Progress report for FNE24-088
Project Information
The Parasitic mite, Varroa Destructor and its associated viruses, is the leading cause of honeybee colony mortality in the Northeast, leading to colony losses that average around 50% annually over the last decade. (1) Standard practice is to use pesticides (miticides), applied in the hive, to kill the
mites. The miticides simply kill mites and have no effect on the viruses in the colonies.
Honeybees can survive a higher temperature than Varroa mites, so by intentionally heating a colony of bees for a period of time, mites can be killed with little to no damage to the bees. These high temperatures also have a reducing effect on the mite vectored viruses. The challenge is to determine the right combination of temperature and time that is fatal to mites and viruses, harmless to honeybees, and not so long as to be prohibitive for beekeepers from a logistical standpoint.
Our objectives in year one are to compare hyperthermia at different time and temperature combinations with a control to determine the combination that results in the greatest mite and virus reduction, and then compare the best combination with a conventional chemical miticide in year two.
After collecting and analyzing data across two beekeeping seasons, we will share the results through online and in person workshops hosted by the Vermont Beekeepers Association and shared with other Northeast associations. If our results are significant, we will submit an article to the American Bee Journal, which if accepted, would share our results throughout the country.
Year one: To compare hyperthermia at different time and temperature combinations with a control to determine the combination that results in the greatest mite and virus reduction.
Year two: To compare the most effective hyperthermia time and temperature combination from year one with a chemical miticide that is relatively safe for the beekeeper to use and can be used when honey supers are on the hive. (Hopguard III)
Post-study, our objective is to share results both with the beekeeping public through social media, workshops, zoom classes and published articles.
Most people are aware that honeybee colonies are dying at an alarming rate. In the past decade, colony mortality in the Northeastern United States has averaged 50% annually. (2) There are may factors contributing to this high rate of mortality, but the biggest single contributing factor is the parasitic mite Varroa Destructor. (3) The Varroa mite feeds on the fat bodies of honeybees, and in so doing, spreads viruses to the bees, similar to the way a deer tick spreads Lyme disease. Colonies that are weakened by viruses are less able to tolerate poor nutrition, pesticide exposure, climate change related extreme weather and other stressors. These viruses can overwhelm a colony leading to sickness and eventual colony death.
Standard practice at this time is to use pesticides (miticides) to kill the mites within a honeybee colony. There are currently three classes of pesticide approved for use in honeybee colonies: synthetic pesticides (coumaphos, fluvalinate), organic acids (formic, oxalic), and plant based (Thymol, Hopguard). Limitations of these pesticides include leaving toxic residues in the honeycomb, the development of resistance in mites (4), health risks to the beekeeper (5), and variable efficacy. The biggest limitation of the pesticides, however, is that they only have one mode of action: they kill mites. Any virus transmitted by the mites will remain in the colony, continuing to impact colony health, even after a mite control treatment. The high colony mortality seen at the current time is mortality with the use of chemical miticides.
In our proposed research, we will test a mite control method that has dual modes of action. We hypothesize that it can reduce mite levels and reduce virus levels at the same time, allowing colony health to rebound after a mite infestation (6). If our hypothesis proves correct, this will be a game changer for sustainable beekeeping, reducing colony mortality rates, the dependence on toxic chemical miticides, and the huge expenditure of resources and funds needed to replace half of the honeybee colonies in the Northeast every year.
A replacement nucleus colony cost roughly $200 in 2023, and a package of bees (loose bees with no comb) cost roughly $120. A beekeeping operation with 1000 colonies, that has lost half of its bees over the winter, would have an expenditure of $100,000 to replace them with nucleus colonies or $60,000 for replacement with package bees. These amounts could easily approach the entire annual net income of a beekeeping operation of this size. We do not believe that losses of this magnitude are sustainable long term for the beekeeping industry in the Northeast. In year one of testing our thermal device, we reduced winter losses to 12.5% in our test population. This was a very small group of 30 colonies, but if use of a thermal device could even reduce winter losses from 50% to 20% consistently over time, that would represent a savings of $36,000 to $60,000 annually in funds that do not need to be directed at colony replacement.
Health risks to beekeepers will be reduced as beekeepers can opt for thermal mite control instead of exposing themselves to potentially harmful organic acids (5).
Health risks to the bees will be reduced as thermal mite control will leave no chemical residues in the comb.
Mites that have become resistant to one or both of the synthetic miticides available will not have developed resistance to hyperthermia and will be controlled effectively.
Hyperthermia can be performed when honey supers on the colony, allowing for control of mites as soon as levels start to increase, rather than having to wait for harvest. Currently only two chemical miticides are labelled for use when honey supers are on. (Formic Pro, Hopguard)
Due to all of these impacts, we feel strongly that successful research into hyperthermia for mite and virus control would be a huge boost to the sustainability of beekeeping in the Northeast.
