How do varroa mites kill bees

Despite their advantages, most biotechnical methods are only suitable for restricted periods of the year and it is beneficial to combine these control methods, with other methods, such as chemicals, for an effective IPM strategy. A workshop detailing the non-chemical and minimum chemical use options for managing Varroa was held in Australia in The workshop report, Non-chemical and minimum chemical use options for managing Varroa , is available for free download and was funded by the Rural Industries Research and Development Corporation.

Two of the major issues with treating Varroa that have been experienced overseas include mite populations developing resistance to the chemicals used to control them, as well as residues being found in the honey and wax that are the results of the beekeeper treating hives for Varroa.

Both of these issues are very serious, and all beekeepers need to be aware of the risks associated with each of these problems. Chemical resistance As with any other pest, Varroa mite populations will eventually develop resistance to any chemical used. Individual variation within a mite population may result in small numbers of mites with resistant traits eg a thicker cuticle that prevents the entry of the active ingredient, or a metabolism that may break down the active ingredient before it does the mite damage.

These characteristics are genetic and thus heritable. Although mites with these traits are generally reproductively weaker and are initially present in only very small numbers, when strong selection pressure is placed on the mite population, such resistant traits may begin to dominate.

This can happen when a population of mites is repeatedly exposed to a Varroa chemical, leaving more of the resistant mites alive to reproduce, and further pass on their favourable genetics.

Over many generations, these mites will tend to become increasingly common until they comprise the majority of the mite population. How long this process takes depends on a number of factors, such as how often Varroa mites are exposed to a Varroa chemical and what dose. Frequent treatments of the same chemical over time, or when treatments are misused ie lower than recommended doses or when treatments are left in the hive, will greatly accelerate the development of Varroa mite resistant to chemicals.

Problems with resistant Varroa mite populations have started to appear around the world and are widely documented.

These resistant mite populations have subsequently increased and spread with predictable consequences. In an effort to slow down the development of resistance, and to control Varroa, many beekeepers in these countries appear to be managing Varroa by using other registered chemicals on an alternating basis, as well as biotechnical methods through an integrated pest management IPM program. For Australia, as the last remaining country to have Varroa, the management options available will depend greatly on whether the Varroa mite is resistant to a variety of chemicals.

For this reason, it is critical to understand how beekeepers overseas have managed this issue, and how they are managing it in their beekeeping operations. Even if the Varroa mite that enters Australia is not resistant to common chemicals, it is important that beekeepers do not speed up the resistance process. Instead, we should learn from the mistakes made overseas in the control of this mite and the development of resistant populations and work to avoid this at all costs.

Chemical residues There is increasing pressure on all agricultural industries to ensure that food produced does not contain excessive chemical residues. Honey and wax are no exception. The variety of chemical options available to beekeepers listed above can leave harmful residues in honey and wax.

This has resulted in many residue issues overseas, not only for the beekeepers, but also for consumers. All chemical controls applied to a hive have a risk of leaving chemical residues behind. The risks of chemical residues have been minimised by beekeepers overseas using the following simple guidelines:.

The selective breeding of Varroa tolerant bees is considered to be the only long-term solution to control the Varroa mite. This has been possible because honey bees around the world have developed a variety of ways by which they can live successfully with Varroa mites. Varroa tolerant colonies inhibit the growth of the Varroa population to such a degree that they can survive long term in a healthy, productive manner without major chemical treatments by beekeepers.

Few, if any of these mechanisms of resistance are completely understood, but many can be selected for in a breeding program. The most notable of the natural defensive behaviours are hygienic behaviour and grooming behaviour. Honey bees that exhibit grooming behaviour use their legs to comb themselves.

They do this both to themselves and to other bees in the colony. This grooming behaviour increases the number of Varroa mites that fall off the adult bees and sometimes die , which lowers the number of adult female Varroa mites in the colony. Hygienic behaviour is the most studied of all of the natural defences against Varroa mite, and has been discussed for many years as an important selection criterion for breeding programs. Although it is not a behaviour specifically targeting Varroa mite control, hygienic colonies have been proven to maintain lower mite loads, especially at moderate mite infestation rates and the trait is quite heritable.

Honey bees that are hygienic can detect many problems that affect brood American foulbrood, Sacbrood virus, Chalkbrood, etc , even if the brood is capped, and remove the affected brood.

Because Varroa mites can evade detection and move into developing brood before capping, honey bees are given little time to find and remove the Varroa mite before this occurs. Hygienic bees have a refined ability to detect Varroa mite in capped cells, remove the capping and abort the brood. Often, this behaviour can lead to the death of the mite, thus lowering Varroa populations.

