First ever drawing of a honey bee mite, Varroa jacobsoni from Semarang in Java.
Source: Oudemans (1904b)
Alan Wade
Parasites, in a phrase, are predators that eat prey in units of less than one. Tolerable parasites are those that have evolved to ensure their own survival and reproduction but at the same time with minimum pain and cost to the host.
Edward O. Wilson (2014)
One hundred and twenty years ago highly revered Dutch zoologist and mite taxonomist Anthonie Cornelis Oudemans (1904b) proclaimed:
The Museum above mentioned [Zoological Museum at Leyden] received these mites (four females) and the bees, from Mr. Edward Jacobson at Semarang [Java]…
At all events the discovery of these female mites is a fortunate one and a brilliant contribution to parasitism.
This is an understatement. The parasite Oudemans so described (Frontispiece) was none other than the genus type species Varroa jacobsoni, later split off from the now widespread mainland Asian species Varroa destructor: Together the two varroa species, both parasites of their native honey bee host Apis cerana, are emphatically not natural predators of the honey bees we keep. Indeed both mites did not parasitise Apis mellifera until the mid 20th Century. As a footnote, Varroa destructor was not recognised as separate from the Varroa jacobsoni taxon, that was not until the pioneering study of Anderson and Trueman (2000).
The first and only parasitic mite of the western honey bee known to science – and beekeepers – was not discovered until 1921. The role of this parasite, the tracheal mite, as the ‘cause of Isle of White disease’ led to one of the great disputes of bee disease science. The aetiological role Acarapis woodi (the tracheal mite) as a parasite was sadly and badly overstated.
The tracheal mite enigma
You may not have read John Rennie’s account of the parasitic mite Tarsonemus woodi (Acarapis woodi) associated with western honey bees. Published as a lengthy memoir by the North of Scotland College of Agriculture (Rennie, 1923), it was anticipated by an earlier note published in Bee World as ‘Short Notes on Acarine Disease’ (Rennie, 1921a) and by a taxonomic dissertation in the Transactions of the Royal Society of Edinburgh (Rennie 1921b). The published 1923 narrative tells us much of what we might want to know about tracheal mite biology and its beekeeping import. As Bailey (1961) later recounted:
The mite Acarapis woodi (Rennie) is often assumed to be highly pathogenic for its host, the honeybee, but recent field and laboratory experiments have shown that, although individual bees have their lives shortened by infestation, the effect is very slight and may always have been so. Disease was not usually visible in summer, even in very heavily infested colonies, but the mortality of colonies in winter was correlated with their infestation (Bailey, 1958; Bailey and Lee, 1959).
So we might assume that early and foreboding notes in the austere journal Nature – and popular press – attributing mass colony mortality to the tracheal mite Acarapis woodi (Anon, 1912, 1916, 1917; Ellis, 1918) were in error. We must conclude that this mite is hosted naturally by Apis mellifera and that the parasite and host had long learnt to live with one other. There were other, if not well defined, causes of the wholesale 1910s losses of colonies in the United Kingdom and in Europe later in the 1920s.
To digress and nearer to home we again recall Uncle Harry’s uncanny, if mistaken, observations of wild bush creatures and the maladies that befall them (Figure 1):
‘It was just after a big flood and all the gilguys were full. Plenty of fish in them too. I threw a few lines in one day and had just sat down when I heard a frog croaking just near me. I looks around and here’s a big carpet snake with the frog in his mouth.
‘I decided to try and get that frog for a cod bait. Had a flask of rum in me pocket, so I poured a drop into the crown of me hat and puts it in front of the snake. Sure enough he dropped the frog at my feet, then looks at me in a real appealing sort of way. I poured him a big dose this time and he downed it straight away. It made him cough a bit, then he staggers up to a wilga and collapses in the shade. He was as drunk as a brewer’s donkey.
‘There was no shortage of bait after that. Day after day he brought frogs to pay for his rum. I had a big supply in the hut, and after the first month he got lazy and just hung about bludging. I decided to do something about it.
Figure 1 The proof is in the pudding.
Keith Garvey (1981)
All good things must come to an end so Uncle Harry got his snake thoroughly drunk and packed him off to Taronga Zoo:
Uncle Harry paused to light his pipe. He took a long pull of smoke, and the noise was like a toilet regurgitating when the chain is pulled.
‘And you never heard of the snake again’ I prompted.
Uncle Harry’s leathery countenance assumed a sad expression. ‘Yes,’ he said mournfully. ‘The zoo wrote to me and told me he died on arrival. Too long without a drink in that box, and the DTs killed him. He was doomed anyway, as the post-mortem showed. He was in bad physical shape with silicosis of the liver.’
‘You mean cirrhosis of the liver’ I corrected.
‘That’s what I said, ‘chrissos of the liver’ replied Uncle Harry. ‘I’m well read on diseases, even if I didn’t study medicine. Anyhow, boy, it proved to me that rum is a dangerous drink for those that can’t handle it. There’s still a couple of nips there in the bottle, we better finish her off.’
Invertebrates in general are host to a range of Acarapis species. Of these only A. woodi, A. dorsata and A. externus are associated with honey bees. Another putative species Acarapis vagans (Schneider, 1941; Delfinado-Baker and Baker, 1982; Sapcaliu et al., 2015) has since been shown to be synonymous with Acarapis woodi so there remain just three bothersome and rather similar parasites. You may not realise it but both A. dorsata and A. externus are known in Australia, but neither are common nor known to inflict significant damage.
I have long taken the view that A. woodi is relatively harmless, noting that Denmark et al. (2004), Carreck and Neuman (2010), and Johnston (2023) are similarly dismissive of the mite causing much damage mainly based on the findings of Dr Leslie Bailey [1922-2017] (1958, 1959, 1961, 1963, 1964a, 1964b).