Cooperators
- - Technical Advisor
Research
Year one of testing and sampling has taken place. Early in the summer 5 new hive heating devices were constructed by the grantee (beekeeper) with parts ordered locally and online. The heating devices (toasters) consist of a deep hive body with a mounted 10002 100v fan assisted heater, a line voltage thermostat with a hardwired thermocouple, and a spring wound 110v timer switch. Ducts and bottom board pans were constructed to direct the heated air from the toaster on top of the hive down the side and up through the screen bottom of the colony's bottom board. These new toasters differed from the prototypes (3) in that the bottom trays contained a second (booster) blower as an experiment to see if they lessened preheating times. A generator and associated cables to power all 8 toasters used in the study were also acquired.
At the beginning of July, August and September eight beeyards totaling 96 colonies were sampled for Varroa mites using the alcohol wash method to determine the number of colonies above the treatment threshold of 1% infestation. Sampling was conducted by the beekeeper and technicians from UVM's Bee Lab. In July and August only a small number of colonies were above the treatment threshold. In consultation with the bee lab, it was decided to delay the experiment until there were enough colonies above the treatment threshold to run the entire study at once. Comparing colonies toasted in July with ones toasted in September would not be scientifically valid.
In September, 60 colonies were determined to be above the mite threshold. Plans were made to use 52 of those colonies to perform toasting at a fixed temperature, while 8 were to be used to experiment with variable temperatures. The colonies in the fixed temperature tests were randomly assigned by bee lab personnel to be toasted at times ranging from 2 hours to 4 hours inclusive in 1/4 hour increments. The results of this system would allow us to perform a regression analysis on the resulting data.
Mite counts and virus levels were taken 72 hours before toasting, 72 hours after toasting, and 21 days after toasting in all 52 colonies. In addition, colony strength was measured 72 hours before and 21 days after toasting, and collection pans for dead bees were placed in front of all colonies to see if the mortality rate increased in toasted colonies over controls, and if so, if that rate correlated with length of toasting time.
Mite count data has been analyzed for this summer's testing, but the PCR assay virus levels have not yet come back from the lab, so we have been unable to analyze that data yet.
1)Due to a decrease in the cost of virus testing, we were able to include all 52 colonies in the virus sampling. This will give us much greater accuracy in assessing the effect of toasting on virus levels in honeybees.
2) We observed that some colonies were suffering from the high heat of the toasting setup, so we added empty 'cluster boxes' above the hives being toasted to allow the bees room to expand while undergoing toasting. This addition decreased the mortality of the toasted bees significantly.
3) Due to lower than normal mite loads in the beeyards, we needed to delay the entire experiment by a couple of months. Overall, having low mite counts is a wonderful problem to have. It may be related to ongoing bee breeding for mite resistance or may simply be chance, but it did cause us to change the original testing plan, and the overall number of colonies in the study. The choice was made to use only one temperature, midway between the two we wanted to test in order to reduce the number of variables. This gives us more colonies at each of the time points for the regression analysis, leading to more robust data and results.
4)One of the toasters was constructed using parts from ebay as an experiment in cost saving. That particular device was substantially cheaper than the toasters with 'store boughten' parts. It also worked a little better than the other units. This info will be shared with any beekeepers wanting to construct their own units.
5) We found that 'toasting' did in fact reduce mite levels, and they remained low at the 21 day testing date. By the 21 day mark, all of the sealed brood that was in the colony at the time of toasting will have emerged. This leads us to believe that the mites feeding on the developing brood were also affected by the 'toasting'.
6) We further found that there was no significant statistical difference in mite reduction between the various time cycles that we tested. This leads us to believe that cycles longer than 2-2.5 hours are likely not necessary for mite control. Virus reduction times may be different, so we will wait on those results.
We set out to find out if subjecting honeybee colonies to hyperthermia would reduce mite and virus levels in those colonies as compared with an untreated control. At this point, with only the first season of testing completed, we are quite pleased to state that the hyperthermia does indeed appear to reduce mite levels below the treatment threshold. We have no test results yet to determine if the hyperthermia affects virus levels.
Any significant changes to our apiary's management will wait until another season of testing is complete, but we fully intend to use the toasters to treat all colonies in our operation that have mite levels that rise above the treatment threshold.
Education & Outreach Activities and Participation Summary
Participation Summary:
Since our results are incomplete at this time, we have cancelled a scheduled workshop which was planned for the state beekeeping association on Feb 1st.
If our virus results (miraculously) come in before then, we will consider giving the workshop as planned. Otherwise it will be moved to summer 2025 or February 2026.