Understanding Malpighamoeba mellificae

Thursday, 28 August 2025

Honey bees face a wide range of threats from visible pests to microscopic pathogens, all of which can impact their health and survival. While some diseases like Varroa destructor or Nosema spp. are well known among beekeepers, others remain less recognizable but are still important to understand. One disease is caused by the protozoan parasite Malpighamoeba mellificae, which infests the bee’s excretory system.

Understanding Malpighamoeba mellificae 

This amoeba disease of honey bees was first discovered over a century ago in Germany 1Malphighamoeba mellificae is a protozoan parasite that infects an essential organ in honey bees known as the Malpighian tubules which is part of the digestive system. It is transmitted through the fecal-oral route 2. Usually, infection occurs when the feces of infected bees get on the comb, which then gets ingested 3.  

The life cycle of Malphighamoeba mellificae begins when honey bees ingest the cysts. Once inside the bee, the cysts transform into trophozoites, which are the active feeding stage of the amoeba 1. These trophozoites invade and damage the Malpighian tubules. Eventually, they form new cysts that pass through the honey bee’s hind gut and are excreted.

The Malpighian tubules, as part of the excretory system in the bee’s abdomen, play a vital role in osmoregulation.  Osmoregulation is a cellular process which maintains fluid and salt balance within the bee’s body 1. The tubules also remove nitrogenous waste from the hemolymph by passing it into the hindgut for excretion 1. Additionally, the Malpighian tubules help filter out foreign substances that could cause harm to the bees, like insecticides, fungicides or antibiotics 4. When these tubules are damaged, their inability to function properly can significantly compromise the honey bee’s overall health. 

Figure 1: Malpighamoeba mellificae disease a) showing amoebic cysts in fecal samples from western honey bee. b) Cysts observed in Malpighian tubules under a light microscope. c) Normal appearance of Malpighian tubules in a non-infected honey bee and d) Discolored Malpighian tubules of honey bees who were infected with Malpighamoeba mellificae (image: Iredale et al, 2023 2). 

When infected by Malpighamoeba mellificae, the Malpighian tubules become swollen and filled with cysts, which impairs their function and weakens the bee 4. This enlargement may result from thinning of the epithelial layer, caused by the accumulation of cysts or by trophozoites feeding on the tissue 4. At the colony level, this disease may lead to population decline, reduced lifespan, and signs of dysentery 3. It is often found alongside Nosema spp. infections 1.

Diagnosing Malpighamoeba mellificae requires a compound light microscope and follows a similar method to screening for Nosema. About ten bees should be collected from the front of a hive and placed into a sealable bag with 10 mL of distilled water 3. The bees are then crushed to release internal contents, and a drop of the resulting liquid is placed on a microscope slide for examination of the 8-10 μm in diameter cysts at 400x magnification 3. However, this technique can also have its limitations. The amoeba can remain in its trophozoite stage for extended periods and only form cysts when its environmental conditions are poor 1. While cysts are easy to identify due to their consistent shape, the trophozoites are much harder to recognize, especially in mild infections 1.

Figure 2: Distribution of M. mellificae showering where disease is present (yellow), suspected presence (teal) and no presence/unreported (purple) (image: Gurland et al, 2024 3). 

This disease has been reported in various regions where European honey bees are kept, including Canada 3. The disease may be seasonal, with higher prevalence in winter and early spring 3. Despite its long history, Malpighamoeba mellificae remains understudied, and no specific treatments are available. Malphigamoeba mellificae has not been proven to be a problem for beekeepers in our region. But we do need to understand the presence of the pathogen and the implications for honey bee health in the Maritimes.

 Written by Kaitlyn Newton, ATTTA Seasonal Apiculturist 

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email attta@perennia.ca

References:

  1. Schäfer, M.O., Horenk, J. and Wylezich, C., 2022. Molecular detection of Malpighamoeba mellificae in honey bees. Veterinary Sciences9(3), p.148.
  2. Iredale, M.E., Viadanna, P.H., Subramaniam, K., Tardif, E., Bonning, B.C. and Ellis, J.D., 2023. Report of amoebic disease in a colony of Western honey bees (Apis mellifera). Veterinary Pathology60(5), pp.709-713. 
  3. Gurland, H.N., Fulton, J.C., Iredale, M.E. and Vu, A.T., 2024. Monitoring for Amoebic Disease (Malpighamoeba mellificae) in Honey Bee Colonies: ENY2112/IN1431, 10/2024. EDIS2024(5).
  4. Rossi, M., Ott, S.R. and Niven, J.E., 2020. Malpighamoeba infection compromises fluid secretion and P-glycoprotein detoxification in Malpighian tubules. Scientific Reports10(1), p.15953.