I recently encountered informed views that we should not be so complacent about the potential impact of the tracheal mite though it’s also hard to argue against such sober opinions. Brother Adam (1968) was certainly not of the now consensus view. He carefully referenced several reports (Cooper, 1905, 1906; Editorial, Notices, &c. 1906a, 1906b, 1907; Silver, 1907) that indicated that factors such as weather could not be attributed to wholesale bee losses, the Swiss Bee Research Unit (Sammataro 2006; Sammataro et al., 2023), in conjunction with the USDA, reflecting a similar view. I have no informed opinion beyond suggesting that the tracheal mite, appears to be causing mortality in Apis cerana japonica in Japan (Kojima et al., 2011). As a parasite A. woodi does take some toll on honey bees so we should be vigilant in ensuring this mite is not brought into Australia or New Zealand. It is certainly now very widespread, for example seemingly rampant in Mexico (Lozano et al., 1989).
Concerning mites
Though Varroa is in the spotlight we might hope that our bees will not someday be put at further risk from other predacious mites. In surveying the spectrum of honey bee phoretics that may come our way we may conclude that only Euvarroa (mite bee parasites of the dwarf honey bees) and Acarapis will not bring our bees down. So what might these other mites be?
The world of mites and microbes are forever a mystery to all but those who spend their lives peering down the eponymous microscope, an instrument that satirist Hilaire Belloc was wont to purloin (Figure 2):
Figure 2 The microbe
Hilaire Belloc
On each of which a pattern stands,
Composed of forty separate bands
His eyebrows of a tender green
All these have never yet been seen—
But Scientists, who ought to know,
Assure us that they must be so—
Oh! let us never, never doubt
What nobody is sure about.
The Microbe
Hilaire Belloc
Table 1 lists the parasitic mites we know to be of concern. Of considerable interest will be the eventual fallout of the present Australian invasion of Varroa destructor and the potential import of Varroa jacobsoni (now present widely in the Pacific) and Tropilaelaps mercedesae (present in Papua New Guinea, the Solomon Islands and Fiji).
Table 1 Discovery and spread of destructive honey bee mites.
* The various routes of spread of the two Varroa halotypes on Apis mellifera are detailed by Solignac et al. (2005). Navajas et al. (2010) map the K and J halotypes including variants and indicate that there are additional halotypes infecting Apis mellifera that are yet to move out of Asia.
Studies by the CSIRO (Roberts and coworkers, 2019, 2020a, 2020b) showed that while these two mites initially caused major damage to beekeeper enterprises in Papua New Guinea and the Solomon Islands that bees have now adapted in the absence of deformed wing virus and are operating without treatment. We now know much about measures to control Varroa, while others such as Woyke (1987) have begun the long process of finding ways to control Tropilaelaps (Pettis, et al., 2017). What may happen in Australia, also in the present absence of deformed wing virus, is conjectural though Roberts et al. (2020b) note:
We conclude from these findings that A. mellifera in PNG may tolerate V. jacobsoni because the damage from parasitism is significantly reduced without DWV. This study also provides further evidence that DWV does not exist as a covert infection in all honey bee populations, and remaining free of this serious viral pathogen can have important implications for bee health outcomes in the face of Varroa.
Will Acarapis, Varroa, Tropilaelaps or a new species of Nosema (Chemurot et al., 2017) come to bother our bees? It seems fairly certain that Euvarroa and the south American parasite of Apis mellifera scutellata, Leptus ariel, are of little concern but others – two species each of Varroa and Tropilaelaps – may well plague our bees and that Varroa destructor is spreading in Australia and doing so now.
But from a honey bee perspective the problem with mites is not new. Ben Oldroyd and Siriwat Wongsiri (2006) tell us that the mites troubling our honey bees came from a suite of Asian honey have been in a long battle with their native hosts: these are of course the longstanding parasites of the Apis cerana, Apis dorsata and Apis florea clades. Now and then pockets of these bees get stressed and they, too, like the unloved street dog, fall victim to their free-loading parasites.
In a ‘real appealing sort of way’, let’s hope our bees can learn to live with Varroa and urge our quarantine guardians to keep out lurking fates worse than (or as bad as) Varroa destructor, not least the honey bee deformed wing virus, the insidious Tropilaelaps mites, Varroa jacobsoni and sundry other pests such as Asian hornets.
In the likely event that our bees will end up with several parasitic mites, one really hopes that our bees learn to adapt and that ‘the suckers’ end up in units of less than one. In such a very optimistic scenario our bees might be operated, well provisioned, treatment free. More likely the parasites will present themselves in E.O. Wilson’s terminology of ‘units greater than one’ and we, together with our bees, will be in for a battle royale.
Readings
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Adam, Brother. (1968). Isle of Wight or acarine disease: Its historical and practical aspects. Bee World 49(1):6-18. http://www.pedigreeapis.org/biblio/artcl/BAacarine68en.pdf
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Anderson, D.L. and Trueman, J.W.H. (2000). Varroa jacobsoni (Acari: Varroidae) is more than one species. Experimental and Applied Acarology 24:165-189. https://www.researchgate.net/profile/Denis-Anderson/publication/283318630_Anderson_and_Trueman_2000/links/5632c7c908ae242468da00af/Anderson-and-Trueman-2000.pdf
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Woyke, J. (1987). Length of stay of the parasitic mite Tropilaelaps clareae outside sealed honeybee brood cells as a basis for its effective control. Journal of Apicultural Research 26(2):104-109. https://www.wellesu.com/10.1080/00218839.1987.11100745