VSH honey bee stock has the ability to detect Varroa mites in capped cells and remove only the Varroa mites that are reproducing in the cell. Russian bees are a European subspecies of honey bee introduced into eastern Russia over years ago.

Because Varroa mites are native to the area, Russian bees have developed a general resistance or tolerance to the mite.

These honey bees do not have a single defensive behaviour against Varroa mites; however, various reports have confirmed that these bees can maintain a significantly lower population when compared to other strains of European honey bees. Their increased tolerance to Varroa mites was attributed to several factors, among them the lower attractiveness of brood cells, reduced mite reproduction and extended phoretic periods for the mites.

The most successful of the breeding programs using Russian bees has been through the United States Department of Agriculture, with stock now widely available to beekeepers in the United States.

The Varroa mite is capable of infecting honey bees with numerous viruses. It is not possible for beekeeping operations to directly control viral infections within honey bee colonies, but good management will help. Management of colonies to prevent losses associated with bee viruses should include:.

It is recommended that mite populations be kept as low as possible to avoid potential threshold levels within the honey bee colony and potential colony collapse. Sugar shaking is an effective means of monitoring Varroa mite levels. Integrated pest management IPM refers to a whole of system approach aimed at managing a pest with a minimum use of pesticides.

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 level , and 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. 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. 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. 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 populations , which 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.

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. Varroa mites V. Surveillance programs, such as the National Bee Pest Surveillance Program are also in place in high risk ports around Australia to detect this pest if it does enter Australia, and attempt to eradicate it.

If you observe any symptoms that you think may be caused by Varroa mites, or if you observe any mites on the brood or in a honey bee colony, call your local department of agriculture or the Exotic Plant Pest Hotline on Varroa mites could enter Australia on infected adult honey bees or brood. The most likely entry pathway for Varroa mites into Australia is by accidentally introducing infected honey bees on ships or shipping containers.

Research has shown that V. Honey bees from overseas have been intercepted at various Australian ports. Beekeepers may take advantage of this preference by placing special combs with drone-sized cells in their hives to attract mites to the brood. These combs can then be removed before the drones—and the mites—emerge from their cells. Depending on the time of year, this practice can dramatically reduce the mite populations within colonies.

Inert dusts. Adult mites move through the hive by clinging to the backs of adult bees. Some research has shown that covering all the adults in a colony with fine dust particles, such as powdered sugar or talc, can cause the mites to lose their grips and fall off their hosts.

This technique can be laborious and quite disruptive to a colony, but it requires no chemical pesticides. Some of the more exciting advances in varroa mite control has been in honey bee genetics. In recent years, much work has been done with the development of particular strains of honey bees that have shown tolerance to the varroa mite.

Though the mechanisms are not completely understood, some behavioral and physiological traits likely play a role in varroa resistance.

Today, several strains of bees are available that have been shown to reduce the number of varroa mites within their colonies. Russian strain. Because these Russian bees have been exposed to the mite for a longer period compared to other strains, it follows that they may have developed a resistance to the mite. Indeed, research has shown that they are over twice as resistant to varroa as other commercial stocks.

Moreover, for reasons that are yet unclear, this stock appears to be highly resistant to the tracheal mites, a second parasitic mite that infests honey bee colonies. The Russian strain has been made available for commercial purchase in the U. VSH stock. Standing for Varroa Sensitive Hygiene, this trait was selected for by USDA researchers using classical bee breeding and instrumental insemination techniques. The bees have been selected to detect varroa mites in the cells of developing pupae and remove them before the mites can reproduce.

This stock has been crossed with other, more common commercial stocks in an attempt to integrate this useful trait into other bee strains. Hygienic behavior. Much research has demonstrated lower levels of numerous diseases in colonies selectively bred to uncap and removed diseased or parasitized brood e.

While these stocks are not immune to varroa parasitism, they may significantly reduce the need for other control methods. Biopesticides are defined as naturally occurring organisms or their by-products, and several have been registered for controlling varroa mites in honey bee colonies. The efficacy of many biopesticides can equal to that of conventional chemical pesticides. However, the delivery of these chemicals can be quite different, and understanding these differences is important to insure successful control of varroa.

This product—containing a combination of the essential oils thymol, eucalyptol, and menthol—has been approved by the US Environmental Protection Agency EPA for its use in North Carolina to treat both varroa and tracheal mites. The delivery medium of this product is a vermiculite tablet, which must be broken into four pieces and placed in the four corners of the hive between the brood chambers.

