Over-achieving Tropi mites
By: Jay Evans
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Tropilaelaps mites have been under scrutiny in their native range in Asia for decades, and their interactions with several honey bee species are well known. The western honey bee, Apis mellifera, is now managed throughout Asia, and Tropilaelaps welcomed this newcomer as a resource for growth and reproduction. Studies of this interaction with the favored pollinator worldwide have shaped current thinking about Tropilaelaps applied biology, including strengths, weaknesses, and possible treatment strategies. These studies offer a preview of what this mite could do as it follows the host trail into a more expansive range. Geoffrey Williams and an ace team from the U.S., Thailand, The United Kingdom, and Germany (Williams, G. R., Aurell, D., Gill, M. C., Khongphinitbunjong, K., Tokach, R., & Traynor, K. S. (2026). Tropilaelaps mercedesae: rapid geographic expansion in a novel honey bee host. Trends in Parasitology, 42(9), 912–927. https://doi.org/10.1016/j.pt.2026.07.002) have provided a recent recap of this expansion. Following in the creeping footsteps of Varroa, Tropi has spread swiftly, especially in the past decade. Since the first studied population in the 1950s, Tropi mite movement into Apis mellifera colonies has led to noticeable increases in colony mortality and massive surges in mite numbers and infested colonies.
Williams and co-authors map out recent expansions of Tropi mites, showing that these mites are doing quite well outside the tropics and in climate zones that mirror much of the United States. This fact is somewhat surprising given experimental evidence that adult Tropi mites survive poorly on adult honey bees, especially Apis mellifera. As such, these mites were predicted to experience extreme population crashes whenever honey bee brood were absent, and to be an issue primarily for tropical regions. How dire are the predictions for managed A. mellifera colonies in temperate climates such as those found in much of the United States?
In China, where the original Tropi hosts such as the giant honey bee Apis dorsata co-occur with more recent conquests (e.g., A. cerana and A. mellifera), Tropi mites are widespread across all climates except for the Tibetan plateau. Liuchang Miao and team provide an insightful review of the current Tropi range in China, recent leaps from China to elsewhere, and the ensuing impacts on managed western honey bees (Miao, L., Chen, X., Zheng, H., & Martin, S. (2026). Living with Tropilaelaps mercedesae: its history and impact on Chinese beekeeping. Apidologie, 57(5), 72. https://doi.org/10.1007/s13592-026-01302-3). The authors noted high losses in A. mellifera colonies when Tropi discovered this new species in China in the mid-1900’s, along with subsequent known leaps from China to South Korea, countries in Central Asia, and Russia.
The Russian incursion of Tropi, and more recent expansions beyond Russia, reflect an ominous blend of climate adaptability and the tendency for humans to provide a helping hand to invasive species. Anna Brandorf and colleagues provide an extensive review of this immense range expansion and give some hints into what the rest of the world might expect if the Tropi march continues (Brandorf, A. Z., Frunze, O., Bakulina, A., Bessolitsyna, E., Nuraliyeva, U., Torekhanov, M., Krupskiy, O., Saurov, S., & Kwon, H.-W. (2026). Persistence, seasonal dynamics, and regional differentiation of the parasitic mite Tropilaelaps mercedesae in Apis mellifera l. Colonies under non-endemic climatic conditions. Insects, 17(9), 964 (https://www.mdpi.com/2075-4450/17/9/964). They start their review by documenting how we humans are often our own worst enemy in enabling parasites. Russia has imported 100s of thousands of Western honey bee packages in recent years from countries with known or suspected Tropi infestations. These imports and their Tropi hitchhikers have officially transited the central Asian countries of Kazakhstan and Uzbekistan, but seem likely to have originated in Tropi-containing regions of China. This ambitious, if misguided, pattern of importation has led to established populations in several regions of Russia, with devastating impacts on bees and beekeepers.
As in China (and remembering Dr. Zhivago), Russian winters have not presented a huge barrier for Tropi. One study site was in Makhachkala, Russia, with a temperature pattern similar to New York City (albeit with less rainfall). Despite minimal bee brood production from November to May, mites were persistent and, when given fresh brood, capable of rapid growth. Mites were not detected in brood cells in May but showed 80% infestation rates by November. Mite (and often bee) numbers then collapsed for Winter. This rapid reproduction rate is one of the scariest elements of Tropi biology: Varroa mites grow as a population over the Summer, but not nearly as fast as Tropi. This rapid growth and high mite movement can help spread viruses among bees and between colonies. The researchers also measured established Tropi populations in Zhetisay, Kazakhstan, a region with a climate similar to (ughhh!) the Central Valley of California, albeit with somewhat colder Winters. Here, mite presence was even more confined, growing rapidly in brood cells from September to November but reaching infestation rates of more than 40% of sealed brood cells. Ongoing studies in temperate regions of Eastern Europe, Korea, and China suggest that climate will not be an insurmountable barrier for Tropi in much of its potential maximum range.
The Branford review does not resolve how Tropi mites survive broodless periods for A. mellifera colonies. Active research by Maggie Gill (https://www.phira-science.org/about) and others in Kazakhstan and other regions in Central Asia (and now Eastern Europe) is addressing this conundrum, while also testing potential treatments for temperate regions (e.g., Janashia, I., Kovačić, M., Wilson, G., Uzunov, A., Costa, C., Chen, C., & Gill, M. C. (2026). Timing matters: Seasonal variations in the efficacy of formic acid treatments against the honey bee parasites Tropilaelaps mercedesae and Varroa destructor in the Caucasus. Veterinary Parasitology, 345, 110771. https://doi.org/https://doi.org/10.1016/j.vetpar.2026.110771. As shown in Thailand by Madison Sankovitz and colleagues (Sankovitz, M., Steinhauer, N., Yemor, T., Cook, S. C., Evans, J. D., & Ramsey, S. D. (2025). Evaluation of efficacy of formic acid and thermal remediation for management of Tropilaelaps and Varroa mites in central Thailand. Journal of Apicultural Research, 64(4), 1049–1058. https://doi.org/10.1080/00218839.2025.2495393), formic acid, with its cap-penetrating ability, is a viable route for control, assuming many ounces of prevention do not avoid the need for a cure.
On an optimistic note, the authors of the Tropi review in China note that beekeeping with Apis mellifera persists in China, with annual increases in colony numbers. This is despite the newish and universal burdens of Tropi and Varroa mites. What it takes in terms of government support to maintain those numbers is unclear. For now, it is clear that the best solution for Tropi in uninfested countries is to maintain barriers for its arrival.
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