© Maggie Gill 2024
How does Tropilaelaps spread?
For many years it was assumed that Tropilaelaps mites could only survive for a few days without honey bee brood. If true, this would severely limit their ability to spread.
However, our research suggests the story is more complicated.
By investigating both mite survival and mite movement, we found evidence that Tropilaelaps mercedesae may be capable of surviving long enough to exploit transmission routes previously considered low risk - including swarming, dead bees, and used beekeeping equipment.
The challenge
Why transmission matters
The recent arrival of Tropilaelaps mercedesae in Europe has raised an important question:
How does the mite move from one colony to another?
Understanding transmission is critical because even a small number of mites can rapidly build damaging populations once brood becomes available.
Historically, brood movement was considered the main risk. But could mites survive long enough to exploit other routes?
© Maggie Gill 2024
Can Tropilaelaps survive without brood?
In laboratory survival trials, mites were placed in conditions that mimic possible transmission scenarios, including live adult bees, dead pupae, dead adult bees, and empty containers.
The results challenged the long-held belief that Tropilaelaps mites are unable to persist away from brood.
What we found
Mites survived:
📍 More than 4 days on live adult honey bees
📍 Up to 7 days on decomposing pupae
📍 Up to 8 days on decomposing adult bees
📍 Significantly longer than in containers with no food source
Mites survived far longer on decomposing bees and pupae than in empty containers, suggesting that dead bees, dead brood, and contaminated equipment may deserve greater attention in biosecurity planning.
Why this matters?
Brood remains the main concern, but it may not be the only risk.
Used beekeeping equipment, dead bees, dead brood, queen shipments, package bees, and colony movements could all create conditions where mites survive long enough to be transported.
This does not mean every dead bee or old frame is dangerous, but it does mean that assumptions about “low-risk” broodless material should be revisited.
Can swarms carry Tropilaelaps?
The next question was whether mites could survive long enough to move naturally with bees.
In Georgia, we studied a natural swarm from a Tropilaelaps-infested colony. Eight female mites left the parent colony with the swarm.
Four died within the first week.
The remaining four survived long enough to enter the first sealed brood produced by the new colony.
Most importantly, two mites reproduced.
This provided the first evidence that a natural Apis mellifera swarm can carry viable Tropilaelaps mites and allow them to restart their life cycle in a newly established colony.
From survival to spread
Together, these studies tell an important story.
Tropilaelaps may be more resilient than previously thought. Some mites can survive for several days away from brood, and some can persist through the short broodless period after swarming until new brood becomes available.
For beekeepers, this means that transmission risk should not be considered only in terms of brood movement.
Swarms, dead bees, decaying brood, used equipment, and transported colonies may all play a role in how this mite spreads.
Key take home for beekeepers -
Do not assume that broodlessness means mite free
Treat swarms as a possible transmission risk.
Inspect early sealed brood in newly established swarms.
Treat dead brood, dead bees and used equipment with care.
Maintain good biosecurity.
Report suspicious mites to your local bee health agency.
This project was generously funded by Bee Disease Insurance and with a donation from the Worshipful Company of Wax Chandlers. You can find out more about their work on their websites.
Dr Bajaree Chuttong of Chiang Mai University kindly hosted the team and supported our work.
