistance to the chemical. Coordinated treatments The Varroa population in a hive increases at an exponential rate.
In other words the population increases faster and faster over time. If only a single hive or apiary was treated and neighbouring hives are not treated the Varroa mites from nearby hives can quickly invade eg be brought in on drifting or robbing bees and repopulate treated hives.
For this reason treatments are most effective when all the hives in an area are treated simultaneously. Coordinated treatments have the advantage that there is less cross-colony introduction of Varroa mites as all hives in the immediate area are treated and therefore have reduced Varroa populationswhich means that it takes longer for the Varroa population in each hive to build up to damaging levels.
The disadvantage of such a system is that it can be difficult to coordinate and it is less effective if hives are frequently moved between areas. Lessons from overseas Some of the key lessons from the UK of effective strategies to manage and control the Varroa mite are listed below.
Although these are only relevant to beekeepers that have to manage Varroa, they provide an insight into what is important for beekeepers to consider when looking to implement effective management options. Monitor the infestation in your hives. You need to know if the mite population is building up faster than you thought or your treatments are not proving effective.
Talk to other local beekeepers about the Varroa problems you experience and the control strategies you are using. It may then be helpful to work together, for example in co-ordinating treatments. Practice integrated pest management IPM using a combination of varroacides and biotechnical methods. This will give the most effective control.
Slow the development and spread of resistant Varroa and minimise the risk of treatment residues by treating no more often than is necessary. Monitoring will help you decide how often this should be. Use only authorised varroacides. These have proven efficacy against Varroa and proven safety for bees, beekeepers, consumers and the environment.
Always follow the label instructions. Where possible rotate the use of two or more unrelated varroacides ie varroacides with different active group ingredients. This is an effective strategy to slow the development of resistance. Avoid using the same varroacide year after year. Remember that the use of unauthorised chemicals in your colonies or the misuse of authorised varroacides may leave harmful and detectable residues in your bee products.
Be prepared to check for Varroa resistance. Learn to test for resistance and gain experience of using other controls. When resistance arrives you will have to stop using those medicines to which mites are no longer susceptible, and rely on alternatives. Be flexible and adaptable in your control of Varroa. Methods that work well in some circumstances may not work well in others. Keep up to date with new developments in the control of Varroa.
As the situation develops you need to make sure you have the latest information to help you respond appropriately. Select for and retain bees that appear to show increased tolerance to Varroa. Not all mite infested pupae develop these symptoms, but all adult honey bees with symptoms develop from parasitized pupae.
Varroa mites « Bee Aware
Bees infected as adults can have high virus titers but do not develop symptoms. DWV may also affect aggression Fujiyuki et al. DWV appears to replicate in Varroa, making it a biological as well as physical vector.
Infection of pupae may be dependent on DWV replication in Varroa prior to transmission. Winter colony mortality is strongly associated with DWV presence, irrespective of Varroa infestation. This suggests that Varroa infection should be reduced in a colony far in advance of producing overwintering bees, to ensure reduction in DWV titers. Although generally understood as being asymptomatic in adult bees, Shutler et al. Queen pupae with symptoms display a pale yellow sac-like skin similar to sacbrood.
The pupae rapidly darken after death and turn the wall of the queen cell dark brown to black. Symptomatic drone pupae have also been observed.
It can also be transmitted by injection to pupae. BQCV has a seasonal relationship similar to Nosema, with a strong peak in spring.
Dysentery on the front of a hive is a symptom but not indicative of Nosema disease. It is unique among honey bee viruses in that it has a distinct particle size and genome composition.
It is also the only common honey bee virus to have both visual behavior and physiological modifications resulting from infection. Type 1 symptoms include trembling motion of the wings and bodies of adult bees, who are unable to fly, and crawl along the ground or up plant stems, often clustering together.
The bees may also have a bloated abdomen, causing dysentery and will die within a few days after displaying symptoms. Type 2 symptoms are greasy, hairless, black adult bees that can fly, but within a few days, become flightless, trembling, and soon die Image 5. Both of these syndromes can occur within the same colony. Severely affected colonies, often the strongest in an apiary Ribiere at al. These symptoms, however, are similar and often confused with other honey bee maladies including Nosema apis, colony collapse disorder CCDtracheal mites, chemical toxicity, and other viruses.
