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By Helen Paynter 4 July 2022 5 min read

Australia has been the largest honeybee producing country to be free of Varroa mites (Varroa destructor and V. jacobsoni). However, biosecurity officers found V. destructor at Newcastle Port on 22 June 2022. Our scientist Dr John Roberts comments on the problem with this invasive pest.

What is Varroa mite?

Varroa mites are deadly parasitic pests that feed on developing and adult European honey bees (Apis mellifera). They are the greatest biological threat to Australia’s honey bee and pollination-dependent plant industries. The mite has a reddish-brown body that is less than two mm wide and visible to the naked eye.

Left untreated, Varroa mites will eventually kill any bee colony it infests. Between 90 and 100 per cent of feral colonies are expected to be lost.

A Varroa mite attached to a bee. Photo credit: Denis Anderson

Where does Varroa mite come from originally?

Varroa mites are originally parasites of Asian honey bees (A. cerana). However, some have adapted to be a pest of European honey bees. Varroa mites now inhabit most parts of the world.

Has Australia detected Varroa mite before?

This is the first incursion of V. destructor in Australia. Authorities are responding quickly to try to contain and eradicate the mite. In 2018, there was an interception of V. destructor in a honey bee swarm on a ship in the Port of Melbourne. Authorities had to eradicate the swarm.

How did Varroa mite reach Australia?

At this stage it is unknown how and when Varroa arrived in Australia. Although it is possible that an infected honey bee swarm has entered the Port of Newcastle on a shipping vessel.

What do we know about this new incursion in Australia?

Australia has a network of sentinel bee hives at several Australian ports. These hives are like security guards and provide an early warning system for biosecurity threats to honey bees. The incursion of Varroa mite was discovered on 22 June 2022 in two of these sentinel hives at the Port of Newcastle. Biosecurity officers inspect sentinel hives every six weeks for exotic mites and other pests.

Is Varroa likely to spread?

This biosecurity response is specifically aimed at stopping the spread of Varroa mites and eradicating this incursion. An emergency order is in place in NSW that prohibits the movement of bees and bee hives. On the other hand, feral bee colonies are a challenge to the response as they can help spread Varroa mites. The NSW Department of Primary Industries have been updating the amount of affected hives at their website. [Link will open in a new window]

How does Varroa mite spread?

Varroa mite is spread by bees and hives that have come into contact with the pest. Bees can spread Varroa mites if they ‘drift’ into other hives and even between honey farms (apiaries). If a bee colony dies, other bees coming to steal the honey from that colony can spread Varroa mites back to their hives. It is even possible for Varroa mites to spread to bees when they are visiting flowers.

A mite family at the base of a brood cell. The white mites are juveniles. Photo credit Denis Anderson.

How does the Varroa mite affect bees?

The Varroa mite attaches to the bee and feeds on their ‘fat body’. This is a part of the bee that plays a role in energy production, growth and immunity. The feeding mite weakens the bee, as do the deadly bee viruses that Varroa mites can carry. Deformed Wing virus (DWV) is the most serious of these viruses. The combination of the Varroa mite and DWV is a leading cause of bee colony deaths in other countries.

Has Australia detected the virus?

Our previous research has shown Australian bees do not have DWV. Virus testing for the current Varroa mite incursion has also not detected DWV, indicating it has not been introduced with the mite. Continued virus monitoring will be important, as the damage from Varroa on bee colonies without DWV will be reduced.

If Varroa mite gets into a hive, is there anything bee keepers can do?

At this point in the current eradication response, bee keepers must euthanise all infested hives to give us the best chance of getting rid of the mite.

How can beekeepers protect their hives from Varroa mite?

If Varroa mites do establish in Australia, there are a number of management strategies used overseas to reduce mite populations in hives. Mite-targeting pesticides and organic acids are the main form of management, particularly for commercial beekeepers. There are also ongoing breeding programs around the world developing Varroa resistant bees.

What does the arrival of the Varroa mite mean for our bee and agricultural industries?

While not native to Australia, European honey bees have an essential role in providing pollination for Australia’s agricultural sector. If Varroa mite establishes, it will increase management costs for beekeepers. This will make it harder to provide enough healthy hives to meet the growing demand for pollination.

Dr John Roberts works on pests and diseases of honey bees. ©  CSIRO, Bradley Cummings

How have we managed to keep Varroa out of Australia for so long?

Australia’s isolation has been important for keeping Varroa mites out. However, we also have an excellent biosecurity system with robust preparedness plans for biosecurity threats, like the Varroa mite. State and federal governments have prepared and modelled numerous scenarios should Varroa arrive in Australia. These plans are currently being implemented.

Does Varroa mite affect native bees?

The Varroa mites in this incursion are host-specific to European honey bees. Native bees cannot be hosts of Varroa mites, but viruses spread by the mite can spill over into native bees.

Tips for bee keepers

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