Hitching a Ride: Why a New Mite Might Vex U.S. Beekeepers
If it’s not one mite plaguing beekeepers, it’s another. Reeling from the spread of colony-killing Varroa destructor mites, introduced in North America half a century ago, beekeepers are edgy about another unwelcome mite from Asia that could arrive on our shores and parasitize bees here with potentially devastating impact.
Like the Varroa mite, the bee-killing Tropilaelaps mercedesae can spread by hitchhiking on adult bees, including, as a study published in January in the Journal of Economic Entomology reports, the western honey bee (Apis mellifera). The most common of honey bees and pollinators in general, the western honey bee lives on all continents except Antarctica and is supremely important to agriculture and apiculture.
The mite was found by researchers on western honey bees that were trapped while leaving experimental colonies at Chiang Mai University in Thailand to forage. It was the first evidence that the mites, which parasitize only immature bees, hitch rides on adults that could spread them while drifting to other colonies or entering them to steal honey. Carried by air, the mites could spread much faster than they could when transferred by beekeepers on materials such as brood frames, which is assumed to be a route by which the mites disperse.
Having swept across Asia in only 50 years, T. mercedesae showed up last year in the country of Georgia and nearby areas of Russia. Given the vast distribution of the western honey bee, the fact that it can provide a vehicle for dispersal of T. mercedesae puts beekeepers in Europe and even here in the U.S. on the alert. The U.S. Department of Agriculture’s Animal Plant Health Inspection Service (APHIS) has its guard up and monitors for the mite, which “is a relatively understudied parasitic threat to honey bees,” says Auburn University doctoral student Rogan Tokach, lead author on the study.
The Auburn and Chang Mai researchers collected bees from six experimental colonies in funnel traps in July and August of 2023 and January and February last year. The bees were obtained from a beekeeper near Chang Mai. The fact that the mite was found on adults freely flying out of and away from the colony demonstrates that it potentially could be spread by bees from one colony to the next.
The process by which one organism attaches itself to a host solely for moving about is called phoresy. A well-known example of phoresy is that used by ticks. Originally, T. mercedesae used the Apis dorsata, often known as the giant honey bee, as a host for phoresy. Its shift to the western honey bees vastly increases its destructive potential.
That’s all scary news for beekeepers. Tropilaelaps mercedesae has the ability to do even more damage to bee colonies the dreaded Varroa mite, which is now the top cause of colony losses.
A key finding of the research was that mites attach to exiting adults only when brood infestations are high. No mites were detected on adults from colonies with infestations below 2.5 percent per 100 brood cells. This suggests that high infestation rates—which use up the brood that is the mites’ food source—force them to attach to adults.
“Tropilaelaps can be found attached to adult honey bees in the colony. The research suggested that the mite is more likely to be found on adults when there is limited brood available. Even though the mite cannot feed on the adult honey bee, it will climb on and attach as a potential source of dispersal,” says Tokach.
The mites invade bee brood cells and mate inside them just before capping; then they feed on the larvae. Females lay eggs during the bee pupal stage. Interestingly, the research team found only female mites on their trapped bees. Successful dispersal to a new colony occurs when it is reached by either a single gravid female or males and females together, although the chances of mating at the new colony are slim, says Tokach.
“Males only live for five days compared to 50 for females, so the likelihood of a male and unmated female mite attaching and drifting to the same colony is not very high,” he says. “If a mated female attaches to an adult bee, then she could begin laying in a new colony if that bee were to drift into an uninfested colony.”
Confirmation that the mite can be spread on bees is a key to stopping its spread, which requires a rapid response once a colony is infested.
“This research helps illustrate that these mites are capable of dispersing in multiple ways, whether it be beekeeper-mediated or through their own devices,” says Tokach. “This information is important when considering how Tropilaelaps may be able to be eradicated if introduced to a new area or region. This research helps improve action plans for how to deal with this parasitic mite as it continues to spread into new geographical areas.”
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