Bee Buzz Box June 2026 Protesting Protists Part I Amoebae, Gregarines, Microsporidians and Trypanosomatids

Alan Wade
5 days ago
16 min read

Updated: 17 hours ago

Alan Wade

Canberra Region Beekeepers

Affected juniors

Yes there are other nasty honey bee pathogens that you may or may not have heard of.

In examining our buzzers for common maladies, we always check on bee brood (bee juniors) health. We search for evidence of chalkbrood outbreaks – the causitive organism Ascosphaera apis that arrived in Queensland in 1993 – sacbrood virus and the bacterial diseases American and European foulbrood. We collectively ignore rare diseases such as bacterial spiroplasma (Spiroplasma apis and Spiroplasma melliferum) and fungal stonebrood (Aspergillus flavus and Aspergillus fumigatus) because they require specialist diagnosis and we simply do not run into them.

Checking further we often find white or yellowish grubs chomping unprotected combs. These, the greater and lesser wax moths, also hide under brood cappings and in bottom board debris. We think of them as bee friends – they clean up bee fras debris and diseased comb – and beekeeper enemies – the reduce stored combs to an unholy webbed mass and drill holes in bee gear. Close to home we first saw the arrival of hive beetles in New South Wales in 2002. We adjudge their prevalence by the numbers scurrying across frame top bars. We were soon to learn that they, the beetles, would slime out whole hives with their grubby oozing larvae if their numbers got away.

Adulterated adults

But what about checking for pests of ‘grown up’ (adulterated adult) bees? Sensible keepers are not only learning how to manage beetles – we don’t have the two large African beetles (Oplostomus fuligineus and Oplostomus haroldi) – but also to manage mites, both varroa and assorted viruses.

An even bigger danger will likely come from the Asian hornets, widely dismissed by keepers as ‘just a possible’ threat. This is a mistake. New Zealand is trying desperately to squash a recent incursion of the yellow legged hornet, a marauder that is simultaneously ravaging European, Russian and Asian apiaries and indeed also chomping on insect fauna at large. The February Bee Buzz Box issued a peremptory warning suggesting we might not be so complacent about such an existential hornet threat.

Yet there is another family of predatory organisms rarely mentioned in polite beekeeping circles. These are low life protists, invisible single-celled gut parasites that routinely knock the daylights out of our buzzers. Fitting in with Scott Morrison’s ‘nothing to see here’ they display few clear signs of disease and are nowhere to be seen. They are what they are, rarely whispered about microscopic nasties:

Protists are eukaryote life forms less advanced than animals, plants and fungi. They comprise a diverse assemblage of unrelated organisms spanning many phyla and of extraordinary diversity.

Whitaker (1969) debunks the many attempts to place a wide range of organisms into the ambit of animals and plants being the two principle life forms, singling out the protists as an example of organisms that fit into neither:

Protists are conceived as unicellular and as organisms which as a rule remain unicellular throughout life (Monobia), less frequently they form loose cell communities (Coenobia) by repeated cleavage, but never real tissues.

They are contrasted with the tissue-forming organisms of the kingdom Histonia, comprising the Metaphyta (including higher fungi, higher algae, and higher land plants) and Metazoa (multicellular animals).

The tree of life (Wikipedia, 2025).

Amongst these enigmatic protists are a number of honey bee parasites, some extremely damaging. In the main they are simple single-celled gut organisms. Invisible to the beekeeper, they come into full view under the microscope. These low lifers comprise amoeba, gregarines, microsporidians and trypanosomatids (Table 1). By tossing in the bacterial, fungal and mite parasites, Evans and Schwarz (2011) note that:

Honey bees face a diverse pathosphere and their ability to resist these threats depends upon commensals, nutritional status, the accumulation of toxic compounds, and genetically based resistance and tolerance mechanisms.

Schwarz and Evans (2013) also found that both single and mixed trypanosome and microsporidian infections caused honey bee immune responses.

Table 1 Reported protist honey and bumble bee-gut and body-cavity parasites.

