By Lucy Hayward,
BioSciences Student, The University of Melbourne

One third of our global food production depends on bees. In Australia, around 35% of crops need bees for pollination.¹ 

Varroa destructor – yes, that’s its scientific name – is a tiny mite that has decimated honeybee colonies around the world. And an outbreak of this destructive parasite has been confirmed for the first time in Victoria near Mildura.²

Also known as the varroa mite, it is a parasite for honeybees, weakening entire colonies. It is one of the major factors contributing to widespread colony collapse disorder, when most worker bees in a colony disappear.

The mites spread between bee colonies through contaminated hive equipment and by hitchhiking on foragers as they are agile and transfer through contact.³

Until last year, Australia was the only continent on Earth – excluding Antarctica – free of the pest. But, despite strict biosecurity laws and protocols, Varroa destructor breached our borders in June of 2022.² 

Following an unsuccessful attempt to eradicate the pest, in September 2023 the Australian Federal Government announced they were abandoning their eradication strategy, turning instead to management.² Now, these pests have broken through into Victoria’s ecosystems too.

A forbidden fatty snack

Scientific literature for the past five decades has stated that Varroa destructor feeds on the blood (haemolymph) of honeybees. Samuel Ramsey – a PhD student at University of Maryland College Park at the time – noticed that this understanding was cited back to one paper. When he translated the text from its native Russian, he found nothing that mentioned the mites’ feeding behaviours. What we knew about the parasite feeding on the bees was based on a single mistranslation.

Ramsey examined varroa mite excrement and found that it contained a high level of purine – an observation that he was reminded of when visiting his parents, and it was his father’s diagnosis of gout that tipped him off. Gout is a form of arthritis that occurs when uric acid crystallises in the joints of the body, and uric acid is a derivative of excess purines. Upon researching the best meal plans for his father, Ramsey discovered that the number one thing listed as what you shouldn’t eat with this condition was liver. At that moment it struck him that maybe varroa mites were feeding on the bees’ liver (or rather, their equivalent).

While bees don’t have livers per se, their fat body tissue is an analogous structure, essential for the bee’s immune response and survival over winter. With further testing, Ramsey found that the fat body was the main source of varroa mites’ sustenance, meaning that a large amount of varroa research has been done looking up the wrong hypothetical tree.⁴

A bee-llion dollar industry

European honeybees are a large and lucrative industry in Australia, worth more than $14 billion annually.¹ There is significant concern for the effect of a varroa establishment disrupting these systems.

Commercial pollination services see the movement of hundreds of hives across state borders, increasing the risk of the pest spreading. In the United States and parts of Europe, Varroa destructor has wiped out 95-100% of wild European honeybee populations within a four-year infestation period.⁵ This trend is likely to occur in Australia and it will have a significantly detrimental influence over the agricultural industry as many crops depend on pollination by wild honeybees.

Biocontrol agents are of strong consideration due to the aversion to pesticide use that would affect the health of bees too. One contender is a predatory mite, Stratiolaelaps scimitus, which does not harm honeybees but has been found to attack Varroa destructor in the lab (could this be “mite-ception”?).⁶ However, field tests were less successful and more rigorous studies would need to be done before this could be applied at a large scale – we can’t be having another cane toad situation.

Varroa mite does not appear to attack native bees, and there is the possibility that these native species will benefit from the outbreak due to reduced competition with European honeybees.⁷ Although it is also possible that they will suffer indirect effects due to increased disease transmission through a varroa mite vector.

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Lucy Hayward is a Master of Science student in the School of BioSciences at the University of Melbourne.

References:

1. DAFF. (2022). Honey bees. Agriculture Victoria. www.agriculture.gov.au/agriculture-land/farm-food-drought/hort-policy/honeybees
   Varroa mite (Varroa destructor). (2022). Outbreak. www.outbreak.gov.au/current-outbreaks/varroa-mite
2. DAFF. (2024). Varroa mite frequently asked questions. agriculture.vic.gov.au/biosecurity/pest-insects-and-mites/priority-pest-insects-and-mites/varroa-mite-of-honey-bees/varroa-mite-frequently-asked-questions
   
3. Ramsey, S. D., et al. (2019). Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph. Proceedings of the National Academy of Sciences, 116(5), 1792–1801. DOI: 10.1073/pnas.1818371116
   
4. Rondeau, S. (2019, January 27). Mite versus mite: The search for an effective way to save honeybees. The Conversation. theconversation.com/mite-versus-mite-the-search-for-an-effective-way-to-save-honeybees-108873
5. Heard, T., et al.(2022, August 16). Varroa incursion – what does it mean for native bees? Australian Native Bee Association. www.anba.org.au/notices/varroa-incursion-what-does-it-mean-for-native-bees/