Are Tropilaelaps resistant to synthetic miticides?
One issue beekeepers in Asia face is finding effective ways to control Tropilaelaps in their colonies. Tropilaelaps are more damaging than Varroa destructor when they infest Western honey bee colonies and cause significant colony losses.
To combat the high level of mortality colonies kept in infested areas require continual prophylactic treatment with miticides. Unfortunately, this can cause mites to develop resistance to the active ingredients found in treatments, which has been well documented with Varroa.
Less is known about miticide resistance in Tropilaelaps but there is anecdotal evidence to suggest that Tropilaelaps do have resistance to chemicals such as Amitraz, Coumaphos, Flumethrin and Fluvalinate. We set out to test this and establish just how effective the most commonly used synthetic miticides for honey bee colonies are when used to control Tropilaelaps.
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Methods
The ‘Beltsville test’, which is commonly used by beekeepers to test for pyrethroid resistance in Varroa mites, was adapted for this study and 500 ml clear plastic containers were adapted to be used as experimental cages. A 13mm ø ventilation hole covered by 0.025mm nylon mesh cloth was added to allow ventilation for the bees, while preventing mites from escaping. A section of miticide strip (either Coumaphos, Amitraz, Fluvalinate or Flumethrin) equivalent to a 3% dose was added to each cage and attached with a steel pin. A section of brood comb containing larvae was also fixed inside the cages to provide food for mites, and finally a sticky trap was attached to the inside of the pot lids to catch dead mites.
Honey bees and Tropilaelaps mites were collected from colonies at Chiang Mai University (see the Tropilaelaps survival and transmission section for details). A ½ cup scoop containing on average 300 adult bees was added to each cage along with 20 Tropilaelaps mites. Finally a circle of 3 mm plastic mesh was added 10 mm from the top of the cage to prevent the bees from becoming stuck to the sticky trap. The lid was then fixed onto the cages before being inverted (see Fig 1).
Five replicates per treatment group were used with the addition of a control group with no miticide treatment (n = 100 mites/treatment). The cages were stored in an incubator at 34°C / 60% R.H . for 24 hours before mite mortality was assessed.
Fig 1. Design of experimental cages.
Fig 2. Median (±SE) mortality (%) of T. mercedesae exposed to different treatments.
Results
Statistical analysis showed a slight statistically significant difference between the treatment groups and further analysis revealed that Amitraz had a significant effect on the average mortality of Tropilaelaps mites and was shown to be 64% effective.
These results demonstrate that this population of mites were resistant to all the synthetic chemical treatments tested apart from Amitraz. While treatment efficacy of <50% indicates chemical resistance an efficacy of only 64% indicates a developing chemical resistance, and there would be only limited control of mites after using Amitraz.
Future work is needed to explore how genetic or environmental factors may contribute to miticide resistance in different Tropilaelaps populations as it spreads globally. This method also offers a novel test for chemical resistance in Tropilaelaps spp. which has not previously been available. Understanding and managing miticide resistance in this species is critical to prevent further spread and colony losses.
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.