Let’s look at each of these ‘low life’ protists so we are at least aware of the damage they may and do cause. Many of these parasites are poorly characterised although the microsporidians (e.g.Nosema/Vairimorpha) and the trypanosomatids (notably Lotmaria) routinely collapse colonies.

The Amoebic Malpighians

Not often reported, Malpighamoeba (Vahlkampfia) mellificae has been co-detected with Nosema apis (Bailey, 1968) and seemingly only reported from Europe and North America although Plischuk and Lange (2010) have also recorded its being found in Argentina. Ingested cysts of this amoeba develop into trophozoites that in turn feed on and damage excretory malpighian tubules (insect kidneys). This upsets the balance of waste excretion and hemolymph exchange resulting in amoebic dysentery and poor bee and colony fitness. As already noted the malphigian bumble bee parasite Apicystis bombi has been widely reported on by Plischuk (Plischuk et al., 2011, 2017a, 2017b; Plischuk and Lange, 2024; Saidi and Plischuk, 2025).

In practice detection of these amoebae is dependent on microscopic examination of the malpighian tubules though molecular testing (Schäfer et al., 2022) has now been developed. As an amoebic parasite, maintaining good hive nutrition and hygiene – not relying on laboratory diagnoses – may be as much the apiarist can do to minimise the impact to honey bee health. That this debilitating disease is largely unrecognised is signalled by Schäfer, Horenk and Wylezich (2022):

Most reports of this amoeba are from the 1960s and earlier, and knowledge of the disease and its spreading is very poor.

Anyone who knows anything about Entamoeba histolytica, the causative agent of amoebic dysentery, may know that is was a life threatening disease amongst troops in PNG during World War 2: Ask my father. However Malpighamoeba mellificae, the equivalent parasite that lodges in the excretory malpighian tubules of the honey bee is of uncommon occurrence and rarely results in symptomatic disease (Shimanuki,1980, 1983).

The Microsporidians (Vairimorpha syn Nosema)

In a brief overview of the range of microbial parasites afflicting honey bees, Ebeling, Fünfhaus and Gisder (2022) signify their importance in reducing crop pollination globally. They list wax moths, the acari varroa and tropilaelaps mites, chalkbrood, the foulbrood bacteria and the deformed wing and acute bee paralysis viruses as well as the protist microsporidia. They note the role of microsporidia in upsetting gut excretory and osmoregulatory function of honey bees and hence their health and survival. Perhaps the earliest hint of bees battling pests and disease comes fromAristotle’s [384-322 BCE] Historia Animalium (D'Arcy Wentworth Thompson, 1910):

In bee-hives are found creatures that do great damage to the combs; for instance, the grub that spins a web and ruins the honey-comb...

The microsporidian genus Nosema, renamed Vairimorpha (Tokarev et al., 2020), is still best known by its old and familiar name. There are about eighty one species of this genus affecting a wide range of insects and invertebrates, notably Vairimorpha necatrix (syn Vairimorpha ephestiae) (Malysh et al., 2018) that targets moth species (Solter et al., 2012) including the greater wax moth Galleria mellonella and Vairimorpha invictae (Oi et al., 2005) that has been trialled to control the destructive fire ant Solenopsis invicta.

Other invertebrates such as Cherax destructor, the delectable freshwater yabbie, do not escape. Vairimorpha cheracis parasitises this ten-legged nipper. Our regular friend Uncle Harry reports of the ever-present dangers of these formidable crustaceans, if not their parasites:

'Yabbies are pretty hard to get’, I said to Uncle Harry. We had just made an unsuccessful attempt to obtain some yabbies, or freshwater crayfish by dragging a portion of the bore-drain with a piece of netting.

'They don't grow very big around here', the old boy replied. 'Out in the West I've seen 'em grow as big as fox-terriers. Some sort of mineral in the water develops em.'

'No way!', I said disgustedly. 'A lobster wouldn't grow that big.

Uncle Harry revealed one of his two remaining teeth in a knowing grin and began. 'Me and Stevo were on a fencin' job out West at a place called Uppaquei. There was a big dam near the camp, where we used to get our water. About the third night we were there, a hawker come along and sold us two bottles of wine. We had tea, and then knocks down the plonk. We falls into a deep sleep, and just about daylight I gets woke up by a scratchin' sound.'