Bees with CBPV type 2 symptoms: The Food and Environment Research Agency FeraCrown Copyright Transmission of the virus primarily occurs through direct body contact, although oral transmission also occurs but is much less virulent. Feces from infected bees within a colony can also spread the disease, and other transmission routes are still being investigated, including possible Varroa transmission.
The virus is widespread and an outbreak can occur at any time of year. Spring and summer are the most common seasons for mortality from the virus, but it will persist in a colony year-round without displaying any overt symptoms de Miranda et al. New molecular tools have allowed researchers to identify the presence of these and other new viruses and their seasonality in test colonies. Little else is know of the Lake Sinai viruses, including its pathogenic or epidemiological significance.
Other described honey bee viruses that were discovered before the advent of molecular techniques have no genomic data to reference; therefore newly discovered viruses may in fact be the already discovered viruses of the past such as Bee virus X and Y, Arkansas Bee Virus or Berkeley Bee Virus Runckel et al.
These viruses are widespread at low titers and can quickly develop high titers due to extremely virulent pathology. Frequently associated with colony loss, this virus complex is especially deadly when colonies are heavily infested with Varroa mites. Ball ; GenerschGenersh et al. These viruses have not been shown to cause symptoms in larval life stages, but show quick mortality in pupae and adult bees. APBV is transmitted in larval jelly from asymptomatic infected adult bees to developing larva or when vectored by Varroa mites to larvae and pupae.
ABPV is common and typically cause covert infections no obvious symptoms when transmitted orally from adult to developing bee.
When the virus is picked up by Varroa, the transmission rate to pupae is between 50 and 90 percent. The longer the feeding period of Varroa, the greater the transmission rate will become. Pupae infected with ABPV die before emerging, making the appearance of paralysis symptoms less obvious. The decline in emerging bees causes a colony to dwindle towards collapse. Kashmir Bee Virus KBV Kashmir bee virus has widespread distribution and is considered the most virulent of honey bee viruses under laboratory condition Allen and Ball When KBV is injected in to adult bee hemolymph, death occurs in just 3 days de Miranda et al.
KBV does not cause infection when fed to developing bees, but does persist in adult and developing bees without any obvious symptoms. When Varroa mites transmit the virus, it becomes deadly to all forms of the bee lifecycle but displays no clearly defined symptoms. Control of Varroa mites is necessary to prevent colony losses from KBV. IAPV is found in all life stages and castes of bees. IAPV is extremely virulent at high titers, as when vectored by Varroa and is covert at low titers.
SBPV persists as a covert infection and is transmitted by Varroa to adults and pupae. The disease will kill adult bees and eventually the entire colony de Miranda et al.
Prevalence of the virus is limited. It has not been found in the U. Summary Most pathogens invade the digestive system through oral ingestion of inoculated food.
These pathogens infect the mid gut epithelial cells, which are constantly being replaced and are protected by membranes and filters which confine the pathogen to gut tissues. Parasites that infect gut tissue like Nosema apis and Nosema cerana can create lesions in the epithelium that allow a virus like BQCV to pass into the hemolymph and infect other cells in the body. In contrast the external parasite Varroa destructor feeds directly on bee hemolymph providing an opening in the cuticle for viruses to enter.
Most virus infections rarely cause infection when ingested orally, but only a few virus particles are necessary to cause infection when injected directly into the hemolymph. Many viruses can be directly transmitted by Varroa mites, such as: DWV, those in the acute bee paralysis virus complex, and slow bee paralysis virus.
Varroa destructor - Wikipedia
Other viruses, like sacbrood, have been detected in Varroa mites but Varroa has not been shown to directly transmit the virus. Knowledge about the presence, role, and transmitting routes of these viruses in native bees, and other potential non-Varroa transmission routes is also lacking in detail, complicating recommendations for control.
Research does show viruses clearly affect honey bee health and warrant attention from the beekeeper and researcher alike. Control Viruses persist in normal, healthy colonies, only to explode during times of stress. Many viruses are only damaging when in combination with another stressor like Varroa or Nosema.
Active, integrated management of Varroa and other stressors is essential to minimizing virus titers. To learn more about reducing stressors with best management practices see here.
Routinely inspect your colonies for possible disease. Have a thorough knowledge of symptoms and identify when colonies are slow to build up or have sporadic brood patterns, indicating brood has been pulled out and removed Image 6.