Tropilaelaps

Varroa and Tropilaelaps are parasitic mites that feed and reproduce on honey bee brood.
Varroa naturally infests Asian honey bees (Apis cerana), while Tropilaelaps targets giant Asian honey bees, (Apis dorsata). In the late 19th and throughout the 20th century, Western honey bees (Apis mellifera), which are native to Europe, the Middle East, and Africa, were introduced to Asia due to their easier management and higher productivity when compared to native Asian species. Western honey bees are closely related to all the Asian honey bee species, which unfortunately means they are susceptible to the same pests and pathogens. However, Western honey bees have not co-evolved with parasitic mites, and therefore have no natural defences against an infestation which has led to significant global colony losses caused by Varroa and Tropilaelaps. The global movement of Western honey bees has further enabled the spread of these pests, leading to the detection of Varroa in the UK in 1992 and it now being present in nearly every country where Western honey bees are found. Tropilaelaps, while less widespread, was first identified in Europe in the spring of 2024 and is following a similar path towards the UK as Varroa did.

The current (Jan 2025) confirmed distribution of Tropilaelaps mercedesae and the distribution of its natural host the giant Asian honey bee Apis dorsata.

Tropilaelaps can be spread in several ways. One route of transmission is on the various species of honey bees (Apis spp.) that are found in Asia. Giant Asian honey bees (A. dorsata) are found in South East Asia and India, and these areas should form the distribution of Tropilaelaps. However, as well as being able to infest and reproduce in Western honey bees (A. mellifera) Tropilaelaps also infest species such as the red dwarf honey bee (A. florea), and this has been one route that has allowed Tropilaelaps to spread further westwards, as the red dwarf honey bee can naturally be found as far west as the United Arab Emirates. There have also been several reports of wild honey bee colonies being found on shipping containers, boats and airplanes in Europe and North America which have originated from Asia, which offers one potential route for Tropilaelaps to reach new regions. In fact, this is the most likely route which has allowed the red dwarf honey bee to reach Malta.

Beekeepers are the most likely cause of transmission for Tropilaelaps, in particular migratory beekeeping and the sale of bees in the form of colonies, packages, and queens.
The UK does not allow the importation of colonies or packages directly from Europe; however, many importers opt to bring bees from mainland Europe via Southern and then Northern Ireland. The importation of queens from Europe is still permitted and in 2020 21,405 queens were imported into England and Wales (this number does not include those which arrived via the Northern Ireland route). Until recently it was believed that Tropilaelaps needed brood to be able to survive, and the movement of packages and queens were not considered a risk. Recent research has demonstrated that Tropilaelaps can survive in colonies during broodless periods over winter and on adult bees for up to 5 days, dead brood for up to 7 days and dead bees for up to 8 days. It is fairly common for attendant bees to die during the caging and transportation process of queen sales and similarly when package bees are produced and transported meaning that these commodities now pose a transmission risk for Tropilaelaps. Canada has been one of the first countries to proactively mitigate for this risk and banned the importation of queens and packaged bees from Ukraine in 2024 as Ukraine cannot establish a Tropilaelaps free status.

In areas where both Tropilaelaps and Varroa are present it has been reported that Tropilaelaps are a far more damaging pest than Varroa and cause colony losses of between 50% to 80%. This is in part due to their lifecycle and more rapid reproductive rate. Tropilaelaps can mate outside of brood cells and unmated females can reproduce via deuterotokous parthenogenesis, a form of asexual reproduction whereby unfertilised eggs can develop into either males or females. These reproductive differences mean that Tropilaelaps have roughly double the reproductive rate of Varroa and will out compete Varroa when both mites are present in a colony.