'It was just light enough to see, and what I saw nearly scared me to death. Here's a great big yabbie the size of a dog, rootin' round in the tucker-box! I hears a yell from Stevo, and looks round to see him stonker another big cray that's tryin' to lift the wallet out of his moleskins! Then a terrible burst of snarls erupt from under the waggon, and it's Tiger crushin' a yabby to death, while another monster is hangin' onto his tail! Two more are carryin' the meat bag away between 'em, and what got me really wild was the fact that one old whiskery brute was sittin' on the pole of the waggon, smokin' me pipe! And there's more of 'em comin' from the dam!'

We can skip the ensuing battle that Stevo’s dog Tiger, Stevo and Uncle Harry had with the crustaceans, but if a Vairimorpha can knock off giant yabbies pity help bees mixing its kind. However it seems that those yabbies got cleaned up:

'What became of all the dead ones that you killed' I asked, thinking I had caught Harry off guard, but he was ready. 'There was a mob of crows sittin' up in the trees lookin' very full bellied', he replied. 'They had evidently cleaned up the bodies of the casualties. Now this story should give you an idea of how potent the water is in Western bore-drains.'

'Wine sold by Indian hawkers must be pretty potent too,' I replied. 'Come on, let’s look for a few normal yabbies.

The Plague of Yabbies

Keith Garvey

Perhaps few will be familiar with the story of the 1909 first description of a microsporidian, Vairimorpha (Nosema) apis, by Zandler (Fries, 1993; Zander, 1909). However it was discovered far earlier (Dönhoff and Eucharist, 1857) but then thought to be a fungus. In more recent times it has spread globally (see for example Williams et al., 2008). White (1918) at the US Department of Agriculture suggests that:

Nosema disease… has probably existed among bees longer than history records the keeping of bees by man.

However it came as quite an unwelcome shock when, in 1996, a related species Vairimorpha ceranae (syn Nosema ceranae) was found to have jumped from its native Asian honey bee host (Apis cerana) to the western honey bee. This Asian parasite has inflicted broad cross-seasonal damage (Fries, 2010; Fries et al., 1996; Eiri et al., 2015) to honey bees. And of course there are always surprises. As recently as ten years ago a new species of this parasite Vairimorpha neumanni turned up on Apis mellifera in Uganda (Chemurot et al., 2017).

Diagnosed cases of nosemosis turning up locally appear are elusive although former club member Dick Johnson (2023) sent off a sample for diagnosis when one of his colonies collapsed for a reason he could not fathom. The disease is however widely prevalent. So apart from keeping bees in an open sunny position and requeening them regularly there seems little one might do to avert its devastating impact.

In a broad survey of bee diseases, Ocepek and coworkers (2021) identify a number of protist and viral pathogens shared by both Apis and Bombus species. The spillover effect of disease organisms being transmitted from one bee species to another arising from their being kept in large numbers at single locations is shown in Table 2.

While this study was focussed on spillover of diseases from honey bees to bumble bees, the results of this extensive survey show that each species of bumble bee and of the honey bee appear to be a reservoir for transmission for these common disease entities. This Slovenian study made many subtle observations on the occurrence and prevalence of bee pathogens in bumble bees, noting the very common occurrence of black queen cell virus in worker bees, the absence of chronic bee paralysis virus, the common occurrence of the trypanosomatid Lotmaria passim. The authors also note that the detection of honey bee pathogens in bumble bees is a likely consequence of flowers heavily contaminated by honey bees. We might further conclude that many protist diseases are transmitted by a wide range of foragers.

Table 2 Parasite sharing between bumble bees and western honey bees at several locations in Slovenia (Aggregated findings of Ocepek et al., 2021). A tick signals one or more +ve detections: a cross signals absence of parasite in all tests collected at the same area in the same year:Site A Sevno; Site B Lukovica; Site C Naklo; Site D Ljubljana.