Mid-Season Varroa Mite Trends in the Maritime Region

Thursday, 21 August 2025

As the beekeeping season progresses, the Atlantic Tech Transfer Team for Apiculture has been continuing to survey regional varroa mite levels. Our team has now completed the second trial of the season which assesses mite levels mid-season following wild blueberry pollination. Continue reading this week’s blog to learn more about mid-season trends in varroa mite populations across our Maritime region, and for insight to how this year’s mite levels compare to 2024.

Mid-Season Varroa Mite Trends in the Maritime Region

For the second season, ATTTA is conducting a regional varroa mite survey to assess temporal trends in mite levels and to assess the efficacy of amitraz (active ingredient in Apivar® - a synthetic miticide). The second trial of the survey consisted of 23 beekeepers (9 in Nova Scotia, 7 in New Brunswick and 7 on Prince Edward Island). Our team aims to include as many commercial beekeepers representing the 3 Maritime provinces as possible, and we often reach out to more beekeepers than reflected by those who are able to participate. The second trial took place between July 3 and August 6, 2025 following wild blueberry pollinations, and consisted samples from 76 colonies. These colonies are all from commercial beekeepers who provide pollination services.

Overall, the average mite load for trial 2 was 0.16% infestation rate per sample, 76% of samples had 0 mites, and 5% of samples had a mite load greater than 1% (Figure 1). The average number of bees per sample for trial 2 is 291, with a target sample size of 300. In comparison, in 2024, the average mite load per sample for trial 2 (July 3, 2024 – August 22, 2024) was 0.3%, 73% of samples had 0% mite load, and 7% samples had a mite load greater than 1% (Figure 1). More data is needed to help establish a baseline for mite levels mid-season across our region. Although there is a decrease in the percentage of colonies with detectable varroa, and the percentage of colonies with mites levels above 1%, between 2024 and 2025 (Figure 1), additional data is needed to support a downward trend, or assess if levels are potentially increasing or remaining stable from year to year. The slight difference across beekeeping seasons, as determined from the survey over the past 2 years, may reflect the normal range of mite levels across our region, and a main priority of the survey is to establish a baseline of the region’s mite levels.

Figure 1. Comparison of mid-season varroa mite loads in the Maritime region between 2024 and 2025.

It is important to understand that the population of varroa mites increases throughout the beekeeping season, which is reflected by the increase in mites sampled between May/June (trial 1) and July/August (trial 2). The results of this survey support the fact that the population of mites increases as the beekeeping season progresses (Figure 1). This makes early spring monitoring and treatment for varroa mites crucial, because the population can quickly get beyond the economic threshold if waiting until the fall to treat colonies again.

Beekeepers need to be vigilant with monitoring for mites each month to ensure that colonies will be strong and healthy by the time winter preparations occur as varroa mites continue to be a top reason for colony winter loss. If a beekeeper is seeing mites during the early part of the beekeeping season, then they should be prepared to provide treatment by fall. There is also the potential that the number of mites will exceed the economic threshold prior to the fall if colonies are not treated in the spring, in which case a mid-season knock down treatment may be indicated to keep the mite population under control until fall treatments can occur. Through a range of management practices, beekeepers should manage their mite levels to be below 1% all throughout the beekeeping season, and intervene with treatment when levels reach or surpass 1% (1 mite per 100 bees). Beekeepers should also start late-summer/early-fall mite treatments as soon as possible when levels are at or exceeding 1% to help ensure healthy winter bees with low virus loads.

Figure 2. Sampling for ATTTA Varroa Mite Survey 2025 (ATTTA©2025).

It is important that beekeepers understand that 0% mite load, as determined by an alcohol wash, does not mean that no mites are present within the colony. There is always a background population of varroa mites within a single colony and, without frequent and representative monitoring, undetected population increases will quickly increase to beyond treatment thresholds.

Beekeepers must remain vigilant when monitoring for mites, and practice integrated pest management in all aspects of their mite management. There was good opportunity for growing bee populations this beekeeping season, which also provided the opportunity for mite populations to increase. Late summer to early fall will be a crucial time frame for monitoring mite levels and starting any required treatments as soon as possible. For questions regarding mite management and treatment please reach out to the ATTTA team. We would like to thank all beekeepers who participated in trial 2 of our survey. We will be reporting on the complete survey following trial 3 which will take place in September.

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email attta@perennia.ca