Each section must be wrapped in wire mesh to prevent the bees from chewing it and removing it from the hive prematurely. New tablets must be used every week for three weeks for complete effectiveness. The product may cause significant mortality of bee brood, thus it may be most useful as a fall treatment when brood rearing naturally declines.

Formic acid. The EPA has recently permitted the use of formic acid for the control of varroa mites in the United States.

It is important when varroa is suspected in an apiary that the following steps are taken by the beekeeper to reduce the risk of spread:. If you see or suspect varroa is present in your apiary, you must report it immediately by calling the Exotic Plant Pest Hotline: 24 hours a day, every day of the year.

Notification is required by the Livestock Disease Control Act To not notify is to break the law. Early recognition of varroa is one of the most important factors influencing the chance of controlling them and reducing their economic and social impact on the whole community. If you require further information or assistance, please contact the Customer Service Centre on or email honeybee. Biosecurity Protecting Victoria Moving livestock and animals Moving plants and plant products Animal diseases Marine pests Pest animals Pest insects and mites Report an unusual plant pest or disease Priority pest insects and mites Armyworms Australian Plague locusts Balaustium mite Brown marmorated stink bug Blackheaded pasture cockchafer Blue oat mite Bumblebee Codling moth Diamondback moth Electric ant European house borer European wasp Exotic honey bee parasites Exotic Liriomyza leafminers Fall armyworm Fire ants Giant pine scale Giant willow aphid Green snail Hazelnut mite Hover flies Khapra beetle Mediterranean fruit fly Olive lace bug Potato cyst nematode Queensland fruit fly Redheaded pasture cockchafer Silverleaf white fly Tomato potato psyllid Two-spotted mite Varroa mite of honey bees About varroa mite of honey bees Sugar shake test to detect varroa mite Varroa mite detection Wax moth a beekeeping pest Other species detected Plant diseases Weeds Food safety.

Sugar shake test detection of Varroa Mites Varroa mite Varroa destructor and Varroa jacobsoni is a parasite of adult honey bees and honey bee brood. Description Adult female varroa are reddish-brown, shaped like a scallop shell, about 1. Adult males are smaller and are yellowish-white. Both sexes have eight legs. The eggs are 0. Life cycle Varroa only produce offspring when honey bee brood is present in hives.

The single male varroa mates with its sisters while they are in the brood cell. How varroa spreads The mites are very mobile and readily transfer between adult bees. Field diagnosis Field diagnosis of exotic honey bee parasites and pests in beehives provides detailed notes on the field diagnosis of varroa. Steps if you find or suspect presence of varroa in your apiary It is important when varroa is suspected in an apiary that the following steps are taken by the beekeeper to reduce the risk of spread: Collect a specimen of the suspect varroa mite and place it in a small jar of methylated spirits.

The use of predators has shown mixed results and was unsuccessful when applied to honey bee colonies, as was recently the case in an evaluation of the predatory mite Stratiolaelaps scimitus , which demonstrated interesting results in vials but no effect on honey bee colonies [ ]. Hyperthermia has been used since the s, and is based on the better heat resistance of the bees compared with Varroa [ ].

Artificially heating the hive stops Varroa reproduction and kills the parasite, without harming the bees, because Varroa reproduction is significantly compromised at Heating systems have been proposed to control the mites in different parts of the world, and there are a few systems available on the market at the moment [ , ].

One other option is to use RNA interference to knock down specific genes of Varroa , which has been studied since with successful results [ 43 , , ].

To date, there is no product available for beekeepers [ ] Figure 2. A variety of tools available for beekeepers make the development and use of the IPM concept in Varroa control possible Figure 2. IPM is partly based on limiting pesticide use to when it is only necessary. This requires regular monitoring of the Varroa population levels, in order to detect critical infestations and decide on a treatment.

As critical infestation levels differ worldwide, these must be defined for specific regions and biotopes. Efficient but time-consuming techniques exist to diagnose a Varroa infestation [ ]. Mites can be counted in the brood, on adults or on debris at the bottom of the hive.

Brood examination consists of opening capped cells to verify Varroa infestation by removing the pupae and counting mites [ 77 , ]. Mite count on adult bees is better documented and increasingly used. It consists of collecting — bees, separating the mites from bees with a surfactant substance, such as chloroform, alcohol, icing sugar or acaricide treatment, and counting the removed mites [ 77 ].

Debris examination can be operated with a sticky sheet placed on the floor of the hive with a thin wire mesh on top of it to prevent bees from cleaning out the fallen mites. Fallen mites stick to the board and honey bees are not able to remove the parasite from the hive [ 77 ].

