© Maggie Gill 2024
Tropilaelaps survival and transmission
It has been widely believed that Tropilaelaps can only survive when there is live bee brood available for feeding and reproduction. However, during the course of our research on Tropilaelaps we were astonished by their resilience, leading us reconsider their survivability and, consequently, their potential for transmission.
Migratory beekeeping, bee sales in the form of colonies, packages, and queens, the sale of beekeeping equipment, honey, wax, pollen and propolis and their ability to survive on other honey bee species all pose possible transmission routes. We were keen to investigate Tropilaelaps' survival in conditions that mimic these different scenarios.
Methods
Mite collection -
Adult mites were collected from colonies located at Chiang Mai University. Sealed brood taken from infested colonies was uncapped using forceps and mites were collected either with a pooter or a slightly moist fine tipped paintbrush. Mites could be encouraged to leave the brood cells by gently blowing over the uncapped cells or by tapping the side of the brood frame on a solid surface. Mites were pooled in a sealable plastic container with fresh bee larvae prior to being individually transferred to the experimental containers.
© Maggie Gill 2024
The survival study -
Three sealable plastic containers (350 ml) were used for each treatment group and the treatment groups comprised of -
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an empty container (control),
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five A. dorsata adults collected from a wild colony at Chiang Mai University,
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five A. mellifera pupae at the pink eyed pupal stage,
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five newly emerged A. mellifera adults,
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five newly emerged freshly euthanised A. mellifera adults.
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A sugar cube was glued to the side of containers containing live bees to act as a feeder and a ventilation hole covered with 0.025 mm nylon mesh was also added. The pupae and adult bees were collected from frames and colonies at Chiang Mai University. Thirty T. mercedesae mites (N = 90 mites per treatment) were carefully individually introduced to the treatment containers with a fine tipped paintbrush. Containers were then sealed with parafilm and randomly placed in an incubator at 34°C and 60% R.H. to limit possible spatial effects of temperature and humidity. The mortality of the mites was assessed every 24 hours until all the mites were dead. It should be noted that the pupae and dead honey bee adults were not replaced and decomposed throughout the duration of the trials.
© Maggie Gill 2024
Results
Fig 1. Kaplan-Meier curve displaying the survival of T. mercedesae mites associated with live A. mellifera adults, dead A. mellifera adults, dead A. mellifera pupae, live A. dorsata adults and the empty control treatment (p < 0.0001) (N = 30 mites / treatment).
What can't Tropilaelaps survive on?
Preliminary work carried out in 2023, which used the same methods as this work, reassuringly demonstrated that Tropilaelaps mites were unable to survive for longer than 48 hours on dry pollen, fabric from a bee suit, honeycomb and in the empty control containers.
What can Tropilaelaps survive on?
In 2024 we also found that T. mercedesae mites did not survive for longer than 48 hours on giant Asian honey bee (A. dorsata) adults.
However, we were concerned to find that some mites could survive for up to 5 days on newly emerged Western honey bees (A. mellifera), up to 7 days on dead honey bee (A. mellifera) pupae and 8 days on dead honey bees (A. mellifera) (see Fig 1).
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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.