Several studies point to the importance and widespread occurrence of these parasites amongst both honey and bumble bees (Plischuk et al., 2011, 2017a, 2017b, 2024; Stejskal, 1955, 1964, 1965; Schulz et al., 2019; Vavilova et al., 2017). However, as Brian Johnson (2020) points out, pathogens are widely shared amongst hymenopterans (bees and wasps) (Graystock et al., 2016), a topic explored in the Bee Buzz Box article on honey bee viruses. Honey bee pathogens may be widely shared when colocated but does not imply disease causation.

The Protozoan gregarians

Protozoans gregarines are gut parasites, but do not appear to be significantly pathogenic. Like the amoebic malpighians, the gregarians (or neogregarines) are not well known to keepers of bees. Indeed most of the substantive studies on these organisms appears to have been conducted by the United States Department of Agriculture laboratories up until the early 1990s and published in their now archived Agriculture Handbooks (Shimanuki,1980, 1983). Shimanuki and Knox (1991) list gregarine parasites known from the United States as Acuta rousseaui, Apigregarina stammeri, Leidyana apis and Monoica apis. They are all scantly referred to in the contemporary literature. They appear not to be significant honey bee parasites though Hachiro Shimanuki and David Knox signal that they may have an adverse affect when co-infected with the flagellate trypanosomatids and Vairimorpha microsporidians. However there is a singular reference to a new gregarian species Fusiona geusi by Stejsal (1965). Stejskal (1964) reports the discovery of Monoica apis and makes reference to other species (Stejskal, 1955) found in Venezuela seeming to indicate that several species of cephaline gregarines of the genus Pileocephalus and likely of the genus Stenophora or of Gregarina chagasi. The obscurity of these findings, suggests they – if indeed they exist – are an unlikely threat to honey bees.

Schoonvaere and coworkers (2020) signal that gregarine parasites cause fat body swelling (hypertrophism) in bees.

The flagellate Trypanosomatids

The trypanosomatids are widely known as the causitive agents of the serious human diseases, sleeping sickness, chagas disease and leishmaniasis. Amongst bees Crithidia bombi and Crithidia mellificae (Langridge and McGhee, 1967; Runckel et al., 2014; Aguado-López et al., 2023; Ravoet et al., 2013, 2015; Schlüns et al., 2010) are well known hind gut parasites of bumble and honey bees respectively. Crithidia mellificae is also known to infect a few solitary Osmia (Mason bee) species (Strobl et al., 2019) but its pathogenicity and importance as a honey bee parasite has been questioned.

Schwarz et al. (2015) found that while Crithidia mellificae remains a parasite of honey bees, Lotmaria passim, described by Ruth Lotmar long ago (Lotmar, 1946) is now the globally dominant trypanosomatid that adversely impacts honey bees. Also listed by Wallace (1966) are Leptomonas apis (referencing Lotmar) and Synosternon cleopatrae although the contemporary literature (Kaufer et al., 2017) restricts the trypanosomatid listing to just Crithidia mellificae and Lotmaria passim. The Schwarz consortium conclude that Lotmaria passim is found globally and commonly infects honey bees (Apis mellifera) while Crithidia mellificae is found comparatively infrequently. Their genomic studies signal that the evolution of these two trypanosomatids is extremely complex. The two named species represent at least four clades, several genera and a number of species parasitising bumble bees, honey bees and wasps. Their findings confuse much of the earlier studies based solely on parasite morphology.

Several recent studies (Markowitz, et al., 2025; MacInnis et al., 2023, 2025) expand on the significance of Lotmaria passim to honey bee wellbeing, eponymously signalling that the organism is everywhere (‘passim’ in Latin means hither and thither). Nanetti and coworkers (2021) have found that small hive beetle harbours Lotmaria passim, Crithidia mellificae and replicative forms of deformed wing virus and Kashmir bee virus.

Pay attention. Lotmaria passim along with Crithidia mellificae have just been found to be alive and well here in Australia. Until now they have been off the radar (Bhasi, Zerna, and Beddoe, 2026). We will look at these two trypanosomatids and the nosema microsporidians in Part II.

But if you are left as bewildered as I am by these unseen yet common and destructive pests, we might all take comfort in Hilaire Belloc’s view of these unseen microbes saying that:

Oh! let us never, never doubt– What nobody is sure about.

Readings

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