As it is a time consuming and tedious method, a stratified method has been proposed to make an accurate estimation of the mites [ ]. New techniques, using technological developments such as gas sensors or computer vision systems, are being tested to estimate Varroa infestation [ , ]. They have yet to be transferred to the field and to the beekeeping community.

In parallel to the development of control solutions to fight the mite, quantitative geneticists and bee breeders have started to search for a longer-term, sustainable solution: selecting honey bee populations that can survive mite infestation without treatments. Several surviving honey bee populations have been identified or bred throughout the world for a review of these efforts, see [ — ]. Examples of large-scale use of such populations in beekeeping are scarce [ , ] and currently limited by the lack of tools that allow selection of surviving honey bee colonies in the field.

Such tool development relies on the identification of specific phenotypes that characterise these populations. To do so, a better understanding of the mechanisms that undergird the ability to survive is necessary. Surviving can occur through the expression of resistance or tolerance traits, with resistance involving a reduction in Varroa growth, while tolerance reduces parasitic burden despite similar levels of Varroa growth [ ].

A wide range of traits involved in honey bee survival to Varroa have been identified, and mainly relate to resistance mechanisms [ ]. Tolerance has so far been suggested only in cases e. Recent investigations highlight the importance of behavioural defences displayed by Varroa resistant honey bee populations Figure 3.

Hygienic behaviour specifically targeting Varroa -infested capped brood cells VSH, Varroa- sensitive hygiene has been confirmed as a major trait contributing to reduced mite population growth in European and African bee populations [ — ]. Two other adult bee traits, grooming [ ] and recapping [ , ], have been confirmed as important mechanisms for Varroa resistance.

At the colony level, swarming can enhance resistance in surviving populations living in the wild [ 71 , ]. Brood traits could also be involved in resistance abilities, if they confer hypersensibility of the brood that leads to the accelerated death or an increased rate of removal, thereby preventing the spread and reproduction of Varroa [ , ]. Altogether, these traits participate in limiting mite population growth as characterised by high levels of mite non-reproduction within the brood.

Together with grooming and swarming these traits lead to colony resistant through low mite population growth. Research has mostly focused on host traits to explain the survival of untreated colonies, but the parasite itself may play a central role too.

Indeed host fitness can directly be affected by parasite fitness, as suggested by studies showing that Varroa infesting surviving colonies are genetically distinct from Varroa infesting neighbouring susceptible colonies [ , ].

Progress in understanding the mechanisms that underlie resistance abilities along with the recent boost in genomic tool development has opened the possibility of devising a diagnostic tool of resistance based on phenotype, directly accessible to beekeepers.

So far, available methods are very tedious and difficult to apply in the field on large numbers of colonies. This is true for measures of mite population growth, mite non-reproduction or hygienic behaviours.

The recent identifications of molecular and protein markers of several traits related to resistance grooming, hygiene, VSH and mite non-reproduction , although very limited in overlap between different studies [ ], opens up the possibility for marker-assisted selection [ — ]. It would allow beekeepers to easily select their colonies for on the basis of interesting resistance traits when the phenotype are difficult to characterise. To date, there are no products available on the market and research is continuing in this area.

Another perspective for the development of selection tools originates specifically from a detailed understanding of the mechanisms of VSH behaviour, a trait in which honey bees are able to specifically detect Varroa -infested brood. Strong evidence suggests that the recognition step involves the detection of Varroa infestation-associated semiochemicals [ 16 , — ].

Evaluation of the bee response following application of such candidate compounds in colonies, by acting as a reliable proxy of the VSH activity of the colony, could result in a practical field tool to phenotype resistant colonies.

Despite the amount of research done on the A. Future developments, both in fundamental and applied research, are necessary to generate sustainable control solutions for this deadly parasite.

The latest findings on the physiology of Varroa and its behaviour provide a better understanding of its negative impact on bee health. IPM methods can be used to limit the use of acaricides to control Varroa. The selection of resistant or tolerant honey bee populations could bring a sustainable mite control solution for beekeeping and wild honey bee populations. Research needs to focus on the development of control methods, especially new active compounds to counter the mite's resistance against acaricides and to efficiently fight V.

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Google Scholar. Hauke Koch. Previous Article Next Article. All Issues. Cover Image Cover Image. Biology of Varroa destructor. What can it do? What can be done? Competing Interests. Author Contributions. Article Navigation. Review Article June 15 Varroa destructor : how does it harm Apis mellifera honey bees and what can be done about it?

Fanny Mondet Fanny Mondet. Correspondence: Fanny Mondet fanny. Emerg Top Life Sci 4 1 : 45— Article history Received:. Revision Received:. Get Permissions. Figure 1.