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Found in Translation
Tropilaelaps and Co.
By: Jay Evans, USDA Beltsville Bee Lab
Much has been written about Tropilaelaps mites and their impacts on honey bees both in their native range and, following recent hops, in the Middle East and Eastern Europe. These mites can adapt to temperate climates and, therefore, have the potential to harm managed bees in the United States and most beekeeping countries. While government agencies at various levels are doing all they can to prevent the arrival of Tropi into the U.S. and to swiftly identify new arrivals, it could well be a beekeeper who first notices a live Tropi infection. A beekeeper with pretty good eyesight. These mites are smaller than Varroa, well camouflaged against cappings and wax, and they spend much of their time inside brood cells.
Several near misses in the past couple of years have highlighted the fact that beekeepers are good agents of discovery and raising alarms. A striking video from beekeeper Stephanie Kyles in Texas reached many of us via social media in March 2024, many months before a lengthy peer review process would have allowed. This astute beekeeper provided video and photographic evidence of bees covered with dozens of small, tan, oval-shaped, mites that were not all that different from Tropilaelaps. This finding triggered regulator and scientist responses, and the mites in question were soon identified as an odd and relatively benign relative of Tropilaelaps that enjoys a worldwide distribution. James Fulton from the Florida Department of Agriculture and colleagues provided the first ID for these mites and, very fortunately, that ID did not have the word Tropilaelaps (Fulton, J.C.; Bolton, S.J.; Moore, M.R.; Kyles, S.; Klimov, P.; Ellis, J.D. Macrocheles muscaedomesticae, a first record of phoresy on Apis mellifera. Journal of Apicultural Research:1-3. doi:10.1080/00218839.2025.2485698). The current best placement of these mites, based on physical traits and genetics, is to the species Macrocheles muscaedomesticae. Mites in the worldwide genus Macrocheles exploit a diverse set of invertebrates (from insects and mites to nematodes) and further species-level divisions in this group are likely, given its far-flung geography and variable habits. Generally, these are a tribe of predatory mites with the potential for positive, negative or neutral effects on social bees. Occasionally, they have been observed to pile onto individual bees in a way that seems harmful (as in this instance for bumblebees, https://www.theguardian.com/environment/the-northerner/2013/may/22/crook-county-durham-bees-infested-mites). Nevertheless, while some members of the group feed on the eggs of flies, they do not appear to target honey bee eggs or larvae, nor do they seem to thrive in bee hives.
The presence of mites that mimic Tropi highlights the need to refine monitoring schemes for this mite. Several primers this year have advertised the value of monitoring for Tropi, alongside the risk of false alarms. The Honey Bee Health Coalition assembled a diverse group of authors to raise awareness about Tropi among beekeepers through an online primer (https://honeybeehealthcoalition.org/wp-content/uploads/2024/11/Tropi-Full-Primer.pdf). This primer points out how closely some non-Tropi mites found in beehives resemble the would-be invaders. Similarly, Brianna Price and a Washington State University team also put out a nice review of Tropi and current U.S. honey bee mites (Price, B.E.; Buckley, K.; Hopkins, B.K.; Basu, P.C. Navigating the mite spectrum in honey bee colonies: from harmful Tropilaelaps to harmless counterparts; Washington State University Extension: Pullman, Washington, 2025. https://doi.org/10.7273/000007298).
Francisco Posada-Florez and Steven Cook in our USDA Bee Lab have mounted a year-long survey of non-parasitic mites in and around beehives, aided by international mite experts Ronald Ochoa and Austin Fife. Francisco has documented numerous mite species in debris adjacent to hives (photograph), some of which scavenge across bottom boards. They will publish on the habits of non-Tropi mite associates soon, so stay tuned.
Formal surveillance for Tropi requires an accurate and sensitive screen that can be done without huge effort or equipment and with minimal damage to hives. Maggie Gill and collaborators in England and Thailand have vetted the leading candidates for surveillance in Thai colonies hosting natural Tropi infections (Gill, M.C.; Chuttong, B.; Davies, P.; Etheridge, D.; Panyaraksa, L.; Tomkies, V.; Tonge, G.; Budge, G.E. Assessment of the efficacy of field and laboratory methods for the detection of Tropilaelaps spp. PLoS ONE19. doi:10.1371/journal.pone.0301880’. 2024). They first gave each of 60 colonies a Tropi baseline score using either commercial ‘sticky’ bottom boards or bottom boards coated with vegetable oil. They compared 24-hour mite drop counts to several active screening methods, involving ‘bumping’ brood combs on a scoring sheet, dislodging mites from 300 bees using Veto Pharma EasyCheck filters after exposure to either alcohol, powdered sugar or anesthetization with CO2, and carefully removing brood with tweezers and checking each brood and brood cell for mites. As luck would have it, checking individual bee brood was both the most time-consuming and most accurate screen, but powdered sugar shakes were also quite effective. In something that only careful experiments can resolve, alcohol proved to be less effective at separating mites from bees, despite its wide success for Varroa counts. The authors credit the success of powdered sugar shakes to the ability of this substrate to ‘clog the legs’ of mites and trigger their fall. For brood-checking, they updated prior methods to account for sparse or variable brood patches, eventually settling on opening 100 brood cells and carefully screening for Tropi in each. This was far and away the most sensitive method, a key trait when infection levels are minimal, as they might be early in an invasion event.
Despite all the difficulties in accurately identifying Tropilaelaps, this is definitely a “see something, say something” moment. Beekeepers should be vigilant for this threat, take high-resolution photos or videos of any suspicious signs, and spread the word, especially if mites of any non-Varroa shape are observed on frames. Your local bee extension lead (or apiarist, if your state is lucky enough to have one) is a good starting point, or consider tagging the Apiary Inspectors of America or its active members with your concerns. If these people have a worried look, do not hesitate to escalate the warning on social media. We have a good chance to receive these mites in the next decade or so, and if there is hope of slowing or stopping incursions, it will need to come in the season of their first arrival.
Diversity of mites collected from debris surrounding beehives, showing the possible hive visitors.
